1. Leaves and Photosynthesis
What adaptations do leaves have for photosynthesis?

2. The Structure and Function of a Leaf
Learning Objectives:
2.13: Describe how the structure of a leaf is adapted for photosynthesis, including:
A large surface area
B containing chlorophyll in chloroplasts to absorb light
C stomata for gas exchange (carbon dioxide, oxygen and water
vapour)

3. The structure and function of a leaf
Watch the following short video about the structure and function of a leaf.
While you are watching, make a note of key words and important points.
Pay particular attention to the names of the different parts of the leaf. Label your diagram with the information from the video.

6. Plant cell cell wall cell membrane cytoplasm nucleus vacuole
chloroplast

7. Name the structure… Function Structure
Controls what goes in and out of the cell.
Contains the genetic material.
Surrounds the cell and gives support.
Contains chlorophyll and absorbs sunlight.
Contains cell sap and gives support.
Where all the chemical reactions happen.
cell membrane
nucleus
cell wall
chloroplasts
vacuole
cytoplasm

8. Chloroplasts absorb sunlight

9. External: How leaves are adapted for efficient photosynthesis
Side vein
Apex
Mid-rib vein
Leaf stalk (petiole)
Leaf blade (lamina)

10. Draw this table in your books
Feature of leaves
How it aids photosynthesis
Broad, flat leaves
Stomata
Veins
Chloroplasts
Waxy layer
Thin

11. How leaves are suited to photosynthesis
Leaves are broad and flat, giving large surface area to absorb as much light as possible.

12. They have ‘holes’ in the leaves to allow carbon dioxide in and oxygen out. These are STOMATA.
Guard cells

13. There are veins in the leaves to transport water and sugar around.

14. Many of the cells are packed with chloroplasts which contain a light trapping pigment- chlorophyll.

15. There is a waxy layer on top to stop water being lost from the leaf.

16. Thin leaves provide a short diffusion distance for carbon dioxide to reach the palisade and mesophyll cells

17. HT: How structure of the leaf is adapted for efficient photosynthesis
• Epidermis is transparent;
• Palisade layer at the top containing most of the chloroplasts;
• Air spaces in the spongy mesophyll allow diffusion between stomata and photosynthesising cells;
• Internal surface area / volume ratio very large.

18. Leaf cross section
In pairs examine a slide of

19. Use microscopes to observe internal structure of leaves

20. Your notes Collect a summary sheet of the structure of a leaf
Complete this sheet and check your answers with your teacher.
Once it is all correct, stick this into your exercise book. These will be your notes for today’s lesson so it is important that you get this done!

21. Plenary – What we have learned today
Test your knowledge of the words you have learned today.
Collect a matching sheet and match each structure with its function.

22. Investigating Stomata
Give the function of stomata
Describe how stomata regulate gas exchange.
Explain why the extent to which stomata are open is considered a ‘balancing act’ between survival and death.

23. Light
Carbon dioxide + Water Glucose + Oxygen

24. Photosynthesis and Chlorphyll
Learning objectives:
2.13 Describe how the structure of the leaf is adapted for photosynthesis, including:
large surface area
containing chlorophyll in chloroplasts to absorb light
c) stomata for gas exchange (carbon dioxide, oxygen and water vapour)

25. Sunlight & Starch Production
Cells in green plants make their own food in a process known as……….
photosynthesis

26. Carbohydrates Carbohydrate Carbon (C) Hydrogen (H) Oxygen (O)
Plants make glucose. Some of this is used immediately as an energy source and the rest is converted to starch for storage.
Starch is a large molecule so it cannot leave the plant cell.
Glucose and starch are carbohydrates made up of the following elements:
These are:
Carbon (C)
Hydrogen (H)
Oxygen (O)
Carbohydrate

27. Carbohydrates
You now know that glucose is converted to starch for storage
Presence of starch shows that plants have first made glucose by photosynthesis

28. How is starch made? Small, soluble glucose molecules
Large, insoluble starch molecule

29. Sunlight
Sunlight is extremely important as it provides the energy for plants to make their own food

30. Chloroplasts
Light energy from the sun is “trapped” or fixed by the green pigment chlorophyll
Chlorophyll is found in disc-shaped structures called chloroplasts in green leaves
chloroplasts

31. Role of Chlorophyll What is chlorophyll?
Chlorophyll is a green pigment that is found in chloroplasts
It captures light energy from the sun for photosynthesis

32. Evidence for the importance of chlorophyll
Some plants have variegated leaves which have green areas containing chlorophyll
White or yellow areas do not contain any chlorophyll
Variegation is the appearance of differently coloured zones in the leaves of plants

33. Variegated leaf White area: No chlorophyll Green area:
Contains chlorophyll
Variegated leaf

34. Practical Experiment
Your teacher will now take you through a practical on how to test a variegated leaf for starch
Copy and complete the table below:
Area of Leaf
Starch Present?
White
Green

35. chlorophyll
light energy
chemical energy

36. carbon dioxide absorbed by the air
Raw Materials
sunlight
carbon dioxide absorbed by the air
water absorbed
from soil

37. Leaf Chromatography
Ever wondered why leaves change colour in the autumn?
Leaves actually have different types of chlorophyll to “catch” as many different wavelengths of light as possible.
When the green chlorophyll dies in the autumn, the red and yellow pigments are exposed.

38. Leaf Chromatography
Your task is to safely carry out an experiment to separate out the different pigments.
This is known as chromatography.
Your teacher will demonstrate how to do this

39. Lesson starter
Which letter is pointing to the waxy cuticle in this cross section of a leaf?

40. Photosynthetic pigments
Plants use more than one photosynthetic pigment to absorb light. This maximises the use of energy from the Sun.
These pigments include:
Chlorophyll a
Chlorophyll b
Xanthophyll
Carotene

41. Photosynthetic pigments
Chlorophyll a is the main pigment. It absorbs light mainly in the red and blue regions of the spectrum.
Chlorophyll b, xanthophyll and carotene are 'accessory pigments'. They absorb light from other regions of the spectrum and pass the energy onto chlorophyll a.

42. Photosynthesis and light energy
Learning objectives
2.14 Demonstrate an understanding of how photosynthesis uses light energy to produce glucose and how this process can be modelled using the word equation for photosynthesis

44. The importance of light energy
Green plants need 4 raw materials for photosynthesis to occur:
Carbon dioxide
Water
Chlorophyll
Light energy
If any of these are missing, photosynthesis will not happen. The raw material that is missing becomes a limiting factor

45. The importance of light energy
Your teacher will give you a leaf to test for starch.
Some of the leaves have been covered with paper to stop light from getting to them. These leaves should not contain any starch.
Other leaves were left uncovered and should contain starch.
Your task is to find out which leaf you have by testing it for the presence of starch.

46. Limiting factors
2.15 Demonstrate an understanding of how limiting factors affect the rate of photosynthesis, including:
a) light intensity
b) CO2 concentration
c) temperature

47. Measuring rate of photosynthesis with Elodea (pondweed)
Upside down test tube
(to collect oxygen gas)
Thermometer
Solution of sodium carbonate (a source of CO2)
funnel
elodea
lamp
How could the light intensity be altered?
How could the temperature be altered (and kept constant)?
How could the CO2 concentration be altered?
How can the rate of photosynthesis be measured?

48. Elodea

49. Carbon Dioxide + Water Glucose + Oxygen
Limiting Factors
There are three limiting factors that affect the rate of photosynthesis:
Light intensity
Carbon dioxide concentration
Temperature (remember that photosynthesis is an enzyme-controlled reaction and enzymes can be denatured at high temperatures)
Carbon Dioxide + Water Glucose + Oxygen
Light energy

50. Limiting Factors Light Intensity
At this point, something other than light intensity is the limiting factor
As a general rule, whatever is on the x-axis is the limiting factor on the slope of the graph
At this point, light intensity is the limiting factor
Light Intensity

51. Limiting Factors
The rate of photosynthesis can be measured in the following ways:
Measuring the increase in dry mass of a plant over a period of time
Measuring the volume of oxygen given off over a period of time
Measuring the volume of carbon dioxide taken in over a period of time

52. Task Complete all textbook questions on pages 66-67
Write all answers in full sentences and copy diagrams where appropriate.