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What is photosynthesis?
- A chemical reaction that converts carbon dioxide into carbohydrates
- Takes place within chloroplasts
What energy forms does photosynthesis require?
- Light energy from the sun
- Electrons from water
What two stages can photosynthesis be divided into?
- Light dependant
- Light independent
What pigment absorbs energy from the sun?
What happens once light energy has been absorbed?
An electron is boosted to a higher energy level
What happens to the electron once it has been boosted to a higher energy level?
It is passed down a series of electron carriers and the energy released is used to produce ATP
Write a word equation for the production of ATP from ADP and Pi
Adenosine Diphosphate + Inorganic Phosphate =Adenosine Triphosphate
What happens at the end of the electron transport chain?
A molecule of NADP accepts the electron, reducing it to NADP (NADPH)
How is the electron lost from the chlorophyll replaced?
- A water molecule is split, releasing electrons
- This is called photolysis
Write a word equation for photolysis
2H2O = 4H+ + 4e- + O2
What happens to the products of photosynthesis?
- The oxygen is released into the atmosphere as a waste product
- The protons are used to reduce NADP
What is used as an energy source for light independent photosynthesis?
- The energy from ATP
- Electrons from reduced NADP
What does Carbon dioxide react with at the first stage of the calvin cycle?
Ribulose Biphosphate- a 5 carbon molecule
What is formed from the first stage of the calvin cycle?
Two 3 carbon molecules called glycerate-3-phosphate (GP)
What does stage 2 of the calvin cycle involve?
ATP and reduced NADP are used to reduce the GP into Triose phosphate (TP)
What occurs at the end of the calvin cycle?
- Some TP is converted into carbohydrates
- Some TP is converted back into RUBP in order to continue the cycle
What are thylakoids?
- Structures composed of membranes containing many chlorophyll molecules to absorb light.
- The light dependant stage occurs here
What is a Granum?
- A stack of thylakoids
- Increases efficiency of light absorption
What is a stroma?
Fluid within the chloroplast containing enzymes for light independent reactions
What is the purpose of starch grains within the chloroplast?
Temporarily storing the products of photosynthesis in the stroma
What does the chloroplast possess in terms of DNA?
A circular loop of DNA with ribosomes capable of synthesising its own proteins
How can rate of photosynthesis be measured?
The volume of oxygen produced divided by time
What conditions does photosynthesis require?
- Optimal temperatures
- High levels of light
- High levels of carbon dioxide
What limits photosynthesis?
The factor at the least favourable value
How may a shortage of carbon dioxide affect photosynthesis?
- Conversion of RUBP to GP is limited
- Buildup of RUBP and fewer carbohydrates produced
- Increasing light intensity or temperature will have no effect
How may a less than optimal temperature affect photosynthesis?
- Kinetic energy of enzymes in the stroma will limit all of the reactions in the calvin cycle
- Increasing carbon dioxide concentrations or light intensity will have no effect
How may a low light intensity affect photosynthesis?
The amount of ATP and NADP produced by the light dependant reaction will limit the reduction of GP to TP
What conditions must be met in order for a crop plant to grow?
- The rate of photosynthesis must be greater than that of respiration
- Otherwise all of the glucose produced would be used in respiration
Give three ways in which farmers create conditions suitable for crop growth within greenhouses
- Enrich the air with carbon dioxide to levels on 0.1%
- Use heaters to maintain temperatures of 25oc
- Use artificial lights to increase light intensity
What is the success of greenhouse measures dependant on?
- The limiting factors
- Whether the costs of providing optimal conditions is compensated with additional profits gained from the increased growth
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