KCSE PIVOT BIOLOGY

Q  .Dispersed by wind - Seeds / fruits are light in weight / small in size; to be carried easily away; -  Some have wing like structures; to increase surface area for them to remain buoyant / float in the air; -  Some have perforations; and hang on a slender stalk; when swayed the seeds are scattered away;    Water dispersed -Fruits / seeds have fibrous mesocarp; with a lot of air spaces for buoyancy;             - Fruits / seeds have impermeable seed coat / mesocarp to avoid soaking; Animal dispersed -            Fruits / seeds have hooks; to stick on to animal body and carried away -            Some fruits seeds are freshly; scented; brightly coloured; to attract animals which may carry them away. -            Some seeds / fruits have hard / indigestible seed coats; and are released in animal droppings away from parent plants; Self dispersal / explosive mechanism             -Some when dry split open along lines of weakness and scatter the seeds away;

EGGS AND SPERM Eggs (ova) and sperm have half the number of chromosomes of normal body cells. They are called haploid cells rather than diploid cells. A single egg cell is called an ovum. Collectively, eggs and sperm are called gametes or sex cells. When fertilization occurs, an egg (ovum) and a sperm fuse to form a zygote. EGGS AND SPERM HAVE SEVERAL IMPORTANT ADAPTATIONS LINKED TO THEIR STRUCTURE. EGGS An egg cell (ovum) is one of the largest cells in the human body and can just be seen without using a microscope. -           Has a haploid nucleus - containing only half the number of chromosomes of a normal cell nucleus -           Has a large cytoplasm- which contains the nutrients for the developing embryo. -           Many mitochondria- needed for mitosis (cell division) after fertilization. -           Has a special cell membrane- which only allows one sperm to fertilize it. SPERM Has a haploid nucleus- containing only half the number of c

5 CHARACTERISTICS OF AN ARTHROPODA A lobster's exoskeleton, segmented body and jointed appendages are clearly visible. Arthropods, members of the phylum Arthropoda, are a diverse group of animals including insecta, crustacea, arachnida, as diplopoda and chilopoda. The members of this phylum, despite their incredible diversity and sheer numbers, share a number of important distinguishing characteristics. 1. Exoskeleton Arthropods are invertebrates, which means their bodies do not have internal bones for support. To compensate for this, they produce a hard exoskeleton made of chitin, a mixture of lipids, carbohydrates and protein, which covers and protects their bodies like a suit of armor. As arthropods grow, they must shed or molt their exoskeletons. They first produce new, softer exoskeletons underneath the old ones. Once their hardened, old coverings crack and shed, they sport roomier, albeit soft, exoskeletons. Arthropods are incredibly vulnerable during the molting proce

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; - Secretion of progesterone hormone;  (2 marks) 4.        The diagram below illustr

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 from a

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 eutrophication causing reduced oxygen co