Biology GCSE OCR Gateway B4 Revision Cards

• Leaves are adapted by:
• Large Surface area to absorb maximum light
• Thin so CO2 and water vapor only have short distance to move
• Air Spaces to allow gas exchange easily
• Leaves contain a lot of chlorophyll at the top of the leaf
• Upper epidermis is transparent
• Stomata pore lets gases in and out
• Network of veins deliver water and nutrients in and out.

• Plants exchange gases through diffusion.
• Diffusion is the net movement of an area high to an area low concentration.
• It is vital for photosynthesis which uses Carbon Dioxide and respiration which uses Oxygen at night. 

• Osmosis is the net movement of water molecules across a partially permeable membrane  from a region of high to a region of low concentration.
• Osmosis causes turgor pressure in plant cells. Low turgor pressure = flaccid cell which can become plasmolysed. Normal cells become turgid if they have increased turgor pressure.

• Root hairs take up water through osmosis .
• Transpiration is the loss of water from the plant:- evaporation & diffusion creating a shortage of water in the plant so water is drawn up through the xylem- it's constant.

Advantages of water loss through the Stomata pores:-

• Constant = keeps plants cool
• Guard cells go turgid and flaccid
• Thin outer walls = thick inner walls
• Open Stomata allows photosynthesis
• Light sensitive.

Phloem tubes Transport food:-

• They are made of living plant cells with perforated end plates
• It travels in both direction
• Translocation. Xylem tubes take up water.

Xylem tubes take up water:-

• Made of dead cells
• Thick walls help support the walls
• Carry both water and minerals from roots to leaves as transpiration system 

They're both kept together in vascular bundles. Xylem on the inside Phloem on the outside.

• Nitrates= For amino acids and proteins needed for cell growth. Needed if plants are stunted and yellow.
• Phosphates= For DNA, cell membranes, respiration and growth. Needed if poor root growth and purple leaves.
• Potassium= For Enzymes for photosynthesis and respiration. Needed if poor flower and fruit growth with discovered leaves.

Minerals are taken in by roots and active transport, using energy from respiration to pull in minerals against the concentration gradient. 

• We all get energy from the sun
• Plants use some for energy then pass the rest along the food chain.
• Energy is lost at each stage of the food chain by:- respiration, heat and egestion.
• efficiency=(energy available to the next level / energy from previous level) x100

Pyramids of numbers and biomass are different things, this diagram shows how they are different:-                

• Powered by photosynthesis
• Converts carbon in the air to sugars
• Easting passes it along the chain
• Respiration releases carbon as CO2 into the air
• Carbon goes into the soil when they die and decay, some is turned into CO2
• Burning also releases CO2

• 78% of the air is Nitrogen
• Nitrogen is needed for proteins and growth
• Nitrifying bacteria= ammonia into nitrates
• Denitrifying bacteria= Useful nitrates into N2 n the air
• Nitrogen fixing bacteria= N2 into nitrates
• Legumes on plant roots have a mutual relationship with plants and change N2 into nitrates which the plants can use.

Rates of decay depend on:-

• Temperature- Needs to be fairly warm so enzymes work but not hot enough to denature them.
• Moisture- Water is needed to help things decay.
• Oxygen- Aerobic respiration makes decay faster.

Preservation methods:-

• Cooling- Slows decay down.
• Freezing- Kills bacteria.
• Canning- Keeps Oxygen and decomposers out.
•  Adding salt- Decomposers loose water by osmosis when salt is added
• Adding vinegar- Low pH inhibits enzymes. 

Pesticides can harm the environment so you can use biological control to:-

• Introduce ladybirds to eat aphids.
• Wasps and flies produce larvae which kill insects and pests.
• Introduce myxomatosis to kill an out of control rabbits population.
• Advantages of Biological control- Only effects pests, no chemicals used- less pollution.
• Disadvantages of Biological control- Slower, won't kill all pests, takes more management and planning and it could drive out native species.

• Energy stored in biomass can be used for other things e.g. eating, feed it to livestock, and growing seeds for fuels.
• Fuels- Fast growing trees used- "Carbon neutral".
• Fermentation biomass using bacteria or yeast e.g. biogas, to fuel things.
• Unlike coal and oil its renewable.
• Using biofuels air pollution will be reduced.
• You can make self-reliant energy.

Intensive farming produces more foods.

• Herbicides = Kills weeds.
• Pesticides = Kills insects.
• Battery farming animals.

But destroys environment.

• Removal of hedges
• Fertilizers carelessly end up in rivers.
• Pesticides damage food chain (e.g. DDT)
• Cruelty to animals (battery farming)

Hyponics- plants grown without soil.

• Advantages- less land/ space needed, no soil/ weeding, grow plants in areas of poor soil, minerals are more accurately controlled.
• Disadvantages- expensive, needs specially formulated soluble nutrients, skilled and trained growers needed, no soil for anchorage so plants need support.

  Organic Farming

• Organic fertilisers e.g. manure.
• Crop rotation systems.
• Weeding by hand.
• Vary times for seed planting.
• biological control.