Cells and Tissues

leaf

growing point

bud

stem

© Biophoto Associates

0.02cm

1

Cutting sectionsThe slice of tissue must be only 0.01-0.1 mm

thick if cells are to be seen clearly

Thin slices of plant tissue can be made by hand using a sharp razor blade

The slices are called sections

Special apparatus and techniques are needed to make very thin sections

The next slide shows the difference between a transverse and a longitudinal section

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Cutting sections

Transverse section Longitudinal section

3

A group of cells from animal tissue

cytoplasmcell membrane nucleus

4

Cytoplasm

cytoplasm

5

The cytoplasm is a living, semi-liquid material

Although it looks structurelessit contains many structures which are not visible at thismagnification

All the processes which keep the cell alive, take place in the cytoplasm or nucleus

Nucleus

nucleus

6

The nucleus is a specialised region of cytoplasm which regulates allthe chemical changes which takeplace in the cytoplasm

It sends chemical signals to thecytoplasm which start or stop thechemical processes going on in it

The nucleus also controls cell division

Cell membrane

cell membrane

7

The cell membrane encloses thecytoplasm and stops it flowing out

It also controls which substancescan get into and out of the cell

It is only about 0.00001mm thick

If it is damaged, the cell will die

Cells from the cheek lining

© Biophoto Associates

cytoplasm

nucleus

cell membrane

0.01mm

8

Plant cells

Plant cells differ from animal cells in having a cell wall

outside the cell membrane, and a large, fluid-filled vacuole

nucleus

cell wall

cytoplasm

vacuole

9

Chloroplasts

Cells from the green parts of plants, such as leaves, contain chloroplasts.

The chloroplasts are always in the cytoplasm

vacuole

chloroplast

cell wall

© Biophoto Associates

0.2mm

10

Cells are 3-dimensional

Cells seen in sections look flat, 2-dimensional. This is misleading and the picture shows how three plant cells might look if you could see them in 3 dimensions

cell wall

cytoplasm

nucleus

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Structure of a leaf cellcell wall

cell membrane

cytoplasm

Longitudinal section

Transverse section

vacuole

nucleus

The diagram shows how a 3-dimensional leaf cell would appear in transverse and longitudinal section

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Plant and animal cells

• All cells have cytoplasm, a nucleus and a cell membrane.

• Plant cells have also a cell wall, a central vacuole and in many cases, chloroplasts.

• Animal cells do not have these structures

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Plant cells Animal cells

Cytoplasm Cytoplasm

Nucleus Nucleus

Cell membrane Cell membrane

Cell wall

Chloroplasts

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Organs, cells and tissues

The stomach is an organ, part of the digestive system

The stomach wall contains muscle tissueThe muscle tissue

consists of muscle cells

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Self test

• The following slides contain questions with alternative answers, only one of which is correct. Click on the button next to your answer to see if it is correct.

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Question 1

Which of these structures controls cell division?

• Cytoplasm

• Nucleus

• Cell membrane

• Cell wall

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Question 2

In a plant cell, which of these describes the vacuole?

• A semi-liquid living material

• A specialized region of cytoplasm

• A region containing chloroplasts

• A solution of salts and sugars

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Question 3

The cell structure which controls the entry or exit of substances is

• the nucleus

• The cell wall

• The cell membrane

• The cytoplasm

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•Plant cells do not have cell walls

•Plant cells have no vacuoles

•Plant cells have nuclei

•All plant cells have chloroplasts

Which one of these statements is correct?

Question 420

Answer

Incorrect

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Answer

Correct

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