1. What could’ve gone wrong?
These plants are the same species so why are they so different?

2. How does gas exchange happen in plants?
Diffusion
How does gas exchange happen in plants?
Lesson Learning Outcomes:
Define the term diffusion
Carry out experiments into the rate of diffusion
Describe how gases enter and leave a leaf
Increasing Difficulty 2

3. Dictionary definition
Diffusion: the movement of particles from a region of higher concentration to an area of lower concentration

4. Diffusion Experiments
Copy the following table:
Medium
Distance/m
Time/s
Speed m/s
Gas
Liquid
Solid
Make a prediction, demo gas and solid, studnets carry out tea practical and work out liquid

5. Liquids Your task is to carry out diffusion in liquid
Pour water into the beaker (about 200ml)
Measure the distance from the bottom of the beaker to the top of the water line in the beaker using a ruler and record it in your table
Put in the tea bag and push it to the bottom with the stirring rod
Start the stop clock and time how long it takes for the water at the top to become tea coloured. Record this in your table then calculate the speed

6. Draw a storyboard
Think about the tea, how did the tea get from the bottom to the top
Try to describe the stages using the word diffusion
Now exchange books and try to draw a molecular diagram to explain

7. Diffusion The particles are separate when first put together.
They slowly start to mix due to their random motion.
The particles are now nearly fully diffused.
The particles are fully diffused. 7

8. Rate of diffusion Steep concentration gradient
Diffusion increases if there is a steeper gradient…
Steep concentration gradient
Shallow concentration gradient 8

9. Plants...
A leaf

10. Plants Many small pores, called stomata, mostly on the lower epidermis
A stoma

11. Gas Exchange...
In the light: Carbon dioxide diffuses into the leaf through the stomatal pore The carbon dioxide diffuses through the air space Then it diffuses into the cells

12. Gas Exchange...
In the light: Oxygen diffuses out of the cells into the air space Then it diffuses out through the stomata to the surrounding air REMEMBER: diffusion relies on a concentration gradient!

13. Gas Exchange...
In the dark: Oxygen diffuses into the leaf taking the same path as carbon dioxide in the light

14. Summarise
Draw two pictures to show how carbon dioxide and oxygen are exchanged in leaves in the light and in the dark

15. To set up for next time...
We are going to set up an experiment for next lesson.
In pairs you have been given a sucrose concentration
Use a core borer to cut a tube of potato
Use the knife to cut the potato to 4cm
Weigh the potato and record it in the back of your book
Collect a test tube and write your initials on the test tube and the concentration you were given
Put 30cm3 of your sucrose solution concentration into the tube
Pop it on the side until next week