BIO BOTANY [2 Mark Questions]

60 microspore mother cells are involved in providing 240 pollen grains. Because each microspore mother cell undergoes meiosis producing four pollen grains (i.e. 60 × 4 = 240). Each pollen grain produces two male gametes of which one undergoes true fertilization of ovule producing seeds. Other male gamete participate in double fertilization.

Ramu’s wound was healed because of the mitotic division. As a result of mitosis, new cells are produced and damaged tissues were repaired resulting the damaged skin to become normal.

Though born to same parents, siblings show dissimilarities and variation due to the crossing over and recombination of chromosomes during meiosis.

During S phase of interphase, the genetic material of the cell is duplicated. So during metaphase, the chromosome number(chromatid number) will be doubled thus 64 chromosomes (chromatids) will be present.

301 – Pollen mother cells: 301 Pollen mother cells undergo meiosis producing 1204 pollen grains. Because at the end of meiosis, each pollen mother cells produces 4 pollen grains.

Whether a cell is Prokaryote or Eukaryote, while undergoing division, the following events must occur in common.

1. Replication of DNA.
2. Cytokinesis at the end of cell division.

Prokaryotes like bacteria undergo simple form of cell division called binary fission which will get completed with in a hour, whereas Eukaryotic cell division (mitosis) takes nearly 24 hours to get completed. Hence Prokaryotes have shorter cell division time.

Microspores are haploid spores produced from diploid microspores mother cells. Each microspores mother cell (2n) undergoes meiosis producing four Microspores (n). Because a complete meiotic division yields 4 cells. Thus microspores are produced in multiples of four.

Uncontrolled cell division & abnormal growth of cells leads to the pathological condition called tumor or cancer.

Events in Prophase:

1. Nuclear membrane disappears
2. Nucleolus disappear
3. Spindle fibre begins to form
4. Chromosomes threads condeme to form chromosomes

Events in Telophase:

1. Nuclear membrane reappears
2. Nucleolus reappears
3. Spindle fibre disappears
4. Chromosomes decondeme to form chromosomes

One cells takes 80 minutes to form 16 cells. If 2 cells undergoes division simultaneously, it take 160 minutes (2 hours 40 minutes) to form 32 cells.

The Amitosis:

Between Anastral & Amphiastral:
Anastral:

1. This is present only in plant cells.
2. No asters or centrioles are formed only spindle fibres are formed during cell division.

Amphiastral:

1. This is found in animal cells.
2. Aster and centrioles are formed at each pole of the spindle during cell division.

Certain chemical components act as inhibitors of the mitotic cell division and they are called mitotic poisons.

The factors which promote cell cycle proliferation is called mitogen. Example: gibberellin. These increase mitotic rate.

The random distribution of homologous chromosomes in a cell in Metaphase I is called independent assortment.

In Zygotene, pairing of homologous chromosomes takes place and it is known as synapsis.

Meiosis takes place in the reproductive organs. It results in the formation of gametes with half the normal chromosome number.

Length of the S period = Fraction of cells in DNA replication × generation time.

Kinetochore is a DNA – Protein complex present in the centromere DNA, where the microtubules are attached. It is a trilaminar disc like plate.

The alignment of chromosome into compact group at the equator of the cell is known as metaphase plate.

In animal cell the centrioles extend a radial array of microtubules towards the plasma membrane when they reach the poles of the cell. This arrangement of microtubules is called an aster. Plant cells do not form asters.

Mitosis is divided into four stages prophase, metaphase, anaphase and telophase.

At the end of mitosis the number of chromosomes in the parent and the daughter (Progeny) cells remain the same so it is also called as equational division.

The disadvantages of Amitosis:

• Causes unequal distribution of chromosomes.
• Can lead to abnormalities in metabolism and reproduction.

Amitosis is also called incipient cell division. Since there is no spindle formation and chromatin material does not condense.

Mature neurons and Skeletal muscle cells.

Between Karyokinesis & Cytokinesis:

• Karyokinesis: Karyokinesis refers to the nuclear division.
• Cytokinesis: Cytokinesis refers to the cytoplasmic division.

Maturation Promoting Factor (MPF) brings about condensation of interphase chromosomes into the mitotic form.

Kinases & Cyclins.

Interphase is the longest phase. Cells are metabolically active and involved in protein synthesis and growth.

C – Value is the amount in picograms of DNA contained within a haploid nucleus.

Prevost & Dumans in 1824.

A series of events leading to the formation of new cell is known as cell cycle.

The two types of nuclear division:

1. Mitosis and
2. Meiosis.