BIOLOGY LESSON NOTE ON DIFFUSION

Topic: Diffusion

Class: Senior Secondary School (SSS 2)

Duration: 80 minutes

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Specific Objectives

By the end of the lesson, students should be able to:

1. Define diffusion and explain its significance in biological systems.
2. Describe the process of diffusion with real-life examples.
3. Differentiate between diffusion, osmosis, and active transport.
4. Explain the factors affecting the rate of diffusion.
5. Describe the role of diffusion in plants and animals.
6. Conduct simple experiments to demonstrate diffusion.
7. Explain the importance of diffusion in biological processes.

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Lesson Content

Introduction to Diffusion

Diffusion is a fundamental biological process that allows molecules to move freely from one region to another. It is essential for the transport of gases, nutrients, and waste materials in living organisms. Understanding diffusion helps explain how cells exchange materials with their environment.

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Definition of Diffusion

Diffusion is the movement of molecules or particles from a region of higher concentration to a region of lower concentration until equilibrium is reached. It occurs in gases, liquids, and solids without the need for external energy.

Key Terms:

• Concentration Gradient – The difference in the concentration of molecules between two regions.
• Equilibrium – The point at which molecules are evenly distributed, and there is no net movement.
• Passive Transport – The movement of substances without the use of cellular energy (ATP).

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How Diffusion Works

Diffusion occurs when molecules move randomly due to their kinetic energy. They spread from an area of high concentration to an area of low concentration until there is no concentration gradient.

Examples of Diffusion in Daily Life:

1. Perfume Spreading in a Room – When perfume is sprayed in one corner of a room, its scent spreads throughout due to diffusion.
2. Dissolving Sugar in Water – Sugar molecules spread evenly in water without stirring due to diffusion.
3. Oxygen Exchange in Lungs – Oxygen diffuses from the alveoli (high concentration) into the blood (low concentration), while carbon dioxide diffuses out.

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Diffusion vs. Osmosis vs. Active Transport

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Factors Affecting Diffusion

1. Concentration Gradient: The steeper the gradient, the faster the rate of diffusion.
2. Temperature: Higher temperatures increase the kinetic energy of molecules, speeding up diffusion.
3. Molecule Size: Smaller molecules diffuse faster than larger ones.
4. Membrane Permeability: The nature of the membrane affects how easily molecules can pass through.
5. Distance: The shorter the distance, the faster the diffusion process.

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Role of Diffusion in Living Organisms

1. In Plants:

   • Gas Exchange in Leaves: Oxygen and carbon dioxide diffuse through the stomata during photosynthesis and respiration.
   • Nutrient Absorption: Minerals and nutrients diffuse into plant cells from the soil.

2. In Animals:

   • Respiration: Oxygen diffuses from the lungs into the blood, and carbon dioxide diffuses out.
   • Digestion: Nutrients from digested food diffuse into the bloodstream through the small intestine.
   • Excretion: Waste products diffuse from cells into the blood for removal by the kidneys.

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Experiment: Demonstrating Diffusion Using Potassium Permanganate

Materials Needed:

• Beaker
• Water
• Potassium permanganate (purple crystals)

Procedure:

1. Fill a beaker with water.
2. Gently drop a few potassium permanganate crystals into the water without stirring.
3. Observe how the purple color spreads over time.

Observations:

• The color slowly spreads from the point where the crystal was added.
• After some time, the entire beaker becomes evenly colored.

Conclusion:

This demonstrates diffusion as the potassium permanganate molecules move from a high concentration (where the crystal was added) to a low concentration (rest of the water).

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Evaluation

1. Define diffusion.
2. State two differences between diffusion and osmosis.
3. List three factors affecting diffusion.
4. Explain what happens to oxygen molecules in the lungs during diffusion.
5. Why is diffusion important in plants?

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Objective Questions on Diffusion

1. Diffusion is the movement of molecules from ___ to ___ concentration.
   a) High to low
   b) Low to high
   c) Equal to high
   d) High to equal

2. Which of these does NOT affect diffusion?
   a) Concentration gradient
   b) Temperature
   c) Distance
   d) Color of molecules

3. Diffusion in living organisms is an example of ___.
   a) Active transport
   b) Passive transport
   c) Chemical transport
   d) Selective transport

4. Oxygen moves from the alveoli to the blood by ___.
   a) Active transport
   b) Diffusion
   c) Osmosis
   d) Filtration

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Conclusion

Diffusion is a vital biological process that helps in the movement of gases, nutrients, and waste in plants and animals. It occurs passively and does not require energy. Understanding diffusion explains how cells interact with their environment, ensuring the survival of living organisms.