Difference between Rough Endoplasmic Reticulum (RER) and Smooth Endoplasmic Reticulum (SER) :-
RER :- These appear rough under a microscope because of the attachment of a large number of grain - like ribosomes over their cytoplasmic surface. The ribosomes are the sites of protein synthesis. Thus RER, is engaged in the synthesis and transport of proteins. Generally RER, is more abundant in the deeper part of cytoplasm near the nucleus where it is connected with the outer membrane of the cytoplasm near the nucleus where it is connected with the outer membrane of the nuclear envelop. RER is well devloped in that synthesize and secret proteins.
SER :- It consists mainly of tubules and vesicles. It is free of ribosomes and and is more abundant near the peripheral part of the cytoplasm where it may be attached to the plasma membrane. The SER helps in the synthesis of fats or lipids molecules. It is therefore well developed in the cells that secret lipids. It forms the transport vesicles in which the large molecules of proteins and lipids are transported from on cell to the another ( via plasmodesmata in plant cells.) within the cells.
Difference between diffusion and osmosis :-
Diffusion : - The process by which a substance uniformly spreads by random movement of its particles from a region of higher concentration to a region of its lower concentration due to their kinetic energy is called diffusion.
For instance, carbon dioxide is produced as an end product of metabolism in cells and its concentration inside the cell becomes high. However the concentration of of CO₂ in the external environment of cells is low. Due to difference in the concentration of CO₂ between the inside and outside of the cells, CO₂ moves out from the region of its high concentration to the region of its low concentration through plasma membrane of respective cells by diffusion. This process continue till the concentration of CO₂ becomes equal on both the sides.
Significance of diffusion :-
1. Diffusion helps in the distribution of various substances throughout the cytoplam of the cell without much delay.
2. It helps in the exchange of respiratory gases ( O₂ and CO₂) Between the body cells and their environment.
3. Various materials such as gases, liquids and solids dissolve in the medium i.e. , air or liquid by diffusion.
4. Loss of water in vapours from the aerial parts of the plants ( transpiration) occurs through diffusion.
5. Flowers of plants spread aroma through diffusion. It attracts the insects and other insects for pollination.
Osmosis :- If two solutions having different concentration of a solute are seprated by a semipermeable or selectively permeable membrane i.e. a membrane which is permeable to small molecules and not permeable to large molecules of dissolved substances, then a different kind of diffusion occurs. in such a case on will see the movement of solvent from its region of lower concentration to a region of higher concentration. Such a phenomenon is known as osmosis.
The diffusion of water or solvent through a semi permeable membrane from a solution of lower concentration of solutes to a solution higher concentration of solutes to which the membrane is relatively permeable, is called osmosis.
Osmosis is of two types :-
Endosmosis :- It is the entry of water molecules into the cells through semipermeable plasma membrane when surrounded by hypotonic solution.
Exosmosis :- It is the exit of water molecules from the cells through semipermeable plasma membrane when surrounded by hypertonic solution.
Significance of osmosis :-
1. Fresh water unicellular organisms continuously gain water in their bodies due to osmosis.
2. Most plant cells have the tendency to gain water due to osmosis.
3. Plants absorb water from the soil through root hairs by osmosis.
4. Certain plant movements occur due to loss or gain of water.
5. Stomata open or close at different times of the day due to osmotic movement of water.
6. In plant cells tissues and soft organisms maintain turgidity or stretched form due to osmotic absorption of water.