Marking Scheme > Biology 2004 Paper 1 Marking Scheme

HKCE-BIO I/2004/ Marking Scheme/1

CE-Bio-I 2004 Biology Paper 1 1. (a) (i) X is a finger-like projection of the intestinal wall. (1) This feature provides a large surface area for food absorption. (1) The epithelium of X is very thin / one-cell thick. (1) This shortens the distance of diffusion / transport of digested food substances. (1) (ii) X → hepatic portal vein → liver → hepatic vein → vena cava → (heart) (2) (iii) The peristaltic contraction of the muscle layer (1) pushes food along the small intestine. (1) This also helps to mix food with digestive enzymes. (1) (b) (i) (1) Plumule (1) (2) Stem and leaf (1,1) (ii) Amylase hydrolyses the starch stored in the seed (1) into maltose / sugar, (1) which is used for forming new cells (1) and for respiration / release of energy for the growth of the seedling. (1) (iii) The seedling has developed green leaves. (1) The rate of photosynthesis of the leaves is greater than the rate of respiration of the seedling, (1) so there is a net gain in the amount of organic substances / new cells are produced. (1) (c) (i) Oxygen in air dissolves in the water film, (1) so that it can diffuse readily through the wall of the air sac into the blood capillary. (1) (ii) The accumulation of fluid increases the distance for diffusion/reduces the surface area for dissolving oxygen, (1) hence decreases the rate of diffusion of dissolved oxygen into the blood capillaries. (1) Thus the oxygen content of the blood decreases / becomes lower than normal. (1) (iii) The antigen of the SARS virus (1) stimulates the white blood cells of the patient to produce the specific antibodies. (1) (iv) Injection of the weakened virus / the antigen into the body. (1) This will stimulate the white blood cells to develop memory for the antigen. (1) When the same virus enters the body, (1) a large amount of antibodies can be produced rapidly to kill the virus. (1) 2. (a) (i) Both of them are based on the use of a barrier / prevent the sperms from meeting the egg. (1) (ii) IUD prevents the implantation of the embryo. (1) (iii) (1) Egg and sperms are viable for only a few days once they are released. (1) The rhythm method is to avoid sexual intercourse around the time of ovulation, (1) so that sperms and egg will have no chance of meeting each other. (1) (2) Because it is hard to predict the time of ovulation accurately. (1) (iv) Time of intercourse does not necessarily fall in the period around ovulation. ) Gametes produced may not be viable / may be defective. ) I:\BioTch\CB\HKEA\MS\CE-BIO-I_2004MS.doc

P.1

HKCE-BIO I/2004/ Marking Scheme/2

Oviducts of some women may be blocked. ) any two The sperm count of the husbands may be too low. ) (1,1) (v) This is because the development of secondary sexual characteristics is controlled by the male sex hormone, (1) which is still produced by the testes (1) and transported in the blood after the operation. (1) (b) (i) The bacteria distributed evenly in I, (1) but concentrated on the chloroplast in II. (1) (ii) In the presence of light, the chloroplast produced oxygen during photosynthesis. (1) This led to the movement of bacteria toward the chloroplast. (1) (iii) To study the effect of light of different colours on (the rate of) photosynthesis. (1) (iv) Photosynthesis occurs at similar rates in red and blue lights (1) which are higher than that in green light. (1) (v) (1) Workable set-up: (must include light source, water, waterweed & colour filters) (1) Labels: colour filters, waterweed, water / lamp / gas or oxygen (1) Title (1)

(2) Measure the volume of oxygen produced / number of oxygen bubbles released per unit time / over a period of time. (1) (c) (i) Receptor: taste buds / smell receptor (1) Effector: salivary glands (1) (ii) (light) → light sensitive cells relay neurone in brain sensory neurone motor neurone muscle of iris → (contraction of iris muscle / pupil constriction) (3) (iii) (1) Cerebrum (1) (2) The responses can be controlled voluntarily. ) They are not stereotyped. ) any two (1,1) They need to be learned. ) 3. (a) (i) Plant A is homozygous for the green-leaf allele. (1) Plant B is homozygous for the variegated-leaf allele. (1) This is because all the offspring of each plant have the same phenotype as the parent. I:\BioTch\CB\HKEA\MS\CE-BIO-I_2004MS.doc

P.2

HKCE-BIO I/2004/ Marking Scheme/3

(1) (ii) Both plants A and B are homozygous, but of different phenotypes. (1) When they are crossed, all their offspring will be heterozygous. (1) In heterozygous condition, the phenotype shown by the offspring is the dominant phenotype. (1) (iii) Magnesium (1) For the formation of chlorophyll (1) Or Nitrate For the formation of chlorophyll / protein (b) (i) Glomerular filtrate (1) The high blood pressure in the glomerulus (1) forces some plasma / blood except some large proteins / blood cells out of the glomerulus (1) through the thin / porous wall of the glomerulus and the Bowman's capsule into X. (1) (ii) Some glucose in the blood of vessel A are filtered into the Bowman's capsule. (1) At the first coiled tubule it is then reabsorbed (1) into the capillaries which drain back to vessel B. (1) Some glucose in vessel A is carried in blood flowing toward vessel B. (1) (iii) The flow rate of blood in vessel A is higher due to the dilation of the vessel. (1) The rate of formation of the glomerular filtrate will increase, (1) while the rate of water reabsorption in the kidney tubule remains relatively the same, (1) thus the rate of urine production increases. (c) (i) To withstand the high blood pressure. (1) To regulate the blood flow to the organ / control the diameter of the vessel lumen. (1) (ii) The blood pressure in vessel type II is lower. (1) The larger lumen would have a smaller resistance, thus facilitating the blood flow. (1) (iii) Lung (1) (iv) (1) Vessel type II of organ A has a lower carbon dioxide content than vessel type I. (1) As blood flows from vessel type 1 to the lung, then to vessel type II, (1) carbon dioxide diffuses out of the blood to the air sac in the lungs. (1) (2) Blood in vessel type I of organ A comes from the veins / the right side of the heart, (1) which collect blood from the body tissues (1) where oxygen is consumed in respiration. (1) 4. (a) (i) The muscles carry out anaerobic respiration (1) to release additional energy for muscle contraction. (1) As anaerobic respiration produces lactic acid, it will lead to an increase in blood lactic acid concentration. (1) (ii) glucose + oxygen → carbon dioxide + water (2) (iii) Because it lowers the pH of the blood / tissue fluid which I:\BioTch\CB\HKEA\MS\CE-BIO-I_2004MS.doc

P.3

HKCE-BIO I/2004/ Marking Scheme/4

adversely affects cellular activities / it inactivates enzymes. (1) (iv) Slow jogging (1) This is because slow jogging can maintain a relatively high rate of heart beat / blood flow / breathing, (1) which increases the rate of oxygen supply to the body, (1) thus enhances the breakdown of lactic acid / conversion of lactic acid to glycogen. (1) (b) (i) microscopic algae → shrimp → squid → tuna fish (1) (ii) Tuna fish feed on a large number of squids, which in turn feed on a large number of shrimps. (1) As mercury cannot be broken down or excreted by the organisms, (1) it accumulates along the food chain and reaches a high level in tuna fish. (1) (iii) nervous system (1) (iv) Protein in shrimp is broken down into ammonium compounds (1) by putrefying bacteria. (1) The ammonium compounds are in turn converted into nitrates (1) by nitrifying bacteria. (1) (c) (i) (1) Presence of cuticle helps to reduce water loss / transpiration of the leaf. (1) (2) Absence of cuticle allows water movement / gaseous exchange to occur freely at the root epidermis. (1) (ii) The leaf epidermis has stomata (1) which allow diffusion,/ free movement of gases. (1) (iii) Cell type X carries out photosynthesis (1) to produce sugar (1) which will be transported through the phloem to the root. (1) The sugar will then be converted to starch in cell type Y. (1) (iv) Active transport (1) This is because the mineral concentration in the cell sap is higher than that in the soil water, (1) thus the minerals are absorbed against a concentration gradient. (1)

I:\BioTch\CB\HKEA\MS\CE-BIO-I_2004MS.doc

P.4