B1 Cells - Active transport

root hairs take in minerals and water
1. the cells on the plant roots grow into 'hairs' which stick into the soil
2. each branch if a root will be covered in millions of these microscopic hairs
  1. this gives the plant a large surface area for absorbing water and mineral ions from the soil.
3. plants need these mineral ions for healthy growth
4. the concentration of minerals is usually higher in the root hair cells than in the soil around them.
  1. so the root hair cells can't use diffusion to take up minerals from the soil.
root hairs take in minerals using active transport
1. minerals should move out of the root hairs if they followed the rules of diffusion. the cells must use another method to draw them in.
  1. this method is a conveniently mysterious process called active transport.
2. active transport allows the plant to absorb minerals from very dilute solution, against a concentration gradient
  1. this is essential for its growth
3. active transport needs energy from respiration to work
4. active transport also happens in humans, e.g taking in glucose from the gut and from the kidney tubules
we need active transport to stop us starving
1. active transport is used in the gut when there's a lower concentration of nutrients in the gut but a higher concentration of nutrients in the blood
2. when there's a higher concentration of glucose and amino acids in the gut they diffuse naturally into the blood
  1. but sometimes there's a lower concentration of nutrients in the gut than there's in the blood
    1. this means that the concentration gradient is the wrong way
3. active transport allows nutrients to be taken into the blood, despite the fact that the concentration gradient is the wrong way
  1. this means that glucose can be taken into the blood stream when its concentration in the blood is already higher than in the gut, it can be transported to cells, where it's used for respiration
organisms exchange substances with their environment
1. cells can use diffusion to take in substances they need and get rid of waste products.
  1. EXAMPLE: oxygen and carbon dioxide are transferred between cells and the environment during gas exchange
  2. EXAMPLE: in humans. urea diffuses from cells into the blood plasma for removal from the body by the kidneys
2. how easy it's for a organism to exchange substances with its environment depends on the organisms surface area to volume ratio (SA : V)
you can compare surface area to volume ratio
1. a ratio shows how big one value is compared to another. The larger the organism is, the smaller its surface area is compared to its volume. You can show this by calculating surface area to volume ratio
2. A hippo can be represented by a 2cm x 4cm x 4cm block
  1. the area of the surface is found by the equation LENGTH x WIDTH
    1. so the hippo's total surface area is
      1. top and bottom surfaces of the block = (4 x 4) x 2
      2. 4 sides of the block = (4 x 2) x 4
      3. total surface area = 64 cm2
    2. the volume if a block is found by the equation LENGTH x WIDTH x HEIGHT
      1. the hippo's volume is 4 x 4 x 2 - 32 cm3
      2. the surface area to volume ratio of the hippo can be written as 64 : 32 to simplify the ratio, divide both sides of the ratio by the volume so the surface area to volume ratio of the hippo is 2 : 1
multicellular organisms need exchange surfaces
1. in single cell organisms, gases and dissolved substances can diffuse directly into or out of the cell across the cell membrane
  1. it's because they have a large surface area compared to their volume, so enough substances can be exchanged across the membrane to supply the volume of the cell
2. multicellular organisms have a smaller surface area compared to their volume - not enough substances can diffuse from their outside surface to supply their entire volume
  1. this means they need some sort of exchange surface for efficient diffusion.
  2. the exchange surface structures have to allow enough of the necessary substances to pass through
3. exchange surfaces are adapted to maximise effectiveness
  1. they have a thin membrane, so substances only have a short distance to diffuse
  2. they have a large surface area so lots of substance can diffuse at once
  3. exchange surfaces in animals have lots of blood vessels, to get stuff into and out of the blood quickly
  4. gas exchange surfaces in animals are often ventilated too - air moves in and out

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B1 Cells - Active transport

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