WJEC Biology 3 - Plants

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  • Created by: Molly
  • Created on: 22-04-13 17:34


Transpiration is the process whereby plants expel water.

Water is absorbed by the roots and travels in vessels up the stem called xylem tubes to the leaves.

There are pores on the leaves called stomata, surrounded by guard cells.

When the plant has lots of water, the pressure of the turgidity forces the guard cells open, and water is lost through the stomata.

When the plant has little water and is flaccid, the guard cells stay closed, and transpiration comes to a stop.

Factors affecting transpiration are the light level, wind, humidity, and temperature.

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Nutrients needed by plants


What do they do?

      Used to build proteins and essential for growth.

What happens when there is a deficiency?

      There will be yellow leaves and poor growth.


      All amino acids contain nitrogen. Amino acids are the building blocks of proteins.

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Nutrients needed by plants part 2


What do they do?

      A necessity for photosynthesis and respiration.

What happens when there is a deficiency?

      There will be poor flower and fruit growth and discoloured             leaves.


      Potassium must be present for photosynthesis and respiration enzymes to function.

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Nutrients needed by plants part 3


What do they do?

        A necessity for photosynthesis and respiration.

What happens when there is a deficiency?

        There will be poor root growth and discoloured leaves.


        Phosphate a key component of DNA molecules and all membranes.

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Why is water important to plants?

  • Reactant in photosynthesis 
  • Helps in the transport of minerals and support

Use in photosynthesis 

Water is used in photosynthesis for its hydrogen and it prevents dehydration.

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NPK Fertiliser

If a plant shows poor growth it may be due to a lack of one or more minerals in the soil. It's possible to do chemical tests to find out which minerals are deficient, but it's often more convenient to add a general fertiliser. This is sometimes called NPK fertiliser because it contains the elements nitrogen (N), phosphorus (P) and potassium (K). These elements, plus magnesium (Mg), are the minerals that plants need in the greatest quantities.

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How minerals are absorbed

The concentration of minerals in the soil is very low. They dissolve in water and move around the soil in solution. Root hair cells are adapted to absorb the water out of soil by osmosis – they have a large surface area, thin walls and are close to the xylem cells used for transporting water up the plant. Minerals cannot be absorbed by osmosis (which is the movement of water only) or diffusion (because the minerals are in very low concentration). The root hair cells have carrier molecules on their surface that pick up the minerals and move them into the cellagainst the concentration gradient. This requires energy, and is called active transport.

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The phloem carries sugar from the photosynthetic areas to other parts of the plant. Sugar is moved to other plants for use in respiration and converted ino starch for storage. The transport of sugar is not fully understood so it is still being investigated by plant scientists.

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Leaf Diagram


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