Transport Materials through the Cell
In living organisms, transport of material takes place through cell membrane.
Following are the some process by which transport of materials takes place.
Diffusion:
The movement of molecules or ions from higher concentration to lower concentration is called diffusion.
Water, Co2, 02 and some other simple molecules diffuse across the cell membrane.
Diffusion is slow process, yet it is enough to meet the needs of plants.
Examples of diffusion:
- i) Take a crystal of KMnO4 and drop it in bowl of water. Initially, colour will remain at its initial area. After some time its molecules diffuses in whole water.
- ii) When we open a perfume bottle in a corner of room, its fragrance is strongest in particular area, and then it spread in the room by diffusion.
Efficiency of diffusion depends upon following factors:
- i) Distance
- ii) greater concentration gradient difference.
Temperature and Pressure also affect the rate of diffusion.
Diffusion of gases is more than liquids and solids.
Diffusion that takes place with the help of carrier proteins is called facilitated diffusion. It is also without the expenditure of energy. Diffusion plays an important role in transportation of materials.
Active Transport:
Sometimes movement of molecules takes place against the concentration, i.e. from lower concentration to higher concentration. This type of movement needs expenditure of energy. This is called active transport.
Osmosis:
A membrane which allows some substances to pass through it but prevent other is called selectively permeable membrane or differentially permeable membrane The movement of water molecules from higher concentration to lower concentration through selectively permeable membrane is called osmosis.
Turgor:
When plant cell is in water then water tends to move into the cell and enters into the vacuole. It exerts pressure on the walls of vacuole and pushes cell content against the wall. This pressure is called turgor.
The cell wall prevents the surplus water into the cell with opposing force. In this state cell is called turgid.
When whole cells are turgid, plants becomes rigid, stiff and upright. In this state cell is called flaccid.
Flaccid results in the limping of leaves and drooping of stem of plants called wilting.
Importance of Turgor is:
- i) It maintains the shape of soft tissues.
- ii) It helps in movement of certain plant parts. For example opening and closing of stomata.
iii) It helps in opening of flowers.
- iv) Turgor causes the cell walls to expand and the cells to enlarge in size.
- v) It helps to keep the leaves and stems of young plants upright.
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