4.2.3 Plant tissues, organs and systems

4.2.3.1 Plant tissues

Xylem and Phloem

• Plants have a transport system.
  • Water, food and ions are transported by the xylem and phloem in a plant.
• The xylem transfers water and mineral ions.
  • It is a vascular bundle that transports water and ions to the leaf.
• The phloem transfers food.
  • It moves glucose away from the leaf.

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Meristem

• The meristem is a site of cell division in the plant.

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4.2.3.2 Plant organ system

Defining Transpiration

• Transpiration is the movement of water away from the plant’s leaves from the inside of the plant.
  • It occurs as water diffuses through the plant from the roots and evaporates from the leaves.
  • The evaporation of water from the leaves causes a shortage of water in the plant, allowing more water to be taken up from the roots.
  • Water then moves through the transpiration stream in the plant.

Temperature

As temperature increases, so does the rate of transpiration as the water particles gain more

energy to diffuse into the plant evaporate out of the stomata.

Humidity

• When the air is more humid, the concentration gradient is reduced.
  • This means that the rate of diffusion is lowered and so the transpiration rate is reduced.

Air Movement

As the movement of air increases, the concentration gradient is increased, so the rate of

transpiration increases.

Light Intensity

• As the light intensity decreases, the stomata close up and there is a reduction in photosynthesis.
  • This means that very little water can escape and so the rate of transpiration decreases.

Rate of Transpiration

• The rate of transpiration is an important measure.
  • It is the amount of transpiration per unit time.

Transpiration Organ System

• Water moves through the xylem as part of the transpiration stream.
• Stomata are small gaps in the leaves that allow water to move through.
• Guard cells open the stomata when they take in water.
  • This allows gas exchange for photosynthesis.