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Notes on B2 for the written exam...

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  • Created on: 09-01-11 11:01

Cells - Animal

Animal Cells have:

  • Cell membrane - controls movement of materials.
  • Cytoplasm - where many chemical reactions happen.
  • Nucleus - controls the activities of the cell.
  • Ribosomes - proteins are synthesised (made) here.
  • Mitochondria - energy is released during aerobic                      respiration.
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Cells - Plant

Plant cells have the same 5 as animal cells.


They also have:

  • Cell Wall - to shape & support the cell.
  • Chloroplasts - contain chlorophyll for photosynthesis.
  • Permanent Vacuole - contains cell sap.


Materials such as Carbon Dioxide, Glucose & Oxygen can move across the cell membrane.

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Cells - Specialised Cells

Differentiation occurs as organisms develop and some become specialised to carry out certain jobs.


Types of specialised cells:

  • In animals -nerve & sperm cells.
  • In plants - xylem & root hair cells.
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Cells - How substances get in & out of cells?

Diffusion is the random movement of molecules from a HIGH area of concentration to a LOW area of concentration. Doesn't require any energy from the cell.


The larger the difference in concentration, the faster the rate of diffusion. The diffusion of:

  • simple sugars & amino acids from the gut through the cell membrane.
  • CO2 into actively photosynthesising plant cells.
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Cells - Osmosis

Osmosis is the movement of water.


It is a special case of diffusion involving a semi-permeable barrier.


Like diffusion, osmosis is also random and requires no energy from the cell.


No solute molecules can move across the membrane.

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How Plants Produce Food - Photosynthesis

Photosynthesis can only be carried out by green plants.

Chlorophyll traps the Sun's energy.


The equation for photosynthesis is:

carbon dioxide + water (+light energy) = glucose + oxygen


The sugar glucose is a carbohydrate

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How Plants Produce Food - Leaf Structure

The waxy cuticle’s the first one on the list, and next comes the upper epidermis,

Then the palisade mesophyll, and then the spongy mesophyll,

And finally the lower epidermis.

 And the bottom of a leaf isn’t too hard, there are holes surrounded by some cells that guard,

And the holes are called stomata, and they’re stopping all the water,

And the CO2 from coming out too fast.

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How Plants Produce Food - Limiting Factors

If certain things are in short supply, they will slow down the rate of photosynthesis.

Plant growers need to know this, otherwise they could waste money.


Light - lack of light would slow down rate.

Temperature - enzymes don't work effectively if too cold.

CO2 levels - too little CO2 then rate will slow (in      greenhouses on sunny day & rapidly   photosynthesising rain forest).

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How Plants Produce Food - How Plants Use Glucose

Plants use glucose for energy (respiration).


Most plants can store glucose as starch.


Glucose is also combined with other nutrients (mineral ions) to produce new materials.


Glucose is stored by some plants as insoluble starch. It is stored as an insoluble so that it has no effect on osmosis.

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How Plants Produce Food - Why do plants need miner

Plants produce sugars through photosynthesis.

Plant roots take up mineral salts for healthy growth.

Nitrates are taken up from the soil to produce amino acids. They are used to make proteins for growth. A plant that is nitrate deficient will have stunted growth.

Magnesium ions are essential for making chlorophyll. If the plant is deficient in chlorophyll then it will have yellow leaves.

Deficient means lacking something.

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Energy Flows - Pyramids of Biomass

Biomass is the mass of living material in plants & animals.


Pyramids of biomass show the mass of all the organisms at each stage in a food chain.


Pyramids of biomass are more likely to give a more accurate picture than a pyramid of numbers.


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Energy Flows - Energy losses

Not all of the energy taken in by an organism results in the growth of that organism.

The equation for efficiency is:


                          useful energy transferred

efficiency % = ------------------------------------ x 100

                                energy supplied   

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Energy Flows - Energy in food production

By shortening the food chain it makes it more efficient for us.


We can artificially produce meat more efficiently by:

  • Preventing the animal from moving so it doesn't waste energy on movement.
  • Keeping the animal at a warmer temperature so it doesn't use as much energy from food to keep itself at constant temperature.
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Energy Flows - Decay

Detritus feeders (some types of worms) may start the process of decay by eating dead animals or plants producing waste materials.

Decay organisms then break down the waste and dead plants and animals.

Decay  organisms are microorganisms (bacteria & fungi).

Decay is faster if it is warmer or wet.

All the materials from the waste and dead organisms are recycled.

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Energy Flows - The Carbon Cycle

Photosynthesis removes CO2 from the atmosphere.

Green plants as well as animals respire which also returns CO2 to the atmosphere.

Animals eat green plants which builds up the carbon in their bodies.

When plants or animals die microorganisms release the CO2 back into the atmosphere through respiration.

A stable community recycles all of the nutrients it takes up.

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