CBSE Class 10 Science How do humans reproduce Notes

REPRODUCTION

Reproduction is an integral feature of all living beings. The process by which a living being produces its own like is called reproduction.

IMPORTANCE OF REPRODUCTION:

Reproduction is important for each species, because this is the only way for a living being to continue its lineage. Apart from being important for a particular individual, reproduction is also important for the whole ecosystem. Reproduction helps in maintaining a proper balance among various biotic constituents of the ecosystem. Moreover, reproduction also facilitates evolution because variations come through reproduction; over several generations.

TYPES OF REPRODUCTION:

There are two main types, viz. asexual and sexual reproduction.

Asexual Reproduction: When a single parent is involved and no gamete formation takes place; the method is called asexual reproduction. No meiosis happens during asexual reproduction.

Sexual Reproduction: When two parents are involved and gamete formation takes; the method is called sexual reproduction. Meiosis happens during gamete formation; which is an important step of sexual reproduction.

INTEXT QUESTIONS 

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

Ans: The importance of DNA copying during reproduction is that:

(i) It is responsible for the transmission of parental characteristic to its offsprings.

(ii) It also leads to certain genetic variation.

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

Ans: Variations allow organisms to exist in diverse habitats or niches. In the absence of variations, a species may be restricted to particular area. If this area gets drastically altered, due to various natural or man-made causes, the species may be wiped out. However, if some variations were present in a few individuals, these colonize other habitats and could survive. But if variations are present in a single organism there would be very little for it to survive.

ASEXUAL REPRODUCTION

MODES OF REPRODUCTION USED BY SINGLE ORGANISMS

Modes of reproduction involving a single parent, without involving gametes. These are known as asexual modes of reproduction. 

Organisms can reproduce asexually in many ways. Some of them are given here.
FISSION
♦BINARY FISSION
Most of the unicellular animals prefer this method for reproduction. These organisms reproduce by binary fission; especially when conditions are favourable, i.e. adequate amount of
food and moisture is available. Binary fission is somewhat similar to mitosis. The mother cell divides into two daughter cells; and each daughter cell begins its life like a new individual. The parent generation ceases to exist, after binary fission. Amoeba is a very good example of the organism which reproduces by binary fission.

♦MULTIPLE FISSION
When conditions become unfavourable, i.e. food, moisture, proper temperature, etc. are not available; this is the preferred mode of reproduction by unicellular organisms. The organism develops a thick coating around itself. This is called cyst. The cyst helps the organism to tide over the bad phase. The nucleus divides into several nuclei and each daughter nucleus is surrounded by a membrane. All metabolic activities stop in the organism, after cyst formation. When favourable conditions return, the cyst dissolves or breaks down; releasing the daughter nuclei. The daughter nuclei; in turn; grow into new individuals. Plasmodium and entamoeba undergo cyst stage, when they are not in the body of their prime host, i.e. humans.

FRAGMENTATION
In multicellular organisms with simple body organization, simple reproductive methods have been noticed. Reproduction by fragmentation is seen in filamentous algae, e.g. spirogyra. In Spirogyra algae, the plant body breaks up into smaller fragments. Each fragment grows into a new individual.

REGENERATION
If the individual is somehow cut or broken up into many pieces, many of these pieces grow into separate individuals. For example, simple animals like Hydra and Planaria can be cut into

any number of pieces and each piece grows into a complete organism. This is known as regeneration (see the below figures). Regeneration is carried out by specialised cells. These cells proliferate and make large numbers of cells.
BUDDING
Organisms such as Hydra use regenerative cells for reproduction in the process of budding. In Hydra, a bud develops as an outgrowth due to repeated cell division at one specific site (see below figure). These buds develop into tiny individuals and when fully mature, detach from the parent body and become new independent individuals.

VEGETATIVE PROPAGATION
Vegetative propagation is the ability of plants to reproduce by bringing forth new plants from existing vegetative structures without sexual reproduction. Some examples of vegetative propagation are given below.

Tuber of Potato: The potato tuber is a modified stem. Many notches can be seen on the surface of potato. These are called ‘eyes’ of potato. Each ‘eye’ of a potato can give rise to a new potato plant. Farmers utilize this capability of potatoes to grow potato more quickly; which is not possible by using the seeds of potato.

Modified roots of Carrot and Sweet Potato: Carrot and sweet potato are examples of modifications of roots; for food storage. These roots can give rise to new plants; when keptunder  the soil.
Rhizomes of Ginger and Turmeric: Rhizomes are examples

of modified underground stems for food storage. These contain nodes, internodes and scaly leaves. When buried under the soil, the rhizomes produce new plants.

Leaf of Bryophyllum: Leaves of bryophyllum have notches on the margin. If a leaf is put under the soil, small saplings grow from the notches on the leaf margin. (see above figure) Artificial Vegetative Propagation: Man has used artificial vegetative propagation to grow many plants. This has enabled farmers and horticulturists to grow many plants in shorter duration and has helped them to earn more profit. Artificial vegetative propagation has also helped in developing many new varieties of plants. Stem cutting, layering and grafting are the preferred means of artificial vegetative propagation.

SPORE FORMATION
Rhizopus produces hundreds of microscopic reproductive units called spores. When the spore case (also called sporangium) bursts, the spores spreads into air. These air-borne spores land on food or soil, under favourable conditions like damp and warm conditions, they germinate and produce new individuals. Most of the fungi like Rhizopus, Mucor etc., Bacteria and nonflowering plants such as ferns and mosses reproduce by the method of spore formation.

ADVANTAGES OF ASEXUAL REPRODUCTION:
•The organism does not have to depend on another organism for carrying out reproduction; because a single parent is needed.
•It takes less time than sexual reproduction and hence more number of offspring can be produced in shorter time.
•The offspring are exact clones of their parent.
•Desirable characteristics can be easily incorporated into plants with artificial vegetative propagation.
DISADVANTAGES OF ASEXUAL REPRODUCTION:
•As a single parent is involved, so there is negligible chance of variation.
•In most of the cases in simple organisms, the parent generation ceases to exist after asexual reproduction.
•Asexual reproduction cannot give rise to biodiversity which is important for a healthy ecosystem.
INTEXT QUESTIONS PAGE NO. 133


Question. How will an organism be benefited if it reproduces through spores?
Answer. Spores are tiny, spherical, asexual reproductive bodies which under favourable conditions, like damp and warm conditions, germinate to produce new plants. They are
covered by the hard protective wall, which enables the plant to survive unfavourable conditions.

CBSE Class 10 Science Chapter 8 How Do Organisms Reproduce MCQs

Question. DNA copying is necessary during reproduction because
(a) it leads to the transmission of characters from parents to offsprings
(b) it leads to variation
(c) it helps in survival of the species over time
(d) all of these.
Answer. D

Question. Which of the following is a sexually transmitted viral disease?
(i) Gonorrhoea  (ii) Syphilis
(iii) Warts         (iv) HIV-AIDS
(a) (i), (iii) and (iv)
(b) (ii) and (iv)
(c) (iii) and (iv)
(d) (i) and (ii)
Answer. C

Question. Unisexual flowers contain
(a) both stamen and carpel
(b) only stamen
(c) only carpel
(d) either stamen or carpel.
Answer. D

Question. Sexual reproduction is the mode of reproduction that
(i) depend on the involvement of two different gametes.
(ii) incorporates a process of combining DNA from two gametes.
(iii) gives better chances of variations as compared to asexual reproduction.
(iv) gives rise to genetically identical offspring.
(a) (i) and (ii)
(b) (i), (iii) and (iv)
(c) (i), (ii) and (iv)
(d) (i), (ii) and (iii)
Answer. D

Question. Factors responsible for the rapid spread of bread mould on slices of bread are
(i) large number of spores
(ii) availability of moisture and nutrients in bread
(iii) presence of tubular branched hyphae
(iv) formation of round shaped sporangia.
Which of the above statements are true?
(a) (i) and (iii)
(b) (ii) and (iv)
(c) (i) and (ii)
(d) (iii) and (iv)
Answer. C

Question. The number of chromosomes in parents and offsprings of a particular species remains constant due to
(a) doubling of chromosomes before zygoteformation
(b) halving of chromosomes during gamete formation
(c) doubling of chromosomes during gamete formation
(d) halving of chromosomes after gamete formation.
Answer. B

Question. Which of the following is not a vegetative propagule?
(a) Root
(b) Stem
(c) Leaf
(d) Seed
Answer. D

Question. Which of the following layers of uterus breaks off during menstruation?
(a) Epimetrium
(b) Myometrium
(c) Endometrium
(d) Perimetrium
Answer. C

Question. Select the correct match.
Organism Mode of reproduction
(a) Bryophyllum – Leaf bud
(b) Hydra – Binary fission
(c) Paramecium – Multiple fission
(d) Spirogyra – Vegetative propagation
Answer. A

Question. In humans, gestation is completed in
(a) 40 weeks
(b) 60 weeks
(c) 120 weeks
(d) 240 days.
Answer. A

CBSE Class 10 Science Chapter 8 How Do Organisms Reproduce Very Short Answer Type Questions

Question. Why is cell division considered as a type of reproduction in unicellular organisms?
Answer. Cell division results in the formation of two daughter cells, i.e., it results in the production of more individuals of the organism like the process of reproduction.

Question. How regeneration is carried out?
Answer. Regeneration is carried out by specialised cells which proliferate and make large numbers of cells. From this mass of cells, different cells undergo changes to become various cell types and tissues.

Question. Name any two type of asexual reproduction.
Answer. (i) Fragmentation (ii) Budding

Question. Name the parts of a bisexual flower that are not directly involved in reproduction.
Answer. The parts of a bisexual flower that are not directly involved in reproduction are : sepals (calyx), petals (corolla) and thalamus.

CBSE Class 10 Science Chapter 8 How Do Organisms Reproduce Assertion & Reasoning Based MCQs 

For question numbers 41-50, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
(a) Both assertion and reason are true, and reason is correct explanation of the assertion.
(b) Both assertion and reason are true, but reason is not the correct explanation of the assertion.
(c) Assertion is true, but reason is false.
(d) Assertion is false, but reason is true.

Question. Assertion : In human male, testes are extra abdominal and lie in scrotal sacs.
Reason : Scrotum acts as a thermoregulator and keeps testicular temperature lower by 2°C for normal spermatogenesis.
Answer. A

Question. Assertion : Vagina acts as copulation canal and fertilisation canal both.
Reason : Insemination occurs in vagina of female.
Answer. D

Question. Assertion : One pollen mother cell forms four microspores.
Reason : Microspores are formed due to reduction division.
Answer. B

Question. Assertion : Regeneration cannot be regarded as reproduction.
Reason : Most organism would not normally depend on being cut up to be able to reproduce.
Answer. A

Question. Assertion : Spores of Rhizopus can survive under extreme climatic conditions.
Reason : Spores are the reproductive parts in Rhizopus.
Answer. B

Question. Assertion : Contraceptive pills can cause side effects in females.
Reason : They prevent pregnancy by blocking the incoming sperms.
Answer. C

Question. Assertion : Male gametes are motile.
Reason : They are free-living diploid cells.
Answer. C

Question. Assertion : Corolla is a floral part.
Reason : It helps in pollination.
Answer. B

Question. Assertion : The uterine line in human females becomes thick and spongy every month.
Reason : The lining breaks and comes out through the vagina as blood and mucus if fertilisation does not occur.
Answer. B

Question. Assertion : Gametogenesis is the production of gametes through the meiosis.
Reason : In oogenesis polar bodies are formed.
Answer. B

CBSE Class 10 Science Chapter 8 How Do Organisms Reproduce Short Answer Type Questions

Question. How Spirogyra reproduces?
Answer. Spirogyra reproduces through the fragmentation process.
Fragmentation is the mode of reproduction in which parent body breaks into two or more fragments and each fragment develops into a new individual. It is a method of
reproduction in many filamentous algae, mycelial fungi and thalloid bryophytes.

Question. How do insects help in pollination?
Answer. In entomophily (insect pollination), when an insect visits a flower for nectar, the pollen grains get deposited on the body of insect. When this insect visits another flower, some of the pollen grains stick to stigma of another flower. This leads to pollination.

Question. Why do multicellular organisms use complex way of reproduction?
Answer. In multicellular organisms, cells are organised into specialised groups; tissues, organs or organ systems, each of which occupy specific locations in the body. In such an organised condition cell-by-cell division would be impossible.
Hence, multicellular organisms need complex methods of reproduction.

Question. Describe the role of prostate gland, seminal vesicle and testes in the human male reproductive system.
Answer. Prostate glands - Secretion of the prostate gland nourishes and activates the spermatozoa to swim.
Seminal Vesicles - They produce an alkaline secretion which forms 60% of the volume of semen. Alkaline nature of the removal fluid helps to neutralise the acidic environment of the male urethra as well as that of female reproductive tract which otherwise would inactive and kill sperms.
Testes are responsible for producing sperm and secreting male sex hormones e.g., testosterone.

Please click the link below to download CBSE Class 10 Science How do humans reproduce Notes.