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