CBSE Class 10 Science How Do Organisms Reproduce VBQs Set 04

Do Organisms Create Exact Copies of Themselves?

Question. Newly formed DNA copies may not be identical at times. Give one reason.
Answer: No biochemical process is absolutely reliable. Therefore, during the process of DNA copying, some variations are likely to occur, leading to newly formed DNA copies that are not identical to the original.

Question. When a cell reproduces, what happens to its DNA?
Answer: When a cell reproduces, it creates a copy of its DNA through biochemical reactions. This is followed by the division of the cell into two, so that each daughter cell receives a copy of the DNA along with the necessary cellular apparatus.

Question. What is DNA?
Answer: DNA stands for Deoxyribonucleic Acid. It is the genetic material found in the chromosomes of the cell nucleus and carries information for the inheritance of features from parents to the next generation.

Question. Name the life process of an organism that helps in the growth of its population.
Answer: Reproduction.

Question. Reproduction is one of the most important characteristic of living beings. Give three reasons in support of the statement.
Answer: 1. It ensures the continuity of a species from one generation to the next.
2. It helps in increasing the population of a species.
3. It introduces variations, which are essential for the process of evolution.

Question. Define reproduction. How does it help in providing stability to the population of species?
Answer: Reproduction is the biological process by which existing organisms produce new individuals of the same species. It provides stability to the population of a species by replacing individuals that die due to age, disease, or predation, thereby maintaining the birth-to-death ratio and ensuring the survival of the species in a particular niche.

Question. What is DNA copying? State its importance.
Answer: DNA copying is the process of creating a duplicate copy of the genetic material (DNA) before cell division.
Importance:
1. It ensures that each daughter cell receives the same set of genetic instructions as the parent cell.
2. It carries the blueprints for body design and functions from parents to offspring.
3. It allows for minor variations during copying, which drives evolution.

Question. What is the effect of DNA copying, which is not perfectly accurate, on the reproduction process? How does the amount of DNA remain constant through each new generation is a combination of DNA copies of two individuals?
Answer: Inaccurate DNA copying leads to variations in the offspring. These variations can be beneficial, neutral, or harmful, and they form the basis of evolution.
In sexual reproduction, the amount of DNA remains constant because gametes (sperm and egg) are produced through a special type of cell division called meiosis, which reduces the DNA content to half. When the two haploid gametes fuse during fertilization, the diploid (original) amount of DNA is restored in the zygote.

Question. (a) What is reproduction? List its two types. (b) How are the modes of reproduction different in unicellular and multicellular organisms?
Answer: (a) Reproduction is the biological process of producing offspring of the same species. Its two types are Asexual Reproduction and Sexual Reproduction.
(b) In unicellular organisms, reproduction usually occurs by simple cell division (fission), where the entire parent organism divides to form two or more new individuals. In multicellular organisms, reproduction is more complex. While some simple multicellular organisms can reproduce asexually (budding, fragmentation), most use specialized reproductive cells and organs for sexual reproduction to ensure genetic diversity.

Modes of Reproduction Used by Single Organisms

Question. Assertion (A) : Amoeba always produces two daughter amoebae while Plasmodium divides into many daughter cells.
Reason (R) : Amoeba undergoes binary fission while Plasmodium undergoes multiple fission.
(a) Both (A) and (R) are true and (R) is the correct explanation of the assertion (A).
(b) Both (A) and (R) are true, but (R) is not the correct explanation of the assertion (A).
(c) (A) is true, but (R) is false.
(d) (A) is false, but (R) is true.

Answer: (a) Both (A) and (R) are true and (R) is the correct explanation of the assertion (A).

Question. Define fragmentation.
Answer: Fragmentation is a mode of asexual reproduction in which a simple multicellular organism (like Spirogyra) upon maturation breaks up into smaller pieces or fragments, and each fragment then grows into a new individual.

Question. Name the method by which Spirogyra reproduces under favourable conditions. Is this method sexual or asexual?
Answer: Spirogyra reproduces by fragmentation. This is an asexual method of reproduction.

Question. How does Plasmodium reproduce? Is this method sexual or asexual?
Answer: Plasmodium reproduces by multiple fission. This is an asexual method of reproduction.

Question. Name the part of Bryophyllum where the buds are produced for vegetative propagation.
Answer: In the notches along the leaf margins.

Question. What happens when a mature Spirogyra filament attains considerable length?
Answer: When a mature Spirogyra filament attains a considerable length, it breaks up into smaller fragments, and each fragment grows into a new complete filament.

Question. Name the method by which Hydra reproduces. Is this method sexual or asexual?
Answer: Hydra reproduces by budding (and also by regeneration). Budding is an asexual method of reproduction.

Question. Name two simple organisms having the ability of regeneration.
Answer: Hydra and Planaria.

Question. Name the causative agent of the disease ‘‘Kala-azar’’ and its mode of asexual reproduction.
Answer: The causative agent is Leishmania. It reproduces by binary fission which occurs in a definite orientation relative to its whip-like structure.

Question. (a) Name the reproductive and non-reproductive parts of bread mould (Rhizopus). (b) List any two advantages of vegetative propagation.
Answer: (a) Reproductive parts: Sporangia (contain spores). Non-reproductive parts: Hyphae (thread-like structures).
(b) 1. Plants can bear flowers and fruits much earlier than those produced from seeds.
2. It allows for the propagation of plants that have lost the capacity to produce seeds, such as banana, jasmine, and orange.

Question. After examining a prepared slide under the high power of a compound microscope, a student concludes that the given slide shows the various stages of binary fission in a unicellular organism. Write two observations on the basis of which such a conclusion may be drawn.
Answer: 1. The nucleus is seen elongated and dividing into two parts.
2. A constriction or furrow appears in the middle of the cytoplasm, indicating its division into two daughter cells.

Question. Define multiple fission. Give its one example.
Answer: Multiple fission is a mode of asexual reproduction in which a single parent cell divides into many daughter cells simultaneously. Example: Plasmodium.

Question. Write two differences between binary fission and multiple fission in a tabular form.
Answer:

Question. List four modes of asexual reproduction other than fission in the living organisms.
Answer: 1. Budding
2. Fragmentation
3. Regeneration
4. Spore formation

Question. List four advantages of vegetative propagation.
Answer: 1. Early flowering and fruiting compared to seed-grown plants.
2. Propagation of seedless plants (e.g., banana).
3. Offspring are genetically identical to the parent, preserving desired traits.
4. It is a faster and cheaper method for growing large numbers of plants.

Question. How do Plasmodium and Leishmania reproduce? Write one difference in their mode of reproduction.
Answer: Both reproduce by fission. Plasmodium undergoes multiple fission, producing many daughter cells at once. Leishmania undergoes binary fission, where the cell divides into two in a definite longitudinal plane.

Question. What is vegetative propagation? List with brief explanation three advantages of practising this process for growing some types of plants. Select two plants from the following which are grown by this process : Banana, Wheat, Mustard, Jasmine, Gram
Answer: Vegetative propagation is an asexual method where new plants are grown from vegetative parts like roots, stems, or leaves of the parent plant.
Advantages:
1. Faster growth: Plants produced reach maturity quicker.
2. Genetic consistency: Offspring are clones of the parent, ensuring uniform quality.
3. Seedless propagation: Essential for plants that cannot produce viable seeds.
Selected plants: Banana and Jasmine.

Question. What happens when (a) accidently, Planaria gets cut into many pieces (b) Bryophyllum leaf falls on the wet soil (c) on maturation sporangia of Rhizopus bursts?
Answer: (a) Each piece of Planaria regenerates the missing parts and grows into a complete new individual.
(b) The buds present in the notches of the Bryophyllum leaf margin develop into tiny plantlets which root in the soil.
(c) Thousands of tiny spores are released into the air, which can grow into new Rhizopus colonies on reaching a suitable moist organic surface.

Question. Describe reproduction by spores in Rhizopus.
Answer: Rhizopus produces spores in structures called sporangia located at the tips of specialized hyphae. When the sporangia mature, they burst, releasing large numbers of thick-walled spores. These spores are light and dispersed by air. On landing on a moist, warm surface with food (like bread), the spores germinate to form a new fungal mycelium.

Question. What is vegetative propagation? State two advantages and two disadvantages of this method.
Answer: Definition: Mode of asexual reproduction where new plants are produced from vegetative parts like stem, root or leaf.
Advantages: 1. It is a rapid method. 2. Desirable characteristics of the parent are maintained.
Disadvantages: 1. No genetic variation, leading to low adaptability. 2. Diseases present in the parent plant are easily transmitted to the offspring.

Question. What is multiple fission? How does it occur in an organism? Explain briefly. Name one organism which exhibits this type of reproduction.
Answer: Multiple fission is the simultaneous division of a single-celled organism into many daughter cells. In Plasmodium, the nucleus of the parent cell divides repeatedly inside a protective cyst to form many small nuclei. Each nucleus gets surrounded by cytoplasm and a cell membrane. When conditions are favourable, the cyst bursts, releasing many daughter cells. Example: Plasmodium.

Question. Explain the term “regeneration” as used in relation to reproduction of organisms. Describe briefly how regeneration is carried out in multicellular organisms like Hydra.
Answer: Regeneration is the process of getting back a full organism from its body parts. If an organism is accidentally cut into pieces, specialized regenerative cells proliferate and undergo changes to form various cell types and tissues in a controlled sequence (development). In Hydra, if it is cut, these cells reorganize and grow to form a new head and body for each piece.

Question. In the context of reproduction of species state the main difference between fission and fragmentation. Also give one example of each.
Answer: Fission occurs in unicellular organisms where a single cell divides into two or more daughter cells (Example: Amoeba). Fragmentation occurs in simple multicellular organisms where the body simply breaks into fragments upon maturation, each growing into a new individual (Example: Spirogyra).

Question. What happens when (a) Planaria gets cut into two pieces (b) a mature Spirogyra filament attains considerable length (c) on maturation sporangia burst?
Answer: (a) Both pieces will regenerate into two complete Planaria.
(b) It undergoes fragmentation, breaking into smaller pieces that grow into new filaments.
(c) Released spores germinate under favourable conditions to form new fungal hyphae.

Question. (a) Name the following: (i) Thread like non-reproductive structures present in Rhizopus. (ii) ‘Blobs’ that develop at the tips of the non-reproductive threads in Rhizopus. (b) Explain how these structures protect themselves and what is the function of the structures released from the ‘blobs’ in Rhizopus.
Answer: (a) (i) Hyphae. (ii) Sporangia.
(b) The spores inside sporangia are protected by thick walls that help them survive unfavourable conditions. The function of the released spores is dispersal and germination to form new Rhizopus individuals when they land on a suitable substrate.

Question. Explain the process of regeneration in Planaria. How is this process different from reproduction?
Answer: Regeneration in Planaria occurs when its body is cut into pieces; specialized cells at the cut ends divide rapidly to form a mass of cells that differentiate into different tissues to recreate the whole organism. It is different from normal reproduction because organisms do not usually depend on being cut up to reproduce; it is more of an accidental repair mechanism.

Question. List any two modes of asexual reproduction in animals. Under which mode of reproduction is vegetative propagation placed and why? List two advantages of vegetative propagation.
Answer: Modes: 1. Budding (in Hydra). 2. Regeneration (in Planaria).
Vegetative propagation is placed under asexual reproduction because it involves only one parent and does not involve the fusion of gametes.
Advantages: 1. Preserves traits of the parent. 2. Allows for fast multiplication.

Question. What is vegetative propagation? List its two advantages. Select two plants raised by this method from the list given below: Wheat, Tomato, Rose, Pea, Gram, Corn, Banana
Answer: Definition: Growth of new plants from vegetative parts (root, stem, leaf).
Advantages: 1. Propagation of seedless plants. 2. Faster maturation.
Selected plants: Rose and Banana.

Question. (i) Name and explain the two modes of asexual reproduction observed in Hydra. (ii) What is vegetative propagation? List two advantages of using this technique.
Answer: (i) 1. Budding: A small bud develops as an outgrowth, grows into a tiny individual, and detaches. 2. Regeneration: If cut into pieces, each piece can grow into a complete Hydra.
(ii) Vegetative propagation is growing plants from parts like stem or root. Advantages: 1. Rapid propagation. 2. Offspring are genetically identical to the parent.

Question. (a) State the name of the organism in which binary fission takes place in a definite orientation. Also name the disease caused by this organism. (b) List any two advantages of producing plants through vegetative propagation. (c) Explain the process of budding in Hydra. OR (c) What happens when : (I) a Spirogyra filament matures and attains a considerable length, and (II) a sporangia in Rhizopus bursts on maturation ?
Answer: (a) Leishmania; it causes Kala-azar.
(b) 1. Early yield of flowers and fruits. 2. Genetic clones are produced.
(c) Budding in Hydra: Repeated cell division at one site produces a bud. It develops a mouth and tentacles while attached, then detaches.
OR (c) (I) It breaks into fragments that grow into new filaments. (II) Spores are released which germinate into new fungal colonies.

Question. (a) Name the mode of reproduction of the following organisms and state the important feature of each mode : (i) Planaria (ii) Hydra (iii) Rhizopus (b) We can develop new plants from the leaves of Bryophyllum. Comment. (c) List two advantages of vegetative propagation over other modes of reproduction.
Answer: (a) (i) Planaria: Regeneration (missing parts regrow). (ii) Hydra: Budding (outgrowth grows and detaches). (iii) Rhizopus: Spore formation (tiny spores are released from sporangia).
(b) Bryophyllum leaves have adventitious buds in their margins. When a leaf falls on moist soil, these buds grow into new plantlets, which is a unique form of natural vegetative propagation.
(c) 1. Enables propagation of seedless varieties. 2. Ensures the exact replica of the parent plant's characteristics.