biology unit 2

AQA unit 2 GCSE biology

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  • Large protein molecules
  • Biological catalysts so increase the rate of reaction in an organism in the living system
  • Have a specific shape- they also ave an active site which exactly fits the substrate moleule it breaks down. Lock and key mechanism
  • It's shape can be changed by pH-this can alter the active site
  • If an enzyme is put in a solution o the wrong pH, then its active site will be the wrong shape and the substrate will not fit.
  • This will prevent the chemical reaction from happening.
  • High temperatures destroy most enzymes' special shape. This is why it is dangerous for a humans body temperature to go above 37 degrees.
  • Enzymes are protein molecules made up of long chains of amino acids.
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Digestive Enzymes

Enzyme ...digests              Substrate                    Product                 Site                    


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Enzymes in the home and industry

Some mirco-organisms produce enzymes which pass out of the cells. These enzymes have many uses in the home and in industry.

In the home, biological detergents may contain protein-digesting (protease) and fat-digesting enzymes (lipase)

In industry:

  • Proteases are used to 'pre-digest' the protein in some baby foods.
  • carbohydrases are used to convert starch into sugar syrup.
  • Isomerase is used to convert glucose syrup into fructose syrup, which is muh sweeter and therefore can be used in smaller quantities in slimming foods.
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Areobic Resperation

  • During Aerboic resperation ( respiration uses oxygen) chemical reactions occur which

                 - use glucose ( a type of sugar) and oxygen

                 - release energy

  • Most of the reactions in aerobic respiration take place inside mitochondria

Aerobic respiration is summarised by the equation:

Glucose + Oxygen --> Carbon dioxide (+energy)  + Water



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The energy that is released during respiration is used:

      - to build up larger molecules using smaller ones (growth)

      - in animals, to enable muscules to contract

      - in mammals and birds, to maintain a constant temperature in colder surroundings

      - in plants to build up sugars, nitrates and other nutrients into amino acids which are then built up into proteins.

Aerobic respiration releases energy through the breakdown of glucose molecules.

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human characteristics

  • Body Cells contain 46 chromosomes arranged as 23 pairs.
  • Chromosomes are made up of large molecules of DNA. A gene is a section of DNA.

Gametes- female eggs and male sperm- have 23 chromosomes( one from each pair) The fusion of these 2 cells produces a zygote with 46 chromosomes in total (23 pairs)

Of the 23 pairs of chromosomes in human body cells, one pair is the sex chromosomes.

  • X chromosomes are females
  • Y chromosomes are males and much shorter than Y chromosomes.


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Like all pairs of chromosomes, offspring inherit one sex chromosome from the mother and one from the father.

The physical characteristics of organisms are controlled by :

-Their genes

- The environment

In humans genetically controlled characteristics include eye + hair colour, sex and number of fingers.

Environmentally controlled charateristics include hair + nail length, scars and language.

Some characteristics are controlled by a combination of skin colour, weight, height and fitness.

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Mitosis is the division of body cells to produce new cells. This occurs for growth and repair (also in asexual reproduction). Before the cell divides, a copy of each chromosome is made so the new cell has exactly the same genetic information. This means that the cells of asexually reproduced offspring contain the same genes as the parents.

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When gametes join at fertilisation, one chromosome comes from each parent and a single body cell with new pairs of chromosomes is formed.

This then divides repeatedly by mitosis to form  new individual, giving rise to variation.

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