Reproduction in Organisms Important Questions for CBSE Class 12 Biology Reproduction
1.The period between birth and natural death of an organism is called its lifespan. It can vary from less than a day to more than 400 yrs.
Whatever be the lifespan, death of every individual organism is a certainty,
i.e. no individual is immortal, except single-celled organisms.
Lifespan of some organisms are given in the following table:
2.Reproduction is a biological process of continuity of a race in which the grown up individuals give rise to offsprings similar to them.
It performs the following functions:
- Enables continuity of the species.
- Maintains life on the earth.
- Creates variations among population.
The mechanism to produce offsprings shows large variations, depending on organisms habitat, its internal physiology and several other factors.
Based on the participation of one or two organisms, reproduction can be of following two types:
(i)Asexual reproduction (ii) Sexual reproduction
3.Asexual reproduction A single parent is capable of producing offsprings. Thus, the offsprings are genetically and morphologically identical to one another and to their parent. These are often referred to as clone. The unit of reproduction is commonly formed from the somatic cells of the parent. Meiosis does not occur in asexual reproduction.
Asexual reproduction is common among single-celled organisms and in plants and animals with simple organisations. Cell division in itself is a mode of reproduction in protists, e.g. bacteria and monerans, e.g. Amoeba (the parent cell divide into two to give rise to new individuals).
Types of asexual reproduction are as given below:
I.Fission can be further classified as:
(i)Binary fission The body of an individual divides into two equal halves.
It can be following types:
(a)Simple binary fission When division occurs in any plane but it is always right angle to the elongated dividing nucleus, e.g.
(b)Longitudinal binary fission When division occurs along the longitudinal axis, e.g. Euglena, Vorticella.
(c)Oblique binary fission When division occurs at an angle to the transverse axis, e.g. Ceratium, Gonyaulax.
(d)Transverse binary fission When division occurs along the transverse axis of the individual, e.g. Paramecium, diatoms, bacteria,Planaria.
(ii)Multiple fission The division of the parent body into many daughter organisms, e.g. Amoeba,Plasmodium, Monocystis (all Protozoa).
II.Budding, (torulation) an outgrowth or bud develops, grows, constricts at the base and separates from the parent body, e.g. yeast and Hydra. The complex budded condition is called torala stage.
III.Sporulation occurs by tiny, single-celled, thin-walled spores that are extremely resistant to environmental extremes. The spores form new individuals. It commonly occurs in Monera, Protista, Fungi and Algae.
Spores formed can be of following main types:
(i)Pseudopodio spore (with fine pseudopodia) – Amoeba
(ii)Zoospores (motile with flagellated) – Chlamydomonas and Ulothrix
(iii)Conidia (non-motile) – Penicillium
(iv)Sporangiospores (non-motile) – Rhizopus
(v) Gemmules (internal buds) – Sponges
IV.Fragmentation occurs by breaking of the parent body into two or more parts, each of which grows to form an independent individual, e.g. algae like Spirogyra and bryophytes such as Marchantia, Riccia.
V.Regeneration is a type of asexual reproduction in which the missing part of the organism is repaired by the proliferation of cells, e.g. Hydra, planaria and sponges.
VI.Vegetative propagation is the formation of a new plants from vegetative parts like root, stem, leaf, etc., naturally, e.g. water hyacinth (scourage of the water bodies or Terror of Bengal) propagates very quickly by vegetative mode and drains out dissolved 02 from water bodies. Some artificial methods of vegetative propagation are also developed by the farmers like cutting, layering, grafting, etc.
The units of vegetative propagation such as runner, rhizome, sucker, tuber, offset, bulb all have capability to give rise to new offsprings. These structures are known as vegetative propagules.
Previous Year Examination Questions
1 Mark Questions
1.Name the vegetative propagules in the following:
(i)Agave (ii) Bryophyllum [Ail India 2014 C]
Ans.The vegetative propagules are as follow:
(i) In Agave – Bulbil
(ii) In Bryophyllum – Leaf buds/adventitious buds
2.Write the name of the organism that is referred to as ‘Terror of Bengal’.
[Delhi 2014]
Ans.Water hyacinth is referred to as the ‘Terror of Bengal’.
3.Give one example each of a fungus which reproduces by
(i) budding (ii) conidia [Delhi 2014 C]
Ans. Fungus that reproduces by
(i) budding – Yeast
(ii) conidia – Penicillium
4.Give one example of a plant that reproduces by
(i) runner (ii) offset [Delhi 2014 C]
Ans. Below is the example of a plant that reproduces by
(i) runner – Oxalis
(ii) offset – Pistia
5.Name an organism, where cell division in itself is a mode of reproduction.
[All India 2013; Foreign 2010]
Ans. In unicellular organisms like Amoeba, bacteria, etc., cell division in itself is a mode of reproduction
6.Name an alga that reproduces asexually through zoospores. Why are these reproductive units so called?[All India 2013]
Ans.Chlamydomonas is an alga that reproduces asexually through zoospores.Due to mobility
(motile), these are referred to as zoospore.
7.Which one of the following statements is true for yeast?
(i)The cell divides by binary fission. One of them develops into a bud.
(ii)The cell divides unequally. The smaller cell develops into a bud.
(iii)The cell produces conidia which develop into a bud. [Delhi 2013 C]
Ans.Statement (ii) is true for yeast. The cell divides unequally. The smaller cell develops into a bud
8.How does Penicillium reproduce asexually? [Delhi 2013]
Ans. Penicillium reproduces asexually by conidia formation, which is quite commdn in fungi
9.Offsprings produced by asexual reproduction are called clones. Justify giving two reasons. [hots; ah India 2010]
Ans. Offsprings produced by asexual reproduction are called clones, because
(i)they are morphologically similar to their parent.
(ii) they have same genetic composition as their parent.
10.Mention a characteristic feature and a function of zoospores in some algae. [All India 2010]
Ans.(i) Characteristic feature Zoospores are motile, microscopic and thin-walled
(ii)Function Zoospores are asexual reproductive structures, which help in multiplication of algae
11.Identify this reproductive structure and name the organism they are being released from. [Delhi 2010]
Ans.The reproductive structure in the figure are zoospores. These are released by Chlamydomonas for asexual reproduction.
12.Name the organism and the mode of reproduction represented in the diagram given below.[All India 2010]
Ans.Organism Yeast
Mode of reproduction Asexual by budding.
2 Marks Question
13.Banana crop is produced by farmers without sowing of seeds. Explain how the plant is propagated? [All India 2014 C]
Ans.Banana crop is cultivated by farmers through vegetative propagation.
For this purpose, a rhizome of banana is taken instead of a seed. Each piece from a rhizome is able to give rise to a new plant
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