3.8.1 State that photosynthesis involves the conversion of light energy into chemical energy.(1) Location: chloroplast or prokaryotic equivalent. Reaction: Traps light energy (photons) and converts it into chemical energy. Organisms: Prokaryotic and Eukaryotic

Substrate: Inorganic CO 2 and H 2 O Products: Organic compounds (sugars) and O 2 Environments: Aquatic environments with light, terrestrial environments with light. There are even extremophiles that can photosynthesis at some extreme latitudes and altitudes. At extreme high temperatures we see photosynthesis in geothermal active regions

What is photosynthesis? All life on Earth depends on photosynthesis. The process is described by the following word and symbol equations: These equations are summaries of a complex two-step process that takes place in the chloroplasts of green plants. The end products are not just glucose, but complex organic molecules such as carbohydrates, amino acids, lipids and nucleic acids. carbon dioxide + wateroxygen + glucose light energy 6CO 2 + 6H 2 O6O 2 + C 6 H 12 O 6 light energy

Why do plants photosynthesize? Photosynthesis is an essential biological process. This is because it produces: energy for processes in the organism complex organic molecules needed for growth oxygen, which is then used for respiration. The oxygen produced is released into the atmosphere and is available for other organisms. If the plant is eaten, the organic molecules are used to provide energy to organisms higher up the food chain. There are not just advantages for the plant itself:

3.8.2 State that light from the Sun is composed of a range of wavelengths (colours).(1) Light form the sun is composed of a range of wavelengths (colours). The visible spectrum to the left illustrates the wavelengths and associated colour of light. Combined together these wavelengths give the 'white' light we associate with full sunlight. The shortest wavelengths are the 'blues' which have more energy. The longer wavelengths are the 'reds' which have less energy.

3.8.3 State that chlorophyll is the main photosynthetic pigment.(1) Chlorophyll is the main photosynthetic pigment. This is where light energy is trapped and turned into chemical energy. The head of the molecule is polar and composed of a ring structure. At the heart of this ring structure is the inorganic ion magnesium. This is the light trapping region of the chlorophyll molecule.

The tail of the molecule is non polar and embeds itself in membranes in the chloroplast. chloroplast There are other pigments, reds, yellows and browns but these are only usually seen in the experimental chromatography or if you have been lucky enough to witness the autumnal colours of deciduous trees in a temperate climate

3.8.4 Outline the differences in absorption of red, blue and green light by chlorophyll.(2) The details of this image are not important and need not be learnt for the SL course. The 'peaks' show which wavelength of light are being absorbed. Look at the x-axis for colours of light absorbed at the 'peaks'. The main colour of light absorbed by chlorophyll is red and blue. The main colour reflected (not absorbed) is green. Hence why so many plants are seen as green, the light is reflected from the chlorophyll to your eye.

In plants there are two types of pigments: chlorophylls and carotenoids. They are coloured because they absorb particular wavelengths of light and reflect others. A photosynthetic pigment is a coloured biological compound that is present in chloroplasts and photosynthetic bacteria, and which captures light energy for photosynthesis. Chlorophyll is the pigment that gives plants their green colour by reflecting green light. Carotenoids reflect red, orange or yellow light. Photosynthetic pigments

3.8.5 State that light energy is used to produce ATP, and to split water molecules (photolysis) to form oxygen and hydrogen.(1)

(a) Light is absorbed by chlorophyll molecules (green) on membranes inside the chloroplast. This is the light trapping stage in which photons of light are absorbed by the chlorophyll and turned into chemical energy (electrons).

(b) The chemical energy (electrons) is trapped in making ATP. Photolysis (c):Water used in photosynthesis is split which provides: hydrogen for the formation of organic molecules, e.g. (C 6 H 12 O 6 ) oxygen gas is given off.

3.8.6 State that ATP and hydrogen (derived from the photolysis of water) are used to fix carbon dioxide to make organic molecules.(1)

State means to give a specific name, value or other brief answer without explanation or calculation. H + from the splitting of water are combined with carbon dioxide to form organic compounds like sugar. Bonds are formed between the carbon, hydrogen and oxygen using the energy from ATP (which came form the sun).

C, H, O are enough to form lipids and carbohydrates. With a Nitrogen source amino acids and therefore proteins can be made. Plants have this remarkable ability to manufactory all their own organic molecules and by definition all the basic organic molecules required by all life forms.

To summarise: Photosynthesis has 2 stages Light dependent stage Light independent stage.

Light dependent stage Photolysis, light energy is used to split water molecules into H + plus O 2 + electrons.

Light independent stage H + and ATP, produced in the light dependent stage, are used to fix CO 2 TO MAKE ORGANIC MOLECULES.

ASSESSMENT STATEMENT COMPLETE THE ASSESSMENT STATEMENT AND MAKE NOTES.