KERALA PSC / BIOLOGY / THE CELL THEORY / NOTES / OBJECTIVE QUESTIONS / STUDY MATERIALS / GENERAL KNOWLEDGE / KERALA PSC PRELIMINARY

 

KERALA PSC / BIOLOGY / THE CELL THEORY / NOTES / OBJECTIVE QUESTIONS / STUDY MATERIALS / GENERAL KNOWLEDGE / KERALA PSC PRELIMINARY

KERALA PSC / BIOLOGY / THE CELL THEORY / NOTES / OBJECTIVE QUESTIONS / STUDY MATERIALS / GENERAL KNOWLEDGE / KERALA PSC PRELIMINARY

·      Schleedan a botanist and Schwan, a zoologist together formulated the cell theory, it includes two basic ideas. They are:

Ø All living organism are composed of one or more cell

Ø Cell is the structural unit of life

·      In 1858, the German Pathologist Rudolf Virchow added a third principle to the cell theory that all the cells arise from the division of pre-existing cell.

·      The smallest cell size is of a bacteria

·      The largest cell is of an ostrich egg

·      The largest human cell is the ovum (.2mm)

·      Nerve cell (neuron) is the longest cell.

·      Human cells have 23 pairs (46 number) of chromosomes.

·      The cell with longest life span in our body is Nerve Cells.

·      The average size of the cell is 3-30 microns (1 micron = 1/1000 mm)

 

Cell Wall: Found only in plant cells. It consists of non-living substances. Eg: lignin, pectin, cellulose etc….

Cell membrane:

·      It is the outer membrane of the cytoplasm found both in animals and plants. It is made of protein.

·      It prokaryotes, there is no definite membrane bound nucleus. Eg: Bacteria, Blue-green algae. In Eukaryotes, there is a nucleus with definite double membrane

·      Plasma membranes are composed of phospholipids and protein

·      Cytosol: It is the soluble material in embryonic cell in which various organelles are embedded.

 

Endoplasmic Reticulum (ER)

·      Endoplasmic reticulum provides an ultra-structural skeletal framework and mechanical support to the cell. So it is called Skeltan of the Cell.

·      A network of tubes or channels of membrane in the cytoplasm which helps in protein synthesis and conduction of materials.

 

Ribosomes: Externally small, dense, granular, spherical bodies found in free state in the cytoplasm, composed of RNA and proteins. They help in synthesis of proteins.

·      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. It is generally a small component but from it transport vesicles.

·      Nucleus: The nucleus is the most prominent structure usually found in the centre as it contains the genetical materials and also functions in the control of cellular activities such as protein synthesis, cellular growth and reproduction.

 

Golgi bodies: Bag like structures formed of membranes. Their functions include secretion of various substances:

·      Two types of vesicles – coated vesicles, larger secretary vesicles.

·      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.

 

Mitochondria:

·      Rod like or spherical, semi-solid structures containing DNA. They synthesize ATP (Adenosine Tri Phosphate)

·      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 micro bodies. They are enzyme bags.

Lysosomes: are known as “suicide bags”, as they contain hydrolyzing 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 plant cell. Chloroplast is a green plastid.

·      Chloroplasts have double membrane, lamellar or thylakoids which absorb solar energy and pigments like chlorophylls and carotenoids.

Ø Leucoplasts: Colourless starch storing particles

Ø Chromoplasts: Are coloured particles which give colour to fruits and flowers.

 

Nucleus: The nucleus controls all cell activities and enclose the nucleoplasm. Nucleus is responsible for transfer of heredity characteristics.

Centrosome:

·      A rather dense area of protoplasm, lies close to nucleus.

·      Plant cell is different from animal cell as it contains cell wall surrounding plasma membrane and chloroplasts and devoid of centrioles which is seen only in animal cells.

·      Adenosine Triphosphate (ATP) provides energy for all kinds of activities of a cell.

·      ATP is called the ‘universal biological energy currency’.

·      ATP synthesis takes place in mitochondrion

·      Energy is stored in the mitochondria as ATP molecules

·      The physical basis of life is ‘protoplasm’

·      Chromosome is made up of DNA & Proteins

·      Chromosomes, other than the sex chromosomes, are called autosomes

·      The ribosomes are chiefly concerned with the synthesis of protein

·      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.

·      Inter-relationship of DNA, RNA and Protein commonly called Central Dogma of Life.

·      Apoptosis: It is the programmed cell death or cells suicide. This occur when the cell has fulfilled its biological functions.

·      The structure of DNA was first deduced by JD Watson and F.H Crick in 1953

KERALA PSC / BIOLOGY / THE CELL THEORY / NOTES / OBJECTIVE QUESTIONS / STUDY MATERIALS / GENERAL KNOWLEDGE / KERALA PSC PRELIMINARY