How does light affect the rate of Photosynthesis.

BIOLOGY October 2003

HOW DOES LIGHT AFFECT THE RATE OF PHOTOSYNTHESIS

GURDEEP SIAN

INTRODUCTION

Photosynthesis is the process that produces food in plants. The ‘food’ it produces is glucose. In order for photosynthesis take place you need a green plant sunlight and water. The carbon dioxide enters the leaf through the leaves, and the water goes through the roots of the plant. The water and carbon dioxide is mixed in the chloroplast, which is where the light is trapped. The mixture of carbon dioxide and water make the substance glucose which is sugar. The mixture of the two also gives off oxygen. Green plants use the light energy from the sun to combine carbon dioxide and water to make food. Light energy is converted into chemical energy and is stored in the food. The light used in photosynthesis is absorbed by a green pigment called chlorophyll. The three features that leaves have to make photosynthesis an efficient process are thinness, flatness and a large surface area to catch lots of sunlight. The leaf also has palisade cells are near the top of the leaf and are also packed wit chloroplasts. The guard cells on the leaf control the movement of gases into and out of the leaf. The four things needed for photosynthesis are:

Light – This comes from the sun

Chlorophyll – the green substance which is found in chloroplasts, Carbon dioxide – enters the leaf from the surrounding air,

Water – comes from the soil, up the stem and into the leaf.

The formula for photosynthesis is:

The rate of photosynthesis is affected by several factors. They are the amount of available carbon dioxide and water. Only 0.03% of the surrounding air around is CO2. The third and final factor is the temperature. Chlorophyll works best when it’s warm but not too hot, as they then denature. Enzymes denature when the temperature reaches approximately 40oC. There were quite a few people involved in the discovery of making photosynthesis known. One of the main people involved in the discovery was Melvin Calvin and also one of his assistants A. A. Benson. They were the first to realise that Carbon 14 couldn’t solve the mystery of photosynthesis. Calvin and Benson began doing experiments. They created a cycle to explain photosynthesis to others. The process was named the Calvin cycle. In 1961 Melvin Calvin won the Nobel Prize for chemistry. Other people were involved in the discovery of photosynthesis. A person who went by the name of Philip Hauge Abelsone made replicas of some of the proteins found in oxygen. An English Biochemist John B. S. Haldane made an excellent point and when he said “that if life was responsible for the oxygen in the atmosphere, photosynthesis ought to have started when there was no oxygen in it and carbon dioxide was present instead.’’ R. Emerson and W. Arnold illuminated plant cells with extremely short flashes of light. An English Botanist called Stephen Hales had the idea that if plants can give off gases then this means that they could also take in gases. Rudolf Fittig discovered that there were six carbon atoms, twelve Hydrogen atoms, and six Oxygen atoms in glucose. Other people who helped make photosynthesis known are Joseph Bienaime Caventou and Pierre Joseph Pelletier. These people secluded the green substance and named it chlorophyll after the Greek name for ‘green leaf’. A German biochemist named C. Benda used a dye system and named the cytoplasm and mitochondria. Daniel Arnon was able carry through the complete and photosynthetic reaction working with disrupted spinach cells. For this project I will be looking at how light affects the rate of photosynthesis. Does light increase the rate of photosynthesis? Or does light decrease the rate of photosynthesis? I set up some apparatus to find out the answer to these questions. Here’s what I came up with.