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Online Int. Science Lesson Transport: Diffusion & Osmosis WAEC Standard

 

Transport: Diffusion, osmosis and plasmolysis.

WASSCE-WAEC OBJECTIVES

  • Explanation of diffusion, osmosis, and plasmolysis.
  • Simple experiments to demonstrate diffusion in air and in liquids;
  • osmosis in living tissue and in non-living tissue.
  • Examples of diffusion and osmosis in nature

 

In humans there are two types of transport systems – the blood circulatory system (made up of the heart, blood vessels and blood.) and the lymphatic system (carries materials around the body).

Plants also have their own transport system – xylem and phloem tissues

 

The xylem tissue transports water and dissolved minerals.

The phloem tissue transports food substances through the plant.

Importance of Transport System

  1. It connects different parts of the body with one another.
  2. It transports food materials to all cells, tissues and organs.
  3. It distributes water to various parts of the body.
  4. It transports waste products from different parts of the body to the excretory organs.
  5. It transports raw materials such as oxygen to the cells, tissues and organs that need them

Diffusion

Diffusion is the movement of molecules from a region of high molecular concentration to the region of low molecular concentration until the molecules are evenly distributed.

Or

Diffusion is the movement of particles or ions from a region of higher concentration to a region of lower concentration

 

Examples of diffusion in living organisms

  1. Diffusion of oxygen into the blood and carbon dioxide out of the blood in the lung of mammals.
  2. Diffusion of hormones out of the endocrine glands.
  3. Absorption of end products of digestion, e.g. glucose, amino acids in the ileum (small intestines) of mammals.
  4. Diffusion of carbon dioxide into the blood and oxygen out of the blood in the tissue of vertebrates.
  5. Diffusion of oxygen into the cells and carbon dioxide out of the cells of unicellular organisms such as amoeba.
  6. Diffusion of carbon dioxide into the leaves and oxygen out of the leaf through the stomata.
  7.  Diffusion of mineral salt from the soil water into root hair cells. 8. Diffusion of oxygen into the leaves and carbon dioxide out of the leaves of plants at night

 

Factors that Affect the rate of Diffusion

  1. The size/ surface Area of the diffusing particles
  2. Nature of the Diffusing particle
  3. Concentration gradient
  4. Temperature
  5. Nature of surface membrane
  6. Stirring

Osmosis

Osmosis is the movement of water molecules from a dilute solution to a more concentrated solution across a semi[1]permeable membrane.

Or

Osmosis is the movement of water or solvent molecules from a solution of higher concentration of water (high water Potential) to a region of lower concentration of water through a semi-permeable membrane.

 

A semi-permeable membrane is a membrane that allows certain substances to pass through and blocks the passage of some other substance depending on the nature and size of the substance.

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Examples of Osmosis

  1. Absorption of water from the soil by roots of plant.
  2. Movement of water across the cell of plants.
  3. Movement of water from the root hair into the cortex.
  4. Absorption of water in the colon (large intestines) of mammals.
  5. Absorption of water in the nephron of the kidney of mammals.
  6. Entering of water into the cells of amoeba

Factors affecting the rate of osmosis

  1. Concentration gradient
  2. Temperature
  3. Nature of the semipermeable membrane

 

 

Some terminologies

Hypertonic solution

This is a solution which has higher concentration than the one it is being compared to.

Hypotonic solution

This is a solution which has lower concentration than the one it is being compared to.

Isotonic solution

This is a solution which has the same concentration as the one it is being compared to.

Active transport

Active transport is the movement of substances from a low concentration region to a high concentration region across a living cell membrane using energy from the cell.

Examples of Active Transport

  1. Absorption of digested food into the blood in the intestines of mammals.
  2. Movement of glucose into the phloem tissues of plants.
  3. Absorption of mineral salt from the soil by plant roots
  4. Re-absorption of glucose, amino acids and ions in the kidney of mammals.

 

Crenation

Crenation: Is the process by which an animal cell placed in a hypertonic solution loses water to the solution and shrinks or becomes wrinkled.

Plasmolysis

It is the shrinkage of the cytoplasm of a plant cell when placed in a hypertonic solution.

OR

Plasmolysis is a a process by which a plant or animal cell loses water by Osmosis as a result of the cell being placed in a solution more concentrated than the cell content.

Turgidity

Turgidity: is the process by which plants cell absorbs water so much that they become strong and rigid and gives mechanical support to the plant.

Transpiration

Transpiration: is the loss of water vapour or evaporation from the leaves or stems of plants or upper part of a plant or shoot.

 

NB

Detail Explanations will be given during face-to-face session with your facilitator.

 

 

The practical lessons will be in our next lesson.

 

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Assignment 

1.What do you understand by the following

i. Diffusion

ii. Osmosis

iii. Plasmolysis

2. State two

i. differences between diffusion and Osmosis

ii. similarities between diffusion and Osmosis

3. i.  What is Transpiration?

ii. State three reasons why transpiration is necessary in plants.

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OBJECTIVES  WASSCE PAST QUESTIONS ONLY

  1. Salting of fish fish for preservation usess the principle of

A. Diffusion

B. Osmosis

C. Plasmolysis

D. Active transport

Ans; A. Diffusion 

2. Movement of water into plant cell causes the cell

A. Become turgid

B. Become Flaccid

C. Burst its cell wall

D. Become Plasmolyzed

Ans: A. turgid

3. Plasmolysis Demonstrates

A. Turgidity in cells

B. insufficient intake of water by a cell

C. Absorption of salt solution by a cell

D. Excessive loss of water from a cell

Ans: D, Excessive loss of water from a cell 

4. One major role of water in plants is that it

A. Keeps the plants green

B. allows evaporation to take place

C. Prevents fungal attack

D. Keeps the stem turgid

Ans: D. Keeps the stem turgid

6. The physical process which involves the free movement of material in a living cell is known as

A. absorption

B. Osmosis

C. Diffusion

D. Plasmolysis

Ans:  C. Diffusion 

7. When plant cell is placed in a concentrated solution, it will

A. enlarge and becomes turgid

B. expand and then shrink

C. expand and burst

D. decrease in size and becomes flaccid

Ans: D. decrease in size and becomes flaccid

8. Which of the following factors will not affect the rate of diffusion

A. Temperature

B pressure

C. surface area to volume ratio

D. Concentration gradient

Ans; C. surface area to volume ratio 

9. In flowering plants, mineral salts are transported through the

A. cambium

B. Ploem

C. Stomata

D. xylem

Ans: D. xylem

10. The tissue which is likely to sustain red when a herbaceous plant is placed in a red solution for about two hours is the

A. cambium

B Phloem

C. parenchyma

D. Xylem

Ans: D. Xylem

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