Theory question 102
Reproduction in Plants(a) Describe the processes that occur from the time a pollen grain is deposited on the stigma of a flower to the formation of a zygote.
(b) Explain the importance of the amniotic sac to the mammalian embryo.
(c) The following are the names of some common diseases; malaria, typhoid, amoeboid dysentry, tuberculosis, tetanus, leprosy, cholera, yellow fever, poliomyelitis, measles, common cold, small pox, influenza, chicken pox, whooping cough and trypanosomiasis. Use the format below to classify the diseases according to their causative organisms.
Viral Diseases | Bacterial Diseases | Protozoan Diseases
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(a) The pollen grain absorbs sugary fluid from the stigma and germinates; a pollen tube grows out through a pore; the tube grows down the style, digesting its way and taking food from the style tissues; it carries the tube nucleus (at the tip) and the generative nucleus; the generative nucleus divides to form two male nuclei; the tube enters the ovule through the micropyle and reaches the embryo sac; the tip bursts and the tube nucleus breaks down; one male nucleus fuses with the egg cell (ovum) to form the zygote; the other fuses with the polar/definitive nucleus to form the endosperm nucleus (double fertilization).
(b) The amniotic sac holds the amniotic fluid around the embryo; it protects the embryo from shocks and injury; keeps it moist and stops it drying out; keeps its temperature steady; lets the embryo move freely and develop normally; helps prevent infection.
(c) Viral: yellow fever, poliomyelitis, measles, common cold, small pox, influenza, chicken pox.
Bacterial: typhoid, tuberculosis, tetanus, leprosy, cholera, whooping cough.
Protozoan: malaria, amoeboid dysentery, trypanosomiasis.
Describe the steps in order, from germination of the pollen grain to fusion of the gametes.