Transport in animals



Transport in plants:

  • Food is synthezised in the green parts of a plant. The non- green parts are depended on the photosynthetic cells for nourishment./
  • The food in the form of sucrose is transported by the vascular tissue phloem. The transportation occurs in the direction of the source to sink.
  • Transport of organic solutes from one part of the plant to the other through the phloem sieve tubes is called translocation of organic solvents.
  • Transports dissolved substances- sucrose (sugars).
  • Living cells
  • companion cells- between sieve tubes with many mitochondria to produce ATP needed for active transport.

Movement in the Phloem:

  • sucrose is loaded into the phloem at a source, usually a photosynthesizing leaf.
  • For this to occur, hydrogen ions are pumped out of the companion cell using ATP.
  •  Sucrose is loaded (moved into companion cells) by active transport, against the concentration gradient.
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Made up from 4 different parts:

  • Phloem fibres- fibre found in or associated with the phloem because of its strength.
  • Phloem parenchyma- they function in the transport of foods.
  • Sieve tubes- a series of sieve tube elements placed end to end to form a continuous tube.
  • Companion cells- closely associated in the development and function with a sieve tube element.

Sieve tubes:

  • Cell membrane broken down
  • Fluid cytoplasm
  • No vacuole
  • No nucleus

The movement of substances in the phloem tissue is called Translocation. The main substances that are moved are sucrose and amino acids, which are soluble in water. these substances have been made by the plant and are called assimilates.

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  • The products from the source are usually translocated to the nearest sink through the phloem. The multidirectional flow of phloem contrasts the flow of xylem, which is always undirectional.
  • Translocation of sucrose and other assimilates is an energy- requiring process.
  • Respiration in companion cells at a source point provides ATP that fuels the active transport of sucrose into the companion cells.
  •  This increases the concentration of sucrose in the companion cell meaning it moves by diffusion down a concentration gradient into the phloem sieve element.

Source and Sinks:

  • A source- is an organ that produces more sugar that is required. That's where assimiliates enter the phloem.
  • A Sink - is an organ that consumes sugar for its own growth and storage. That's where assimilates leave the phloem.
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  • Transports water and minerals.
  •  only from root to leaves.
  • Dead vessles impregnated with ligin for support.
  • Have pits to let water flow from one Xylem vessel to another incase of collapsing.

Xylem vessels:

consist of dead hollow cells because the walls are lignified and the cell contents disintegrate. The ligin makes the cell wall impermeable so they are in effect waterproof. It also makes the vessels extremely strong and prevents them from collapsing. 

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