AQA Biology- Unit 2

An overveiw of everything in the AQA unit 2 specification for Biology

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  • Created by: Deni
  • Created on: 21-01-12 14:12

Plant Cells

  • Cell wall- made of cellulose, strengthens the cell.
  • Permanent vacuole- filled with sap, supports the cell.
  • Chloroplasts- contain chlorophyll that absorb light and aid in photosynthesis.
  • Cytoplasm- where most chemical reactions take place.
  • Nucleus- contains cells genetic information and controlls what the cell does.
  • Ribosomes- attached to membrame coming out of the nucleus, where protine synthesis occurs.
  • Cell membrame- controlls movement into and out of the cell.

http://www.youtube.com/watch?v=uohe2V4yOzE

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Animal Cells

  • Ribosomes- attached to membrame coming out of the nucleus, where protine synthesis occurs.
  • Nucleus- contains cells genetic information and controlls what the cell does.
  • Cell membrame- controlls movement into and out of the cell.
  • Cytoplasm- where most chemical reactions take place (may contain mitochondria)
  • Mitochondria- produce cells energy.

http://www.youtube.com/watch?v=Fzj6TRnXmps

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Specialized Cells

  • Root hair cell- have tiny hairs to increase the surface area of the cell enabling it to absorb water and ions better
  • Palisade cells- are column shaped and are found on the top of a leaf, they are packed with choloroplasts for photosynthesis.
  • Xylem- long, thin and hollow. transport water through the stem and the root.
  • nerve cells- (Neurons) long thin axons that can carry impulses over a large distance.
  • Egg cell- larger then other cells so can carry food for the embryo.  only contains half the amount of chromosomes. 
  • Sperm cell- most mobile as has to travel a large distance. contains lots of mitochondria to produce lots of energy. half the amount of chromosomes.
  • Red blood cell- no nucleus, packed with haemoglobin in order to carry oxygen.
  • White blood cell- can change their shape to destroy microbes that have invaded the body.

Most cells are made up of water containing dissolved substances. These are usually in the process of being made into something the cell needs. This involves chemical reactions controlled by the enzymes. Enzymes are found in cytoplasm and in all mitochondria.

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Diffusion

- living things have to replace substances that are used up and remove other substances which would otherwise gather.

  • This can take place automatically without energy in the process diffusion.

-Diffusion is the spreading of the particles of a gas or substance in a solution from a high concentration to a low 

- The greater the difference in concentration, the faster the rate of diffusion.

  • as the cell uses up certain substances the concentration gets lower so they get replaced by diffusion.

http://www.youtube.com/watch?v=gXJMBgyT_hk

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Photosynthesis

Plants make their own food by photosynthesis when the plants are exposed to light.

Four things are needed:
- light from the sun
- carbon dioxide diffused from the air
- water from the soil
- chlorophyll in the leaves.

Two things are produced: 
- Glucose for biomass and energy
- Oxygen released into the atmosphere as a by-product

word equation for photosynthesis: 

- carbon dioxide +water-------------------------> Glucose + Oxygen
                                     (chlorophyll + light) 

light energy is absorbed by green chlorophyll. Some of the glucose produced is used immediately by the plant to provide energy via respiration. but much of the glucose is converted into insoluble starch which is stored in the stem, leaves or roots.

http://www.youtube.com/results?search_query=photosynthesis+demonstration&oq=photosynthesis+demon&aq=0&aqi=g1&aql=&gs_sm=c&gs_upl=1753l2595l0l4247l6l6l0l3l3l0l164l393l0.3l3l0

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Limiting factors of photosynthesis

There are 3 main limiting factors of photosynthesis

  • Carbon dioxide concentration
  • Temperature
  • Light intensity 

    As the temp rises so does the rate of photosynthesis, meaning temp is the  limiting factor of photosynthesis. at too higher temp the enzymes controlling photosynthesis starts to be destroyed and the rate will drop to zero.

    As the CO2 concentration rises so does the rate of photosynthesis- meaning CO2 is a limiting factor. After a certain level the rate of photosynthesis will not rise meaning light or temp is now the limiting factor.

    As the light intensity increases so does the rate of photosynthesis meaning it is the limiting factor of photosynthesis. when the rise has no effect light intensity is no longer the limiting factor. the graph to this will look similar to that of CO2.

  • growth can be controlled by these to allow the plant to grow stronger and faster.

    http://www.youtube.com/watch?v=AWc31uJmf-Y
     http://www.youtube.com/watch?v=pBtQlLrsTXc
     

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