Kerala PSC - Study Material : Biology (Structure of the Cell)

Cell wall found only in plant cells. It consists of non-living substances. eg: lignin, pectin, cellulose etc.
Cell membrane (Plasma membrane)
It is the outer membrane of the cytoplasm found both in animals and plants.
Plasma membranes are composed of phospholipids and protein.
Cytoplasm : It is a jelly like semi-solid ground substance in which various cell organelles are suspended. It helps in exchange of materials between cell organelles.
Protoplasm : Cytoplasm together with the nucleus form the protoplasm - the living matter of the cell.
Ribosomes : Small, dense, granular, spherical bodies found attached to the endoplasmic reticulum or in free state in the cytoplasm, composed of RNA and proteins. They help in synthesis of proteins.
Endoplasmic Reticulum (ER) provides an ultra structural skeletal framework and mechanical support to the cell. So it is called Skeleton of the cell.
Rough endoplasmic reticulum is the normal 'ER' with ribosomes attached to it. Only rough ER is involved in protein synthesis.
Smooth endoplasmic reticulum - without ribosomes in it.
Nucleus : The nucleus is the most prominent structure. It contains the genetical materials and also controls all cellular activities.
Golgi bodies : Bag like structures formed of membrances. Their functions include secretion of various substances.
Golgibodies : are often called traffic police of the cell because it plays a critical role in sorting many cellular protein and guiding them to their destination.
Vacuole : A fluid filled sac within a cell. The watery fluid enclosed in the vacuole is called 'Cell Sap'. It is slightly acidic or neutral. Osmo-regulation is the main function. Membrane of vacuole is called tonoplast.
Mitochondria : Rod like or spherical, semi-solid structures containing DNA. They are the sites of cellular respiration.
Mitochondria is the power house of the cell. It is also a double-membrane bound organelle. The inner membrane is thrown into folds called cristae to increase the surface area.
Peroxisomes and glyoxysomes are known as microbodies. They are enzyme bags.
Lysosomes are sac like structure bounded by a single membrane. It is known as suicidal bags, as they contain hydrolysing enzymes. Occasionally they digest the whole cell or part of it.
Plastids : Small discoid bodies found in the cytoplasm of higher plants. They are of many types.
Chloroplasts : are the centres of photosynthetic activity. it is found only in photosynthetic activity. It is found only in photosynthetic plant cell. Chloroplast is a green plastid.

(i) Leucoplasts : Colourless starch storing particles
(ii) Chromoplasts : Are Coloured particles which give colour to fruits and flowers.

Centrosome : A rather dense are of protoplasm, lies close to nucleus. It is found in animal cell only.
Plant cell is different from animal cell as it contains cell wall and chloroplasts and devoid of centrioles which help in cell division.
Adenosine Triphosphate (ATP provides energy for all kinds of activities of a cell.
ATP is called the 'universal biological energy currency'.
Energy is stored in the mitochondria as ATP molecules.
Chromosome is thread like structure found in the nucleus.
It becomes visible during cell division.
Each Chromosome is made up of two chromatids joined together at a point called centromere.
Genes are hereditary units which are the particular segments of DNA (Deoxyribonucleic acid) and carry genetic information from generation to generation.
Chromosome is made up of DNA & proteins.
Chromosomes, other than the sex chromosomes are called autosomes.
Number of autosomes in a cells is 44 (22 pairs) and number of sex chromosomes is 2.
Microfilaments - are fine thread like fibrils, made up of one of the major protein components, actin of muscle cells.
Microtubules - are straight tubular structure that provide some rigidity to the cell.
DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid) are two different nucleic acids found in the cells of every living organism. Both have significant roles to play a cell biology.
DNA is found mainly in the nucleus of the cell, while RNA is found mainly in the cytoplasm of the cell.
The structure of DNA was first deduced by J.D. Watson and F.H. Crick in 1953.
Apoptosis - It is the programmed cell death or cells suicide. This occur when the cell has fulfilled its biological functions.

Cell Division

Cell division is the process by which a parent cell divides into two or more daughter cells.
Rudolf Virchow was the first to suggest that new cells are formed from the division of the pre-existing cells.
Time taken for one cell division is called cell cycle.
Human cell cycle is 24 hours.
Cell division is of two types : Mitosis and Meiosis.
Mitosis occur in body cells, results in formation of two daughter cells with equal number of chromosomes.
Mitosis is called equational division.
Meiosis occurs in reproductive cells. It causes a reduction in number of chromosomes in the cell.
Meiosis is called reduction division.
Division of nucleus during cell division is called Karyokinesis.
Division of cytoplasm is called cytokinesis
Two complete set of Chromosome is called diploid (found in somatic cell / body cell).
Single set of chromosome in cell is called haploid (found in gametes - sperm/ovum)
Exchange of genetic material between two non sister chromatids takes place during meiotic cell division is called crossing over.