HOW DO ORGANISMS REPRODUCE?
Page No. 128
1. What is the importance of DNA copying in reproduction?
Ans: DNA found in chromosomes in the nucleus of the cells has the code of information to create proteins, which lead to body design of an organism. If the organisms are to make exact copies of themselves, the DNA should replicate to make an exact copy of itself. DNA replication is done with the help of various enzymes and this is accompanied by division of the basic unit called a cell.
2. Why is variation beneficial to the species but not necessarily for the individual?
Ans: Genetic variation is advantageous to a species because it enables some individuals to adapt to drastic environmental changes while maintaining the survival of the population.
Page No. 133
1. How does binary fission differ from multiple fission?
Ans: In binary fission, during favourable conditions nucleus divides into two parts and two individuals are formed.
E.g.: Amoeba and bacteria.
In Multiple Fission, during unfavourable conditions nucleus divides into many nuclei, and a cyst or protective layer is formed around the cell. Many individuals are formed at a time.
2. How will an organism be benefited if it reproduces through spores?
Ans: The spores of Rhizopus and Mucor are covered by thick walls that protect them during unfavourable conditions. When the favourable condition returns the spores come into contact with another moist surface and can begin to grow.
3. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Ans: Because the tissues of complex organisms are highly differentiated to perform specialised functions.
Example: A part of human skin cannot regenerate into a new individual as it is a undifferentiated tissue perform a particular function.
4. Why is vegetative propagation practised for growing some types of plants?
Ans: Advantages of vegetative propagation are;
Reproduction can be done without seeds.
Lifespan is very short.
It helps to preserve the type of character that a plant breeder desire.
It is a very easy and economical method for the multiplication of ornamental plants.
5. Why is DNA copying an essential part of the process of reproduction?
Ans: DNA is the genetic material which makes proteins which in turn give rise physical characteristics of an organism. Copying of DNA results in the transfer of information to form a fully developed organism.
Page No. 140
1. How is the process of pollination different from fertilisation?
Ans: Pollination is the process by which pollens transfer from anther to the stigma of the flower of the same species. Fertilisation is the process in which the male gamete fuses with the ovum to form a zygote.
2. What is the role of the seminal vesicles and the prostate gland?
Ans: The fluid produced by seminal vesicles will contain several key components which is a sugar called fructose, it provides energy for swimming sperm cells. Prostate gland function is to secrets prostrate fluid one of the components of semen. The muscles of the prostate gland also help propel this seminal fluid into the urethra during ejaculation.
3. What are the changes seen in girls and boys at the time of puberty?
Changes in girls during puberty;
Widening of hips and appearance of pubic hairs.
Breast size begins to increase with the darkening of the skin of the nipples at the tips of the breasts.
Menstruation begins at this time.
Changes in the voice box or the larynx and the voice become high pitched and soft.
Changes in boys during puberty;
Facial and pubic hairs started to appear on the face and the genital area respectively.
Their voice box begins to crack and possess a deep voice.
The protruding part of the voice box in boys is called Adam’s Apple.
The penis occasionally begins to become enlarged and erect.