RBSE Class 11 Biology Notes Chapter 10 Cell Cycle and Cell Division

These comprehensive RBSE Class 11 Biology Notes Chapter 10 Cell Cycle and Cell Division will give a brief overview of all the concepts.

RBSE Class 11 Biology Chapter 10 Notes Cell Cycle and Cell Division

→ Cell Division: Cell division is the process by which a parent cell divides and gives rise two or more daughter cells.

→ Nageli (1846) proposed that new cells arise from pre-existing cells. Rudolf Virchow (1855) stated “Omnis cellula e cellula” and support the concept of Nageli.

→ Cell cycle: A cell passes through two phases that are growth phase and division phase alternately. Both the events occur in a sequence or cyclic manner. So this sequence of even is called cell cycle.

→ Eukaryotic cell cycle can be divided into two main phases i.e., interphase and mitotic phase.

→ Cell cycle is controlled mainly by regulatory proteins cyclins and cyclin dependent protein kinases (KDKs).

→ Regulatory proteins control the cell cycle at key checkpoints.

 

→ Cell division is the three types: Amitosis, Mitosis and Meiosis.

→ Amitosis: It occurs in unicellular organisms like bacteria, Amoeba, Yeast etc.

→ Mitosis: It occurs in somatic cells of organisms. In this division one parent cell divides into two daughter cells in which number of chromosomes remain same as parent cell. It is responsible for growth of organisms. 

→ Mitosis: In occurs in somatic cells of organisms. In this division one parent cell divides into two daughter cells in which number of chromosomes remain same as parent cell. It is responsible for growth of organisms.

→ Meiosis: It occurs in germ cells or sex cells (diploid cells of testis and ovary). In this a diploid (2n) sex cell divides into 4 haploid (n) daughter cells (gametes) in which number of chromosomes becomes half than that of parent cell.

→ Cell division can be divided into two main phases karyokinesis (division of nucleus) and cytokinesis (division of cytoplasm).

→ Karyokinesis is always followed by cytokinesis.

→ Crossing over: An important event of the pachytene stage of prophase-I in meiosis I. It is a process by which two chromosomes of a homologous pair exchange equal segments with each other.

→ Genetic recombination occurs due to crossing over and thus play a role in evolution.

→ Meiosis may be of three types: Gametic meiosis (occurs in sex cells to produce gametes), zygotic meiosis (occurs in zygote to prduce haploid organisms) and sporic meiosis (during sporogenesis to produce spores).

→ Sometime certain body cells undergo uncontrolled increase in cell size and cell division forming a tumour. This condition is called cancer.

→ Bivalent: A pair of homologous chromosomes held together by a chiasma.

→ Chiasma: Point of crossing over when chromosomes exchange genetic material.

→ Monad: After separation, each chromosome of a tetrad forms a monad. A dyad without the synopsis to its homologous chromosomes.

→ Dyad: Half of a tetrad, one half of a synapsed pair of homologous chromosomes.

→ Centromere: The. point of constriction of a chromosome.

→ Homologous Chromosomes: Paired chromosomes that have one maternal and other paternal chromosome.

→ Sister Chromatids: The two identical chromatids of a chromosome.

→ Non sister Chromatids: The chromatids of separate chromosome of a homologous pair.
 
→ Nuclear Envelope: The double membrane which encloses the nucleus.

→ Nucleolus: The centre of r-RNA production within the nucleus.

→ Synapsis: The process whereby two homologous chromosomes come into physical contact with one another.

→ Tetrad: Paired homologous chromosomes of a bivalent consist of four chromatids which are referred to as tetrad.

→ Synaptonemal Complex: It is a protein structure that forms between homologous chromosomes during meiosis and is thought to mediate synapsis and recombination during meiosis I in eukaryotes.

→ Mitogenesis: It is a process of inducing mitosis in a cell.

→ Bouquet Stage: A stage is early prophase-I when the leptotene chromosomes converge towards the centrioles in many animals.

→ Kinetochore: It is a complex of proteins that assembles on each chromatid in the centromere region.

→ Quiescent stage or G₀ - phase: The cells which are not to divide further, do not proceed beyond the G₁, phase and start undergoing differentiation into specific types of cells. Such cells are said to be in quiescent stage.

→ Generation time: It is the period between two successive cell divisions.

→ Mitotic apparatus: The asters and the spindle are together referred to as mitotic apparatus.

→ Prometaphase: The events which connect the chromosomes to the spindle fibres and bring them to the metaphase plate are sometimes referred to as prometaphase.

→ Phragmoplast: During cytokinesis in plant cell, at the centre of the cell, the vesicles fuse together, forming a structure called phragmoplast.

→ Anastral Mitosis: In plant cells, mitosis occurs without asters, called anastral mitosis.

→ Endom'itosis: In some kind of cells DNA and chromosomes replicate but nuclei do not divide. This increase the number of chromosome sets per cell. This process is called endomitosis.

→ Meiocyte: A cell in which meiosis takes place is called meiocyte.

→ Polyploidy: When a cell has more than two sets of chromosome in its total genome, it is called polyploid and the phenomenon is called polyploidy.

→ Colchicine: It can stop cell division. Sometimes it is used to stop division of cancer cells.