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Cell Cycle and Cell Division Mock Test:
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| cell cycle and division |
Cell:
- Cell is the basic unit of life and all living organisms are made up of one or more cells.
- . The branch of biology which deals with the study of cell structure, origin and its function is known as cytology.
- The Father of Cytology, Robert Hooke observed the dead cell in the thin slice of cork as small honeycomb chambers in 1665 and 'named them 'Cellula'.
- In 1838-39, M Schleiden and T Schwann proposed cell theory, according to which cell is the structural and functional unit of life and all living beings are made up of cells. Later Rudolf Virchow modified cell theory by adding 'Omnis Cellula-e-Cellula"," i.e. every cell arises from pre-existing cell (exception virus).
Types of Cell:
- Structurally cells are of two types, i.e. prokaryotic (lacks well-organised nucleus and advance cell organelles, e.g. mitochondria, ER, etc.) and eukaryotic (have well-organised nucleus due to the presence of nuclear membrane as well as other advance cell organelles).
- Bacteria and blue-green algae are example of prokaryotic cells, while rest of the living beings are example of eukaryotic cells.
- Bacterial have primitive nucleus without a nuclear membrane and also lack cell organelles like mitochondria. Nuclear region in prokaryotes remains undefined and is called nucleoid.
- On the basis of number of cells in an organism, eukaryotic cells are of two types, i.e. unicellular (e.g. Amoeba, Paramecium, Euglena, etc.) and multicellular (e.g. fungus, plants and animals).
- Mycoplasma (PPLO) is the smallest cell, while ostrich egg is the largest cell.
Structural Organisation of Cell:
Structurally cell can be divided into three parts
- Outer Covering of Cell There are two types of outer covering in bacterial, fungal and plant cells, but only one in protozoan and animal cells. It is cellulosic in plants and chitinous in fungi. It protects inner material of cell from external environmental stress, physical shock or impact, etc. Animal cell only has cell membrane, but rest cells have extra rigid and dead protective layer made up of peptidoglycan called as cell wall. Cell membrane is also known as plasma membrane, it is made up of phospholipid bilayer.
- Protoplasm term was given by Purkinje and it is the sum of all living matter present inside a living cell. It was called as physical basis of life by Huxley. It has two parts, i.e. cytoplasm present between nucleus and cell membrane and nucleoplasm present inside nucleus. It also include cell organelles.
- Cell organelles perform various functions in cell, which are as follows
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Cell organelles |
Discoverers |
Characteristics |
Function |
1.Nucleus
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Robert Broune
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Made up of nuclear membrane, nucleoplasm, nucleolus and chromatin fibres which condense to form chromosomes during cell division.
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• Control all vital functions of
a cell.
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2. Mitochondria-
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Kolliker and Altmann
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Double membrane bound, semi-autonomous cell organelle which has its own DNA and 70s ribosomes to synthesis its own proteins.
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Power house of the cell as it generates ATPS (energy) through aerobic cellular respiration from oxidation of food. Reactions take place in inner membrane of mitochondria.
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3.Plastids-
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Ernst Haekel
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Double membrane bound, semi-autonomous cell organelle, only found in plants.
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• Leucoplast (colourless) stores food as starch or oil.
• Chromoplast provide colour to followers, fruit, etc
• Chloroplasts (green colour) synthesise food through photosynthesis and also known as kitchen of the cell.
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4.Endoplasmic-
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Porter
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These are of two types
Rough Endoplasmic Reticulum (RER) containing ribosomes on surface.
Smooth endoplasmic reticulum (SER) lacks ribosome
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Part of endocytoskeleton system RER synthesises complex proteins SER synthesises complex sugars and lipids Synthesis of cell and nuclear membrane.
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5.Ribosome-
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Palade
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Smallest and non-membranous cell organelle. Made up of RNA and protein.
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Protein synthesis, i.e. protein factory of cell.
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6.Golgi complex-
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Camillo Golgi
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It consists of cups, bags, tubes shaped flattened membranous vesicles arranged parallel to each other in stack called cisterns.
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• Lysosome formation.
• Secretion of various hormones and other compounds. • Cell wall and cell membrane formation.
• Transportation of various compounds.
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7.Lysosome-
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C De Duve
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Single membrane bound cell organelle which contains hydrolytic enzymes. Mainly found in animal cells.
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Digestion of food, foreign particles, dead cell organelles, etc., by hydrolytic enzymes.
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8. vacuole-
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Felix Dujardin
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Single membrane (tonoplast) bound cell organelle which is single but large (70-90% of cell) in plant cells, while small, numerous or absent in animal cells.
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• Covers 70-80% part of a plant cell.
• Stores food, water, pigments, waste material, etc.
• It is responsible for maintaining turgidity of cell. Helps in water regulation through osmosis.
• Acts as food vacuole in Amoeba.
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Cell Division:
It is a process by which a cell divides and produces two or four progeny cells. It is essential for growth, development, repairing of tissues and reproduction. Cell division can occur via two processes, i.e. mitosis and meiosis.
- Mitosis It occurs in both unicellular and multicellular organisms and generalised cells. Each mitotic cell division results in the formation of two daughter cells having number of chromosomes equal to the parent cell. It is divided into following phases.
Prophase - Chromatin undergoes condensation and appear chromosomes. as disappears. Nuclear membrane
Metaphase- Each chromosome gets attached to spindle fibre al centromere. Chromosomes are seen arranged at equator.
Anaphase - Centromere divides into two. Two chromatids start moving towards poles.
Telophase - Nuclear membrane reappears.
Cytokinesis - Division of cytoplasm..
- Meiosis - it occurs in reproductive cells (germ cells) and is called reductional division as, the number of chromosomes becomes half in daughter cells with respect to parent cells. In meiosis, exchange of genetic material occurs which is known as crossing over and results in producing genetic variations.
Meiosis I involves the following phases:
- Prophase I involves further sub-divisions as follows.
- Leptotene Chromosomes in this stage are thin and distinct.
- Zygotene During this stage, the chromosomes become short and thick. Pairing of homologous chromosomes occurs.
- Pachytene It involves exchange of chromatid segments or crossing over. Nucleolus persists.
- Diplotene Chromosomes are further thickened and paired chromosomes start repelling each other. However chromosome separation is incomplete.
- Diakinesis It involves disappearing of nucleolus and nuclear membrane with further condensed chromosomes.
Metaphase I Chromosomes are arranged in the equatorial plane as bivalents.
Anaphase I involves contraction of spindle fibres and moving and separation of homologous chromosomes, known as disjunction.
Telophase I In this stage, chromosomes reach opposite poles and uncoiled. Nucleolus and Nuclear membrane reappears. It is followed by cytokinesis.
- The intermediate stage between Meiosis I and II is called Interkinesis.
- Meiosis II involves prophase-ll, metaphase-II, anaphase-ll and telophase-II. All these phases are similar to the phases of Mitosisnexcept that these phases occur in two haploid cells.
- This stage is followed by cytokinesis and leads to formation of four haploid nuclei (daughter cells).
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