Photosynthesis notes

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Photosynthesis:

Green plants make food using sunlight:

Very few plants can trap or catch ready-made food

Instead, they must make their own food

They make their food by combining CO2 levels from the air with water from the soil

They need energy to do this and this energy comes from sunlight

The energy is trapped by a green pigment, called chlorophyll, in the leaves of a plant

The method plants used to feed itself is called photosynthesis.

Photsynsythesis is summarised by one general word equation:

(The glucose is transfered into starch)

The process of photosynthesis provides food for the plant. The food can be used to provide energy which can be stored as starch and used for the growth of the plant.

The food that the plant keeps inside it's body is called biomass. This biomass eventually provides food for many animals.

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(photosynthesis also gives out the gas oxygen)

The process of resperation and photsynthesis must be balanced against one another to keep a constant composition of the atmosphere

Factors affecting photosynthesis:

Any food the plant has left over, after it has used some for energy, may be used for growing.

The plant will be able to grow, as long as it will respire.

The four factors affecting photosynthesis are

Light intensity: Light provides the energy needed to join CO2 and H2O together

The level of CO2: The air must provide CO2. There is very little CO2 in a normal atmosphere, so this gas must be quickly replaced by respiration

Temperature: Thermal energy is needed so that all the chemical reactions in the plants can happen quickly enough. The best temperature for photosynthesis is around 25°C. Temperatures above 40°C shall damage the cells, and photosynthesis will come to a halt.

H20: H20 is needed to combine with CO2 and to carry food around the plants body.

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Checking how factors effect photosynthesis:

Scientist may be interested in how different factors effect photosynthesis.

If they can understand how plants grow, they may be able to to be interested how a plant can go more quickly. This may be able to provide more food for humans and animals.

When a scientist has a idea(theory) he wants to test, he/she need to carry out an experiment.

There are different ways in which photosynthesis by the plant can be measured.

One of them is to test whenever or not it has starch.

If the scientist wanted to check how variations in temp. light, or CO2 effected the growth of a plant, it would be necessary to use many plants.

The different test could be carried out on different plants. It would be important though, to carry out the test at the same time on plants that were the same size at the start of the experiment

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Oxygen and photosynthesis:

When glucose is produced from CO2 and H20, the gas Oxygen is produced, and is given out as a waste product

We can't see oxygen in the atmosphere but not in water.

This is for 2 reasons

We can prove that the gas given off is oxygen

We can therefore use this to show how fast photosynthesis is happening.

The experiments shown below explains 2 of the points

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Getting it right: Growing plants in Greenhouses

It is possible to control the process of photosynthesis by growing plants in greenhouses

The owner of a greenhouse can control:

The amount of light

The temperature

The amount of CO2

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Cells:

Cells