Cytoplasm



CYTOPLASM 

The substance of a cell between the nucleus and the plasma membrane containing various organelles and inclusions is called cytoplasm.Distribution of protoplasm into cytoplasm and nucleoplasm was made by a Germ biologist Strassburger in 1882.


Cytoplasm and Protoplasm:

Cytoplasm  is jelly_ like semi_ fluid bulk of protoplasm excluding the nucleus.It includes all other components _ cytoplasm matrix, cell organelles and cell inclusions. 

  The term protoplasm is generally  defined  as the cell contents within and  including  the plasma membrane, but excluding the larger vacuoles and material recently  ingested or to be excreted. Cell walls, if present are non_ protoplasmic.The term protoplast has almost the  same meaning. It is defined  as a cell from which the cell wall has been completely removed. It is equivalent to whole cell in zoology. 


Composition 

The cytoplasm is a semifluid,  jelly_ like material. It consists of an aqueous, nearly transparent structurless ground substance called cytoplasmic matrix, or automatic, or hyaloplasm, or cytosol.The latter forms about half of the cell's volume and about 90% of it water. It contains the various cell organelles and inclusions in it. It also contains ions and biomolecules, such as minerals, sugars, amino acids, nucleotides,  tRNAs, enzymes, vitamins, necessary for bio synthetic processes of the cell. These occur as true solution. The cytosol also contains storage products, such as glycogen/ starch, fats and  proteins, in colloidal state. The cytoplasm is, thus a crystallocolloidal system with water as the solvent or dispersion medium. The cytosol contains waste materials too.It is a seat of many metabolic pathways such as glycolysis, synthesis of  fatty acids, nucleotides and some amino acids.  

      Sol and Gel States:  The cytoplasm may be in a sol  ( non_ viscous) state or in a separ  ( viscous) state. Often under the free surface of the cell, the cytoplasm is more gel_ like and called ectoplasm. The internal cytoplasm is more sol_ like and is termed endoplasm.

Important  functions of cytoplasmic matrix are:

(i) The matrix provides raw materials to cell organelles  for their functioning.

(ii) The cell organelles  exchanges material through  the cytoplasmic matrix. 

(iii) The products of cell  organelles  are passed  out  into the matrix.


(iv) The matrix is the seat of synthesis of a number  of biochemicals like fats, nucleotides, some carbohydrates, proteins, coenzymes, etc.

(v) Various  catabolic activities, e.g., glycolysis,anaerobic respiration and pentose pathways type of aerobic respiration occur in the  matrix part of cytoplasm.

(vi) The cytoplasmic matrix  is always  in motion  thus helping in distribution of various  materials  in side the cell.

(vii)Cytoplasmic Streaming ( Cyclosis 

Cytoplasmic streaming is an autonomic vital movement  which occurs continually in the matrix of the cytoplasm of eukaryotic cells. It is also called protoplasmic streaming  or cyclosis 




Autonomic movement  of the matrix of Cytollasm in a cell is called cytoplasmic  streaming, or cyclosis.

It occurs in eukaryotic cells, particularly the large_ sized cells, such as plant cells and protozoan cells ( Amoeba, Paramecium). Large size impedes important physical processes such as diffusion. The cytoplasmic streaming serves to overcome this problem of large cells. In Amoeba, streaming also helps in the formation of pseudopodia. Streaming movement is of 2 types;

 1): Rotation: In rotations, the cytoplasmic matrix streams in one direction around a central vacuole as in the young leaves of Hydrilla.

2): Circulation:  In Circulation, the matrix streams in many directions around different Vacuoles as in the staminal hair of Tradescantia.




    
Cytoplasmic streaming helps in movement  of organelles  inside the cell, distribution  of various substances in the cell, distribution of food vacuoles as in Amoeba  and Paramecium, formation  of pseudopodia in white blood corpuscles and Amoeba, quick repair of membrane  and other constituents and distribution of heat inside the cell.

The rate of cytoplasmic streaming  or cyclosis  depends  upon various  factors, e.g., viscosity  of cytoplasm, temperature,  metabolic  state of cytoplasm, aerobic  respiration , poisons and hormones, etc.
  Streaming depends on the viscosity of cytoplasm, temperature and metabolic state of the cell.

     Cytoplasmic streaming has several possible functions:
 ( a) transport of substances from one part of the cell to another,
( b)   cellular movement as in white cells.

(c) Maintenance of optimal temperature, 

(d) Movement of food vacuoles in the cytoplasm, and 

( e) Provision of optimal light conditions for chloroplasts as in the mesophyll cells of a leaf.

Role of Cytoplasm 

The cytoplasm has 5 main functions ___ 

(i) Metabolic Renetions: Cytoplasm is a seat of metabolic processes including 
( a) Biosynthesis of  fatty acids, saccharides,  nucleotides  and proteins; 

(b) oxidation ( glycolysis).

 (ii) Storage:Cytoplasm is also a storehouse for the raw materials needed for metabolism in both the cytoplasm and the nucleus. 

(iii) Distribution:The cytoplasm also distributes the nutrients the metabolites and enzymes in the cell. 

 (iv) Interorganeller Exchange:Cytoplasm brings about exchange of materials between the cell organelles. 

(v) Exchange with Environment:Cytoplasm exchange materials with the environment or  extracellular fluid too.

 (vi) Streaming (Cyclosis): Streaming of cytoplasmic matrix serves many functions already mentioned. 

Summary of processes Moving Materials Across Biomembranes

 process

1. Passive Diffusion 

Example:  Diffusion of O2 from lungs into capillaries. 

2. Osmosis 


Example :  Resorption of water from kidney tubules.

3. Passive Transport 

Example: Entry of soluble materials into cells by passing lipid bilayer. 

4. Facilitied Diffusion. 

Example: Diffusion of glucose into red blood cells.

5. Active Transport. 

Example: Reabsorption of salts from kidney tubules.

6. Endocytosis 

Example: Uptake of chyle by intestinal cell.

7. Phagocytosis 

Example: Ingestion of bacterium by leucocytes.

8. Exocytosis 

Example: Release of neurotransmitters by nerve cells.

 Characteristics

1. Follows concentration gradient. 

2. Passive diffusion of water. 

3. Moves materials down concentration gradient via channels in carrier proteins. 

4. Follows concentration gradient but assisted by carrier protein.


5. Moves materials against concentration gradient, helped by carrier proteins, uses energy from ATP .

6. Intake of water and macromolecules in membrane __ band vesicles. 

7. Intake of particles in membrane __ band vesicles. 

8.Release of materials  by cells to the exterior through membrane _ band vesicles.


































































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