Photosynthesis Process and Chloroplasts

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Questions and Answers

What substance is oxidized during photosynthesis?

H2O (correct)

CO2

NADP+

What is the primary function of the light reactions in photosynthesis?

To generate ATP and NADPH (correct)

To fix carbon into organic molecules

To release glucose into the stroma

To convert CO2 into glucose

During the Calvin cycle, what is the initial step that occurs?

Carbon fixation occurs (correct)

Electrons are transferred to NADPH

O2 is released

H2O is split

Which of the following wavelengths is most effective in driving photosynthesis?

380 nm to 740 nm Signup and view all the answers

What by-product is released during the light reactions?

O2 Signup and view all the answers

What type of process is photosynthesis categorized as?

Endergonic Signup and view all the answers

The thylakoids are primarily responsible for which part of photosynthesis?

Light reactions Signup and view all the answers

What is the role of NADP+ in the light reactions?

To serve as an electron acceptor Signup and view all the answers

What is the relationship between the wavelength of light and the energy per photon?

Shorter wavelengths have more energy per photon. Signup and view all the answers

What is the primary reason leaves appear green?

Chlorophyll absorbs violet-blue and red light while reflecting green light. Signup and view all the answers

Which pigment is the key light-capturing pigment that directly participates in light reactions?

Chlorophyll a Signup and view all the answers

What does a spectrophotometer measure?

The ability of a pigment to absorb various wavelengths of light. Signup and view all the answers

Which wavelengths of light are most effective for photosynthesis according to the absorption spectrum of chlorophyll a?

Violet-blue and red light. Signup and view all the answers

What is the action spectrum of photosynthesis?

It plots the effectiveness of different wavelengths in driving photosynthesis. Signup and view all the answers

Who first demonstrated the action spectrum of photosynthesis?

Theodor W. Engelmann Signup and view all the answers

What happens to wavelengths of light that are absorbed by pigments?

They disappear and do not contribute to photosynthesis. Signup and view all the answers

What is the primary function of the Calvin cycle?

To synthesize sugar using ATP and NADPH Signup and view all the answers

Which of the following molecules is directly fixed to start the Calvin cycle?

Ribulose bisphosphate (RuBP) Signup and view all the answers

How many molecules of ATP are consumed for the net synthesis of one G3P in the Calvin cycle?

9 Signup and view all the answers

What occurs during the reduction phase of the Calvin cycle?

3-phosphoglycerate is phosphorylated and reduced Signup and view all the answers

What is the final product of the Calvin cycle that serves as a starting point for other metabolic pathways?

Glyceraldehyde 3-phosphate Signup and view all the answers

What role does rubisco play in the Calvin cycle?

It catalyzes the binding of CO2 to RuBP Signup and view all the answers

During which phase of the Calvin cycle is RuBP regenerated?

Regeneration of the CO2 acceptor Signup and view all the answers

For every three molecules of CO2 that enter the Calvin cycle, how many molecules of G3P are ultimately produced?

6 Signup and view all the answers

What is the role of chloroplasts in photosynthesis?

They convert light energy to chemical energy. Signup and view all the answers

Where in the plant are chloroplasts primarily located?

In the mesophyll of the leaves Signup and view all the answers

What gas enters the plant's leaves during photosynthesis?

Carbon dioxide Signup and view all the answers

What is the chemical equation summarizing the process of photosynthesis?

6 CO2 + 12 H2O + Light energy → C6H12O6 + 6 O2 + 6 H2O Signup and view all the answers

What is released as a by-product of the splitting of water during photosynthesis?

Oxygen gas Signup and view all the answers

What pigment is primarily responsible for capturing light energy in chloroplasts?

Chlorophyll Signup and view all the answers

What is the main structural component of a chloroplast that contains the pigment necessary for photosynthesis?

Thylakoid membranes Signup and view all the answers

How do plants primarily transport water to the leaves for photosynthesis?

Through xylem vessels Signup and view all the answers

What role does PEP carboxylase play in C4 plants?

It catalyzes the production of four-carbon precursors in mesophyll cells. Signup and view all the answers

How is pyruvate used in C4 plants following its formation?

One ATP is used to convert it back into PEP in mesophyll cells. Signup and view all the answers

What is a primary advantage of C4 photosynthesis over C3 photosynthesis?

C4 photosynthesis operates more efficiently with lower CO2 levels. Signup and view all the answers

What factors might affect the relative abundance of C3 and C4 plant species?

Rising CO2 levels and increased temperatures. Signup and view all the answers

What mechanism do CAM plants use to conserve water?

They open their stomata at night to incorporate CO2 into organic acids. Signup and view all the answers

What is one significant concern regarding the increase in CO2 levels since the Industrial Revolution?

It might destabilize suitable agricultural land availability. Signup and view all the answers

What is the expected benefit of genetically modifying rice to perform C4 photosynthesis?

It is anticipated to increase yield by 30-50% with given resources. Signup and view all the answers

What happens to stomata in CAM plants during the day?

They close to preserve water. Signup and view all the answers

Study Notes

Photosynthesis: Converting Light Energy to Chemical Energy

Photosynthesis is the process by which plants and other photosynthetic organisms convert light energy into chemical energy in the form of sugars.
Chloroplasts are organelles found in plant cells that are the sites of photosynthesis. They are structurally similar to photosynthetic bacteria, suggesting a common evolutionary origin.
Chlorophyll, the green pigment found in chloroplasts, absorbs light energy and uses it to drive the reactions of photosynthesis.

Chloroplast Structure and Function

Mesophyll: This is the interior tissue of a leaf where most photosynthesis occurs.
Stomata: These microscopic pores on the leaf surface allow for gas exchange, with CO2 entering and O2 exiting.
Veins: Transport water from the roots and sugars to non-photosynthetic parts of the plant.
Chloroplast Envelope: Two membranes surround a dense fluid called the stroma.
Thylakoids: Interconnected sacs within the chloroplast that form a third membrane system. Stacks of thylakoids are called grana.

The Photosynthesis Equation

The overall chemical change during photosynthesis is the reverse of cellular respiration:
- 6 CO2 + 12 H2O + Light energy → C6H12O6 + 6 O2 + 6 H2O

The Splitting of Water

During photosynthesis, chloroplasts split water into hydrogen and oxygen.
Electrons from hydrogen are incorporated into sugar molecules, while oxygen is released as a byproduct.

Photosynthesis as a Redox Process

Photosynthesis is a redox process where water is oxidized and carbon dioxide is reduced.
It is an endergonic process, meaning it requires energy input, which is provided by light.

The Two Stages of Photosynthesis

Light Reactions: Occur in the thylakoids and use light energy to:
- Split water, releasing electrons and protons (H+).
- Release oxygen as a byproduct.
- Reduce NADP+ to NADPH.
- Generate ATP from ADP by photophosphorylation.
Calvin Cycle (aka the dark reactions): Occurs in the stroma and uses the ATP and NADPH generated by the light reactions to:
- Fix carbon dioxide.
- Reduce fixed carbon to sugar.

The Light Reactions

Electromagnetic Spectrum: The full range of electromagnetic radiation, including visible light (380-740 nm).
Photons: Discrete packages of light energy, with shorter wavelengths having more energy per photon.
Photosynthetic Pigments: Absorb light energy, with different pigments absorbing different wavelengths.
- Chlorophyll a: The primary pigment involved in light reactions.
- Chlorophyll b: An accessory pigment that captures additional light energy.
- Carotenoids: Accessory pigments that absorb wavelengths not captured by chlorophyll.

The Calvin Cycle

An anabolic process that builds sugars from smaller molecules using ATP and reducing power from NADPH.
Carbon Fixation: CO2 binds to a five-carbon sugar named ribulose bisphosphate (RuBP), catalyzed by rubisco.
Reduction: 3-phosphoglycerate is phosphorylated (using ATP) and reduced (using NADPH) to produce glyceraldehyde 3-phosphate (G3P).
Regeneration: Five molecules of G3P are rearranged to regenerate three molecules of RuBP.

C4 Photosynthesis

An adaptation that increases photosynthetic efficiency in hot, dry environments.
A three-step process:
- CO2 is initially fixed by PEP carboxylase in mesophyll cells.
- Four-carbon compounds are transported to bundle-sheath cells.
- CO2 is released and used in the Calvin cycle.
C4 plants have higher affinity for CO2 than C3 plants, allowing them to thrive in low-CO2 environments.

CAM Plants

Plants with crassulacean acid metabolism (CAM), a type of photosynthesis that conserves water.
Open stomata at night, taking in CO2 and storing it as organic acids in vacuoles.
Close stomata during the day and release CO2 for use in the Calvin cycle.

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Description

Explore the fascinating process of photosynthesis, where plants convert light energy into chemical energy. This quiz delves into the structure and function of chloroplasts, including the roles of mesophyll, stomata, and thylakoids. Test your knowledge about how plants harness solar energy for growth!