Biology Paper 2 Marking Scheme
KCSE CLUSTER TESTS 16
Biology Paper 2
SECTION A (40 Marks)
Answer ALL the questions8 marks
a) To investigate plant response to gravity;
b)
(i) A- The shoot and root remained horizontal;
(ii) B-The shoot curved upwards and root-tip downwards;
c) Gravity causes greater conc. of auxins on lower sides of seeding/on shoot and root; High conc of auxins in lower side of the root inhibits cell elongation hence than on upper side;(bends downwards);
d) To nullify the effect of gravity/distribute gravity equally on the seedling;
e) Control experiment;
8 marks
a)
A-metaphase.
B-prophase 1
C-Anaphase 1
b)
(i) Centromere of bivalent not split;
(ii) Homologous chromosomes separate;
(iii) Homologous chromosomes moving to poles (opposite) of the cells;
Rej if homologous is not mentioned.
c) Spindles (fibres)
8 marks
a) Growth-Quantitative permanent(irreversible) increase in size of an organism; Development-Qualitative growth of an organism;
b)
(i)Intermittent.
(i) ‗Intermoult;
‗Moulting;
c) Vascular cambium;
Cork cambium;
d) Promotes flowering;
8 marks
a)
(i) They control the opening and closing of stomata; which allows air into the leaf;
(ii)Have large air spaces; hence contain air for gaseous exchange;
b)
(i) Tracheoles;
(ii)Maintain a step concentration gradient which enables maximum absorption of oxygen from water;
c) At high altitude there is low (partial pressure of) concentration of oxygen; hence efficient many red blood cells transportation of oxygen;
8 marks
SECTION B (40 Marks)
Answer questions 6 (compulsory) and either question 7 or 8(a) graphs
Correct scales =2mks
Correctly labelled axes =1mks
Correctly plotted points =2mks
Smooth curves =2mks
(b) Zebra;
Wide fluctuations of zebra population over the period of study;
(c) Total counts/aerial counts/photography/capture recapture;
Animals are mobile and large in size;
Giraffe population is stable ;( OWTTE)
(d) Giraffes are browsers;
They feed on Acacia which are drought resistant;
Vegetation/food (Acacia) was constantly available for giraffe to feed on;
Source of food (Acacia) is not affected adversely by changes of rainfall pattern;
Source of food (Acacia) is not affected adversely by changes of rainfall pattern;
(e) Food; predation; migration; completion; parasitism; human activity/poaching;
(f) Protection of animals from poaching;
Tourism;
Protection of human crops/live stokes;
Centre of research/education;
Conservation of rare species;
20 marks
(a)
Osmosis;
Soil contains water in between its particle; Water is absorbed by root hairs through the process of osmosis; water is at higher concentration in the soil solution than in the cell sap of root hair cell; water therefore moves along the concentration gradient from the soils into the sap vacuole of the root hair cells and dilute the cell sap; It then moves to (the cortex cells, endodermis cells pericycle, and the to) the xylem;
Active transport
Generally the concentration of minerals in the soil is lower than that in the cell sap of the root hair cell; therefore the mineral salts enter the root hair against concentration gradient; Carrier molecules are involved; in moving back and forth carrying the salt ions from the soil water root hair cell membrane;
Diffusion
Mineral salts can also be taken into root hair cells by diffusion; this happens when concentration of the ions is lower in the root hair cell sap than the soil solution ;
(b)
- Vessels are made up of dead cells which allow for easy passage of water; dead cells do not absorb water. Dead cells allow water to move in the xylem without interference;
-Their walls are lignified this makes them firm and rigid enough to avoid collapsing in order to withstand movement of water under pressure;
-Lignifications make the vessels firm to provide mechanical support to the plant;
-Lignin makes the vessels waterproof thus cannot absorb the water being transported;
-Walls of vessels have bordered pits which allow for free movement of water and mineral salts from one vessel to another and to adjacent tissues;
-Xylem tissues do not have cross walls their cells to allow for free movement of water up the stem with less resistance;
-Xylem vessels are long continuous tubes to enhance smooth flow of water from the roots to the leaves;
-They have narrow lumen to enhance capillarity; hence faster movement of water up the stem;
-Have thick walls which enhances adhesion of water molecules to the xylem walls;
-Tracheids are similar to vessels except they have tapering end walls perforated by pits hence less efficient in conducting water and mineral salts;
20 marks
(a)
-The walls of intestines are made of smooth muscles which contract and relax causing peristaltic movement that push food substances along the lumen of the intestine;
-They are long to increase surface area for absorption of digested food substances; it also increases time of stay of food for digestion to be completed; -- They are coiled to increase surface area for digestion and absorption of food; coiling also reduces the speed of movement of food giving it maximum time for digestion and absorption;
-Has narrow lumen which brings about close contact between the food and the walls of the intestines for maximum digestion and absorption of food;
-Their walls have goblet cells which secrete mucus which protect the inner walls of intestines digestion by protolytic enzymes; also mucus lubricates food to allow for smooth movement down the gut;
-The walls have glands which secrete intestinal juice(succus enericus) containing digestive enzymes;
-The walls also have Brunner’s glands which secretes an alkaline fluid for optimum pH for enzymatic activity;
-The inner walls of ileum have villi and micro-villi that increases surface for absorption of food;villi walls are one thick to reduce the distance for diffusion; - Presence of dense network of blood capillaries on the villi to ensure that absorbed substances are effectively transported to body tissues;
-The villi have lymphatic capillaries called lacteals to facilitate absorption of fatty acid and glycerol together with some of fatty soluble vitamins;
-The cells of villi have numerous mitochondria to provide energy for efficient active uptake of substances during absorption;
(b)
Glucose is oxidized to produce energy during respiration; excess glucose is converted to glycogen by the liver cells and stored (for future use); fructose and galactose are converted to glucose ;( and utilized as above)
Amino acids used to make new cells and tissues; to repair worn out tissues; and for synthesis of hormones and enzymes; some are used to make plasma proteins e.g fibrinogen and haemoglobin; excess amino acids are delaminated in the liver;
Lipids are broken down to release energy; excess lipids are stored under the a dipose tissue; stored lipids are also used to provide energy; also they cushion delicate body organs heart, kidneys;
20 marks