IGCSE Biology Workbook Answers

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Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 1

IGCSE Biology Workbook Answers

1 Characteristics and classi?cation of living things

Core 1 nutrition - taking in materials for energy, growth and development respiration - the breakdown of food in cells for energy, growth and development

excretion - the removal from an organism of toxic materials and substances in excess of requirements

sensitivity - the ability to detect and respond to changes in the environment reproduction - making more of the same kind of organism growth - a permanent increase in size

movement - an action by an organism causing a change of position or place [1 mark for each correct statement]

2

Any suitable sentence with seven words linked to the characteristics of life, e.g. Most Rats Start Gathering Rice Every Night [3]

3 Across: 5 excretion, 6 nutrition, 7 respiration [3] Down: 1 sensitivity, 2 reproduction, 3 movement, 4 growth [4] 4

Respiration is the release of energy from food substances in cells. Breathing is the process of ventilation of the lungs. [4]

5 ref. to faeces being undigested food; which has not been formed through metabolic processes [2] 6 (sh and amphibians) Common features - any two from: cold blooded; have eyes; produce jelly-covered eggs (in water) [2] Differences: ref. to gills/lungs; ns/legs; scales/moist skin [1] (amphibians and reptiles) Common features - any two from: four legs; eyes and ears; cold blooded; lungs [2] Differences: ref. to moist skin/scales; jelly-covered eggs/waterproof shell [1] (birds and mammals)

Common features - any two from: eyes and ears; warm blooded; lungs [2] Differences: ref. to feathers/fur; two legs/four legs; eggs with hard shell/live young; beak/no beak (or ref. to teeth); ears/ears with pinna; no mammary glands/mammary glands [1]

7 A insect, B arachnid, C myriapod, D crustacean, E mollusc, F annelid, G nematode [7] 8 [3]

Plant1a1b2a2b3a3bName of plant

A----Primula vulgaris

B ----Narcissus pseudonarcissus

C----Ranunculus caria

D ----Hyacinthoides non-scripta

Extended

9 a i Any three from: multicellular; have roots/ stems/leaves; ref. to seed production [3] ii Any three from: (cellulose) cell wall; sap vacuole; nucleus; cytoplasm; membrane [3] b leaf shape - broad; leaf veins - parallel; cotyledons - two; grouping of ower parts - inthrees [4] 10 protoctists, fungi, plants, bacteria [4] 11 a Fungi - any two from: presence of hyphae; ref. to mycelium; chitin in cell walls; no chlorophyll present; ref. to spores;, enzymes secreted for food digestion [2]

Bacteria - any two from: small; cell wall - not

cellulose or chitin; membrane/cytoplasm present; glycogen granules present; DNA in form of one coiled chromosome; no nucleus [2]

Viruses - any two from: very small; no special

cell structure; have a strand of DNA/RNA; surrounded by protein coat/ref. to capsid; only show reproduction [2] b virus, bacteria, fungi [1] c require a host cell to reproduce [2]

Answers

Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 2

Exam focus

Core 1 B [1] 2 Any three from: movement; excretion; nutrition (feeding); sensitivity (irritability) [3] 3 a Any two from: movement; excretion; sensitivity [2] b

Any two from: growth; reproduction; respiration [2]4 Any three from: sensitivity; nutrition; growth; excretion [3]

5

A - Nucellus lapillus; B - Calliostoma ziziphinum; C - Patella vulgata; D - Littorina obtusata; E - Cerastoderma edule [5]

2 Organisation of the organism

Core 1 a - F; b - F; c - T; d - T; e - F; f - T; g - T; h - F; i - T; j - T [10] 2 a A membrane, B cytoplasm, C cell wall, D chloroplast, E (sap) vacuole, F nucleus [6] b chloroplast, cell wall, sap vacuole [3] 3 chromosome, nucleus, cell, tissue, organ, organ system, organism [3] 4 a magnication actual size = observed size [1] b 12

2.8 = × 4.3 [2]

5 100 =
15 actual size; actual size = 15

100 = 0.15 mm [2]

6 a A group of cells with similar structures; working together to perform a shared function [2] b

Animal tissues and functions - any two examples, e.g. ciliated cells - waft mucus with dust or bacteria away from the lungs; muscle cells - can contract to cause movement; red blood cells - transport oxygen around the body [4]Plant tissues and functions - any two examples, e.g. root hair cells - absorb water and mineral salts/anchor the plant into the soil; xylem cells - transport water and mineral

ions from roots to leaves/provide strength for the stem [4]

Extended

7 a contains cell organelles, site of chemical reactions [2] b prevents cell contents from escaping, controls the passage of substances into and out of cell [2] c controls cell activities, controls cell division/ development [2] 8

Any one plant cell, e.g. root hair cell; on surface of young roots; absorption of water/absorption of mineral salts/anchorage of plant into the soil [3]

Any three animal cells, e.g. sperm cell, produced in testes, fertilisation of egg/reproduction; ciliated cell, found in respiratory tract, waft mucus with bacteria away from the lungs; epithelial cells on villi, on surface of ileum, increase surface area to absorb products of digestion, e.g. glucose [9]

Exam focus

Core 1 a cell membrane, cytoplasm, nucleus [3] b i chloroplast [1] ii chlorophyll, traps light energy for photosynthesis [2]2 a Any two from: cell wall; chloroplast; sap vacuole [2]

b controls cell activities and development - B; contains cell organelles and is the site of chemical reactions - D; waft mucus and bacteria away from the lungs - A; controls whatsubstances enter and leave the cell - C [4]

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Answers

Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 3 3 organ - several tissues grouped together to make a structure with a special function, e.g. heart, leaf [2] ; organ system - a group of organs with closely related functions, e.g. circulatory system, ?ower [2] ; tissue - a group of cells of similar structure that work together to perform a special function, e.g. muscle, xylem [2]

Extended

4 [10]

CellOrganelle(s)More/less/

noneExplanation muscle cellmitochondriamoreneeds a lot of energy from respiration for contracting red blood cellnucleusnoneprovides more space for haemoglobin upper epidermalchloroplastsnonemakes the cell transparent so light can pass through

CellOrganelle(s)More/less/noneExplanation

liver cellmitochondriamorecarries out many chemical reactions, requiring energy from respiration xylemnucleusnoneallows water to flow freely through the vessel 5 a The leaf contains a number of different tissues, which work together to carry out photosynthesis/transpiration. [2] b A - (waxy) cuticle - waterproofs the leaf; B - upper epidermis - allows light to pass through/acts a barrier to microbes; C - palisade (mesophyll) - main site of photosynthesis; D - xylem - transports water and mineral salts; E - phloem - transport products of photosynthesis/carries out translocation; F - guard cell - controls exit of water vapour from the leaf [12]

3 Movement in and out of cells

Core 1 movement of a substance from a region of high concentration to a region of lower concentration down a concentration gradient [3] 2 a i oxygen [1] ii Any three from: short distance; big concentration gradient; small molecules; large surface area; higher temperature [3] b i Rate of diffusion would drop; because the molecules have a lower kinetic (movement) energy/molecules move more slowly [2] ii Rate of diffusion would increase; because the concentration gradient would increase or be maintained [2] 3 a i labels to parts, such as those shown below [4] ii arrows such as those shown below (through a stoma, through air space in spongy mesophyll, into palisade mesophyll cell) [3] upper epidermis palisade mesophyll cell air space stoma b i Upper epidermis has an impermeable layer of waxy cuticle [1] ii The guard cells close the stomata to reduce transpiration, preventing gas exchange [1]

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Answers

Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 4 4 roots, osmosis, higher, lower, membrane, turgid, ?accid, wilting, small, partially [10] 5 a Level in the hollow goes down; level in the dish goes up [2] b

There is a higher concentration of salt in the dish; so water moves from the hollow to the dish; through the potato cells by osmosis [3]

c Water moves out of the root hair cells by osmosis; so the cells become ?accid and die; the plant then dies because it has lost the ability to absorb water [3]

Extended

6 The movement of a substance across a membrane from a region of lower concentration to a region of higher concentration; against a concentration gradient; using energy [3] 7 a

plant A: diffusion only - roots have absorbed nitrate until there is no concentration gradient [2]; plant B: diffusion and active uptake - the roots have absorbed nitrate against a concentration gradient, building up a higher concentration than that present in the soil [2]

b

Plants need energy from respiration to carry out active transport; cyanide prevents respiration [2]c Nitrate is needed for protein synthesis; protein is needed for growth [2]

8 [4]

SubstanceDiffusionOsmosisActive transport

oxygen water (accept) phosphates carbon dioxide 9 Zone A - as the sugar solution becomes less concentrated, more water enters the potato cells by osmosis, so the tissue gains mass. The more dilute the sugar solution, the more mass is gained [3]

Zone B - as the sugar solution becomes more concentrated, more water leaves the potato cells by osmosis, so the core loses mass. The more concentrated the sugar solution, the more mass is lost. Between 0.6 mol dm

- 3 and 1.0 mol dm - 3 , there is no additional mass lost as the potato cells have become fully ?accid in each case [3]

Zone C - at this point there is no net gain or loss of mass by the potato core as the water potential inside the cells is the same as the water potential of the surrounding sugar solution [3]

Exam focus

Core 1 D [1] 2 a A alveolus/air sac, B capillary, C red blood cell [3] b i arrow from inside the alveolus to a red blood cell [1] ii arrow from blood plasma to inside the alveolus [1] iii arrow along capillary from pulmonary artery to pulmonary vein [1] c i diffusion [1] ii ref. to breathing to keep oxygen levels in the alveoli high; ref. to blood constantly moving through capillaries, bringing blood low in oxygen [2]

Extended

3

Type of

cellSubstance absorbedProcess(es) usedDescription of gradientEnergy used? (root hair cell)(water)osmosishigh to lowno (phosphate)

1 diffusion

2 active uptake1 high to low

2 low to high1 no 2 yes (villus cell in small intestine)(glucose)1 diffusion

2 active uptake1 high to low

2 low to high1 no 2 yes [15] 4 a i The concentration of water is higher outside the cell; so water enters the cell; by osmosis; the cell becomes turgid. [4]

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Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 5 ii The concentration of water is higher inside the cell; so water leaves the cell; by osmosis; the cell becomes plasmolysed, then ?accid. [4] b i The concentration of water is lower inside the cells than in the plasma, so water enters the cells, by osmosis, the cells become turgid, then burst because they have no cell wall. [3] ii Red blood cells are no longer able to transport oxygen, so cells are unable to respire, resulting in an energy shortage. [2] 5 a, b

Sugar

concentration / mol dm 3

Start

length/ cmLength after 1 hour/cmChange in length /cm% change in length

0.05.05.3 0.3 6.0

0.25.05.1 0.1 2.0

0.45.04.7- 0.3 -6.0

0.65.04.4- 0.6-12.0

0.85.04.3- 0.7-14.0

1.05.04.3- 0.7-14.0

[4]c % change in length -20.0 -15.0-10.0 10.0 -5.05.0 0.0

0.00.20.40.60.81.0

1.2 sugar concentration/mol dm -3 [4] d i 0.26 mol dm -3 [1] ii The concentration of sugar in the potato cells is the same as the concentration in the surrounding solution; so there is no net movement of water molecules. [2] e

Any two from: leave all the cores in the solutions for the same amount of time; use the same volume of solution in each test tube; cut all the cores to the same diameter [2]

f Set up two or more cores for each concentration, measure the length of the cores in millimetres, weigh the cores instead of measuring length. [1]

4 Biological molecules

Core 1 [1] 2 a carbon, hydrogen, oxygen b carbon, hydrogen, oxygen c carbon, hydrogen, oxygen, nitrogen [3] 3 a starch; obtaining energy glucose chemical bond b fat/lipid; energy/insulation/formation of cell membranes/hormone formation glycerolchemical bond fatty acid c protein; growth/tissue repair/enzymes/cell membranes/hormone formation amino acid chemical bond [13] 4

vitamin C - DCPIP - colourless; reducing sugar - Benedict's solution - brick red; fat - ethanol - white emulsion; protein - Biuret solution - violet (halo); starch - iodine solution - blue-black [5]

Extended

5 a GA T C A A CC T G G T [ 3 ]

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Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 6 b double helix [1] c mutation [1] 6 Any six points from: enzymes need water to work in; so they can digest large insoluble food molecules; e.g. starch/fat/protein; digested food molecules can pass through membranes

in solution; blood plasma is mainly water; substances dissolved in it are transported in blood; e.g. glucose/salts/urea/carbon dioxide/hormones/soluble proteins; waste or toxic materials are dissolved in water to form urine; being diluted in water reduces toxic properties of, e.g. urea; oxygen dissolves in moist layer in alveoli to diffuse into blood cells [6]

5 Enzymes

Core 1 a A substance that increases the rate of a chemical reaction and is not changed by the reaction. [2] b A protein that functions as a biological catalyst. [2] 2 a enzyme substrateend product amylase starchmaltose [ 3 ]

b Any two points from: starch is a larger molecule; starch is insoluble while glucose is soluble; starch is a polysaccharide/polymer while glucose is a monosaccharide/monomer. [2]

c Protease only digests proteins, amylase only digests starch. Enzymes are speci?c. The active site in protease will not have a complementary shape to the active site in amylase, so the substrate (starch) will not ?t. [2]

Extended

3 a 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0

0204060

the reaction is speeding up fastest here denaturing is taking place here optimum reaction rate the reaction is slow here [4] b i The reaction would speed up because the substrate and enzyme molecules would move faster/gain more kinetic energy; so there would be more collisions. [2] ii There would still be no reaction; because all the enzyme molecules have been denatured by the high temperature. [2] 4 temperature, pH, concentration of substrate [3]

Exam focus

Core 1 a i amylase [1] ii maltose [1] iii two from: energy source, to convert to cellulose, convert to materials for growth [2] iv Starch is a large, insoluble molecule while maltose is smaller and soluble. [2] b Enzymes are only active in water; cells become turgid - leading to expansion. [2]

Extended

2 a i lipase [1] ii protease/pepsin [1] b Enzymes digest molecules causing the stains; the small molecules produced are soluble. [2] c The enzymes in the powder would be denatured; so they would not digest the stains. [2] d

Amino acids are small, soluble molecules; while proteins in blood are large, insoluble molecules. [2]

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Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 7 3 a Any ?ve from: the food molecule is the substrate; the enzyme has an active site; which combines temporarily with the substrate to form an enzyme-substrate complex; bonds are broken in the substrate molecule; the products are formed; the products are small and soluble [5]b Enzymes have a speci?city; they have a complementary shape to the substrate molecule they work on; so the active site and substrate ?t closely together to allow the reaction to happen [3]

6 Plant nutrition

Core 1 a carbon dioxide + water s unlight c hlorophyll oxygen + glucose [2] b i sucrose ii starch [2] c Chlorophyll traps light energy. [1] d

Any three from: shortage of oxygen; shortage of food; shortage of nesting sites; shortage of hiding places [3]

2 a palisade (mesophyll) cells [1] b guard cells [1] c (upper) epidermis cells [1] d xylem cells [1] e phloem cells [1] 3 Boil the leaf in water: to kill the leaf - this makes it permeable. Boil the leaf in ethanol: to decolourise the leaf, since chlorophyll dissolves in ethanol. Rinse the leaf in water: boiling the leaf in ethanol makes it brittle, so the water softens it. Spread the leaf out on a white tile: so the results will be easy to see. Add iodine solution to the leaf: to test for the presence of starch. [5]

Extended

4 a Nitrate ions are needed to form amino acids, to build proteins; proteins are needed for growth. [2] b Magnesium ions are needed to make chlorophyll; chlorophyll is needed to trap light energy for photosynthesis. [2] 5 a i violet and orange/red [2] ii green [1] b Use a bright light to shine on the Elodea in a beaker of water. Measure the light intensity using a light meter, or measure the distance between the lamp and the plant. Allow the plant to adjust to the light intensity. Count the number of bubbles produced by the plant over a ?xed time period (e.g. 1 minute). Move the lamp further away from the plant. Measure the new light intensity or the new distance between the lamp and the plant. Allow the plant to adjust to the light intensity. Count the number of bubbles produced by the plant over the same time period. Repeat the process for at least ?ve different light intensities or distances.

Keep the temperature of the water the same,

use the same plant, use the same beaker, use the same time period for counting bubbles.

Alternatively, the oxygen could be trapped

in a graduated container such as an inverted gas cylinder, so the volume of gas could be measured. [6]

Exam focus

Core 1

De-starch two similar potted plants. Place them in sealed bell jars/large transparent containers. To one container add a CO

2 absorber. Expose both plants to the same, optimum conditions, e.g. light, warmth. Leave for 2 days. Test a leaf from each plant for the presence of starch. Only the control plant leaf (without CO 2 absorber) will turn blue- black, indicating the presence of starch. [8]2 a i A - guard cells; B - upper epidermal cell;

C - spongy mesophyll cell; D - palisade

mesophyll cell [4] ii B, D, C, A [2] b xylem - transports water, mineral salts from roots around the plant; phloem - transports sucrose, amino acids from leaves to storage or growth regions of the plant [6]

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Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 8

Extended

3 B [1] 4 a i Description - any two from: plants would show poor growth; stems weak; lower leaves yellow/dead; upper leaves turn pale yellow. Explanation - nitrates needed to produce proteins, which are needed for growth [3]ii Any two from: apply animal manure; crop rotation involving leguminous plants; apply arti?cial fertilisers [2] b

leaves turn yellow/ref. to chlorosis; from the bottom of the stem upwards; poor plant growth, ref. to inability to form chlorophyll [3]

7 Human nutrition

Core 1 a iron b water c ?bre d vitamin C [4] 2 a Any two advantages from: high carbohydrate level - for energy; good source of calcium - for strong bones and teeth/to prevent rickets; protein present - for growth/repair

Any two disadvantages from: high in animal

fat - can cause heart disease/atherosclerosis/ obesity; lack of fresh fruit/vegetables/?bre - to prevent constipation; low in vitamin C - to prevent scurvy; low in iron - to prevent anaemia [4] b

Any two from: constipation; risk of obesity/scurvy/anaemia; risk of heart disease/atherosclerosis [2]

c i A diet that contains all the main nutrients in the correct amounts and proportions [2] ii ?bre [1] 3

A - mouth; B - gullet/oesophagus; C - stomach; D - large intestine/colon; E - rectum; F - anus; G - small intestine/ileum; H - duodenum [8]

4 a

anus - muscular, to control the egestion of faeces; colon - absorption of water; duodenum - ?rst part of the small intestine; ileum - absorption of the products of digestion takes place here; mouth - food is ingested here; oesophagus (gullet) - a tube, carrying boluses of food between mouth and stomach; rectum - stores faeces; stomach - has an acid pH and proteins are digested here [8]

b (mouth), oesophagus (gullet), stomach, duodenum, ileum, colon, rectum, anus [7] 5

Nameincisorcaninepremolarmolar

Descriptionchisel-

shapedslightly more pointed than incisorstwo points/cusps one/two rootsfour/five cusps two/three roots

Functionbiting off pieces of foodbiting off pieces of foodtearing and grinding foodchewing and grinding food

[6]

Extended

6 Any three points from: too much food/too little food; too much carbohydrate/fat/protein; too little ?bre; too few vitamins or minerals; the wrong balance of food [3]

Exam focus

Core 1 C [1] 2 a i

A - root; B - crown; C - enamel; D - dentine; E - pulp cavity; F - gum; G - cement; H - jaw bone; I - nerve [9]ii molar (accept premolar); two cusps visible/

two roots visible [2] b i enamel [1] ii (vitamin) D, (mineral) calcium [2]

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Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 9 c Any six points from: ref. to bacteria present on the surface of teeth; food collects on teeth; combines with bacteria to form plaque; bacteria feed on sugars; producing acids; acid reacts with enamel; forming hole; dentine is softer so dissolves faster; cavity forms [6] 3 a

A - oesophagus/gullet - moves food from

mouth to stomach - presence of circular and longitudinal muscles for peristalsis B - ileum/small intestine - digestion of maltose, peptides/absorption of products of digestion (accept absorption of water) - presence of villi to increase surface area for absorption [6] b i protein [1] ii ref. to secretion of protease; hydrochloric acid; muscular churning to mix food with enzyme [3]iii ref. to deamination; excess amino acids broken down; urea formed; energy source produced [4] 4 A [1]

Extended

5 a Any two reasons and appropriate explanations from: less saturated fat; so less risk of heart disase/atheroma; more ?bre; so less risk of constipation; more calcium; to maintain healthy bones/teeth/to prevent rickets [4] b i Any one from: other red meat; liver; kidney; eggs; green vegetables; chocolate, etc [1] ii Needed for the formation of haemoglobin in red blood cells [2] iii ref. to anaemia, constant tiredness, lack of energy [2] c Any two from: the food is cheaper to produce; farmers have no vets' bills; less energy lost/ more energy available [2]

8 Transport in plants

Core 1 a Any two from: anchoring the plant in the soil; absorption of water; absorption of mineral salts; food storage organ [2] b Root hair cells have a cell extension, increasing the cell's surface area to make it more ef?cient for absorbing water and minerals. [2] c root hair cell, cortex, endodermis, xylem [4] 2 a phloem xylem [2]

b Xylem - transport of water and mineral ions; phloem - transport of sucrose and amino acids [4]c Any three from: long, thin vessels; cells lack

end walls; lack cell contents such as cytoplasm and nucleus; walls may be ligni?ed to provide strength/waterproo?ng [3]

Extended

3 Transpiration - the loss of water vapour from the leaves through the stomata by diffusion.

Translocation - the movement of sucrose and

amino acids from regions of production/storage to regions of use for respiration or growth. [4] 4 a

Any two from: increase in temperature; increase in air movement; decrease in humidity; increase in light intensity [2]

b Wilting happens when the amount of water lost from the leaves of a plant is greater than the amount taken into the roots. This results in the plant having a water shortage. Cells become ?accid and no longer press against each other. Stems and leaves then lose their rigidity and wilt. [3]

Exam focus

Core 1 C [1]2 D [1] 3 Diffusion - the movement of a substance from a higher concentration to a lower concentration

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Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 10 down a concentration gradient; oxygen diffuses from the air into a leaf, carbon dioxide diffuses out of a leaf, mineral salts diffuse from soil into root hairs

Osmosis - the movement of water from a higher concentration to a lower concentration through a partially permeable membrane; osmosis is used to absorb water by roots, cells absorb water by osmosis to become turgid, which keeps young stems rigid

Active transport - the movement of a substance from a lower concentration to a higher concentration against a concentration gradient, using energy; plants obtain mineral salts by active transport when the concentration of salts in the soil is lower than in the root cells

Transpiration - the loss of water vapour from the leaves through the stomata, by diffusion; transpiration results in more water being drawn through the plant, carrying mineral salts from theroots [12]

Extended

4 a Water enters the leaf in the xylem vessels (A), then passes into the surrounding spongy mesophyll cells (B). A thin layer (C) forms on the surface of the cells, which evaporates and saturates the air in the air spaces (D), then the water molecules diffuse into the atmosphere through the stomata (E) [6] b Transpiration from the leaves loses more water than is being taken in by the roots; cells in young stems lack water; become accid and stop pressing against each other; so stems and leaves lose their rigidity and wilt. [4]

9 Transport in animals

Core 1 a left atrium, left ventricle [2] b aorta, pulmonary vein, coronary artery [3] 2 a x -axis drawn and labelled ‘time/min", y -axis drawn and labelled ‘pulse rate/beats per minute"; points plotted accurately, line drawn between points [4] 0

0.02.04.06.08.010.020

40
60

80100120

140
b i 60 beats per minute [1]
ii at 1 minute [1] iii at 8 minutes [1] iv Heart must beat faster to circulate more oxygen; exercising muscles need more oxygen, more glucose; and produce carbon dioxide (or lactic acid), which needs to be removed [3]v Rate starts higher than 60 bpm; reaches a higher peak; takes longer to return to normal [3] vi Keeps heart muscle in good tone; results in the heart being more efcient in maintaining blood pressure [2] c

Any three of the following answers (you must give the cause and the preventive measure for each mark): smoking - stop smoking; obesity - go on a controlled diet/take regular exercise; stress - nd ways of relaxing/identify causes of stress and reduce them; inherited factors - make sure other factors are reduced/monitor health [6]

3 Across: 3 plasma, 4 lymphocyte, 5 platelet;

Down: 1 haemoglobin, 2 nucleus

[5]

Extended

4 a A group of cells with similar structures, working together to perform a shared function [2] b (cardiac) muscle [1] c it can contract [1] d It needs to build up enough pressure; to move blood to all organs; while the right ventricle only moves blood to the lungs [3]

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Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 11 5 a, b, c lungs rest of body [8]6 Any three from: permeable wall - to allow diffusion of materials between the capillary and surrounding tissues; wall is one cell thick - allows fast diffusion/allows white blood cells to squeeze between cells of the wall; lumen is one blood cell wide - slows down blood flow to allow diffusion of materials and transfer of tissue fluid; valves are absent - blood pressure is high enough to keep blood flowing [3] 7

Any two from: returns tissue fluid (in the form of lymph) to blood/prevents build-up of fluid in the tissues; produces lymphocytes; absorbs fatty acids and glycerol from the small intestine [2]

Exam focus

Core 1 B [1] 2 a

A, aorta; B, pulmonary vein; C, left atrium; D, semilunar valve; E, bicuspid valve; F, tendon; G, left ventricle; H, right ventricle; J, tricuspid valve; K, right atrium; L, vena cava; M, pulmonary artery [12]

b i right atrium ii pulmonary vein iii semilunar valve iv left ventricle v tendons vi vena cava vii aorta viii tricuspid valve [8] 3 a transport of dissolved substances to cells/ removal of wastes from cells ii transport of oxygen iii produces antibodies to fight diseaseiv engulfs bacteria to fight disease v forms blood clots [5] b i biconcave disc shape/no nucleus/contains haemoglobin (pink colour) ii large nucleus iii lobed nucleus/cell can change shape [3]

Extended

4 C [1] 5 a

Blood passes through the heart twice, for each complete circulation of the body; so blood pressure is maintained [2]

b Artery: any two from: thick and tough wall; narrow lumen; valves absent

Vein: any two from: thin wall; large lumen;

valves present

Capillary: any two from: permeable wall; wall

one cell thick; lumen one red blood cell wide; valves absent [6]

10 Diseases and immunity

Core 1 a A disease-causing organism [2] b

Any three from: direct contact, e.g. through blood or other body fluids; indirectly, e.g. from contaminated surfaces; from food; from water; from animals; from the air [3]c Mechanical barrier - any one from: skin; hairs

in nose

Chemical barrier - any one from: mucus;

stomach acid; enzymes in tears

Cells - any one from: phagocytosis by white

blood cells; antibody production by white blood cells [3]

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Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 12 2 a A disease in which the pathogen can be passed from one host to another [2] b i phagoctyes engulf and digest bacteria/ ref. to phagocytosis; lymphocytes produce antibodies to make bacteria clump, or mark them so phagocytes can target them [4] ii vaccination [1]

Extended

3 a Produced by lymphocytes, formed in lymph nodes, antibodies make bacteria clump together, so that phagocytes can digest them.

They also neutralise toxins produced by

bacteria, and remain in blood to provide long-term protection [5] b Phagocytes can move out of capillaries, to the site of an infection; they engulf pathogens, and kill them by digestion

[3]4 Any three from: harmless pathogen given, which has antigens; antigens trigger an immune response by lymphocytes; lymphocytes produce antibodies; memory cells are produced to provide long-term immunity [3]

5

Any four from: passive immunity - short-term defence against a pathogen by antibodies acquired from another individual, e.g. mother to infant through breast-feeding; active immunity - longer-term defence against a pathogen, gained after an infection by a pathogen, or by vaccination [4]

6

Any three from: triggered by an event such as a virus infection; which causes the body's immune system to attack cells in pancreas/islets cells; which produce insulin; ref. to slight genetic predisposition; ref. to autoimmune disease [3]

11 Gas exchange in humans

Core 1 a (mouth) trachea bronchus bronchiole alveolus (red blood cell) [4] b i diffusion [1] ii thin; moist; large surface area; has a concentration gradient [4] 2 a G to alveoli; A to trachea; M to edge of diaphragm or any intercostal muscle [3] b rate increase; depth increases [2] c i increases; from 0.04% to about 4% [2] ii Pour limewater into a container, e.g. test tube; insert straw; breathe gently out through the straw [3]

Extended

3 intercostal muscles contract, ribcage moves up and out, diaphragm muscle contracts, diaphragm moves down, volume in the lungs increases, air pressure in the lungs decreases, air moves in to ?ll the lungs [3]4 a 1 keeps the trachea open/prevents trachea from collapsing/allows free movement of air between mouth and lungs; 2 protects the lungs

and heart; moves to increase or decrease the volume of the thorax; 3 contract to force air out of the lungs during exhalation; 4 moves down to increase volume of the thorax during inhalation/moves up to decrease volume of the thorax during exhalation [4] b (goblet cell) secretes mucus; (ciliated cell) beats backwards and forwards to move mucus towards the throat; (mucus) traps dust and pathogens [3] 5 a

(oxygen) used up in respiration to provide energy; (carbon dioxide) produced as a waste product during respiration; (water vapour) evaporates from the surface of the alveoli/produced as a waste product during respiration [3]

b carbon dioxide diffuses into the blood; increased concentration is detected by the brain; brain instructs thorax to increase breathing rate [2]

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Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 13

Exam focus

Core 1 a Volume of air per breath increases, from normal tidal volume, e.g. from 0.5 litres, rate of breathing increases, from 12 to over 20 breaths per minute. [4] b i Before exercise: pour limewater into two containers, e.g. test tubes; insert straw into one; breathe gently out through the straw; count the number of breaths needed to turn limewater; from colourless to milky; then carry out exercise. After exercise: breathe through straw into second test tube; count the number of breaths needed to turn limewater milky [5] ii Results: after exercise less breaths needed;

to turn limewater milky Explanation: during exercise; rate of aerobic respiration increases; so more carbon dioxide produced [5]

Extended

2 a A, spinal cord; B, left lung; C, heart [3] b i lung [1] ii Any four from: contains many alveoli; contains many blood capillaries; for gas exchange; ref. to oxygen and carbon dioxide; ref. to diffusion [4] c Any six from: intercostal muscles contract; ribs move upwards and outwards; diaphragm muscle contracts; diaphragm moves down; volume of thorax increases; air pressure in thoracic cavity decreases; to become lower than atmospheric pressure; so air moves intothe lungs [6]

12 Respiration

Core 1 a glucose water + carbon + energy oxygen dioxide [2] b

Any three uses from: muscle contraction; protein synthesis; cell division; active transport; growth; passage of nerve impulses; maintaining a constant body temperature [3]

c i lactic acid/lactate [1] ii Lactic acid causes muscle cramps (muscle fatigue), which will stop the athlete running. An oxygen debt builds up, which needs to be repaid. [2] 2 1 carbon dioxide - breadmaking/brewing; 2 ethanol/alcohol - brewing [4]

Extended

3 a C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O [1 mark for a correctly balanced equation] [3] b i Place boiling tube in a beaker of water, use a thermometer, to measure the water temperature, allow the seeds time to adjust to the temperature of the water, note position of dye, time for, e.g. 5 minutes, note new position of dye, measure distance moved, repeat process for a range different temperatures [6] ii calculate rate of movement of dye, using formula distance/time, plot graph of temperature ( x -axis) against rate of movement of dye ( y -axis) [3]

Exam focus

Core 1 D [1] 2 a i respiration ii carbon dioxide iii turns from colourless to milky iv ethanol/alcohol [4] b Any ve from: respiration of yeast is very slow at low temperatures, as the temperature is increased to 30 °C the rate of reaction increases because the kinetic energy of the reacting molecules increases, as molecules +

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Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 14 have little kinetic energy so few collisions; 30
°C is optimum temperature for yeast respiration, as molecules have lots of kinetic energy to collide; enzymes in yeast begin to denature at 45 °C, so respiration slows down; all yeast enzymes denatured at 100 °C, so no respiration [5]

Extended

3 a muscles produce lactic acid/lactate; yeast produces ethanol; and carbon dioxide [3] b i muscles respire anaerobically; producing lactic acid/lactate [2] ii continued rapid/deep breathing; to provide oxygen; to break down the lactic acid/ lactate [3]

13 Excretion in humans

Core 1 blood, water, glucose, reabsorbed, more, concentrated, osmosis, diffusion, active uptake [9] 2 a The removal from organisms of toxic materials, and substances in excess of requirements [2] b (aorta), renal artery, capillary, tubule, ureter, bladder, urethra [3]

Extended

3 a Surplus amino acids are removed from the blood by the liver and broken down into urea by the process of deamination. [3] b Any two from: breakdown of poisons/alcohol; breakdown/removal of drugs; breakdown of hormones; storage of vitamins; storage of iron; controlling levels of glucose in the blood; making bile

[2]4 Advantages - any two from: the patient can return to a normal lifestyle - dialysis may require a lengthy session in hospital, three times a week, leaving the patient very tired after each session; a dialysis machine is available for other patients to use; dialysis machines are expensive to buy and maintain

Disadvantages - any two from: transplants require a suitable donor - with a good tissue match; the operation is very expensive; there is a risk of rejection of the donated kidney/immunosuppressive drugs have to be used; transplants are not accepted by some religions [4]

5 a i V - cortex, W - medulla, X - pelvis,

Y - ureter

[2] ii cortex contains glomeruli; ureter transfers urine to the bladder [2] b i lters the blood; any two named contents of ltrate from water, glucose, urea, salts [2] ii reabsorbs; any two named substances from glucose, most water, some salts [2] iii passes urine; to ureter [2]

Exam focus

Core 1 a i A, renal vein; B, left kidney; C, ureter; D, bladder; E, urethra [5] ii Amino acids; and glucose will be present in part A; also more salts than part C [3] iii Any two from: smaller volume; more concentrated; urea more concentrated; salts more concentrated [2] b Vena cava has a thinner wall; larger lumen; contains valves [3]

Extended

2 a i a method of removing one or more components from a solution using the process of diffusion [2] ii Pump: keeps blood owing through the machine; dialysis uid: receives wastes/ toxins from the blood by diffusion; bubble trap: removes any air bubbles before the blood is returned to the patient"s vein; partially permeable membrane: allows small molecules in higher concentrations to pass out of the blood, but prevents loss of blood cells, large molecules from blood [5]

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Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 15 b i Visking tubing/cellulose [1] ii provides a large surface area; for ef?cient diffusion [2] iii Any two from: to maintain a concentration gradient; concentrations of removed substances build up; so diffusion slows down [2] c Any two from: expensive to buy/maintain; very tiring for the user; may require frequent hospital visits [2]

14 Coordination and response

Core 1 a Central nervous system: made up of brain and spinal cord; which have the role of coordination; peripheral nervous system: made up of nerves; which connect all parts of the body to the central nervous system [4] b i A group of receptor cells responding to a speci?c stimulus, e.g. light, sound, touch, temperature, chemicals. [2] ii

Sense organStimulus detected

1. (ear)sound/body movement

2. eye(light)

3. (nose)chemicals/smell

4. tongue(chemicals/taste)

5. skin(temperature,

pressure, touch, pain) [5] 2 a Any three from: sensory neurone has dendron present/very long; sensory neurone has no axon/very short axon; cell body is near the end of the sensory neurone; dendrites are present at the end of the sensory neurone [3] b i acts as electrical insulation/stops impulse leaking out/makes transmission of impulse more ef?cient [1] ii makes connections with other neurones [1] iii transmits the impulse along the neurone [1] iv coordinates the cell/contains DNA [1] 3 a

A chemical substance, produced by a gland, carried by the blood, alters the activity of one or more speci?c target organs. [3]

b

Any three points from: causes heart rate to increase; breathing rate increases; blood supplies muscles with oxygen and glucose more quickly; blood supply to skin reduced; blood supply to digestive organs is reduced; blood is diverted to vital organs; liver is stimulated to convert glycogen to glucose; pupils widen [3]

4 a i A, sensory neurone; B, relay neurone;

C, motor neurone

[3] ii muscle [1]iii Arrows go from pain receptor along sensory, relay and motor neurone to muscle [1] b it contracts [1] c synapse [1] 5 a, b D: circular muscles - contracted; E: radial muscles - relaxed;

F, pupil - constricted [6]

6 a A response in which parts of a plant grow towards or away from gravity [1] b Root; advantage: access to water/access to minerals/better anchorage

Shoot; advantage: access to light

[4]

Extended

7

FeatureNervousHormonal

(endocrine) (form of transmission)electrical impulseschemical/hormones (transmission pathway) nervesblood vessels (speed of transmission) fastslow (duration of effect)short termlong term [4] 8 A, ciliary muscles - contract; B, suspensory ligaments - slacken; C, lens - thickens [6] 9 a auxin [1] b i The shoot bends/grows towards the light. [1] ii When a shoot is exposed to one-sided light, auxins produced by the tip move towards the shaded side of the shoot/auxins are destroyed on the light side, causing an unequal distribution. Cells on the shaded side are stimulated to absorb more water than those on the light side, making them bigger. The unequal growth causes the stem to bend towards the light. [4] c i Weedkiller/chemical which kills weeds [1] ii They are sprayed onto plants; causing rapid, uncontrolled growth and respiration; that results in the death of the plant. [3]

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Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 16

Exam focus

Core 1 a C [1] b i, ii [4] myelin sheath cell body dendrite

X (at the tip

of any dendrite)

Extended

2 Any eight points from: homeostasis means maintaining a constant internal environment; pancreas acts as a sensor in negative feedback and acts as an effector by secreting hormones; if glucose levels rise above normal, change is sensed by the pancreas; insulin is secreted by the pancreas and passed into bloodstream; insulin instructs the liver to remove excess glucose from the blood; glucose is converted to glycogen and stored; rate of respiration in the liver is increased to use up glucose; glucose levels return to normal; if glucose levels fall below normal the pancreas

stops secreting insulin and starts to secrete glucagon; glucagon instructs the liver to convert glycogen to glucose; glucose is passed into the bloodstream, glucose levels return to normal [8]

3 a

Any six points from: Blood vessels - muscles in arteriole walls relax, arterioles dilate, allowing more blood to near the surface of the skin, heat radiated from skin surface, so body cools. Sweat - sweat glands in skin secrete more sweat, passes through pores onto surface of the skin, water evaporates, removing heat from skin, so body cools. [6]

b Glucagon secreted by pancreas; causes liver to convert glycogen to glucose; heart rate increases; so more blood with glucose passes to muscles. [4] 4

Any two points from: frequent urination; increased thirst; tiredness/exhaustion; blurred vision; headache; lapsing into unconsciousness/coma.

Treatment using insulin [3] 5

Auxins produced by the tip of the radical; diffuse, evenly, along from the tip; so all cells grow at the same rate, no bending occurs. [3]

15 Drugs

Core 1 a Any two from: addiction (alcoholism); cirrhosis of the liver; stomach ulcers; cancer of the digestive system; heart disease [2] b Increases risk of miscarriage; results in a decrease in average birth weight. [2] 2

cancer, emphysema, lungs, carcinogen, carbon monoxide, tar, bronchitis, nicotine, tobacco, lter [10]

3

Any three named chemicals and any two effects on the body: carbon monoxide - poisonous gas, combines with haemoglobin to produce carboxyhaemoglobin, preventing red blood cells from carrying oxygen, smoker gets out of breath easily, increases risk of atherosclerosis, thrombosis, coronary heart disease; nicotine - addictive, resulting in prolonged exposure of lungs to other harmful chemicals, raises blood pressure, risk of stroke, stimulates brain, can reduce birth weight of baby if mother smokes during pregnancy; smoke particles - irritates air passages in lungs, causes inammation, increased mucus production, causes chronic bronchitis, emphysema; tar - ref. to carcinogen, increases risk of lung cancer, paralyses cilia in air passages, can cause bronchitis [9]

4 a

Any three from: used to treat disease; reduce sensation of pain; help to calm the patient down; used as anaesthetic; to cause unconsciousness [3]

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Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 17 b i

DrugEffects on the bodyDangers to the person

using the drug

alcoholsmall amounts - relaxes the body; large amounts - acts as a depressant, slows down reactions, coordination impaired, creates mood swings, can trigger violenceincreases reaction times, so driving and handling machinery is impaired; can lead to criminal activity, promiscuity, alcoholism, ?nancial problems, liver disease, etc.

heroinhas narcotic effect, increases relaxation, reduces painaddictive; tolerance to drug increases, so risk of overdosing; risk of infection from using unsterilised needles; can lead to criminal activity, promiscuity, alcoholism, ?nancial problems, etc.

nicotine (in tobacco)raises blood pressure, heart rate addictive; other chemicals in the cigarette can lead to cancer; risk of atherosclerosis, thrombosis, coronary heart disease, etc. [6]ii Any three points from: ref. to criminal activity; sexual promiscuity; financial problems for family; dangers for unborn children [3]

Extended

5 a Any three points from: affects synapses in the brain; has similar structure to neurotransmitter molecules; binds to neurotransmitter sites in synapses; causes pain relief, euphoria [3] b Any three points from: can be taken by injection/needle, needles may be shared by addicts; needle contaminated with blood may carry HIV; so injection with infected needle transmits the infection [3]

Exam focus

Core 1 a Any substance taken into the body that modifies or affects chemical reactions in thebody [2] b Alveoli are where exchange of oxygen happens in the lungs; breakdown of alveoli results less surface area for oxygen absorption; so less oxygen to cells, for respiration [3] c Any three from: lung cancer; chronic obstructive pulmonary disease; coronary heart disease; (chronic) bronchitis [3]

Extended

2 a Any three from: bacteria exposed to sub- lethal levels of antibiotic, e.g. by patient not taking full course of treatment; some bacteria survive; with resistance to antibiotic; reproduce; whole population is now resistant; some bacteria have resistant gene, so have an advantage [3] b Any two from: only taking antibiotics when essential; ensuring course of treatment is completed; good hygiene practices in hospitals [2] c

Any two from: viruses have different structure to bacteria; viruses live in human cells; so are protected from antibiotics [2]3 a anabolic steroids increase muscle mass/muscle strength [1]

b Any two from: they increase sporting performance; allows athletes to recover faster after hard training; allows more vigorous training sessions; allows more frequent training sessions; increases aggression so makes the athlete more competitive; enhances the athlete"s appearance [2] c Any one from: it is illegal; their use is prohibited by most sporting organisations; gives the user an unfair advantage [1] 4 a i bacterium [1] ii Any three from: presence of cell wall; presenceof slime capsule; presence of single strand of DNA; presence of flagellae; ref. to small size [3] b binary fission (accept asexual reproduction) [1] c

Any two from: ref. to mutation; during cell division; variation has provided resistance to the antibiotic [2]

d Any three from: some of the bacteria will have survived; but have been exposed to the antibiotic; so mutations are possible; which can result in a resistant strain forming; so future use of antibiotic will be ineffective; bacteria in the patient will breed again, causing disease symptoms to return [3]

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Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 18

16 Reproduction

Core 1 a The formation of a new organism, without the involvement of gametes or fertilisation [2] b Pollination - the transfer of pollen grains, from the anther to the stigma; fertilisation - the fusion of the male and female gametes in the ovary [4] 2

anther - produces pollen grains containing male sex cells; ovary - contains ovules, the female sex cells; petal - often large and coloured to attract insects; sepal - protects the ower while in bud; stigma - sticky, to receive pollen grains during pollination [5]

3 a A, stigma; B, style; C, ovary; D, ovule (accept seed); E, lament; F, anther [6] b i carpel [1] ii stamen [2] c i Ref. to feathery/with a larger surface area/ hanging outside the ower; to increase the chance of trapping pollen grains. [2] ii Ref. to larger numbers of pollen grains/ pollen grains lighter; to increase chances of pollination/to be more easily carried by thewind. [2] 4

Across: 2 prostate gland, 5 seminal vesicle, 6 testis, 7 sperm duct, 8 penis; Down: 1 urethra, 3 epididymis, 4. scrotum [8]

5 a

Sperm released from the testes pass through the sperm duct, into the urethra through the penis. They are ejaculated into the vagina, swim through the cervix and uterus and into the oviduct. [6]

b An ovum passes down the oviduct. A singlesperm penetrates the membrane of the ovum by secreting a protease enzyme. The sperm nucleus fuses with the ovum nucleus to form a zygote. [2]

6 a placenta b 1 cervix, 2 vagina c zygote d Any two from: oxygen; glucose; amino acids e carbon dioxide, urea f amniotic uid g menstruation h ejaculation i oviduct (fallopian tube) j mitosis [10]7 a 1 A rubber sheath placed over the penis; to stop sperm entering the vagina. 2 The sperm ducts are tied or cut; so no sperm can leave the testes. 3

Contains progesterone and oestrogen which prevent ovulation; or progesterone only, which prevents implantation of a blastula.

4 A plastic-coated copper coil surgically

inserted into the wall of the uterus - which prevents implantation of a blastula. [8] b condom [1] c Any two from: abstinence from sexual intercourse; screening of blood used for blood transfusions; use of sterilised needles for drug injections; feeding a baby with bottled milk when the mother has HIV; use of sterilised surgical instruments [2]

Extended

8 A: The lining of the uterus is starting to build up; under the inuence of oestrogen. B: Ovulation occurs - the wall of an ovary ruptures, releasing an egg; this is due to secretion of LH (luteinising hormone). C: The lining of the uterus is maintained, due to high levels of progesterone; produced by the corpus luteum. D: Menstruation occurs - the lining of the uterus breaks down; due to a drop in progesterone. [8] 9 a progesterone; oestrogen [2] b i FSH and LH treatment causes multiple release of ova (eggs). The ova are collected.

Some of them are fertilised in a Petri dish

using the male partner"s sperm. The early embryos produced are then inserted into the uterus to achieve pregnancy. [3] ii Advantage - any one from: increases the chance of pregnancy; can result in pregnancy of a woman with blocked oviducts; fertilised eggs can be screened for genetic diseases Disadvantage - any one from: expensive; relatively low success rate [2]

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Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 19

Exam focus

Core 1 a Wind pollination. Explanation - any six points from: A = stigma, which is feathery; hangs outside the ower; has large surface area;

B = lament, which is long to expose the anther

to the wind; C = anther, which hangs outside the ower; exposed to the wind; contains large amounts of light, smooth pollen grains [7] b Any four points from: mature anthers burst, releasing pollen grains into air; wind carries pollen grains; some are trapped by feathery stigmas; hanging outside owers; of other owers of the same species [4] 2 a C [1]

b Antibiotics don"t work on viruses/viruses are present in cells so antibiotics cannot attack them [1]

c ref. to may not use condom during sex when under the inuence of the drug; drug may be injected using an infected needle/ref. to sharing needles [2]

Extended

3 a i arrows/line from pollen grain down through the stigma (A), style (B), around either side of the ovary wall (C), into micropyle (D) to the ovule [3] ii Any six points from: pollen grain germinates; pollen tube grows; pollen tube contains the male nucleus; grows down

through the stigma, (A); through the style (B); through the ovary wall (C); into the micropyle (D) to the ovule; male nucleus fuses with nucleus of ovule [6]

b i Any one from: pollen grain would be lighter/have a larger surface area/no spikes on surface/smooth surface [1] ii stigma would be feathery; hangs outside the ower [2] 4 a A, ovary; B, oviduct; C, uterus (wall); D, cervix; E, vagina [5] b ref. to both oviducts are closed/blocked; so eggs cannot pass down/sperm cannot reach egg [2] c i in vitro fertilisation [1] ii X placed on lining of uterus [1] iii ref. to being expensive; ref. to low success rate [2] d

Any three from: ref. to maintaining healthy diet; ref. to eating more protein/iron/calcium/vitamin C/energy-containing foods than normal; stop smoking, avoid alcohol; avoid drugs; avoid contact with rubella [3]

5 D [1] 6 a

Involves transfer of pollen from the anther of a ower to the stigma of a ower; on a different plant of the same species; so there is mixing of genetic material leading to variation. [3]

b The runner/stolon is a shoot of the parent plant; so the new strawberry plant cells will have the same DNA as the parent [2]

17 Inheritance

Core 1 allele - a version of a gene; chromosome - a thread of DNA, made up of genes; dominant - an allele that is always expressed if present; gene - a length of DNA, coding for a protein; genotype - the genetic make-up of an organism; homozygous - having a pair of identical alleles for a particular gene; phenotype - the observable features of an organism [7]2

Parent phenotype

Parent genotype

Gametes (sex cells)

First filial

generation (F1)malefemale female

11femalemalemalex

x

Phenotype

The ratio isfemale:male.

XYXX

XXXXXYXYX

YXX [5]

Answers

Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 20 3 a Any two from: mitosis produces cells with the same number of chromosomes as the parent nucleus cell/the diploid number of chromosomes is maintained, meiosis produces cells with half the number of chromosomes/ haploid cells produced; mitosis produces identical cells, meiosis results in variation; mitosis involves body cells/somatic cells, meiosis happens in the gonads/ovaries and testes; mitosis results in growth or replacement of old or damaged cells, meiosis makes sex cells. [2] b leg muscle cell - 8; sperm cell - 4; zygote - 8; skin cell - 8 [4] c i (a punnett square is acceptable)

Parent phenotype

Parent genotype

Gametes (sex cells)

F1 generation

Phenotypegreygreygreygreygreyblack

ggGG GGgg

GgGgGgGgx

x [3] ii (a punnett square is acceptable)

Parent phenotype

Parent genotype

Gametes (sex cells)

F2 generation

Phenotype

Ratio 3 grey: 1 black

greygreygreyblack greygrey GgGg G gGg

GgGgggGGx

x [4]

Extended

4 a A pair of alleles, neither of which is dominant over the other. Both can have an effect on the phenotype when they are present together in the genotype. The result is that there can be three different phenotypes. [3] b i

Parent phenotypered

pinkpinkpinkpink C R C R C R C W C R C W C R C W C R C W C R C R C W C W C W C W x x white

Parent genotype

Gametes (sex cells)

F2 generation

Phenotype

[4] ii 1 red : 2 pink : 1 white [1] 5 a Any three from: enzymes (or a named enzyme); haemoglobin; muscle; hormone (or named hormone, e.g. insulin); antibody; receptor for neurotransmitter [3] b Any ?ve points from: DNA is made of genes; each gene codes for a protein; mRNA carries a copy of the gene to the cytoplasm; mRNA passes through a ribosome; ribosome assembles amino acids into a protein molecule; order of bases is determined by the sequence of bases in the rRNA [5] Core 1 a i rat Brat C [1] ii 50% [1]iii sperm cell; the Y chromosome determines
male, absence of Y in the zygote results in female [2] b i an alternative form of a gene; pairs of alleles that occupy the same relative positions on chromosome pairs [2] ii 1, C; 2, B [2]

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Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 21
c Rat E has genotype Gg, where G = grey fur, g = white fur.

Parent phenotype

Parent genotype

Gametes (sex cells)

First filial

Phenotype

generation (F1)grey greygreygreywhite(rat B)(rat E) grey GgGg GGgg

GgGgggGGx

x [5]

Extended

2 a A characteristic in which the gene responsible is located on a sex chromosome; and this makes it more common in one sex than in the other [2]b Any four points from: gene is present on the

X chromosome; and is recessive; females need

to be homozygous for the gene to suffer; men only need the gene on the X chromosome; no gene on Y chromosome to dominate it [4] 3

Parent phenotypeblood group A

I A I o I A I A I B I A I o I B I o I o I o I o I B I o I B I o x x blood group B

Parent genotype

Gametes (sex cells)

F2 generation

PhenotypeABABO

[5] 4 a Any four points from: cell starts with chromosomes duplicated; copies of the chromosomes separate; cell splits to form two cells; which are identical to parent cell; chromosome number is maintained/ref. to diploid [4] b Unspecialised cells; that divide by mitosis; to produce daughter cells; that can become specialised for speci?c functions [4]

18 Variation and selection

Core 1 a Continuous variation - any three points from: shows a complete range of a characteristic within a population; caused by both genes (often a number of different genes) and the environment; when the frequency is plotted on a graph, a smooth curve is produced; with the majority of the population sample grouped together and only small numbers at the extremes of the graph; e.g. height/body mass/intelligence/ hand span/shoe size

Discontinuous variation - any three points

from: there are obvious, distinct categories for a feature; there are no intermediates between categories; caused by a single gene or a small number of genes; with no environmental in?uence; when the frequencies are plotted on a graph, bars are produced that cannot be linked with a smooth curve; e.g. blood group/ability to tongue-roll/ear lobe shape [6]b Continuous variation graph, e.g. number of students height in a class height / cm

Discontinuous variation graph, e.g.

percentage frequency blood group

ABABO0510152025303540

45
[2]

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Cambridge IGCSE Biology Workbook 2

nd Edition © Hodder & Stoughton Ltd 2014 22
2 a an inherited feature; that helps an organism to survive and reproduce in its environment [2] b Any ?ve points from: named example, e.g. lion; variation within a lion population, e.g. bigger muscles in the legs of some lions enable them to run faster/get food more successfully; ref. to many offspring produced; competition for resources, e.g. if there is a food shortage, the lions with the biggest leg muscles are most likely to survive to adulthood and pass on the advantageous genes to their offspring; struggle for survival, e.g. the weaker individuals die before having the chance to breed; reproduction by individuals that are better adapted to the environment than others; passing on their alleles to the next generation [5]

Extended

3 a i a change in the base sequence of DNA [2] ii Any two from: faulty copying of DNA; faulty separation of chromosomes during cell division; exposure to radiation; exposure to some chemicals [2] b i Any three points from: change in the base sequence of the gene; for haemoglobin; results in abnormal haemoglobin; and sickle-shaped red blood cells [3] ii Any three points from: heterozygous individual has a resistance to malaria; which can be fatal; and is not life-threatening for sickle- cell anaemia; while a homozygous recessive individual may die from sickle-cell anaemia

[3]4 One named example of an animal, e.g. cow; select one variety of cattle with a higher than average milk yield; select another variety that has a very high meat yield; cross-b