Biology 5094 O Level 2011 Answers Scheme

Paper 1

1 2 3 4 5 6 7 8 9 10C D C C C A A D A B

11 12 13 14 15 16 17 18 19 20B C D D D D A C B C

21 22 23 24 25 26 27 28 29 30D A A D C A D B B D

31 32 33 34 35 36 37 38 39 40A B D C D B B B D D

Paper 2: Section A

Qn Answers Topic Link and Notes for Understanding1ai In visking tubing, amylase digested starch producing maltose; [1]

Maltose molecules are small enough; [1]to diffuse out of partially permeable visking tubing into water in beaker [1]

Movement of SubstancesNote: ‘Break down is not accepted’ as it could mean physical breakdown rather than chemical one which produces maltose.Refer maltose as “maltose molecules” is essential

aii Negative results for starch test, iodine solution remain brown [1]Starch is a large molecule, it is not small enough to diffuse across the partially permeable membrane [1]

Stating “starch is absent in water” is an insufficient answer.

b Partially permeable membrane2ai Mutation is a sudden random change in the structure of a gene or in the chromosome

numberHeredity

aii 1. Chemical such as tar and formaldehyde2. Radiation such as gamma and ultraviolet ray

bi 1. Person A has an extra copy of chromosome 21 compared to Person B.2. Person A has 2 X chromosomes while Person B has 1 X chromosomes and 1 Y

chromosomes.bii Down’s Syndromebiii Person B is a male as he has 1 X and 1 Y chromosomes.3a 1. Red blood cell has a circular biconcave shape. To increase surface area to volume

ratio for more efficient diffusion of oxygen in and out of cell2. Haemoglobin present. Haemoglobin binds to oxygen at lungs to allow transport of

oxygen to rest of the body

Cells/Transport in Human/Respiration

3bi 1.3100

×20=0.26cm2

3bii Concentration of oxygen will decrease. [1]Tobacco smoke contains carbon monoxide; [1]which binds irreversibly with haemoglobin, reducing oxygen carrying capacity of red blood cell. [1]

3c Lymphocytes produce antibodies that bind with foreign particles [1]Which will be ingested and digested by phagocytes [1]

4a Excretion is the removal of metabolic waste products, [1]if not removed, accumulation will be toxic to the body. [1]

Excretion“Metabolic” is a key word not just waste“Toxic/poisonous” rather than harmful to body

bi A: UreterB: Urethra

Dot not be confuse with ‘Ureter’, ‘Urethra’ and ‘Uterus’. Spelling must be accurate.

bii Ureaci 840 cm3

cii 1120 units5a A: Placenta

B: Amniotic membrane/sacC: Umbillical cord

Reproduction in Human

b Support and cushions the fetus before birthShock absorberProtects the fetus against physical injury due to incompressibility of amniotic fluid

*any 1 pointc 1. Antibodies

2. Amino acid/fatty acids/glycerol“Nutrients” or “food” is too vague

6ai Chloroplast Nutrition in Plantsaii In – Carbon dioxide

Out – Oxygenb As temperature increases from 0oC-35oC, rate of photosynthesis increases from 10 to 270

units. [1]As photosynthesis is an enzyme controlled reaction, increase in temperature increase the kinetic energy of enzyme and substrate thereby increasing rate of reaction. [1]

Optimum temperature of the enzyme is at 35oC where rate of enzyme action highest. [1]

As temperature increase from 35oC-55oC, rate of photosynthesis decreases from 270 to 0 units. [1]When temperature increases beyond optimum, enzyme starts to denature and loses it active site resulting in decrease enzyme activity [1]

*any 4 points

7a X – AntherY – Stigma

Reproduction in Plants

b 1. In flower A the anthers are positioned below the stigma while in flower B the anther is above the stigma.

2. The style of flower A is longer than the style of flower B.c Pollination is the transfer of pollen grains; [1]

from the anther to the stigma [1]

Paper 2: Section B

Qn Answers Topic Link and Notes for Understanding8ai

aii 390 beats per minutesaiii 1. The mean heart rate of rats in Group C is higher than that of rats in Group B in general.

2. There is greater range of mean heart rate of the rats in Group C (300 to 520 beats per minutes) than that of rats in Group B (280 to 380 beats per minutes)

b Drug injected into the blood will dissolve into the plasma [1]Transported to the heart via the vein [1]Pumped out of the heart via the aorta [1]From the aorta enters the coronary arteries of the heart muscles [1]

Note: Crucial to explain drug will first dissolve in plasma

9ai Diffusion is the movement of substances from a region of higher concentration to a region of lower concentration down a concentration gradient.

aii Osmosis is the movement of water molecules from region of higher water potential to region of lower water potential through a partially permeable membrane.

bi Medicine will pass through the skin epidermis and dermis via diffusion [1]It then diffuse across the one cell thick capillaries in the skin and enter the bloodstream [1]

bii 1. Patch allows a controlled release of medicine into the bloodstream continuously2. Patch is more convenient than taking regular medicine through mouth

biii Patch may cause skin irritation10 Either10a Enzymes are biological catalyst [1]

That can alter or speed up chemical reaction [1]They remain chemically unchanged at the end of the reaction [1]

b

c Salivary amylase produced by the salivary glands in the mouth and works best at ph 7. [1]It digest starch into maltose in the mouth [1]At the stomach, salivary amylase is denatured due to the acidic nature of the environment. [1]No digestion of starch in stomach [1]In small intestine, pancreatic amylase is produced by pancreas which works best at alkaline condition [1]Remaining starch will be digested into maltose at small intestine. [1]

10 Or10ai Digestion is the process where large insoluble food molecules [1]

are broken down into smaller, soluble and diffusible molecules [1]It can be chemical or physical [1]

aii Absorption is the uptake of nutrients, water and dissolved minerals [1] from small intestine to blood capillaries thereby enter the blood stream [1]It enters by diffusion and active transport [1]

b Regulate glucose concentration in blood. [1]When glucose concentration in blood is high, pancreas will produce insulin which causes liver cells to convert excess glucose to glycogen for storage. [1]When glucose concentration in blood is low, pancreas will produce glucagon which causes liver to convert stored glycogen to glucose. [1]

Deamination of excess amino acid to form urea. [1]Detoxification of harmful substance. [1]Breakdown of alcohol. [1]Synthesis of plasma protein. [1]Iron storage. [1]