Reproduction in Organism Important Questions

Reproduction in organisms is diverse from simple to complex living organisms. In unicellular organisms like bacteria and protozoans, cell replication itself is reproduction because the cell is an entire organism. Reproduction may be asexual or sexual. Reproduction is defined as an essential process in which an organism produces young ones (offspring) similar to its body. The daughter organism grows, matures and in turn has young ones. Hence, there is a continuous cycle of birth, growth and death. Reproduction makes possible the continuity of the species. Genetic variation is created and inherited by generations during sexual reproduction. There is a large diversity in the methods of reproduction. The structure, physiology and other factors are responsible for the kind of reproduction.

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Very Short Answer Type Questions (1 Mark)

Ques 1. Name any alga that reproduces asexually by zoospores. Why are these reproductive units so called as your answer?  [CBSE, 2013]

Ans. Asexual reproduction through zoospore formation takes place in an alga called Chlamydomonas. These reproductive units are simply called zoospores because they are motile due to the presence of flagella.

Ques 2. Give an example of a fungus species which reproduces by :

(i) budding (ii) conidia. 

Ans. Budding is seen in the unicellular fungus Yeast (Saccharomyces) Conidia formation is seen in an ascomycetes fungus Penicillium.

Ques 3. Name the vegetative propagules in the following kind of plants : (i) Agave (ii) Bryophyllum 

Ans. (i) Vegetative propagules in Agave are Bulbil (ii) Vegetative propagules in Bryophyllum are Leaf buds or adventitious buds.

Ques 4. Name the vegetative propagules in the following plants (i) Potato, and (ii) Pistia. 

Ans. (i) Axillary buds or eye buds are the vegetative propagules in potatoes (ii) Offsets are the vegetative propagules in Pistia.

Ques 5. Name the type of asexual reproduction where the parent cell does not exist. 

Ans. The types of asexual reproduction where the parent cell ceases to exist are Fission, Binary fission, Longitudinal fission, and multiple fission in Protozoa.

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Short Answer Type Questions (2 Marks)

Ques. 1. Why is a banana plant considered a good example of parthenocarpy? U [Delhi & Outside Delhi Set-I, 2012] Or Why is the banana plant referred to as a parthenocarpic fruit? 

Ans. Parthenocarpy is the phenomenon of fruit formation without seeds. Parthenocarpy can be artificially induced through the growth hormones like gibberellins. As bananas naturally produce fruits without fertilization, it is considered a good example of parthenocarpy.

Ques. 2. Banana fruit is parthenocarpic fruit. Turkey is said to be parthenogenetic. Why? 

Ans. Banana is said to be parthenocarpic as the fruit develops without fertilization from an unfertilized ovary in nature. Turkey is considered to be parthenogenetic as the ovum or the female gamete develops into a new chick without fertilization.

Ques. 4. Which of the following statements is true for Hydra?

(i) It produces asexual gemmules.

(ii) It produces unicellular buds.

(iii) It produces multicellular buds. [CBSE 2013]

Ans. Statement (iii) is correct. Hydra is a multicellular organism. It reproduces asexually by multicellular buds. Asexual gemmules and unicellular buds are absent in hydra.

Ques 5. Coconut palm is a monoecious plant, while date palm is a dioecious plant. Why are they so-called?

Ans. Coconut palm is considered monoecious because both male and female flowers are borne on the same plant. Date palm is considered dioecious because each plant bears either male or female flowers.

Ques 6. Why do algae and fungi undergo a sexual mode of reproduction just before the onset of unfavourable conditions? 

Ans. Organisms belonging to fungi and algae generally switch to a sexual mode of reproduction during unfavourable conditions because asexual reproduction produces a large population of a similar kind that may not survive due to a lack of required resources. Sexual reproduction results in variation in the individuals. This ensures the continuity of species even during adverse conditions.

Ques. 7. Name the units of vegetative propagation in the water hyacinth plant. Explain why it has become the most invasive aquatic weed? 

Ans. Water hyacinth commonly reproduces vegetatively by producing offsets. It propagates at a very fast rate. Hence, it spreads all over the water body within a short period of time. So, it has become the most invasive aquatic weed in India.

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Long Answer Questions (3 Marks)

Ques. 1. Banana crops are cultivated by farmers without sowing seeds. Explain how the plant is propagated so? 

Ans. In banana plants, the seeds are not produced in fruits because they are parthenocarpic. Due to a lack of seeds these plants have to be propagated vegetatively with the help of underground stems or rhizomes which are modified underground stems. The axillary buds that are present at the nodes of the rhizome develop into new plants of bananas called suckers.

Ques. 2. Plants like potatoes and sugarcane do not require seeds for producing new plants in fields. How do they produce new plants in farming? Give two other examples where new plants are produced in the same way as above. 

Ans. Plants like potatoes and sugarcane do not require seeds for producing new plants because they do not produce viable seeds. New plants vegetatively arise from the nodes present on the modified stems of these special plants.

In potatoes, the modified underground stem is called a tuber. It has eyes that give rise to daughter plants. In sugarcane, stem cuttings are planted in soil. When the nodes come in contact with moist soil, they produce roots and new shoots.

Other plants are strawberries and grapes.

Ques. 3. Why is meiosis an essential event in the sexual life cycle of any organism. Give two reasons. 

Ans. Meiosis is an essential event in the sexual cycle of any organism because :

(i) It maintains the fixed number of chromosomes through generations (2n). Haploid gametes (n) are formed as a result of meiosis or reduction division. Diploid (2n) condition is restored during fertilization of the gametes through the zygote formation.

(ii) It increases the chances of genetic diversity and variation in the population due to crossing over between the homologous chromosomes and their random segregation during prophase I.

Ques. 4. Why is a moss plant unable to complete its life cycle in a dry environment? State any two reasons. 

Ans. A moss plant (Bryophyta) can not complete its life cycle in dry conditions because of the following two important reasons :

(i) The moss plant requires water or moist conditions for the imbibition and dehiscence of antheridium (male sex organ) and the opening of the neck canal in the archegonium (female sex organ).

1. ii) Water is required for the flagellated antherozoids (male gametes) to swim toward the female gamete (egg or ovum) for fertilization. It is due to chemotactic movements under the influence of a chemical called maleic acid.

Ques. 5. Why is a whiptail lizard parthenogenetic? 

Ans. The formation and development of eggs into embryos without fertilization is called parthenogenesis or virgin birth. Whiptail lizard is referred to as parthenogenetic because its embryos are developed from eggs without fertilization. The unfertilized embryos give rise to new organisms. Parthenogenesis naturally occurs in some plants and some invertebrate animal species like nematodes, some tardigrades, water fleas, scorpions, aphids, etc.

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Very Long Answer Questions (5 Marks)

Ques 1. What are the differences between sexual and asexual reproduction?

Ans. Here are the differences between sexual and asexual reproduction-

Ques 2. Explain the sexual process of gametogenesis in advanced animals with suitable examples. 

Ans. The sexual process for the formation of gametes, i.e., the production of sperms and ova is called gametogenesis. The process of formation of sperms is known as spermatogenesis and that for ova is known as oogenesis.

Spermatogenesis

• Male hormones like testosterone and Follicle Stimulating Hormones (FSH) are involved in the process.
• Both mitosis and meiosis occur in the seminiferous tubules that help in the formation of spermatozoa or sperms.
• Spermatogonia undergo mitosis to produce diploid (2n) primary spermatocytes.
• The primary spermatocytes (2n)n divide into two secondary spermatocytes (2n) during mitosis I.
• The secondary spermatocytes (2n) further divide by meiosis to form 4 spermatids (n).
• Spermatids (n) differentiate into sperm by spermiogenesis.

Oogenesis

• Female sex hormones like estrogen, follicle-stimulating hormone (FSH), luteinizing hormone (LH) and progesterone are involved in this process.
• Primordial follicles of ovaries (2n) transform into oogonia (2n) to produce diploid primary oocytes (2n).
• Primary oocytes (2n) undergo meiosis to form ootids (2n). These get stopped growth at prophase I of meiosis.
• On reaching puberty, the primary oocytes (2n) undergo meiosis II and form haploid secondary oocytes (n) and a polar body which disintegrates
• The secondary oocytes (n) get arrested at metaphase II of meiosis II.
• If the egg gets fertilized the meiosis completes to form a polar body and an ootid.
• The ovum (egg) matures and the polar bodies disintegrate.

Ques 3. (i) Rose plants but do not produce fruits. On the contrary, tomato plants have small flowers but produce fruits. Comment with a suitable explanation.

(ii) What are the different post-fertilization changes that occur in flowering plants?

Ans. Rose plants cannot produce fruits due to the following reasons:

• The process of fertilization does not take place in a rose flower due to the absence of viable pollen grains.
• The eggs produced in the ovaries are also not functional.
• Pollen and eggs are self-incompatible.
• The ovule is also defective and non-functional.

The post-fertilization changes that occur in flowering plants include

1. Development of Endosperm: The endosperm cell (3n) in the ovule divides to form a triploid endosperm (3n) tissue. The cells store reserve food material that provides nutrition to the future developing embryo.
2. Embryo Development: The zygote divides and redivides to develop into a baby plant.
3. Development of Seed: Ovules get transformed into seeds after fertilization.
4. Fruit Formation: Ovaries get transformed into fruits after fertilization. The wall of the ovary develops into the pericarp of the fruit.

Ques 4: Write about parthenocarpy and plant apomixis. 

Ans. Parthenocarpy: Parthenocarpy is an asexual reproduction that involves only a female parent of the plant. 

• It does not involve fertilization with the male cell. 
• It is the formation of fruits without seeds.
• It may be natural or artificially induced for commercial purposes.
• It is natural in bananas and artificial grapes

Plant apomixis: A sporophyte is a plant phase (diploid) that produces haploid spores. A gametophyte is a plant phase that produces gametes. Apomixis is a type of asexual mode of reproduction in plants that do not involve fertilisation. 

• In some plants, like ferns, the gametophyte produces a sporophyte-like daughter plant with the same ploidy (n) as the gametophyte (n). This is called apogamy. 
• In some plants, a sporophyte produces a gametophyte-like daughter plant with a ploidy level of a sporophyte (2n). This is called apospory.

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