Cells and Tissues

leaf

growing point

bud

stem

0.02cm

Cutting sections

The 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

Cutting sections

Transverse section Longitudinal section

A group of cells from animal tissue

cytoplasmcell membrane nucleus

Cytoplasm

cytoplasm

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

nucleusThe 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

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

cytoplasm

nucleus

cell membrane

0.01mm

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

Chloroplasts

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

The chloroplasts are always in the cytoplasm

vacuole

chloroplast

cell wall

0.2mm

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

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

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

Plant cells Animal cells

Cytoplasm Cytoplasm

Nucleus Nucleus

Cell membrane Cell membrane

Cell wall

Chloroplasts

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