In an experiment to investigate the effects of light intensity on the rate of photosynthesis, a shoot of elodea (water weed) was used. The shoot was immersed in 2% sodium hydrogen carbonate solution maintained at 15oC in an apparatus which allowed for collection of a gas evolved from the shoot. The gas given off was collected for five minutes at each light intensity and its volume recorded as shown below.
(a) Using the data given in the table plot a suitable graph of gas evolved against light intensity (6mks)
see graph
NB
(b) Account for the rate of gas evolved(i) 1 and 18 arbitrary units (3mks)Gas evolved increase with increase in light intensity; increase in light leads to more splitting of water molecules into hydrogen ions and oxygen; hence increase in rate of photosynthesis (ii) 26-46 arbitrary units (2mks)Amount of gas evolved remained constant as rate of photosynthesis constant due to limiting factors Glucose formed is converted into starch for storage in the tissue. (c) Explain why a green leaf is normally tested for the presence of starch instead of glucose (2mks)
Glucose formed in converted into starch is osmotically in activated hence stored
(d) How is the dry mass of a leaf determined (3mks)By heating the leaves in an oven at 110oC and weighing them; then heating and weighing is repeated several knows till constant weight is obtained (e) Describe how the chloroplast is adapted to its functions (4mks)
Has stroma where Carbon (IV) oxide fixation takes place; has a grana containing; chlorophyll that traps light energy for photosynthesis. Has integranna lamellae that hold the grana position
 The experiment illustrated ABOVE was set up to investigate a certain physiological process using a raw tuber (a) Suggest a possible physiological process that was being investigated (1mk)
(b) Explain the results obtained in the above experiment after a few hours (2mks)
(c) State the observations that would have been made if the experiment was repeated using boiled potato (2mks)
CELL PHYSIOLOGY1. 1989 Q14 P1The table below shows the concentration of some ions in pond water and in the cell sap of an aquatic plant growing in the pond.
(i) Sodium ions (ii) Potassium ions (b) For each processes named in (a) (i) and (ii) above, state one condition necessary for the process to take place. K.C.S.E Biology Q & A - MODEL 2019PP1QN11
Explain each of the following physiological observations:
(a) sportsmen release little, concentrated urine at the end of a strenuous exercise (b) a rabbit has a higher oxygen demand than a camel 
answers
(a) during /after the exercise one sweat ; (profusely to cool the body/eliminate some nitrogenous (wastes) a lot of water is lost through this ; one is dehydrated ;(the little) water that is left in the body system (further) selectively reabsorbed in the kidney tubules (resulting in less but concentrated urine;)
(b) a rabbit has a higher surface area to volume ratio/ smaller in size hence has a bigger surface area exposed to heat loss to the environment/ lose heat faster/ its more active than the camel; hence need more oxygen to(aerobically) respire (to synthesize the needed energy to support its activity /lifestyle; K.C.S.E Biology Q & A - MODEL 2019PP1QN04
In investigating a certain physiological process, students set up the apparatus as shown below and made the observations after 30 minutes as illustrated.
(a) Name the physiological process being investigated.
(b) Account for the observation made at the end of the experiment. (c) State the likely identity of G.
answers
. (a) osmosis
(b) solution E is hypertonic/ had more solute molecules compared to solution F; solution F hypotonic to solution E; by osmosis water molecules move through the semi- permeable membrane G (from solution F to E); hence decreases in volume of F/ increased solution E; (c) semi permeable membrane /visking tubing /slice of potato /pawpaw (any other permeable plant tissue) pig bladder/cellophane paper/dialysis membranes. K.C.S.E Biology Q & A - MODEL 2018PP1QN04
A group of form two students placed a fresh leaf in warm water. They observed that air bubbles formed on the surface of the leaf.
(a) What biological process were they investigating? (b) Name the structures from which the air bubbles were coming from. (c) Explain the distribution of the structures named in (b) above on the leaf surfaces of a land plant.
answers
a) Photosynthesis;/gaseous exchange in plants;
b) Stoma/somata; c) Are more on the lower surface of terrestrial plants/fewer on the upper surface; to reduce transpiration; K.C.S.E Biology Q & A - MODEL 2017PP1QN21
The photograph below represents a leaf obtained from a certain plant.
Account for the observations made if the leaf was tested for starch.
answers
K.C.S.E Biology Q & A - MODEL 2017PP1QN15
Explain the physiological process responsible for keeping young seedlings upright.
answers
K.C.S.E Biology Q & A - MODEL 2017PP1QN11
The set up below illustrates a certain physiological process.
(a) (i) Name the physiological process.
(ii) Give two examples of the process named in (a) (i) above in plants. (b) State two ways by which the movement of dye molecules in the set up would be slowed down.
answers
a i) Diffusion;
ii) Gaseous exchange/excretion of carbon (IV) oxide and oxygen; Translocation of materials; Absorption/uptake of mineral ions/salts; b. Lowering the temperature of the medium; Increasing thickness of the membrane; Use less dye/add more water/reducing the concentration gradient; 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.
answers
(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, Chymosin Renin (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 2016PP2QN05
A freshly obtained dandelion stem measuring 5cm long was split lengthwise to obtain two similar pieces. The pieces were placed in two different solutions of different concentrations in petri dishes (L1 and L2) for 20 minutes. The appearance after 20 minutes is as shown.
(a) Account for the appearance of the pieces in solutions L1 and L2
(b) Suite the significance of the biological process involved in the experiment.
answers
(a) L1 - Inner cells gained water by Osmosis; hence increased in length; epidermal cells did not gain water because they are covered by a water proof cuticle leading to curvature.
L2 - Inner cells lost water by osmosis; leading to (flaccidity) decrease in length; epidermal cells did not lose water due to waterproof leading to curvature (b) Absorption of water by the roots Opening and closing of the stomata
K.C.S.E Biology Q & A - MODEL 2016PP1QN25
Distinguish between diffusion and osmosis.
answers
K.C.S.E Biology Q & A - MODEL 2016PP1QN018
Distinguish between haemolysis and plasmolysis.
answers
K.C.S.E Biology Q & A - MODEL 2015PP1QN06
Students set up an experiment as illustrated below.
(a) Name the physiological process that resulted in the observations made after 30 minutes.
(b) State the importance of the physiological process investigated in plants. (c) Explain the observations made after 30 minutes.
answers
(a) Osmosis;
(b) Absorption of water from the soil; opening and closing of stoma; feeding in insectivorous plants; support (in seedlings, leaves,herbaceous plants); Movement of water from cell to cell in plants. (c) The thistle funnel gained water by osmosis; because the sucrose solution was hypertonic; K.C.S.E Biology Q & A - MODEL 2014PP1QN10
What is meant by each of the following terms?
(i) Crenated cell. (ii) Flaccid cell.
ANSWERS
(i) Crenated cell is a shrunk animal cell that has lost water by osmosis;
(ii) Flaccid cell is a flabby /shrunk plant cell that has lost waster by osmosis; |
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