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Difference Between Mitosis and Meiosis:

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

Some cells exit G₁ and enters a quiescent stage called G₀ , where the cells remain metabolically active without proliferation. Cells can exist for long periods in G₀ phase. In G₀ cells cease growth with reduced rate of RNA and protein synthesis. The G₀ phase is not permanent. Mature neuron and skeletal muscle cell remain permanently in G₀ .Many cells in animals remains in G₀ unless called onto proliferate by appropriate growth factors or other extracellular

(c) G1-S-G2-M

Some cells exit G₁ and enters a quiescent stage called G₀ , where the cells remain metabolically active without proliferation. Cells can exist for long periods in G₀ phase. In G₀ cells cease growth with reduced rate of RN A and protein synthesis. The G₀ phase is not permanent. Mature neuron and skeletal muscle cell remain permanently in G₀ . Many cells in animals remains in G₀ unless called onto proliferate by appropriate growth factors or other extracellular signals. G₀ cells are not dormant.

Cells are arrested in G₁ due to:

• Nutrient deprivation
• Lack of growth factors or density dependant inhibition
• Undergo metabolic changes and enter into G₀ state.

The role of nucleus in the cell:

• Control activities of the cell.
• Genetic information copied from cell to cell while the cell divides.
• Hereditary characters are passed onto new individuals when gametic cells fuse together in sexual reproduction.

Mature neurons and Skeletal muscle cells.

1. Cytokinesis in Plant Cells: Division of the cytoplasm often starts during telophase. In plants, cytokinesis cell plate grows from centre towards lateral walls centrifugal manner of cell plate formation. Phragmoplast contains microtubules, actin filaments and vesicles from golgi apparatus and ER. The golgi vesicles contains carbohydrates such as pectin, hemicellulose which move along the microtubule of the pharagmoplast to the equator fuse, forming a new plasma membrane and the materials which are placed their becomes new cell wall.

The first stage of cell wall construction is a line dividing the newly forming cells called a cell plate. The cell plate eventually stretches right across the cell forming the middle lamella. Cellulose builds up on each side of the middle lamella to form the cell walls of two new plant cells.

2. Cytokinesis in Animal Cells: It is a contractile process. The contractile mechanism contained in contractile ring located inside the plasma membrane. The ring consists of a bundle of micro filaments assembled from actin and myosin. This fibril helps for the generation of a contractile force. This force draws the contractile ring inward forming a cleavage furrow in the cell surface dividing the cell into two.

S Phase – Synthesis phase – cells with intermediate amounts of DNA Growth of the cell continues as replication of DNA occur, protein molecules called histones are synthesised and attach to the DNA. The centrioles duplicate in the cytoplasm. DNA content increases from 2C to 4C.

(b) Closed mitosis

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

Karyokinesis: 

1. Involves division of nucleus. 

2. Nucleus develops a constriction at the center and becomes dumbellshaped. 

3. Constriction deepens and divides the nucleus into two.

Cytokinesis: 

1. Involves division of cytoplasm. 

2. Plasma membrane develops a constriction along nuclear constriction. 

3. It deepens centripetally and finally divides the cell into two cells.

Regeneration of arms of star fish is due to Mitosis. 

Meiosis is called as reduction division.

Cells of mammalian cartilage undergoes Amitosis.

Correct Answer is: (a) Amitosis

Kinases & Cyclins.

(c) Diakinesis

The phases which comprises the Interphase: 

1. G₁ Phase 

2. S Phase and 

3. G₂ Phase.

Recombination of chromosomes occur at Pachytene

Correct Answer is: (a) MPF

(d) Anton Schneider

Number of chromosomes in onion cell is 16.

Between closed and open mitosis: 

1. In closed mitosis, the nuclear envelope remains intact and chromosomes migrate to opposite poles of a spindle within the nucleus. 

Example: Yeast and slime molds. 

2. In open mitosis, the nuclear envelope breaks down and then reforms around the 2 sets of separated chromosome. 

Example: Most plants and animals cells.

In plants, phragmoplast are formed between the daughter cells. Cell plate is formed between the two daughter cells, reconstruction of cell wall takes place. Finally the cells are separated by the distribution of organelles, macromolecules into two newly formed daughter cells.

(c) Interphase

Eukaryotic cells divides every 24.

(b) Prevost & Dumans

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

Prevost & Dumans in 1824.

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.

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

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

The two types of nuclear division: 

1. Mitosis and 

2. Meiosis.

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

Amphiastral type cell division is seen in Animal cells.

Correct Answer is: (c) Spindle

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

Genome is a one set of DNA instruction or single set of chromosome in a cell.

The two chemicals that arrest the cell division in a cell are: 

(i) Colchicine 

(ii) Cyanides.

(a) The four nitrogenous bases in the DNA ladder are Guanine, Thymine, Adenine and Cytosine. 

(b) Genes are specific sequences of nucleotides on a chromosome. 

(c) A nucleotide is composed of a phosphate, sugar (pentose) and a nitrogenous base. 

(d) Nucleosomes are groups of histone molecules surrounded by DNA strands. 

(e) If there are 46 chromosomes in a cell there will be 46 chromatin fibres inside the nucleus during interphase.

(a) Nucleotides. 

(b) Nucleosome. 

(c) Hydrogen Bond. 

(d) Phosphate, Sugar and Nitrogenous base.

1. Pachytene: At this stage bivalent chromosomes are clearly visible as tetrads. Bivalent of meiosis I consists of 4 chromatids and 2 centromeres. Synapsis is completed and recombination nodules appear at a site where crossing over takes place between non – sister chromatids of homologous chromosome. Recombination of homologous chromosomes is completed by the end of the stage but the chromosomes are linked at the sites of crossing over. This is mediated by the enzyme recombinase.

2. Diplotene: Synaptonemal complex disassembled and dissolves. The homologous chromosomes remain attached at one or more points where crossing over has taken place. These points of attachment where ‘X’ shaped structures occur at the sites of crossing over is called Chiasmata. Chiasmata are chromatin structures at sites where recombination has been taken place. They are specialised chromosomal structures that hold the homologous chromosomes together.

Sister chromatids remain closely associated whereas the homologous chromosomes tend to separate from each other but are held together by chiasmata. This substage may last for days or years depending on the sex and organism. The chromosomes are very actively transcribed in females as the egg stores up materials for use during embryonic development. In animals, the chromosomes have prominent loops called lampbrush chromosome.

Robert Brown discovered the nucleus in the cells of Orchid roots.

(b) Centromere

(i) Interphase is a series of changes that occur in a newly formed cell and its nucleus before it becomes capable of division again. 

(ii) It is also called intermitosis. It is non-dividing state of the cell and its nucleus is called interphase nucleus.

"Recombinase" is the enzymes on which the process of crossing over is dependent.

Exchanges of segments between non sister chromatids of the bivalents is called Genetic crossing over.

Crossing over is the exchange of genetic material between the non-sister chromatids of homologous chromosomes during pachytene of prophase.