Ans : DNA (Deoxyribonucleic acid) is the genetic material found in the chromosomes, which are present in the nucleus of a cell. DNA copying is important for reproduction:
- It maintains thew continuty of life.
- It maintains the charecteristics of species.
- From this, the charecteristic and features of organisms are transformed to their progeny.
- It produces variations in organisms which is the basis of evolution of new species.
Q.2: Why is variation beneficial to the species but not necessarily for the individual?
Ans : Variations are beneficial to the species than individual because sometimes for a species, the environmental conditions change so drastically that their survival becomes difficult. For example, if the temperature of water increases suddenly, then most of the bacteria living in that water would die. Only few variants that are resistant to heat would be able to survive. However, if these variants were not there, then the entire species of bacteria would have been destroyed. Thus, these variants help in the survival of the species. However, all variations are not necessarily beneficial for the individual organisms.
Q.3: Why is DNA copying an essential part of the process of reproduction?
Ans : DNA (Deoxyribonucleic acid) copying is an essential part of reproduction as it passes genetic information from parents to offspring. It determines the body design of an individual. At the same time some occasional variations are produced in the offspring. The changes in the copy of DNA provide an organism the capability to survive in changing condition.
Q.4: How does binary fission differ from multiple fission?
Ans : Binary fission of the parent cell results in the formation of two small and equal daughter cell. In this fission the parent nucleus divideds into two daughter nuclei. Amoeba and Bacteria divide by binary fission.
Binary Fission in Amoeba
Multiple fission results in the formation of several daughter individuals. In this fission the parent nucleus divides into a number of daughter nuclei. Ex. plasmodium, malarial parasite etc.
Q.5: How will an organism be benefited if it reproduces through spores?
Ans : There are many advantages if an organism reproduces through spores. Advantages of spore formation:
- Large numbers of spores are produced in one sporangium.
- Each spore, upon germination, gives rise to a new individual.
- Spores are distributed easily by air to far-off places to avoid competition at one place.
- Spores are covered by thick walls to prevent dehydration under unfavourable conditions.
Q.6: Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Ans : Simple organisms such as Hydra and Planaria are capable of producing new individuals through the process of regeneration.
The process of regeneration involves the formation of new organisms from its body parts. Simple organisms can utilize this method of reproduction as their entire body is made of similar kind of cells in which any part of their body can be formed by growth and development.
However, complex organisms have organ-system level of organization. All the organ systems of their body work together as an interconnected unit. They can regenerate their lost body parts such as skin, muscles, blood, etc. However, they cannot give rise to new individuals through regeneration.
Q.7: Why is vegetative propagation practised for growing some types of plants?
Ans : Vegetative propagation method is used for growing certain plants which do not produce viable seeds. Ex: banana, seedless grapes, rose etc. It is also used for growing of plants bearing superior traits, because they produce genetically identical plants. It is also used for growing plants which require longer time to grow and become mature. Plant which require lot of care during early stages of development are also grown by this method.
Q.8:How is the process of pollination different from fertilisation?
- Pollination is the process of transfer of pollens grains from the anther of a flower to the stigma of the same or another flower. It occurs with the help of certain pollinators such as air, water, birds, or some insects.
- Whereas fertilization, is the fusion of male and female gametes. It occurs inside the ovule and leads to the formation of zygote.
Q.9: What is the role of the seminal vesicles and the prostate gland?
Ans : The role of
seminal vesicle is to store sperms and to produce viscous fluid stimulates uterine contraction to help sperms move forward into the Fallopian tube of female.
Prostate gland secretes alkaline milky fluid which helps in the mobility of sperms smoothly inside the vagina.Their secretion also provides nutrient in the form of fructose, calcium, and some enzymes.
Q.10: What are the changes seen in girls at the time of puberty?
Ans : The changes seen in the girls at the time of puberty are:
- Growth of breasts and external genitalia (vulva)
- Growth of pubic hair.
- Broadening of pelvis.
- Initiation of menstruation and ovulation.
- Increase in the subcutaneous fat, particularlyin thighs,shoulders, buttocks and face.
Q.11: How does the embryo get nourishment inside the mother’s body?
Ans : The embryo gets nourishment from the mother's blood through placenta. In the placenta, the foetal blood comes very close to the maternal blood. Here The exchange of materials between between the mother's blood and the blood of foetus takes place.
Q.12: If a woman is using a copper-T, will it help in protecting her from sexually transmitted diseases?
Ans : No. Using a copper-T will not provide a protection from sexually transmitted diseases, as it does not prevent the entry of semen. It only prevents the implantation of the embryo in the uterus.
NCERT Text book Questions and Answers
1: Asexual reproduction takes place through budding in
Ans : (b) Asexual reproduction takes place through budding in yeast.
Q.2: Which of the following is not a part of the female reproductive system in human beings?
(c) Vas deferens
(d) Fallopian tube
Ans : (c) Vas deferens is not a part of the female reproductive system in human beings.
Q.3: The anther contains
(d) pollen grains.
Ans : (d) The anther contains pollen grains.
Q.4: What are the advantages of sexual reproduction over asexual reproduction?
Ans : Advantages of sexual reproduction:
- In sexual reproduction, more variations are produced. Thus, it ensures survival of species in a population.
- The new formed individual has characteristics of both the parents.
- Variations are more viable in sexual mode than in asexual one. This is because in asexual reproduction, DNA has to function inside the inherited cellular apparatus.
Q.5: What are the functions performed by the testis in human beings?
Ans : The testes are the male reproductive organs that are located outside the abdominal cavity within a pouch called scrotum.
Functions of testes are:
- Produce sperms
- Produce a hormone called testosterone, which brings about secondary sexual characters in boys.
Q.6: Why does menstruation occur?
Ans : Menstruation is a process in which blood and mucous flows out every month through the vagina. This process occurs every month because one egg is released from the ovary every month and at the s
ame time, the uterus (womb) prepares itself to receive the fertilized egg. Thus, the inner lining of the uterus gets thickened and is supplied with blood to nourish the embryo. If the egg does not get fertilised, then the lining of the uterus breaks down slowly and gets released in the form of blood and mucous from the vagina.
Q.7: Draw a labelled diagram of the longitudinal section of a flower.
Q.8: What are the different methods of contraception?
Ans : The contraceptive methods can be broadly divided into the following types: • Natural method— It involves avoiding the chances of meeting of sperms and ovum. In this method, the sexual act is avoided from day 10th to 17th of the menstrual cycle because during this period, ovulation is expected and therefore, the chances of fertilization are very high. • Barrier method In this method, the fertilization of ovum and sperm is prevented with the help of barriers. Barriers are available for both males and females. Condoms are barriers made of thin rubber that are used to cover penis in males and vagina in females. • Oral contraceptives In this method, tablets or drugs are taken orally. These contain small doses of hormones that prevent the release of eggs and thus fertilization cannot occur. • Implants and surgical methods Contraceptive devices such as the loop or Copper-T are placed in uterus to prevent pregnancy. Some surgical methods can also be used to block the gamete transfer. It includes the blocking of vas deferens to prevent the transfer of sperms known as vasectomy. Similarly, fallopian tubes of the female can be blocked so that the egg will not reach the uterus known as tubectomy.
Q.9: How are the modes for reproduction different in unicellular and multicellular organisms?
Ans : In unicellular organisms, reproduction occurs by the division of the entire cell. The modes of reproduction in unicellular organisms can be fission, budding, etc. whereas in multicellular organisms, specialised reproductive organs are present. Therefore, they can reproduce by complex reproductive methods such as vegetative propagation, spore formation, etc. In more complex multicellular organisms such as human beings and plants, the mode of reproduction is sexual reproduction.
Q.10: How does reproduction help in providing stability to populations of species?
Ans : Living organisms reproduce for the continuation of a particular species. It helps in providing stability to the population of species by producing a new individual that resembles the parents. This is the reason why cats give birth to only cats or dogs give birth to only dogs. Therefore, reproduction provides stability to populations of dogs or cats or any other species.
Q.11: What could be the reasons for adopting contraceptive methods?
Ans : Contraceptive methods are mainly adopted because of the following reasons:
- To prevent unwanted pregnancies.
- To control population rise or birth rate.
- To prevent the transfer of sexually transmitted diseases.
- To regulate the proper spacing between pregnancies.