Photosynthesis Flashcards
What is the main purpose of the light reactions in photosynthesis?
To convert light energy into chemical energy in the form of ATP and NADPH
In which part of the chloroplast does the Calvin Cycle occur?
Stroma
During the Calvin Cycle, carbon dioxide is initially fixed to which molecule?
RuBP
Which of the following molecules is a product of the Calvin Cycle that can eventually be used to form glucose?
G3P
What role do stomata play in photosynthesis?
They regulate gas exchange, allowing CO₂ in and O₂ out.
The process that splits water to release electrons, protons, and oxygen occurs in which phase?
Light Reactions
Which molecule acts as an energy carrier between the light reactions and the Calvin Cycle?
ATP
What happens to the electrons that are excited in chlorophyll during the light reactions?
They move through the Electron Transport Chain, helping to produce ATP and NADPH.
What is the end product of the Calvin Cycle that is a precursor to glucose?
G3P
Which pigment is primarily responsible for absorbing light in photosynthesis?
Chlorophyll
Which phase of photosynthesis is also known as the “dark reactions”?
Calvin Cycle
Which of the following best describes photophosphorylation?
The process of adding a phosphate group to ADP to form ATP during the light reactions.
In non-cyclic electron flow, what is produced in addition to ATP?
NADPH
What is the role of water in the light-dependent reactions?
provides electrons by going through photolysis.
What is chemiosmosis in photosynthesis?
The movement of protons across the thylakoid membrane to make ATP.
Why do plants appear green?
Chlorophyll reflects green light.
What molecule carries electrons from the light reactions to the Calvin Cycle?
NADPH
Which enzyme is essential in carbon fixation during the Calvin Cycle?
Rubisco
The Calvin Cycle requires ATP and NADPH. Where are these molecules produced?
Light Reactions
What process generates the oxygen released during photosynthesis?
Splitting of water molecules during the light-dependent reactions
During the light-dependent reactions, what is the significance of the pigment P680 in Photosystem II?
Light energy excites electrons, which move through the electron transport chain.
Why is the electron flow in photosynthesis described as “non-cyclic” in the light-dependent reactions?
Because electrons are lost from the system and end up in NADPH, not returning to the starting point.
What is the function of the proton gradient across the thylakoid membrane?
It drives ATP synthesis through ATP synthase by allowing protons to flow back into the stroma.
How does cyclic electron flow differ from non-cyclic electron flow in the light-dependent reactions?
Cyclic electron flow only involves Photosystem I and produces ATP but not NADPH.
What role does the enzyme rubisco play in the Calvin Cycle, and why is it considered inefficient?
It fixes CO₂, but can also bind to O₂, leading to photorespiration and loss of efficiency.
Which of the following best describes the purpose of photolysis in Photosystem II?
makes oxygen and replenish electrons lost by chlorophyll.
How is the energy stored in ATP and NADPH used in the Calvin Cycle?
ATP provides energy for carbon fixation, while NADPH provides high-energy electrons to reduce CO₂.
What effect does photorespiration have on the efficiency of photosynthesis in C3 plants?
It reduces efficiency by using ATP and releasing CO₂ without producing sugars.
Why is the Calvin Cycle often referred to as “light-independent” when it still depends on products of the light reactions?
Because it does not directly use light energy but relies on ATP and NADPH produced in the light-dependent reactions.
What is the primary purpose of regenerating RuBP at the end of the Calvin Cycle?
To ensure continuous carbon fixation
Describe the characteristics of chloroplasts.
- Bean-shaped
- contain their own DNA and ribosomes
- self-replicating
- thought to have originated from bacteria
- have an inner and outer membrane with stroma fluid, contain thylakoid stacks
- produce glucose using ATP, NADPH, and chlorophyll pigments.
What plant parts are involved in photosynthesis?
- Endodermis
- Stomata
- Mesophyll cells
Which colors of light have the most energy
Shorter wavelengths (violet and blue) have more energy.
What colors are absorbed by chlorophyll?
Blue and red light, while green is reflected
What are the two types of chlorophyll?
Chlorophyll a and b
What is at the center of the porphyrin ring?
A magnesium ion (Mg²⁺)
What is photoexcitation in the light reactions?
The process where light excites electrons in chlorophyll, starting the transfer of electrons through the photosystems.
Name the proteins involved in photosystem II and photosystem I in the light reactions.
- Photosystem II: Z protein, Pq
- Photosystem I: Pc
What are the main products of the light reactions?
ATP, NADPH, O2
What are the three phases of the Calvin cycle, and why are they important?
- Carbon fixation - CO₂ is fixed to produce a stable molecule
- Reduction - ATP and NADPH reduce intermediates to form G3P
- Regeneration - RuBP is regenerated to continue the cycle.
Which types of plants use C4 and CAM carbon fixation?
C4 and CAM plants (eg pineapple) are adapted to hot, dry environments
How does C4 and CAM differ from C3?
They reduce photorespiration by fixing CO₂ at different times or in different cells than C3 plants
