THE CELL AND ITS ENVIRONMENT

Subject: Biology

Topic: The Cell and its environment

Class: SS1

Age: 14+

Sex: Mixed

Instructional  Materials. Textbook, specimen, pictures, white board, interactive board

Aim of the Lesson: To help the learner understand the cell and its environment

Anticipated Problems: Because of advancement in class, most themes might be new to the learners and might result to difficulty in understanding.

Possible Solution: The teacher explains the concept in details using illustrations and real objects.

Content Objectives: By the end of the lesson, learners should be able to;

1. Define diffusion
2. Define osmosis
3. Define plasmolysis
4. Define Haemolysis
5. Define Turgidity
6. Explain Flaccidity

Time Table fit/ previous knowledge: The learner learnt about the cell in their previous lesson

Set Induction: The teacher asks the student to observe the object on the table.

Differentiation Method/Multiple Intelligence: The teacher uses different teaching technique such as discussion, role playing, questioning and use of picture to ensure all the learner benefit from the lesson.

DIFFUSION

 Diffusion can be defined as the process by which molecules of gas or ions move from a region of high concentration to a region of low concentration until they are evenly distributed.

FACTORS CONTROLLING DIFFUSION

 The rate of diffusion is controlled by a number of factors which include:

i.                     State of matter: (Gas moves faster than the liquid& solids

ii.                   Molecular size (Smaller molecules diffuses faster than big ones)

iii.                   Difference in concentration (the greater the differences in the concentration of the molecules, the greater the rate of diffusion.

iv.                   Temperature: High temperature increase the speed at with molecules move (The higher the temperature, the faster the rate of diffusion)

EXPERIMENT TO DEMONSTRATE DIFFUSION IN GASES Material: Bottles of Ammonia solution

Method: Take a bottle of ammonia solution, open the bottle and move some distance away from the bottle and wait for sometime.

Observation: The smell of the ammonia gas spread to all corners of the classroom.

Conclusion: The smell perceived everywhere in the classroom shows that diffusion of ammonia gas has taken place.

BIOLOGICAL SIGNIFICANCE OF DIFFUSION IN PLANTS

1.       Movement of carbon dioxide through the stomata of the leaves during transpiration and photosynthesis.

2.       Movement of oxygen into the leaves through the stomata during respiration

3.       Movement of the manufactured food from the leaves to other parts of the plants.

BIOLOGICAL SIGNIFICANCE OF DIFFUSION IN ANIMALS

 1. Gaseous exchange in any cells and organisms e.g. amoeba obtains oxygen by diffusion.

2. Exchange of nutrients and oxygen between a foetus and the mother through the placenta.

3. Gaseous exchange in the lungs of mammals

4. Absorption of food from the small intestine through the villi into the blood stream.

OSMOSIS

Osmosis can be defined as the movement of water or solvent molecules from a region of dilute or a weaker solution to a region of concentrated of stronger solution through a selectively permeable membrane (semi-permeable membrane).

CONDITIONS NECESSARY FOR OSMOSIS TO TAKE PLACE

i.                     Presence of a stronger solution e.g. salt solution

ii.                   Presence of a weaker solution e.g. water

iii.                  Presence of a semipermeable membrane

LIVING CELLS AS OSMOMETER

A living cell is usually surrounded by a medium which can be described as hypertonic, hypotonic and isotonic.

A. HYPERTONIC: When the cell is surrounded by a stronger solution, water will be lost by the cell. The cell shrinks.

B. HYPOTONIC: When a cell of a living organism is surrounded by water or solution whose concentration is lower, water passes into the cell by osmosis.

C. ISOTONIC: When the solute concentration of the cell and its surrounding medium are the same, the solution is said to be isotonic. No net movement of molecules.

OSMOTIC PRESSURE

Osmotic pressure can be defined as the pressure which moves water across a membrane into a solution of a higher concentration. Osmotic pressure draws water into the cell. The pressure which a solution can potentially exert is called its Osmotic Potential.

EXPERIMENT ON OSMOSIS

TO DEMONSTRATE OSMOSIS USING A LIVING TISSUE Materials: Yam tuber, sugar solution, water, knife, petri -dishes

Method: Unripe pawpaw is pilled and cut into two equal halves, sugar solution is added to A and ordinary water to B. the two are put inside a petrish dish for three to four hours. Water levels in both are marked with pins

Observation: Water level in A increases while that of B remains the same. Conclusion: The rise in the level of sugar solution in A shows that water has passed from the petrish dish into the unripe pawpaw, hence, osmosis has taken place in A and not in B.

OSMOTIC PROCESSES IN PLANTS

i.                     Absorption of water from the soil by the root

ii.                    Movement of water in and out of quard cells of stomata

iii.                   Movement of water from one cell to another

OSMOTIC PROCESSES IN ANIMAL

i.                     Reabsorption of water from glomerular filtrate in the kidney

ii.                    Absorption of water by the colon

iii.                   Loss of water through sweating

PLASMOLYSIS

Plasmolysis can be defined as the outward movement of water from living cells when they are placed in a hypertonic situation. It involves the withdrawal of water from living cells up to the extent that it will result in the pulling away of cytoplasm from the cell membrane of cell-wall (the cytoplasm shrink) and the whole cell wall collapse).

HAEMOLYSIS

 Haemolysis is defined as the process by which red blood cells burst as a result of too much water passing into it when placed in hypotonic solution

TURGIDITY

 Turgidity Is defined as the condition in which cells absorbs plenty of water up to a point where the cell is fully stretched. Turgidity is useful to the plants because it makes plants to stand erect, gives support to the stem, leaves, flowers and guard cells.

FLACCIDITY

Flaccidity can be defined as the condition in which plants lose water to their surroundings faster than they can absorb when plant loses more water, it is said to be flaccid. Flaccidity may cause wilting & death.

Assessment plan. The teacher uses the following to assess the learners

Class work

1. Define diffusion
2. Define osmosis

Home work

1. Write five importance of osmosis in plant
2. Write five importance of osmosis in animal

Multiple choice questions.

1. The process by which red blood cells burst as a result of too much water passing into it when placed in hypotonic solution is known as  

1. Hemolysis
2. Turgidity
3. Flaccidity
4. Plasmolysis

2. The condition in which cells absorbs plenty of water up to a point where the cell is fully stretched is known as

1. Hemolysis
2. Turgidity
3. Flaccidity
4. Plasmolysis

3. The condition in which plants lose water to their surroundings faster than they can absorb is known as

1. Hemolysis
2. Turgidity
3. Flaccidity
4. Plasmolysis

4. The outward movement of water from living cells when they are placed in a hypertonic situation.

1. Hemolysis
2. Turgidity
3. Flaccidity
4. Plasmolysis

Evaluation

1. Define diffusion
2. Define osmosis
3. Define plasmolysis
4. Define Hemolysis
5. Define Turgidity
6. Explain Flaccidity

Glossary

Hypertonic: When the cell is surrounded by a stronger solution.

 Hypotonic: When a cell of a living organism is surrounded by water or solution whose concentration is lower.

 Isotonic: When the solute concentration of the cell and its surrounding medium are the same.

Conclusion:  Diffusion is the process by which molecules of gas or ions move from a region of high concentration to a region of low concentration