AQA New Specification B2B

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Enzymes

  • Enzymes are biological catalysts that ---> speed up chemical reaction and are not used up. 
  • An enzyme = protein molecule made of a long, folded chain of amino acids. 
  • The digestive enzymes amylases, lipases and proteases break down food. 
  • Catalase catalyses the breakdown of hydrogen peroxide, a poisonous by-product of metabolism: hydrogen peroxide ---> water + oxygen.
  • Enzymes are involved in: respiration, photosynthesis and protein synthesis. 
  • Each enzyme works at an optimum pH and temperature. 
  • High tempretures of extremes of pH denatures enzymes by affecting the shape of their active sites.
  • Enzymes are used in industry for  food production and in the home in biological detergants. 
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Respiration and Waste Removal

  • Aerobic respiration is carried in mitochondria in our cells to provide energy:

=glucose + oxygen ---> carbon dioxide + water + (energy)

  • The tail of a sperm cell is packed with mitochondria to enable it to swim the long distance to the egg. 
  • Breathing allows the diffusion of oxygen into the body for respiration and removal of waste carbon dioxide out of the body via the alveoli in the lungs.
  • The dissolved gases are carried round the body in the blood.
  • Released energy is used: to build large molecules from small ones, by plant to build sugars, nitrates and other nutrients into amino acids, then proteins, by mammals and birds to maintain a steady body temperature, by animals to make muscles contract. 
  • Excess amino acids are broken down by the into the urea. The kidneys make urine, which contains dissolved urea. 
  • The urine is stored in the bladder, then excreted.
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Homeostasis

  • Blood sugar levels are controlled by the pancreas which produces insulin. People with diabetes produce too little insulin. 
  • Human core body temperature is kept constant at about 37°C.
  • The thermoregulatory centre in the brain contains temperature receptors.
  • Sweating cools the body down as it evapourates. Re-routing blood deeper in the body reduces heat loss. 
  • Water inputs from drinking and cell respiration are balanced with water outputs from tears, evapouration from lungs, sweat, urine and faeces. Excess water could burst cells and excess ions could be toxic. 
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Inheritance 1

  • Chromosones = long molecules of DNA made up of genes. 
  • Genes contain the genetic code, which contains the instructions for making proteins, including enzymes. 
  • Body cells divide by mitosis. Each new cell has the same number of identical chromosones as the original cell.
  • Undifferentiated stem cellls can specialise into many types of cells.
  • Sex chromosones = determine the sex of the offspring (male XY, female XX)
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Inheritance 2

  • In reproductive organs, the ovaries and testes, cells divide by meiosis to form gametes (sperm and ova) and thathalf the number of chromosones of body cells. 
  • Gametes fuse at fertilisation to produce --> new organism with the same number of chromosones in body cells as parents. 
  • The mixture of alleles from the parents causes variation in the offspring.
  • Some inherited characterstics are controlled by a single gene.
  • Different forms of a gene are called alleles. 
  • In homozygous individuals, the alleles inherited from each parent are the same.
  • In heterozygous individuals, they are different.
  • Alleles can be recessive or dominant.  
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