Topic 2 Review
2.9 Photosynthesis
U1: Photosynthesis is the product of carbon compounds in cells using light energy.
We already know one carbon compound and that is glucose. (C6H12O6)
Photosynthesis is an example of energy conversion, as light energy is converted into chemical energy in carbon compounds. Carbon compounds that are produced include; carbohydrates and lipids
The word equation for photosynthesis: Carbon dioxide + Water -- Glucose + Oxygen
Photosynthesis takes place in the chloroplasts.
Thylakoid: Is where the first stage occurs (light dependent)
Stroma: Where the second stage happens. (Light independent)
These are the single discs and a stack of these are called the Granum.
The Stroma is the aqueous space that surrounds the Granum, and Thylakoids. But is inside the double membranes.
U2: Visible Light has a range of wavelengths with violet the shortest wavelength and red the longest.
Light is made up of all the wavelengths of the electromagnetic radiation that our eyes can detect.
The range of wavelengths of visible light is 400 to 700 nm
Shorter wavelengths such as radio waves have lower energy.
U3: Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colours.
The first stage in photosynthesis is the absorption of light. (A white or transparent substance does not absorb visible light)
Pigments are substances that do not absorb light and therefore appear coloured to us. Pigments that absorb all of the colours appear black because they emit no light.
The main photosynthetic pigment is chlorophyll
Absorption Spectrum
There are various forms of chlorophyll but they all appear green to us.
This is because they absorb red and blue light but intermediate green light less effectively. Therefore wavelengths of green light are reflected, and not absorbed.
Is a graph showing the percentage of light absorbed by a pigment or group of pigments.
U4: Oxygen is produced in photosynthesis from photolysis of water.
The first stage of photosynthesis is the splitting of water.
One of the essential steps in photosynthesis is photolysis. This is the splitting of water. The H+ are used in the first stage of photosynthesis. The e- are used in the second stage of photosynthesis. Oxygen is a valuable waste product.
U5: Energy is needed to produce carbohydrates and other compounds from carbon dioxide.
Energy is needed for photosynthesis
This energy is obtained by absorbing light. The light energy absorbed is converted to chemical energy in carbohydrates.
Chemical reactions that involve putting energy in are described as endothermic.
2.8 Cell Respiration
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U1: Cell respiration is the controlled release of energy from organic compounds to produce ATP
ATP is converted to ADP + P during hydrolysis reactions and energy is released.
ATP is synthesised from ADP + P during condensation reactions where energy is supplied.
Energy is not made it is simple transferred.
U2: ATP from cell respiration is immediately available as a source of energy in the cell.
Cells require energy for:
Active Transport
Synthesis of molecules
Cell division
Muscle contractions
Explain why ATP is a better immediate energy source than glucose:
ATP is the immediate source of energy in a cell.
The hydrolysis of ATP to ADP is a single reaction that releases immediate energy.
The break down of glucose is a long series of reactions and therefore the energy release takes linger.
U3: Anaerobic cell respiration gives a small yield of ATP from glucose.
Anaerobic respiration is much less efficient than aerobic respiration
This is because less energy is released.
It is important to know that when oxygen supplies run out in respiring cells, oxygen runs out.
When large amounts of energy is needed for strenuous, explosive exercise, the aerobic pathway cannot 'step up' its production of ATP quickly enough.
In environments that are deficient in oxygen.
The products of anaerobic respiration are not the same in all organisms.
Glucose
Animals
Plants and Yeast
Lactic acid + 2ATP
Alcohol
Muscle cramps and the build up of lactic acid in the muscles.
Ethanol and Carbondioxide + 2ATP
U4: Aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose.
Most of aerobic reactions occur in the mitochondria. Anaerobic respiration is only in the chloroplasts.
Aerobic respiration yields approx. 38 ATP while anaerobic respiration yields only 2ATP.
Aerobic
C6H12O6 + 6O2 -- 6O2 + 6H2O + 38 ATP
Glucose + Oxygen -- Carbon dioxide + Water + 38ATP
Anaerobic (In humans)
C6H12O6 -- 2 Lactic Acids + 2ATP