Biology GCSE (Unit 2) Part 2: Plants

Green plants absorb light energy using chlorophyll in their leaves. They use it to react carbon dioxide with water to make a sugar called glucose. The glucose is used in respiration, or converted into starch and stored. Oxygen is produced as a by-product.

Temperature, carbon dioxide concentration and light intensity are factors that can limit the rate of photosynthesis.

Plants also need mineral ions, including nitrate and magnesium, for healthy growth. They suffer from poor growth in conditions where mineral ions are deficient.

Without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and carbon dioxide. Increasing the light intensity will boost the speed of photosynthesis.

Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesise if there is insufficient carbon dioxide.

If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesise if it is too hot/cold.

Maximising Growth - Farmers can use their knowledge of these limiting factors to increase crop growth in greenhouses. They may use artificial light so that photosynthesis can continue beyond daylight hours, or in a higher-than-normal light intensity. The use of paraffin lamps inside a greenhouse increases the rate of photosynthesis because the burning paraffin produces carbon dioxide, and heat too.

Plants need to take in a number of elements to stay alive. The most important are: Carbon, Hydrogen and Oxygen.

Plants get hydrogen and oxygen from water in the soil, they also get carbon & oxygen from carbon dioxide and oxygen in the atmosphere. Water & carbon dioxide are used to synthesise food during photosynthesis. Oxygen is used to release energy from food during respiration.

Plants need a number of minerals for healthy growth. These are absorbed through the roots as mineral ions dissolved in the soil water.If a plant is defficent in a mineral ion it's growth will be poor. Two Mineral Ions needed:

Blue - What the mineral ion is used for.  Purple -  Defficency Symptoms.

Nitrate - for making amino acids which are needed to make protein. It will suffer from stunted growth.

Magnesium - for making chlorophyll. It's leaves will turn Yellow