B4- The Processes of Life

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Photosynthesis and Respiration

Respiration = a series of chemical reactions

and releases energy from food.

Photosynthesis = how plants make food (light energy --> chemical energy) GLUCOSE

Oxygen + Glucose ---> Carbon dioxide +Water

At night- plants only respire and give out CO2

In the day- Plants photosynthesise as well as respiring.

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(think 'ase')

  • Enzymes are chemicals that speed up chemical reaction rates.
  • They are proteins and have long chains of amino acids joined together.
  • Cells assemble them by using instructions provided in genes.
  • Chemicals that enzymes work on = Substrates (molecules before the reaction)
  • This process is called Active Transport

Lock and Key model

1. Only the correct molecule fits the active site

2. A reaction takes place in the active site

3. The product leaves the active site. The enzyme can be used again

Keywords- Active site, Lock and Key, Enzyme, Substrate, Product

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pH of Enzymes

Enzymes need a specific pH in order to work at their optimum

Low temp = low reaction rate

Optimum temp = 37 degrees c = high reaction rate

  • If it gets too hot, the enzyme active site is changed so the molecules cannot fit the active site.
  • The rate of reaction falls to 0 because the enzyme is denatured

The denatured active site can be permanent or temporary...

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Plants making food


Photosynthesis is a series of chemical reactions that use energy from the sun to build food molecules in plant cells

Word Equation= Carbon dioxide + Water   --->   glucose + Oxygen

6CO2 + 6H2O --->C6H1206 + 6O2

Light energy from the Sun drives the reaction between Carbon dioxide and Water to build up glucose.

Sunlight is absorbed by chlorophyll which is found in cell structures called chloroplasts

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  • Used to make chlorophyll
  • Respired to give energy
  • Proteins for growth
  • Cellulose for cell walls
  • Starch/oil for engery storage

Glucose and Nitrates - taken up by the plant roots and used to synthesise amino acids.

(then assembled into proteins)

Oxygenis a waste product of photosynthesis

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Cell as a Factory

All cells have a nucleus, cytoplasm and cell membrane

  • Cell Membrane- allows gases and water to pass in and out freely. In plants, cell wall is made of cellulose
  • Nucleus- contains DNA which stores the genetic code

( carries information the cell needs to make enzymes and other proteins)

- bacteria have no nucleus (they have a circular DNA molecule in their cytoplasm)

  • Cytoplasm- contains mitochondria (animal and plant cells and microorganisms e.g yeast have mitochondria) which have enzymes needed for the release of energy by aerobic respiration.

Animals do not have a cell wall

  • Bacteria- have no nucleus
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Diffusion= the movement of chemicals from a high to low concentration.

Photosynthesis -

  •  WATER is taken up by plant roots
  • CARBON DIOXIDE enters the plant leaves by diffusion
  • OXYGEN leaves the plant leaves by diffusion

Diffusion just happens- it doesn't require energy

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Osmosis = diffusion involving water

  • happens when chemicals are seperated by a partially permeable membrane (e.g the cell membrane)
  • The cell membrane lets water pass through, but keeps other chemicals in or out.

Osmosis is the overall movement water from an area of high concentration to an area of low concentarion.

The movement of water into plant roots from the soil, and across the roots happens by osmosis.

  • Diffusion happens because of the random movement of molecules
  • This movement doesn't stop when the concentrations of molecules in the 2 areas are equal


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Active Transport

Minerals taken up by plant roots are used to make chemicals needed in cells

- e.g nitrogen taken up as nitrates is used to make proteins.

  • Nitrates are normally in a higher concentration in plant cells than in the soil (so root cells CANNOT take up nitrates by diffusion.
  • Root cells use active transport to take up the nitrates
  • -by using energy from respiration to transport chemicals across cell membranes
  • -this happens against a concentration (or diffusion gradient) through "carrier proteins" that change shape.
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Limiting Factors of Photosynthesis

3 factors - temperature

               - carbon dioxide

               - light intensity

  • CO2 is only 0.04% in air composition therefore plant growers increase levels in greenhouses
  • Light intensity/CO2 increased means that photosynthesis increases and then levels off.

when this happens it means that there is a limiting factor (something limiting the rate)

  • Rise in temperature increases the rate of photosynthesis up to a certain point

-the rate then decreases due to the effect of temperature on enzyme activity

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Effects of Light and Plant Growth

  • Ecologists use and identification key to identify the plants that they have found.
  • They measure how common the plants are
  • They use a light metre to measure light intensity

They investigate how many plants there are

  • at different locations in an area and make a comparison
  • in totally different areas and make a comparison

Ecologists don't count the plants, they take a smaple from a quadrat frame

  • they decide how large the quadrat should be based on the size of the organism and the area
  • it's put on the ground 10 times to take an average and the number per m squared calculated
  • This is done at random (throwing the quadrat, picking random coordinates of the area)

If there's an obvious change in the plants in the area, the quadrat is used at measured distances along a transect (a line)

  • Trees, bushes etc can cast shade on an area and this can affect the growth of plants around them.
  • There may be a correlation between the distance from the bush and the growth of other plants
  • Other factors may be involved such as competition for nutrients 
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Aerobic Respiration

  • Organisms use energy released from food by respiration
  • This is a series of chemical reactions
  • It occurs in cells that release energy by breaking down large food molecules.

Respiration happenes in every cell in the body (the chemical for respiration is glucose)

Chemicals in food are converted into glucose or we eat glucose ourselves

Respiration using oxygen is called aerobic respiration

  • Glucose + Oxygen --> Carbon Dioxide + Water + (energy)
  • C6H12O6 + 6O2 -->  6CO2 + 6H2O

Takes place in animal and plant cells and some microorganisms

  • Organisms need energy from respiration for the synthesis of large molecules and movement
  • Plants use food produced by photosynthesis for respiration / active transport (excess glucose is stored as starch)

Respiration is a series of enzyme-controlled reactions with energy being released in stages.

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Anaerobic Respiration

Some organisms can obtain energy when oxygen is in low concentration or absent though anaerobic respiration

  • It occurs in humans when we're doing vigorous exercise
  • Plant roots in water logged soil
  • Bacteria in deep puncture wounds

It releases much more energy per molecule of glucose that anaerobic respiration

Glucose ---> lactic acid + energy

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Fermentation- Type of anaerobic respiration used by some microorganisms.

Some of the products are useful (e.g ethanol produced by yeast)

glucose ---> ethanol + carbon dioxide + energy

Bubbles of CO2 make bread rise and alcaholic drinks sparkle.

Anaerobic respiration is important in biogas production

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