Diffusion: Movement Down the Concentration Gradient

Biology Grades High School 6:06 Video
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Lesson Description

This lesson explores the process of diffusion, explaining how molecules move from areas of high concentration to areas of low concentration and its significance in biological systems.

Video Resource

Diffusion | Membranes and transport | Biology | Khan Academy

Khan Academy

Duration: 6:06
Watch on YouTube

Key Concepts

  • Concentration Gradient
  • Diffusion
  • Equilibrium

Learning Objectives

  • Define diffusion and explain its relationship to the concentration gradient.
  • Describe how molecules move during diffusion and why it doesn't require energy.
  • Explain how diffusion leads to equilibrium and the continuous movement of molecules even at equilibrium.

Educator Instructions

  • Introduction (5 mins)
    Begin by asking students what they already know about diffusion. Introduce the video 'Diffusion | Membranes and transport | Biology | Khan Academy' and explain that it will cover the fundamentals of diffusion.
  • Video Viewing (10 mins)
    Play the video. Encourage students to take notes on key terms like concentration gradient, diffusion, and equilibrium.
  • Discussion (10 mins)
    Lead a class discussion about the video. Focus on clarifying any misunderstandings and reinforcing the key concepts.
  • Activity: Diffusion Modeling (15 mins)
    Have students participate in a hands-on activity to model diffusion (see interactive exercises). This will help them visualize the process.
  • Wrap-up and Assessment (10 mins)
    Summarize the main points of the lesson. Administer the multiple-choice and fill-in-the-blank quizzes to assess student understanding.

Interactive Exercises

  • Diffusion Simulation with Food Coloring
    Students place a drop of food coloring into a glass of water and observe how the dye diffuses over time. This visually demonstrates the movement of molecules from high to low concentration until equilibrium is reached. Discuss how temperature might affect the rate of diffusion.

Discussion Questions

  • What is a concentration gradient, and how does it relate to diffusion?
  • Why does diffusion not require energy?
  • What does it mean for a system to be at equilibrium in terms of diffusion, and are molecules still moving?

Skills Developed

  • Critical Thinking
  • Scientific Modeling
  • Data Interpretation

Multiple Choice Questions

Question 1:

Diffusion is the movement of molecules:

Correct Answer: From an area of high concentration to an area of low concentration.

Question 2:

What is a concentration gradient?

Correct Answer: A difference in concentration of a substance across a space.

Question 3:

Which of the following is NOT a characteristic of diffusion?

Correct Answer: It requires energy input.

Question 4:

At equilibrium, the movement of molecules:

Correct Answer: Continues in both directions, but there is no net change in concentration.

Question 5:

The rate of diffusion is affected by:

Correct Answer: Temperature, size of the molecules, and the concentration gradient.

Question 6:

Which of the following is an example of diffusion in a biological system?

Correct Answer: The movement of oxygen from the lungs into the blood.

Question 7:

What is the term for diffusion of water across a semi-permeable membrane?

Correct Answer: Osmosis

Question 8:

Why does diffusion occur?

Correct Answer: Because cells need to maintain a high concentration of certain molecules.

Question 9:

If a cell has a higher concentration of solute inside than outside, water will tend to move:

Correct Answer: Into the cell.

Question 10:

Diffusion is important for:

Correct Answer: Maintaining homeostasis.

Fill in the Blank Questions

Question 1:

The process by which molecules move from an area of high concentration to an area of low concentration is called ________.

Correct Answer: diffusion

Question 2:

A ________ ________ exists when there is a difference in the concentration of a substance across a space.

Correct Answer: concentration gradient

Question 3:

Diffusion does not require energy input, so it is a form of ________ transport.

Correct Answer: passive

Question 4:

When the concentration of a substance is equal throughout a space, the system has reached ________.

Correct Answer: equilibrium

Question 5:

Even at equilibrium, molecules continue to move randomly, but there is no ________ change in concentration.

Correct Answer: net

Question 6:

________ is the diffusion of water across a selectively permeable membrane.

Correct Answer: osmosis

Question 7:

In the lungs, ________ diffuses from the air into the blood, and carbon dioxide diffuses from the blood into the air.

Correct Answer: oxygen

Question 8:

The movement of molecules during diffusion is driven by their ________ random motion.

Correct Answer: constant

Question 9:

Maintaining ________ in living organisms often relies on diffusion processes.

Correct Answer: homeostasis

Question 10:

A higher ________ difference leads to a faster rate of diffusion.

Correct Answer: concentration

Educational Standards

B.LS1.1:Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins, which carry out the essential functions of life through systems of specialized cells. B.LS1.3:Plan and conduct an investigation to provide evidence of the importance of maintaining homeostasis in living organisms. B.LS1.7:Use a model to illustrate that cellular respiration is a chemical process whereby the bonds of food molecules and oxygen molecules are broken and the bonds in new compounds are formed, resulting in a net transfer of energy.

Teaching Materials

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