Biology

Reproduction In Organisms- Competency-Based Questions

Class 12 Biology Competency-Based Questions Chapter 1

1 Mark Questions

1. Which of the following populations definitely has/have a greater chance of survival in a stable habitat?

P) Those with greater variation.

Q) Those with a greater number of individuals expressing the dominant trait.

R) Those living in environmental conditions that provide an advantage to the species.

A. Only Q

B. Only R

C. Only P and R

D. All – P, Q, and R

Ans: C. Only P and R

2. Which of the following statements is TRUE about the gamete mother cells in human beings?

A. They are diploid and undergo mitotic divisions.

B. They are diploid and undergo meiotic divisions.

C. They are haploid and undergo meiotic divisions.

D. They are haploid and do not undergo cell division.

Ans: B. They are diploid and undergo meiotic divisions.

3. Cultivated potato varieties are generally tetraploid (4n) with 48 chromosomes. These potatoes reproduce through eye buds that sprout or “germinate”. What is the chromosome number in the cells of the eye buds that help in reproduction?

A. 6

B. 12

C. 24

D. 48

Ans: D. 48

4. Which of the following is/are always TRUE for sexually reproducing organisms?

X) Fertilisation involves the fusion of the male and the female gamete.

Y) Both the male and female gametes move towards each other.

A. only X

B. only Y

C. both X and Y

D. neither X nor Y

Ans: A. only X

5. Two statements are given – one labelled Assertion (A) and the other labelled Reason (R).

Assertion (A): Organisms like Amoeba produce multiple minute amoebae through sporulation.

Reason (R): Sporulation involves meiotic division to produce multiple cells from one cell.

Which of the following is CORRECT?

A. Both A and R are true, but R is not the correct explanation of the assertion.

B. Both A and R are true, and R is the correct explanation of the assertion.

C. A is true, but R is false.

D. A is false, but R is true.

Ans: C. A is true, but R is false.

6. Listed below are some phases and events from the life of living organisms.

P) Juvenile/Vegetative

Q) Gametogenesis

R) Fragmentation

Which among the above are usually found in a plant that undergoes only sexual reproduction?

A. Only P

B. Only Q

C. Only P and Q

D. All- P, Q, and R

Ans: C. Only P and Q

7. Given below is a list of some statements about reproduction in organisms.

P) Reproduction must involve the fusion of gametes.

Q) Heterogametes can be formed from two parents.

R) Reproduction always creates genetically different offspring.

Which among the above is/are TRUE?

A. Only P

B. Only Q

C. Only P and Q

D. Only P and R

Ans: B. Only Q

9. A meiocyte has a chromosome number of 34. What would be the chromosome number of the gamete formed, and why?

Ans:

The chromosome number of its gamete would be 17.
Meiocytes undergo meiosis, which results in the halving of the chromosome number in the daughter cells.

2 Marks Questions

10. State whether the following statements are TRUE or FALSE and give a reason for each:

(a) The embryo formed through apomixis is haploid because there is no fertilisation.

(b) Parthenocarpy is an asexual method of reproduction.

Ans:

(a) False. – The diploid egg cells do not go through meiosis to form the seeds.
(b) True. The process does not involve fertilisation or fusion of gametes.

11. Cloning is a method of producing offspring that are genetically similar to the parent organisms. Clones are genetically and morphologically exact copies of their parents and are generally created in controlled laboratory conditions. Mention ONE point each of similarity and difference between cloning and asexual reproduction.

Ans:

Similarity: Offspring are genetically and morphologically similar to their parents in both cloning and asexual reproduction.
Difference: asexual reproduction can be natural, while cloning is always a manmade process.

16. Amoeba reproduce through a process called binary fission as shown in the diagram below:

(a) How is this different from mitosis with reference to:

(i) What types of cells were these processes taking place in?

(ii) How is the genetic material divided?

(b) In case of binary fission, are the daughter cells genetically similar to the parent cells? Justify.

Ans:

(a)
- Mitosis occurs in eukaryotic cells while binary fission occurs in prokaryotic cells.
- In binary fission, the genetic material is simply cut into two halves / there is no spindle formation, while in mitosis, spindle formation divides the nuclear material.
(b)
- Yes
- The parental genetic material is divided into two and passed on to the daughter cells formed by binary fission.

3 Marks Questions

8. One of the major advantages of sexual reproduction is that it ensures genetic variation and helps in evolution because of the involvement of two parents. Asexual reproduction, on the other hand, involves only one parent.

(a) Can genetic variation take place in the case of asexual reproduction? Justify.

(b) How is the constancy of chromosomal numbers maintained in both sexual and asexual reproduction?

Ans:

(a) Yes it can happen because of a random mutation.

(b)

In sexual reproduction, gametes are formed by meiotic or reduction division so that gametes have haploid/ half the number of chromosomes. Thus, zygotes have the actual /diploid set.
In asexual reproduction, organisms divide by simple mitosis, and thus the chromosomal number is maintained.

12. The images below show methods of reproduction in bacteria (top) and ferns (bottom) through spore formation:

(a) State TWO points of difference between the two methods shown in the images.

(b) Which of the methods above is more likely to create a genetically variant offspring? Give a reason for your answer.

Ans: (a)

Bacteria	Fern
Spores formed by mitosis	Spores formed by meiosis
Reproduction is asexual.	Reproduction is sexual

(b)

The fern
It involves fertilisation

It is a sexual mode of reproduction

13. Arm autotomy is a phenomenon in starfish where starfish typically shed arms with part of the central disk attached. This arm regenerates into a full starfish.

(a) Can the process of arm autotomy be called reproduction? Give a reason for your answer.

(b) What is the ploidy of the cells and genetic constitution of regenerated starfish as compared to that of the original starfish?

(c) Justify your answer to (b).

Ans:

(a) Yes, it can be called reproduction. Because a new individual is created from an existing one.
(b)
- Ploidy: the regenerated starfish will be diploid
- The genetic constitution of the regenerated starfish is the same as the parent starfish
(c) The process of regeneration does not involve gametes or meiotic division. Hence, the new individual is exactly similar to the parent starfish.

14. Water hyacinth or Eichhornia crassipes is a perennial aquatic plant that is native to the tropical regions of South America. It was introduced in India for its beautiful flowers and leaves. It reproduces sexually as well as asexually. However, it has been found to be depleting the oxygen content in water.

Raghav rears fish in a pond in his farmland. He introduces water hyacinths to beautify his farm.

(a) What can be the possible impact of the water hyacinth on his fish production?

(b) Raghav removes the reproductive parts from the flowers of water hyacinths to control their growth. What will happen to the water hyacinth population?

(c) Raghav’s friend Roshni collects a leaf with a stalk from Raghav’s pond and plants it in the soil in her garden. She notices that the plant does not spread as much as it did in Ragav’s pond. What could be the possible reason for this?

Ans:

(a) The fish will eventually die due to a lack of oxygen.
(b) The water hyacinth population will eventually continue to increase as it will propagate asexually.
(c) Water hyacinth is an aquatic plant and will not be able to propagate asexually due to a lack of water in the soil.

5 Marks Questions

15. Amoebiasis is an infection with Entamoeba histolytica. It is acquired by faecal-oral transmission. Infection is commonly asymptomatic, but symptoms ranging from mild diarrhoea to severe dysentery may occur. Extraintestinal infections include liver abscesses. Such infection by amoeba is treated with drugs like metronidazole.

The mechanism of action of metronidazole occurs through a four-step process where step one is the entry into the organism by diffusion across the cell membranes of anaerobic and aerobic pathogens.

(a) In a case where metronidazole does not work in curing a patient suffering from amoebiasis, what characteristic of the structure of the amoeba could be hindering the action of metronidazole?

(b) The amoeba is able to reproduce through binary fission immediately after infection till it reaches the human stomach. Why does an amoeba not reproduce in the stomach?

(c) Mention TWO characteristics of binary fission that distinguish it from a sexual reproduction process.

(d) Which part of the amoebic cell should the drug attack to control its growth? Justify.

Ans:

(a) Amoeba could be encysted.
(b) Growth and replication of amoeba are impacted by the acidic environment of the stomach.
(c)
- Sexual reproduction involves the fusion of two gametes, while binary fission involves the splitting of one cell into two individuals.
- Sexual reproduction involves gamete formation through meiotic division, while binary fission involves mitotic division only.
(d)
- The nucleus
- It will disrupt mitotic division