Plant Nutrition

What you need to know

Reflections and Exam tips

Plant Nutrition

Green plants do not eat, so they have to make their own food, through the process of Photosynthesis.

During photosynthesis, plants join Carbon dioxide from the air with Water from the soil to make Glucose and Oxygen.

The energy to drive this process comes from light which is absorbed by the green pigment Chlorophyll.

This can be shown using an equation:

Carbon Dioxide + Water —› Glucose + Oxygen

Plant leaves are the main photosynthetic organ and they are perfectly adapted for this.

Leaf adaptaions for photosynthesis

The diagram below shows the different layers of cells (tissues) in a leaf and their functions in photosynthesis.

T/S leaf goes here

Fate of the end products of photosynthesis

Glucose made in photosynthesis can not be stored as it is because its soluble. It is converted into a number of products:

1. Starch- Glucose is changed into starch which is stored in the leaf, seeds and at times in the roots.

You can test a leaf with Iodine solution to find out if contains starch

• Starch test
• Is light needed for photosynthesis?
• Is Carbon Dioxide needed for photosynthesis?
• Variegated leaf.

2. Proteins

Some of the glucose is changed into proteins, which are either stored or are used as enzymes. They can bee stored in seeds, for example beans and peas are good sources of plant proteins.

3. Oils

Some glucose is used to make oils which are stored in seeds, for example sunflower and oilseed rape seeds, which are used to make cooking oil.

4. Cellulose

Plants use some of the glucose to make cellulose, fibrous carbohydrate that is used for building up cell walls.

This is the fibre that we need in our diet.

Inorganic nutrients

Besides the food which plants make for themselves, they also need some chemical elements from the ground. These are major ones are N, P, K, and Mg:

Nitrogen- for growth i.e. used to make proteins, which are enzymes that speed up growth reactions

Phosphorous- For good root development

Potassium- For flowering and fruiting

Magnesium- To make Chlorophyll