STD-11 UNIT-3 CHA-8
CELL : STRUCTURE AND FUNCTIONS
Cytoplasm
- Cytoplasm (Strasburger, 1882) Cytoplasm is jelly - like semi - fluid general mass of protoplasm excluding the nucleus but including all other components, cytoplasmic matrix, cell organelles and cell inclusions.
- It is the clear fluid part of the cytoplasm which can exist in two states, sol and gel.
- The two are respectively called plasmasol and plasmagel.
- Plasmagel is usually present below the plasma membrane.
- It is called ectoplast.
- Plasmasol is internal and is known as endoplast.
- Water constitutes 90% of the matrix. Matrix is actually a crystallo-colloidal complex in water where some chemicals are present in the form of a true solution while others are present as colloidal solution, e.g. minerals, sugars, amino acids, tRNAs, nucleotides, vitamins, proteins, enzymes, etc.
- Proteins the major colloidal particles of the complex.
- Fats usually occur as emulsion either in the form of globules in the matrix or as component of various biomembranes.
- Cytoplasmic matrix performs a number of functions.
- Important ones are
- Raw Materials - The matrix contains raw materials and provide the same to cell organelles for their functioning.
- Exchange - The cell organelles are usually unconnected.
- They exchange materials through the cytoplasmic matrix.
- Products - The products of cell organelles are passed out into the matrix.
- Biosynthesis - The matrix is the seat of synthesis of a number of biochemicals like fats, nucleotides, some carbohydrates, proteins, coenzymes, etc.
- Catabolic Activities - Glycolysis, anaerobic respiration and pentose pathway type of respiration occur in the matrix part of the cytoplasm.
- Cytoplasmic streaming - The cytoplasmic matrix is always in motion.
- It is autonomic and is called cytoplasmic or protoplasmic streaming (Amici, 1818).
- This helps in distribu tion of various materials inside the cell.
- They are sub-cellular structures with characteristic morphological forms, distinctive chemical constitutions and definite functions, which can be carried out by them even outside the cytoplasm provided they are supplied with substances which are normally provided by the cell.
- A cell contains a number of organelles like mitochondria, plastids (of several types), endoplasmic reticulum, Golgi complex, lysosomes, microbodies, ribosomes, etc.
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