Question

(a) Give an example of a unisexual and bisexual flower.
(b) Mention the change a flower undergoes after fertilization.
(c) How does the amount of DNA remain constant through each new generation is a combination of DNA copies of two individuals?

Answer 1

The angiosperm is the flowering plants considered as the most advanced plant. They are also classified according to their habitat, size, reproduction system, and number of cotyledons they bear.

Complete Answer:
(a) To answer this question, we have to first know about flowering plants or angiosperms. In flowering plants, the ovules and the pollen grains are formed in a structure called flower and the fruits are enclosed and protects the seeds. They are found in a wide range of habitats and the size varies; they can be tiny as microscopic to all trees of Eucalyptus.
- The flowering plants provide us with food, fuel, medicines, fodder, and many commercially essential products. They are further divided into cotyledons and dicotyledons, the monocotyledons are those that give one seed while the dicotyledons flowering plants have two.
- Based on the habitats the flowering plants are divided into herbs, shrubs, and trees. The herbs are the small, non-woody plants, the shrubs are smaller height and woody plants, the branches are near to the base for example, rose, and the trees are woody, branched, and have trunk, for example, mango tree.
- Now, the flowers are either unisexual or bisexual depending on the type of plants. The unisexual flower comprises both the male and female reproductive organs in separate individual flower while the bisexual flower bears both the male and female gametes in one flower. Papaya, watermelon, and white mulberry are bisexual and tulip, lily, and sunflower are unisexual flower.

(b) We know about the reproductive process in the plants, they undergo pollination through which the male gametes that is the pollen grain get fused with the female gametes that is the ovule to form the zygote, but the plant also undergo a significant phenomenon called double fertilization.
- Let’s understand about double fertilization. Double fertilization is the phenomenon in which two male gametes fuse with the female gametes and also with the secondary nucleus to produce the zygote and the endosperm.
- During this phenomenon, two male gametes are involved in the fertilization process one gamete is fused with female gamete and zygote is formed that developed into seed, another gamete fused with the secondary nucleus of the central cell to form the triploid primary endosperm nucleus that forms the endosperm. This endosperm gives nourishment to the developing embryo.
- Now, after fertilization the diploid zygotes are formed into an embryo that later forms the plants. The endosperm serves as a source of nutrients for the nourishment and the development of embryo and the ovule transforms into the seed.

(c) As we know that sexual reproduction involves the fusion of male and female gametes. As a result, the chromosome number in gametes is half of the chromosome number in somatic cells. Therefore, during fertilization, the number of chromosomes becomes equal to that of the somatic cells. Hence, the offspring and the parents of an organism that undergo sexual reproduction have the same number of chromosomes.

Note: In gymnosperm, they do not undergo triple fusion as they are non-flowering plants they produce diploid zygote by the fusion of pollen grains and ovule. The pollen grain is the male gametophyte and the ovule is the female gametophyte. The seed gets nourishment directly from the plants.