Photosynthesis Flashcards
What is the word equation for photosynthesis?
Carbon Dioxide + Water + Light = Glucose + Oxygen
What is the chemical question for photosynthesis?
6CO2+6H2O+Light—Chlorophyll—>C6H12O6+6O2
What is the role of photosynthesis?
- plants use it to make food
- animals get their food from plants
- photosynthesis produces oxygen
- photosynthesis has responsibility for forming fossil fuels
What are the main events in photosynthesis?
- Light is absorbed
- Water is split
- The products if splitting water
- Light energises electrons
- Glucose is formed
What happens when light is absorbed?
Sunlight that strikes a plant is trapped by the chlorophyll
What happens when the water is split?
- the trapped sunlight energy is used in the chloroplast to split water molecules
- 2H2O—>(4H+)+(4e-)+(O2)
What happens to the products of splitting water?
- the electrons are passed to the chlorophyll
- the protons are released to a storage pool of protons in the chloroplast
- the oxygen may pass out through the leaf into the atmosphere or be used within leaf cells during respiration
What happens when light energises electrons?
Sunlight energy trapped by the chlorophyll is passes on to the electrons in chlorophyll to form high-energy electrons
What happens to form glucose?
High-energy electrons from the chlorophyll, along with protons from the storage pool, are combined with carbon dioxide to form a carbohydrates (glucose)
What is a source of light?
Sunlight
What is a source if carbon dioxide?
- External: Enters the leaf from atmosphere
- Internal: respiration
What is a source of water?
Absorbed in soil through roots of plant
How can we increase the rate of photosynthesis?
- Artificial light
- Artificial sources if carbon dioxide (e.g burning gas)
- Regulate temperature (enzymes)
What are features of the light stage of photosynthesis?
- Dependent on light
- Energy provided by light allows reactions to proceed
- Reactions occur so quickly that no enzymes are required
What are features of the dark state of photosynthesis?
- Independent of light
- Energy for the reactions is provided by ATP
- Enzymes control the reactions
Where do the events of the light stage occur?
In the chloroplast
What events occur in the light stage of photosynthesis?
- Light absorption
- Light energy transferred to electrons
- The flow of electrons along pathways 1 and 2
What happens in the light absorption stage of photosynthesis?
- Chloroplasts contain a range of pigments including chlorophyll.
- Each of the chloroplasts pigments absorbs a different colour of light (the spectrum).
- In general plants absorb all the colours of white light except green as it is normally reflected.
What happens when light energy is transferred to electrons during the light stage of photosynthesis?
- The different pigments in a cluster transfer the absorbed energy from one another until it reaches the reaction centre chlorophyll associated with the electron acceptor.
- Here energy is transferred to electrons causing them to become energised or high-energy electrons.
- The energised electrons are passed from the chlorophyll to the electron acceptor.
- The energised electrons then flow from the electron acceptor along one of two different pathways.
What is created in electron pathway 1?
ADP+P+Energy = ATP+Water
What is another name for electron pathway one?
Cyclical Electron Flow
What happens during electron pathway 1 (cyclical electron flow)?
- The high-energy electrons pass from the reaction centre chlorophyll to an electron acceptor.
- They then pass from the electron acceptor to a series of other electron acceptors and back again to the chlorophyll molecule.
- When electrons return in this way they lose energy.
- The energy they release is trapped by ADP and a phosphate, and used to form ATP and water.
What is created in electron pathway 2?
NADPH
What is another name for electron pathway 2?
Non-cyclical electron flow
