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Cells - PowerPoint PPT Presentation


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Cells. All livings things are made of cells. Cells are very small, so large organisms contain mil­lions of cells. Some organisms are unicellular. These are the bacteria, protozoa and some algae . Microscopes are used to study cells. To see cells clearly, you need to use a microscope

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cells

Cells

All livings things are made of cells.

slide2
Cells are very small, so large organisms contain mil­lions of cells.
  • Some organisms are unicellular.
  • These are the bacteria, protozoa and some algae
microscopes are used to study cells
Microscopes are used to study cells
  • To see cells clearly, you need to use a microscope
  • The kind of microscope used in a school labo­ratory is called a light microscope because it shines light through the piece of animal or plant you are looking at
light microscope
Light microscope
  • . It uses glass lenses to magnify and focus the image.
  • A very good light microscope can magnify about 1500 times, and then show all the structures shown next
electron microscope
Electron microscope
  • To see even smaller things inside a cell, an electron microscope is used.
  • This uses a beam of electrons instead of light, and can magnify up to 500 000 times. This means that a lot more detail can be seen inside a cell, as shown in Next
all cells have a cell membrane
All cells have a cell membrane
  • Whatever sort of animal or plant they come from, all cells have a cell membrane around the outside
  • Inside the cell membrane is a jelly-like substance called cytoplasm,
cell structure
Cell structure
  • In the cytoplasm is found many small structures called organelles.
  • The most obvious of these organelles is usually the nucleus.
  • The whole content of the cell is called protoplasm.
plant cells
Plant cells
  • All plant cells are surrounded by a cell wall mademainly of cellulose
  • Paper, which is made from cell walls, is also made of cellulose
  • Animal cells never have cell walls made of cellulose
cell wall
Cell Wall
  • Cellulose forms fibres which criss-cross over one another to form a very strong covering to the cell
  • This helps to protect and support the cell.
  • Because of the spaces between fibres, even very large molecules are able to go through the cellulose cell wall.
  • It is therefore said to be fully permeable
cell membranes
Cell Membranes
  • All cells have a membrane surrounding the cell.
  • It is called the cell surface membrane or plasma membrane.
  • In a plant cell, it is very difficult to see, because it is right against the cell wall.
partially permeable
Partially Permeable
  • The cell surface membrane is a very thin layer of protein and fat.
  • It is very important to the cell because it controls what goes in and out of it.
  • It is said to be partially permeable,
  • it will let some substances through but not others.