Science 8th grade
UNIT 1: Plants 1.2 Leaves
Science 8th grade
UNIT 1: Plants 1.2 Leaves
In most plants, the leaves are the organs that carry out photosynthesis.
Chlorophyll
Most leaves are green. This is because they contain a green pigment called chlorophyll. (A pigment is a coloured substance.)
Chlorophyll is essential for photosynthesis.
Chlorophyll captures energy from light. The leaf can then use this energy to make food.
Questions
1) Think about what you know about the structure of cells. What is the name of the part of a plant cell - also beginning with chloro'-that contains chlorophyll?
$A + I$: 2) Suggest why leaves are green, but roots are not.
$A + I$: 3) Think back to Activity 1.1, where you grew some seedlings in the dark.
What happened to the chlorophyll in them?
The structure of a leaf
The picture shows the different parts of a leaf.
Inside a leaf
The diagram on the right shows what a leaf looks like if you cut it across, and then look at the cut edge.
Leaves are so thin that it is difficult to imagine they contain several layers of cells. It is the cells in the middle of the leaf that carry out photosynthesis.
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A waxy layer on the leaf surface stops the leaf cells from drying out.
The upper epidermis protects the cells inside the leaf.
The palisade layer contains cells that do most of the photosynthesis.
The lower epidermis protects the cells inside the leaf.
A stoma (plural: stomata) is a tiny hole in the lower epidermis, These holes let carbon dioxide from the air get into the leaf.
The spongy layer has lots of air spaces. The cells in the spongy layer do a small amount of photosynthesis.
A vein carries water to the cells in the leaf.
Activity 1.2 (Which surface has the most stomata?)
SE: Take a fresh, green leaf. Push the leaf into some warm water. Watch carefully to see where air bubbles appear on the leaf surface.
Questions
${A_1}$: On which surface of the leaf did most bubbles appear?
${A_2}$: The bubbles contained gas that came out from inside the leaf Which part of the leaf do you think the gas came from? (Look at the diagram of the inside of the leaf above.)
${A_3}$: Suggest how the gas got out of the leaf.
${A_4}$: Use what you know about the effect of heat on gases to explain why the gases came out of the leaf when it was put into warm water.