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  • Created by: Mae Ghali
  • Created on: 08-04-13 12:00


Enzymes are proteins that speed up chemical reactions. The instructions to make enxymes are found in genes.

Chemical reactions usually involve splitting or bonding things together. Enzyme reactions bond together a substrate (the molecule changed in a reaction) to its active site.

The 'lock and key model' shows that only a certain substrate can bond to the active site.

The temperature or pH of a solution can determine the rate of reaction. These both need to be at  a specific constant temperature to work at their optimum.

However,if the temperature is too high it denatures the active site and chemical reaction cant happen as the shape has now changed.

This is the same with the pH if its too high or too low the active site denatures due the bonds beign interferred with or broken.

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Aerobic Respiration

Respiration is a series of chemical reactions that release energy by breaking down food molecules. It happens in every living cell.

The energy released in respiration is used for:

  • Movement - to make muscles contract 
  • Active transport -movement between the inside of cells
  • Synthesis of large molecules made by joining together smaller molecules- glucose is joined together to make starch and cellulose. Plants also glucose and nitrogen to make amino acids

Aerobic just means 'with oxygen'. It releases more energy per glucose molecule than anaerobic respiration. This is the formula:

Glucose       + Oxygen --> Carbon Dioxide + Water (+energy released)

C6 H12 O6  +   6O2     -->     6CO2            + 6H2O (+energy released)

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Anaerobic Respiration

Anaerobic means 'without oxygen'. It takes place when there is little or no oxygen, for example:

  • Human Cells- When we exercise vigorously the body cant supply enough oxygen
  • Plant Cells- If the soil a plants growing in becomes waterlogged there wont be any oxygen available
  • Bacterial Cells- Bacteria can get under your skin through wounds and there isnt any oxygen below the skin

The products of the reactions are different for each cell however energy is always released.

It can produce lactic acid in animal cells and some bacteria: Glucose--> Lactic Acid

It can also produce Ethanol and Carbon dioxide in plant cells and some microorganisms: Glucose--> Ethanol + Carbon Dioxide  (+energy released)

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Fermentation is when microorganisms break down sugars into products due to anaerobic respiration.

We use this to make:

Bread is made using yeast- the yeast ferments the carbohydrates in the flour and releases carbon dioxide causing the bread to rise.

Biogas is a fuel used for things like heating and lighting- lots of different microorganisms are used to produce biogas by fermenting plant and animal waste which contain carbohydrates. They mainly produce methane and carbon dioxide.

Alcohol- yeast ferments to form ethanol (alcohol). the sugar used in alcohol comes from grapes (used in wine) and barley (used in beer)

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Photosynthesis is a series of chemical reaction that use energy from sunlight to produce food. The food produced is glucose.

Photosynthesis happens in cells in the green areas of plants and some microoraganisms such as phytoplankton.

Chlorophyll is the green substance which absorbs sunlight to allow energy to be used to convert carbon dioxide and water into glucose.

Oxygen is a waste product of the reaction. Here is the equation:

Carbon Dioxide + Water -->light energy-->    Glucose  + Oxygen

      6CO2          + 6H2O -->light energy--> C6 H12 O6 +    6O2

Glucose is used in 3 main ways: 

  • Respiration- to release energy
  • To make chemicals for growth- converted to cellulose to make cell walls, combined with nitrogen to make amino acids and used to make cholrophyll
  • Stored as Starch in roots, stems and leaves- used when rate of photsynthesis is slow, e.g. winter
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Rate of Photosynthesis

There are 3 Factors that can affect the rate of photosynthesis:

  • The amount of light
  • The amount of CO2
  • The temperature

Any of these factors can become limiting factorsWhich one is limiting depends on the environmental conditions e.g. at night it will be light, during the winter the temperature is likely to limit it and if its warm enough or bright enough it's usually CO2.

Both light and CO2 will slow down the reaction if not enough is supplied. However, these will only increase the rate of reaction up to a point and then it will no longer be the limiting factor.

Usually if temperature is the limiting factor its due to it being too low and not enough energy is being supplied for the enzymes to work quickly.However if the plant gets too hot the enxymes needed for the reaction will become denatured and the reaction wont be able to take place. This happens at about 45'C which usually only occurs in greenhouses.

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Investigating Photosynthesis

A Transect is a way of investigating how something changes over an area.

This is how to make a transect:

  • Run a tape measure between two fixed points
  • Start at one end and collect the wanted data
  • Move along and collect it again
  • Continue to do so until you reach the other end

Equipment used to collect data:

  • Light Meter- Measures the level of light with accuracy
  • Quadrat (a grid of 100 small squares)- used to find percentage covers of plant species on the ground for example.
  • Indentification key- a series a questios used to determine what plant is in question. start at question one and the answer is used to narrow it down. as you answer more question you will end up with one answer. Similar to magazine flow charts.
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Diffusion, Osmosis and Active Transport

Diffusion is the passive (without needing any energy) overall movement of partciles from a region of theri higher concentration to a region of their lower concentration.

Osmosis is a specifc case of diffusion- its in water.

Osmosis is the overall movement of water from a dilute solution to a more concentrated solution through a partially permeable membrane. Plants take in water by osmosis as there is usually a higher concentration of water in the soil than in the roots.

Some chemicals such as Glucose need to be moved from a region of their lower concentration to a region of their higher concentration across a cell membrane. This is done through a process called active transport by using energy from repsiration. 

Active Transport is the overall movement of chemicals across a cell membrane from a region of lower concentration to a region ofhigh concentration using enery realesed by respiration.

Plants take in nitrates from the soil through active transport.

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Key Card

Blue means that it is an important word

Red shows that it is a formula formula

Green displays a definition of a word

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