Contents Sub-Title Page Introduction to Photosynthesis - History of Photosynthesis - What is Photosynthesis? 1-2 Structure of A Leaf - A Two-dimensional Cross Section of The Leaf - A Three-dimensional Cross Section of A leaf 3-4 Adaptation of Leaves for Optimal Photosynthesis - Features of A Leaf - Adaptation of Plants from Different Habitats for Photosynthesis 5-6 Mechanism of Photosynthesis - Light Reaction - The Dark Reaction 7-8 Factors That Affect Photosynthesis - Light Intensity - Concentration of Carbon Dioxide - Temperature - Water 9-11 Experiment to Determine The Effect of Light Intensity on The Rate of Photosynthesis. 12-13 Examples of Past Year SPM Questions about Photosynthesis 1
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Contents
Sub-Title Page
Introduction to Photosynthesis
- History of Photosynthesis
- What is Photosynthesis?
1-2
Structure of A Leaf
- A Two-dimensional Cross Section of The Leaf
- A Three-dimensional Cross Section of A leaf
3-4
Adaptation of Leaves for Optimal Photosynthesis
- Features of A Leaf
- Adaptation of Plants from Different Habitats for
Photosynthesis
5-6
Mechanism of Photosynthesis
- Light Reaction
- The Dark Reaction
7-8
Factors That Affect Photosynthesis
- Light Intensity
- Concentration of Carbon Dioxide
- Temperature
- Water
9-11
Experiment to Determine The Effect of Light Intensity on The
Rate of Photosynthesis.12-13
Examples of Past Year SPM Questions about Photosynthesis
14
References
15-19
1
Introduction to Photosynthesis
Discovery of Photosynthesis
In 1649, Jan Baptista Van Helmont did the first biological experiment in which the ingredients were
measured accurately and all changes noted precisely. Van Helmont began by transplanting the shoot of a
young willow tree into a large bucket of soil. He weighed the willow and then the soil separately. If the willow
tree formed its tissues by absorbing the nutrients from the soil then the soil should lose weight as the plant
grew. Van Helmont carefully kept the soil covered so that absolutely nothing could interfere with his
experiment.
Naturally, Van Helmont had to water the willow tree or else it wouldn’t grow. He concluded that the
water he was adding helped carry the nutrients to the tree and then simply evaporated into the air. For five
years, Van Helmont waited patiently, watching the tree grow until finally he removed it from the pot, shook
off all the soil and weighed the plant. In five years the willow tree had added 164 pounds to its original
weight. Then, for the second part of the experiment, Van Helmont dried and weighed the soil. It had only lost
2 ounces. From this, Van Helmont concluded that the willow tree drew its nutrients, not from the soil but from
water. Accidentally, he made a mistake and said that the material that made up the bark, wood, roots and
leaves came from the water he had added over the five years!
The next big important step in the understanding of photosynthesis came in the early 1770’s. Joseph
Preistly, the British man who received the recognition of discovering oxygen, found that a piece from a mint
plants could restore the air in a container with a burning candle, so that it <the candle> could be used again.
Accidentally, one day, Joseph Preistly placed the candle in a dark corner of his laboratory. Since the mint
plant could not photosynthesize, the candle’s flame extinguished. Unfortunately, Mr. Preistly never did really
understand that great role which light played in his experiment.
Several years later, in 1979, a Dutch physician, Jan Ingenhousz, wanted to find out whether flowers
really did help cure illnesses. After many different tests, he finally concluded that only the green parts of
plants cleaned the air and only when placed in strong light. Flowers and other non-green parts of plants
used up oxygen just like animals. Ingenhousz suggested that this process of photosynthesis causes carbon
dioxide to split into carbon and oxygen. Then the oxygen is released as a gas.
Later, other scientists discovered that sugars contain carbon, hydrogen and oxygen atoms in a ratio
of one carbon molecule per molecule of water (CH2O). This is where the word carbohydrate comes
from, carbo- for “carbon” and hydrate for “water”. Carbohydrates are a family of chemical compounds
including sugars and starches, which are made up of large numbers of sugar units linked together. In 1804,
the Swiss scientists, Nicholas Theodore de Saussure repeated Van Helmont’s experiment but carefully
measured the amounts of carbon dioxide and water that were given to the plant. He showed that the carbon
in the plants came from carbon dioxide and the hydrogen from water. Then, forty years later, a German
scientist, Robert Mayer, showed that the energy of sunlight is captured in photosynthesis.
2
What is Photosynthesis?
Photosynthesis originates from the Greek word photo, meaning "light," and synthesis, from the
Greek work syntithenai, which means "to combine". Photosynthesis is basically the conversion of the
energy from the sun in to a usable chemical energy. Photosynthesis occurs in plants, algae and many
species of Bacteria. Photosynthetic organisms are called photoautotrophs, since it allows them to create
their own food. The photosynthesis process uses carbon dioxide and water, releasing oxygen as a waste
product.
It is also defined as a biochemical process through which light energy is absorbed by chlorophyll
and is used to fuel the synthesis of sugar molecules (i.e.; glucose). Photosynthesis is vital for life on Earth.
As well as maintaining the normal level of oxygen in the atmosphere, nearly all life either depends on it
directly as a source of energy, or indirectly as the ultimate source of the energy in their food. Photosynthesis
can be represented using a chemical equation. The overall balanced equation is: