How do organisms reproduce-NCERT Solutions

Q1.   What is the importance of DNA copying in reproduction?

Ans. DNA copying is an important phenomenon of reproduction through which the organisms pass on their characteristics to their offspring. It maintains the characteristics in different generations of the species. It also produces variations which are useful for the survival of species for long time.

Q2.   Why is variation beneficial to the species but not necessary for the individual?

Ans. Accumulation of variations after several generations results in new set of traits required for survival.

         As they show results after many generations so they are not important for individual.

Q3.   How does binary fission differ from multiple fission?

Ans. Binauy Fission: An organism is divided into two individuals. Mitotic division takes place resulting in two identical individuals or daughter cells. e.g., Amoeba.

         Multiple Fission: Mitotic division takes place. The nucleus a ii diumrepeatedly to form a number of equal sized and similar individuals, e.g.,

Q4.   How will an organism be benefited if it reproduces through spores?

Ans. During adverse circumstances spore remain coated are means po tideve over layer. This helps an organism survive adverse conditions. Spores are means to tide over bad phases.

Q5.   Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?

Ans. More complex organisms cannot give rise to new individuals because:

         1. Their body design is highly complicated.

         2. There are specific organs to do specific functions.

         3. There is a labour division in the body of complex organisms.

         4. Exception is lizard, which can regenerate its tail.

Q6.   Why is vegetative propagation practised for vowing same types of plants?

Ans. The process by which some plant can reproduce asexually It has their vegetative pars like roots, stems and leaves is called vegetative propagation.

         Plants raised by this method can befit flowers and fruits earlier than those produced from seeds.

         Plants that have lost capability to produce seeds like banana, organge, rose and jasmine can be propagated. All plants produced are genetically similar to the parent plant.

Q7.   Why is DNA copying an essential part of the process of reproduction?

Ans. DNA copying is needed because information stored in DNA is used to e make protein. Synthesis of different proteins will lead to altered body design. Thus, reproduction at its most basic level involves making copies of the blueprints of body design.

Q8.   How is the process of pollination different from fertilization?

Ans. Pollination is the transfer of pollen grains from the anther of a stamen to the stigma of a carpel. These are transferred by agents such as insects, birds, wind or water.

         Fertilization is defined as the fusion of a mele gamete (sperm) with a female gamete (ovary) to form a zygote by sexual reproduction.

Q9.   What is the role of seminal vesicles and prostate gland?

Ans. Seminal vesicles are a pair of thin-walled muscular and elongated sacs which secrete a fluid for nourishment of sperms.

         Prostate glands also produce a fluid which is released in the urethra along with secretion of seminal vesicle. It affects the vaginal pH so that sperms move smoothly inside the vagina.

Q10.   What are the changes seen in girls at the time of puberty?

Ans. At the time of puberty, breast size begins to increase, with darkening of the skin of the nipples. Also, girls begin to menstruate at around this time.

Q11.   How does the embryo get nourishment from its mother�s body?

Ans. The embryo grows inside the mother�s womb and gets nourishment from its mother�s blood through placenta. Placenta contains villi which connects the embryo with the mother�s blood. These villi provides a large surface area for glucose and oxygen to pass from mother to the embryo.

Q12.   If a woman is using copper-T, will it help in protecting her front sexually Transmitted diseases?

Ans. No, it will not protect the woman from sexually transmitted diseases as fluid to fluid contact occurs in the vagina.

Q1.   Asexilal reprodnction takes place through budding in

         (a) amoeba         (b) yeast.         (c) plasnrodium.         (d) leishrnaniia.

Ans. (b) yeast

Q2.   Which of the following is not a part of the temule reproductive system in human begins?

         (a) Ovary         (b) Uterus         (c) Vas deferens         (d) Fallopian tube

Ans. (c) Vas deferens

Q3.   The anther cantains

         (a) sepals         (b) ovules         (c) carpel         (d) pollen grains

Ans. (d) pollen grains

Q4.   What are the advantage of sexual reproduction acre asexual reproduction?

Ans. In asexual reproduction, the offspring is almost identical to the parent because they have the same gene as their parent. Thus, variation is not present.

         Sexual reproduction involves fusion of male and female gametes. The offspring exhibits diversity of characters because they receive some genes from the mother and some from the father. The mixing of genes in different combinations, results in genetic variations. This variation leads to the continuous evolution of various species to produce various organisms.

Q5.   What are the functions performed by testis in human beings?

Ans. The function of testis is to produce sperms and male sex hormone called testosterone.

Q6.   Why data menstruation occur?

Ans. Menstruation occurs in females when the egg produced inside the cervix is not fertilized. Since the egg does not fuse with the male gamete, so the thick and soft lining of uterus having a lot of blood capillaries in it are not required. This unfertilized egg dies within a day and the lining breaks down shedding blood along with other tissues. This comes out of the vagina in the form of bleeding.

Q7.   Draw a labelled diagram of the longihaltnal section of a flower.

Q8.   What are the different methods of contraception?

Ans. Contraception is the method to avoid pregnancy. Various methods of contraception are as follows:

         Physical Barrier Methods: Use of condoms, diaphragms, cervical caps can be used. These prevent the entry of sperms into the female genital tract by acting as a barrier between them.

         Chemical Methods: Oral pills can be used which change the hormonal balance and stop release of egg. Vaginal pills kill the sperms.

         Surgical Methods: This includes vasectomy (sperm duct is removed) in males and tubectomy (removal of small portion of fallopian tube) in females.

Q9.   How are modes of reproduction different in unicellular and multicellular organisms?

Ans. Unicellular organisms have only one cell. There is no separate tissue for reproduction. So, they can reproduce by the process of fission or budding. Multicellular organisms contain various cells and have separate system for reproduction. So, they can reproduce by both sexual and asexual methods.

Q10.   How does reproduction help in providing stability to the population of species?

Ans. Stability is provided by equalizing the birth and death ratio. Thus, the rate of birth should approximately be equal to the rate of death.

Q11.   What could be the reasons for adopting contraceptive methods?

Ans. The reasons for adopting contraceptive methods could be:

         1. Protection from sexually transmitted diseases such as HIV-AIDS, gonorrhoea, syphilis, warts etc.

         2. Restricting the number of children.

         3. Sufficient gap between successive births.

         4. Enjoying a good reproductive health.

         5. Controlling population.