Bihar Board Class 10 Science Solutions Chapter 8 How do Organisms

 

Bihar Board Class 10 Science Chapter 8 How do Organisms InText Questions and Answers

Intext Questions (Page 128)

Question 1.
What is the importance of DNA copying in reproduction ?
Answer:
Organisms look similar because their body designs are similar. If body designs are to be similar, the blueprints for these designs should be similar. Thus, reproduction at its most basic level will involve making copies of the blueprints of body design.

Question 2.
Why is variations beneficial to the species but 1 not necessarily for the individual ?
Answer:
The DNA copies generated in a reproducing cells are similar but may not be identical to the original. Some of these 1 variations in the DNA copies do not lead drastic outcomes. ‘ These surviving cells are similar but subtly different from each other. This inbuilt tendency for variation during reproduction . cause to develop new species. So, variations are beneficial,to the species but not necessarily for the individual.

Intext Questions (Page 133)

Question 1.
How does binary fission differ from multiple fission ?
Answer:
Binary fission : Some unicellular organisms split into two halves to create two new individuals. This is called binary . fission. Example : Many bacteria and protozoa such as Amoeba.
Multiple fission : Some unicellular organisms like malarial parasite (Plasmodium) divide into many daughter cells to form many new individuals. This process of fission is called multiple fission.

Question 2.
How will an organism be benefited if it reproduces through spores ?
Answer:
The spores are covered by thick walls that protect them until they come into contact with another moist surface and can i begin to grow. Thus, it is benefited for the organisms like Rhizopus to reproduces through spores.

Question 3.
Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration ?
Answer:
More complex organisms cannot reproduce by regeneration process because :

1. Their body 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. Regeneration is carried out by specialised cells, which are not present in complex organisms.

Question 4.
Why is vegetative propagation practised for growing some types of plants ?
Answer:
Some plants bear no seeds. This method makes possible the propagation of plants such as banana, orange, rose and
jasmine that have lost the capacity to produce seeds. Vegetative propagation takes place only in those plants whose parts like the root, stem and leaves have the property of propagation. By this process, we can reproduce the plants having more similar
characteristics.

Question 5.
Why is DNA copying an essential part of the process of reproduction ?
Answer:
DNA copying is a basic event in reproduction. Two copies are built in reproducing cells. These two copies need to separate from each others. One copy of DNA remain in the original cell and other copy need to have any organised cellular structure fort maintaining life processes. So, DNA copying is accomplished by creation of an additional cellular structure. In this way, two copies are separated and two new cells are formed.

Bihar Board Class 10 Science Chapter 8 How do Organisms Textbook Questions and Answers

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:

• Sexual reproduction promotes diversity.
• It results in new combination of genes, i.e., causes genetic variations.
• It plays a prominent role in the origin of new species.

Question 5.
What are the functions performed by the testis in human beings ?
Answer:
Testis is the main reproductive organ of male reproductive system. There are two testis located outside the abdominal cavity in scrotum. Scrotum lower the temperature than the normal body temperature to activate the testis. Testis produce the germ cells or sperm. The sperms are the tiny bodies that consist of mainly genetic material and a long tail which helps them to move towards the female germ cell.

Question 6.
Why does menstruation occur?
Answer:
If the egg is not fertilised then it is lost after one day. The uterus prepares itself to receive a fertilised egg. The lining of uterus becomes thick and spongy. These lining slowly breaks and comes out through vagina as blood and mucous. This process is called menstruation. So, it takes place when no fertilisation of egg takes place.

Question 7.
Draw a labelled diagram of the Longitudinal section of a flower.
Answer:

Question 8.
What are the different methods of contraception ?
Answer:
There are various methods of contraception :
1. Barriers : It prevents the sperm to reach near the egg. For example, condoms on the penis or similar coverings worn in the vagina can used for this purpose. Intra uterine devices such as copper-T are also popular. However, they can cause side effects due to irritation of the uterus. It prevents implantation of embryo.

2. Chemicals : There are various chemicals or the pills which act by changing the hormonal balance of the body so that eggs are not released and fertilisation cannot occur.

3. Surgical : If the vas deferens in the male is blocked, sperm transfer will be prevented. If the fallopian tube in the female is blocked, transfer of egg is prevented and no fertilisation takes place.

Question 9.
How are the modes for reproduction different in unicellular and multicellular organisms ?
Answer:
The unicellular organisms have only one cell. There is no separate tissues for reproduction. So, they can be reproduce by the process of fission (binary or multiple) or budding as in yeast. The multicellular organisms contains various cells and separate systems, so they can reproduce by both sexual and asexual reproduction.

Question 10.
How does reproduction help in providing stability to population of species ?
Answer:
Population of organisms fill well defined places or niches in the ecosystem using their ability to produce. The rate of birth must be at par with the rate of death to provide stability j to population of a species. And it is possible only by reproduction.
Further, the consistency of DNA copying during reproduction is , important for the maintenance of body design features that , allow the organism to use that particular niche. Reproduction , is therefore linked to the stability of population of species.

Question 11.
What could be the reasons for adopting contraceptive methods ?
Answer:
RepFSStTction is the process by which organisms increase their population. But the size of the human population is a cause for concern for many people. This is because an expanding population makes it harder to improve everybody’s standard of living. It is the main reason for poor standards of living for many people. So to balance the size of population, j‘ contraceptive methods are adopted.

Bihar Board Class 10 Science Chapter 8 How do Organisms Textbook Activities

Activity 8.1 (Page 1291)

• 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
Observe the slide under a microscope.
Answer:
Observation : Yeast cells may be seen. Some of the yeast cells may show chain budding.

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:
Observation : On observing the surface of the slice with the help of a hand lens.a white cottony mass is seen spreading on the surface. After a week, white cottony mass turns into black mass due to formation of sporangia and spores.

Activity 8.3 (Page 129)

• Observe a permanent slide of Amoeba under a microscope.
• Similarly observe another permanent slide of Amoeba showing binary fission.

Question 1.
Now, compare the observations of both the slides.
Answer:
Observation : In the permanent slide of amoeba, an amoeba cell is seen containing normal cytoplasm and nucleus. In permanent slide showing binary fission, nucleus seen to be dividing and the constriction is also seen in cytoplasm, suggesting formation of two daughter nuclei as shown in the Fig. 8.13.

Fig. 8.13. Binary fission in Amoeba.

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.

Question 1.
Observe the slide under a microscope. Can you identify different tissues in the Spirogyra filaments ?
Answer:
Observation : Spirogyra filament consists of many cells. These cells are attached in linear fashion to form a filament.

Activity 8.5 (Page 132)

• Take a potato and observe its surface. Can notches be seen ?
• 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.
Which are the potato pieces that give rise to fresh green shoots and roots ?
Answer:
Observation : The potato pieces which were having buds in notches shown growth of young shoot and roots. The pieces which were not having eye buds did not show any growth of shoot or root.

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 ?
Answer:
The portion of the money-plant having leaf/leaves at the node shows formation of fresh leaves. It also shows formation of branch from axillary buds present in the exile of the leaf.

Question 2.
What can you conclude from your observations ?
Answer:
Green leaves can synthesise food and have the, ability to grow into a plant, i.e., vegetatively propagate.

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.

Question 4.
How does the embryo get nourishment inside the mother’s body ?
Answer:
After fertilisation, zygote is formed which developed into embryo. The embryo is attached with uterus walls. This process is called implantation. The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta. Placenta is a disc which is embedded in the uterine wall. It contains villi on the embryo’s side of the tissue. On the mother’s side there are blood spaces, which surround the villi. This provides a large surface area for glucose and oxygen to pass from the mother to the embryo. In this way, embryo gets its nutrition.,

Question 5.
If a woman is using a copper-I, will it help in protecting her from sexually transmitted diseases ?
Answer:
No, copper-I will not help in protecting her from sexually transmitted diseases.

Bihar Board Class 10 Science Chapter 8 How do Organisms NCERT Exemplar Problems

Short Answer Type Questions

Question 1.
In a bisexual flower inspite of the young stamens : being removed artificially, the flower produces fruit. Provide a suitable explanation for the above situation.
Answer:
The pistil remain intact. Thus cross pollination occurrs ; leading to fertilisation and formation of fruit

Question 2.
Can you consider cell division as a type of reproduction in unicellular organism? Give one reason.
Answer:
Yes, because it results in the formation of two daughter cells, that is, it results in the production of more individuals of the organism.

Question 3.
What is a clone? Why do offsprings formed by asexual reproduction exhibit remarkable similarity?
Answer:
Clone refers to offspring of an organism formed by asexual method of reproduction. Since they possess exact copies of the DNA of their parent, clones exhibit remarkable similarity.

Question 4.
Explain how, offspring and parents of organisms reproducing sexually have the same number of chromosomes ?
Answer:
Reduction division (meiosis) during gamete formation halves the chromosome number in both male and female v gametes. Since these two gametes fuse during fertilisation, the ,original number of chromosomes (as in the parent) is restored , in the offspring. ’

Question 5.
Colonies of yeast fail to multiply in water, hut multiply in sugar. Give one reason for this.
Answer:
Sugar provides energy for sustaining all life activities in yeasts. In water, it fails to reproduce because of inadequate energy in its cells.

Question 6.
Why does bread mould grow profusely on a moist slice of bread rather than on a dry slice of bread?
Answer:
Moisture is an important factorfor the growth of hyphae. Moistened bread slice offers both moisture and nutrients to the bread mould, hence it grows profusely. Dry slice of bread offers nutrients but not moisture hence hyphae fail to grow on them.

Question 7.
Give two reasons for the appearance of variations among the progeny formed by sexual reproduction.
Answer:
(a) Sexual reproduction involves two parents with different sets of characters
(b) The gene combinations are different in gametes.

Question 8.
Would a Planaria cut vertically into two halves regenerate into two individuals? Complete Figure D and E by indicating the regenerated regions.

Answer:
Yes, shaded part in Figures D and E represent the regenerated halves.

Question 9.
From the internet, gather Information about the chromosome numbers of five animals and five plants. Correlate the number with the size of organism and answer the following questions.
(a) Do larger organisms have more number of chromosomes/cells ?
(b) Can organism with fewer chromosomes reproduce more easily than organisms with more number of chromosomes?
(c) More the number of chromosomes/cells greater is the DNA content. Justify.
Answer:
(a) No, there is no relationship between size of organism and its chromosome number.
(b) No, process of reproduction follows a common pattern and is not dependent on the number of chromosomes
(c) Yes, since the major component of chromosome is DNA, if there are more chromosomes in a cell, the quantity of DNA
will also be more.

Question 10.
In tobacco plant, the male gametes have twenty : four chromo-somes. What is the number of chromosomes in the female gamete? What is the number of chromosomes in the zygote?
Answer:
Number of chromosomes in female gamete is 24. 1 Number of chromosomes in the zygote is 48.

Question 11.
Why cannot fertilisation take place in flowers if pollination does not occur?
Answer:
In flowers, fertilisation requires both male and female gametes. If pollination does not occur, male gamete is not available hence fertilisation cannot take place.

Question 12.
Is the chromosome number of zygote, embryonal cells and adult of a particular organism

Question 13.
Reproduction is linked to stability of population of a species. Justify the statement.
Answer:
Reproduction maintains continuation of generation in . reproduction, DNA passes from one generation to the next. Copying of a NA takes place with consistency but with minor variations. This consistency also leads to stability of species.

Question 14.
How are general growth and sexual maturation different from each other?
Answer:
General growth refers to different types of developmental process in the body like increase in height, weight gain, changes in i shape and size of the body but sexual maturation is specific to changes reflected at puberty like cracking of voice, new hair patterns, development of breast in female etc.

Question 15.
Trace the path of sperm during ejaculation and mention the gland and their functions associated with the male reproductive system.
Answer:
Sperm comes out from testis into the vas deferens and then passes through urethra before ejaculation. The secretions of seminal vesicle and prostrate glands provide nutrition to the sperms and also facilitate their transport.

Question 16.
What changes are observed in the uterus if fertilisation does not occur?
Answer:
The thick and spongy lining of the uterus slowly breaks and comes out through the vagina as blood and mucus.

Question 17.
What changes are observed in the uterus subsequent to implantation of young embryo?
Answer:
The uterine wall thickens that is richly supplied with blood. A special tissue called placenta develops which connects embryo to the uterine wall that provides nutrients and oxygen to it.

Question 18.
What are the benefits of using mechanical barriers during sexual act?
Answer:
Mechanical barriers like condom prevents the sperms from reaching the egg. Thus, it is an effective method to avoid pregnancy. It also prevents transmission of infections during sexual act.

Question 19.
In the given figure label the parts and mention their functions

(а) Production of egg
(б) Site of fertilisation
(c) Site of implantation
(d) Entry of the sperms
Answer:
(a) Ovary (production of egg)
(b) Oviduct (site of fertilisation)
(c) Uterus (site of implantation)
(d) Vagina (entry of the sperms)

Question 20.
What would be the ratio of chromosome number between an egg and its zygote? How is the sperm genetically different from the egg?
Answer:
The ratio is 1 : 2. Sperms contain either X or Y chromosome whereas an egg will always have an X chromosome.

Long Answer Type Questions

Question 21.
Why are budding, fragmentation and regeneration all considered as asexual types of reproduction? With neat diagrams explain the process of regeneration in Planaria.
Answer:
Budding, fragmentation and regeneration are considered as asexual types of reproduction because all of them 1 involve only one parent and gametes are not involved in reproduction

Question 22.
Write two points of difference between asexual and sexual types of reproduction. Describe why variations are observed in the offspring formed by sexual reproduction.
Answer:
Asexual reproduction :
(a) Involves only one parent.
(b) Gametes are not produced.
(c) No fertilisation and zygote formation.
(d) Meiosis does not occur at anytime during repro- ductiop.

Sexual reproduction :

• Often involves two parents.
• Gametes are produced.
• Fertilisaton and zygote forma-tion is observed.
• Meiosis occurs at the time of gamete formation.

During sexual reproduction two types of gametes fuse. Although the gametes contain the same number of chromosomes, itheir DNA is not identical. This situation generates variations mpiong the offsprings.

Question 23.
Distinguish between pollination and fertilisation. Mention the site and product of fertilisation in a flower. Draw a neat, labelled diagram of a pistil showing pollen tube growth and its entry into the ovule.
Answer:
The process or mechanism of transfer of pollen grains from the anther to the stigma is termed pollination. The fusion of male and female gametes giving rise to zygote is termed fertilisation. The site of fertilisation is ovule. The product of fertilisation is zygote.

Fertilisation in a flowering plant

Question 24.
Distinguish between a gamete and zygote. Explain their roles in sexual reproduction.
Answer:
Gamete represents the sex cell or germ cell in sexual reproduction. There are two types of gametes, male and female. Zygote is the product of fertilisation in which a male and a female gamete fuse with each other. The two fusing gametes possess characters of their parents in their DNA. Fertilisation brings characters of both parents into one zygote cell. Zygote is the first cell of the next generation. It divides to form an embryo which subsequently grows into a new individual.

Question 25.
Draw the diagram of a flower and label the four whorls. Write the names of gamete producing organs in the flower.
Answer:

Question 26.
What is placenta? Mention its role during pregnancy?
Answer:
Placenta is the special tissue connection between embryo and uterine wall. This is a disc which is embedded in the uterine wall.
Placenta plays an important role during pregnancy. The embryo gets nutrition from the mother’s blood with its help. It contains villi on the embryo’s side of the tissue. On the mother’s side there are blood spaces, which surrohnd the villi. This provides a large surface area for glucose and oxygen to pass from the mother to the embryo. Also the waste substances produced by embryo are removed through placenta.

Question 27.
What are various ways to avoid pregnancy ? Elaborate any one method.
Answer:
(a) The various ways to avoid pregnancy are :

• creating a mechanical barrier which include use of I condoms on the penis or similar coverings worn in the vagina.
• taking drugs (as pills).
• placing a loop or copper-T in the uterus.
• adopting surgical methods which include blocking of the vas deferens in the male or the fallopian tube in the female.

(b) Surgical methods can be used to create blocks in male or female spxual parts. If the vas deferens in the male is blocked, sperm transfer will be prevented. If the fallopian tube in the female is blocked, the egg will not be able to reach the uterus, In both cases, fertilisation would not take place and hence, pregnancy would not occur.

Question 28.
How does fertilisation take place? Fertilisation occurs once in a month. Comment.
Answer:
The sperms enter through the vaginal passage during sexual intercourse. They travel upwards and reach the oviduct. Egg released from the ovary reaches the oviduct. The sperm encounters the egg in the oviduct then fertilisation takes place. Fertilisation occurs once in a month because egg is released once every month by ovary.

Question 29.
Reproduction is essentially a phenomenon that is not for survival of in individual but for the stability of a species. Justify.
Answer:
Organisms need energy for survival which they obtain from life processes such as nutrition and respiration. Reproduction, a process by which new individuals of the same species are produced, requires a lot of energy. The basic event in reproduction is the creation of a DNA copy. Cells use chemical reactions to build copies of their DNA. This creates two copies of the DNA in a reproducing cell and they need to be separated from each other.

For this it is necessary to create an additional cellular structure. Then, DNA copies separate to these two cells. Thus, genetic material is transferred from one generation to the next as a result of reproduction through DNA copying. DNA copying takes place with high constancy and considerable variations, that is, advantageous to the species for stability in the changing environment. Hence, it is clear that reproduction is essentially a phenomenon that is not for survival of an individual but for the stability of a species.

Question 30.
Describe sexually transmitted diseases and s mention the ways to prevent them. .
Answer:
The infectious diseases which are transmitted by the sexual contact of any healthy person with an infected person are called sexually transmitted diseases (STDs). These include bacterial infections such as gonorrhoea and syphilis and viral infections such as warts and HIV-AIDS. It is possible to prevent the transmission of such diseases during the sexual act by using mechanical barrier like condom.