Nutrition in Plants

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Photosynthesis: the fundamental process by which plants manufacture carbohydrates using energy from light

All living things require a source of energy from the environment to stay alive

2 Types of Nutrition

1. Autotrophic: simple compounds are absorbed and built up into complex substance which may be oxidized (broken down) to release energy

2. Heterotrophic: Complex food material is broken down to simple substances during digestion which may be absorbed or oxidized to release energy.

Plants show autotrophic nutrition and the central process in plant nutrition is PHOTOSYNTHESIS

Raw Materials: carbon dioxide and water

Products: glucose and oxygen

Carbon dioxide is obtained through stomate, Water enters through root hair cells

Oxygen diffuses out of stomata into atmosphere

Energy Source: Sunlight absorbed by chlorophyll (contained in chloroplasts)

Carbon Dioxide + Water + Light --> Simple Sugar + Oxygen

first product of photosynthesis is a sugar

- sugar molecules are polymerized (joined together) to produce starch (which can be stored)

Stomata:

- opening in the surface of plants which allow gases to pass in or out

- guard cells (on either side of the stomata) can change shape to widen or reduce the opening and control gas exchange

Stomata are most common on the underside of leaves

-

they let:

- water vapour our of the plant

- oxygen out of the plant

- carbon dioxide in the plant

6C02 + 6H20 + light --> C6H1206 + 602

Chlorophyll traps light energy and converts it into chemical energy for the formation of carbohydrates and their subsequent storage

Main product of photosynthesis (glucose) is a valuable food

- has other uses in plants

CAN BE POLYMERIZED IN TWO DIFFERENT WAYS

1. glucose --> starch

- used to store food reserves

- insoluble so can be stored easily

- polymerization is easily reversed (when food is needed)

2. glucose --> cellulose

- polymerization is not easily reversed

- cellulose is a hard substance which is formed in plant cell walls

- provides strength and support for the woody parts of plants

Cells in the green parts of plants contain small structures called chloroplasts

Photosynthesis takes place in the chloroplasts (chlorophyll)

- Chloroplasts contain a green substance: chlorophyll

- Chlorophyll traps light energy

This energy is used in the reactions which produce glucose from carbon dioxide and water which can be converted into starch (polymerization) and stored.

CHLOROPHYLL DOES NOT ABSORB ALL COLORS OF LIGHT EQUALLY WELL

Red or blue light is best for promoting photosynthesis

- Leaves look green because chlorophyll absorbs red and blue light but reflects most of the green

1. Dip a leaf into boiling water

2. Put the leaf in a boiling tube

3. Add ethanol

4. Plae it in the water bath until the ethanol is green

5. Pour out the ethanol

6. Rinse in cold water

7. Completely cover the leaf with iodine solution

8. Blue/black colour shows that leaf contains starch

L

Leaf is placed in boiling water to kill it

Ethanol gets rid of the chlorophyll in the leaf

Ethanol turned green because of the chlorophyll

Iodine showed that leaf had starch

Nitrate Ions:

- combines with glucose to produce amino acids (which makes proteins)

- if nitrates are not present in the soil the growth of the plant is stunted and the stem is very weak + leaves die

(AFFECTS GROWTH)

Magnesium:

- forms part of the chlorophyll molecule

- if magnesium is not present then the plant has yellow leaves and cannot photosynthesis effectively = poor growth

Phosphate:

- component of DNA and cell membranes

- deficiency symptoms include poor root growth and discolored leaves

Potassium:

- must be present for photosynthesis and respiration enzymes to work

- lack of potassium = poor flower and fruit growth + discolored leaves

Photosynthesis Rates

Photosynthesis increases with:

- increased temperature

- increased CO2 concentration

- lighter colour

- increased light intensity

Photosynthesis

Gas Exchange in Plant Leaves

Products and Chloroplasts

Testing Leaves for Starch

Minerals required by Plants