Lesson: How do Organisms Reproduce
In the list of organisms given below, those that reproduce by asexual method are:
(a) (ii) and (iv)
(b) (i), (iii) and (iv)
(c) (i) and (iv)
(d) (ii), (iii) and (iv)
In a flower, the parts that produce male and female gametes (germ cells) are:
(a) Stamen and anther
(b) Filament and stigma
(c) Anther and ovary
d) Stamen and style
Which of the following is the correct sequence of events of sexual reproduction in a flower?
(a) Pollination, fertilisation, seedling, embryo
(b) Seedling, embryo, fertilisation, pollination
(c) Pollination, fertilisation, embryo, seedling
(d) Embryo, seedling, pollination, fertilisation
Offspring formed by asexual method of reproduction have greater similarity among themselves because:
(i) Asexual reproduction involves only one parent
(ii) Asexual reproduction does not involve gametes
(iii) Asexual reproduction occurs before sexual reproduction
(iv) Asexual reproduction occurs after sexual reproduction
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iv)
(d) (iii) and (iv)
Characters transmitted from parents to offspring are present in:
(c) Golgi bodies
Characters that are transmitted from parents to offspring during reproduction show:
(a) Only similarities with parents
(b) Only variations with parents
(c) Both similarities and variations with parents
(d) Neither similarities nor variations
A feature of reproduction that is common to Amoeba, Spirogyra and Yeast is that:
(a) They reproduce asexually
(b) They are all unicellular
(c) They reproduce only sexually
(d) They are all multicellular
In Spirogyra, asexual reproduction takes place by:
(a) Breaking up of filaments into smaller bits
(b) Division of a cell into two cells
(c) Division of a cell into many cells
(d) Formation of young cells from older cells.
The ability of a cell to divide into several cells during reproduction in Plasmodium is called:
(b) Reduction division
(c) Binary fission
(d) Multiple fission
The correct sequence of reproductive stages seen in flowering plants is:
(a) Gametes, zygote, embryo, seedling
(b) Zygote, gametes, embryo, seedling
(c) Seedling, embryo, zygote, gametes
(d) Gametes, embryo, zygote, seedling
The number of chromosomes in parents and offspring of a particular species remains constant due to:
(a) Doubling of chromosomes after zygote formation
(b) Halving of chromosomes during gamete formation
(c) Doubling of chromosomes after gamete formation
(d) Halving of chromosomes after gamete formation
In Rhizopus, tubular thread-like structures bearing sporangia at their tips are called:
Vegetative propagation refers to formation of new plants from:
(a) Stem, roots and flowers
(b) Stem, roots and leaves
(c) Stem, flowers and fruits
(d) Stem, leaves and flowers
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
(a) (i) and (iii)
(b) (ii) and iv)
(c) (i) and (ii)
(d) (iii) and (iv)
Length of a pollen tube depends on the distance between:
(a) Pollen grain and upper surface of stigma
(b) Pollen grain on upper surface of stigma and ovule
(c) Pollen grain in anther and upper surface of stigma
(d) Upper surface of stigma and lower part of style
Which of the following statements are true for flowers?
(i) Flowers are always bisexual
(ii) They are the sexual reproductive organs
(iii)They are produced in all groups of plants
(iv) After fertilisation, they give rise to fruits
(a) (i) and (iv)
(b) (ii) and (iii)
(c) (i) and (iii)
(d) (ii) and (iv)
Which among the following statements are true for unisexual flowers?
(i) They possess both stamen and pistil
(ii) They possess either stamen or pistil
(iii) They exhibit cross pollination
(iv) Unisexual flowers possessing only stamens cannot produce fruits
(a) (i) and (iv)
(b) (ii), (iii) and (iv)
(c) (iii) and (iv)
(d) (i), (iii) and (iv)
Which among the following statements are true for sexual reproduction in flowering plants?
(i) It requires two types of gametes
(ii) Fertilisation is a compulsory event
(iii) It always results in formation of zygote
(iv) Offspring formed are clones
(a) (i) and (iv)
(b) (i), (ii) and (iv)
(c) (i), (ii) and (iii)
(d) (i), (ii) and (iv)
In the given figure, the parts A, B and C are sequentially:
(a) Cotyledon, plumule and radicle
(b) Plumule, radicle and cotyledon
(c) Plumule, cotyledon and radicle
(d) Radicle, cotyledon and plumule
Offspring formed as a result of sexual reproduction exhibit more variations because:
(a) Sexual reproduction is a lengthy process
(b) Genetic material comes from two parents of the same species
(c) Genetic material comes from two parents of different species
(d) Genetic material comes from many parents
Reproduction is essential for living organisms in order to:
(a) Keep individual organism alive
(b) Fulfil their energy requirement
(c) Maintain growth
(d) Continue the species generation after generation
During adolescence, several changes occur in human body.
Mark one change associated with sexual maturation in boys:
(a) Loss of milk teeth
(b) Increase in height
(c) Cracking of voice
(d) Weight gain
In human females, an event that reflects onset of reproductive phase is:
(a) Growth of body
(b) Changes in hair pattern
(c) Change in voice
In human males, testes lie in the scrotum, because it helps in the:
(a) Process of mating
(b) Formation of sperm
(c) Easy transfer of gametes
(d) All the above
Which among the following is not the function of testes at puberty?
(i) formation of germ cells
(ii) secretion of testosterone
(iii) development of placenta
(iv) secretion of estrogen
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iv)
The correct sequence of organs in a male reproductive system for transport of sperms is:
(a) Testis → Vas deferens → Urethra
(b) Testis → Ureter → Urethra
(c) Testis → Urethra → Ureter
(d) Testis → Vas deferens → Ureter
Which among the following diseases is not sexually transmitted?
(c) HIV - AIDS
In a bisexual flower in spite of young stamens being removed artificially, the flower produces fruit.
Provide a suitable explanation for the above situation.
A flower produces fruit when the process of pollination and fertilisation take place. In absence of stamens, cross pollination can take place to facilitate fertilisation and formation of fruit.
Can you consider cell division as a type of reproduction in unicellular organism? Give one reason.
Yes, because cell division results in the formation of two daughter cells, that is, it results in the production of more individuals of that organism.
What is a clone? Why do offspring formed by asexual reproduction exhibit remarkable similarity?
An exact copy of something is called a clone. An offspring of an organism formed by asexual method of reproduction possess exact copies of the DNA of their parent. Hence, the offspring formed after asexual reproduction exhibit remarkable similarity.
Explain how, offspring and parents of organisms reproducing sexually have the same number of chromosomes?
Gamete formation is the first step in sexual reproduction. Reduction division (meiosis) during gamete formation halves the chromosome number in both male and female gametes. When these two gametes fuse during fertilisation, the original number of chromosomes (as in the parent) becomes equal in the offspring. Therefore, the offspring and parents of organisms reproducing sexually have the same number of chromosomes.
Colonies of yeast fail to multiply in water, but multiply in sugar solution.
Give one reason for this.
For all life processes, an organism requires nutrition.
Yeast gets inadequate nutrition in water which prevents its multiplication. On the other hand, yeast gets all the energy required for sustaining all life activities including reproductions in a sugar solution. Thus, colonies of yeast fail to multiply in water, but multiply in sugar solution.
Why does bread mould grow profusely on a moist slice of bread rather than on a dry slice of bread?
Moisture is an important factor for the growth of hyphae. When compared to a dry slice of bread, the moist slice of bread offers much needed water to the spores of the bread mould. Hence, bread mould grows profusely on a moist slice of bread.
Give two reasons for the appearance of variations among the progeny formed by sexual reproduction.1
The reasons for the appearance of variations among the progeny formed by sexual reproduction are:
(a) Gene proof of a progeny is contributed by two parents with different sets of characters
(b) The gene combinations are different in both male and female gametes.
Would a Planaria cut vertically into two halves regenerate into two individuals? Complete the given figure D and E by indicating the regenerated regions.
Yes, shaded part in Figures D and E represent the regenerated halves.
From the internet, gather information about the number of chromosomes present in five animals and five plants.
Correlate the number of chromosomes 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.
(a) No, there is no relationship between size of an organism and its chromosome number.
(b) No, the process of reproduction is not dependent on the number of chromosomes. It depends on various factors like availability of nutrients, water, conductive environment and suitable mate.
(c) Yes, the major component of chromosome is DNA. If there are more chromosomes in a cell, the quantity of DNA will also be more.
In a tobacco plant, a male gamete has twenty-four chromosomes.
What is the number of chromosomes in a female gamete?
What is the number of chromosomes in the zygote?
Number of chromosomes in a female gamete is 24.
Number of chromosomes in zygote is 48.
Why fertilisation cannot take place in flowers, if pollination does not occur?
Fertilisation requires both male and female gametes. This can happen only when pollen grains are transferred to the stigma through any means of pollination. Hence, fertilization cannot take place in flowers if pollination does not occur.
Is the chromosome number of a zygote, an embryonal cell and an adult of a particular organism always constant?
How is the constancy maintained in these three stages?
Yes, the chromosome number of a zygote, an embryonal cell and an adult of a particular organism is always constant.
The constancy is maintained because cells in all these three structural phases undergo only mitotic divisions.
Where is the zygote located in a flower after fertilization?
After fertilization, zygote is located, inside the ovule present inside the ovary.
Reproduction is linked to stability of population, of a species.
Justify the statement.
Every species on Earth has to constantly struggle for its survival. The natural cycle of birth and death, natural predators and vagaries of nature will continue to remove a large section of population of a particular species. So, living organisms reproduce to replenish the lost section of their population. Thus, reproduction helps in providing stability to the population of a species by producing new individuals that resembles their parents.
How are general growth and sexual maturation different from each other?
General growth refers to the growth, where body parts become larger. Examples: Increase in height, weight gain, changes in shape and size of the body.
Sexual maturation: These are certain changes that occur when one attains a certain age. In human beings, this starts at an early age, teenage years. These changes are signs of one gaining more sexual maturity like the ability to reproduce. Examples: Cracking of voice, new hair patterns, development of breast in females etc.
Trace the path of sperms during ejaculation and mention the gland and their functions associated with the male reproductive system.
Sperms come out from testes into the vas deferens, and then passes through urethra before ejaculation.
The secretion from seminal vesicles adds fluid content to the semen, which lubricates the sperms and provides a fluid medium for easy transport of sperms.
The prostate gland makes the medium of semen alkaline.
What changes are observed in the uterus if fertilisation does not occur?
The thick and spongy lining of the uterus slowly breaks and comes out along with blood, mucus, and the discarded egg.
What changes are observed in the uterus subsequent to implantation of young embryo?
Once the zygote is implanted in a uterine wall, the uterine wall thickens. So that it gives support to the growing embryo. It is richly supplied with blood to provide nourishment to the embryo. A special tissue called placenta develops and it connects the embryo to the uterine wall to provide nutrients and oxygen to the embryo.
What are the benefits of using mechanical barriers during sexual act?
Benefits of using mechanical barriers:
a) It prevents sperms from reaching the egg. Thus, it helps avoiding unwanted pregnancy.
b) A condom on a penis or similar covering worn in a vagina, and used as mechanical barriers also prevents transfer of sexually transmitted diseases.
In the given figure label the parts and mention their functions:
(a) Production of egg
(b) Site of fertilisation
(c) Site of implantation
(d) Entry of the sperms
a) Ovary (production of egg)
b) Oviduct (site of fertilisation)
c) Uterus (site of implantation)
d) Vagina (entry of the sperms)
What would be the ratio of chromosome number between an egg and its zygote? How is the sperm genetically different from the egg?
The ratio is 1:2. Sperms are genetically different from an egg in a way that it contains either X or Y chromosome whereas an egg always carries X chromosome.
Why are budding, fragmentation and regeneration considered as asexual types of reproduction?
With a neat diagram explain the process of regeneration in a Planarian.
Budding, fragmentation and regeneration are considered as asexual types of reproduction because only one parent carries out the process of reproduction and gamete formation does not happen during this mode of reproduction.
The following diagram shows the regeneration in a Planarian:
When the body of a Planarian is cut off into several parts, each part regenerates its complimentary part to develop a new individual.
Write two points of difference between asexual and sexual types of reproduction. Describe why variations are observed in the offspring formed by sexual reproduction.
Involves only one parent
Often involves two parents
Gametes are not produced
Gametes are produced
No fertilisation and zygote formation
Fertilisaton and zygote formation is observed.
Reason for variations in offspring produced by sexual reproduction:
During sexual reproduction, two sets of genes are contributed by different parents. This brings different sets of characters in the offspring.
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 an ovule.
Pollination: Transfer of pollen grains from anther to stigma is termed as pollination. It is a physical process in which pollen grains move due to certain physical factors such as air, water, birds or some insects.
Fertilisation: Fusion of male and female gametes is termed fertilization. The site of fertilisation is ovule. The product of fertilisation is zygote.
The following diagram shows fertilisation in a plant:
Distinguish between a gamete and zygote.
Explain their roles in sexual reproduction.
Gamete: It is a sex or germ cell that takes part in fertilization. There are two types of gametes male and female.
Zygote: The fertilisation of male and female gametes leads to the formation of zygotes. It is the first cell of a new generation.
Role of gamete in sexual reproduction:
Gamete formation results in halving of number of chromosomes. This is necessary to maintain the number of chromosomes in an organism that reproduces sexually.
Role of zygote in sexual reproduction:
Zygote formation makes the number of chromosome equal to the somatic cells. Further, it is the zygote which undergoes mitosis to develop into an embryo and subsequently into a new individual.
Draw diagram of a flower and label the four whorls.
Write the names of gamete producing organs in a flower.
Male gamete forming part: anther/stamen
Female gamete forming part: pistil/ovary/ovule
What is placenta? Mention its role during pregnancy?
Placenta is a tissue that connects embryo to the uterine wall. It is a disc-like structure which 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. Placenta works as a channel between the mother and the embryo and provides nutrients and oxygen to the embryo. This also provides a large surface from mother to the embryo and waste products from embryo to mother.
What are various ways to avoid pregnancy? Elaborate any one method.
The various ways to avoid pregnancy are:
(i) Mechanical barriers
(ii) Drugs (as pills)
(iii) Loop or copper T
(iv) Surgical method
Copper-T: Copper-T is in the shape of ‘T’ and is made of copper. Copper-T makes a barrier at the opening of the fallopian tubes in the uterus and thus prevents sperms from entering the fallopian tubes and prevents fertilization.
How does fertilisation take place? Fertilisation occurs once in a month. Comment.
During the ovulation cycle, one egg is released by either of the two ovaries and it reaches the fallopian tube. During sexual intercourse, sperms enter through the vaginal passage. Sperms are highly active and mobile and thus move up through cervix into the uterus. From there, it reaches the fallopian tube. Millions of sperms are released into the vagina at one time, but only one sperm encounters the egg in the fallopian tube and fertilization takes place.
Since only one egg is released in a single ovulation cycle and ovulation cycle happens once in a month, therefore, fertilisation occurs once in a month.
Reproduction is essentially a phenomenon that is not for survival of an individual but for the stability of a species. Justify.
All organisms on Earth need energy for survival and growth. This energy is obtained from life processes such as nutrition and respiration. Compared to these life processes, reproduction needs a lot of energy. Reproduction helps in the production of new individuals of its own kind. During reproduction, genetic material is transferred from one generation to the next through DNA copying, with high constancy and considerable variations. Variations are important for maintaining features that allow an organism to survive in the changing environment. Therefore, reproduction is essential for the stability of a species and for the survival of an individual.
Describe sexually transmitted diseases and mention different ways to prevent them.
A disease that can be transmitted through sexual contact is called sexually transmitted disease or STD. This includes bacterial infections such as gonorrhoea and syphilis and viral infections like HIV.
Some of the ways to prevent STDs are as follows:
• Being faithful to one’s life partner.
• Avoiding sexual contact with unknown person.
• Using condom during sexual intercourse.
• Maintaining personal hygiene.