2024 Pure Biology TYS Answers

2024 Biology 6093/01 Answers

2024 Biology 6093/02 Answers Section A Qn Answers Remarks 1a • underground / not exposed to sunlight + no need to absorb / convert light energy to chemical potential energy; • (function of a root hair cell) to absorb water and mineral salt + does not carry out photosynthesis; Weaker responses described the root hair cell as being ‘underground’ without reference to light or simple stated the function of root hair cells is to absorb water and mineral ions. 1b(i) mitochondrion; 1b(ii) • (mitochondrion) site of aerobic respiration + to release energy; • energy released is used to absorb mineral salts from the soils to the root; • against concentration gradient / from low concentration in the soil to high concentration in the cell sap of root hair cell; • mineral salts are used to synthesis amino acids / proteins or chlorophyll; A common incorrect answer was to describe the uptake of water by active transport. Weaker responses indicated that energy could be used for photosynthesis or respiration. 1b(iii) • endoplasmic reticulum • Golgi body / Golgi apparatus A common incorrect response was ‘ribosomes’ [Total: 9 marks]

2a (from distant object to near object) • diverging light rays reflected from the book are refracted through the cornea and the aqueous humour into the pupil; • ciliary muscles contract + relaxing their pull on the suspensory ligaments; • suspensory ligaments slacken + relaxing their pull on the lens; • lens becomes thicker and more convex + light rays reflected from the book are sharply focused on the retina; Many candidates described the details of nervous coordination to bring about the changes, which were not required. 2b(i) 5.8 – 2.5 x 100 5.8 = 56.897 = 56.9 % (to 3 sf) Weaker responses omitted the instruction and did not round the answer to three significant figures. 2b(ii) to prevent excessive light from entering the eye + damaging the retina; Weaker responses only referred to allowing less light to enter the eye. 2b(iii) (moves into bright light) • circular muscles in iris contract + radial muscles of iris relax; • pupil becomes smaller / constricts; Weaker responses referred to muscles constricting rather than contracting, referred to the radial muscles as the longitudinal muscles or referred to the circular muscles as the ciliary muscles. [Total: 10 marks]

3a(i) (variation) refers to the differences in traits between individuals of the same species; Many responses needed more details, often referring to differences without specifying between what. 3a(ii) examples of continuous variation: human skin colour height weight 3a(iii) examples of discontinuous variation: green or yellow seeds in pea plants smooth of wrinkled seeds in pea plants ABO blood groups double to single eyelids Ability to roll the tongue 3b(i) • difference in shell shape, tortoise P has domed / rounded surface shell shape while tortoise Q has intermediate shell shape; • difference in the length of legs, tortoise P has shorter legs while tortoise Q has longer legs ignore: difference in body size Some candidates talked about the overall size of the tortoises which could not be determined from the photographs without a scale. 3b(ii) • spontaneous mutation took place + producing a new variant, i.e. long-necked tortoise; • longer neck tortoise were able to feed on other types of plants; • less competition among long-necked tortoise to feed on other types of plants / higher competition among shorter-necked tortoise to feed on ground level grass; • natural selection favoured long-necked tortoise; • long-necked tortoise were better adapted to the environment + survived and passed down the long neck gene / allele to the next generation; • over many generations, long-necked tortoise population increased and evolved into a distinct form; Stronger responses began with a reference to ‘mutation’ and ‘variation’, as the basis for the evolution of the long- necked tortoise. Stronger responses described the passing of favourable alleles to the offspring and the increased frequency of these allleles in the population. [Total: 10 marks]

4a carbon dioxide (gas); 4b(i) accept any value between 15 to 19; 4b(ii) using a gas syringe / measuring cylinder to measure the volume of carbon dioxide; measure carbon dioxide concentration using a probe; Accept: measure pH of water Imprecise response referred to measuring the amount of gas using syringe / measuring cylinder. 4b(iii) • limiting factor at light intensity 6 to 7: carbon dioxide concentration; • at 0.01% CO2 concentration, as light intensity increases from 6 to 7, the number of bubbles per minute produced remains constant, at 27 per minute; Some candidates mainly described how they knew it was not light intensity rather than giving evidence for why it was carbon dioxide. 4c(i) (at 4C) prediction: rate of photosynthesis decreases and remains low; explanation: enzymes are involved in photosynthesis + at 4C, enzymes are inactive + lower rate of formation of enzyme-substrate complex; Weaker responses referred to enzyme inactivity with no further explanation. 4c(ii) (at 80C) prediction: rate of photosynthesis is at 0 a.u. explanation: enzymes are involved in photosynthesis + at 80C, all enzymes have been denatured; [Total: 9 marks]

5a(i) mitosis Common errors included: 1. reference to production of genetically similar cells instead of genetically identical cells. 2. refence to mitosis enabling the growth of cells instead of growth of a tissue or the organism. 3. refence to mitosis enabling the repair of cells instead of growth of tissue repair. 5a(ii) meiosis Weaker responses showed lack of specificity, such as referring to ‘haploid cells’ rather than to ‘gametes’ or to ‘reproduction’ alone without qualification. Some referred to the production of genetically different cells without going to state how this results in genetically different offspring (leading to variation) 5b human cells produced by mitosis contain 46 chromosomes while human cells produced by meiosis contain 23 chromosomes; [Total: 5 marks]

6a elements in a fat molecule: carbon, oxygen and hydrogen 6b • in the duodenum / small intestine, large fat droplets are emulsified / broken up into small fat droplets + by bile salts; • emulsification increases surface area to volume ratio of fats + speeding up digestion of fats by lipase; • in the small intestine, lipase digests fats into fatty acids and glycerol; • in the ileum, fatty acids and glycerol diffuse across the epithelium / wall of the villus into the bloodstream; • each villus contains a lacteal to transport the absorbed fats away and maintain a steep diffusion gradient; Many candidates described the action of both bile and lipase in the digestion of fat molecules and gave comprehensive accounts. 6c Any 2 from: • as a source and a long-term energy storage; • as an insulating material to prevent excessive heat loss, e.g. thick layer of fat beneath the skin; • a solvent for fat-soluble vitamins / hormones; • an essential part of cells, e.g. cell membranes; • oily substance secreted by the glands in the skin reduces water loss from the skin surface; Weaker responses used imprecise language such as ‘keeping us warm’. [Total: 7 marks]

7a • only 10% of energy is transferred from one trophic level to the next, e.g. from arctic plants to arctic hare + • 90% of energy lost to the environment as heat released via respiration / uneaten body parts / faeces / excretory products; • energy is needed to build biomass + less energy available will result in less biomass at higher trophic levels; • polar bear occupies trophic level 4 / final consumer in the food chain; Some candidates only d