C3 vs C4 Photosynthesis Mechanisms

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Questions and Answers

What is the primary function of transporters for HCO3- in the inner membrane of cyanobacteria?

To facilitate the efflux of harmful substances

To help regulate oxygen levels in the cell

To assist in the synthesis of chlorophyll

To bring inorganic carbon into the cell (correct)

What structural feature do carboxysomes possess?

An icosahedral protein shell that resists CO2 efflux (correct)

A bilayer membrane for selective permeability

A cylindrical protein shell for gas exchange

A vesicular structure for lipid storage

Which enzyme is packed into carboxysomes for carbon fixation?

Phosphofructokinase

PEP carboxylase

Rubisco (correct)

Fructose-1,6-bisphosphatase

What type of transporters do thylakoids have to assist in carbon processing?

CO2 transporters Signup and view all the answers

Why are bicarbonate transporters considered for improving leaf photosynthesis in C3 crops?

They improve the uptake of inorganic carbon Signup and view all the answers

What is the primary function of pyrenoids in cyanobacteria?

Site of Rubisco organization Signup and view all the answers

Which of the following structures is found interspersed within pyrenoids?

Thylakoid membranes Signup and view all the answers

What was revealed by the in situ cryo-electron tomography study of Chlamydomonas chloroplasts?

The native architecture of chloroplasts Signup and view all the answers

Which process is influenced by light modulating the electron flow in cyanobacteria?

Carbon fixation machinery organization Signup and view all the answers

What specific enzyme is crucial for the carbon fixation process in the chloroplasts of cyanobacteria?

Rubisco Signup and view all the answers

What temperature range primarily favors C3 plants over C4 plants?

Between 10°C and 35°C Signup and view all the answers

Why has C4 photosynthesis not evolved universally in all plants?

The conditions favoring C4 plants are not present everywhere. Signup and view all the answers

What is a key disadvantage of C4 photosynthesis compared to C3 photosynthesis?

C4 photosynthesis requires more energy. Signup and view all the answers

At which temperature does photorespiration significantly increase for plants?

Above 35°C Signup and view all the answers

Which of the following scenarios would most benefit C4 plants?

Development in high temperature areas with abundant light. Signup and view all the answers

What structures do C4 plants use to concentrate CO2?

Carboxysomes Signup and view all the answers

Which compound is primarily involved in the carboxylation reaction in C4 plants?

Phosphoenolpyruvate Signup and view all the answers

In algae, where is CO2 concentrated?

Pyrenoids Signup and view all the answers

What is the role of carbonic anhydrase in CO2 concentration mechanisms?

Converts HCO3- to CO2 Signup and view all the answers

What protein is primarily involved in the Calvin-Benson cycle?

Rubisco Signup and view all the answers

Which of the following best describes pyrenoids in algae?

Protein structures that concentrate CO2 Signup and view all the answers

What type of organisms use carboxysomes for CO2 concentration?

Cyanobacteria Signup and view all the answers

What is the significance of using phosphoenolpyruvate in C4 plants?

It initiates the fixation of CO2 Signup and view all the answers

Which of the following is NOT a function of carboxysomes?

Storing C4 acids Signup and view all the answers

What is the primary purpose of concentrating CO2 in C4 plants?

To increase the efficiency of photosynthesis Signup and view all the answers

What is a primary characteristic of C4 plants in relation to CO2 assimilation?

They are more efficient at CO2 assimilation in dry, hot, sunny regions. Signup and view all the answers

What is the role of glycine decarboxylase (GDC) in the photorespiratory pathway?

It decarboxylates glycine in the mitochondria of bundle sheath cells. Signup and view all the answers

What is a potential strategy for engineering more efficient C3 plants?

Raise CO2 levels at Rubisco through HCO3- transporters. Signup and view all the answers

What is the significance of centripetal microanatomy in C4 plants?

It facilitates the reassimilation of CO2 in bundle sheath cells. Signup and view all the answers

Which of the following is a common challenge that C3 plants face compared to C4 plants?

They are less efficient in warm temperatures. Signup and view all the answers

What adaptation do C4 plants have that helps them perform better in warm climates?

They utilize PEP carboxylase for initial CO2 fixation. Signup and view all the answers

What is a potential consequence of introducing carboxysomes into C3 crops?

Enhanced carbon fixation at lower light intensities. Signup and view all the answers

What is the primary function of HCO3- transporters in the context of improving C3 plants?

They facilitate the transport of bicarbonate, improving CO2 availability. Signup and view all the answers

Study Notes

### Carbon Concentration Mechanisms

Cyanobacteria use carboxysomes to concentrate CO2, these are icosahedral structures with a protein shell containing Rubisco
C4 plants use PEP carboxylase for the primary carboxylation reaction, to concentrate CO2 upstream of Rubisco
Many algae concentrate CO2 in pyrenoids within their chloroplasts
Pyrenoids are highly packaged Rubisco, interspersed with thylakoid membranes