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NCERT Solutions for class 10 Science chapter 8 – How do Organisms Reproduce

Back Exercise

Question 1.
Asexual reproduction takes place through budding in
(A) Amoeba
(B) Yeast
(C) Plasmodium
(D) Leishmania.
Answer:
(B) Yeast

Question 2.
Which of the following is not a part of the female reproductive system in human beings.
(A) Ovary
(B) Uterus
(C) Vas deferens
(D) Fallopian tube.
Answer:
(C) Vas deferens

Question 3.
The anther contains
(A) Sepals
(B) Ovules
(C) Carpel
(D) Pollen grains.
Answer:
(D) Pollen grains.

Question 4.
What are the advantages of sexual reproduction over asexual reproduction ?
Answer:

Following are the advantages of sexual reproduction:

Question 5.
What are the functions performed by testis in human beings ? (CCE 2011)
Answer:

  1. Formation of sperms from germinal cells found in seminiferous tubules.
  2. They also produce hormone called testosterone, which is responsible for secondary sexual characters in boys.

Question 6.
Why does menstruation occur ?
Answer:
If the egg is not fertilised, it lives for about one day. Since the ovary releases one egg every month, the uterus also prepares itself every month to receive a fertilised egg. Thus its lining becomes thick and spongy. This would be required for nourishing the embryo if fertilisation had taken place. Now, however, this lining is not needed any longer. So, the lining slowly breaks and comes out through the vagina as blood and mucous. This cycle takes place roughly every month and is known as menstruation. It usually lasts for about two to eight days.

Question 7.
Draw a labelled diagram of L.S. flower.
Answer:
NCERT Solutions for Class 10 Science Chapter 8 How do Organisms Reproduce 6

Question 8.
What are the different methods of contraception ?
Answer:

  1. Mechanical Barriers like condoms, cervical cap, diaphragm.
  2. Oral Contraceptives or oral pills like Mala D, Saheli
  3. Intrauterine Contraceptive Devices (IUCD) like loop, bow, Cu-T.
  4. Surgical Methods like vasectomy in males and tubectomy in females.

Question 9.
How are the modes for reproduction different in unicellular and multicellular organisms ?
Answer:

Unicellular Organisms Multicellular Organisms
1. Reproductive Cell. The same cell which functions as the body of the organism also gets transformed into reproductive cell. Specific cells take part in reproduction.
2. Technique. Techniques of reproduction are simple. Techniques of reproduction are commonly complex.
3. Asexual Reproduction. It occurs through fission, budding and spore formation. It occurs by several methods like fragmentation, regeneration, budding, spore formation, vegetative reproduction, etc.
4. Sex Organs. No special sex cell or sex organ is present. They are present.
5. Sexual Reproduction. It occurs through isogamy to heterogamy. It is commonly oogamous.

Question 10.
How does reproduction help in providing stability to population of species ?
Answer:

Reproduction is the process of producing the same kind of species by the existing species. This is done so as to maintain the population of that species and also to take forward their species to next generations. Stability is maintained by keep a check of rate of births and rate of deaths.

Question 11.
What could be the reasons for adopting contraceptive methods ?
Answer:

  1. Enjoying a good reproductive health.
  2. Protecting from sexually transmitted diseases.
  3. Controlling population.

In-Text Questions

Question 1.
What is the importance of DNA copying in reproduction ? (CCE 2011, 2015)
Answer:
DNA copying is the basic event during reproduction. DNA (Deoxyribo Nucleic Acid) is present in the chromosomes in the nucleus of a cell. DNA has the blueprint for the body design and body functioning. It is the information source for making proteins. If the information is changed, different proteins will be made, leading to altered body design so for inheritance of features from parents to next generation creation of DNA copy is necessary.

Question 2.
Why are variations beneficial to the species but not necessarily for the individual ? (CCE 2011, 2012)
Answer:
Many of the variations are pre-adaptations which have no immediate benefit to the individuals. However, they remain in the population. Whenever, environment undergoes a drastic change, the pre-adaptations present in some members of the population allow the latter to survive, grow and regain its former size. Therefore, it is not necessary that variations are beneficial to individuals developing them but can prove useful to the species.

Question 3.
How does binary fission differ from multiple fission ?
Answer:

Binary Fission Multiple Fission
It gives rise to two individuals. It forms several (more than two) individuals.
Binary fission occurs under favourable conditions. Multiple fission occurs both under favourable and unfavourable conditions.
Nucleus of the parent cell divides only once to form two daughters. Nucleus of the parent undergoes repeated divisions to form a number of daughter nuclei.
Cytoplasm undergoes cleavage after each nuclear division. Cytoplasm does not divide after every nuclear division.
No part of the parent body is left unused. A part of the body, covering and residual cytoplasm, is left behind.
Examples. Amoeba, Paramecium. Examples. Plasmodium, Amoeba (encysted).

Question 4.
How will an organism be benefited if it reproduces through spores ? (CCE 2011, 2012)
Answer:
Sporulation or spore formation is a method of asexual reproduction where each individual produces a number of spores. On germination each spore forms a new individual, e.g., Rhizopus.

  1. All the daughters formed through spores are genetically similar.
  2. Large numbers of spores are produced in one sporangium.
  3. Spores are covered by thick walls which provides protection under unfavourable conditions.

Question 5.
Can you think of reasons why more complex organism cannot give rise to new individuals through regeneration.
Answer:
Regeneration is the ability of an organism to form the whole from a cut out part or fragment.Higher complex organisms cannot give rise to new individuals through regeneration because 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.

Question 6.
Why is vegetative propagation practised for growing some types of organisms ?
Answer:
Vegetative propagation is practised in a number of horticulturally and economically important plants because it is advantageous.
Advantages:

  1. Seedless Plants. Vegetative propagation is the only known method of multiplication of seedless plants, g., Banana, Sugarcane, Pineapple, Jasmine, some varieties of Orange, Rose.
  2. Uniform Yield. Seeds and fruits are of uniform quality, size, taste and aroma.
  3. Genetic Uniformity. Vegetative propagation gives a genetically uniform population.
  4. Good Qualities. Good qualities of a variety can be maintained indefinitely.
  5. Survival Rate. Survival rate of the daughters is nearly 100% while in case of seed grown plants, it is 10%.
  6. Quicker Method. Vegetatively reproduced plants bear flowers and fruits earlier than the plants raised through seeds. Potato requires only three months for forming a new crop if raised from tubers. It takes 15 months if raised from seeds.
  7. Introduction in New Areas. In areas where seed germination fails to form mature plants, vegetative reproduction can help in establishing the plants.

Question 7.
Why is DNA copying an essential part of the process of reproduction ?
Answer:
DNA copying is an essential part of the process of reproduction because it carries the genetic information from the parents to offspring. A copy of DNA is produced through some chemical reactions resulting in two copies of DNA. Along with the additional cellular structure, DNA copying also takes place which is then followed by cell division into two cells..

Question 8.
How is the process of pollination different from fertilization ?
Answer:

Pollination Fertilization
It is transfer of pollen grains from anther to the stigma of a flower. It is the fusion of male and female gametes.
It carries the male gamete producing pollen grains to the female sex organ. It is actually about fusion of gametes.
Pollination is a physical process. Fertilization is a biological process.>
It occurs only in seed plants. It occurs in both plants and animals of various types.

Question 9.
What is the role of seminal vesicles and the prostate gland ? (CGE 2011, 2012)
Answer:
The secretions from seminal vesicles and prostate glands lubricate the sperms and provide a fluid medium for easy transport of sperms. Their secretion also provides nutrient in the form of fructose, calcium, and some enzymes.

Question 10.
What are the changes seen in girls at the time of puberty ?
Answer:

  1. Breast size begins to increase. There is darkening of skin of nipples below the tips of breasts.
  2. Menarche or beginning of menstruation.
  3. More secretion of oil from the skin, which results in the appearance of pimples.
  4. Appearance of hair in other areas of skin like underarms, face, hands, and legs.
  5. Increase in the size of uterus and ovary.
  6. High pitched voice,
  7. Slow growth of ovaries, fallopian tubes, uterus, vagina, enlargement of labia, etc.

Question 11.
How does the embryo get nourishment inside the mother’s body ? (CCE 2012)
Answer:
After fertilization the lining of uterus thickens and is richly supplied with blood to nourish the growing embryo. The embryo gets nutrition from the mother’s blood with he help of a special tissue called placenta. It is embedded in the uterine wall. Placenta contains Villi on the embryo’s side of the tissue and blood spaces on mother’s side surrounding the villi. This provides a large surface from mother to the embryo and waste products from embryo to mother.

Question 12.
If a woman is using a copper-T, will it help in protecting her from sexually transmitted diseases ?
Answer:
No, sexually transmitted diseases occur due to fluid to fluid contact that takes place in the vagina.