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Transcript
Answers to CSEC® Biology Examination Practice Section A 2a i Accurate calculations [2]; parts of pie chart labelled [1]; appropriate title [1] Pie chart showing the data collected to represent the organisms found in a sampling area 50 (29 °) 30 (17°) 2 (1°) 550 (313 °) Key Producer Primary consumer ■■ Figure Secondary consumer Tertiary consumer A1 ii Pitfall trap. [1] It is a trapping pit (container placed into the ground) for small mobile organisms to fall in. Once they fall into the trap, they cannot escape. [1] iii A food chain is a diagram that shows the feeding relationships within an ecosystem or how energy in the form of food is moved from one organism starting with the producer to subsequent organisms. [1] Diagram showing the feeding relationships between organisms in a sampling area BIRDS HIBISCUS LEAVES → WORMS → (producer) (primary (secondary consumer) consumer) [1] for title; [1] for diagram. iv Producers are first in the food chain and have the greatest access to energy directly from sunlight. Hence there is more energy to support a larger number of organisms. [1] The tertiary consumer get less energy, as energy is lost as you go up the trophic levels. Therefore if there is less energy available, there will be fewer organisms. [1] CSEC® Biology Examination Practice © Kathryn Bennett 2016 1 Answers to CSEC® Biology Examination Practice bi Include an aim; list of apparatus; procedure or sequence of steps for carrying out the investigation. For example: Aim: To determine the percentage of air found in a sample of soil [1] List of apparatus and materials: Soil, beaker, triple beam balance, water, stirring rod [2] Method: Weigh empty beaker, soil sample and volume of water being used. [1] Pour water into soil sample and stir. [1] Stir until no more air bubbles escape or water reaches surface of the soil. [1] Weigh the mixture of soil sample and water. [1] Carry out calculations to show difference in weight of soil sample without water and soil sample with water. [1] ii Air in the soil provides oxygen for plant roots [1]; bacteria that are integral to the process of cycling nutrients need oxygen [1]; the oxygen is used in aerobic respiration and energy is produced to drive certain processes such as active take-up of minerals into plant roots. [1] iii Three (for [1] mark each) from: mineral particles; humus; water; air; organisms. 3a i Plant is placed in a dark cupboard for 24 hours. [1] ii To ensure that the plant uses up the starch that was stored. [1] Then any starch produced in the investigation is a result of action of light in photosynthesis. [1] iii Diagram showing the leaf in a boiling tube of ethanol in a water bath as it is being heated by the Bunsen burner. Suitable labels. boiling tube with ethanol [1] beaker with water [1], heated using Bunsen burner [1] (heat turned off before test tube containing ethanol is placed in beaker, to avoid risk of ethanol catching fire) leaf [1] tripod stand [1] ■■ Figure A2 iv Green region covered by foil would not contain starch and would take colour of iodine; white region covered by foil would be the same; white region not covered by foil would also take the colour of iodine. [1] 2 Green regions not covered by foil would be blue-black, indicating starch present. [1] CSEC® Biology Examination Practice © Kathryn Bennett 2016 Section A area of leaf covered by foil blue-black red-orange (colour of iodine) colour of iodine colour of iodine Key Green areas of leaf blue-black White areas of leaf ■■ Figure A3 v Light [1] and chlorophyll [1] are necessary for photosynthesis to take place. bi To investigate the effect of light [1] on the growth of a plant. [1] ii Ensure plants are of the same type [1] and size. [1] iii First plant would grow upwards [1]; second plant would bend and grow towards the light [1]; the third plant would experience rapid growth, yellow leaves, spindly stem. [1] iv First plant: auxin diffuses evenly down the stem causing even growth of cells. [2] Second plant: auxin accumulates on shady side (side not exposed to light) causing those cells to grow rapidly resulting in the bending of the stem. [2] Third plant: since it had no access to light, it used up its food reserve and grew rapidly in search of light. [2] 4a i Appropriate title [1]; accurate representation of data [3]; label x- and y-axes [2] ii Continuous [1] iii Any two named and described from: sexual reproduction (meiosis); crossing over; environment; mutations. Sexual reproduction [1]: when a gamete from each parent fuses to form a zygote, a unique combination of genes is produced as each gamete has a different set of DNA. [1] Crossing over [1]: homologous chromosomes pair up and bits of information are exchanged between them as they break and re-join, trading genes. [1] Environment [1]: for example, nutrition affects growth. [1] Mutations [1]: small changes that occur when cells divide which may or may not be advantageous. [1] iv Discontinuous [1] bi Gametes [1] ii Chromosomes are pulled to opposite poles [1] with the sister chromatids still joined at the centromere. [1] CSEC® Biology Examination Practice © Kathryn Bennett 2016 3 Answers to CSEC® Biology Examination Practice iii Circle any two chromosomes that are identical in length or size. [1] iv Meiosis produces four haploid daughter cells [1] that are not identical to each other. [1] Mitosis produces two diploid daughter cells [1] that are identical. [1] v Allows for variation [2]. Since organisms are not identical, [1] only those susceptible to a particular disease will be wiped out, for example. [2] 5a i Obtain three papaya trees of the same size, type, age, etc. [1] For a month, give each plant the same volume of water each day; same amount of exposure to sunlight; apply the same amount of fertiliser. [1] Get two different fertilisers with different percentages of nitrogen content. [1] Do not use any fertiliser on one of the plants (control). Use one fertiliser on the second plant and the other fertiliser on the third plant. [2] Record the colours of the leaves, measure the height of each plant and sizes of the leaves each day. [1] ii Two from: same type of papaya plant; same size plants; equally healthy plants; same volumes of water; same amount of sunlight. [2] iii Type of fertiliser (amount of nitrogen in the fertiliser) [1] iv The control is there to show the comparison between what would normally happen and what happens when the independent variable is changed in the experimental groups. [2] b Two (for [1] mark each) from: magnesium; iron; phosphorus; sulfur; potassium; calcium c Magnesium and iron – help make chlorophyll; phosphorus and sulfur – needed for protein synthesis; potassium – salt balance maintained in cells; calcium – needed to make cell walls. [2] di Plant shoots respond positively to light in order to make chlorophyll [1] and to photosynthesise. [1] ii Plant roots respond positively to gravity in order to obtain water and dissolved minerals from the soil [1] and also to anchor the plant firmly in the soil. [1] iii For the root in response to gravity: auxins accumulate on lower part of the root [1], this slows down the growth on that side [1], making the cells of the upper side grow faster. [1]. This results in the downward growth of the root. [1] iv No. [1] Auxins respond differently in the shoot and the root. Shoots need to grow upwards or above ground in order to make their food. [1] 4 CSEC® Biology Examination Practice © Kathryn Bennett 2016 Section A 6a i Accurate, neat drawing [3]; title [1]; accurate labels and annotations [6] apex tip of leaf blade / margin edge of leaf midrib main vein vein transport of substances through the leaf lamina surface of the leaf petiole attaches leaf to the stem of the plant Drawing of the external structure of a hibiscus leaf ■■ Figure A4 ii For example, using the measurements of the diagram here: Magnification = length of drawing length of actual specimen = 9.4 cm 10 cm = 0.94 [2] iii Diagram half the size; resembles the original drawing [1]; accurate [2] ■■ Figure A5 b •Leaves are broad and flat to increase surface area for absorption of carbon dioxide and capture of light needed for photosynthesis. [2] •Leaves are thin so that gases can diffuse rapidly to and from cells. [2] •The cells of the palisade mesophyll layer have numerous chloroplasts as this layer is closest to the sunlight to trap the energy to make food. [2] •Specialised cells/vessels called xylem transport water from the root to the leaves. [2] CSEC® Biology Examination Practice © Kathryn Bennett 2016 5 Answers to CSEC® Biology Examination Practice •Cells of upper epidermis are transparent, allowing light to enter the leaf and get to the photosynthesising cells. [2] 7a i Before: Test for starch – crush a cotyledon and add a few drops of iodine in potassium iodide solution and look for colour change. [4] After: Test for reducing sugars (Benedict’s test) – crush a cotyledon and add 2 cm3 of Benedict’s solution. Shake the mixture and then boil and look for colour changes. [4] ii Test for starch: colour change to blue-black indicates the presence of starch. [1] Test for reducing sugars: colour changes: blue → green → yellow → brick-red precipitate indicate presence of reducing sugars. [1] iii Starch is present in cotyledon (stored food) before it germinates. [1] During germination, enzymes break down the starch into glucose. [1] iv The cotyledon has stored food for the germinating seed. [1] Respiration can take place and the energy is used for growth of the plumule and radicle. [1] The radicles have enough energy to grow down into the soil and form the root system. [1] The plumule grows upwards to form the shoot of the plant. [1] bi The height of the plants; size of the leaves (length or width) [3] ii Growth of the plant [1] iii Same age seeds [1]; seeds germinated from same set [1]; same amount of sunlight [1]; same size container [1]; same type of soil [1] 8a iAlgae → water flea → small fish → duck [2] ii Algae at base of the pyramid (20 000); fleas (1930); small fish (14); at the top of the pyramid is the duck (1) [3] ducks (1) small fish (14) fleas (1930) algae (20 000) ■■ Figure A6 iii Pyramid of energy OR pyramid of biomass [1] Pyramid of energy shows the amount of energy found at each trophic level of the food chain. Energy is lost/ decreases as it moves from one level to the next. [2] OR 6 Pyramid of biomass shows the dry mass of the organisms at each trophic level. As you go up the trophic levels, biomass decreases. [2] CSEC® Biology Examination Practice © Kathryn Bennett 2016 Section A b, cFood web. [4] Trophic levels marked. [1] Secondary consumers include: mice, frogs, sparrows, foxes. [1] Autotroph: grass [1] Trophic levels 5 4 foxes hawks sparrows 3 2 snakes frogs rabbits 1 mice (secondary consumers) grasshoppers grass (autotroph) ■■ Figure A7 di Mutualism [1] ii The leguminous plants get fixed nitrogen in the form of nitrates to make their proteins [2]. The bacteria get shelter and protection by living within the nodules of these plants [2]. iii • Commensalism [1], e.g. remora and shark. [2] The remora benefits by getting food and protection while the shark is unaffected by its presence, i.e. neither benefits nor is harmed. [2] OR • Parasitism [1], e.g. tick and dog. [2] Tick gets food, shelter, protection while the host (the dog) is being harmed in the process. [2] 9a Diagram: correct apparatus [2]; labels [2] rubber bung boiling tube respiring yeast lime water ■■ Figure A8 bi Describe the apparatus [1]; identify the independent and dependent variables [2]; list at least two controlled variables. [2] Several sets of the apparatus are set up as shown in part a). Place different organisms in each set of apparatus (independent variable), for example lice in one set of apparatus, yeast in the second set of apparatus and germinating seeds in the third. Ensure that each set of apparatus is the same size; same CSEC® Biology Examination Practice © Kathryn Bennett 2016 7 Answers to CSEC® Biology Examination Practice volume of lime water used in each; use the same number or mass of organisms (controlled variables). If lime water changes from transparent to white cloudy colour for all sets of apparatus, then all the organisms produce carbon dioxide (dependent variable) when they respire. ii Set up experiment as described in part b) i) and include the use of the stop watch. As the lime water changes colour from transparent to white precipitate, record the time. [2] ci Intercostal muscles, ribcage, diaphragm [3] ii During inhalation: intercostal muscles contract to move the ribcage up and out. The diaphragm muscles contract which results in the flattening of the diaphragm. [3] During exhalation: intercostal muscles relax to move the ribcage down and in. The diaphragm muscles relax which results in the raising of the diaphragm (domes upward). [3] iii The function of the cilia is to move mucus that contains microorganisms and dust upwards and out of the lungs. [2] d Breathing causes air to be taken into the lungs (inhalation) so that the oxygen can be used by the cells for respiration. Respiration produces carbon dioxide, which is removed from the body by breathing (exhalation). [3] 10a iTable showing number of males and females at six different heights. Neat table with correct column headings [2]; correct values [3] Number of people (1000s) Height (cm) Male Female 140 5 5 150 5 30 155 6 90 160 15 118 165 35 120 170 75 75 ii Most people of a height less than 170 cm are female. [2] bi Continuous variation. Examples include finger length; weight; human skin colour; human foot length. [3] ii Things in the environment like sunlight may affect skin colour in humans; food humans eat may cause variation in weight. [2] iii Diagram showing crossing over (homologous chromosomes interacting and exchanging genetic material) [4] 8 CSEC® Biology Examination Practice © Kathryn Bennett 2016 Section A homologous chromosomes crossing over between chromatids ■■ Figure A9 ci A mutation is a change in the structure of a gene or the number or amount of chromosomes resulting in a variant form that can be passed on to subsequent generations. [2] ii Bacteria become resistant to antibiotics because of random mutations. Resistant bacteria will survive an antibiotic treatment and be able to reproduce more bacteria that are also resistant to the antibiotic. [4] iii Evolution is the slow process by which a species adapts to its environment and may eventually give rise to another species. Evolution may depend on mutations as new alleles are created, which allow for more genetic variation and individuals surviving to pass down their genes from one generation to the next. [3] CSEC® Biology Examination Practice © Kathryn Bennett 2016 9 Answers to CSEC® Biology Examination Practice Section B 2a i Diagram of typical plant and animal cell [2] mitochondrion cell membrane nucleus cytoplasm ■■ Figure B1 ii Label the mitochondrion, cell membrane, cytoplasm, nucleus [4] bi 1) Muscle cell – contracts and relaxes to bring about movement [1] 2) Red blood cell – contains haemoglobin for oxygen transport [1] 3) Sperm cell – fertilises the ovum [1] ii Palisade cell – rectangular and contains many chloroplasts that contain chlorophyll to trap sunlight needed for photosynthesis [2] Xylem cell – hollow, no living content so that water can pass through easily [2] OR Root hair cell – increases surface area of the root for more absorption of water [2] iii Cell membrane only; no cell wall like that of plant cells [1] iv In multicellular organisms cell specialisation is important so that the work is divided, making the organism more efficient. [1] 3a i Population – a group of organisms of the same species occupying the same habitat. [1] ii Community – different populations of organisms occupying the same habitat/area. [1] iii Abiotic factors – physical or non-living components of the environment, for example air, water and soil. [1] b Any three from: predator/prey – predator hunts and kills its prey [2]; parasitism – symbiotic relationship in which one organism benefits (the host) and the other is harmed [2]; commensalism – symbiotic relationship in which one organism benefits and the other is unaffected [2]; mutualism – symbiotic relationship in which both organisms benefit. [2] 10 CSEC® Biology Examination Practice © Kathryn Bennett 2016 Section B ci Diagram must include: plants removing carbon dioxide for photosynthesis; organisms respiring to release carbon dioxide in the air; death of organisms; fossilisation; combustion [5] carbon dioxide in the air respiration combustion/ burning respiration feeding animals photosynthesis plants death and decay (fossilisation) fossil fuels ■■ Figure B2 ii Carbon is used to make carbohydrate, which is a respiratory substrate. [1] 4a [1] mark for each correct row. Feature motility size of gamete number of gametes produced number of chromosomes Ovum non-motile relatively large 1 produced/matures each month 23 Sperm motile very small many sperm in one ejaculation 23 bi Fertilisation occurs in oviduct or fallopian tube. [1] ii Implantation occurs in the lining of the uterus. [1] iii The cervix is found at the base/neck of the womb. [1] iv Oestrogen is produced by the ovaries. [1] c Oestrogen results in the development of secondary sexual characteristics of females: hair in armpits and pubic region; hips widen; breasts enlarge; menstrual cycle. [2] d The fallopian tube has cilia that help to move the ovum along. [1] e Sperm cell has a tail that moves in a whip-like manner to propel the sperm. [2] The acrosome in the head has enzymes that digest a path through the layer of cells that surround the ovum. [2] OR Mitochondria in the sperm provide energy for movement. 5a The substance the enzyme acts on is the substrate [1]; in this experiment, hydrogen peroxide. [1] b The temperature at which the enzyme works best by making most products. [1] c Approximately 30 °C [1] CSEC® Biology Examination Practice © Kathryn Bennett 2016 11 Answers to CSEC® Biology Examination Practice d The temperature has altered the shape of the enzyme and so it can no longer fit with its substrate. [1] The enzyme is said to be denatured. [1] ei Properties of enzymes include: 1) enzymes are specific – an enzyme will only catalyse one type of reaction [2] 2) enzymes work best at an optimum temperature – at low temperatures enzymes are inactive and at high temperatures they are denatured [2] 3) enzymes work best at an optimum pH – different enzymes work best in an acidic, alkaline or neutral pH [2] 4) enzymes are not damaged during the reactions they catalyse and so they can be reused once the active site is free [2]. ii The enzyme is acting as the lock [1] as it has the active site which represents the ‘key hole’. 6a i Drawing should show longitudinal section and labels should be accurately done. [4] cortex medulla renal pelvis ureter ■■ Figure B3 ii Bowman’s capsule, 1st and 2nd convoluted tubule in the cortex while the loop of Henle and collecting duct extends into medulla. Collecting duct should lead to renal pelvis. [2] iii Afferent and efferent arterioles [1] b Excretory products in animals: urea, carbon dioxide, uric acid [2] Excretory products in plants: oxygen, tannins, calcium oxalate [2] c Plants: transfer wastes to old or dying leaves. When the leaves fall off, the wastes are excreted. Some wastes are stored in, for example, the bark. [2] Animals (including humans) get rid of waste like urea by creating urine and some is removed in sweat. Carbon dioxide is removed by the lungs by exhaling. [2] 12 CSEC® Biology Examination Practice © Kathryn Bennett 2016 Section B 7a i The sea turtle is adapted for getting rid of the excess salt from its environment. Putting it in fresh water means that water will enter the animal’s body and it is not adapted to get rid of excess water. Its kidneys cannot handle the volume of water. This results in death of the organism as animal cells swell and burst if they take in too much water. [2] ii 1) Plant cell will lose water. Cell membrane pulls away from cell wall. The cell is said to be plasmolysed. [3] 2) No net movement of water as the concentration within the cell and outside the cell are the same. [2] bi Fishermen use nets to capture the fish. When turtles come to the surface for air, they may get caught in nets. [2] The black-market may kill turtles for their exquisite shells or to sell their meat for food. [2] Sea turtles lay their eggs in the sand. If the beach is developed there may not be any place for them to lay their eggs or baby sea turtles may have a longer distance to travel to get to the sea, exposing them to predators or other dangerous factors. [2] ii Protect beaches used for nesting; dispose of trash properly so that turtles don’t mistake it for food; educate persons about sea turtles and the challenges they face. [2] 8a i Autotrophic (most plants), e.g. hibiscus plant, algae, etc. [2] Heterotrophic nutrition (most animals), e.g. humans, goat [2] ii A type of heterotrophic nutrition that occurs in saprotrophs, which feed on dead or decayed organic matter. [2] b Fewer trees to remove carbon dioxide from air for photosynthesis (contributes to increased levels of carbon dioxide in the air) [2]; fewer trees producing oxygen for organisms to use for respiration [1]; trees may be habitats for organisms and removal may lead to extinction of the species [1]; less food for birds and other animals [1]; increased soil erosion c No fishing – to protect sensitive species of fish [2]; no removal of resources like shells or corals; no littering – substances thrown away may negatively affect the organisms living in the area. Protect the habitat for organisms to successfully age and reproduce. [2] 9a i AIDS: unprotected sex; dirty needles; childbirth – from mother to baby; by blood transfusions. [4] Malaria/dengue [1]: transmitted by the mosquito who bites organisms like humans giving them the disease. [1] ii AIDS: abstaining from sexual activities; use a condom; test blood for disease before donation; never share or use dirty needles. [1½] Malaria/dengue: destroy vector by using sprays; secure/ cover up stored water that provides vector breeding sites; cover water with oil; use repellents. [1½] bi Reproduction occurs at a faster rate (speed); if parent plants are successful, it is advantageous to make clones. [2] CSEC® Biology Examination Practice © Kathryn Bennett 2016 13 Answers to CSEC® Biology Examination Practice ii Asexual methods include cuttings – cut a portion of the stem of a plant about 7 inches long and at a 45 degree angle, plant it in a good medium and water regularly [2]; grafting – remove the bud from a deflowering stem with a smooth straight cut and insert into the stock of a tree. (Transfer the living tissue from one plant to another.) [2] iii Crops were identical because of the means of reproduction. So all plants died from same disease. [2] 10aAccommodation is the ability of the eye to adjust the lens to see objects at various distances. [1] To see near objects, the ciliary muscles contract and suspensory ligaments slacken, causing the lens shape to fatten. [2] To see far objects, the ciliary muscles relax and the suspensory ligaments stretch and the lens becomes thin. [2] b Glaucoma – build-up of pressure in eye that may result in damage to the optic nerve. [2] Cataract – clouding of the lens in the eye. [2] c Differences (two for [2] marks each): • hormones transmit chemical messages for endocrine system via the blood circulation while neurons/nerve cells transmit messages in the form of electrical impulses for nervous system • messages are transmitted at a slower rate via the endocrine system; response to stimuli is almost instantaneous in the nervous system • effects of the endocrine system may be widespread in the body while the nervous system has a localised effect. Similarity: they both detect and respond to stimuli. [2] 11aiAnimal dispersal: animals eat fruits containing seeds and deposit seeds in their droppings; animals eat fruits and carry the seeds far away from the parent plant. [2] Wind dispersal: some seeds have wings or long feathery tails so that they can be transported by the wind and travel/fly long distances. [2] Explosive: the heat from the Sun dries out the water from these seed pods which causes them to shoot seeds from the pods at a high speed. [2] ii Competition for nutrients in the soil; insufficient nutrients in the soil to supply all the plants; since they are the same type of plant, they take in the same types of nutrients, depleting them from the soil making it less fertile. [2] Competition for light and water. Also, plants cannot develop their normal shape if crowded together (some restriction in growth movement would occur). [2] b Dormancy is when a seed remains inactive until it finds favourable conditions to germinate and grow into a plant. [2] c Water is used to initiate chemical reactions within the seed so that the embryo can germinate [1]; enzymes convert the insoluble substances like starch, proteins and 14 CSEC® Biology Examination Practice © Kathryn Bennett 2016 Section B lipids stored in the cotyledons into soluble substances – glucose, amino acids, fatty acids and glycerol. [2] 12ai Natural method – e.g. rhythm [1] Barrier method – e.g. condom, cap (diaphragm) [1] Hormonal method – e.g. birth control pills, implants [1] Surgical method – e.g. tubal ligation, vasectomy [1] ii For example, for the condom: Disadvantages: condom not 100% effective; inconvenient to put on in ‘heat of moment’. [2] Advantages: may protect individuals against some sexually transmitted diseases [2]; cheap and easily accessible in pharmacies without the need of a doctor’s prescription. [2] iii Accept any answer that is properly supported. For example: I would recommend the hormonal methods [1] as the effects are reversible [1] and they are not used at the time of sexual intercourse. [1] b Prostate cancer and cervical cancer [2] OR sexually transmitted diseases such as syphilis; endometriosis. 13a Diagram for [5] marks. anther filament stamen petal stigma style carpel/ pistil ovary ■■ Figure B4 b [2] marks for each correct row. Characteristic Wind-pollinated flower Insect-pollinated flower petals small/inconspicuous large, brightly-coloured/ conspicuous anthers loosely attached and firmly attached inside flower for hang outside flower insects to brush against them nectary no nectar nectar present to attract insects c After fertilisation, the following changes occur in the flower: diploid zygote develops into an embryo which forms the future plant [1]; the ovary develops into a fruit [1]; the fertilised ovules become seeds [1]; petals and sepals fall off. [1] CSEC® Biology Examination Practice © Kathryn Bennett 2016 15 Answers to CSEC® Biology Examination Practice 14ai Cell body [1], axon [1], dendrites [1], knob [1] dendrite axon knob cell body ■■ Figure B5 ii Motor neuron [1] iii The motor neuron transmits impulses to the effector muscles. [2] iv Sensory neuron; intermediate/relay neuron [2] biSensitive cells (receptors) in the eye detect the stimulus of light [1]; the sensory neuron takes the impulse to the CNS [1]. The message is interpreted and the impulse is carried by a motor neuron to the effector. [1] Pupil constricts [1]. ii The knee-jerk reflex is a spinal response while the pupil reflex is a cranial response. [2] 15a Hypothalamus, pituitary gland [2] b Hypothalamus has sensitive cells that detect the concentration of water in the blood. [1] Message is then sent to the pituitary gland. The pituitary gland releases antidiuretic hormone (ADH). [1] The ADH travels in the blood stream to the kidneys where it makes the nephron more permeable and so water is reabsorbed back into the blood stream. [2] Urine is highly concentrated and of small volume. [1] c Ultra-filtration and selective reabsorption [2] d The pancreas is malfunctioning. [1] Not enough insulin is produced to convert glucose to glycogen. [1] e Negative feedback is a regulatory mechanism of the body to maintain the normal level of whatever is being regulated [1]; for example, if there is too much sugar in the blood, the pancreas produces insulin that converts the excess glucose to glycogen for storage, which reduces the amount of sugar in the blood. [2] If there is too little sugar, glucagon is produced which converts stored glycogen to glucose increasing the glucose levels in the blood. [1] 16 aiDigestion is the breaking down of large insoluble food particles into small soluble particles that can be used by the cells. [1] Egestion is the removal of undigested food. [1] ii Mouth and stomach [1]: mouth has teeth to crush and grind food [1]; stomach has muscular walls to churn the food. [1] iii Test for protein. Biuret test [1] – crush food and add a little distilled water. Add solution and if a lilac/purple colour is formed then protein is present. [1] b Any three from: age, occupation, sex, whether pregnant, and whether person is affected by deficiency or 16 CSEC® Biology Examination Practice © Kathryn Bennett 2016 Section B physiological diseases (for example, kwashiorkor and diabetes respectively) [3] ci Deficiency disease [1] ii Any two categories and two examples (for [1] marks each, total [4] marks): •physiological, e.g. asthma and lung cancer •hereditary, e.g. sickle-cell anaemia and haemophilia •pathogenic, e.g. influenza and malaria. 17aFor example, carbon dioxide, oxygen, hormones, urea, glucose. [5] They dissolve in the blood and are transported around the body. [1] biPhagocyte and lymphocyte [2]: the phagocyte engulfs and destroys invading organism while the lymphocyte releases antibodies. [2] ii An antigen is a protein that is found on the surface of foreign cells invading the body, for example [1], while an antibody is a protein produced by the body’s own lymphocytes and is found in the plasma. [1] c Higher altitude means less oxygen is available. [1] More red blood cells are made [1] to carry as much oxygen as possible. [1] 18aDiagram should show the shape of the red blood cell: disc-shaped/biconcave [1] and no nucleus [1], which is important for creating more surface area for absorbing and carrying as much oxygen as possible. [1] Contains the red pigment haemoglobin to which the oxygen binds. [1] cytoplasm contains haemoglobin spherical and biconcave shape no nucleus within cell ■■ Figure B6 b The skin acts as a barrier and is the first line of defence. [2] If there is a break in the skin, then platelets are responsible for blood clotting. [2] White blood cells get rid of invading organisms by phagocytosis or releasing antibodies. [2] c Immunity is the body’s natural ability to resist disease and infection. [1] Natural immunity can either be passive (effect is short-lived), e.g. passing of antibodies from mother to child through breast milk; or active (effect is long-lasting), e.g. body produces antibodies in response to direct exposure to the antigen. [2] Artificial immunity can also be passive, e.g. antibodies from an individual are injected into another person; or active, e.g. antigens are injected or given orally as vaccine. The vaccine stimulates the body to make its own antibodies. [2] CSEC® Biology Examination Practice © Kathryn Bennett 2016 17 Answers to CSEC® Biology Examination Practice 19aDiagram should include representation of a pump and vessels [3]; should show the blood passing through the pump twice. [2] lungs pump veins arteries body capillaries ■■ Figure B7 b•Heart – for pumping blood around the body [2] •Blood – for transporting useful and waste substances around the body [2] •Blood vessels – conduct blood throughout the body, i.e. from heart (arteries) to tissues (capillaries) back to the heart (veins) [2] ciA potometer measures the rate at which a plant loses water as it transpires. A shoot of a plant is cut under water and inserted into the potometer. A bubble of coloured dye is inserted into the capillary tube. As water is lost from the plant, water from the capillary tube replaces it, pulling the bubble along. The movement of the bubble is timed to measure the rate at which transpiration is occurring. [2] ii Cut the shoot under water so that air bubbles are not introduced. [1] Conditions outside the potometer should be kept constant, e.g. temperature. [1] 20a Missing substances and type of respiration as follows: • lactic acid [1] – anaerobic respiration [½] • oxygen, carbon dioxide, water [1] – aerobic respiration [1] • carbon dioxide [1] – anaerobic respiration [½] bi Lime water/calcium carbonate [1] ii Transparent [1] to cloudy white [1] ci Alveoli in humans; gills (lamellae) in fish [2] iiSimilarities: 18 CSEC® Biology Examination Practice © Kathryn Bennett 2016 Section B • thin – walls of alveoli are one cell thick for rapid exchange of gases; lamellae are thin. [2] • rich blood supply – dense capillary network to transport substances to and from the gas exchange surfaces. [2] • moist – gases dissolve in water to be transported across the membrane easily. [1] 21aA stimulus is any change in the environment that can bring about a response in an organism. A stimulus is detected by cells found within sense organs. [2] b To find a mate; in search of food; to find a more suitable environment. [2] c Movement in plants is usually growth movement which is slow [1] and can be described as irreversible. [1] The type of movement is also ‘part’ movement. [1] Movement in animals is more rapid and reversible. Animals also move by locomotion. Animals may do ‘part’ or ‘whole’ movement. d Choice chamber for small invertebrates. Include list of materials; logical step-by-step procedure; identify the variables. For example: Set up the choice chamber. Cover one-third of the chamber with black cartridge paper. Cover a second section with black cartridge paper, but bore holes in the paper. Leave the third section open to light/uncovered. [3] Cover the chamber and leave it to equilibrate for about 5 minutes. [1] Introduce the woodlice into the chamber via the centre or in a way that doesn’t favour any of the three conditions. [1] Record the distribution of the organisms after 10 minutes. [1] Repeat the experiment for accuracy and reliability. [2] 22aiA species is a group of closely related organisms that are able to interbreed [1] and produce fertile offspring. [1] ii Two from the following: Geographical separation – a physical barrier such as a body of water or a mountain separates two populations of the same species, for example the Anole lizards of the Caribbean Islands. [2] Ecological differences – changes in the environment may cause organisms to adapt and change. Once these changes occur, organisms may no longer recognise each other as being of the same species and so do not mate and occupy different niches. [2] Behavioural differences – organisms develop differences in behaviours, such as courtship and mating behaviour, so that groups no longer mate. [2] b Natural selection is the process by which a population retains those genes which better adapt it to its environment. This is driven by naturally occurring processes. [2] With artificial selection, the selection is imposed by humans. [2] CSEC® Biology Examination Practice © Kathryn Bennett 2016 19 Answers to CSEC® Biology Examination Practice ciIn the industrialised areas soot was produced [1] and so the black peppered moth could blend in with the environment. [1] Dark moths were not easily identified by their predators and so were able to survive and become common [1], unlike the light coloured peppered moths that were no longer camouflaged and became easy targets for their predators. ii Charles Darwin concluded that biological evolution was as a result of natural selection. Some organisms are more likely to survive and reproduce than others. If the advantageous traits are inherited, the next generation will also have these advantageous traits and hence be more likely to survive and reproduce in that environment. [2] 23ai Diabetes [1] ii Exercise; changes in diet; drugs (insulin injections) [3] iiiMaking insulin from bacteria: 1) Enzyme is used to cut a piece of circular DNA in bacteria. [1] 2) Human insulin gene is isolated/extracted from human pancreatic cells. [1] 3) The insulin gene is placed/inserted into the bacterial plasmid. [1] 4) The recombinant DNA is introduced into a bacterium. [1] 5) Plasmids are produced as the bacteria multiply. [1] b Social – control genetic diseases like cystic fibrosis; loss of genetic diversity as small farmers would choose to stop growing local varieties of crop plants as it would not be beneficial to them economically. [2] Ethical – exploitation of living things and/or misusing the environment for the benefit of humans. [2] c Any two from the following (for [1] mark each): • development of high performance food crops that will grow quickly and use less fertiliser • resistance to insect pests in many crop plants • increase in yield and size of many crops and cattle and dairy animals • more nutritious food. 24aSickle/crescent-shaped red blood cells; joint pains; shortage of oxygen in blood [2] bi Individuals 1, 4 and 11 [2] ii 3 and 4 – married/couple; 4 and 5 – siblings [2] iiiHeterozygous (Aa) [1]; produced a daughter that has the disease. Hence both parents must have the recessive allele to produce an offspring with the disease that exists in homozygous recessive (aa). [1] 20 CSEC® Biology Examination Practice © Kathryn Bennett 2016 Section B ivLet A represent normal allele Let a represent sickle-cell allele Genotype of individual 5 Genotype of individual 6 Gametes Aa Aa A a AA Aa × A a Aa aa Random fertilisation Offspring [1] Probability 1/4 or 25% chance [1] ■■ Figure B8 ciCodominance: both alleles expressed in the heterozygous genotype. [1] ii Human blood groups are an example of codominance. Blood group is controlled by alleles A, B and O. [1] A and B are equally dominant and both are dominant to O. [2] Hence four phenotypes are possible: blood type A (AA or AO); B (BB or BO); AB; and OO. [1] 25a i sclera; ii aqueous humour; iii cornea; iv lens; v optic nerve [5] b Stimulus: any change in the environment (internal or external) that brings about a response from an organism. Light is the stimulus detected by the eye. [2] c Rods: sensitive to dim light and only let you see in black and white. [2] Cones: let you see colour in bright light. [2] d In bright light, the circular muscles of the iris contract, which makes the pupil small so that the retina isn’t damaged by excessive light. [2] In dim light the radial muscles of the iris contract, making the pupil dilate or get larger. [2] CSEC® Biology Examination Practice © Kathryn Bennett 2016 21 Answers to CSEC® Biology Examination Practice Multiple Choice Answers Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 22 Answer B D B A D C B B D C A B A B D Number 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Answer D D A B C D C B A D D A B A D Number 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 CSEC® Biology Examination Practice © Kathryn Bennett 2016 Answer A C B D D B A B D C C D A C C Number 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Answer D B C C B A A A D A D A A C A