Gaseous Exchange in Plants & Transporting Systems


Transport in Plants

There are two types of Transporting Systems in a Plant

  • Xylem tubes transport water and mineral salts from the roots up to the shoot to the leaves in the transpiration stream
  • Phloem tubes transports food, like sugars, amino acids from where they're made in the leaves to other parts of the plant.

Root Hairs Take in Water 

The cells on plant roots grow into long "hair" which stick out into the soil. This goves the plant a big surface area for absorbing water from the soil.


It is caused by Evapouration and diffusion. The evaporation creates a slight shortage of water in the leaf, and so more water is drawn up from the rest of the plant through the Xylem vessels to replace it. This means more water is drawn up from the roots and so there's a contant transpiration stream of water through the plant.

Because there is more water in the plant than the air, it diffuses out of the stomata.

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Transpiration Rate

  • Light Intensity- the brighter the light, the greater the transpiration rate. Due to little water escaping in the dark as there is no light but in daylight the whole day it opens the Stomata to photosysthesis.
  • Temperature- the warmer the air, the faster the transpiration rate. As water particles have more enery to evapourate and diffuse out of the stomata.
  • Wind Speed- the higher the wind speed around the leaf, the greater the transpiration rate. As the wind pushes water vapour away from the plant,so it can diffuse from a high concentration to a low concentration.
  • Humidity- The drier the air around the leaf, the faster transpiration happens.

How leaves are adapted for Effiecient Gas Exchange

  • Leaves are broad, so there is a large surface area for diffusion
  • They are thin so it is a short distance for gases to reach the cells needed.
  • There are air spaces in the leaf which means it increases the surface area for gas exchange.
  • The lower surface is fuul of little holes called Stomata. They're there to let gases in and out. They allow water to escape known as Transpiration
  • Stomata closes when it gets dark due to no photosysthesis, as no CO2 is let in. When it is closed water cannot escape. Stomata also closes when water from the roots start to dry up.
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Gas Exchange - Plants

Hydrogen Carbonate Indicator shows CO2 Concentration 

  • With a normal CO2 concentration is Orange
  • When it increases it becomes Yellow
  • When it decreases it becomes Purple.

Experiment- All in front of Bright Light for an day and Expected Results

  • You need the Control Tube
  • One tube with a leaf only which is completely wrapped with foil which gives a Yellow colour as Respiration takes place and not Photosysthesis as there is no light.
  • One tube with a leaf and a snail gives a normal CO2 concentration which is Orange as there is an equal amount of photosysthesis and respiration taking place.
  • A tube with the leaf only gives a colour of Purple as there will be some Respiration but lots of photosysthesis, leading uptake of CO2. This means there will be a lower CO2 concentration in tube.

Photosysthesis - Carbon Dioxide + Water = Glucose + Oxygen

Respiration - Glucose + Oxygen = Energy + Carbon Dioxide + Water

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