Cells - B2

How cells work and what is required for them to work. 

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Animal and Plant Cells.

NUCLEUS: Controls all activities of the cell. Contains instructions for making new cells or new organisms.

CYTOPLASM: Liquid gel which most of the chemical reactions needed for life take place. One of the most important of these is respiration.

CELL MEMBRANE: Controls the passage of substances in and out of cell.

MITOCHONDRIA: Structures in the cytoplasm where oxygen is used and most of the enegry is released during respiration.

RIBOSOMES: Protein synthesis takes place. All proteins needed in the cell are made here. 

CHLOROPLASTS: Found in green parts of the plant. Contain green substance - chlorophyll. Absorbs light energy to make food by photosynthesis.

PERMANENT VACUOLE: Important for keeping the cells rigid to support plant.

Enzymes control the chemical reactions inside the cells.

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Specialised Cells

FAT CELL: Storage cells. Help us survive when food is in short supply. Very little normal cytoplasm - leaves plenty of room for large amounts of fat. Very few mitochondria as they use little energy. They expand. 

CONE CELL FROM HUMAN EYE: In the light-sensitive layer of your eye. Make it possible for you to see in colour. Outer segment filled with special chemical, changes chemically in coloured light. Middle segment is full of mitochondria - produces a lot of energy. Specialised nerv ending/synapse connects to the optic nerve which carries impulses to your brain. 

ROOT HAIR CELLS: Enables plants to take in the water which they need. Increased surface area for water to move into the cell. Large permannent vacuole, affects the movement of water from soil across the root hair cell. Postioned close to the xylem tissue that carries water up into the rest of the plant.

SPERM CELLS: Fertlises egg. Contain genetic information from the male. Long tails to swim. Middle section full of mitochondria - provides tail with energy. Acrosome stores digestive enzymes for breaking down the outer layers of the egg. Large nucleus to store genetics. 

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How do substances get in and out of cells?

Dissolved substances move in and out of cells by diffusion, osmosis and active transport. 

Diffusion is the net movement or particles from an area where they are at a high concentration to an area where they are at a lower concentration.

The overall or net movement = particles moving in - particles moving out

The bigger the difference in concentration, the faster the rate of diffusion.

When a substance is moving from a higher concentrated area to one which is just a bit lower, the movement toward the less concentrated area will appear to be quite slow.  

Concentration gradient: The difference between two areas of concentration. 

Increase in temperature means the particles move more quickly. This then means diffusion will take place more quickly as movement of the particles speeds up. 

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Osmosis - special case of diffusion.

Osmosis is the diffusion/movement of water from a high water concentration to a low water concentration through a partially permeable membrane. 

Partially permeable cell membranes will allow water to move across them. 

A cell is basically some chemicals dissolved in water inside a partially permeable bag of cell membrane. The cell contains a fairly concentrated solution of salts and sugars. Water will move from a high concentrated solution of salts and sugars. Water will move from a high concentration of water particles to a less concentrated solution of water particles across the membrane of the cell. 

The internal concentration of your cells needs to stay the same all the time for the reactions of life to take place. 

Plants rely on well-regulated osmosis to support their stems and leaves. Water moves into plant cells by osmosis, making the cytoplasm swell and press against the plant cell walls.

If a cell uses up water in its chemical reactions, the cytoplasm becomes more concentrated and more water will immediately move in by osmosis. 

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