Page 15 - 新思维科学学生用书9 样章

1 Photosynthesis and the carbon cycle

Chloroplasts and chlorophyll

In the previous topic, you saw that chlorophyll is
essential for photosynthesis. Chlorophyll captures cell wall
energy from sunlight. The energy helps water and cell membrane

carbon dioxide to react together.

Chlorophyll is kept inside chloroplasts, inside plant
cells. cytoplasm

This means that photosynthesis happens inside vacuole
chloroplasts. Not all plant cells have chloroplasts, so
not all of them can photosynthesise. nucleus

In most plants, the cells in the leaves have the

most chloroplasts. Inside the cells in a leaf, carbon chloroplast
dioxide and water are made to react, to produce containing
chlorophyll
carbohydrates and oxygen. We can think of the field
of lettuces in the photograph as a giant carbohydrate

factory.

On warm, sunny days, plants can make more carbohydrate than they need to use immediately. So
they store some of it for use later on – perhaps at night, or at a time of year when there is less sunlight.
Plants store carbohydrates as starch. They store the starch inside the chloroplasts in their cells. One
way to check whether a leaf has been photosynthesising is to test it for starch.

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