Question

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

Answer 1

(a) Unisexual flowers: Cucumber, pumpkin, water melon, papaya, etc. Bisexual flowers: Hibiscus, rose, lily, etc. (Any one example can be written). (b) Changes in a flower after fertilisation: The outer layers of the ovule become impervious and hard and function as a seed coat. An ovule with an embryo inside is called a seed. The ovary enlarges and ripens to become a fruit. Other floral parts such as sepals, petals, stamens, styles and stigma may fall off. However, in some cases, they remain persistent in the fruit. (c) Deoxyribonucleic acid (DNA) copying is an essential part of reproduction, as it passes genetic information from parents to offspring. The reproducing cells produce a copy of their DNA through some chemical reactions and result in two copies of DNA. The copying of DNA always takes place along with the creation of additional cellular structure. This process is then followed by the division of a cell into two cells. In this way, the amount of DNA remains constant through each new generation.

Answer 2

a) watermelon for unisexual and rose for bisexual b) After fertilization, the zygote divides many times to form an embryo in the ovule. The ovule develops a hard coat and is gradually converted in a seed. Ovary grows rapidly and ripens to form a fruit.  Meanwhile, the petals, sepals, stamens, style and stigma may fall off. c) During sexual reproduction, germ cells have half the number of chromosomes and DNA as compared to somatic cells. As offspring receives one DNA from each parent, this complex mechanism helps to maintain the amount of DNA constant in an individual. If it would have doubled, then each generation would have double amount of DNA to previous generation.