Would a Planaria cut vertically into two halves regenerate into two individuals? Complete Figure 8.2 D and E by indicating the regenerated regions. 

Planaria has the capability of regeneration. Due to this, a cut portion of planaria would develop complementary portion to become a new individual. Following figures show new individuals from D and E:

From the internet, gather information about the chromosome numbers of five animals and five plants. Correlate the number with the size of organism and answer the following questions.

(a) Do larger organisms have more number of chromosomes/cells?

ANS: (a)  No, there is no relationship between size of organism and its chromosome number.

(b) Can organism with fewer chromosomes reproduce more easily than organisms with more number of chromosomes?

ANS : (b) No, process of reproduction follows a common pattern and is not dependent on the number of chromosomes

(c) More the number of chromosomes/cells greater is the DNA content. Justify.

ANS: (c) Yes, since the major component of chromosome is DNA, if there are more chromosomes in a cell, the quantity of DNA will also be more.

Number of chromosomes in both the gametes is equal. Hence, female gametes of tobacco plant will have 24 chromosomes. Number of chromosomes in zygote would double the number in gametes, hence it would be 48.

Pollination is the process by which pollen grains are transferred to the sigma. Once pollen grains land on stigma, they germinate to produce pollen tubes and subsequently to facilitate fertilization. Hence, fertilization cannot take place in flowers if pollination does not occur.

After the formation of zygote, further development takes place through mitosis. We know that after mitosis, the number of chromosomes in daughter cells is same as in mother cell. Due to this, number of chromosomes in embryo is same as in zygote. For the same reason, number of chromosomes in an organism is same as in zygote or embryo. So, it is clear that the chromosomes number of zygote, embryonal cells and adult of a particular organism is always constant.

After fertilization, zygote is located in the ovary.

Every organism faces a lot of competition for survival. Barring a very few, most of the organisms end up being food for some other organism. Competition and predation result in drastic reduction in population of a species. But reproduction ensures that population of a species is maintained at optimum level. So, it can be said that reproduction is linked to stability of population of a species.

General growth is about growth in size of an organism. Sexual maturation is about the accomplishment of ability to reproduce. General growth begins right from the time an organism comes into this world. Sexual maturity begins at a later stage. In most of the animals, general growth stops after a certain age and this coincides with attainment of sexual maturity.