·      Farmers use big greenhouses to control temperature, CO2 concentration, and light intensity. These levels are varied to get the fastest possible rates of photosynthesis. For example:

  • CO2 levels are increased during the day when light levels are at their highest, so they do not act as a limiting factor
  • The optimum temperature for enzyme activity is maintained all the time
  • Artificial lighting is used to prolong the hours of photosynthesis and to increase light intensity

·      Because of this, plants photosynthesise for as long as possible and grow increasingly quickly

·      The greenhouses are huge and conditions are controlled using computer software. It takes a lot of energy to keep conditions in the greenhouse just right but fewer staff are needed. It costs a lot of money but:

  • Profits can be high and no plowing or preparation of land 
  •  Crops are clean and unspoiled and can be grown where light is poor
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·        Photosynthesis is summarised by the following equations:

o                                          light energy
                carbon dioxide + water --> glucose + oxygen

o                                   light energy
                       6CO2 + 6H2O --> C6H12O6 + 6O2

      Plants produce hormones to coordinate and control growth. The hormone auxin                   controls phototropism and gravitropism (geotropism)

·         The responses of plant roots and shoots to light, gravity and moisture are the                      result of unequal distribution of auxin, causing unequal growth rates

          The glucose produced in photosynthesis may be:

  •  used for respiration to provide energy for growth
  •  converted to sucrose to transport glucose
  •  converted into insoluble starch for storage
  •  used to produce cellulose, which strengthens the cell wall
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Variation and Inheritance

·         A gene is a small section of DNA. Each gene codes for a specific protein. A sequence of 3 bases codes for 1 amino acid. The order of bases controls the order of amino acids to produce a protein. Proteins are long chains of amino acids

·         A change in a gene can lead to a different phenotype

  • A mutation is a change in order of bases
  •  so, the order of amino acids changes
  • so, the mutation changes the shape of the protein
  •  so, enzyme doesn’t work


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Variation and Inheritance

       Embryo screening involves tests to diagnose genetic disorders before the baby is born. The results of the tests give parents a choice over what to do with the embryo. In IVF the embryos are screened and only healthy embryos are implanted into the mother. Embryos carrying faulty genes are destroyed and some people think this is unethical

·     Concerns and disadvantages about embryo screening include:

  • the risk of miscarriages (baby can be aborted)
  • the reliability of the information from the screening procedure as sometimes there can be false positive and false negative results
  • decisions about terminating pregnancy
  • it could cause selection where embryos are picked for their characteristics

·     However, positives for embryo screening include:

  • future offspring less likely to inherit disorder
  • it saves money later in life as children with disorders are costly to keep
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Cell division

 Embryonic stem cells

Advantages- they can treat lots of diseases; there are many available; it is better to use them than to waste them; it’s a painless procedure

Disadvantages- it causes possible harm to embryos involved; the long-term effects are unknown; embryos cannot be asked 

Adult bone marrow stem cells

Advantages- there are no ethical issues; there is a quick recovery; they are well tested, and we know how they work

Disadvantages- there are operational hazards i.e. infection; there are few types of cell produced; it’s a painful procedure, which may deter donors

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·      People can be immunised against a disease by introducing small amounts of dead or inactive pathogen into the body (vaccination). Vaccines stimulate WBCs to produce antibodies that destroy the pathogen. This makes the person immune to future infections by the microorganism, and these antibodies produced quickly in future infections

      Bacteria can mutate, sometimes causing them to be resistant to antibiotics. Antibiotics can only kill individual pathogens of the non-resistant strain, but individual resistant pathogens will survive and reproduce, and the population of the resistant strain will increase. Vaccinations may no longer work against this resistant strain, and it could cause a serious infection that can’t be treated by antibiotics.  The new strain would then spread rapidly because people are not immune to it and there is no effective treatment

·      Many strains of bacteria have developed resistance to antibiotics. Overuse and inappropriate use of antibiotics has increased the rate of development of antibiotic-resistant strains of bacteria. Therefore, doctors do not currently prescribe antibiotics for the treatment of non-serious infections, such as throat infections, to slow down the rate of development of resistant strains

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Cell Transport

·         Osmosis is the net movement of water molecules across a partially permeable membrane         from a region of high water concentration (dilute solution) to a region of low water                 concentration (concentrated solution)

  • Tissue fluid surrounds the cells in our bodies. This fluid will usually have a different water concentration than the fluid inside the cell- so water will either move into or out of the cell via osmosis
  • If the water concentration in the tissue fluid is higher than the cell fluid, the tissue fluid is called a hypotonic solution as water moves INTO the cell
  • If the water concentration in the tissue fluid is lower than the cell fluid, the tissue fluid is called a hypertonic solution as water moves OUT OF the cell
  • If the water concentration in the tissue fluid is the same as the cell fluid, the tissue fluid is called an isotonic solution as there is NO NET MOVEMENT

·         Active Transport moves substances along the cell membrane, against the concentration          gradient, via a carrier protein, using energy from respiration

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 Protease, produced by the stomach, pancreas, and s. intestine catalyses the breakdown      of proteins into amino acids in the stomach and s. intestine 

·         Bile is produced in the liver:

  • Stored in the gall bladder before being released into the s.intestine
  • The HCl acid in the stomach is too acidic for enzymes in the s.intestine to work properly. Bile is slightlyalkaline and it neutralises the acid to make conditions alkaline. Enzymes in the s.intestine work best in these alkaline conditions
  • Emulsifies fat (breaking down the fat into tiny droplets). This gives a much bigger surface area of fat for lipase to work on, speeding up digestion
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Nervous System

·         When an impulse reaches a synapse

o   It causes the release of a chemical

o   Which diffuses across synapse

o   And causes an impulse

o   To be sent to the next neurone

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·         The blood glucose concentration is monitored and controlled by the pancreas. Much of the glucose is stored as glycogen in the liver and muscles

·         If blood glucose levels are too high, the pancreas produces the hormone insulin, which allows the glucose to move from the blood into the cells

·         When blood glucose levels fall, the pancreas produces a second hormone, glucagon. This causes glycogen to be converted into glucose and released into the blood

      If we’re too hot:

  •  Blood vessels supplying the skin capillaries vasodilate to allow more blood to flow closer to the surface of the skin. These vessels now have a larger surface area, which means more heat can be lost to the environment via radiation
  • Sweat is produced by sweat glands. More water is lost, and this water and evaporates from the skin, removing heat
  • Hairs lie flat
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Breathing & Respiration

·         Anaerobic respiration in muscles is the incomplete breakdown of glucose, which causes           a  build-up of lactic acid. An oxygen debt needs to be repaid to oxidise the lactic acid            to carbon dioxide and water

·         The alveoli have a large surface area (greater the surface area, the greater the rate             of gas exchange), richly supplied with blood capillaries, so gasses can easily diffuse in             and out of the blood

·         Oxygen from the air diffuses across the walls of alveoli into the bloodstream, as                     oxygen is of a higher concentration in the alveolus than the bloodstream. Carbon                    Dioxide diffuses from the bloodstream into the lungs as it is of a higher                                  concentration in the bloodstream  than the alveolus

·              Because the breakdown of glucose is incomplete, much less energy is released in                     anaerobic  respiration than during aerobic respiration

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Cell division


  • Growth and Replacement of damaged tissue
  • Chromosomes are copied
  • Then they divide once
  • To form 2 body cells
  • Which are genetically identical


  • Makes 4 gametes for sexual reproduction
  • Chromosomes are copied
  • Then they divide into 2
  • They divide again, making 4 sex cells
  • Which are genetically unique
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Carbohydrates, lipids, proteins and enzymes

·         Starch, proteins, and lipids are big, insoluble molecules. This means that they are unable     to pass through the walls of the digestive system

  • They are broken down by digestive enzymes into smaller, soluble molecules, so they can be absorbed into the blood stream in the wall of the small intestine

·         Protease, produced by the stomach, pancreas, and s. intestine catalyses the breakdown      of proteins into amino acids in the stomach and s. intestine 

·        Some microorganisms produce enzymes that pass out of the cells.  These enzymes have      many uses in the industry.

  • In the industry, proteases are used to ‘pre-digest’ protein in baby foods so food is easier for baby to digest
    • proteases are used to ‘pre-digest’ protein in baby foods so food is easier for baby to digest
    • carbohydrases are used to convert starch into sugar syrup
    • isomerase is used to convert glucose syrup into fructose syrup, which is used in slimming foods
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Distribution of organisms

·         You can sample along a transect (line)

  • You stretch a tape between 2 points, often where you suspect a change is linked to an abiotic factor (number of plants to light intensity)
  • You sample the organisms along that line at regular intervals using a quadrat
    • showing how the distribution of organisms changes along that line
  • You can also measure physical factors, such as light levels and soil pH, that might affect the growth of plants along a transect
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Energy, biomass & decay

·      Energy from the sun is captured by plants. The energy stored in chemicals in cells and is then passed up food chain. Less energy stored at each stage in food chain because only part of the energy taken in is used for growth

  •  some lost in waste
  • some used for repair
  •  some lost in respiration
  •  some converted into other forms of energy e.g. movement
  •  much lost as heat

·       By time detritus feeders have decomposed remains, all energy has returned to environment

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