Understanding Cells and Their Environment: Diffusion and Osmosis Biology SS 1 First Term Lesson Notes Week 5

Subject: Biology

Class: SS1

Term: First Term

Week: 5

Age (years): 15-16

Topic: The Cell and Its Environment

Sub-topic: Diffusion and Osmosis

Duration: 2 hours

Behavioural Objectives:

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

1. Define diffusion and osmosis.
2. Explain the processes of diffusion and osmosis in cells.
3. Describe the significance of these processes in biological systems.
4. Identify examples of osmosis, including haemolysis and plasmolysis.
5. Use an osmometer with living material to demonstrate osmosis.

Keywords:

Diffusion, Osmosis, Selectively Permeable Membrane, Haemolysis, Plasmolysis, Osmometer, Biological Significance

Set Induction:

Begin the lesson by asking students to consider how substances move in and out of their cells. Engage them in a discussion about everyday examples, such as why salt can preserve food.

Entry Behaviour:

Students should have a foundational understanding of cell structure and the previous lesson on the cell.

Learning Resources and Materials:

• Diagrams showing diffusion and osmosis
• Microscopes and osmometer kits for practical demonstration
• Projector for presentations
• Samples for practical activities (potato slices, salt solution)

Building Background / Connection to Prior Knowledge:

Connect this lesson to the previous topic by discussing how cells maintain homeostasis through processes like diffusion and osmosis.

Embedded Core Skills:

• Problem-solving: Understanding how substances move through membranes.
• Collaboration: Working in pairs to conduct experiments.
• Critical thinking: Analyzing results from experiments.

Learning Materials:

• Textbook: “Modern Biology for Senior Secondary Schools”
• Diagrams illustrating diffusion and osmosis
• Videos demonstrating these processes in cells

Reference Books:

1. Classic Practical Biology for Senior Secondary Schools by Nneka N. Ekechukwu
2. New Comprehensive Practical Biology by Emedo A. B. C et al.

Instructional Materials:

• Interactive PowerPoint presentation
• Models of cells demonstrating diffusion and osmosis
• Online videos and simulations

Content:

1. Diffusion:

• Definition: Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached.
• Process: This process occurs naturally and does not require energy (passive transport). For example, when food coloring is added to water, it spreads out evenly through the water over time.
• Significances:
  • Helps cells acquire nutrients.
  • Assists in the removal of waste products.
  • Crucial for gas exchange in organisms (e.g., oxygen and carbon dioxide in the lungs).

2. Osmosis:

• Definition: Osmosis is the diffusion of water molecules through a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration.
• Example Processes:
  • Haemolysis: The bursting of red blood cells when placed in a hypotonic solution (low solute concentration). For example, if red blood cells are placed in distilled water, water enters the cells, causing them to swell and burst.
  • Plasmolysis: The shrinking of plant cells when placed in a hypertonic solution (high solute concentration). For instance, if a plant cell is placed in concentrated salt water, water leaves the cell, causing it to shrivel.
  • Osmometer with Living Material: An osmometer can be used to measure the osmotic pressure of solutions. For instance, a potato slice placed in saltwater can show how osmosis works.
• Biological Significance:
  • Maintains cell turgor in plants, which is essential for support.
  • Regulates the movement of water in and out of cells, maintaining homeostasis.

Evaluation:

Fill-in-the-Blank Questions (15 Questions):

1. The movement of molecules from high to low concentration is called _____. a) Osmosis
   b) Diffusion
   c) Filtration
   d) Evaporation
2. Osmosis specifically refers to the movement of _____. a) Glucose
   b) Proteins
   c) Water
   d) Ions
3. The process that results in the bursting of red blood cells is known as _____. a) Plasmolysis
   b) Haemolysis
   c) Osmosis
   d) Diffusion
4. A selectively permeable membrane allows _____. a) All substances
   b) Some substances to pass
   c) No substances
   d) Only gases
5. When a plant cell is placed in salt water, it undergoes _____. a) Haemolysis
   b) Plasmolysis
   c) Osmosis
   d) Diffusion
6. Diffusion is a type of _____ transport. a) Active
   b) Passive
   c) Facilitated
   d) Bulk
7. An example of diffusion is _____. a) Water moving through a membrane
   b) Sugar dissolving in tea
   c) Salt moving into a cell
   d) None of the above
8. The process of water moving out of a cell is called _____. a) Absorption
   b) Osmosis
   c) Evaporation
   d) Filtration
9. In a hypotonic solution, the concentration of solutes is _____ compared to the inside of the cell. a) Higher
   b) Lower
   c) Equal
   d) None of the above
10. The movement of molecules without the use of energy is called _____. a) Active transport
    b) Passive transport
    c) Diffusion
    d) Osmosis
11. Plasmolysis occurs when plant cells are placed in a _____ solution. a) Isotonic
    b) Hypotonic
    c) Hypertonic
    d) Saturated
12. The term _____ refers to the concentration of solute in a solution. a) Solvent
    b) Osmosis
    c) Tonicity
    d) Diffusion
13. When substances move across the cell membrane against the concentration gradient, it is called _____. a) Active transport
    b) Passive transport
    c) Diffusion
    d) Osmosis
14. Water moves from an area of _____ concentration to an area of high solute concentration during osmosis. a) Low
    b) High
    c) Equal
    d) None of the above
15. An osmometer can demonstrate the process of _____. a) Diffusion
    b) Active transport
    c) Osmosis
    d) Filtration

Class Activity Discussion: FAQs (15 Questions and Answers):

1. Q: What is diffusion? A: Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration.
2. Q: What is osmosis? A: Osmosis is the diffusion of water through a selectively permeable membrane.
3. Q: Why is osmosis important for cells? A: Osmosis helps maintain the balance of water in cells, which is essential for their function and survival.
4. Q: What happens to a cell in a hypotonic solution? A: The cell swells and may burst due to the influx of water.
5. Q: What is plasmolysis? A: Plasmolysis is the process where plant cells shrink due to the loss of water when placed in a hypertonic solution.
6. Q: What causes haemolysis? A: Haemolysis occurs when red blood cells burst in a hypotonic solution due to excess water intake.
7. Q: How can osmosis be demonstrated practically? A: By using an osmometer with a potato slice in different salt concentrations.
8. Q: Can diffusion occur in solids? A: Yes, diffusion can occur in solids, but it is slower compared to liquids and gases.
9. Q: How does temperature affect diffusion? A: Higher temperatures increase the rate of diffusion because molecules move faster.
10. Q: What role do cell membranes play in diffusion? A: Cell membranes control the movement of substances in and out of cells, allowing some to pass while blocking others.
11. Q: What is a selectively permeable membrane? A: A membrane that allows certain substances to pass while restricting others.
12. Q: How does osmosis differ from diffusion? A: Osmosis specifically refers to the movement of water, while diffusion refers to the movement of all types of molecules.
13. Q: What is an isotonic solution? A: A solution with the same concentration of solutes as the inside of the cell, resulting in no net movement of water.
14. Q: Why do plant cells need to maintain turgor pressure? A: Turgor pressure helps plants maintain structure and support.
15. Q: How can you tell if a cell is in a hypertonic environment? A: If the cell appears shriveled or shrinks in size, it is likely in a hypertonic environment.

Presentation:

Step 1: Review the previous topic on cell structure, emphasizing the importance of cell membranes.
Step 2: Introduce diffusion and osmosis, using diagrams and examples to illustrate these processes.
Step 3: Encourage students to share their thoughts and examples of diffusion and osmosis in everyday life, providing corrections as necessary.

Activities:

Teacher’s Activities:

• Introduce concepts with interactive presentations.
• Conduct practical demonstrations using an osmometer.
• Facilitate group discussions on the importance of these processes.

Learner’s Activities:

• Participate in discussions and ask questions.
• Conduct experiments to observe osmosis and diffusion.
• Complete fill-in-the-blank and evaluation questions.

Assessment:

Evaluation Questions (10 Questions):

1. What is the process by which water moves through a cell membrane called?
2. Explain what happens to red blood cells in a hypotonic solution.
3. Describe the significance of diffusion in cellular processes.
4. What are the differences between osmotic and hydrostatic pressure?
5. How can you measure the rate of osmosis?
6. Why do plant cells not burst in hypotonic solutions?
7. Provide an example of a real-life situation where diffusion is important.
8. What type of solution would cause plasmolysis in plant cells?
9. How does temperature influence the rate of diffusion?
10. Why is the concept of tonicity important in biology?

Conclusion:

The teacher will circulate the classroom to assess students’ understanding, marking their responses and providing feedback. Students will be encouraged to reflect on the importance of diffusion and osmosis in maintaining life processes within cells.