Lecture 8: Photosynthesis II

Question 1

Noncyclic electron transport

Answer 1

1. Electrons are supplied to system from the splitting of H2O by photosystem II, with release of O2, as a by-product. When photosystem II is activated by absorbing photons, electrons are passed along electron transport chain and are eventually donated to photosystem I
2. Electrons in Photosystem I are “reenergized” by absorption of additional light energy and are passed to NADP+, forming NADPH

Question 2

Cyclic electron transport

Answer 2

• cyclic flow of electrons through Photosystem I and electron transport chain between PS1 and PS2
• electrons are not passed to NADP+ but continuously cycled through PS1
• water is not split
• O₂ is not produced
• additional ATP is made

Question 3

Proton accumulation in the thylakoid lumen:

Electrochemical gradient

Answer 3

• “electro” generated by charge on protons
• “chemical” arises from the acidified lumen resulting from proton build-up

Question 4

Chemiosmosis

Answer 4

• proton gradient established using the energy released during electron transport to run proton pump and photolysis of H₂O
• Protons flow through channel in ATP synthase complex providing energy to assemble ATP from ADP and Pi known as photophosphorylation

Question 5

photophosphorylation

Answer 5

• using light to add a phosphate group to something

Question 6

summarize the events of light-dependent reactions of photosynthesis

Answer 6

• photosynthesis and calvin cycle

Question 7

carbon fixation

Answer 7

• CO₂ taken up from atmosphere and the carbon is incorported
• Calvin cycle (C3 pathway)
  
  • most common pathway of carbon fixation, the reduction of carbon dioxide into simple sugars
  • uses energy stored in ATP and NADPH during light-dependent reactions to chemically fix CO₂

- ATP and NADPH are used to run the calvin cycle

Question 8

Light Compensation Point

Answer 8

• the point at which photosynthetic gains match respiratory losses
• AKA net CO₂ exchange is zero

Question 9

Light Saturation Point

Answer 9

• the point at which you can add more light and you don’t see a big increasee in the photosynthetic rate

Question 10

Photosynthetically Active Radiation (PAR) or Photosyntheti Photon Flux Density (PPFD)

Answer 10

• measuring the visible light spectrum
• x-axis
• PAR - the wavelengths of light that can be used in photosynthesis
• PPFD - the amount of usable light energy impinging upon a leaf per unit time

Question 11

A

Answer 11

• Assimilation Rate
• units: micromoles/m²/s
• rate at which CO₂ is taken up by the leaf AKA CO₂ uptake by leaf

Question 12

Maximum rate of net photosynthesis

Answer 12

• if you go over to the y-axis, at the LSP then this number is your maximum rate of net photosynthesis

Question 13

Photosyntehtic rates and light environment

Answer 13

• Canopy light levels high in early spring, low in mid-summer, and high again in autumn

Question 14

Allium tricoccum

Answer 14

• wild leek
• spring ephemeral
• aboveground leaves April-May

Question 15

Viola pubescens

Answer 15

• yellow violet
• summer-green
• abovegrund leaves May-September

Question 16

Tiarella cordifolia

Answer 16

• foam-flower
• semi-evergreen
• aboveground leaves mid-May thru mid-November

Question 17

Seasonal shifting of LCP

Answer 17

• Allium - high & consistent LCP
• Viola - LCP shifts downward from spring to summer
• *Tiarella *- LCP shifts downward from spring to summer and upwards again in the fall