Describe what happens to a meal rich in proteins along the alimentary canal from ingestion to egestion.
K.C.S.E Biology Q & A - MODEL 2018PP2QN08
Describe what happens to a meal rich in proteins along the alimentary canal from ingestion to egestion.
The meal is ingested through the mouth; (In the mouth), it is chewed/masticated (by teeth); to reduce/break it into smaller particles; mixed with saliva (from salivary gland);
The food is then rolled (by the tongue) into boluses; and pushed down into the oesophaghus/swallowed; The boluses move by peristalsis (into the stomach);
Constant contractions/relaxations of the stomach walls mix the food, (giving rise to chime); Presence of food in the stomach further stimulates production of gastric juice; which contains pepsinogen; and rennin/chymosin; Pepsinogen is activated to pepsin; by hydrochloric acid; (contained in the gastric juice). Pepsin breaks down proteins to peptides;
Rennin converts/coagulates the protein, caseinogen; in milk to casein; (which is abundant in young children). It is then pushed into the duodenum (through the pyloric sphincter); Pancreatic juice in the duodenum contains trypsin; which digests proteins into peptides; (secreted in an inactive form, trypsinogen)
In the ileum, intestinal juice/Succus enfericus is secreted; It contains peptidase enzymes; which breaks down polypeptides into amino acids; It also contains polypeptidase enzyme; which breaks down peptides to amino acids,completing the process of digestion of the proteins;
The amino acids are absorbed into the bloodstream/pass through the epithelia of the villi, and the capillary walls into the blood-stream; by active transport;
The undigested/indigestible proteins/food substances pass through to the colon/large intestines; where water is absorbed; leaving a semi-solid waste material being passed on to the rectum; then out through the anus (as faeces);
K.C.S.E Biology Q & A - MODEL 2018PP2QN07
Describe the role of hormones in the human menstrual cycle.
After/at the onset of menstruation, (the anterior lobe of) the pituitary gland; secretes follicle stimulating hormone (FSH); the FSH causes the Graafian follicle; to develop into the ovary; and stimulate the ovary tissues to secrete oestrogen hormone; Oestrogen brings about repair/healing of the endometrium/uterine wall; its concentration increases to a level which stimulates the (anterior) pituitary gland; to secrete lutenizing hormone (L.H.) and stops further secretion of FSH;
The L.H. stimulates the maturation of the Graafian follicle; LH also stimulates the Graafian follicle to release an ovum into the (funnel of the) fallopian tube/causes ovulation; it also stimulates the remains of the Graafian follicle to form a yellow body/corpus luteum (in the ovary;
The corpus luteum is stimulated by the L.H. to produce progesterone; Progesterone then stimulates the thickening of the endometrium/inner lining of the uterine wall; in readiness for implantation; as progesterone level increases, it inhibits (the pituitary gland) from secreting FSH; further increase in progesterone level inhibits the pituitary gland from secreting L.H. This causes the corpus Luteum to degenerate; this reduces the amount of progesterone; the sudden drop in secretion of progesterone causes the endometrium to slough off/menstruation occurs; and the cycle is repeated;
K.C.S.E Biology Q & A - MODEL 2018PP2QN06
The effect of auxin concentration on growth response of two parts of a plant, X and Y was investigated over a period of time. The results were tabulated as shown in the table below.
(a) On the same axis, draw line graphs of the effect on growth of the two parts, X and Y (percentage inhibition or stimulation) against the concentration
(b) With reasons, name the two parts of the plant, X and Y.
(c) From the graph identify: .
(i) the point at which the percentage stimulation was the same for both X and Y.
(ii) the optimum concentration of auxins required for part Y
(d) State three ways in which the effects of auxins on plants is applied in flower farming.
(e) Distinguish between simple and conditioned reflex action
Low auxin concentration stimulates (rapid/faster) cell division and elongation/growth in roots;
High concentration of auxins inhibits growth in roots;
Low auxin concentration has little effect on the growth of shoots/shoots are stimulated to grow with high auxin concentration (up to a given optimum);
c) i. 33%±2;
ii. 1.0 parts per million;
(d)Faster maturity of flowers/earlier flower formation/flowering;
Prunning/decapitating shoot tips to allow sprouting of lateral buds, hence more yield;
Keeping flowers fresh;
Stimulate formation/development of (adventitious) roots;
K.C.S.E Biology Q & A - MODEL 2017PP2QN08
Describe how the mammalian eye is structurally adapted to its function.
K.C.S.E Biology Q & A - MODEL 2017PP2QN07
Explain the importance of protecting the forest ecosystem with reference to the following:
(a) climate change
(d) water conservation
a) Climate change
K.C.S.E Biology Q & A - MODEL 2017PP2QN06
In an investigation, two potted plants G and H belonging to the same species were exposed to increasing light intensities at different temperatures, 30°C and 20°C respectively. The rate of photosynthesis was measured for each plant and results recorded as shown in the table below:
(a) On the same axis, plot graphs of rate of photosynthesis against light intensity for plants G and H.
(b) State the aim of the investigation.
(c) Account for the difference in the rate of photosynthesis in the two plants.
(d) Account for the difference in the rate of photosynthesis in the two plants between the following light intensities:
(i) 1—4 units
(ii) 4—8 units.
(e) (i) Predict the rate of photosynthesis at light intensity of 16 units.
(ii) Give a reason for your answer in (e) (i) above.
(f) State one internal and one external factor that could be limiting in the investigation.
b) To investigate/compare the effect of (varying) light intensity/temperature on the rate of photosynthesis;
c) Rate of photosynthesis is higher in plant G (than H); (Photosynthesis being an enzymatic process), enzymes were subjected to favourable/optimal temperatures (of 30°C): hence more activated, unlike in plant H where temperatures were lower (20C);
d) (i) 1-4 units
Rapid increase in rate of photosynthesis increases with the increase in light intensity; due to increase in light energy for photosynthesis/formation of more ATP molecules;
(ii) 4 — 8 units
Slower/gradual increase in the rate of photosynthesis as the light intensity increases: because other factors become limiting/some chlorophyll molecules start bleaching;
e) i) Slight increase/no significant increase/remains constant;
ii) The optimum light intensity has been exceeded/some chlorophyll could be destroyed;
f) Internal factor — Chlorophyll/enzyme concentration;
External factor — Carbon (IV) oxide concentration/amount of water;
K.C.S.E Biology Q & A - MODEL 2016PP2QN08
Describe how the mammalian heart is structurally adapted to its function.
K.C.S.E Biology Q & A - MODEL 2016PP2QN07
Using a relevant example in each case, describe simple and conditional reflex actions.
Simple reflex action eg. withdrawal of finger from a sharp object/ hot object; its an automatic response to a specific stimulus; when the finger touches sharp object/ hot object, the pain receptors/ thermoreceptors in the skin are stimulants; and trigger off a nerve impulse; the nerve impulse is transmitted via the senses neurone; to the grey matter of the spinal cord/ CNS/ brain; the impulse is then transmitted via synapse; to the relay neurone; and then through another synapse; to the motor neurone; and then through another synapse; to the motor neurone; the impulse is then transmitted to the effector muscles in the hand; ace - efferent neurone for motor neurone Afferent neurone for sense neurone intermediate/ associative/ connector/interauncial neurone - for relay. The effector muscles/ biceps contract; and the finger is withdrawn from the hot object/ sharp object;
Conditioned reflex action - salivation in a dog/ human being (ace. any other relevant example) student in response to sound; it is an automatic response evoked from an animal by unrelated stimulus; substituted for the one which normally elicits the response; it develops from a past experience; and involves modification of behaviour/involves learning; it weakens with time; and must be reinforced by repeating the related stimulus; the dog/ student salivates when the bell (for meals) rings; because they have learnt to associate the ringing of the bell at meal time with food; everytime it rings (accept use of other relevant examples) they are offered food.
K.C.S.E Biology Q & A - MODEL 2016PP2QN06
An experiment was carried out to investigate the effect of temperature on the rate of reaction catalysed by an enzyme. The results are shown in the table below.
(a) On the grid provided plot the rate of reaction against temperature.
(b) When was the rate of reaction 2.6 mg of product per unit time?
(c) Account for the shape of the graph between:
(i) 5°C and 40°C
(ii) 45°C and 60°C
(d) Other than temperature name two ways in which the rate of reaction between 5°C and 40°C could be increased.
(e)(i) Name one digestive enzyme in the human body which works best in acidic condition.
(ii) how is the acidic condition for the enzyme named in (e) (I) above attained’?
(f) The acidic condition in (e) (iii) above is later neutralized.
(i) Where does the neutralization take place?
(ii) Name the substance responsible for the neutralization.
(b) 330C and 51.5 (± 0.50C)
32.5 - 33.5 and 51.0 – 52.0
(c) (i) 5°C and 40° C
As temperature is increased rate of reaction is increased/ more products are formed (per unit time) because enzymes become more active
(ii) 45° C and 60° C
As temperature increase rate of reaction decreases less/products are formed (unit per time) because enzymes become denatured by high temperatures above 40, hence cannot act on substrate.
(d) Increase in enzyme and substance concentration
Use of co-factors and co-enzymes
(e) (i) Pepsin,
(ii) Wall of stomach/ gastric gland/ oxyntic/ pariental/ cell produced Hydrochloric
(f) (i) Duodenum
(ii) Bile juice/ e.g. NaHCO3
K.C.S.E Biology Q & A - MODEL 2015PP2QN08
How is a mammalian heart structurally adapted to its function?
K.C.S.E Biology Q & A - MODEL 2015PP2QN07
Explain the various ways in which seeds and fruits are adapted to dispersal.
Wind - dispersed seeds / fruits are light / small to be carried by air currents;
Some seeds / fruits have developed hairy structure feather-like projections; wing like structure which increase their surface area to be blown about /carried away by wind; open capsules; borne on long stalks, which are swayed by wind scattering seeds.
Water - dispersed fruits / seeds are also light; to float on water;
Some, (like coconuts) have fibrous /spongy mesocarps to trap air; making them buoyant/floating on water; Others (like the water lily) produce seeds whose seed coats trap air bubbles; making them float on water; Some have water-proof seed testa / pericarp; remain afloat without soaking /sinking immediately they are released from parent plants;
Animal - dispersed fruits have developed hooks; to stick on (the fur of passing) animals;
In some cases, fruits are succulent, brightly coloured / scented; to attract animals, birds;
The seed coats (of some seeds) are hard; and resistant to the digestive enzymes; hence passing out through the gut undigested;
Self dispersal by explosive mechanism;
Fruits have sutures/lines of weakness; which split open when drying scattering seeds.
K.C.S.E Biology Q & A - MODEL 2015PP2QN06
The graph below shows the relative numbers of three main species of organisms in a pond.
(a) Giving a reason for your answer, which of the species is a
(ii) secondary consumer?
(b) State the depths at which each of the populations labelled L, M and N is at its optimum.
(c) (i) Which method may have been used to determine the population of organisms labelled N in the pond?
(ii) Give a reason for your answer in (c) (j) above.
(iii) State the assumptions made when using the method in (c) (i) above.
(d) State two reasons why primary productivity in the pond decreases with depth.
(e) Explain the ecological importance of fungi to plants.
(f) Why is flooding likely to lead to a cholera outbreak?
(a) (i) Producer - M
Reason Largest in number hence source of food for the other species
Abundant on the water surface to trap light for photosynthesis;
(ii) Secondary consumer - N
Reason - Smaller in number than L and M
(b) L -1.125m;
(c) (i) Capture - Recapture (method) /Capture - mark - release - recapture;
(ii) Animals are highly mobile;
(iii) No migration during the period of survey/study;
No deaths/variation/reproductiori in population during the period;
Method of marking does not affect the animal behaviour;
Marked/released animals will freely mix with others in the pond;
Released/marked animals will have enough time to mix with the others;
There is uniform/random distribution of animals within the period.
(d) Decrease in light intensity as depth increases;
Decrease in temperature as depth increases;
(e) Breakdown of organic materials/decompose/rot/decay of materials; to release plant nutrients;
(f) Flood water may mix with human waste contaminated with cholera bacteria; The flood water may then contaminate food / water sources; The contaminated water/food causes cholera infection when ingested;
K.C.S.E Biology Q & A - MODEL 2014PP2QN08
Describe the role of the human skin in homeostasis.
When body temperature is lowered below normal; arterioles in the skin constrict; blood is diverted to a shunt system; less blood flows to the skin/less heat is lost; when body temperature is raised above normal;arterioles in the skin dilate;more blood flows to the skin; more heat is lost by convection and radiation;when body temperature is lowered below normal:erector-pilli muscle s contract, hair stands erect; more air is trapped, air is a bad conductor;and insulates the body against heat loss; when body temperature is raised above normal: erectorpi11i muscles relax, hair lies on skin;less air is trapped, more heat is lost; when body temperature is lowered below normal: less fluids are absorbed by sweat glands;less sweating, less vaporisation of water;
when body temperature is raised above normal:sweat glands are more stimulated and more sweat is produced; water in sweat evaporates and takes up heat from the body;body is cooled/body temperature is lowered;
K.C.S.E Biology Q & A - MODEL 2014PP2QN08
How does excretion take place in plants?
K.C.S.E Biology Q & A - MODEL 2014PP2QN07
Describe the process of carbohydrate digestion in human beings.
In the mouth;