essay biology form 2

KCSE 2023 Biology Essay Questions and Answers (KCSE 2023 Prediction Questions)

Here are KCSES 2022/2023 Biology Essay Questions and Answers (KCSE 2022 Prediction Questions). Content: 31 pages with 60 questions and answers.

BIOLOGY (231/2) Revision Questions (Essays): Expected Responses

Q1. Explain the various ways in which a typical cell is adapted to its functions

   Has a cell membrane; with pores; that regulates substances entering and leaving the cell; cytoplasm; contain sugars and salts; for maintaining its osmotic pressure; also has a liquid medium; for all biochemical reactions; nucleus; contain chromosomes having hereditary material; and controls all the activities of the cell; ribosomes; are sites for protein synthesis; golgi bodies/apparatus; for secretion of hormones and enzymes; formation of lysosomes; lysosomes; contain lytic enzymes for breaking down worn-out organelles; secretory vesicles; formed from golgi apparatus for secreting substances; smooth endoplasmic reticulum; synthesizes and transports lipids; rough endoplasmic reticulum; transport proteins; nucleolus; controls the activities of the nucleus; produces ribosomes; mitochondria; form sites for energy production; centrioles; formation of cilia and flagella; forms spindle fibres used in cell division; plant sap vacuoles; store salts and other dissolved substances; controls osmotic pressure and turgidity of cells; food vacuoles involved in digestion of engulfed food; chloroplasts; form sites for photosynthesis in plant cells;  Max. 20 mks

Q2. Explain how the various specialized cells are modified to carry out their functions in plants and animals

   Animal cells: Sperm cell; has acrosome containing lytic enzymes; that digest the egg membranes for penetration during fertilization; has a long tail; containing numerous mitochondria; to generate maximum energy for propulsion/swimming in the vaginal fluid after ejaculation; Red blood cells; are flattened, circular/spherical biconcave in shape; to increase the surface area for packaging of haemoglobin; has haemoglobin; that combines with respiratory gases; for transport to and from body tissues; White blood cells; are amoeboid in shape hence able to change shape; to engulf pathogens through phagocytosis; lymphocytes produce antibodies to fight pathogens; Nerve cell; has extensions/dentrites; to receive and send information for sensation; Ciliated epithelial cells; have cilia for propulsion of mucus that traps dust and micro-organisms in the respiratory tract; Muscle cells; elongated, striated and contractile; to bring about movement; Plant cells: Guard cells; bean-shaped; to regulate the size of the stomata allowing gaseous exchange; and control water loss; has chloroplasts with chlorophyll; for photosynthesis; Root hair cell; elongated; thin-walled; with dense cytoplasm for absorption of water and mineral salts; Epidermal cell; thin; for protection of inner tissues from mechanical and micro-organism attack; Palisade cell; contains numerous chloroplasts with chlorophyll; for photosynthesis; elongated; to increase surface area for trapping maximum amounts of light energy; Meristematic cell; thin-walled; with dense cytoplasm; for primary and secondary growth; Max. 20 mks

Q3. Describe how the mammalian body protects itself against infections

   Pathogenic microbes are found on the skin, respiratory tract, mouth, vagina and the intestinal tract; the skin; has a keratinised and waterproof cornified outer layer; that provides a mechanical barrier to microbes/prevents entry of microbes; sebaceous gland; produces sebum; which has antiseptic properties; the respiratory tract; produce mucus secretions that trap dust; cilia sweep/waft/propel the microbes to the pharynx for swallowing or to be coughed out; reflex actions of coughing/sneezing/vomiting help remove foreign materials from the respiratory tract/digestive tract; lysozymes/enzymes in saliva/nasal secretions/tears; digest walls of bacteria destroying them; gastric secretions such as hydrochloric acid lowers the pH in the stomach killing micro-organisms; clotting of blood; prevents entry of microbes after damage of blood vessels; phagocytosis; by phagocytes engulf and destroy microbes and other foreign bodies; lymphocytes are stimulated to produce antibodies; by proteins present in microbes protecting the body; antibodies destroy/kill micro-organisms through various ways: agglutinins; bind to pathogens making them clump together; killing them; Lysins; bind to pathogens and make them burst or disintegrate; opsonins; bind to pathogens making them easily recognized hence be engulfed/destroyed by other lymphocytes; anti-toxins; bind and neutralize toxins produced by micro-organisms; vagina is acidic; hence making it not conducive for growth and reproduction of micro-organisms; Max: 20 mks

Q4. How are the leaves of higher plants adapted to their functions?

    Broad and flattened lamina; to increase surface area; for absorption of light; thin blade; to reduce distance for diffusion of gases and penetration of light waves; transparent epidermis and cuticle; to allow light to penetrate to tissues; cuticle layer absent on stomata; to allow for gaseous exchange; one-cell thick epidermal layer; to reduce the distance over which sunlight penetrates; palisade cells have numerous chloroplasts containing chlorophyll; to trap maximum amounts of light energy; have stomata on the epidermis; to allow for gaseous exchange; and control of water loss through transpiration; palisade layer have elongated cells located at right angles to the leaf surface; for maximum absorption of light energy; spongy mesophyll; consists of spherical and loosely-packed cells; to create air spaces; which communicate with the atmosphere through stomata; for purposes of gaseous exchange and control of water loss; veins have conducting tissues: xylem; for movement of water and dissolved mineral salts; phloem; for translocation of manufactured food; Max. 20 mks

Q5.  Explain how the various teeth adapt mammals for nutrition

   Incisor; sharp; chisel-shaped; for biting; and cutting food; one root for support in the jaw bone; Canines; long; sharp; pointed; for holding prey; piercing; and tearing flesh from prey; single root; for support in the jaw bone; Premolars; large/wide; to increase surface area for grinding food; highly cusped; to increase surface area for grinding food; two roots; for firm support/anchorage in the jaw bone; molars; large/wide; to increase surface area for grinding food; highly cusped; to increase surface area for grinding food; Max. 20 mks

Q6. Describe what happens to a meal of oily beans and maize from the time of ingestion up to the time of absorption

   In the mouth; starch in maize; is digested by salivary amylase/ptyalin/diastase into maltose; food is chewed and mixed by teeth and the tongue; rolled into boluses by peristalsis; it enters into the stomach via the cardiac sphincter; in the stomach, gastric juice containing pepsinogen that is activated to pepsin; digests proteins in the beans; into shorter peptides; food is churned and allowed into the duodenum; via the pyloric sphincter muscle; in the duodenum; bile juice secreted by the gall bladder; emulsifies the oils in the beans into tiny oil droplets; pancreatic juice; secreted by the pancrease; contains pancreatic amylase; that digests starch to maltose; pancreatic lipase; that digests the oil in the beans to fatty acids and glycerol; trypsin; digests proteins into shorter peptides;  food enters into the ileum; where succus entericus is secreted; it contains maltase enzyme; that digests the maltose into glucose; that is absorbed; peptidase; digests peptides into amino acids; lipase digests the remaining lipids (oil) into fatty acids and glycerol; which is absorbed through the lacteals of the villi; Max. 20 mks

Q7. How are the small intestines in mammals adapted to their functions?

Small intestines consists of the duodenum and the ileum; most digestion of food occurs in the duodenum; bile from the gall bladder of the liver is secreted through the bile ducts; and it is used to emulsify fats/break fat particles into tiny droplets; to increase the surface area for enzyme action; the pancreas secretes pancreatic juice to the duodenum; the juice contains pancreatic amylase; that helps to breakdown the remaining starch into maltose; trypsin; (that is secreted in its inactive form, trypsinogen , and activated by enterokinase enzyme); hydrolyses proteins into shorter peptides; pancreatic lipase; converts lipids into fatty acids and glycerol; sodium hydrogen carbonate is also produced; to neutralize the acidic chyme from the stomach; and provide a suitable alkaline medium for pancreatic and other intestinal enzymes; the ileum is long; and narrow; to increase the surface area for complete digestion of food; and maximum absorption of digested food; highly-coiled; to reduce speed of food flow; for maximum digestion; and absorption; presence of villi; and microvilli; to increase surface area; for maximum absorption; dense network of capillaries; to transport blood; for efficient transport of absorbed food; presence of lacteals in the villi; for absorption of fatty acids and glycerol molecules; presence of enzymes: Lipase; for digestion of lipids into fatty acids and glycerol; maltase; for digestion of maltose to glucose molecules; peptidase; for breakdown of peptides into amino acids; sucrase; for digestion of sucrose into glucose and fructose; lactase; for digestion of lactose into glucose and galactose; goblet cells; produce mucus; to lubricate the walls of the ileum; for smooth flow of food; coats the walls of ileum to prevent digestion by peptidase enzyme; Max. 20 mks

Q8. Outline and explain the various homeostatic functions of the liver in mammals

   Deamination; process of removal of an amino group from an amino acid molecule; the process gets rid of excess amino acids in the body; as the body is not able to store them; the amino group enters the ornithine cycle; where it is combined with carbon (IV) oxideto form urea; which is excreted in urine through the kidney; Heat production; many metabolic activities take place in the liver; releasing heat energy; that is distributed by the blood to other parts of the body; this helps in thermoregulation; Storage of vitamins and mineral salts; Vitamins A, B, D, E and K; are stored in the liver; worn-out red blood cells, are broken down to yield iron; which is stored in the liver in form of ferritin; this is used later in case of shortage; Formation of red blood cells; occurs in the liver of the foetus; the liver also breaks down old/exhausted red blood cells; leading to formation of more in the bone marrow to replace the worn-out cells; to enhance oxygen and carbon (IV) oxide distribution; Regulation of blood sugar level; liver cells convert excess glucose into glycogen and fats under the influence of insulin hormone; the stored glycogen is however converted back to glucose; when glucose levels are low; by the liver cells; under the influence of glucagon hormone; Regulation of plasma proteins; plasma proteins such as prothrombin and fibrinogen are manufactured in the liver using the amino acids found in the liver; they play a major role in blood clotting; that prevents excessive blood loss and infection at the injured area; other plasma proteins produced by the liver such as serum and albumen; contribute to the maintenance of osmotic pressure in the body; non-essential amino acids are also synthesized by the liver; for use by the body; Storage of blood; the liver is highly vascularised; hence it is capable of holding a large volume of blood when the blood vessels dilate during hot conditions; when the temperatures are low, the blood vessels constrict under the influence of the endocrine and nervous systems; hence less blood is stored in the liver; this contributes to thermoregulation; Detoxification; this is the process where harmful compounds such as drugs and poisons; are converted to less toxic compounds in the liver; toxicity is caused by medication, drugs and microorganisms; the toxic compounds are later excreted in urine; detoxification prevents the accumulation of toxins in body cells; which could lead to death or malfunctioning of the body cells; Max. 20 mks

Q9. Explain why the following conditions are necessary for photosynthesis

  • Carbon (IV) Oxide

Required in the dark stage of photosynthesis; it combines with the hydrogen ion from the light stage; to form glucose, proteins and lipids; low concentrations reduces the rate of production of energy and food; while high concentrations leads to an increase in the amount of energy and food formed;

It is used to break down water molecules (through photolysis); into hydrogen ions, oxygen and energy; the energy and hydrogen ions formed are used in the dark stage;

  • Chlorophyll

Green pigment that traps light energy from the sun; that is used in photolysis of water molecules;

  • Suitable temperature and pH

Temperature affects the enzymes involved in photosynthesis; suitable/optimum temperatures activate enzymes; for maximum production of food; while extremely low temperatures inactivate enzymes; leading to less or no production of food; high temperatures denature enzymes; stopping the process of photosynthesis; photosynthetic enzymes work well in low pH; so the rate is high; while higher pH reduces enzyme activity; lowering the rate of photosynthesis;

Forms a medium for the chemical reactions; it is split to yield hydrogen ions, oxygen and energy for use in the dark stage; solvent for the materials used in photosynthesis; Max. 20 mks

Q10. How is the ileum adapted to its functions?

      Long; and narrow; to increase the surface area for complete digestion of food; and maximum absorption of digested food; highly-coiled; to reduce speed of food flow; for maximum digestion; and absorption; presence of villi; and microvilli; to increase surface area; for maximum absorption; dense network of capillaries; to transport blood; for efficient transport of absorbed food; presence of lacteals; for absorption of fatty acids and glycerol molecules; presence of enzymes: Lipase; for digestion of lipids into fatty acids and glycerol; maltase; for digestion of maltose to glucose molecules; peptidase; for breakdown of peptides into amino acids; sucrase; for digestion of sucrose into glucose and fructose; lactase; for digestion of lactose into glucose and galactose; goblet cells; produce mucus; to lubricate the walls of the ileum; for smooth flow of food; coats the walls of ileum to prevent digestion by peptidase enzyme; Max. 20 mks

Q11. a) What is homeostasis?

         (Mechanisms of) control and maintenance of a constant internal environment regardless of the external conditions; 2 mks

  • b) Name any three factors that must be maintained constant in mammalian bodies

          Temperature; Water; Salt or ion content; Carbon (IV) oxide; Glucose; amino acids; Max. 3 mks

  • c) Explain how endotherms respond to heat and cold conditions in their environment

         Heat/hot conditions: Increased sweating; to lose heat through latent heat of vaporization; dilation of arterioles under the skin; to bring more blood to the skin surface to lose heat to the atmosphere; decreased body metabolism; to reduce heat generation; erector pili muscles relax; making hair follicles to relax hence hair lies flat on skin, no air is trapped; to lose heat; slow/reduced muscular activity due to slow metabolism; to reduce heat production; panting to expose tongue and mouth; to release heat; moving to shades to avoid direct heat; aestivation; to escape the extreme heat; flapping of ears to create currents to carry away heat; Cold conditions: stamping of feet; to generate heat; basking in the sun to gain heat directly; less production of sweat; to reduce water loss through latent heat of vaporization; vasoconstriction of arterioles; hence less blood flow to the skin surface to reduce heat loss; increased metabolism through release of more thyroxine hormone; to generate heat; erector pili muscles contract; pulling hair follicles hence hair is raised; to trap a layer of moist air; to prevent heat loss; shivering/rapid contraction of muscles; to yield heat to warm body; Max. 15 mks

Q12. Describe the route taken by water from the soil up to the evaporating surface of a plant

      Water is drawn into the root hair cells by osmosis; due to the presence of dissolved substances in the cell sap of root hairs, the concentration of cell sap is greater than that of the surrounding solution in the soil/concentration gradient; this exerts a higher osmotic pressure, thus drawing the water molecules across the cell wall and cell membrane into the root hair cells; more water drawn into the root hair cells dilutes the cell sap; making it less concentrated than that in the adjacent cortex cell of the root; due to osmotic gradient, water moves from the adjacent cells to the next by osmosis; until it enters the xylem vessels located in the center of the root; the xylem vessels of the root then conduct the water up into the xylem vessels in the stem into the leaves; there is a force in the roots which pushes water up the stem; this force is known as root pressure; and can be considerably high in some plants; energy from the endodermal cells of the root is responsible for driving this force; in the xylem vessels, water would rise up by capillarity; to some extent because the vessels are narrower and there is  a high attractive force between the water molecules and the cell walls; the cohesive; and adhesive forces are important in the maintenance of a continuous and uninterrupted water column in the xylem vessels up the tree to the leaves; water vaporizes from the spongy mesophyll cells; their cell sap becomes concentrated than the adjacent cells. This increases the osmotic pressure of the spongy mesophyll cells; as a result of this, water flows into the cell from other surrounding cell, which in turn takes in water from xylem vessels within the leaf veins; this creates a pull/suction force that pulls a stream of water from xylem vessels in the stem and roots. This force, known as transpiration pull; helps in maintaining a continuous column of water from the roots to the leaves; water flows from the midrib into leaf veins from where it enters leaf cells; from the mesophyll cells, it enters the airspaces; then the substomatal air chambers; from where it evaporates through the stomata; to the atmosphere; Max. 20 mks

Q13. How is the mammalian heart adapted to its functions?

Heart is enclosed in a pericardial membrane/pericardium; that produces a fluid; to lubricate it; the membrane also keeps the heart in position; It is covered in a fatty layer; that acts as a shock absorber; made up of cardiac muscles; which are interconnected/interacted hence contract and relax without fatigue or nervous stimulation/myogenic; for continuous pumping of blood throughout the lifespan of the animal; the muscles are supplied by nutrients and oxygen; by the coronary arteries; and the coronary veins take away wastes and carbon (IV) oxide; heart is divided into 4 chambers; for efficient double circulation/ avoid mixing of oxygenated and deoxygenated blood/carry large volume of blood; has interventricular septum; to separate oxygenated and deoxygenated blood; ventricles are thick/muscular; to generate high pressure to pump blood out of the heart; left ventricle has thick muscles/more muscular; to pump blood to all body tissues; heart has bicuspid; and tricuspid valves; to prevent back flow of blood to left auricle; and right auricle respectively; valves have tendinous cords/valve tendons; to prevent them from turning inside out; semi lunar valves located at the beginning of major arteries; prevent backflow of blood into the ventricles; has sino-artrio node located in the muscles of the right auricle; to initiate heart beat/contractions of heart muscles/cardiac muscles, rate of heart beat is controlled by nerves; vagus nerve; slows down heartbeat; while sympathetic nerve; speeds up the heartbeat; has aorta; to transport oxygenated blood to all body parts; has pulmonary artery; that transports deoxygenated blood from right ventricles to lungs for oxygenation; has pulmonary vein; that transports oxygenated blood from lungs to the left ventricles; for distribution to all body parts; has the venacava; that  receives deoxygenated blood from all body parts to right ventricles; Max. 20 mks

Q14. Describe double circulation in mammals

 Deoxygenated blood from body tissues (except lungs); enters the heart via the right auricle; through the venacava; it flows to the right ventricle; via the tricuspid valve; the right ventricle contracts; pumping blood; via the semi lunar valves; through the pulmonary artery; to the lungs for oxygenation; the oxygenated blood from the lungs; flow through the pulmonary vein; to the left auricle; via the bicuspid valve; to the left ventricle; the left ventricle contracts; pumping blood via the semi lunar valves; through the aorta; to the rest of the body tissues; Max. 20 mks

Q15. Describe the process of urine formation in the mammalian kidneys

      The afferent arteriole which is a branch of the renal artery supplies blood to the glomerulus; the afferent arteriole has a wider lumen/diameter than the efferent arteriole; which takes away blood from the glomerulus; the differences in the diameter of the afferent and the afferent vessels causes high pressure; leading to ultrafiltration of blood; the walls of the blood capillaries are one-cell thick; hence glucose, amino acids, vitamins, hormones, salts, creatine, urea and water filter into the Bowman’s capsule; to form glomerular filtrate; white blood cells, red blood cells, plasma proteins such as globulin and platelets are too large to pass through the capillary wall; hence remain in the blood capillaries; useful substances in the human body are selectively reabsorbed; back into the blood stream at the proximal convoluted tubule; the tubule is highly coiled; to increase the surface area for reabsorption of the substances; the useful substances include amino acids, glucose, vitamins, hormones, sodium chloride and water; many mitochondria found at the proximal convoluted tubule; provide energy for reabsorption of these substances against a concentration gradient; the glomerular filtrate flows into the descending and the ascending limb of the loop of Henle; blood in the capillaries and the glomerular filtrate in the loop of Henle move in opposite directions/counter-current flow; this provides a steep concentration gradient that leads to maximum absorption of water through osmosis; sodium chloride is actively absorbed from the ascending limb into the blood capillaries; under the influence of aldosterone hormone; the glomerular filtrate flows into the collecting tubule from where, more water is reabsorbed into the blood stream; antidiuretic hormone influences the amount of water to be reabsorbed depending on the osmotic pressure of the blood; the glomerular filtrate from several collecting tubules now referred to as urine; is emptied into the collecting duct; the urine passes through pyramid, pelvis and ureter into the bladder; where it is stored for some time. The sphincter on the urethra relaxes to allow urine to be released from the body; Max. 20 mks

Q16. Explain the role of the following hormones during homeostasis

  • Antidiuretic Hormone (ADH)

Secreted by the (posterior lobe/end) pituitary gland; in response to an increase in the osmotic pressure of blood; the hormone stimulates the distal convoluted tubules and the collecting ducts; to increase their permeability to water; this increases the reabsorption of water into the bloodstream; concentrated and less urine is excreted; when the osmotic pressure decreases, less or no hormone is produced; hence the tubules become impermeable to water; less water is reabsorbed into the bloodstream; hence more dilute urine is excreted; fluctuations in the osmotic pressure is detected by the hypothalamus;

Secreted by the pancrease; in response to a rise in blood sugar level; it stimulates liver cells to convert the excess glucose into glycogen and fats for storage in the liver and muscle cells; increases the oxidation of glucose in respiration to yield water energy and carbon (IV) oxide/increases metabolism in the body; this leads to a fall in blood glucose to normal level;

Secreted by the pancrease; in response to a decline in blood glucose level; it stimulates liver cells to convert the stored glycogen and fats back to glucose; stimulates the conversion of amino acids to glucose; and stops the oxidation of glucose in the body cells; the glucose formed is released to the bloodsteream causing a rise of blood glucose level to normal; Max. 20 mks

Q17. a) Distinguish between Diabetes mellitus and Diabetes insipidus

            Diabetes mellitus is a condition/disease caused by failure of the pancrease to produce adequate insulin hormone; leading to excess glucose levels in the body some of which is released in urine while diabetes insipidus is a condition caused by failure/inability of the kidney tubules to control the amount of water in urine as a result of a defect in production of antidiuretic hormone (ADH) leading to production of more dilute urine; Max. 2 mks

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Biology form 2 topics.

  • Classification Of Living Things
  • Balance Of Nature
  • Transportation Of Materials In Living Things
  • Gaseous Exchange And Respiration

Strategies for answering exam and test questions

Click on the accordions below to see more information about how best to tackle the following question types in your exam.

Multi-choice questions

Things to remember about multi-choice questions

  • Read through the options and try to eliminate the ones that aren’t right . Multi-choice questions usually have one option that is obviously wrong, and three or four others that are similar.  It is important to look carefully at how they are worded in order to select the correct  answer.
  • Don’t struggle over a question . Do all of the easy questions first and come back to harder ones later to maximise efficient use of test/exam time.
  • Answer all the questions . Even if you are not sure, your educated guess may well be correct. It is better to have a go at answering a question than potentially miss out on a mark.
  • When you check back through your paper and think an answer is wrong - change the answer . Research indicates that you will probably be correct in doing so.

Short answer questions

Short answer questions range from a sentence or two through to a paragraph in length.

  • Keep to the point . Short answers are usually two-three sentences.
  • Main ideas . Your answers should incorporate the key points, words, ideas and phrases the marker will be looking for.
  • Leave one or two lines after each answer . This is so you can add important points later on.
  • Try to answer all the questions .  If you don’t know the complete answer, put down what you do know, as this is likely to get you some marks.

Exam essay questions

The advice here is in four parts: Time allocation | Task analysis | Planning | Presentation

Time allocation

  • Use the reading time at the start of the exam to choose which essay questions you will answer .
  • Check how much time you might have to answer each essay question , and stick to it. You can come back and add more to your answer in your revision time at the end of the exam session.
  • If you haven’t finished your answer, jot down the rest in note form . This will show the marker what you know, and you might get some marks for it.

Task analysis

  • Read the question carefully .
  • Underline or highlight the content words . What is the topic?
  • Pick out the instruction words in the question, e.g. identify, describe, compare and contrast, evaluate. What are you being asked to do with the topic?
  • Take some time to think and plan your answer . For example: use the reading time to select which essay questions you will answer. Then use the start of the writing time (5-20mins) to make notes of all the points you remember that are relevant to the essay. General guide for timing: for 30 minutes of writing, allow 5-7 minutes for planning .
  • Plan out the structure by organising your points into a logical order :e.g. by numbering them according to intended sequence.
  • General writing rule for exam essays - one paragraph = one point . Follow standard essay-writing procedure, e.g. start with a topic sentence that contains your key point, and then support this with examples, explanations, and evidence.

Presentation

  • Make sure your handwriting is legible . Markers should not have to decipher your handwriting. If your handwriting is illegible, it could compromise your marks.
  • Make sure that you can express ideas effectively in terms of sentence structure and word use .  Incoherent sentences and incorrect terminology will likely result in the marker not being able to understand your answer properly.
  • Don’t worry too much about punctuation, grammar and spelling . Getting your ideas down is more important than ‘perfect’ writing (and markers usually take this into account given that students are writing under pressure in an exam situation). However, you do need a basic level of competency in these areas: an answer that lacks any punctuation and is full of spelling mistakes will probably be incoherent for the marker.
  • Don't waffle . Get straight to the point in terms of your answer so that you don’t waste time and word space on unessential or irrelevant detail. Planning your essay beforehand is key to avoiding waffle.

Problem solving questions

Usually these types of questions target formulae, steps in a process, or rules.

  • Make sure you write down relevant formulas, equations, and rules . Important: For numerical problems involving computation, make sure you include the appropriate mathematical units in your final answer (e.g. ml, m/sec).
  • Clearly show the steps you have taken in working out the answers.
  • If necessary, write notes to explain your answers .
  • Do the easier answers first , and return to the difficult ones later.

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essay biology form 2

Introduction to Transport in Plants and Animals

  • Transport is the movement of substances within an organism.
  • All living cells require oxygen and food for various metabolic processes.
  • These substances must be transported to the cells.
  • Metabolic processes in the cells produce excretory products which should be eliminated before they accumulate.
  • The excretory products should be transported to sites of excretion.
  • Organisms like amoeba are unicellular.
  • They have a large surface area to volume ratio.
  • The body is in contact with the environment.
  • Diffusion is adequate to transport substances across the cell membrane and within the organism.
  • Large multi-cellular organisms have complex structure where cells are far from each other hence diffusion alone cannot meet the demand for supply and removal of substances.
  • Therefore an elaborate transport system is necessary.
  • Simple plants such as mosses and liverworts lack specialized transport system.
  • Higher plants have specialized transport systems known as the vascular bundle.
  • Xylem transports water and mineral salts.
  • Phloem transports dissolved food substances like sugars.

Plant Roots

Functions of roots in plants.

  • absorption.
  • gaseous exchange.

Structure of Roots and Root Hairs

Internal structure of a root hair cell, function of the stem.

  • Support and exposure of leaves and flowers to the environment,
  • Conducting water and mineral salts
  • Conducting manufactured food from leaves to other parts of the plant.

a) Collenchyma

Collenchyma

b) Parenchyma

Parenchyma

c) Sclerenchyma

Sclerenchyma

Absorption of Water and Mineral Salts

Absorption of water, absorption of mineral salts, transpiration, definition of transpiration, types of transpiration, a) stomatal transpiration, b) cuticular transpiration, c) lenticular transpiration, structure and functions of xylem, a) xylem vessels.

  • Simple spiral.
  • Double spiral.
  • Reticulate.

b) Tracheids

C) xylem fibres, d) xylem parenchyma, forces involved in transportation of water and mineral salts, 1. transpiration pull, 2. cohesion and adhesion, 3. capillarity, 4. root pressure, importance of transpiration.

  • Replacement of water lost during the process.
  • Movement of water up the plant is by continuous absorption of water from the soil.
  • Mineral salts are transported up the plant.
  • Transpiration ensures cooling of the plant in hot weather.
  • Excessive loss of water leads to wilting' and eventually death if water is not available in the soil.

Factors Affecting Transpiration

A) environmental factors, b) structural factors, translocation of organic compounds, functions of phloem.

  • sieve tubes,
  • companion cells.
  • parenchyma, a packing tissue.
  • sclerenchyma, a strengthening tissue.

Sieve Tubes

Companion cells, phloem parenchyma, transport in plants quiz, question - of -, hello esoma-ke member, please help review these notes.     why review, students' and teachers' reviews, here's what our users had to say ....

Free Biology Essay Examples & Writing Tips

Don’t know what to write about in your essay on biology? Looking for good biology essay examples for inspiration? This article has all you need!

A biology essay is a type of academic paper that focuses on a particular topic of biology. It can discuss animal life, cycles in biology, or a botanic subject. You will need to demonstrate your critical thinking skills and provide relevant evidence to support your perspective.

On this page, you will find examples of biology essays. You will also find here tips and topics prepared by our experts . They can assist you in nailing your short or extended essay.

Areas of Research for Biology Essays

If you’ve been assigned to write a biology essay, you probably know which area of research you have to choose. However, it might be beneficial to explore other available scopes. It’s useful for both interdisciplinary study and the cases when you are free to pick your area of research. In this section, let’s figure out what you can study in biology.

Here are biological areas of research you should be familiar with:

  • Cancer Biology studies this type of disease to prevent, detect, diagnose and cure it. The ultimate goal of such biologists is to eliminate cancer.
  • Cell Biology is a branch that studies the structure, function, and behavior of cells. Here, biologists study healthy and sick cells to produce vaccines, medication, etc.
  • Biochemistry is an application of chemistry to the study of biological processes on cell and molecular levels. It is a cross-discipline between chemistry and biology. The focus is on the chemical processes of living organisms.
  • Computation Biology is a study of biological data that develops algorithms and models to understand biological systems. Here, scientists either work for institutions or research for private enterprises.
  • Genetics is an area that focuses on the study of genes and genetic variations for health benefits. It looks at the way DNA affects certain diseases.
  • Human Disease is an area within which scientists study different diseases. The field covers cancer, developmental disorders, disease genes, etc.
  • Immunology is a branch of biology that focuses on immunity. Immunologists look at the way the body responds to viruses as a way to protect the organism.
  • Microbiology studies all living organisms that are too small for our eye to see. It includes bacteria, viruses, fungi, and other microorganisms.
  • Neurobiology is the study of the nervous system. Biologists examine the way the brain works and look into brain illnesses.
  • Stem Cell and Developmental Biology seeks to examine how the processes behind stem cell’s ability transform cells. The biologists in this area use the power of stem cells to model human illnesses.

Essay on Biology: Writing Tips

Want to know how to start a biology essay? Wondering about the best way to write your essay on biology? Then check out the following tips.

When you’re writing about biology, pay attention to the following features:

  • Introduction . Just as in any other form of academic writing, the first section of your paper introduces the subject. Here, explain why your ideas are relevant to biology as a science.
  • Thesis Statement. The final one or two sentences of the first paragraph should include your original hypothesis and experiment. You will be proving them in the main body. You do not have to include the results as the reader will encounter them later. If you’re struggling with this part, try our thesis generator .
  • Main Body. In this part, write about all the experiments in detail. Often, teachers require to include visual aid to prove your point. For Zoology, Anatomy, Botany, it is pretty easy to find some photos and illustrations.
  • Conclusion. Here, restate your thesis. Reemphasize the most critical aspects described in the main body. You can do it by using our summarizing tool . The goal of this last paragraph is to leave an everlasting impression on the reader.

Thank you for reading our article. We hope you found it helpful. Share it with your class peers who also study biology. Additionally, have a look at the biological essay examples below.

803 Best Essay Examples on Biology

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Browning Reactions Explained

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Plant Growth and Development with Music

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The Effect of Different Shampoos on the Bacteria Growth

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Cloning of Plants at the Botanic Garden

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The DNA Extraction Procedure: Scientific Experiment

Life in the bottom of the ocean and its protection.

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Shapes of Cells and Their Functions

Venus flytraps and arthropods: plant-animal interactions.

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Soil Impact on the Growth of Plants

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Transpiration Process in Plants

Responsible house plant keeping.

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The Brain: Structure and Functions

Genetic engineering: is it ethical to manipulate life.

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The Human Family Tree Development

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Green Fluorescent Protein – Applications in Biochemistry

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Description of Mitosis and Meiosis

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Chlamydia Sexually Transmitted Disease

The pomegranate or “punica granatum l.”.

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The Psychological Nature of Memory

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The Role of Microorganisms, Biotechnology

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The Anatomy and Physiology of the Nervous System of a Rat

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Climate Change and Threat to Animals

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The Biological Basis of Sleep

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FORM 2 BIOLOGY END TERM 2 EXAMS PLUS MARKING SCHEMES

FORM II BIOLOGY END TERM OF TERM II  

NAME: ……………………………………………………………………………..  ADM NO: ………………

  • Study the diagram below

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  • Name the apparatus (1mk)
  • Suggest the use of the apparatus. (1mk)
  • Name the part labeledA and state its function. (2mks)
  • Name the field of biology that specializes in the study of the following; (3mks)
  • Interrelationships between organism and their environment.
  • Heredity and variations.
  • The structure below was observed under the light microscope.
  • Identify the cell structure. (1mk)
  • Name the parts labeled A and B (2mks)
  • State two functions of the above structure. (2mks)
  • The diagram below shows a certain cell in living organisms.
  • Identify the cell               (1mk)
  • Give two reasons for your answer (2mks)
  • Name the parts labeled; (3mks)

A     ……………………..                                    D……………………….

B     ……………………..                                    E…………………………

C    ……………………..                                 F………………………..

  • State the functions of the parts labeled C, D and E.                        (3mks)

C…………………………………………………………………………….

D……………………………………………………………………………

E…………………………………………………………………………….

  • Name the organelles in a cell which perform the following functions.(3mks)
  • Excretion in Amoeba
  • Secretion of synthesized proteins and carbohydrates.
  • Formation of cilia and flagella.
  • The diagram below representsa cross section of a plant part.
  • From which part of the plant was the section obtained? (1mk)
  • Name the parts labeled A,B and C. (3mks)

A……………………………..    B………………………..    C……………………..

  • What is the function of the part labeled C? (2mks)
  • What is transpiration? (1mk)
  • Give two importance of transpiration in plants (2mks)
  • Name two sites for transpiration                                                                          (2mks)
  • Name the instrument which is used to determine transpiration rate. (1mk)
  • Name the :                                                                                                                        (2mks)
  • Material that strengthens the xylem tissue
  • Tissue that is removed when the bark of a dicotyledonous plant is ringed.
  • Name the blood vessel that transports blood from; (2mks)
  • Lungs to the heart
  • The aorta to the liver

SECTION B 40 MARKS

  • The diagram below illustrates blood circulation in certain organs in humans.
  • Name the part labeled A ………………………………                 (1mk)
  • Name the blood vessels labeled B,D,E and F. (4mks)

B……………………..                               E……………………………

D……………………..                             F……………………………

  • State how the composition of blood in vessel E differs from that in vessel D. (3mks).

E                                                                      D

  • Explain the role of bile in the process of digestion (2mks)
  • Below is a diagrammatic summary of the main biochemical events in photosynthesis. Study it carefully and answer the questions that follow.

Stage A ——————— Chlorophyll

Molecule P       Water

Hydrogen atoms         Gas Q

Stage B —————————————–

  • Define photosynthesis (1mk)
  • Name the stages  A and B                                                                  (2mks)

A……………………………….                     B ……………………………

  • Name the gases represented by the letters (2mks)

Q ………………………………..   W………………………………….

  • Name the specific site for the reactions in stage A and B     (2mks)

A …………………………………….. B…………………………………….

  • Name reaction Z ………………………………………….. (1mk)
  • What name is given in splitting water molecule into hydrogen atom and gas Q? (1mk)
  • Name one factor that affect the rate of photosynthesis (1mk)
  • An experiment was set up as shown in the figure below.

The glucose solution was boiled and cooled before adding yeast. The set up was left in stand for about 30 minutes.

  • What changes occurred in the
  • lime water (1mk)
  • glucose and yeast?                                                              (2mks)
  • Explain your answer in (a) above (3mks)
  • Name the process that was being investigated. (1mk)
  • What was the role of oil in the boiling tube? (1mk)
  • Suggest control experiments for the above experiment. (2mks)
  • Suggest the reason for boiling and cooling glucose before adding yeast. (2mks)
  • Distinguish between heterodonts and homodonts. (2mks)
  • What is the significance of diastema in herbivorous mammals? (1mk)
  • State the role of carnassial teeth in a lion? (1mk)
  • An organism was found to have the dental formula:

1    0               3            4

1                 0               2                4

  • Calculate the total number of teeth in the organism (1mk)
  • With a reason suggest the mode of feeding of the organism from which dental formula was obtained.                                                                                                   (2mks)
  • State one adaptation of the animals that uses the mode of feeding above. (1mk)
  • Briefly describe the role of Osmosis in living organisms (10 mks)
  • Explain 5 factors affecting the rate of breating in human beings. (10 mks)

MARKING SCHEME

FORM II BIOLOGY END TERM OF TERM II

  • For sucking small animals from rock’s surface or barks of trees.
  • Mosquito netting;

To prevent dirt from entering the suction tube;

  • Cell membrane
  • B- Protein layer
  • A- Phospholipids layer
  • Allows selective movement of substances in and out of the cell;
  • Encloses cell contents;
  • Presence of cell wall;

iii. Large vacuole which is centrally located.

  • [A – Cell wall B- Cell membrane    C – Nucleus  D- Chloroplasts   E – Sap Vacuole  F- Cytoplasm] 6/2 mks
  • D- They form sites for photosynthesis

E- store sugars and salts

-Osmoregulation/contribute to the osmotic properties of the cell.

C- controls all activities of a cell.

  • Contractile vacuoles
  • Golgi apparatus/bodies
  • Stem; of the dicotyledonous plant.
  • A- phloem               B- Cambium         C- Xylem
  • Offers support

-transport water; and dissolved mineral salts up the plant;

  • It is the process by which water in form of water vapour is lost to atmosphere.
  • -It helps in replacing water lost through leaves,

-Through transpiration mineral salts and water are transported up the plant

-Brings  about cooling effect to plants

  • Stomata; lenticels and cuticles ( any 2)
  • pulmonary vein
  • hepatic artery
  • Ileum /small intestines

D- Hepatic portal vein

F- venacava

E- hepatic vein

E                                                                                  D

-more urea                                                              -less urea

-Less    glucose                                                       -more glucose

-less amino acids                                                    – more amino acids

-less oxygen                                                            – more oxygen

-more carbon(iv)oxide                                          –less carbon(iv)oxide

Any 3 comparison at 3mks

  • – common bile juice which emulsifies/break down fats into(small)droplets;decreasing their surface for action by lipase enzymes

-neutralizes acidic chime; (from stomach)

-Provides a suitable alkalinemedium for pancreatic enzyme                                     ( Any two correct)

  • Process by which green plants manufacture their own food in presence of sunlight as a source of

energy.                                                                                         (1mk)

  • A- Light stage       (1mk)

B- dark stage        (1mk)

  • Q- Oxygen (1mk)

W – carbon(iv) oxide (1mk)

  • A- Granum    (1mk)

B –    stroma (1mk)

  • Condensation (1mk)
  • -Temperature

-Carbon(iv) oxide

-Light intensity

-Water availability      (Any correct)

  • There was formation of a white precipitate (1mk)
  • glucose/ yeast mixture- there was a rise in temperature (1mk)
  • effervescence occurred (1mk)

B   -An   anaerobic respiration/ fermentation occurred leading  to production of energy and carbon(iv) oxide.  (1mk)

– Fermentation led to rise in temperature, (1mk)

– carbon(iv)oxide turned limewater into a precipitate.    (1mk)

C           Aerobic respiration/fermentation

D         To prevent entry of air into the mixture

E  use of same apparatus but in place of glucose/yeast mixture, one could use glucose alone , or yeast alone,

or boiled yeast with glucose (2mks)

F      to expel any air, and cooled to avoid destroying the yeast cells      (1mk)

  • Heterodont dentition is the one where there are different types of teeth while homodont dentition refers to a situation where all teeth are of same size and shape. (2mk)
  • It provides space for the tongue to turnand move food during chewing. (1mk)
  • Modified smooth sides and sharpedges to slice through flesh and crush bones (1mk)
  • 1 0 3 48 2     = 30(1mk)
  • 0               2                4              6
  • Herbivorous ; (1mk)

-Because they lack canines      (1mk)

  • prescence of diastema for manipulation of food during chewing
  • Absorption of water from soil by root hair ; Root hair cells of a plant absorb water from the soil by osmosis. Osmosis also helps in distribution of water from cell to cell. (2mks)

-plant cells gain water by osmosis; become firm and rigid giving support to seedlings and herbaceous plants.

  • Opening and closing of stomata ;

-the guard cells synthesize glucose by photosynthesis; accumulation of glucose increases their osmotic pressure thus enables them to draw water from adjacent cells by osmosis.                      (2mks)

  • Facilitates feeding insectivorous plants;

-plants trap insects; this changes the turgor pressure (2mks)

  • Osmoregulation
  • Re-absorption of water from the kidney tubules occur by osmosis (2mks)

(5×2= 10mks)

  • – Physical activities- vigorous activities increase the breathing rate.
  • Age – young people have higher metabolic rate andtherefore breath faster than old people.
  • Health – the rate of breathing increases during sickness to remove toxins from the body
  • Altitude – the rate of breathing is higher at high altitudes than low altitudes because there is lower oxygen in higher altitudes.
  • Emotions – body emotions affect the production of hormone adrenaline which increases the general metabolisms and hence increased breathing.
  • Temperature – high temperature cause the breathing rate to increase.
  • Age – young people have higher demand for oxygen . they therefore have higher breathing rate

( Any 5×2= 10mks)

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Form 3 latest exam papers and answers term 1 to 3 free, physics topical questions with answers form 1 to 4 in all topics, free geography notes, exams, schemes of work, lesson plans: form 1 to 4, this post has 3 comments.

essay biology form 2

Am in secondary school kakuma Kenya it student for easy ready and simple answers.

essay biology form 2

So amazing…

essay biology form 2

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BIOLOGY TOPIC BY TOPIC QUESTIONS AND ANSWERS

Biology topic by topic questions and answers , you can download all the biology questions and answers for all topics for form 1, form 2, form 3 and form 4., the list includes all biology questions with their answers. use  the links below. click on  a link to a specific material., form 4_heredity questions, form 4_heredity answers, form 4_cell divsion questions, form 4_cell division answers, form 4_applied genetics questions, form 4_applied genetics answers, form 4_4. support and movement in plants and animals q, form 4_4. support and movement in plants and animals a, form 4_3. reception response and co ordination q, form 4_3. reception response and co ordination a, form 4_2. evolution q, form 4_2. evolution a, form 4_1. genetics q, form 4_1. genetics a, form 4 - support and movement in plants and animals questions - teacher.co.ke, form 4 - support and movement in plants and animals a - teacher.co.ke, form 4 - reception, response and co-ordination questions - teacher.co.ke, form 4 - reception, response and co-ordination a - teacher.co.ke, form 4 - genetics questions - teacher.co.ke, form 4 - genetics a - teacher.co.ke, form 4 - evolution questions - teacher.co.ke, form 4 - evolution a - teacher.co.ke, form 3_plant reproduction questions, form 3_plant reproduction answers, form 3_personal health questions, form 3_personal health answers, form 3_human reproduction questions, form 3_human reproduction answers, form 3_asexual reproduction questions, form 3_asexual reproduction answers, form 3_4. growth and development q, form 3_4. growth and development a, form 3_3. reproduction in plants and animals q, form 3_3. reproduction in plants and animals a, form 3_2. ecology q, form 3_2. ecology a, form 3_1. classification ii q, form 3_1. classification ii a, form 3 - reproduction in plants and animals questions - teacher.co.ke, form 3 - reproduction in plants and animals a - teacher.co.ke, form 3 - growth and development questions - teacher.co.ke, form 3 - growth and development a - teacher.co.ke, form 3 - ecology questions - teacher.co.ke, form 3 - ecology a - teacher.co.ke, form 3 - classification ii questions - teacher.co.ke, form 3 - classification ii a - teacher.co.ke, form 2_transport plants questions, form 2_transport plants answers, form 2_skin temperature questions, form 2_skin temperature answers, form 2_food diet questions, form 2_food diet answers, form 2_excretion questions, form 2_excretion answers, form 2_digestion questions, form 2_digestion answers, form 2_breathing questions, form 2_breathing answers, form 2_blood circulation questions, form 2_blood circulation answers, form 2_5. excretion and homeostasis q, form 2_5. excretion and homeostasis a, form 2_4. respiration q, form 2_4. respiration a, form 2_3. gaseous exchange q, form 2_3. gaseous exchange a, form 2_2. transport in animals q, form 2_2. transport in animals a, form 2_1. transport in plants q, form 2_1. transport in plants a, form 2 - transport in plants questions - teacher.co.ke, form 2 - transport in plants a - teacher.co.ke, form 2 - transport in animals questions - teacher.co.ke, form 2 - transport in animals a - teacher.co.ke, form 2 - respiration questions - teacher.co.ke, form 2 - respiration a - teacher.co.ke, form 2 - gaseous exchange questions - teacher.co.ke, form 2 - gaseous exchange a - teacher.co.ke, form 2 - excretion and homeostasis questions - teacher.co.ke, form 2 - excretion and homeostasis a - teacher.co.ke, form 1_respiration questions, form 1_respiration answers, form 1_photosynthesis questions, form 1_photosynthesis answers, form 1_diffusion osmosis questions, form 1_diffusion osmosis answers, form 1_cells tissues questions, form 1_cells tissues answers, form 1_cell chemistry questions, form 1_cell chemistry answers, form 1_6. nutrition in animals q, form 1_6. nutrition in animals a, form 1_5. nutrition in plants q, form 1_5. nutrition in plants a, form 1_4. cell physiology q, form 1_4. cell physiology a, form 1_3. the cell q, form 1_3. the cell a, form 1_2. classification i q, form 1_2. classification i a, form 1_1. introduction to biology q, form 1_1. introduction to biology a, form 1 - the cell questions - teacher.co.ke, form 1 - the cell a - teacher.co.ke, form 1 - nutrition in plants questions - teacher.co.ke, form 1 - nutrition in plants a - teacher.co.ke, form 1 - nutrition in animals questions - teacher.co.ke, form 1 - nutrition in animals a - teacher.co.ke, form 1 - introduction to biology questions - teacher.co.ke, form 1 - introduction to biology a - teacher.co.ke, form 1 - classification i questions - teacher.co.ke, form 1 - classification i a - teacher.co.ke, form 1 - cell physiology questions - teacher.co.ke, form 1 - cell physiology a - teacher.co.ke.

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BIOLOGY FORM TWO NOTES-Gaseous Exchange

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By Dean of Studies

Gaseous Exchange

  • This is the process by which respiratory gases (oxygen and carbon IV oxide) are passed across the respiratory surface.
  • Gases are exchanged depending on their concentration gradient.
  • In simple organisms such as amoeba, diffusion is enough to bring about gaseous exchange.
  • CO 2 diffuses out into the surrounding water while oxygen diffuses from the water across the plasma membrane into the amoeba.

Importance of Gaseous Exchange

  • Promote oxygen intake for respiration.
  • Facilitate carbon IV oxide removal from the body as a metabolic waste product.

Gaseous Exchange in Plants

  • During the day, green plants take in carbon IV for photosynthesis.
  • Oxygen is given out as a byproduct of photosynthesis and is released into the atmosphere.

Examples of respiratory Surfaces in Plants

  • Stomata in leaves
  • Roots e.g. pneumatophores
  • Lenticels in woody stems

Structure and Function of the Stomata

  • They are tiny openings on the leaf surfaces. They are made up of two guard cells.
  • Guard cells are the only epidermal cells containing chloroplasts. They regulate the opening and closing of the stomata.

Adaptations of Guard Cells

  • They are bean shaped/sausage shaped.
  • Contain chloroplast hence can photosynthesize.
  • Inner walls are thicker while outer wall is thin to facilitate the opening and closing of stomata.

Mechanism of Opening and Closing of Stomata

  • There are three theories that try to explain how the stomata open and close.

Photosynthetic theory

  • Starch Sugar inter-conversion Theory. (effect of changes in pH of guard cells)
  • Potassium Ion Theory.
  • During the day, guard cells photosynthesize forming glucose.
  • This glucose increases the osmotic pressure in the guard cells.
  • Guard cells draw in water from the neighbouring epidermal cells and become turgid.
  • The stoma opens.
  • During the night, there is no photosynthesis due to absence of light.
  • Glucose is converted into starch lowering the osmotic pressure in the guard cells.
  • Guard cells lose water and become flaccid closing the stomata.
  • This is under the influence of pH in the guard cells.
  • During the day CO 2 is used up during photosynthesis raising the pH in the guard cells.
  • In this high pH, enzymes convert more starch into glucose.
  • Osmotic pressure of the guard cells increases and water enters into them, making them turgid hence opening the stomata.
  • During the night, there is no photosynthesis. The level of CO 2 increases lowering the pH.
  • Enzymes become inactivated and starch is not converted into glucose.
  • Osmotic pressure of guard cells falls making them to lose water by osmosis.
  • Guard cells become flaccid and stoma closes.

Mechanism of Gaseous Exchange in Plants

  • Oxygen diffuses from the atmosphere where it is more concentrated into the plant.
  • CO 2 diffuses out as a metabolic waste product along a concentration gradient into the atmosphere.
  • Gaseous Exchange through the Stomata
  • Stomata are modified in number of ways depending on the habitat of the plant.

Xerophytes: These are plants adapted to life in dry areas.

  • They have less number of stomata that are small in size.
  • Stomata may be sunken, hairy and in some they open during the night and close during the day.

Hydrophytes: These are the aquatic plants (water Plants)

  • They have many stomata that are large in size and mainly found on the upper leaf surface.
  • Hydrophytes have the aerenchyma tissue with large air spaces to store air for gaseous exchange.

Mesophytes : They are plants growing in areas with adequate amounts of water.

  • They have a fairly large number of stomata found on both leaf surfaces.
  • Gaseous Exchange through the Lenticels
  • They are openings found on woody stems and they are made of loosely packed cells.
  • They allow gaseous exchange between the inside of the plant and the outside by diffusion.
  • Actual gaseous exchange occurs on some moist cells under the lenticels.
  • Gaseous Exchange through the Roots
  • Plants like the mangroves growing in muddy salty waters have specialized aerial breathing roots called pneumatophores.
  • Pneumatophores rise above the salty water to facilitate gaseous exchange.

Gaseous Exchange in Animals

Types and Characteristics of Respiratory Surface

  • Different animals have different respiratory surfaces depending on the animal’s size, activity and the environment in which it operates as shown below.
  • The respiratory surface is the basic unit of any breathing system upon which actual gaseous exchange occurs by diffusion.
  • Respiratory surfaces have the following main characteristics.
  • Must have a large surface area.
  • Must be moist to allow gases to diffuse in solution form.
  • Have a dense network of blood capillaries for efficient gaseous exchange.
  • Have a thin membrane to reduce the diffusion distance .

Gaseous Exchange in Insects

 Insects have their gaseous exchange system made of many air tubes forming the tracheal system.

  • Tracheal system is made up of spiracles and Tracheoles.
  • Spiracles are external openings found on both sides of the abdomen and thorax.
  • Spiracles have valves to control their opening and closing. They also have hairs to prevent excessive water loss from the body tissue.
  • Spiracles open into tubes called trachea. Trachea is reinforced with spiral bands of chitin to keep them open.
  • Trachea subdivides into finer air tubes called Tracheoles. Tracheoles are in direct contact with body tissues and organs and they supply individual cells with oxygen.
  • Tracheoles do not have bands of chitin and therefore they allow gaseous exchange across their thin moist walls.

  Mechanism of Gaseous Exchange in the Tracheal System of an Insect

  • Air is drawn into and out of the tracheal system by muscular movement of the abdominal wall.
  • When spiracle valves are open, air is drawn into the tracheal system. The valves close and air is forced along the system by muscle movement.
  • Oxygen diffuses into the tissue fluid and into the cells.
  • CO2 diffuses out of the cells and into the tissue fluid then into the tracheal system.

Gaseous Exchange in Fish

  • Mouth (buccal) cavity.
  • Opercular cavity.
  • Gills are made of a long curved bone called the gill bar.
  • Gill filaments arise from one side of the gill bar. They are many and suspend freely in water providing a large surface area for gaseous exchange.
  • Gill rakers arise from the other side of the gill bar. They are teeth like and they prevent solids present in water from damaging the delicate gill filaments.
  • Blood vessels enter the gill bar and branch into the gill filaments as blood capillaries.
  • Operculum is found on either side of the body near the head and it also protects the delicate gills.

Mechanism of Gaseous Exchange in the Gills of a Bony Fish

  • Floor of the mouth cavity is lowered increasing the volume of the mouth cavity but lowering the pressure.
  • Water flows into the mouth cavity and the operculum closes.
  • Operculum on either side bulge outwards without opening. This increases volume in the gill cavity but the pressure drops.
  • Water containing dissolved oxygen flows from the mouth cavity to the gill chamber over the gills.
  • The mouth closes and the floor of the mouth cavity is raised.
  • The remaining water in the mouth is forced to flow towards the gill chamber.
  • Oxygen diffuses from the water into the blood through the thin walls of the gill filaments. It combines with haemoglobin for transportation to all body parts.
  • CO 2 diffuses from the blood into the flowing water.
  • To ensure maximum gaseous exchange, the water flowing over the gills and the blood in the gills flows in opposite directions.
  • This is called counter current flow system and it ensures that at all the points, concentration of oxygen is always higher in the water than in the blood.
  • If the water and blood were flowing in the same direction, gaseous exchange will not be that effective.
  • Where the oxygen is 50% in water, there is no concentration gradient because blood also has 50% oxygen concentration.

Mechanism of Gaseous Exchange in Amphibians

  • Amphibians live on both land and water and therefore exhibit the following methods of gaseous exchange.
  • Gaseous exchange through the lining of the buccal cavity
  •  Gaseous exchange through the lungs
  • Gaseous exchange through the skin
  • Gaseous exchange through the mouth (buccal) cavity
  • Air is taken in or expelled from the mouth cavity by raising and lowering of the floor mouth.
  • Lining of the mouth cavity is moist to dissolves oxygen.
  • There is a rich supply of blood capillaries under the lining of the mouth cavity. Oxygen diffuses into the blood and is carried by haemoglobin to all parts of the body.
  • Carbon IV oxide from the tissues is brought by the blood to the mouth cavity where diffuses out.
  • Gaseous exchange through the lungs
  •  The frog has two lungs which are connected to the buccal cavity.
  • T he inner lining of the lungs is moist, thin and is richly supplied with blood capillaries.
  • During inspiration, the floor of the mouth cavity is lowered and nostrils are open. Air rushes through the open nostrils into the mouth cavity.
  • Nostrils close and the floor of the mouth cavity is raised. This reduces the volume and increase the pressure in the mouth cavity forcing air into the lungs.
  • Carbon IV oxide from the tissues diffuse into the lung while the oxygen from the lungs diffuses into the tissues.
  • Frogs have a thinner and moist skin than the toads.
  • There is large network of blood capillaries below the skin to carry the respiratory gases.
  • Oxygen from the air and water diffuse through the skin into the blood stream.
  • Carbon IV oxide diffuses out of the blood capillaries through the moist skin into the surrounding water and air.

Mechanism of Gaseous Exchange in Mammals

  • The following structures are involved in gaseous exchange in mammals;
  • Nose (Nostrils)
  • Chest cavity (ribs and intercostals muscles)
  • Diaphragm .
  • It has two openings called nostrils which let in air into the air passages.
  • As air moves in the passages, it is warmed and moistened
  • The lining of the nasal cavity has also the sense organs for smell.
  • It is located on top of the trachea
  • It is called the voice box. It controls the pitch of the voice.
  • It is a tube made of rings of cartilage which prevents it from collapsing during breathing.
  • Inside it is lined with ciliated epithelium. Cilia beat in waves and move mucus and foreign particles away from the lungs towards the pharynx.
  • As the trachea enters the lungs, it divides into two branches called Bronchi (Bronchus).
  • They are found in the chest cavity and they are enclosed by a double membrane called the pleural membrane.
  • The space between the membranes is called the pleural cavity.
  • Pleural cavity is filled with pleural fluid which reduces friction making the lungs to move freely in the chest cavity during breathing.

Diagrams 

  • In the lungs each bronchus divides into small tubes called bronchioles.
  • Bronchioles branch further to form air sacs called alveoli (alveolus)
  • Alveolus is covered by a fine network of blood capillaries.

The mechanism of breathing

  • Breathing is achieved by changes in the volume and air pressure of the thoracic cavity.
  • Thoracic cavity is enclosed by ribs.
  • Ribs are covered by intercostals muscles.
  • The diaphragm is a muscular sheet of tissue below the chest cavity. It curves upwards in the form of a dome shape.
  •  Breathing mechanism involves two processes.
  • Inspiration (Inhalation) i.e. breathing in.
  • Expiration (Exhalation) i.e. breathing out.

Inspiration (Inhalation) i.e. breathing

  • This occurs when the volume of thoracic cavity increases and the pressure decreases.
  • External intercostals muscles contract while the internal intercostals muscles relax.
  • Ribs are pulled upwards and outwards.
  • Diaphragm flattens increasing the volume of the thoracic cavity while decreasing the pressure inside it.
  • Air rushes into the lungs through the nose and trachea inflating the lungs.

Diagrams page 62

Expiration (Exhalation) i.e. breathing out

  • Volume of thoracic cavity decreases while pressure increases. This is brought about by the following;
  • External intercostals muscles relax while internal ones contract.
  • Ribs move downwards and inwards.
  • Diaphragm relaxes and regains its original dome shape.
  • Volume of the thoracic cavity decrease and pressure increases.
  • Air is forced out of the lungs through the air passages to the atmosphere.

Gaseous exchange in the alveolus

  • Alveoli and blood capillaries are made of very thin walls.
  • The wall of the alveolus is covered b a film of moisture which dissolves oxygen in the inhaled air.
  • Oxygen diffuses through the epithelium of the alveolus, the capillary wall and through the cell membrane of the red blood cells.
  • In the red blood cells it combines with haemoglobin.
  • Carbon (iv) oxide is more concentrated in the blood capillaries than in the alveoli.
  • It therefore diffuses from the capillaries into the alveoli.
  • Water vapour also passes out of the blood by the same process.

Diagram page 64 KLB

Percentage composition of gases in inhaled and exhaled air

Regulation of Breathing

This is controlled by a part of the brain called Medulla oblongata .

Factors affecting the rate of breathing in humans

Breathing rate increases during vigorous activity.

Younger people have a faster breathing because their bodies have more energy demand.

Things like anxiety, fear and fright increases the breathing rate.

  • Temperature

Relatively high temperatures increase the rate of breathing.  However, very high temperatures reduce the breathing rate.

If there is fever (high body temperature), the breathing rate increases. Some respiratory diseases however, make breathing difficult.

Lung Volumes

  • Lung capacity

This is the total amount of air the lungs can hold when completely filled. The lungs of an adult have a capacity of about 5,500cm 3

  • Tidal volume

This is the amount of air taken in and out of the lungs during normal breathing. Tidal volume is about 500cm 3

  • Inspiratory reserve volume

This is an additional volume attained after having a forced inhalation in addition to the tidal volume. It is about 2000cm 3

  • Inspiratory capacity

This is the tidal volume +Inspiratory reserve volume.

  • Expiratory reserve volume

This is air removed after a forced exhalation. It can be up to 1,300cm3

  • Vital capacity

This is the deepest possible exhalation. This air can only be forcibly pushed out of the lungs.

  • Residual volume

This is the air that normally remains in the lungs after the deepest exhalation. It is normally about 1,500cm 3

  Diagram

Diseases of the Respiratory System

It is caused by:

  • Allergens such as pollen grains, certain foods and drugs
  • Infections of the lungs by bacteria and viruses
  • Difficulty in breathing
  • Wheezing sound when breathing

Treatment and Control

  • Avoiding the causative agents
  •  Injection of drugs and oral application of pills
  • Spraying directly into the bronchial tubes with a muscle relaxant

There are two types; Acute and Chronic

  • Production of thick greenish or yellowish sputum
  • Difficulty in walking and sleeping
  • Seeking early medical assistance
  • Whooping cough

It is caused by a bacterium called Bordetella pertussis.

  • Prolonged coughing and vomiting
  • Conjuctival haemorrhage (bleeding)
  • Convulsions and coma
  • Severe pneumonia in the bronchioles
  • Ulcers and heart complications
  • Emaciation due to repeated vomiting
  • Use of antibiotics
  • Use of a balanced diet on patients
  • Children immunization at early age

It is caused by a bacterial called Streptococcus pneumoniae

  • Chest pains
  • Deposits of fluids in the lungs
  • Use of antibiotics such as penicillin and sulphonamides
  • Avoid overcrowding.
  • Good ventilation in living houses
  • Pulmonary Tuberculosis

It is caused by a bacterium called Mycobacterium tuberculosis .

  • Weight loss
  • Coughing with blood stained sputum.
  • Use of antibiotics such as streptomycin
  • Pasteurization of milk
  • Immunization using BCG (Bacille Calmette Guerin)
  • Use of radiography (X-Ray)
  • Lung cancer

Cancer is uncontrolled cell growth in the body causing tumours.

Some general causes

  • Inhalation of cancer causing substances such as asbestos
  •  Exposure to radiations such as X-rays, radioactive substances such as uranium and substances that alter the genetic composition of the cell such as mustard gas

Treatment and control

  • Surgery to remove the tumour
  • Radiotherapy
  • Chemotherapy
  • Use of some drugs
  • Not smoking

Download More Revision Questions and Answers in pdf:

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Essays About Biology: Top 5 Best Examples and 6 Prompts

Writing essays about biology can be difficult because it’s composed of many subtopics. Check out this article for our top essay examples and writing prompts.

Biology came from the Greek words “bios” (life) and “logos” (study). It’s why biology is the study of life or living organisms. Aside from being a natural science, it also has consolidated themes, such as cells making all organisms. Because it’s a broad topic, biology is divided into specialized fields such as botany, genetics, zoology, microbiology, medicine, and ecology. 

Biologists consider living beings’ origin, evolution, growth, function, structure, and distribution. It’s a comprehensive subject, so there are many things you can write about in your essay. However, at the same time, you might find it challenging to focus on just one area. 

Below are examples to give you an idea of how to write your essays about biology:

1. Essay About Biology by Kelli Wilkins

2. my interests in biology by anonymous on essaywriting.expert, 3. essay on the importance of study of biology by akhila mol, 4. what biology means to me by anonymous on studymode.com, 5. how my biology teacher changed my perspective of learning the subject by sankalan bhattacharya, 1. biology in my everyday life, 2. something i realized because of biology, 3. my memorable biology class experience, 4. genetics’ role in people’s diseases, 5. my experience during the pandemic, 6. biology and health.

“Studying Biology is important for a number of reasons, but in particular because it is used in every field. If we did not have a good understanding of Biology then nobody would be able to understand how bodies work, and how life on earth functions.”

Wilkins shares her desire to study anatomy, a branch of biology, and expounds on what makes biology an essential field. Because biology lets people know more about the world, she digs into why she’s interested in anatomy, specifically to find ways to cure illnesses and develop technologies to discover new treatments. She ends her essay by relating biology to the existence of doctors and hospitals. 

“It is known that education plays an important role in the life of any individual. It gives an opportunity to develop personality and gain specific skills, to get profound knowledge and experience in order to apply them practically in the future. As for me, my major goal is to study Biology in order to get appropriate knowledge and skills required for my future profession.”

The author shares why they want to study biology, referring to the human body as the “perfect machine” and curious about how it performs each of its systems’ functions. The writer also mentions how biology is critical to their future profession. They aim to help people with their health problems and relay their desire to research the brain to find more data on it. 

“The study of biology owes great significance in human life, because man for its day-to-day requirements is dependent on plants and animals either directly or indirectly.”

Mol lists seven reasons why humans need biology in their daily lives. Her list includes health, diseases, agriculture, horticulture, food, animal breeding, and entertainment. She expounds on each point and how they affect a man during his time on Earth. She explains each relationship in a simple manner that’s easy to understand for the readers.

“Without biology, we would have no idea about an organism’s makeup, or the most basic unit of life, a cell… Biology influences me in many ways. Biology influences me by teaching me why to take care of the environment, why I am to take care of my body, and by giving me a better overall view of all scientific areas of study.”

In this short essay, the writer lists down reasons why biology is essential. These reasons include taking care of the environment, one’s body, and others. The author also expounds on their reasons by presenting facts supporting biology’s importance to the world and human lives.

“He told that the syllabus may be a good way to prepare for an exam but our knowledge should not be limited to any syllabus and the questions that were asked in the examination were related to the topic only. He told that if we try to know things in detail and understand them properly then the interest in the subject will develop, otherwise, students will not treat the subject as a subject of their choice. 

Bhattacharya shares his experience with a teacher with a unique teaching style. His Biology teacher from Class 7, before the era of the internet, don’t just carry one book to get all his lessons from. Instead, he has a notebook with the collated information from many books to teach his class. 

Bhattacharya’s teacher taught them things that were not in the curriculum, even if following the curriculum would give him higher points in his evaluation. He only wanted his students to learn more and share with them why learning differs from just knowing. 

Do you want to be sure you have an excellent essay? See our round-up of the best essay writing apps to help you check your output.

6 Prompts for Essays About Biology

Prompts for essays about biology

You don’t have to be a biology student to write an essay about the subject. If you’re looking for easy prompts to write about, here are some to get you started:

If mitochondria are the powerhouse of the cell, who is the powerhouse of your classroom? Your home? Relate a biology topic to a similar structure in your life, then explain why you think they are the same. 

For instance, you can compare your mother to mitochondria which generate the energy needed to power a cell. The cell being you. You can say that she gives you energy every day by being there and supporting you in whatever way she can. This prompt bodes for a creative and intriguing essay.

Relay a lesson you learned from biology and how it perfectly explained something you were once hesitant about. Such as being insecure about your big ears – only to know from a biology trivia that ears never stop growing. You can then share how this help lessen your insecurity because you now know large ears are normal. 

Do you have a memory you won’t forget that happened during biology class? Narrate this story and explain why it’s something that left an impression on you. To give you an idea, you can talk about the first time you dissected an animal, where you first realized how complex organisms are and that they are made of many systems to function, no matter how small.

Gene action and heredity are evolving. If you have a genetic illness or know someone who has it, you can share your experience. Then explain what your genes have to do with the disease. Is it something you got from your parents? Did they inherit it from your grandparents? Finally, you can add what your parents’ and grandparents’ lives were like because of the disease.

Virology, another branch of biology, studies viruses and viral diseases. A recent example is the coronavirus pandemic, where more people realized the importance of knowing a virus’ origin, structure, and how they work. Write an essay where you explain how the pandemic operates, such as why people should wear masks, social distance, etc.

For this essay, you can write about how biology helps you care for your health. For example, you can include how biology helped doctors give you the appropriate diagnosis, how you had the opportunity to have the proper treatment, etc. 

If you want to write on a related topic, here are essay topics about nature you can consider for your next essay. 

essay biology form 2

Maria Caballero is a freelance writer who has been writing since high school. She believes that to be a writer doesn't only refer to excellent syntax and semantics but also knowing how to weave words together to communicate to any reader effectively.

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2024 Essay Preparation for A Level Biology AQA

2024 Essay Preparation for A Level Biology AQA

Subject: Biology

Age range: 16+

Resource type: Lesson (complete)

Julwilliams

Last updated

6 February 2024

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essay biology form 2

This is the latest and only version, recently updated with last year’s (2023) accessible essay

**This resource makes PRACTISING and REVISING for the AQA Paper 3 Biology Essay, SPECIFIC, and EASY.

TEACHERS , use as a lesson resource, throughout upper 6, and as a preparation session before Paper 3. STUDENTS use for focused revision and to practise writing essay paragraphs. You can even memorise paragraphs to rewrite.

All my students using this resource scored in double figures, with many scoring over 19/25 in 2023.

CONTEXT: Every year at least one essay is very accessible, usually both are. This resource is to prepare for the accessible essay(s).

Included is

  • key revision of the 14 common topic areas (AO1) to learn.
  • written importance examples (AO2) to learn, from the 14 common topics.
  • a figure on how often each topic has appeared on essay mark schemes from 2017-2023.
  • a list of the accessible titles in the essays (from 2017-2023)
  • an easy-to-understand essay mark scheme

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I hate to say it but, yes, you should dress for success

  • Maybe work attire shouldn't matter, but it does. 
  • For better or worse, studies show humans form impressions about each other at a glance.
  • These impressions are based in part on clothes.

Insider Today

We've covered how to make a fortune , how to manage (or fire ) your boss, what it means to work smarter , and many other career topics. And now, it's finally time to discuss the perennial and important work-related question: How should you dress?

The short answer is:

You should "dress for success."

That usually means dressing professionally, the way most successful people in your organization and industry dress — those people whose jobs and reputations you eventually want.

Now, especially early in your career, it's easy to resent that.

For example, you might feel that your personal clothes are part of your identity and that having to dress differently at work is an affront to who you are. Or you might be confused about what it means to dress professionally.

Also, "professional" clothes can be expensive and a pain to care for.

And sometimes they're uncomfortable.

I sympathize — because I used to think that way!

When left to my own devices, I dress extremely casually. For example, thanks to a moth invasion, most of my sweaters look like they were used as targets at a shooting gallery. But when I'm home, I still wear them. Because they work. Also, from April to October, when it's hot and humid in the northeast, I usually wear shorts. Because they're comfortable.

(My editor, Hayley Peterson, once wrote a story about "short suits" — a short-lived fashion trend that tried to blend suits with shorts. Fortunately, I never read it. Because I might have tried it. And then I would have looked even more ridiculous.)

Anyway, at the beginning of my career, my desire to "just be me"—and my hatred of formal clothing—actually factored into the kind of work I chose to do. (Freelance writing, teaching tennis, etc.)

Even today, I have to remind myself that the clothes that I reach for instinctively at home are not suitable for work — including Zooms.

But I no longer resent society or my employers or colleagues for making me dress up a bit.

This is because I now see that, whether or not it should, appearance and professionalism in the workplace (including clothing) affect how you're perceived — and, therefore, can impact career progression and, in some cases, the quality of your work. (I'll come back to this.)

I also see — and this is key — that it's not about me .

It's about respecting my colleagues and job enough to make an effort to look and act professionally and represent my organization in a way that helps it.

No, you don't necessarily have to wear suits

Importantly, "dressing for success" does not mean always wearing a high-end suit. In fact, in today's workplaces, that would rarely be appropriate — and could even be considered bizarre, ostentatious, or stuffy.

It also doesn't mean you have to look "sharp" or "stylish." (No one will ever accuse me of that!)

"Dressing for success" just means looking professional and in keeping with your workplace culture — as opposed to how you might dress on the weekend or at home.

In some workplaces, that means suits.

In others, it means " business casual ."

In others, it's "anything but pajamas or bathing suits."

In others, (it seems), it's almost anything .

It also, of course, matters what kind of work you do. If you're an individual contributor like a software developer or writer, where you rarely interact with colleagues in person or on video and never physically represent your employer to the outside world, your clothes are less important. Your boss may care what you're wearing, so it will behoove you to know that and make an effort. But the less you visually interact with people, the less it matters.

In these cases, moreover, you can argue credibly that you do your best work when you are most comfortable and, therefore, that it's in your employer's interest to define "dressing for success" as "dressing in the way you do your best work."

(Though, even here, it's worth pointing out that some individual contributors — like the biographer Robert Caro — wear a suit and tie every day even when they sit alone in their office and never interact with anyone . Why? In Caro's case, he's said it reminds him that he's a professional who has a job to do, and is at work.)

When you do visually interact with people at work, moreover — internally or externally — your clothes and general appearance make a much bigger difference.

This is because, for better or worse, and whether they should or not, humans form impressions about each other at a glance . These impressions are based on facial and behavioral cues as well as… clothes .

Not surprisingly, research suggests that looking more professional creates a better first impression .

(It also suggests that shelling out to buy a bespoke suit vs. an off-the-rack one pays off. So apparently, in the days when I worked on Wall Street and wore suits, I should have done that!)

Once your bosses, colleagues, and outsiders have formed an impression of you as a competent and respectful professional and an asset to your organization, you have more latitude. In that case, joining a weekend or evening Zoom in your gym clothes will be understood as a situational-specific convenience, not a benchmark of your professionalism and attitude.

But if you always dress in gym clothes, pajamas, or cut-offs, even when meeting in person with colleagues, clients, prospective clients, outsiders, and people who work for you, many of these folks may assume that you care little about your work and job.

These people might further assume that, if you don't care enough to look professional, you also probably don't care enough to behave professionally in other ways that could affect the quality of work you do.

That impression could hurt not only you and your employer and your career prospects, but your ability to do your job.

As with other aspects of professional conduct, dressing for success is not about you . It's about your respect for the organization that is paying you and the colleagues you work with. And it makes a difference.

essay biology form 2

Watch: Psychologists Reveal What People Think About You Based On What You Wear At The Office

essay biology form 2

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  24. 2024 Essay Preparation for A Level Biology AQA

    This resource is to prepare for the accessible essay(s). Included is. key revision of the 14 common topic areas (AO1) to learn. written importance examples (AO2) to learn, from the 14 common topics. a figure on how often each topic has appeared on essay mark schemes from 2017-2023. a list of the accessible titles in the essays (from 2017-2023)

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