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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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Plasmolysis:

When a living plant cell is placed or surrounded in a sugar or salt solution, a more concentrated or hypertonic solution than the cell sap, water will be lost from the cell to the stronger solution resulting in exosmosis.

When the cell is left in the hypertonic solution for a long time, it will result in the pulling away of the cytoplasm from the cell wall, consequently, the cytoplasm will shrink and the cell wall will collapse. At this stage, we may say the cell is plasmolyzed.

Plasmolysis is the shrinking of the cytoplasm away from the cell wall when plant cells are immersed in a hypertonic solution.

plasmolysis-stages-of
The phenomenon of Plasmolysis.

Turgidity:

However, if a plant cell is placed in a hypotonic solution, it behaves differently; water enters the cell by osmosis due to the fact that the cytoplasm solution is stronger than the water. This is called endosmosis.

As water enters the cell the vacuole increases in size and pushes the cell contents against the cell wall. The cellulose cell wall prevents overstretching of the cell by exerting an opposing pressure preventing the entry of more water. In this state the cell becomes turgid.

Turgidity is important in land plants because it makes them firm and gives support. On the other hand, if the plant is not supplied with water, it will die when all its cells become plasmolysed.

Flaccidity:

When the plant cell is placed in an isotonic solution, there is no net flow of water toward the outside or inside. When the flow of water into the cell and out of the cell exists in equilibrium then the plant cells are said to be flaccid.

It is important to note that a plant in an isotonic can build no turgor. A hypotonic solution produces the necessary turgor plants require. Without water, plants would become flaccid and wilt.

osmosis in plant cell
Osmosis in a plant cell. When the cell is left in isotonic (normal), hypotonic and hypertonic solutions.

Crenation:

When an animal cell is placed in a hypertonic solution. It will lose water. The net movement of water out of the cell into the surrounding is exosmosis.

The membrane of the cell forms little spikes as water is lost and the cell shrinks in a process called crenation.

Haemolysis:

When an animal cell is placed in a hypotonic solution, it will swell and burst because it does not have a cell wall.

If a red blood cell is placed in a hypotonic solution, it will take up water & swell. There is a net movement of water molecules from the surrounding fluid to the cell (endosmosis).

As it gets bigger and bigger, its surface area will increase causing the cell to swell and eventually rupture, causing its contents to flow out. If this is allowed to continue, all the contents of the cell would have leaked out living behind a membrane glove. This is known as haemolysis.

Excessive hemolysis can lead to hemolytic anaemia. Hemolytic anaemia is a disorder in which red blood cells are destroyed faster than they can be made.

🤔 What happens when an Animal Cell is placed in an Isotonic Solution?

No change occurs to an animal cell when kept in an isotonic solution.

osmosis

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