Photosynthesis as an example of biochemical pathways

Question 1

Photosynthesis

Answer 1

The purpose of photosynthesis is to capture sunlight and transform the energy into the concentrated chemical energy of organic sugar molecules - such as glucose

Question 2

Formula

Answer 2

6CO2 + 12H2O –> C6H12O6 + 6O2 + 6H2O
carbon dioxide + water –> glucose + oxygen + water

Question 3

Chloroplast

Answer 3

The light-trapping pigment, chlorophyll, is embedded in the thylakoid membranes. Thylakoids provide a large surface area for the capture of sunlight, The stroma is the fluid inside the chloroplast.

Question 4

Light dependent stage

Answer 4

Can only occur in presence of light (sunlight)
Occurs in grana in the thylakoid membranes
Input = NADP+, ADP + Pi, H2O
Output = NADPH, ATP, O2

Question 5

Light independent stage (Calvinc cycle)

Answer 5

Can only occur in presence of high energy coenzymes
Occurs in the stroma
Input = NADPH, ATP, CO2
Output = NADP+, ADP + Pi, Glucose

Question 6

Rubisco

Answer 6

Main enzyme in C3 plants is known as Rubisco, which is vital in carbon fixation (captures CO2 from air and catalysis their conversion to 3-carbon molecule that can then be assembled into glucose molecule)

Question 7

Photorespiration in heat

Answer 7

When the Rubisco enzymes capture oxygen, instead of CO2 disrupting the independent stage.
Hot conditions - enzyme shape change allowing oxygen molecules to better fit than CO2
Dry conditions - less water, C3 plants close stomata to prevent water loss and block entry of CO2 and exit of oxygen - creates high oxygen and low CO2 - Rubisco will likely bind to oxygen

Question 8

C3

Answer 8

• Cool temp, moist conditions,
• Rubisco
• Location of LID in mesophyll cells
• Open stomata
• Carbon fixation during day

Question 9

CAM

Answer 9

• Hot arid environment, exposed to drought
• PEP carboxylase (Rubisco starts LID)
• Location of LID in bundle sheath cells
• don’t open stomata
• Carbon fixation during day

Question 10

C4

Answer 10

• warm temp, tropic regions
• PEP carboxylase (Rubisco starts LID)
• Location of LID in mesophyll cell
• open stomata at night only
• Carbon fixation at night

Question 11

Light availability

Answer 11

• Rate increases as light intensity increases, until reaching a maximal point.
• At low light intensities, the photosynthesis rate is slow or absent.
  Light saturation point is when light intensity increases but the rate of photosynthesis stays constant.

Question 12

Water availability

Answer 12

• If soils dry out and H2O supply is too little, rate of photosynthesis declines and stops as closed stomata prevents the uptake of CO2 needed for the LID stage
• If the water supply increases too much causing water logging of the soil, rate of photosynthesis will decline and stop as the lack of oxygen for cellular respiration in root cells stops water uptake.

Question 13

Temperature

Answer 13

• As temp drops below optimus, reaction rate drops due to low thermal energy (fews collisions between substrate and enzyme) enzyme becomes inactive
• As temp increases above optimum, reaction rate reduces and heat denaturation occurs

Question 14

Carbon dioxide concentration

Answer 14

• As the concentration of CO2 is progressively increased, the rate of photosynthesis will increase until it levels off due to limiting factors.
• The CO2 concentration where photosynthesis CO2 uptake balances respiratory CO2 release is called the CO2 compensation point.