Answer: The different ways in which individuals with a particular trait may increase in a population are following :
Food availability – Individuals with a particular trait may have extra abundance of food in their environment. They will naturally increase in number.
Genetic drift – Individuals with a particular trait may increase in a population due to genetic drift. In it, there is a seasonal or accidental decline in population. The survivors have certain combination of traits which increase in number with increase in population
Natural selection – The particular trait which has survival value is picked up by natural selection. It increases in population through differential reproduction.
Q. What do they tell us about the process of evolution?
Answer: Fossils provide a direct evidence of evolution and are called written documents of evolution. They directly indicate the presence of different types of organisms in different ages.
The path of evolution is known by arranging the fossils in a proper sequence age wise. The early fossils are the simple organisms. Later on different complex forms arose, flourished and died down. They are replaced by newer forms.
Q. state the analogy between wings of a bird and a butterfly. What does it indicate?
Answer: They are analogous because both bats and birds adapted to flight. Bat being a mammal has the finger extension type wing and bird being aves with the full forelimb extending the wing. As structure both the wings are different, so are considered as analogous organ.
Q. Why did Mendel choose pea plant for his experiments?
Answer: Mendel chooses pea plant because:
a. Presence of observable traits with contrasting forms.
b. Produces many offspring in one cross.
c. Short life cycle.
d. Ease in cross pollination.
e. Plants were sexually reproducing with bisexual flowers.
f. Hybrids were perfectly fertile
Q. Why is vegetative propagation practiced for growing some types of plants?
Answer: Vegetative propagation is generally performed in higher plants of ornamental, horticultural, medicinal and other economic importance. It is practiced for growing these plants because
(i) Good qualities of a variety can be maintained indefinitely.
(ii) Vegetative propagation gives a genetically uniform population.
(iii) Vegetative propagation is a quicker method of raising of crops.
(iv) It is the only known method of multiplication of seedless plants
Q. Leaves of Bryophyllum fallen on the ground produce new plants whereas the leaves of Jasmine do not, why?
Answer: In Bryophyllum, vegetative propagation occurs through leaves. Buds occur in notches of Bryophyllum leaf. However, when the leaf falls down and comes in contact with the soil, the buds spout and produce plantlets.
Q. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem? Where will the magnification maximum?
Solution : The accumulation of harmful chemicals in the body of living organisms at different trophic levels in a food chain is called biological magnification.
Yes, the concentration of these harmful chemicals will be different at different levels of the ecosystem.
It will be maximum at the last trophic level which is mostly the top carnivores (quaternary consumers).
Q. What are analogous organs? Explain with examples.
Solution: The organs which are similar in function or appearance but differ in structure and development are called analogous organs.
The wings of a bird and an insect are developmentally and structurally different from each other. Skeleton, flesh and feathers support bird's wings. The insects have a fold of membrane as wing, which is associated with few muscles. Wings of birds and insects are structurally different but perform the same function of flying. They are therefore, termed as analogous organs.
Q. Mrs. Kumar is pregnant for the last three months and she goes for regular check-up to her doctor. During her last visit, the doctor asked Mrs. Kumar to get an ultrasound done. Both Mr. and Mrs. Kumar went to a radiologist and got the ultrasound done. Once the ultrasound is over, Mr. Kumar asked the doctor whether the baby in the womb is a boy or a girl.
(a) What should the doctor reply to the couple?
(b) Is it ethical to determine the sex of a child?
(c) What should government do to discourage sex determination?
Solution : (a) The doctor should not tell the sex of the foetus.
(b) No, it is not ethical to determine the sex of a child.
(c) The government should ban the process of sex determination and should punish or fine whosoever does so.
Q. (a) Why is vegetative propagation practised for growing some types of plants?
(b) Name the different parts of a flower that has germ cells.
(c) List any two agents of pollination.
Answer: (a) Some plants like banana, seedless grapes, rose, which cannot produce viable seeds, can be easily grown by vegetative propagation. To get genetically identical copies and to maintain and preserve a stock of selected varieties, vegetative propagation is the only means. It is an easier less expensive and rapid method of propagation
(b) Style and ovule both have germ cells.
(c) Wind and water
Q. What happens to the pollen which falls on a suitable stigma? Explain.
Answer: The pollen grains absorb water and sugar from the surface of stigma and swell up. A tube grows out of the pollen grain and travel through the style to reach the ovary. The pollen tube carrying two male gametes which liberated inside the embryo sac. One male gamete fuses with the egg to form zygote. The other male gamete fuses with the secondary nucleus to form the endosperm, which provides nourishment to the growing embryo.
Q.How many 'X' chromosomes are present in body cells of humans in a:
(i) Male (ii) Female?
(iii) Describe the role of sex chromosomes in deciding the sex of the child.
Solution : (i) In the body cells of human males one X and one Y chromosome is present. 50 percent male gametes (sperms) carry X-chromosome and the remaining 50 percent carry Y-chromosome.
(ii) The body cells of human female carry two X-chromosomes. Females produce gametes (ova) with similar type of chromosomes, all carry one X-chromosome.
(iii) Sex chromosomes in males are XY type while in female they are XX type. When a sperm carrying X- chromosome fertilizes an egg, the zygote develops into a female (XX condition). When sperm carrying Y chromosome fertilizes an egg, the zygote develops into a male (XY condition).
Q. What is meant by tissue culture? How this technique is performed? In which area this technique is finding its application.
Solution : The production of plants by cells or tissues or organs in a synthetic medium is called tissue culture. This technique is also Know as micro propagation technique. The synthetic medium used in this technique contains all the nutrients and hormones which are required for the growth.
A cell or tissue is transferred into suitable synthetic medium under sterile conditions. The tissue often develops into a fast growing cellular mass called callus. The callus is transferred to another medium for growth and differentiation that forms plantlets. The plantlets can be transplanted into soil or pots where they can be grown to maturity. Tissue culture technique is being popularly used for production of ornamental plants like Orchids, Dahlia and Carnation.