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Reproduction in Organisms

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Biology

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Biology

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Class 10 Class 12

Give an example of an organism that enters 'diapause' and why.


Zooplankton under unfavorable enters ‘diapause’ which is a state of suspended development.

 

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In vitro clonal propagation in plants is characterised by

  • PCR and RAPD

  • Northern blotting

  • Electrophoresis and HPLC

  • Microscopy


A.

PCR and RAPD

RAPD stand for Random Amplified Polymorphic DNA. It is a type of PCR reaction, but the segments of DNA that are amplified are random. Often, PCR is used to amplify a known DNA sequence. 

RAPD stand for Random Amplified Polymorphic DNA. It is a type of PCR reaction, but the segments of DNA that are amplified are random. Often, PCR is used to amplify a known DNA sequence. 

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Monoecious plant of Chara shows occurrence of 

  • antheridiophore and archengoniophore on the same point

  • stamen and carpel on the same plant

  • upper antheridium and lower oogonium on the same plant

  • upper oogonium and lower antheridium on the same plant


D.

upper oogonium and lower antheridium on the same plant

Monoecious or homothallic, a condition in Chara (green algae) is used to denote upper oogonium and lower antheridium on the same plant. The organisms, which possess both the reproductive organs are bisexual. Unisexual condition represents both male or female organs in the same organism.

Monoecious or homothallic, a condition in Chara (green algae) is used to denote upper oogonium and lower antheridium on the same plant. The organisms, which possess both the reproductive organs are bisexual. Unisexual condition represents both male or female organs in the same organism.

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Male gametes are flagellated in

  • Polysiphonia

  • Anabaena

  • Ectocarpus

  • Spirogyra


C.

Ectocarpus

Male gametes are flagellated in Ectocarpus belonging to Phaeophyceae. The flagella of male and gamete plays an important role in establishing initial sexual contact with the female gamete. However, in Ectocarpus the female gamete too is flagellated but is different in structure. 
In Polysiphonia (Rhodophyceae) flagellated gametes are not observed, in Anabaena sexual reproduction through gametes is absent while in Spirogya sexual reproduction takes place by conjugation wherein male gamete passes through a tube to the adjacent filament. The male gametes here are non-flagellated and show amoeboid movement. 

Male gametes are flagellated in Ectocarpus belonging to Phaeophyceae. The flagella of male and gamete plays an important role in establishing initial sexual contact with the female gamete. However, in Ectocarpus the female gamete too is flagellated but is different in structure. 
In Polysiphonia (Rhodophyceae) flagellated gametes are not observed, in Anabaena sexual reproduction through gametes is absent while in Spirogya sexual reproduction takes place by conjugation wherein male gamete passes through a tube to the adjacent filament. The male gametes here are non-flagellated and show amoeboid movement. 

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Which of the following pairs is not correctly matched?

  • Mode of reproduction                               Example
    Offset                                                        Water hyacinth

  • Mode of reproduction                               Example
    Rhizome                                                     Banana
  • Mode of reproduction                                       Example 
    Binary fission                                                      Sargassum 
  • Mode of reproduction                                    Example
    Conidia                                                            Penicillium


C.

Mode of reproduction                                       Example 
Binary fission                                                      Sargassum 

The plant body Sargassum is a diploid sporophyte.  It does not multiply asexually by means of spores. Instead it reproduce by vegetative means, i.e. fragmentation which is the only known method of vegetative reproduction in the free floating species of Sargassum. 

The plant body Sargassum is a diploid sporophyte.  It does not multiply asexually by means of spores. Instead it reproduce by vegetative means, i.e. fragmentation which is the only known method of vegetative reproduction in the free floating species of Sargassum. 

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A flower of tomato plant following the process of sexual reproduction produces 240 viable seeds.

Answer the following questions giving reasons:

(a) What is the minimum number of pollen grains that must have been involved in the pollination of its pistil? 

(b) What would have been the minimum number of ovules present in the ovary?

(c) How many megaspore mother cells were involved?

(d) What is the minimum number of microspore mother cells involved in the above case?

(e) How many male gametes were involved in this case?


The number of viable seeds produced by the tomato plant through sexual reproduction = 240


(a) The minimum number of pollen grains that must have been involved in the pollination of its pistil are 240 because each pollen grain contains two male gametes. Out of these two gametes, one fuses with polar nuclei and forms endosperm, while, the other male gamete fuses with the egg cell to form the zygote that eventually give rise to seeds. Therefore, in order to obtain 240 seeds, number of pollen grains needed would be 240.

(b) The minimum number of ovules involved in this process would be 240, as the number of viable seeds is 240. After fertilisation, the ovary turns into fruit and the ovules turn into seeds. Therefore, the number of ovules corresponds to the number of seeds formed.

(c) During the process of gametogenesis, 240 megaspore mother cells are involved as only one megaspore of the tetrad becomes functional and develops further and the rest three megaspores get degenerated.

(d) In the above case, 60 microspore mother cells must have undergone reduction division prior to dehiscence of anther, as each microspore mother cell would give rise to 4 microspores. Since 1 microspore mother cell would produce 4 microspores, therefore, to obtain 240 microspores, there must be 60 microspore mother cells.

(e) The number of male gametes involved in seed formation would be 240 as each male gamete will fuse with one egg nuclei to form zygote, which will further give rise to the seed.

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