Learn: Photosynthesis and Enzymes: Light Reactions, Calvin Cycle, C₄, and CAM

Where are photosynthetic pigments located in autotrophic bacteria?

In infolded regions of the plasma membrane. Bacteria are prokaryotes and do not have chloroplasts.

During the light reactions, how does the pH of the thylakoid lumen compare with the stroma?

The thylakoid lumen has a lower pH than the stroma because H⁺ ions accumulate inside the thylakoid.

Why is P680⁺ a strong oxidizing agent?

It takes electrons from water to replace electrons lost by Photosystem II; it has a strong ability to attract electrons.

What is the function of an enzyme's active site?

It binds the substrate, where the enzyme-catalyzed reaction occurs.

During which stage of photosynthesis is CO₂ consumed?

The Calvin cycle, where CO₂ is fixed into organic molecules.

Where are photosystems located in a chloroplast?

In the thylakoid membrane, not freely floating in the stroma.

Why don't the absorption spectrum of chlorophyll a and the action spectrum of photosynthesis match exactly?

Accessory pigments, such as chlorophyll b and carotenoids, absorb additional wavelengths and transfer the energy to reaction centers.

An orange pigment reflects which colors and absorbs which colors?

It reflects orange-related wavelengths and absorbs mainly blue and violet wavelengths.

Why did bacteria gather near certain regions in Engelmann's algae experiment?

They gathered where algae released the most oxygen, especially in regions illuminated by red and blue light.

What is the source of the oxygen released during photosynthesis?

The splitting of water molecules during the light-dependent reactions at Photosystem II.

What is reduced during photosynthesis to help form sugars?

CO₂ is reduced as it gains electrons and hydrogen during the formation of carbohydrates.

When does dissolved oxygen in a flask with duckweed reach its highest and lowest levels?

Highest at the end of the light period, when photosynthesis releases oxygen; lowest at the end of the dark period, when respiration consumes oxygen without photosynthesis.

How could you test whether an organism lacks Photosystem II?

Check whether it releases O₂ when exposed to light. Without Photosystem II, it cannot split water to release oxygen.

Where in the chloroplast is CO₂ containing radioactive oxygen incorporated into organic molecules during the Calvin cycle?

In the stroma, where the Calvin cycle occurs.

What are the three phases of the Calvin cycle in order?

Carbon fixation, reduction, and regeneration.

Which photosynthetic system is considered more ancestral: Photosystem I alone or Photosystems I and II together?

Photosystem I alone is considered more ancestral; it can support cyclic electron flow without splitting water or releasing oxygen.

Why can increasing atmospheric CO₂ increase plant growth?

CO₂ is a raw material for photosynthesis and provides the carbon used to make sugars and other organic compounds.

Why does an enzyme-catalyzed reaction rate plateau at high substrate concentrations?

Most enzyme active sites are occupied, so the enzymes are saturated and adding more substrate no longer increases the rate.

What is feedback inhibition in a metabolic pathway?

The pathway's final product inhibits an enzyme earlier in the pathway, preventing unnecessary product formation.

Why can bacteria living in hot springs function at high temperatures?

Their enzymes have high optimal temperatures and are adapted to remain functional in extreme heat.

What treatment can greatly increase reaction rate when substrate concentration is low?

Doubling the enzyme concentration can increase the rate by providing more available active sites.

What is an appropriate negative control for an experiment testing enzyme activity?

Repeat the experiment using denatured enzymes, which should no longer function normally.

How can the rate of an enzyme-catalyzed reaction be measured?

Measure the rate of substrate disappearance or product appearance over time.

Where might mutations in HIV reverse transcriptase cause resistance to a competitive inhibitor?

In or near the active site, changing the site so the drug binds less effectively while the natural substrate may still bind.

What does the induced-fit model describe?

Substrate binding causes the enzyme's active site to change shape and fit the substrate more tightly.

What is zinc's role in carboxypeptidase?

Zinc is an inorganic cofactor required for the enzyme's activity.

In C₄ photosynthesis, where does initial carbon fixation occur and where does the Calvin cycle occur?

Initial carbon fixation occurs in mesophyll cells; the Calvin cycle occurs in bundle-sheath cells.

How does C₄ photosynthesis reduce photorespiration?

It concentrates CO₂ in bundle-sheath cells around Rubisco, reducing the chance that Rubisco binds oxygen.

How does CAM photosynthesis differ from C₄ photosynthesis?

CAM separates steps by time within the same cell; C₄ separates them by location between mesophyll and bundle-sheath cells.