Page 8 - 新思维科学学生用书7 样章

1.1 Plant cells

Cells

If you study a plant by observing part of it
through a microscope, you will see that it is
made up of a very large number of tiny ‘boxes’.

These are called cells. All living organisms are
made of cells.

Cells are so small that you cannot see them with
your eyes alone. The photograph of the plant cells one cell
was taken through a microscope. The microscope

magnifies the view of the cells, so that they look Part of a leaf seen through a microscope
much bigger than they really are.

Parts of a plant cell

The diagram shows a plant cell from a leaf.

cell wall sap vacuole
Every plant cell has a cell wall. The cell wall is This is a large, fluid-filled space inside
strong and sti . It holds the plant cell in a plant cell. The liquid inside it is a
shape. Plant cell walls are made of a substance solution of sugars and other substances
called cellulose. dissolved in water. The solution is
cell membrane called cell sap.
All cells have a cell membrane. The cell chloroplast
membrane is very thin and flexible. It is like Plant cells that are in the sunlight often
the thin skin of a soap bubble. It lies along the contain chloroplasts. This is where
inner edge of the cell wall. The cell membrane plants make their food. Chloroplasts
controls what goes in and out of the cell. look green because they contain a
cytoplasm green substance called chlorophyll.
All cells have cytoplasm. Cytoplasm is like clear mitochondrion
jelly. Chemical reactions happen inside the All plant cells have mitochondria
cytoplasm. These reactions keep the cell alive. (singular: mitochondrion). Inside

nucleus mitochondria, energy is released
Most cells have a nucleus. The nucleus controls from food.
the activities of the cell.
Diagram of a leaf cell

Questions

1 Look at the photograph of the plant cells on this page. What do you think the little green circles
inside the cells are? Why are they green? What happens inside them?
2 Describe four differences between a cell wall and a cell membrane.

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