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 15^oC 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.

(b) Account for the rate of gas evolved

(i) 1 and 18 arbitrary units (3mks)

(ii) 26-46 arbitrary units (2mks)

By heating the leaves in an oven at 110^oC and weighing them; then heating and weighing is repeated several knows till constant weight i​s obtained

In an experiment a variety of garden peas having a smooth seed coat was crossed with a variety with wrinkled seed coat. All the seeds obtained in F1 generation had smooth seed coat. The F1 generation selfed. The total number is F2 generation was 7324.

(a) Work out the total number of wrinkled seeds in the F2 generation (2mks)

 Â½ x 7324=1831 (2mks)

(b) Give an explanation to the absence of plants with smooth seedcoat in the F1 generation (1mk)

Explain how the characteristics of the red blood cells adapt it to its functions and the process of blood clotting

(a) Explain how the characteristics of the red blood cells adapt it to its functions             (4mks)

• Numerous to increase surface area

• Biconcave to increase surface area occupied by haemoglobin

• Lack nucleus-increases surface area

(b) Explain  the process of blood clotting                                 (4mks)

When platelets are exposed to air to release thromboplastin; which neutralize anti-clotting factor/heparin and activate prothrombin to thrombin; in presence calcium ions. Thrombin activates conversion of fibrinogen to fibrin which forms meshwork of fibres on the surface injured trapping red blood cells, clot dries up and forms scab stopping for the bleeding

(a) State the functions of the following

(i) Nerve cells                                            (2mks)    

• Detect changes in the environment; internal and external
• Transmit/conduct impulses to brain an spinal cord/from brain to effector organs/tissues
• In brain –coordinates movements/activities of different body parts

(ii) Plasma                                                (2mks)

• Transport medium; transports glucose, amino acids
• Forms the tissue fluid

(b) Give the functions of the following organ systems

(i) Excretory  system                                            (2mks)

(ii) Endocrine system                                            (2mks)

• Homeostasis/maintains internal environment of the body constant.
• Growth and development of the body