These NCERT Solutions for Class 10 Science Chapter 8 How Do Organisms Reproduce Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.
How Do Organisms Reproduce NCERT Solutions for Class 10 Science Chapter 8
Class 10 Science Chapter 8 How Do Organisms Reproduce InText Questions and Answers
In-text Questions (Page 128)
Question 1.
What is the importance of DNA copying in reproduction?
Answer:
Since, DNA copying is accompanied by the creation of an additional cellular apparatus, a cell divides to give rise to two cells. These two cells are similar, but are they likely to be absolutely identical and it will depend on how accurately the copying reactions involved occur. No biochemical reaction is absolutely reliable. Therefore, it is only to be expected that the process of coying the DNA will have some variations each time.
Question 2.
Why is variation beneficial to the species but not necessarily for the individual?
Answer:
If some variation were to be present in a few individuals in these populations, there would be some chance for them to survive. If there were a population of bacteria living in temperate waters and if the water temperature were to be increased by global warming most of these bacteria would die, but the few variants resistant to heat would survive and grow further. Variation is thus useful for the survival of species over time.
In-text Questions (Page 133)
Question 1.
How does binary fission differ from multiple fission?
Answer:
Binary fission : This method of reproduction occurs in favourable conditions like enough food, water, temperature, etc. In this process of asexual reproduction, the nuclear division takes place for example Amoeba, Paramecium, Euglena is bacteria, blue green algae in multi-cellular animals like planaria.
Multiple fission: Many daughter individuals are formed from single parent is called multiple fission. This method of reproduction occurs in unfavourable conditions. The unicellular organism develops a protective covering the cyst over the cell. On return of farourable conditions the cyst breaks and daughter cells are liberated for e.g. Plasmodium.
Question 2.
How will an organism be benefited if it reproduces through spores?
Answer:
It is common method of reproduction in some bacteria and fungi Rhizopus, Mucor. During spore formation a structure called sporangium develops from the fungal hyphae. The nucleus divides several times within the sporangium and each nucleus with a small amount of cytoplasm develop into a spore. The spores are released; on falling on the suitable substratum they germinate to form new hyphae,
Question 3.
Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Answer:
Mode of reproduction that depend on the involvement of two individuals before a new generation can be created. Bulls alone cannot produce new calves nor can hens alone produce new Chicks. In such cases both sexes, males and females are needed to produce new generations.
Question 4.
Why is vegetative propagation practised for growing some types of plants?
Answer:
This type of propagation also makes possible that have lost the capacity to produce seeds. Another advantage of vegetative propagation is that all plants produced are genetically similar enough to the parent plant to have all its charateristics. This property of vegetative propagation is used in methods such as layering or grafting to grow many plants like sugar can, roses, grapes for agricultural purposes, for e.g. Banana, Orange, Rose, Jamine, etc.
Question 5.
Why is DNA copying an essential part of the process of reproduction?
Answer:
The creation of two cells from one involves copying of the DNA as well as of the cellular apparatus. The DNA copying mechanism, as we have noted cannot be absolutely accurate; and the resultant errors are a source of variations is populations of organisms. Every individual organism cannot be protected by variations, but in population.
In-text Questions (Page 140)
Question 1.
How is the process of pollination different from Fertilization?
Answer:
Pollination: It is the transfer of pollen grains from the anther of a flower to the stigma.
Fertilization: The process of nuclear fusion of the make and one egg nucleus is termed as fertilization.
Question 2.
What is the role of seminal vesicles and the prostate gland?
Answer:
- Seminal Vesicles: There is one pair of seminal vesicle. They lie at the base of urinary bladder above prostate gland. They secrate a viscous fluid for nourishment of sperms.
- Prostate Gland : There is one prostate gland. It surrounds first part of urethra. It secretes alkaline fluid which is discharged into urettra.
Question 3.
What are the changes seen in girls at the time of puberty?
Answer:
Secondary sexual characters in human females include.
- Growth of breasts.
- Growth of pubic hair and extra hair in the armpit.
- Hair on beard, moustache and chest are lacking
- Broadening of pelvis.
- Initiation of menstruation and ovulation.
- Increase in the subantaneous, particularly in thighs shoulders, Buttocks and face.
Question 4.
How does the embryo get nourishment inside the mother’s body?
Answer:
1. Ovaries: Each ovary is of the shape and size of almond. Ovaries are attached to the uterus by ovarian ligaments and also to the oviducts by ovarian fimbriate. Ovaries produce ovary and female hormones estrogen and progesterone,
2. Oviducts: A pair of muscular and internally ciliated tube the oviducts/fallopian tubes.
3. Uterus: It is a muscular; pear shaped hollow organ in pelvic cavity in between urinary bladder (infront). It is held by three ligaments. The upper part of uterus into which oviduct opens is broad and is called body. Its lower narrow constricted part is the neck which contains a cervical canal that leads into vagina; Uterus receives fertilized ovum which develops here into excuate an infant (child), taking about 36 weeks (9 months).
4. Vagina: It is also a muscular tube opening above in the reproduction uterus through internal orifice. Vagina is also known as birth canal since follicles is delivered through vagina.
5. Proliferative/follicular phase: This extends from 6th to 14 day about 10 days. This phase is stimulated by ‘FSH’ of. Pituitary gland due to which growth and development of Griffin follicles takes place. Within each follicle lies an ovum that develops and mature; but usually one ovum matures.
Question 5.
If a woman is using a copper-T, will it help in protecting her from sexually transmitted diseases?
Answer:
Intrauterine Contraceptive Device [IUCD] – These are contraceptive devices made of copper, plastic/stainless steel. A copper-T is inserted into uterus by a practicing doctor or a skilled nurse and left in place It prevents implantation in the uterus. It stop the unwanted birth and pregnancies but will not help protecting her from sexually transmitted diseases.
Class 10 Science Chapter 8 How Do Organisms Reproduce Textbook Questions and Answers
Page No. 141
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 reproduction 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 a sexual reproduction?
Answer:
Advantages of sexual reproducing over asexual reproduction : Sexual reproduction has several advantages over asexual reproduction because it involves (i) Fusion of male and female gametes coming from male and female organisms. Since the fusing gametes come from two different and sexually distinct individuals the off springs exhibit diversity of characters and (ii) Meiosis during gametogenesis provides opportunities for new combination of genes. It plays a prominent role in the origin of new species and leads to variation required for evolution.
Question 5.
What are the functions performed by the testis in human beings?
Answer:
Testes : Testes (Singular-Testis) are the male gonads. They produce both male gametes i.e. Spermatozoa and male sex hormone testosterone (Primary sex organ), testes are suspended in thin pouch of skin called scrotal sac located outside the main body cavity (extra abdominal in position in between the thighs). The testis of man produce sperms from puberty onwards, throughout his life.
Question 6.
Why does menstruation Occur?
Answer:
The menstrual cycle is the cycle of events the place in genital tract, ovaries and uterus and marked by menstrual flow in every 28 days. The days are numbered from the first day of the blood flow in the menstrual Period, starting from first fourteen day is the proliferating period when ovarian follicle grow into mature follicles, At ovulation the mature ovum is release from the ovary on 4th day. During the next day which is also known as secretary phase, the inner wall of uterna thicknes and the ovum moves into fallopian tube. If fertilization does not occur the oocyte under goes antolysis and blood vessels. Rupture causing bleeding. This process is called menstruation/menstral flow. This phase lasts for about four days.
Question 7.
Draw a labelled diagram of the longitudinal section on a flower.
Answer:
Question 8.
What are the different methods of Contraception ?
Answer:
The contraceptive method fall in a number of categories one category is the creation of mechanical barrier so that the sperm does not reach the egg Condom on the penis or similar coverings worn in the vagina can serve this purpose. Another category of contraceptives acts by changing the hormonal balance of the body so that eggs are not released and fertilization cannot occur. As orally pills taken to be commonly drugs can change hormonal balances, they can case side effects too. Other contraceptive devices such as the loop or the copper T are placed in the uterus to prevent pregnancy.
Question 9.
How are the modes for reproduction different unicellular and multicellular organisms?
Answer:
(a) Binary fission : This is the division of parent cell into two small equal sized identical daughter individuals. The two daughter individuals then grow into adult organisms so, fission of single parent cell results in the formation of two new unicellaular organisms. Hence it is called binary fission. For eg. Amoeba, Panamedum.
(b) Budding : The production of new individuals from an out growth of the parent individual. For e.g. in yeast, some protozoans and certain lower animals, e.g. Hydra, in multicellular organisms such as Hydra a bulging on the body appears as a result of repeated mitotic divisions in the cells. It results in the formation of a lateral outgrowth called bud
Question 10.
How does reproduction help in providing stability to populations of species?
Answer:
Every individual organism cannot be protected by variations but in a population variators are useful for ensuring the survival of the species. It would therefore make sense it organization came up with reproductive modes that allowed more and more variation to be generated.
Question 11.
What could be the reasons for adopting contraceptive methods?
Answer:
Reason for adopting contraceptive method:
- To avoid pregnancy.
- To save from sexual diseases.
Class 10 Science Chapter 8 How Do Organisms Reproduce Textbook Activities
Activity 8.1 (Page 129)
- Dissolve about 10 gm of sugar in 100 mL of water.
- Take 20 mL of this solution in a test tube and add a pinch of yeast granules to it.
- Put a cotton plug on the mouth of the test tube and keep it in a warm place.
- After 1 or 2 hours, put a small drop of yeast culture from the test tube on a slide and cover it with a coverslip.
Question 1.
Observe the slide under a microscope.
Answer:
The yeast starts to grow.
Activity 8.2 (Page 129)
- Wet a slice of bread, and keep it in a cool, moist and dark place.
- Observe the surface of the slice with a magnifying glass.
Question 1.
Record your observations for a week.
Answer:
The bread turns green in colour due to the presence of mound in it.
Activity 8.3 (Page 129)
- Observe a permanent slide of Amoeba under a microscope.
- Similarly observe another permanent slide of Amoeba showing binary fission.
- Now, compare the observations of both the slides
Solution : Binary fission : This method of reproduction occurs is favourable conditions like enough food, water, temperature, etc. In this process of asexual reproduction, the nuclear division takes place first followed by the appearance of a constriction in the cell membrane which gradually increases inwards and divides the cytoplasm into two parts, finally two daughter cells are formed. There are genetically and morphologically similar e.g. Like Amoeba, Paramecium, etc.
Activity 8.4 (Page 130)
- Collect water from a lake or pond that appears dark green and contains filamentous structures.
- Put one or two filaments on a slide.
- Put a drop of glycerine on these filaments and cover it with a coverslip.
- Observe the slide under a microscope.
Question 1.
Can you identify different tissues in the Spirogyra filaments?
Answer:
The spirogyra, breaks up into smaller pieces upon maturation. These pieces or fragments grow into new individuals. This is not true for all multicellular organisms. They cannot simply divide cell by cell. The reason is that many multicellular organisms as we have seen are not simply a random collection of cells.
Activity 8.5 (Page 132)
- Cut the potato into small pieces such that some pieces contain a notch or bud and some do not.
- Spread some cotton on a tray and wet it. Place the potato pieces on this cotton. Note where the pieces with the buds are placed.
- Observe changes taking place in these potato pieces over the next few days. Make sure that the cotton is kept moistened.
Question 1.
Take a potato and observe its surface. Can notches be seen?
Answer:
Yes, the notches can be seen
Question 2.
Which are the potato pieces that give rise to fresh green shoots and roots?
Answer:
Those pieces of potato given rise to freshgreen shoots and roots in which cotton was kept moistened.
Activity 8.6 (Page 132)
- Select a money-plant.
- Cut some pieces such that they contain at least one leaf.
- Cut out some other portions between two leaves.
- Dip one end of all the pieces in water and observe over the next few days.
Question 1.
Which ones grow and give rise to fresh leaves?
What can you conclude from your observations?
Answer:
The portion that contain one leaf grows. The plant needs the essential parts to grow.
Activity 8.7 (Page 135)
- Soak a few seeds of Bengal gram (chana) and keep them overnight.
- Drain the excess water and cover the seeds with a wet cloth and leave them for a day. Make sure that the seeds do not become dry
- Cut open the seeds carefully and observe the different parts.
- Compare your observations with the Fig, and see if you can identify all the parts.
Question 1.
Have you ever observe any flower part still persisting in the fruit ?
Answer:
Yes, we can identify the cotyledon, plumule and the radicle.
Class 10 Science Chapter 8 How Do Organisms Reproduce Additional Important Questions and Answers
Very Short Answer Type Questions
Question 1.
Define reproduction.
Answer:
Reproduction is the production of new individuals of the same species produced by existing organisms.
Question 2.
Name the two types of reproduction.
Answer:
A sexual reproduction and sexual reproduction.
Question 3.
Give one example of animal which reproduces asexually by budding
Answer:
Hydra.
Question 4.
Define parthenogenesis.
Answer:
Parthenogenesis is the development of an organisms from egg without fertilization.
Question 5.
Define unisexual organisms.
Answer:
The organisms which bear both male and female sex organism.
Short Answer Type Questions
Question 1.
What methods will you use for growing Jasmine and rose plants?
Answer:
For growing Jasmine plant we will use layering whereas for growing rose plant we will use cutting. In layering the development of adventitious roots is induced before the plant part is detached by covering a branch of plant with moist soil, whereas in cutting a plant part is used, maybe stem and part of it is immersed in the soil it then forms adventitious roots.
Question 2.
Define parturition. What is the approximate weight of the new bom child?
Answer:
Parturition is the birth of fully developed foetus on completion of gestation. The newborn child weighs about 3.5 kg.
Question 3.
What is the role of hypothalamus and pituitary in human reproduction?
Answer:
Hypothalamus and pituitary release certain hormones which control the functioning of ovary and other reproductive organs.
Long Answer Type Question
Question 1.
With the help of a neat tabelled diagram describe the sexual reproduction in plants.
Answer:
Diagram please see on page 176.
A typical angiospermous flower consists of four whorls of floral appendages attached on the receptacle. The receptacle is the of the flower stalk (Pedical). The four whorls of floral appendages are
1. Calyx 2. Corolla 3. Androecium 4. Gynoecium (Pistil).
1. Calyx (sepals): It is the outermost whorl of floral leaves aled sepals. Sepals are generally green in colour and protective in function.
2. Corolla (Petals): It is the collection of petals. Petals are generally large, showy and brightly coloured to attract the insect pollinators, Calyx and corolla are non-essential parts of the flower because they are not directly involved in reproduction.
3. Androecium: It is the collection of stamens. The male reproductive organs of the flower each stamen consists of anther and filament. Anthers are bilobed and contain four pollen sac. The pollen grains are made inside the pollen sacs.
4. Gynoecium (Pistil): It is the collection of carpels. The female reproductive organs of the flower.
Multiple Choice Questions
Question 1.
In which of the following organism multiple fission takes place?
(a) Bacteria
(b) Plasmodium
(c) Planaria
(d) Paramecium
Answer:
(b) Plasmodium
Question 2.
Grafting is successful in
(a) Dicots
(b) Monocots
(c) Both
(d) None of these
Answer:
(a) Dicots
Question 3.
In drone honey bees develop by :
(a) Fertilization
(b) Parthenocarpy
(c) Parthenogenesis
(d) Fission
Answer:
(c) Parthenogenesis
Question 4.
Which of the following organism is hermaphrodite?
(a) Rabbit
(b) Hydra
(c) Earthworm
(d) Both (a) & (b)
Answer:
(d) Both (a) & (b)
Question 5.
Which of the following statement is incorrect?
(a) Ovule change into seed
(b) Ovary changes into fruit
(c) Self pollination takes place in maize
(d) Each member of calyx whorl is called sepal.
Answer:
(c) Self pollination takes place in maize