Photosynthesis Investigation

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Photosynthesis Investigation

Introduction

Flowering plants, like all living organisms, need a supply of food. They need it as a source of energy in respiration and they need it as raw material for growth and repair. Animals and most micro- organisms get their food in an organic form: they eat products from other organisms (such as fruit and eggs) or, nowadays, the organic substances made in laboratories and factories. Animals and the microorganisms that do this are called consumers.

Due to the flowering plants can make their own organic food from simple inorganic substances and an outside source of energy, they are called producers. Once the producers have made their food they use it in the same way as the consumers do as a source of energy and as raw material for growth and repair

Photosynthesis

The simple inorganic substances from which flowering plants make their food are carbon dioxide (CO2) and water (H2O). These contain no energy that a flowering plant can use an outside source of energy is needed to combine them into a compound that the plant can use as food. The source of energy is sunlight; the food compound that is made up the simple sugar, glucose (C6H12O6), and the waste product that is left photosynthesis, is shown in an equation as:

Carbon dioxide + Water Glucose + Oxygen

6CO2 + 6H2O C6H12O6 + 6O2

Light energy is trapped by photosynthesis and converted into chemical energy in compound glucose.

Carbon Dioxide

Carbon dioxide is a gas which is present in air only in small amounts about 0.04% of air is carbon dioxide. But carbon dioxide is continually added to air by respiration of all living organisms and by burning of fuel such as wood, coal, gas, oil and petrol all give off carbon dioxide when they burn. There is no danger that carbon dioxide will run out in fact it is slowly increasing in the air because so much burning takes place. Carbon dioxide dissolves in water, which can release carbon dioxide: flowering living plants living in water therefore also have a supply of carbon dioxide.

Water

Flowering plants that live on land get the water for photosynthesis through their roots from water in the soil. The water travels through the plants in veins called vascular bundles. Plants that live in water get it from their surroundings.

Energy

Light rays are a form of energy they are wave movements traveling at great speed. Those of a certain wavelength, which are seen by our eyes, are light rays. Flowering plants have a green pigment called chlorophyll which can absorb some of these light rays and use their energy to build up the simple sugar, glucose , from carbon dioxide and water. The light energy is trapped as chemical energy in the glucose molecule. Plants can use any source of light rays, but the source that does not run out is sunlight. Artificial light is used in glasshouses when extra light is needed. In water, only the top few meters get sufficient light for plants to use in photosynthesis. Plants that are able to detect a source of light grow towards it, for example, cress.

The growth of plants in relation to the direction of light is called phototropism. Because the stem grows it is said to be positively phototropic. Phototropism is an example of a plant responding, in the direction of its growth, to the stimulus of light. Growth responses in plant is positive phototropism: it puts its leaves into the light for photosynthesis.

The products of photosynthesis

If you look at the equation for photosynthesis , there are two products called glucose and oxygen. They cannot accumulate in the mesophyll cells indefinitely.

A the glucose forms, it is usually stored in the chloroplasts as starch. If you test a leaf for glucose during photosynthesis, you are likely to find very little because it is changed to starch so quickly after it is formed. If you test a leaf for starch during photosynthesis, you find quite a lot. But at night, when photosynthesis stops because there is no light, the starch is changed back into sugar and removed from the leaf through the veins either to a growing part of the plant or to a more permanent storage place.

Throughout photosynthesis waste oxygen is given off as a gas, because it is in a high concentration in the cells, it diffuses to the outside of the leaf, where it is in a lower concentration, via the air spaces and open stomata. The formation of oxygen during photosynthesis is of great importance to all living organisms. All living organisms, including plants, carry out respiration, and most of that respiration is aerobic (using oxygen). Photosynthesis is the only way in which oxygen used in respiration is replaced in the air.

The site of photosynthesis

For photosynthesis to occur, carbon dioxide, water and light energy must come together where there is chlorophyll in the flowering plant. Leaves, which are usually broad and flat, are the parts of the plant most suitable for photosynthesis.

* Contain chlorophyll

* Have a broad flat area which is supported by veins and is exposed to the rays of the sun.

* Contain veins (vascular bundles) which supply water
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* Are thin, allowing quick diffusion of carbon dioxide to all parts inside the leaf.

The site of photosynthesis is in the cells inside the leaf. The diagram below show a view of the sort of cell that caries out photosynthesis in the leaf. The living parts of the cell, the cytoplasm and nucleus, are surrounded by a non-living cell wall of cellulose: the cell wall keeps the cell in shape. The green pigment chlorophyll is held in small disc-like shapes, made from specialized parts of the cytoplasm, called chloroplasts. The central part of the cell ...

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