# 48 Summary of plant nutrition
- Photosynthesis takes place in chloroplasts in the leaves of plants.
- The word equation for photosynthesis is:
- The balanced equation is:
- Chlorophyll traps energy from light. In photosynthesis, this energy is converted to chemical energy in carbohydrates.
- Photosynthesis takes place in the cells of the mesophyll layer, especially the palisade mesophyll. Leaves are thin and have a large surface area, to speed up the supply of carbon dioxide to the palisade cells and to maximise the amount of sunlight that hits the leaf and can be absorbed by chlorophyll. Stomata and air spaces allow carbon dioxide to diffuse quickly from the air to the chloroplasts. Xylem vessels bring water, and phloem tubes take away the products of photosynthesis.
- Some of the glucose that is made is used in respiration, to provide energy to the plant cells. Some is stored as starch. Some is used to make cellulose for cell walls. Some is transported around the plant in the form of sucrose, in the phloem tubes. Some is combined with nitrate or ammonium ions to make proteins. Some is used to make other substances such as fats. With the addition of magnesium ions, chlorophyll can be made.
- When testing a leaf for starch, it must first be boiled to break down cell membranes and allow iodine solution to make contact with any starch inside the cells. Hot alcohol will remove chlorophyll from the leaf, making it easier to see any colour changes.
- Plants need light and carbon dioxide for photosynthesis.
- If either light or carbon dioxide are in short supply, they limit the rate of photosynthesis and are said to be limiting factors. The rate of photosynthesis is also affected by temperature.