Topic 11: Photosynthesis Flashcards
Name some leaf adaptations for photosynthesis
- Large sa:v
- Thin to keep diffusion distance short
- Transparent cuticle and upper epidermis
- Columnar palisade cells to maximise the number of photosynthesising cells
- Palisade cells are full of chloroplasts to maximise photosynthesis
- Lots of stomata for gas exchange
- Stomata open and close depending on light intensity
- Air spaces allow for diffusion of O2 and H20
- Xylem to transport water to leaf cells
Explain the structure of the thylakoid membrane
Folded membranes which contain photosystems. Electron carrier protiens are embedded in these memebranes.
Involved with LDR
Explain the structure of the stroma
Fluid centre, contains enzymes involved in LIR
What is the quation for photosynthesis
6CO2 + 6H20 –> C6H12O6 + O2
with chlorophyll and light
What do the light dependant reactions produce
ATP and Reduced NADP
What wavelength do plants not absorb
Green (its reflected which is why we see it)
How do you calculate Rf value
distance moved by pigment / distance moved by solvent
Where do the LDR and LIR take place
LDR- Thylakoid memebrane
LIR - Stroma
What is oxidation
- Gain of Oxygen
- Loss of electrons
- Loss of H+
Releases energy
What is reduction
- Loss of Oxygen
- Gain of electrons
- Gain of H+
Absorbs energy
What are the three stages of photosynthesis
- Photoionisation
- Photolysis
- Chemiosmosis
Describe photoionisation
- Sunlight hits the chlorophyll on the thylakoid membrane, which absorbs the light energy via its electrons
- Energy is so great it causes the electron o be released from the chlorophyll where it eneters the electron transport chain
Mg excites 2 electrons to become Mg2+
Describe photolysis
Light enery that was absorbed the chlorophyll splits water into oxygen, two H+ ions and 2 electrons
What happens to each of the products of photolysis
- H+ ions are used to reduce NADP, released into the thylakoid lumen creating a gradient
- E- are used to replaced the electrons from Chlorophyll
- O2 used for respiration or just diffuses out
Describe chemiosmosis
- Electrons released by photoionisation are captured by carrier protiens in an electron transport chain oin the thylakoid membrane.
- As the electrons move down the chain from one protien to another they release energy
- This energy is used to phosphorylate ADP –> ATP.
- The final electron accept is NADP+, which turns into reduced NADP
- Some of the energy released will actively transport H+ ions into the thylakoid membrane, creating a gradient. H+ will then diffuse back out through ATP synthase, which will form ATP from ADP.
What are the two steps of the Light Independant reactions
- Carbon fixation
- Reduction of Gp
Describe what happens during the LIR
- CO2 will react with a 5-carbon molecule (RuBP), catalysed by the enzyme Rubisco forming a very unstable 6 carbon molecule
- Due to its instability, this molecule will split down the middle, creating two molecules of GP, each with three carbons
- GP is reduced into Triose Phosphate (TP), using energy from ATP, and by accepting H from reduced NADP. These two molecules have come from the LDR
- One of the carbons from TP will leave to be converted into useful organic substances (like glucose), and the rest is used to regenerate RuBP.
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What are the limiting factors of photosynthesis
- Carbon Dioxide concentration
- Light intensity
- Temperature
Explain in detail how temp affects photosynthesis
- The LIR are enzyme controlled, therefore it is sensitive to temperature
- Anything above the optimal temperature will decrease the rate of reaction as the enzymes begin to denature.
Explain in detail how CO2 concentration affects rate of photosynthesis
CO2 is the substrate for the enzyme Rubisco in the LIR. The higher the CO2 conc, the faster the rate of the Calvin Cycle
CO2 is often the limiting factor for Photosymthesis
Explain in detail how light intensity affects the rate of photosynthesis
Light is the source of energy for the production of ATP and NADP in the LDP, which then influences the rate of the LIR. The higher the light intensity, the faster the rate of photosynthesis.
Explain how limiting factors of photosynthesis are used in agriculture to maximise yield
- CO2, fuels (paraffin burners) are used to release CO2
- Light, Artificial lighting is used to maximise the absorbance of wavelengths
- Temperature, Grown in temp controlled grenehouses to use the optimal temp
what two measurements are needed to find rate of photosynthesis
- Measure of time (s)
- Measure of volume of gas released (O2) OR gas absorbed (CO2), in m3
What are the limitations when investigating photosynthesis by Volume of O2 released
- Some O2 used in respiration
- May be dissolved nitrogen in the gas (not pure)
- Ambient light will differ
How do you find volume of gas (photosynthesis)
by bubbles
Volume of gas released = lenght of bubble x (π r²)
What are the 4 steps of aerobic respiration
- Glycolysis
- Link reaction
- Krebs cycle
- Oxidative phosphorylation
Where does each step of aerobic respiration take place
- Glycolysis - Cytoplasm
- Link reaction - Mitochondrial matrix
- Krebs cycle - Mitochondrial matrix
- Oxidative phosphorylation - Mitochondrial inner membrane (Cristae)
Explain Glycolysis
- Glucose is phosphorylated into glucose phosphate, using ATP.
- Glucose phosphate is hydrolysed into two molecules of triose phosphate.
- Triose phosphate is oxidised into pyruvate (while NAD –> reduced NAD, and ADP –> ATP
What is the net gain of Glycolysis
- 2 ATP molecules,
- 2 Reduced NAD
Why does glucose phosphate split by hydrlysis
its very unstable, therefore hydrolysed immediately
Explain the link reaction
- Pyruvate is oxidised into Acetate (2 C) (decarboxylation), while NAD –> reduced NAD
- Acetate joins with CoEnzyme A to form Acetyl CoA, which enters the Krebbs cycle.
ِِExplain Krebbs cycle
- AcetylCoA (2 C), will join with a 4 carbon molecule, to form citrate (6C)
- This will undergo decarboxylation, and oxidation into a 5 C intermediate compound (NAD –> reduced NAD)
- This will be oxidised further, to reform the 4 carbon molecule, (NAD –> reduced NAD, FAD –> reduced FAD, NAD–> reduced NAD, ADP–> ATP)
Per Krebbs cycle, what are the products
- 3x reduced NAD
- 1x reduced FAD
- 1x ATP
- 2x CO2
What is the purpose of FAD and NAD
Electron carriers
What was the whole point of producing all this reduced FAD and NAD
FADH and NADH can be oxidisied during the final step to split away the hydrogen into electrons and protons,, which means their electrons can then undergo the electron trnasport chain
Explain what happens during oxidative phosphorylation
- The electrons released by reduced FAD and NAD are carried down the electron transport chain on the inner memebrane of the mitchondria.
- Every time an electron moves from one carrier protien to the other it releases energy that is used to actively transport H+ ions, into the intermembrane space which creates a electrochmical gradient.
- This means the H+ ions are able to diffuse (facilllitated) back across the membrane using a protein called ATP synthase, which will use the H+ ions to form ATP from ADP
- Oxygen is the final proton acceptor, accepting e- and H+ to form water molecules.
What is another word for the H+ gradient
- electrochemical gradient
- pH gradient
- H+ gradient
Where does anaerobic respiration take place
- In the cytoplasm
