All Of Main Points For biology Unit 4

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Leaf Structure

Waxy cuticle - Helps prevent water loss, stops leaf from drying out                             

Upper Epidermis -  Protective skin, No chloroplast so cells are transparent and sunlight passes through

Palisade Layer - Regular shaped cells packed tightly together, cells contains lots of chlorephyll- main photosynthesis layer

Spongy Mesophyll Layer - Cells are irregular shapes allowing lots of air spaces. These increase the efficency of diffusion (co2 + O2) contains chlorophyll to trap any sunlight that has passed through the pallisade layer.     

Lower Epidermis - Protective layer, Guard cells surround pores in the lower epidermis called stomata. Stomata allow      

Vein (vascular bundle) - Xylem - carries water and dissolved nutrients to the leaf                   Phloem - transports glucose around the plants for the leaves                                                                                                               

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Leaf Diagram


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Osmosis - is the net movement of water molecules across a partially permeable membrane.


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  • A plant uses nitrates to make proteins
  • Proteins are needed for growth
  • Nitrogen in the nitrates is used to make amino acids
  • Amino acids are joined to make different proteins such as enzymes
  • No Nitrate - Poor Growth, Yellow Leaves
  • A plant uses phosphates in respiration (releasing energy)
  • Phosphates are also needed for growth especially in roots
  • Phosphorus in phosphates is used to make cell membrane and DNA
  • DNA carries genetic information
  • No phosphates - poor root growth, discoloured leaves
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  • Plants use these in respiration and in photosynthesis
  • Pottasium is used to help make some enzymes, Ensymes speed up chemical reactions
  • Enzymes are needed in photosynthesis and respiration
  • No pottasium - Poor fruits and flowers, Discoloured leaves
  • A plant needs magnesium to photosynthesis
  • Magnesium is used to make chlorophyll molecules
  • No magnesium - Yellow leaves
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Tracking Energy Flow

Each level in a food chain is called a trophic level

Rose Bud - Aphid - Spider - Starling

Producer - Primary Consumer - Secondary Consumer - Tertiary Consumer

Two types of pyramid number and biomass

Pyramid of number


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Tracking Energy Flow Part 2

Pyramid of biomass

Biomass is the mass of living organisms

Pyramid of biomass are beneficial because they gave a clearer indication of the amount of matter at each trophic level.

The negative aspect is that in order to record mass you must disturb or destroy the habitat


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Energy Transfer Efficency

Efficency = Useful Energy/Energy Input x 100


Respiration = 1900kj

Excretion = 950kj

Growth = 150kj

150/3000 x 100 = 5% efficency

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These are fuels made from or by living organisms

Examples Wood, Biogas, Alcohol, Plant Oils

Wood - We can use fast growing trees like willow or grasses ( elephant grass)

Biogas - Excrement from cows, for example are rich sources of methane when put in big digesters that methane can be collected and used landfill sites also give off methane

Alcohol - Some countries (Brazils) produce lots of sugar cane, which can be used with microbes (respiration) to produce alcohol. This carn be mixed with petrol to fuel cars.

Oils - Plant oils like **** seed oil can be mixed with diesel to fuel vehicles

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Organic Farming

  • natural/traditional techniques
  • No Chemicals - Pesticides - Kills Pesticides
  • Herbicides - kills weeds
  • Insectisides - kills insects
  • Artificial Fertiliser
  • Drugs
  • Labour Intenstive - Weeding,Maintaining Lifestock
  • Less Product per acre
  • More Expensive
  • Better Taste
  • Better nutritional value
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Alternative To Pesticides

Biological control - the introduction of a predator to pests ( e.g ladybirds to kill aphids) This doesn't totally wipe out posts but reduces them to acceptable levels

Intensive Farming

  • Uses chemicals not used in organic farming
  • Higher yield = more profit
  • Live stock - cramped conditions e.g battery farms - Cruelty to animals
  • Food is loaded with chemicals can be dangerous to consumers
  • Cheaper for consumers - economic advantage in times of heartship
  • Higher yield beneficial for supporting countries with food shortages

Hydroponics are crops which are grown in tanks of water with no soil         

Advantages - No soil - reduces chances of diesease _  Controls the quantities of nutrients added to water for most effective growth

Disadvantages - initel set up costs are high _ Artificial nutrients expensive

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Carbon Cycle


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Nitrogen Cycle


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Is essential for recycling vital elements like carbon and nitrogen

Microbes cause decay as they feed off dead organisims

Like all living organisims these microbes need to respire. For decay to occur effectivley they need to respire anerobically

Anerobic respiration creates acidic conditions, slowing decay

Optimum Conditions - 37 for bacteria   25 for fungi   Moist   Oxygen - For aerobic respiration

Saphrophyte - usually fungi - extremley digest dead matter by secreting enzymes to break them into simple molecules and then absorbing these

Preserving Food - Freezing,Vacum Packed,Dehydration,Canning,Pickling,Preserving

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