Topic 11: Photosynthesis

Question 1

Name some leaf adaptations for photosynthesis

Answer 1

• 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

Question 2

Explain the structure of the thylakoid membrane

Answer 2

Folded membranes which contain photosystems. Electron carrier protiens are embedded in these memebranes.

Involved with LDR

Question 3

Explain the structure of the stroma

Answer 3

Fluid centre, contains enzymes involved in LIR

Question 4

What is the quation for photosynthesis

Answer 4

6CO2 + 6H20 –> C6H12O6 + O2

with chlorophyll and light

Question 5

What do the light dependant reactions produce

Answer 5

ATP and Reduced NADP

Question 6

What wavelength do plants not absorb

Answer 6

Green (its reflected which is why we see it)

Question 7

How do you calculate Rf value

Answer 7

distance moved by pigment / distance moved by solvent

Question 8

Where do the LDR and LIR take place

Answer 8

LDR- Thylakoid memebrane
LIR - Stroma

Question 9

What is oxidation

Answer 9

• Gain of Oxygen
• Loss of electrons
• Loss of H+

Releases energy

Question 10

What is reduction

Answer 10

• Loss of Oxygen
• Gain of electrons
• Gain of H+

Absorbs energy

Question 11

What are the three stages of photosynthesis

Answer 11

1. Photoionisation
2. Photolysis
3. Chemiosmosis

Question 12

Describe photoionisation

Answer 12

• 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+

Question 13

Describe photolysis

Answer 13

Light enery that was absorbed the chlorophyll splits water into oxygen, two H+ ions and 2 electrons

Question 14

What happens to each of the products of photolysis

Answer 14

• 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

Question 15

Describe chemiosmosis

Answer 15

• 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.

Question 16

What are the two steps of the Light Independant reactions

Answer 16

1. Carbon fixation
2. Reduction of Gp

Question 17

Describe what happens during the LIR

Answer 17

• 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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Question 18

What are the limiting factors of photosynthesis

Answer 18

• Carbon Dioxide concentration
• Light intensity
• Temperature

Question 19

Explain in detail how temp affects photosynthesis

Answer 19

• 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.

Question 20

Explain in detail how CO2 concentration affects rate of photosynthesis

Answer 20

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

Question 21

Explain in detail how light intensity affects the rate of photosynthesis

Answer 21

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.

Question 22

Explain how limiting factors of photosynthesis are used in agriculture to maximise yield

Answer 22

• 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

Question 23

what two measurements are needed to find rate of photosynthesis

Answer 23

• Measure of time (s)
• Measure of volume of gas released (O2) OR gas absorbed (CO2), in m3

Question 25

What are the limitations when investigating photosynthesis by Volume of O2 released

Answer 25

- Some O2 used in respiration - May be dissolved nitrogen in the gas (not pure) - Ambient light will differ

Question 26

How do you find volume of gas (photosynthesis) | by bubbles

Answer 26

Volume of gas released = lenght of bubble x (π r²)

Question 27

What are the 4 steps of aerobic respiration

Answer 27

- Glycolysis - Link reaction - Krebs cycle - Oxidative phosphorylation

Question 28

Where does each step of aerobic respiration take place

Answer 28

1. Glycolysis - Cytoplasm 2. Link reaction - Mitochondrial matrix 3. Krebs cycle - Mitochondrial matrix 4. Oxidative phosphorylation - Mitochondrial inner membrane (Cristae)

Question 29

Explain Glycolysis

Answer 29

- 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

Question 30

What is the net gain of Glycolysis

Answer 30

- 2 ATP molecules, - 2 Reduced NAD

Question 31

Why does glucose phosphate split by hydrlysis

Answer 31

its very unstable, therefore hydrolysed immediately

Question 32

Explain the link reaction

Answer 32

- 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.

Question 33

ِِExplain Krebbs cycle

Answer 33

- 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)

Question 34

Per Krebbs cycle, what are the products

Answer 34

- 3x reduced NAD - 1x reduced FAD - 1x ATP - 2x CO2

Question 35

What is the purpose of FAD and NAD

Answer 35

Electron carriers

Question 36

What was the whole point of producing all this reduced FAD and NAD

Answer 36

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

Question 37

Explain what happens during oxidative phosphorylation

Answer 37

* 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.

Question 38

What is another word for the H+ gradient

Answer 38

- electrochemical gradient - pH gradient - H+ gradient

Question 39

Where does anaerobic respiration take place

Answer 39

- In the cytoplasm