Mind map is given at end of this page👇👇
Cell cycle and cell division is chapter 10 of class 12th NCERT biology. This chapter tells about how a cell divides and what is cell cycle.
Sequence by which cell duplicates its genome, synthesize other constituent of cell and finally divides into two is known as cell cycle.
The cell cycle is the process by which a cell grows, replicates its DNA, and divides into two daughter cells. It is made up of four distinct phases: G1 (Gap 1), S (Synthesis), G2.
The cell cycle is the process by which cells divide and reproduce. It is an essential part of life and allows for the growth, development, and maintenance of all living organisms. The cell cycle consists of four distinct phases: interphase, mitosis, cytokinesis, and G0 phase. During each phase, different processes take place to ensure that cells can divide accurately and efficiently.
Interphase is the first stage of the cell cycle. During this stage, a cell grows in size and prepares for DNA replication. This includes synthesizing proteins and other molecules needed for DNA replication as well as assembling components necessary for proper chromosome segregation during mitosis. Interphase typically lasts around 10 hours in most eukaryotic cells; however, this time can vary depending on the type of cell being studied.
The second stage of the cell cycle is mitosis. During this stage, chromosomes are duplicated so that each daughter cell has a complete set of genetic material after division occurs. This process involves several steps including prophase (chromosomes condense), metaphase (the chromosomes align at the equator), anaphase (the sister chromatids separate) and telophase (the nuclear envelope reforms). Mitosis typically takes about one hour to complete in most eukaryotic cells; however again this can vary depending on the type of cell being studied.
After mitosis comes cytokinesis – the third stage in which two daughter cells are formed from a single parent cell by cleavage furrow formation or pinching off from one another at a specific site along their common plasma membrane surface area called “cleavage plane” . In animal cells, cytokinesis begins with contractile ring formation near mid-cell region while in plant cells it involves vesicle trafficking along actin microfilaments towards mid-cell region followed by deposition at cleavage furrow sites resulting in formation of new plasma membrane surfaces between two daughter cells . Cytokinesis usually takes about 30 minutes to complete but again it varies depending on type of organism being studied .
Finally comes G0 phase – also known as gap 0 or quiescence – which is when a parent or daughter cell enters into a resting state where no further division will occur . In some cases G0 may be temporary while other times it may be permanent such as when stem cells enter into G0 phase until they receive signals to differentiate into other specialized types.
Cell division is the process by which a single cell divides into two daughter cells. It is an essential part of growth, development, and reproduction in all living organisms. Cell division occurs in two main forms: mitosis and meiosis.
Mitosis is the process by which a single parent cell divides into two genetically identical daughter cells. In this process, the nucleus of the parent cell divides into two equal parts, each containing an exact copy of the genetic material (DNA) present in the parent nucleus. The cytoplasm then splits between these two nuclei to form two new daughter cells with identical genetic material as that of the original cell. This type of cell division is used for growth and repair in most multicellular organisms.
Meiosis is a type of cell division that produces four haploid cells from one diploid parent cell. During this process, the number of chromosomes in each daughter cell is reduced to half that found in its parent nucleus by a series of nuclear divisions called meiotic divisions or reductional divisions. This type of cell division is used for sexual reproduction in many species including humans and other animals as well as plants and fungi.
Cell division plays an important role in maintaining homeostasis within multicellular organisms by replacing old or damaged cells with new ones and ensuring that each new generation contains individuals with similar characteristics to those found within their parents’ generation. It also enables species to evolve over time through natural selection as changes occur within individual genes or chromosomes during these processes that can be passed on from one generation to another through sexual reproduction or through mutations occurring during mitosis or meiosis itself.
Duration of cell cycle varies in different types of cell. For example a human cell divides once in 24 hours wild Yeast divides in 90 minutes only.
The cell cycle consists of two phases. One is interface and other is M phase. Phase between two between two M phase is called Interphase. Interphase state exists for 95% of time of cell division. M phase is divided further into three different phases - G1 phase, S Phase, G2 phase.
G⁰ phase or quiescent stage is phase when the cell is metabolically active but does not divide.
There are two types of cell division, one is mitosis and other is known as meiosis.
Mitosis is known as equational division because the number of chromosome in the parent and the daughter cells remain same. After division the parent cell forms two daughter cells. Mytosis occurs in 4 different phases, these are -
Prophase - in this stage the chromatin condense and starts forming chromosome. Nuclear membrane starts disintegrating.
Metaphase - During this phase, the metaphase plate is formed. This phase is considered best phase to study morphology of chromosomes.
Anaphase - During Anaphase, the centro mayor split and chromatids separate and move to opposite ends.
Telophase - Chromosome clusters at opposite ends and nuclear membrane reappears in this phase.
After telophase the chromatin is moved to the end and new nuclear membranes are made. Now the division of the cell starts and this can be achieved in two ways -
In animals the cell divides by furrow formation. Furrow starts forming from both ends of cell and develops to meet at centre dividing cell in two. In plants the cell divides by cell plate formation. Cell plate formation starts from middle of the cell and extends to the ends dividing the cell into two.
The second type of division is meiosis. Meiosis is known as reduction division because the chromosome number gets half and four haploid cells are formed. In meiosis the division occurs twice. The first division is known as meiosis one in which two cells are formed. The second division is known as meiosis to and it is same as the mitosis.
The gap between meiosis 1 and meiosis 2 is known as interkinesis. Prophase of meiosis one is divided into 5 different sub phases. These are - leptotene, zygotene, patchytene, diplotene, diakinesis.
Meiosis generally increases variation and also conserves number of chromosome throughout generations.
Some of the previous year questions that came in NEET exam from this chapter are given below -
1. Identify the correct statement with regard to G1 phase (Gap 1) of interphase
(a) DNA synthesis or replication takes place.
(b) Reorganisation of all cell components takes place.
(c) Cell is metabolically active, grows but does not replicate its DNA.
(d) Nuclear division takes place.
2. Cells in G0 phase
(a) terminate the cell cycle
(b) exit the cell cycle
(c) enter the cell cycle
(d) suspend the cell cycle
3. In the somatic cell cycle
(a) in G1 phase DNA content is double the amount of DNA present in the original cell
(b) DNA replication takes place in S phase
(c) a short interphase is followed by a long mitotic phase
(d) G2 phase follows mitotic phase.
4. During the metaphase stage of mitosis, spindle Fibres attach to chromosomes at
(a) kinetochore
(b) both centromere and kinetochore
(c) centromere, kinetochore and areas adjoining centromere
(d) centromere.
5. Select the correct option with respect to mitosis.
(a) Chromatids separate but remain in the centre of the cell in anaphase.
(b) Chromatids start moving towards opposite poles in telophase.
(c) Golgi complex and endoplasmic reticulum are still visible at the end of prophase.
(d) Chromosomes move to the spindle equator and get aligned along equatorial plate in metaphase.
6. Which one of the following precedes reformation of the nuclear envelope during M phase of the cell cycle?
(a) Decondensation from chromosomes and reassembly of the nuclear lamina
(b) Transcription from chromosomes and reassembly of the nuclear lamina
(c) Formation of the contractile ring and formation of the phragmoplast
(d) Formation of the contractile ring and transcription from chromosome
7. Crossing over takes place between which chromatids and in which stage of the cell cycle ?
(a) Non-sister chromatids of non-homologoush Chromosomes at Zygotene stage of prophase I.
(b) Non-sister chromatids of homologoush chromosomes at Pachytene stage of prophase I.
(c) Non-sister chromatids of homologous chromosomes at Zygotene stage of prophase I.
(d) Non-sister chromatids of non-homologous Chromosomes at Pachytene stage of prophase I.
8. During cell division in apical meristem, the nucleaer membrane appears in
(a) telophase (b) cytokinesis
(c) metaphase (d) anaphase.
9. Dissolution of the synaptonemal complex occurs during
(a) pachytene (b) zygotene
(c) diplotene (d) leptotene.
10. Which typical stage is known for DNA replication?
(a) S-phase (b) G2-phase
(c) metaphase (d) G1-phase
To join telegram - Click here
To download PDF - Click here
0 Comments