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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