Photosystems and Role of Stomata and Guard Cells

What are the two photosystems used in photosynthesis? What are they used for?

PS I and PSII; used for converting light energy

PS I: Location

Stroma lamellae membrane (thylakoid membrane that connects grana)

PS I: Peak/best wavelength

700nm

PS I: Transfer of e^-

Reduces NAPH to NADPH

PS I: Source of replacement e^-

2 e^- from plastocyanin

PS II: Location

Grana/thylakoid membrane (surrounds each disk)

PS II: Peak/best wavelength

680nm

PS II: Transfer of e^-

to the carrier in the ETC (plastoquinone)

PS II: Source of replacement e^-

Photolysis of water

What three things can be used to measure the rate of photosynthesis? (both direct and indirect)

-CO₂ used (direct measurement)

-O₂ produced (direct measurement)

-Biomass (indirect measurement)- weigh plant matter→ more growth if more photosynthesis occurs

Where are stomata located?

the opening on the underside of leaves

What does the stomata allow?

allows gas exchange during photosynthesis (oxygen out, carbon dioxide in)

Guard cells’ function and what does it contain?

control whether stomata opens and it contains chlorophyll

Why do guard cells open up and close in?

open due to turgor pressure (water moving in)and close due to water moving out

Why does water loss or gaining water occur in the guard cells?

the movement of K⁺ ions (potassium)

What is the purpose of light in the guard cell?

It causes protein pumps in the guard cell membrane to pump K⁺ ions into the guard cell (active transport)

Why does water go into the guard cell? (a process)

Osmosis

If K⁺ leaves the guard cell, what also leaves?

Water

What plant hormone affects the guard cells under hot conditions or when no photosynthesis occurs?

Abscisic acid

Describe the affects of abscisic acid to guard cells?

Causes K⁺ to move out quicker from the guard cell, which means water move out too, and the stomata closes

Summarize what is happening when stomata opens

Increased light, increased K⁺, increased water (turgor pressure)

Summarize what is happening when stomata closes

Decrease light, increase abscisic acid, decreased K⁺ decreased water (less turgor pressure)