KCSE PIVOT BIOLOGY

Answer all the questions. 1.        State the importance of each of the following in living organisms:[2m] (a) Nutrition (a) Acquisition and utilization of nutrients; (1 mark) (b) Excretion. (b) Elimination of metabolic wastes to prevent accumulation to toxic level; (1 mark) 2.        (a) What is meant by the term seed dormancy? ( a) A period of rest in which a seed performs its physiological processes slowly and utilizes little food; (1 mark) (b) State three causes of seed dormancy. [1m] (b) - Chemical/growth inhibitors; - Hard/impermeable seed coat; - Low/freezing temperatures; - Under developed embryo/immature embryo; - Low concentration of hormones; - Lack of appropriate light wavelength; (max 3 marks) 3.        State two functions of the placenta in mammals. [3m] - Exchange of nutrients /metabolic wastes/gases between the mother and foetal circulatory systems;...

PART FUNCTION 1 EYE PIECE -Where the eye of the viewer is placed -Has a lens that magnifies the image 2 COARSE ADJUSTMENT KNOB -Brings the image into rough focus 3 FINE ADJUSTMENT KNOB -Brings the image into sharp focus 4 ARM/LIMB -Handle held when transporting the microscope 5 HINGE SCREW -To tilt the microscope 6 BASE -Is the seat of the microscope 7 BODY TUBE -To hold the eye piece and the revolving nose piece. -Allows passage of light from the mirror to the eye of the viewer.  8 REVOLVING NOSE PIECE -Selects the desired objective lens 9 OBJECTIVE LENS -Magnifies the image 10 CLIP -Hold the object firmly on the stage 11 STAGE -Platform on which the object is placed. 12 CONDENSER -converge light fro...

Describe causes and methods of controlling water pollution. (20 mks) It is the addition of substance or forms of energy into the water that may cause harm to organisms and are destructive to the ecosystem. Causes of water pollution are :  Industrial effluents. - Industrial effluents that may be toxic chemicals which kill the aquatic organisms; this can be controlled by treating the effluents before discharging them; - Hot water reduces the concentration of oxygen, killing the animals; it is controlled by replacing hot water with cold water; - Oil spillage from oil tankers that reduces ability of oxygen to dissolve in water, reduce penetration of light and clog feathers of marine birds; it can be controlled by regular servicing of oil tankers to prevent spillage; Domestic effluents; - Untreated sewage that causes water borne diseases; it can be controlled by treating sewage before being discharged; -Detergents that cause eutrophicat...

(a) Explain the roles of the mammalian placenta. (7 mks) ·          Prevents mixing of maternal and foetal blood; ·          Protects the foetus against microorganisms; ·          Prevents some chemicals/hormones passing to the foetus; ·          Protects foetal blood vessels from damage by high blood pressure of maternal blood. ·          Allows exchange of gases ·          Allows supply of nutrients and water to the foetus; ·          Removes metabolic wastes from the foetus to be excreted through maternal blood ·          Produces progesterone and oestrogen. Total 8 marks Max 7 marks (b) Describe how hormones regulate the menstrual cycle in human...

a.       Outline the characteristics of the meristematic tissues .[4mks]   Characteristics of meristematic tissues Retain the ability to divide mitotically Remain undifferentiated Cells are thin walled   Cells with large nucleus Cells with dense cytoplasm The cells have high density of mitochondria ; b.       State and describe the types of meristems. [16mks ]             b)i)         Apical meristems; Found at the root and shoot apex; they are responsible of increase in length of shoot and root i.e. primary growth; at the apex are the zones of cell division; cell elongation; and cell Differentiation;             ii)           Vascular cambium; Found between the xylem and phloem of woody plants; cells decide ...

Giving examples give an account of the evidences of organic evolution. (20mks)              Comparative anatomy Comparisons of structures of different organism show resemblances in structure and functions.  E.g. Digestive systems; Homologous structures; like pentadactyl limb; have similar origins but perform different functions showing divergent evolution or adaptive radiation. Invertebrates have similar structures that perform different functions; showing common ancestry; Analogous structures; are morphologically different but perform similar functions; showing convergent in Evolution; Comparative embryology; Embryos of vertebrates have great similarity showing common ancestry; e.g. the long thin shape and other body systems; Cell biology; Comparative serology;   Cells from different organism have similarity in structure; and functioning; closely related animals have similar plasma proteins;...