Q1. What is apomixis and polyembryony?
Ans: The phenomenon of asexual reproduction that imitates sexual reproduction by the formation of seed without fertilization is called apomixis or agamospermy.
The occurrence of more than one embryo in a seed is called polyembryony, e.g., orange.
Q2. What is emasculation?
Ans: The process of removal of anther from bisexual flowers without affecting the pistil is called emasculation.
Q3. Mention any five features of insect pollinated flowers.
The form of pollination in which insects distribute pollens is called entomophily.
Flowers are large, sticky and brightly coloured.
They have honey and nectar glands, which are highly fragrant to attract insects.
The pollen grain surface is sticky due to exine layer and stigma is sticky due to mucilaginous secretion.
The flowers offer floral rewards like nectar and pollen grains for pollination to insects.
In some species, floral rewards provide safe place to lay eggs, e.g., Amorphophallus.
The flower sometimes secretes foul odour to attract insects like flies and beetles.
Q4. Mention two strategies evolved to prevent self-pollination (autogamy) in flowers.
Unisexuality: Male and female flowers are present on different plants.
Dichogamy: The condition in which the stamens and stigma of a bisexual flower mature at different times.
Protandry: This is the condition where anthers mature earlier than the stigma and release pollens.
Protogyny: This is the condition where the stigma matures earlier than the anther.
Self-sterility or self-incompatibility: It is a genetic mechanism that prevents self-pollination.
Chasmogamous flowers: These are open flowers with exposed stamens and stigma which facilitate cross-pollination.
Q5. Differentiate between perisperm and pericarp.
It represents the persistent nucellus in the seed.
It is a part that belongs to seed.
It is usually dry.
It represents the fruit wall formed by the ovarian wall.
It is a part of fruit.
It can be dry or fleshy.
Q6. Describe the structure of pollen grains.
They develop from Pollen Mother Cell by meiotic division.
They represent the male gametophyte.
Pollen grains are generally spherical in structure.
They possess two prominent layered walls - outer exine and inner intine.
The exine is a hard layer made of sporopollenin which is one of the most resistant organic material present in nature.
The inner thin layer of intine is made up of cellulose and pectin.
The exine has an aperture where sporopollenin is absent, called germ pore.
The newly differentiated pollen grain has a central nucleus and dense cytoplasm.
The protoplast mitotically divides into two unequal cells - bigger vegetative cell which is rich in food reserve and smaller spindle-shaped generative cell with dense cytoplasm and a nucleus. This is called 2-celled stage.
Q7. Explain the process of megasporogenesis or explain the events of development of female gametophyte.
The female gametophyte (embryo sac) develops from a single functional megaspore.
This megaspore undergoes three successive mitotic divisions to form eight nucleate embryo sacs.
The first mitotic division in the megaspore forms two nuclei. One nucleus moves towards the micropylar end while the other nucleus moves towards the chalazal end.
Then, these nuclei divide at their respective ends and re-divide to form eight nucleate stages. As a result, there are four nuclei each at both the ends i.e., at the micropylar and the chalazal end in the embryo sac.
At the micropylar end, out of the four nuclei only three differentiate into two synergids and one egg cell. Together they are known as the egg apparatus.
Similarly, at the chalazal end, three out of four nuclei differentiates as antipodal cells.
The remaining two cells (of the micropylar and the chalazal end) move towards the centre and are known as the polar nuclei, which are situated in a large central cell.
Hence, at maturity, the female gametophyte appears as a 7-celled structure, though it has 8 nucleate.
Q8. What are autogamy and xenogamy?
Autogamy: Transfer of pollen grains from the anthers to the stigma of the same flower.
e.g., pea, rice, wheat, etc.…
Xenogamy/allogamy: Transfer of pollen grains from the anthers to the stigma of a different plant of the same species.
e.g., papaya, maize
Q9. Describe the structure of anatropous ovule or megasporangium with a neat labelled diagram.
The ovule is a small structure attached to the placenta by means of a stalk called funicle.
The junction between an ovule and a funicle is called hilum. Sometimes, the funicle extends beyond the hilum to form a ridge called raphae.
The ovule is surrounded by one or two protective envelopes called integuments.
Integument encircles the ovule entirely except at the tip, resulting in a small opening called micropyle.
The basal part of an ovule opposite to micropyle is called chalaza.
The cells with high or abundant reserve food material enclosed within integument is called nucellus.
The female gametophyte located within the nucellus is called an embryo sac.