Biology 2

Animal cells

• Nucleus- contains genetic material that control what goes on in the cell.
• Cell membrane- holds the cell together and controls what goes in and out.
• Cytoplasm- where the chemical reactions in the cell take place.Contains enzymes that controls these reactions.
• Ribosomes- the proteins are made here.
• Mitochondria- Reactions for respiration take place here.

Plant Cells

• Cell wall- made of celluose. Holds the cell together and strengthens it.
• Chloroplasts- Used for photosynthesis and contains a green substance called chlorophyll which is good for this.
• Vacuole- contains cel sap (a weak solution of sugar and salts)

Palasade cells

• Thin - so more can be packed into the top of the leaf
• Tall - Large surface area (more CO2 can be absorbed)
• Packed with chloroplasts - good photosynthesis (more efficient)

Guard Cells

• Special kidney shape which opens and closes the stomata
• When the plant has lots of water, they become turgid (plump) so reactions in the stomata can take place for gas exhange (photosynthesis)
• When the plant is short of water, the guard cells go flacid in order to close the stomata and reduce loss of water vapour.
• Thin outer walls and thick inner walls help the cell to open and close.

Red Blood Cells

• Cocave shape so large surface area and they are easy to pass through the capillaries smoothly to reach body cells.
• Packed with haemoglobin (the pgment that absorbs the oxygen)
• They have no nucleus - so more room for the haemoglobin.

Egg cell

• contains huge food reserves to feed the embryo
• When a sperm fuses with egg, the egg's membrane instantly changes to prevent any more sperm from entering. (this is so the offspring end up with the right amount of DNA)

Sperm Cell

• Long tail and streamlined head to help it swim to the egg
• They carry enzymes to digest through the egg cell membrane

Diffusion - The passive movement of particles from an area of high concentration to an aread of low concentration. e.g. perfume.

The rate of diffusion depends on

• Distance - substances diffuse faster when they have less distance to travel
• Concentration difference (gradient) - substances diffuse faster if there is a big difference in concentration
• Surface area- the bigger the surface area, the faster it takes to diffuse (becasue there are more particles)

Osmosis - The movement of water molecules across a partially permeable membrane from a region of high concentration to a region of low water concentration.

A partially permeable membrane is just one with very small holes in. This means only tiny molecules get get through like, of course, water. Bigger molecules like 'sucrose' cannot.

Carbon dioxide + water -> glucose + oxygen

Photosynthesis is the process that produces food in plants. The food it produces is glucose. It happens in the leaves of all green plants. It happens in the chloroplasts which are found in palisade cells. The chlorophyll in these chloroplasts absorbs sunlight and uses the energy to convert CO2 and water into glucose. Oxygen is also produced.

4 things are needed for photosynthesis to happen

• Light (from the sun)
• Chlorophyll (green substance found in chloroplasts)
• Carbon dioxide (enters the leaf from the air around)
• Water (comes from the soil, up the roots and stem and into the leaf)

Limiting factors-

• at night - there is no light.
• in winter - temperature drop
• If it warm and bright enough, the amount of CO2 is usually limiting

a catalyst is a substance which increases the speed of a reaction without being changed or used up in the reactiong

• enzymes are catalysts produced by living thigns
• enzymes are all proteins
• all proteins are made up of chains of amino acids. The chains are folded into unique shapes which enzymes need to do their jobs.

ENZYMES HAVE SPECIAL SHAPES SO THEY CAN CATALYSE REACTIONS