3 • Photosynthesis Flashcards
0
Q
Equation of photosynthesis
A
6CO2 + 6H2O –> C2H12O6 + 6O2
1
Q
Structure of the leaf
A
- Large surface area: absorb as much sunlight as possible
- Arrangement to avoid overlapping and shadowing
- Thin: short diffusion pathway
- Transparent cuticle and epidermis: let light through
- Long, narrow upper mesophyll packed with cloro plasta máximo se sunlight absorption
- Numerous stomata for gas exchange
- Air spaces in mesophyll to aloe gas diffusion
- Xylem (water) and phloem (sugars)
2
Q
Where does the light-dependent reaction takes place?
A
In the thylakoids: they make up graba un chloroplasts
3
Q
Where does the light-independiente reaction takes place?
A
It takes place in the stroma: the fluid-filled matrix in a chloroplast
4
Q
What is oxidation and reduction?
A
- When oxygen has been added it is called oxydation
* When oxygen is lost it is called reduction
5
Q
Making of ATP in the LDR
A
- Light hits a chlorophyll molecule
- Electrons get excited
- They move to a higher energy level
- Electrons them pass along electron carriers
- Oxidation reduction reactions
- Electrons lose energy at each stage
- This energy is usted to combine Adp and Pi to form ATP
6
Q
Photolysis of water
A
- The electrons lost need to be replaced
- Water molecules split using light
- 4 Protons (Hydrogen ions)
- 4 Electrons
- Oxygen
- H+ ions are taken up by electron carrier NADP, which becomes reduced
- NADP then enters the LIR
- Oxygen by-product is used in respiration or diffuses out of the leaf as waste product of photosynthesis
7
Q
Adaptations of chloroplasts for the Light-dependent reaction
A
- Membrane: largue surface area for the attachment of chlorophyll, electron carriers and enzymes
- Network of proteins in the grana hold chlorophyll in a precise manner that allows maximum absorption
- Granal membrane have enzymes attached to them, which help manufacture ATP
- Chloroplasts contain DNA and ribosomes so they can quickly manufacture proteins needed for the light depende y reaction
8
Q
What is the Light-independent reaction?
A
- Products of the light-dependent reaction of photosynthesis, ATP and reduced NADP, are used to reduce carbon dioxide
- This stage doesn’t require light directly and, in theory, occurs whether or not light is available
9
Q
Calvin Cycle
A
- CO2 from the ATM diffuses into the leaf through stomata and dissolves in water. Ir then diffusses through the plasma membrane, cytoplasm and chloroplast membranes into the stroma of the chloroplast
- CO2 combines with RuBP (5C) using an enzyme
- 2molecules of GP (3C) are produced
- ATP and reduced NADP are used to reduce GP to TP (3C)
- NADP is reformed and goes back to the light-dependent reaction
- Some TP molecules are converted to useful organic substances (glucose)
- Most TP molecules are used to regenerate RuBP using ATP from LDR
10
Q
Where does the light-independent reaction occurs?
A
Takes place in the stroma
11
Q
Adaptations of the Chloroplasts for the light-independent reactions
A
- Fluid of the stroma contains all the enzymes needed to carry out the LIR
- Stroma fluid surrounds the grana and so the products of the light-dependent reaction in the grana can diffuse into the stroma
- It contains DNA and ribosomes so it can quickly and easily manufacture some of the proteins needed for the LIR
12
Q
Effect of light intensity in the rate of photosynthesis
A
- Rate of photosynthesis is directly proportional to light intensity
- As light intensity increases, volume of O2 produced and CO2 absorbed will increase to a point querer they balance
- At this point there will be no net exchange of gases into or out of the plant
- This is called compensation point
- Further increase in light intensity will cause a proportional increase in the rate of photosynthesis
- Increasing volumen of O2 will be given off and CO2 taken up
- A point will be reached at which further increase in light intensity will have no effect in photosynthesis
- At this point other factor (CO2, temperature, etc) is limiting the reaction
13
Q
Effect of CO2 concentration on the rate of photosynthesis
A
- CO2 in the atm at a concentration of around 0.04%
- Continues to increase as a result of human activities (burning fossil fuels) and clearing of rain forests
- Optimum concentration 0.1%
- CO2 affects enzyme that catalyses the combination of RuBP snd CO2 in the LIR
14
Q
Effect of temperature on the rate of photosynthesis
A
- When other factors are not limiting, the rate of photosynthesis increases proportionally to the temperature
- Between 0 and 25, the rate of photosynthesis doubles for each 10 degrees rise in temperature
- Many plants, optimum temperature is 25
- At which the rate levels off and then declines (denaturation)
