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SS1: BIOLOGY - 1ST TERM

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  1. Introduction to Biology | Week 1
    6 Topics
    |
    1 Quiz
  2. Recognizing Living Things | Week 2
    3 Topics
    |
    1 Quiz
  3. Organisation of Life | Week 3
    3 Topics
  4. Classification of Living Organisms | Week 4
    7 Topics
    |
    1 Quiz
  5. Kingdom Prokaryotae / Monera & Kingdom Protista | Week 5
    3 Topics
    |
    3 Quizzes
  6. Kingdom Fungi & Kingdom Plantae | Week 6
    9 Topics
    |
    2 Quizzes
  7. Kingdom Animalia I | Week 7
    6 Topics
    |
    1 Quiz
  8. Kingdom Animalia II | Week 8
    5 Topics
    |
    1 Quiz
  9. The Cell | Week 9
    3 Topics
    |
    1 Quiz
  10. The Cell Structure and Functions | Week 10
    4 Topics
    |
    1 Quiz
  11. The Cell and its Environment | Week 11
    4 Topics
    |
    1 Quiz
  12. Nutrition in Plants | Week 12
    4 Topics
    |
    1 Quiz



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Osmosis is defined as the movement of water molecules from a region of higher water potential (dilute solution or lower concentration of the solute) to a region of lower water potential (higher concentration of the solute or concentration of the solution) through a semi-permeable/selectively permeable membrane.

OR

Osmosis is defined as the movement of water molecules from a dilute solution to a concentrated solution through a semi-permeable / selectively permeable membrane.

If a concentrated solution is separated from the dilute solution by a semi-permeable membrane, water diffuses across the membrane from the dilute solution by the process of osmosis.

The weaker solution is said to be hypotonic and the stronger solution is described as hypertonic, when both solutions have the same concentration, they are described as isotonic.

Osmosis

Osmosis provides the primary means by which water is transported into and out of cells.

Common Terms:

(i) Osmotic Pressure: The pressure that a solution can potentially exert is called Osmotic pressure.

(ii) Water Potential: The water potential of a solution is a measure of whether it is likely to gain or lose water molecules from another solution.

Experiment – Osmosis in a Non–living System:

1. Tie a piece of cellophane paper over the mouth of a thistle funnel using a rubber band. 

2. Fill the thistle funnel with a strong sugar solution. Mark the level of the sugar solution.

3. Lower the thistle funnel into a beaker of water such that the levels of the sugar solution in the thistle funnel and in the beaker are the same.

4. Set up a control experiment; add water into the thistle funnel instead of sugar solution.

5. Allow the experiment to stand for some hours.

Thistle funnel experiment 11 e1616422398921

Observation:

The level of water in the beaker drops while the level of the sugar solution rises

Interpretation:

Water molecules move from a region of higher concentration (the beaker) through the selectively permeable membrane (cellophane paper) into the thistle funnel by osmosis.

Experiment – Osmometer with Living Material:

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Activity – osmosis in living tissue:

1. Remove the skin of a potato tuber. Cut it into two equal halves with a blade.

2. Make a square or a circular shaped cavity in the centre of the slice.

3. Place the slices of yam in a trough containing water. 

4. Add freshly prepared 20% sugar solution into the cavity of the tubers and water into the second.

5. Mark the level of water and sugar in the trough and yam cavity.

6. Allow the set-up to stand for some hours.

7. Notice the sugar solution in the osmometer towards the end of the experiment.

Observation: 

The level of the sugar solution has risen resulting in a decrease in the level of the water trough.

Interpretation:

The yam tissue is acting as a semi-permeable membrane. Water molecules moved through the yam tissue into the cavity of the yam by osmosis as a result of the difference in the concentration. This shows that osmosis has taken place.

Differences between Diffusion & Osmosis:

Diffusion:Osmosis:
1.Diffusion occurs in gases and liquidsOsmosis occurs only in liquids mediums
2.Semi permeable membrane not requiredSemi permeable membrane is required
3.Occurs in living and non-living organismsOccurs naturally in living organisms

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