Cells

Every animal cell contains these features:

• Cell membrane: Holds the cell together, controls what goes in and out
•  Nucleus: Contains the DNA, which controls the cell's activities by controlling protein synthesis
• Mitochondria: Site of respiration - energy is released from glucose
• Ribosomes: Site of protein synthesis, where proteins are made
• Cytoplasm: A gel-like substance where the chemical reactions take place

Each reaction in the cell is controlled by enzymes, and these stop the reactions from becoming mixed

The enzymes for different reactions are found in different parts of the cell
Eg - enzymes controlling respiration are found in the mitochondria

Plant cells contain all the features of an animal cell, and in addition:

• Cell wall: Made of cellulose and keeps the cell rigid supporting the plant
• Sap vacuole: Keeps the cell ridgid, contains sap (week sugar and salt)
• Chloroplasts: Contains chlorophyll and is the site of photosynthesis

Cells are all organised toegther to make up an organism

Cells: Start off with single cells
Eg - Skin cell 

Tissues: Similar cells group to make a tissue
Eg - Muscle

Organs: Have a similar job to do
Eg - Heart

Organ system: Groups of organs work together
Eg - Digestive system

Organisms: All of the above together make up an organism
Eg - Cat 

Diffusion: The movement of molecules from a region of high concentration to a region of lower concentration

The rate of diffusion increases with:

• Large surface area
• High temperatures (the particles move faster)
• Short distances (so thinner cells)
• Large concentration (can be achieved by using up substances)

Net movement = particles moving in - particles moving out

Cell membranes hold the cell together and control which substances travel in and out

Small molecules can diffuse through
Eg -  Glucose, amino acids, water, oxygen

But not starch or proteins

Osmosis: The movemnt of water molecules from an area of high water potencial to a reigon of lower water potencial through a partially permiable membrane

Water will move both ways, but the overal net movemtn wil be towards teh concentrated area

As a result the water potencial will reach an equalibium that is equal

Inside cells the concentration needs to remain constant so that th reactions can take place

Cells are surounded by a liquid containing the substances they need

Osmosis causes these substances to be absorbed into the cell when they are used up

If water is used up in chemical reactions the cytoplasm becomes more concentrated, so water will move into the cell, the opposite will happen if excess water is produced

However if the concentration of the solutionis wrong then:

Animals

• Too concentrated: water will move out of the cell, the cell will shrivel up and not be able to carry out its function
• Too dilute: water will move into the cell, it will swell up burst

Plants

• Too dilute: wster moves into the cell and the cell is turgid as cell walls can't bend - the cells are hard and ridgid so the plant remains upright
• Too concentrated: water moves out of the cell, the cell membrane pulls away from the cell wall - the cell is plasmolised