Lecture #8- Photosynthesis

Question 1

what are autotrophs

Answer 1

• use inorganic C as C source to fix C into an organic compounds, this process is anarobic
  1. photoautotrophs - use light energy to fix C eg. photosynthesis
  2. chemoautotrophs (lithotrophs) - use redox energy to fic C eg. bacteria only

Question 2

what are heterotrophs

Answer 2

• use organic C as C source and energy source
  1. chemoautotrophs - use organic as main nutrient eg. humans
  2. photoheterotrophs - use light energy and organic C eg. prok only and rare

Question 3

where is the site of photsynthesis and draw it out,

Answer 3

pg 2.
- the site of photosynthesis is in the chloroplast, more specific light rxns happen in the thylakoid membranne

Question 4

overall rxn of photosynthesis: what C is oxidized and what is reduced
- why use CO2?
- draw it out (including the calvin cycle)

Answer 4

6CO2 + 6H2O + light -> C6H12O6 + O2
- CO2 is the lowest energy and is oxidized
- The C in glucose is reduced, meaning more energy
- O2 is a wanted product

Question 5

What is the point of light rxns?
and what happens to the light that is absorbed?

Answer 5

• use energy carried by light and convert it into chemical energy in the form of ATP: NADPH that will be used to power the Calvin cycle
• light is absorbed by pigments, this absorbed energy is released as heat or fluorescence

Question 6

define photosystems and draw out the ETC

Answer 6

• composed of a protein complex called the rxn centre surrounded by several light harvesting complexes
• sits in te thylakoid membrane and contains pigments: includes: chlorophyll a, xanthophylls, carotenoids
• ETC: electron transport chain, a set of increasing strength of e- acceptors

Question 7

define chemiosmosis and ATP synthase

Answer 7

• formation of ATP in photosynthesis using a [H+] gradient and ATP synthesis
• if the energy source of the H+ gradient is light=photosynthesis
• if the energy source for H+ gradient is oxidation of a nutrient = oxidative phosphorylation
• ATP synthase = an enzyme complex that couples ATP synthesis (endergonic) with the dissipation [H+] gradient (exergonic)

Question 8

Describe the three phases of the Calvin Cycle

Answer 8

• it happens in the stroma
  1. Carbon Fixation - one CO2 is added per turn of the cycle, enzyme used is Rubisco
  2. Reduction - the NADPH from light rxns are used to reduce the fixed C
  3. regeneration - RuBP (ribulose biphosphate) is regenerated = a set of complex rxns requiring ATP