Sexual Reproduction in Flowering Plants MCQs for NEET — Botany Questions with Answers

In cereals, one or few outer layers of endosperm are thick walled with dense cytoplasm having pits. These are manly filled with aleurone grains hence calld aleurone tissue. These layers secret some hycrolytic enzymes like amylases and proteases which break down starch and protein during seed germiation. Since this layer is formed from endosperm it is triploid in nature.

Apple is false fruit as the ovary does not form the fruit but the fleshy thalamus modifies into fruit which is edible.

Pollination by bat is called chiropteriphily.

The direct or indirect effet of male parent (pollen grain) on structures inside embryo sac except embryo has been termed by Focke, 1881 as xenia. this phenomenon is limited to endosperm part only and seen in Zea mays. Metaxenia may be defined as the effect of pollen on the sead coat or pericarp lying outside the embryo sac. In Phoenix dactylifera, the size and time of maturity of fruits depend on the type of pollen grains fertilizing the ovules. There is secretion of certian hormones or similar substances by endosperm or embryo or both which diffuse out into the wall of the sed and fruit and exer specific effect. the secretion of these substances, in turn, is influenced by the pollen grains whcih fertilise the ovules.

Exine is outer layer of pollen grain which is acetolysis resistant layer. It is also resistant to physical and biological degradation. Because of this property of exine, pollen grains are found well preserved for long periods in fossil deposits.

After entering the wall of the embryo sac the pollen tube during its entry into the embryo sac passes through the nucellar cells and the synergids, e.g. Fagopyrum. The pollen tubes passes between the egg and one synergid. In Cardiospermum, it passes between embryo sac wall and synegid. In Oxalis, it passes directly through a synergid. In Viola, it enters a synergid and makes its way thorough the base of the synergid. In normal cases only one synergid destroys by the impact of the pollen tube and the other remains intact until sometimes afterwards.

(d)  During the post-pollination development, germination of pollen grain takes place. The pollen grain absorbs water and nutrients on the stigma from the stigmatic secretion through its germ pores. The tube or vegetative cell enlarges and comes out of the pollen grain through one of the germ pores or germinal furrows to form a pollen tube. Generative cell does not produces pollen tube instead it passes into the pollen tube and divides into 2 male gametes. Thus even after killing the generative cell with a laser beam, the pollen grain produces normal pollen tube because the vegetative cell has not been damaged.

Cleistogamous flowers do not open at all. In such flowers, the anhters and stigma lie close to each other. Anthers when dehisce in the flower buds, pollen grains come in contact with the stigma to effect pollination Thus, cleistogamous flowers are autogamous asn there is no chance of cross-pollination. So, no pollination agent is required in these flowers. 

The outer layer of pollen grain is called exine. It is thick and smooth and culticularised. The cutin is called sporopollenin. It is not degraded by any enzyme. It is not affected by high temperature, strong acid or strong alkali. Thus it is resistant to chemical and biological decomposition. Because of sporopollenin, pollen grains are well preserved as microfossils. 

Pollen viability is the period for which pollen grians retian the ability to germinate. Pollen viability is little in flowers which are pollinated in bud condition. It is 30 minutes in rice and wheat. It depends upon environmental conditions of temperature and humidity.