Biology

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  • Cells are the building blocks of life.
  • A living cell is called an organism.
  • All living things are made up of cells.
  • Plants and animals are organisms.
  • A uni-cellular organism is an organism made up of one cell, like an Amoeba.

Animal Cell

Each part of a cell has a special job to do.
[Diagram].
Cell Membrane - controls what passes in and out of the cell.
Nucleus - controls all the chemical reactions that take place inside the cell. The nucleus also contains chromosomes that contain all the information needed to produce a new living organism.
Cytoplasm - where all the chemical reactions take place.

Plant Cell

Each part of a plant cell has a special job to do.
[Diagram].
Chloroplasts - contain a green substance called chlorophyll. This absorbs the sun's energy so that the plant can make it's own food during photosynthesis.
Cell Wall - made of cellulose, which gives a plant cell strength and support.
Vacuole - contains a weak solution of salt and sugar called cell sap. The vacuole also gives the cell support.
The nucleus, cell membrane and cytoplasm are also still found within a plant cell.

Similarities and Differences

The typical plant cell and animal cell look different to each other, for example, they are different shapes and the nucleus is in a different position.
They both have:

  • Nucleus.
  • Cytoplasm.
  • Cell membrane.

Only plant cells have:

  • Cell wall.
  • Vacuole.
  • Chloroplasts.

Diffusion is the movement of molecules from an area of high concentration to an area of low concentration.
In other words, it is the natural tendency of molecules to move into all the available space, until they are evenly spread out.
Two rules to remember:

  • The larger the molecule, the slower the rate of diffusion.
  • The greater the difference in concentration, the greater the rate of diffusion. The difference is called a concentration gradient. 

Osmosis

  • Each cell is surrounded by a cell membrane which as tiny holes init. This membrane is selectively permeable. It allows a small molecules to pass through, but not larger ones.

Osmosis - A Special Case of Diffusion

The definition of Osmosis - The movement of water molecules from an area of high water concentration (weak solution) to an area of low concentration (strong solution) through a selectively permeable membrane. Water moves both ways to balance up the concentrations. If there is more movement one way, we say there is a net movement of water into the area where there is less water.

Osmosis makes plant cells swell. Water moves into the plant cell vacuole and pushes against the cell wall. The cell wall stops the cell from bursting. We say that the cell is turgid. This is useful as it gives plant stems support.
If a plant lacks water, it wilts and the cells become flaccid as water has moved out of the cell.
If a lot of water leaves the cell, the cytoplasm starts to peel away form the cell wall. We say the cell has undergone

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