Photosynthesis: Physiological and Ecological Insights

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Questions and Answers

What does the rate of net photosynthesis represent?

Total carbon assimilation in plants

Only the rate of CO2 loss

Total energy conversion efficiency

Difference between carbon assimilation and CO2 loss (correct)

Which environmental factor directly affects photosynthesis according to the document?

Ambient CO2 concentrations (correct)

Soil nutrients

Presence of herbivores

Atmospheric pressure

What hypothesis did F.F. Blackman propose regarding photosynthesis?

Photosynthesis is unlimited under optimal conditions.

Photosynthesis is always limited by light availability.

Photosynthesis can be limited by multiple factors simultaneously.

The slowest step in the process limits the rate of photosynthesis. (correct)

Why is understanding photosynthesis important to agronomists?

It directly influences crop yield. Signup and view all the answers

Which of the following is not mentioned as an indirect environmental factor affecting photosynthesis?

Soil temperature Signup and view all the answers

What aspect of photosynthesis is of great interest to ecologists?

Variation among different environments Signup and view all the answers

What does the term 'limiting factor' refer to in photosynthesis?

The slowest step limiting the overall photosynthetic rate Signup and view all the answers

Which of the following is NOT a physiological variable affecting photosynthesis?

Soil nutrient levels Signup and view all the answers

What is the main effect of dynamic photoinhibition under moderate excess light?

Decrease in quantum yield without changing the maximum rate Signup and view all the answers

Which factor influences chronic photoinhibition in intact leaves?

Amount of light exposure Signup and view all the answers

Which of the following describes chronic photoinhibition?

Damage to chloroplasts from excess light Signup and view all the answers

Under which conditions is dynamic photoinhibition most likely to occur?

During maximum light exposure Signup and view all the answers

How does dynamic photoinhibition affect carbon fixation?

It decreases carbon fixation correspondingly Signup and view all the answers

What climatic condition intensifies chronic photoinhibition?

Low temperatures Signup and view all the answers

What type of photoinhibition appears to be a daily occurrence?

Dynamic photoinhibition Signup and view all the answers

What is observed in leaves when photoinhibition occurs under favorable environmental conditions?

Increase in thermal dissipation of excess energy Signup and view all the answers

What effect does high light intensity have on biomass production in crops?

It increases biomass production. Signup and view all the answers

Which xanthophyll is the most effective for heat dissipation?

Zeaxanthin Signup and view all the answers

What must leaves do when exposed to excess light energy?

Dissipate the surplus absorbed light energy. Signup and view all the answers

How many aromatic rings in violaxanthin have a bound oxygen atom?

Two Signup and view all the answers

What is the relative effectiveness of antheraxanthin in heat dissipation compared to zeaxanthin?

Half as effective as zeaxanthin. Signup and view all the answers

What happens to violaxanthin under high light conditions?

It is converted to antheraxanthin and then to zeaxanthin. Signup and view all the answers

At what PPFD level can a shade plant maximize photosynthetic oxygen evolution?

150 μmol m–2 s–1 Signup and view all the answers

In which xanthophyll does neither of the aromatic rings have a bound oxygen atom?

Zeaxanthin Signup and view all the answers

What is the maximum photosynthetic CO2 assimilation rate observed for Atriplex triangularis grown in full sun conditions?

30 µmol m–2 s–1 Signup and view all the answers

How does photosynthesis in Atriplex triangularis compare between plants grown in sun and shade at low PPFD levels?

Photosynthesis is higher in shade at low PPFD. Signup and view all the answers

What does PPFD stand for in the context of photosynthesis?

Photosynthetic Photon Flux Density Signup and view all the answers

At what PPFD level does Atriplex triangularis reach its peak photosynthetic CO2 assimilation when grown in the shade?

92 µmol m–2 s–1 Signup and view all the answers

What is likely to happen to photosynthetic activity in Atriplex triangularis as PPFD increases beyond optimal levels?

Photosynthetic rates will plateau after a certain point. Signup and view all the answers

What can be inferred about the light-response curve of Atriplex triangularis grown in sun conditions compared to those in shade?

The light-response curve in shade conditions shows lower maximum rates. Signup and view all the answers

In the context of photosynthesis, what does an increase in PPFD typically lead to in Atriplex triangularis?

Increased photosynthetic CO2 assimilation up to a point. Signup and view all the answers

Which factor likely affects the ability of Atriplex triangularis to perform photosynthesis in shaded conditions?

Light saturation point and adaptations to low light. Signup and view all the answers

What year did C. David Keeling begin systematic measurements of CO2 at Mauna Loa?

1958 Signup and view all the answers

What is the predicted atmospheric CO2 concentration by the year 2100 if current emissions continue?

600 to 750 ppm Signup and view all the answers

What primarily influences the diffusion rate of CO2 into the leaf?

CO2 concentration gradient Signup and view all the answers

What is the main entry point for CO2 into the leaf?

Stomatal pore Signup and view all the answers

What happens to water vapor as CO2 diffuses into the leaf?

It diffuses out through the same pore. Signup and view all the answers

Since 1958, by more than what percentage have atmospheric CO2 concentrations increased?

25% Signup and view all the answers

Which process is essential for photosynthesis in relation to CO2?

CO2 fixation by rubisco Signup and view all the answers

What factor does the impermeability of the cuticle affect regarding CO2 and H2O?

Diffusion resistance Signup and view all the answers

Study Notes

Photosynthesis: Physiological and Ecological Considerations

Chapter focuses on the photosynthetic responses of the leaf to its environment
Net photosynthesis: The difference between photosynthetic carbon assimilation and CO2 loss via respiration
Factors influencing photosynthesis: Light, CO2 concentrations, temperature, humidity and soil moisture
Agronomists study photosynthetic variation to improve crop yield
Blackman’s Limiting Factor Hypothesis: This hypothesis proposes that at any given moment, the rate of photosynthesis is constrained by the most limiting factor, which can be light intensity, carbon dioxide concentration, or temperature. When one of these factors is insufficient, it can restrict the photosynthetic process, regardless of the abundance of other factors. A single factor can limit photosynthetic rate, such as light or CO2 concentration
Sun Plants: Atriplex triangularis, commonly known as saltbush, is particularly well adapted to environments with intense sunlight. When cultivated under conditions of elevated light intensity, these plants exhibit markedly increased rates of photosynthesis. This enhanced capability allows them to efficiently convert light energy into chemical energy, supporting their growth and survival in arid and saline conditions.
Shade Plants: Adaptations to low light conditions, including lower photosynthetic capacity and thicker leaves
Photoinhibition: occurs when leaves are exposed to excess light
- Dynamic Photoinhibition: Decreases quantum yield without affecting maximum photosynthetic rate
- Chronic Photoinhibition: Causes damage to the chloroplast due to excess light or failed protective mechanisms
Temperature: Optimal temperature range for photosynthesis varies between species and is significantly affected by light intensity and CO2 concentration
CO2 Concentration Increase: Since 1958, atmospheric CO2 concentration has increased by over 25%, reaching 600-750ppm by 2100 if emissions aren't reduced.
- C3 Plants: Benefit from higher CO2 levels due to Rubisco’s increased activity
- C4 Plants: Show a smaller response to elevated CO2 levels, which reduces the difference in photosynthetic rates between C3 and C4 plants
CO2 Diffusion: Essential for photosynthesis. CO2 diffuses from the atmosphere through the leaf, into the substomatal cavity, and finally to the carboxylation site of Rubisco.
- Diffusion Rate: Depends on the CO2 concentration gradient and resistances along the diffusion pathway.
Stomata: Main entry point for CO2 into the leaf. The pathway for CO2 diffusion is also used by H2O for transpiration.

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Description

This quiz covers key concepts related to photosynthesis, focusing on how environmental factors influence leaf responses. Topics include the net photosynthesis calculations, Blackman’s Limiting Factor Hypothesis, adaptations of sun and shade plants, and the effects of photoinhibition. Perfect for understanding the physiological and ecological aspects of plant biology.