SUBJECT : SCIENCE
CLASS: 10CHAPTER - 8: How Do Organisms Reproduce?
BOARD: CBSE
TEXTBOOK : NCERT
How Do Organisms Reproduce? Extra Question
The various types of asexual reproduction are
• Fission – binary and multiple
• Budding
• Spore formation
• Regeneration
• Vegetative propagation – It is a process by which new organisms arise without production of seeds or spores. It can occur naturally or be induced by horticulturists.
2. Differentiate between binary fission and multiple fission.
Solution:
Binary Fission:
1.In this type of fission, the parent cell gives rise to two daughter cells.
2.It is expressed by organisms like amoeba, paramecium, etc.
Multiple Fission:
1.In this type of fission , the parent cell gives rise to more than two daughter cells.
2.It is expressed by organisms plasmodium.
3. List the advantages of vegetative propagation.
Solution:
The advantages of vegetative propagation are as follows
• It helps in the easy propagation of non–flowering plants.
• It helps in producing hybrids of various plants, with improved qualities.
• It helps in the propagation of a large number of populations in a very short duration.
• It helps in the propagation of plants that do not produce seeds or produce them in very small quantities.
4. Name the male and the female gametes in human beings.
Solution:
The male gamete is called sperm and the female gamete is called ovum in human beings.
5. Define fertilization.
Solution:
The process of fusion of the male gamete with the female gamete of the same species, i.e., the sperm with the ovum is known as fertilization. After fertilization, the product obtained is the zygote, which eventually develops into a complete organism.
6. Define sexual reproduction.
Solution:
The type of reproduction that involves both the sexes of the species is known as sexual reproduction. This kind of reproduction requires the fertilization of the gametes of both the sexes.
7. Mention any two functions of human ovary.
Solution:
The two functions of human ovary are as follows
(i) It is responsible for the production of the female gamete, ovum.
(ii) It secretes hormones like estrogen and progesterone.
8. What is syngamy?
Solution:
The process of fusion of the two gametes is known as syngamy. It is the initial step in the process of fertilization.
9. Where does fertilization take place in human females?
Solution:
Fertilization in the case of humans is internal. The process of fertilization takes place inside the fallopian tube of females.
10. Define menopause.
Solution:
At the age of around 45-50 years, the ovaries of the females stop producing ova.
The stoppage of menstrual flow and other events like the changes in the hormonal composition is known as menopause.
11. Discuss briefly the types of reproduction.
Solution:
Reproduction is a unique biological process that is essential for the continuity and propagation of species. It is a process by which new individuals of the same species are produced by parental organisms. It takes place by two methods: –
Asexual Reproduction
This method of reproduction generally involves only one parent and is observed only in lower organisms. Fission, budding, spore formation and vegetative propagation are some of the types of asexual propagation.
Sexual Reproduction
This method of reproduction involves two parents. It requires the fusion of gametes of both the sexes of the species. Almost all animals and higher forms of plants reproduce by this method.
12. Describe asexual reproduction in amoeba.
Solution:
Amoeba reproduces by the process of binary fission. During this process, the nucleus divides first, followed by the formation of a constriction in the cellular membrane of amoeba. This gradually increases inwards and divides the cytoplasm into two parts. Finally two daughter organisms are obtained.
13. Explain various steps of budding in yeast.
Solution:
Budding is a form of asexual reproduction usually observed in yeast.
• During this process, a small protrusion appears on the upper portion of the body of the organism. This bulge is called a bud.
• The bud gradually grows in size and forms an individual cell.
• From this newly budded cell, another bud appears at the tip.
• This process continues and a chain of yeast cells is obtained.
14. What are the various methods of vegetative propagation? Discuss any one method with example.
Solution:
The various types of vegetative propagation are
• Cutting
• Layering
• Grafting
• Parthenogenesis
• Micro-propagation in vitro
Grafting
• It is a method in which two parts of different plants are joined together in such a way that they unite and grow as one plant.
• The portion of the plant that is grafted onto another plant is known as the scion, and the plant on which grafting is performed is known as the stock.
• The stock and the scion are tied in such a way that the cambium of the scion and the stock come in contact with each other.
• The stock is so chosen that it possesses qualities like disease resistance, high water absorbing capacity, deep penetrating roots for a firm hold, etc. The scion is so chosen that it possesses qualities like high yield of pulp or seeds (as desired) from a single fruit, etc.
• For example citrus-root stock is used for a variety of grafts like sweet orange, lime, grape, etc.
15. Define the terms unisexual and bisexual giving examples of each.
Solution:
An animal or an organism, which can be differentiated as male or female.
i.e., The two sexes are present in separate individuals, then such an organism is said to be unisexual.For example, human beings, all mammals. An animal or an organism that possesses both the sexes in a single body is said to be a bisexual animal. For example, earthworm, starfish, etc.
16. Mention the reproductive parts of a flower.
Solution:
The reproductive parts of a flower are as follows
Male reproductive part – Stamens
Female reproductive part – Pistil.
17. What is pollination? Describe cross-pollination.
Solution:
The transfer of pollen grains from anther to stigma is called pollination. Pollen grains are shed from the anther and reach the stigma of either the same flower or a different flower.
Cross-pollination
The transfer of pollen grains from the anther of one flower to the stigma of another flower of the same species is termed as cross-pollination.
18. Describe double fertilization in plants.
Solution:
In the case of plants, the pollen grain releases two male gametes. One fuses with the egg and forms the zygote. The other male gamete fuses with the two polar nuclei. This fusion is said to be triple fusion. Thus, inside an embryo sac, two fusions, syngamy and triple fusion, take place. This mechanism of two fusions occurring in an embryo sac is called double fertilization.
19. What are the male and the female gonads in the human beings? Mention their functions.
Solution:
Testes are the male gonads in human beings. Their functions are
• To produce male hormones like testosterone.
• To produce the male gamete – sperm.
Ovaries are the female gonads in human beings. Their functions are
• To produce female hormones like estrogen and progesterone.
• To produce the female gamete – ovum.
20. Mention the secondary sexual characters in human males and females.
Solution:
The male secondary sexual characters are the growth of hair on the chest, near the genitals, on the face in the form of beard and moustache, development of deep hoarse voice, etc.
The female secondary sexual characters are the development of breasts and mammary glands, axial and pubic hair, etc.
21. Write names of one male and female sex hormones.
Solution:
The names of one male and one female sex hormones are as follows
Male sex hormone – testosterone
Female sex hormone – progesterone.
22. Describe the menstrual cycle.
Solution:
• The commencement of menstruation at puberty is termed menarche and marks the beginning of the reproductive life of a female.
• Initially, inside the ovary, an oogonium or an ovarian follicle is developed into a mature ovum and released into the fallopian tube. This is termed as ovulation.
• After the release, the uterus and the fallopian tubes undergo changes like the thickening of the uterine wall, development of the endometrial lining, etc. to prepare the body for a probable pregnancy.
• If fertilization does not occur, then the thickened inner wall of the uterus breaks down along with its blood vessels and moves out of the vagina in the form of bleeding, called menstrual flow (menstruation).
• It lasts for about 4-7 days.
• This cycle of events taking place in the ovaries and the uterus every 28 days and marked by the menstrual flow is known as the menstrual cycle.
• In a normal healthy woman, ovulation takes place around the 14th day and menstruation occurs every 28 to 30 days.
23. Differentiate between menarche and menopause.
Solution:
• Menarche marks the beginning of the reproductive cycle of a female whereas menopause marks the end of the reproductive cycle.
• Menarche generally takes place at puberty, i.e., at the age of 12-16 years while menopause takes place around the age of 45-50 years.
• After menarche, there is an increased amount of production of female sex hormones whereas after menopause, the secretion of female sex hormones declines and sometimes completely stops.
24. What is ovulation?
Solution:
The ovarian follicles present inside the ovaries develop into mature follicles. Usually, one mature ovarian follicle develops into a mature ovum. It pinches off from the surface of the ovary and enters the fallopian tube. This process is termed as ovulation. Generally ovulation takes place in only one ovary at a time.
25. Write whether the following statements are true or false.
1. Fertilization is the fusion of the sperm and the ovum.
2. Duration of menstrual cycle in human female is 20 days.
3. Onset of menstruation is termed menopause.
4. In human beings, male attains puberty little later than females.
Solution:
1. True
2. False
3. False
4. True.
26. Fertilization is possible if copulation has taken place during the middle of the menstrual cycle.Give reasons.
Solution:
During copulation, a large number of sperms enter the fallopian tube. If copulation takes place during the middle of the menstrual cycle, then fertilization is possible as at this time the ovum would have entered the fallopian tube from the ovary. If copulation takes place before ovulation then fertilization is not possible. Fertilization is marked by the absence of the regular menstrual flow.
27. Mention the methods used for regulation of childbirth.
Solution:
A number of techniques are employed for the regulation of childbirth. They are classified as follows
Barrier methods – Use of physical devices to prevent the entry of sperms inside the female genitals. They include:
1. Condoms
2. Diaphragms
3. Cervical caps
4. Intrauterine contraceptive devices (IUCD) like Copper-T.
Chemical methods – Use of specific drugs by females.
1. Oral pills – Oral contraceptives of mainly hormonal preparations.
2. Vaginal pills
Surgical methods –
1. Vasectomy – Removal or ligation of a small portion of the vas deferens in males.
2. Tubectomy – Removal or ligation of a small portion of fallopian tube in females.
28. Write the full forms of IUCD, AIDS, HIV, and OC.
Solution:
The full forms for the above abbreviations are as follows
IUCD – Intrauterine Contraceptive Devices
AIDS – Acquired Immuno-Deficiency Syndrome
HIV – Human Immuno Virus
OC – Oral Contraceptives.
29. Describe the surgical method of birth control.
Solution:
In the surgical methods of birth control, a small portion of vas deferens in males and the fallopian tube in females is surgically removed or ligated (tied). This process is called Vasectomy in males and Tubectomy in females. As a result of this surgery, gametes cannot be released from the body (in males) and cannot enter the uterus (in females).
30. Define sexually transmitted disease and give two examples.
Solution:
There are certain infectious diseases that spread by sexual contact. Such diseases are called STDs (Sexually Transmitted Diseases). In most cases, the symptoms are burning sensation on urination and urethral discharge. Gonorrhea and Syphilis are the two examples for sexually transmitted diseases. These diseases are curable.
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