ADVERTISEMENTS:
Here is a term paper on ‘Diffusion and Osmosis’ for class 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Diffusion and Osmosis’ especially written for school and college students.
Term Paper on Diffusion and Osmosis
Term Paper Contents:
- Term Paper on the Definition of Diffusion
- Term Paper on the Examples of Diffusion in Plants and Animals
- Term Paper on the Definition of Osmosis
- Term Paper on Understanding the Processes of Diffusion and Osmosis
- Term Paper on How Water is Taken Up by a Plant?
- Term Paper on the Effect of Osmosis on Plant and Animal Cells
- Term Paper on Active Transport of Molecules
ADVERTISEMENTS:
Term Paper # 1. Definition of Diffusion:
ADVERTISEMENTS:
Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration, down a concentration gradient.
For plants and animals to stay alive, chemicals must be able to move easily:
(i) From one part of a cell to another
ADVERTISEMENTS:
(ii) Into and out of a cell
(iii) From one cell to another.
It is an advantage to the plant or animal if this chemical movement does not require effort, or more correctly, ‘expenditure of energy’. As long as there is no obstruction, chemical molecules carry out this process by diffusion.
Before diffusion can occur, there must be a concentration gradient of the molecules – a region of (relatively) high concentration next to a region of (relatively) low concentration.
Term Paper # 2. Examples of Diffusion in Plants and Animals:
Examples of Diffusion in Plants:
(i) The movement of carbon dioxide during photosynthesis. Carbon dioxide, in solution, moves from the water film surrounding the mesophyll cells inside a leaf, to the chloroplasts in the leaf.
(ii) The movement of water vapour during transpiration. Water vapour moves from the water film surrounding the mesophyll cells inside a leaf, through the intercellular spaces of the leaf, and out through the stomata.
Examples of Diffusion in Animals:
ADVERTISEMENTS:
(i) The movement of oxygen into the blood for respiration. Oxygen is dissolved in the moisture lining the air sacs of the lungs (ALVEOLI), then moves through the walls of the alveoli into the blood.
(ii) The movement of carbon dioxide into the blood. Carbon dioxide, in solution, moves from the cells, through tissue fluid, into the blood in capillaries.
Term Paper # 3. Definition of Osmosis:
Osmosis can be defined as the passage of water molecules from a region of high water potential, to a region of lower water potential, through a partially permeable membrane.
ADVERTISEMENTS:
Water is actually obtained by osmosis. Osmosis is a physical phenomenon where diffusion takes place when two liquids of different concentration are separated by a semi-permeable membrane, and it continues till the two liquids attain same concentration.
If water and strong sugar solution are separated by a permeable membrane, water will flow more rapidly towards sugar solution and sugar solution will move towards water till an equilibrium is secured. By the term membrane is meant a thin sheet or layer of plant, animal or of artificial origin. Permeable membrane is one through which a liquid with dissolved matters may diffuse safely, e.g. cellulose cell wall.
There are membranes, natural or artificial, which allow only the solvent, i.e. water to pass and not the solute. They are called semi-permeable or selectively permeable, e.g. fish bladder, parchment, etc. An impermeable membrane is one which allows neither the solvent nor the suberised walls.
If plasma membrane were perfectly semi-permeable, no absorption of dissolved substances from the soil by osmosis would have been possible. But it becomes possible because this layer allows certain substances to pass through it under one set of circumstances, while under another set their entry is restricted; so this is selective absorption.
ADVERTISEMENTS:
Complexity of the structure of the plasma membrane and its behaviour under different circumstances are thought to be responsible for this permeability. Flow of weaker solution towards the more concentrated one, called endosmosis, is always more rapid than the flow of stronger solution to weaker one, referred to as exosmosis. Due to endosmosis a pressure, called osmotic pressure, is set up.
Term Paper # 4. Understanding the Processes of Diffusion and Osmosis:
A. The Movement of Molecules by Diffusion:
1. Suppose a container is divided into two sections using a piece of cloth.
ADVERTISEMENTS:
2. A dilute sugar solution, which contains a lot of water, is poured into one side of the container. A concentrated sugar solution, which contains less water, is poured into the other. The container is left to stand for a few minutes.
3. When checked, the concentration of the solution has changed on both sides of the container. Each side has the same concentration of water and sugar.
By diffusion, both the water molecules and the sugar molecules moved down their respective concentration gradients, until both sides were at the same concentration. The pores in the cloth did not obstruct the movement of the molecules in either direction.
B. The Movement of Molecules by Osmosis:
1. Suppose a container is divided into two sections using a membrane with microscopic holes.
ADVERTISEMENTS:
2. The same dilute sugar solution is poured into one side, and concentrated sugar solution is poured into the other. Again, the container is left to stand for a few minutes.
3. When checked, the dilute solution has lost water molecules, thus becoming more concentrated, while the concentrated solution has gained water molecules and become more dilute.
The microscopic holes of the membrane were so small that they allowed the passage of water molecules but not the sugar molecules. The water molecules diffused down their concentration gradient, while the sugar molecules stayed where they were.
This specialised case of diffusion is called osmosis, and the separating membrane is described as partially permeable.
Dilute solutions, which have a relatively large number of water molecules, are said to have a high water potential.
ADVERTISEMENTS:
Concentrated solutions, with fewer water molecules, are said to have a low water potential.
Term Paper # 5. How Water is Taken Up by a Plant?
Simple Diffusion:
1. The cell wall of a root hair cell is made of cellulose, a completely permeable substance.
2. The cell wall does not obstruct the passage of water into the root hair cell.
3. Where the walls of neighbouring cells touch, water can pass into the root by simple diffusion – through the cellulose of the cell walls (the ‘cell wall’ pathway).
Osmosis:
1. All cell membranes are partially permeable.
2. The cell sap of root hair cells has a relatively low water potential.
3. Soil water has a relatively high water potential.
4. Water molecules will move into the vacuole of root hairs by osmosis (the ‘vacuolar’ pathway).
When water molecules enter a root hair cell, they increase the water potential of that cell. Osmosis then causes the water to move from the root hair cell to the next cell, closer to the centre of the root. The water molecules move like this from cell to cell until they reach the xylem vessels in the centre of the root, where they are transported away to the stem.
A demonstration of osmosis using an artificial partially permeable membrane
Term Paper # 6. The Effect of Osmosis on Plant and Animal Cells:
A. The Intake of Water by Osmosis:
Water enters plant (root) cells by osmosis, because the water potential of soil water is usually higher than the water potential of a plant’s cell sap. As water enters the plant cell, the vacuole increases in volume. It presses the cytoplasmic lining of the cell against the flexible, box-like cell wall. This pressure is called Turgor pressure, and helps to make plant cells firm.
Turgor, or turgidity, in plant cells helps:
(i) To keep stems upright
(ii) To keep leaves flat so they can better absorb sunlight.
Turgor resulting from osmosis can be demonstrated using a tightly-tied bag made of Visking tube (an artificial partially permeable membrane) filled with sugar solution, and placed in water for 20 minutes.
The water potential inside most animal cells is often the same as the solution in which the cells are naturally bathed (see the section on kidney function, below). There is little movement of water by osmosis into or out of the cell.
However, if a red blood cell is placed in a solution with a relatively high water potential, it starts to take in water by osmosis. Since there is no cell wall to resist the increased pressure that results, the cell bursts.
B. The Loss of Water by Osmosis:
Plant cells placed in a solution of relatively low water potential lose water from their vacuoles. The cells lose their turgor because the cytoplasm is no longer being forced against the cell wall. They become flaccid. If the cells remain in the solution of lower water potential, so much water will be drawn from the vacuole that the cytoplasm will pull away from the cell wall. This condition is called plasmolysis.
Animal cells placed in solutions of lower water potential lose their shape and turgidity as water moves out of their cytoplasm. A red blood cell shrinks in size and its cell membrane becomes unevenly creased (‘crenated’).
Term Paper # 7. Active Transport of Molecules:
Both plant and animal cells need a range of chemical molecules, other than water, for their metabolism. But these molecules may already be in a higher concentration inside the cell than outside it. In this case, the cell uses a process called active transport, where energy is used to move chemicals from an area of lower concentration to an area of higher concentration.
Definition of Active Transport:
Active transport is an energy-consuming process where substances are transported against a concentration gradient.
The energy required by the cell is provided by the chemical reaction of respiration. Respiration takes place in all living cells.
Examples of Active Transport:
(i) In plant roots, when the ions needed for a plant’s metabolism may be in very short supply in the soil water. Ions are absorbed by root hair cells by active transport (as shown below).
(ii) In the small intestine of an animal, when digested food (such as glucose) is absorbed by the cells of the villi by active transport. (as shown below).
