Tag: the origin of cells and cell division

Questions Related to the origin of cells and cell division

Transformation of the early reducing atmosphere of the earth into an oxidizing atmosphere was mainly due to the activities of

zoology concept of life theories of the origin of life origin of life the origin of cells and cell division

  1. Aerobic photosynthesizers

  2. Anaerobic heterotrophs

  3. Anaerobic photosynthesizers

  4. Anaerobic chemoheterotrophs

Show answer
Correct Option: A
Explanation:

Cyanobacteria are thought to be the first aerobic photosynthesizers evolved which gradually increased the oxygen portion of atmosphere changing it into oxidising one. The aerobic respiration was thus helpful for the animals to survive.

Thus, the correct answer is option A. 

What is the function of germ pore?

botany modes of reproduction introduction to flower pre fertilization - plants sexual reproduction in flowering plants the origin of cells and cell division

  1. Emergence of radicle

  2. Absorption of water for seed germination

  3. Initiation of pollen tube

  4. All of these

Show answer
Correct Option: C
Explanation:

One or more thin areas present in the exine of pollen grains are known as germ pores. The germ pores are apertures in the exine layer of the pollen grain where the sporopollenin is absent. The germ pore helps in the formation of the pollen tube and the release of the male gametes during fertilisation. There are usually three germ pores in dicots(tricolpate) and one in monocots(monocolpate).

In Casuarina, fertilization occurs by 

botany modes of reproduction introduction to flower pre fertilization - plants sexual reproduction in flowering plants the origin of cells and cell division

  1. Chalazogamy

  2. Mesogamy

  3. Porogamy

  4. Apogamy

Show answer
Correct Option: A
Explanation:
  • Pollen tube eventually reaches the micropyle of an ovule to enter the embryo sac and for this purpose, it may follow one of the following three routes:
  • 1. Porogamy- when the pollen tube enters the ovule through the micropyle. It is common for most of the angiosperms.
  • 2. Mesogamy- when the pollen tube enters through the integuments (Cucumber) or through funiculus (Pistacia).
  • 3. Chalazogamy- when the pollen tube enters through the chalazal tissues. For example, Casuarina.
Hence In Casuarina, fertilization occurs by Chalazogamy.
  • So, the correct answer is 'Chalazogamy'.

Chalazogamy occurs in

botany modes of reproduction introduction to flower pre fertilization - plants sexual reproduction in flowering plants the origin of cells and cell division

  1. Cucurbita

  2. Lily

  3. Populus

  4. Casuarina

Show answer
Correct Option: D
Explanation:
Chalazogamy is the entry of pollen tube in the ovule through chalazal tissue. It occurs in plants like Casuarina. In Cucurbita and Populus, pollen tube enters the ovule through the integuments and this is known as mesogamy. In Lily, pollen tube enters the ovule through the micropyle and this is known as porogamy.
So, the correct answer is A.

The phenomenon of pollen tube entering the ovule laterally through integuments is called

botany modes of reproduction introduction to flower pre fertilization - plants sexual reproduction in flowering plants the origin of cells and cell division

  1. Mesogamy

  2. Aporogamy

  3. Chalazogamy

  4. Vegetative fertilization

Show answer
Correct Option: A
Explanation:
•Mesogamy is the entry of pollen tube through the integuments.
•Aporogamy is the condition in which pollen tube enters the ovule through a path other than micropyle.
•Chalazogamy is the entry of pollen tube through chalaza.
•Vegetative fertilisation is a part of double fertilisation in Angiosperms, in which one of the two male gametes fuses with the diploid secondary nucleus and this results in the formation of a triploid primary endosperm mother cell. It is also known as triple fusion.
So, the correct answer is A.

In Casuarina, fertilization takes place through

botany modes of reproduction introduction to flower pre fertilization - plants sexual reproduction in flowering plants the origin of cells and cell division

  1. Mesogamy

  2. Porogamy

  3. Chalazogamy

  4. Apogamy

Show answer
Correct Option: C
Explanation:
• Mesogamy is the entry of pollen tube in the ovule through the integuments (e.g. Cucurbita) or through funiculus (e.g. Pistacia).
• Porogamy is the entry of pollen tube in the ovule through the micropyle. It occurs in most of the angiosperms.
• Chalazogamy is the entry of pollen tube in the ovule through the chalazal tissues. Example, Casuarina.
• Apogamy is a type of reproduction in which sporophyte develops directly from the gametophyte without the fusion of gametes.
Hence, in Casuarina fertilization takes place through Chalaza, as pollen tube enters the ovule from Chalaza to release the male gametes which will fuse with the egg cell and central cell, resulting in fertilization.
So, the correct answer is C.

In ovule, exostome is

botany modes of reproduction introduction to flower pre fertilization - plants sexual reproduction in flowering plants the origin of cells and cell division

  1. Area just outside the micropyle

  2. Area at the tip of nucellus

  3. Part of micropyle enclosed by inner integument

  4. Part of micropyle enclosed by outer integument

Show answer
Correct Option: D
Explanation:

In an ovule, an opening is formed at the tip of ovule by the integuments called as micropyle. The micropyle acts as a pore for the entry of pollen tube into the ovule for fertilization. In bitegmic ovules, the opening is formed by the inner integument and is called endostome. If the opening is formed by the outer integument it is called exostome. Sometimes it is formed by both the integuments, then it is called as amphistome. 

Thus, the correct answer is option D.

In Angiosperms pollen tube liberate their male gametes into the : -

botany modes of reproduction introduction to flower pre fertilization - plants sexual reproduction in flowering plants the origin of cells and cell division

  1. Central cell

  2. Antipodal cells

  3. Egg cell

  4. Synergids

Show answer
Correct Option: D
Explanation:
The contents of the pollen tube are discharged in the synergid from where the first male gamete is transferred to the egg cell, while the other male gamete moves to the central cell through cytoplasmic current. On reaching of pollen tube inside the embryo sac, the 2 male gametes are discharged through a subterminal pore in the pollen tube. The contents of the pollen tube are discharged in the synergid and the pollen tube does not grow beyond it in the embryo sac. Further, the cytoplasm of the pollen tube is restricted to the chalazal end of this synergid cell.

So, the correct answer is 'Synergids'.

Which one of the following was observed for the first time by Treub?

botany modes of reproduction introduction to flower pre fertilization - plants sexual reproduction in flowering plants the origin of cells and cell division

  1. Entry of pollen tube into the ovule through the micropyle in Casuarina.

  2. Entry of pollen tube into the ovule through the chalaza in Casuarina.

  3. Entry of pollen tube into the ovule through the integuments in Hibiscus.

  4. Entry of pollen tube into the ovule through the chalaza in Hibiscus.

Show answer
Correct Option: B
Explanation:
  • Casuarina equisetifolia is a monoecious, wind-pollinated species that undergoes chalazogamy fertilization.
  • In this type of fertilization, the pollen tube penetrates the ovule through the tissue of the chalaza.
  • It was first observed by Treub in 1981 in Casuarina species.

Number of male gemetes present in pollen tube are 

botany modes of reproduction introduction to flower pre fertilization - plants sexual reproduction in flowering plants the origin of cells and cell division

  1. 1

  2. 2

  3. 3

  4. 4

Show answer
Correct Option: B
Explanation:

The pollen tube consists of two male gametes. One male gamete fertilizes the egg cell placed in between the egg apparatus and forms the diploid oospore/zygote which forms embryo after maturation. While the other male gamete fuses with the two polar nuclei of the central cell and forms the triploid PEN (Primary Endosperm Nucleus) which results in the formation of endosperm after maturation.

So, the pollen tube consists of 2 male gametes for the process of double fertilization to take place in angiosperm plants.
So, the correct answer is '2'.