Chapter 10: Photosynthesis

Question 1

What is photosynthesis?

Answer 1

The process of converting light energy from the sun into chemical energy stored in the form of glucose.

6CO2 + 6H20 (light energy) → C6H12O6 + 6O2

Question 2

Where does photosynthesis take place?

Answer 2

In the chloroplast

Question 3

What are chloroplast? Where in the cell is it typically found?

Answer 3

Chloroplasts are disk shaped organelles found in the cells of plants that carry out photosynthesis.

Typically found in the mesophyll (interior tissue of the plant leaf).

Question 4

Chloroplast is filled with chlorophyll molecules. Chlorophyll molecules are…

Answer 4

The green pigment that absorbs light energy from the sun.

Question 5

Chlorophyll is enclosed in a membrane known as _________.

Answer 5

Thylakoids

Question 6

Chlorophyll molecules are embedded in specialized protein complexes known as ________

Answer 6

photosystems

Question 7

Name the two stages of photosynthesis.

Answer 7

1. Light dependent reactions (Photo) - requires light energy
2. Light independent reactions (Synthesis) - does not require light energy (calvin cycle)

Question 8

Describe what happens in the light-dependent reaction stage of photosynthesis and where it takes place.

Answer 8

1. Chlorophyll, the green pigment in chloroplasts, absorbs light energy from the sun.
2. Light energy is used to split water molecules (H2O) into oxygen (O2) and hydrogen ions (H+, protons) and electrons.
3. Electrons are transferred through a series of electron transport chains, generating ATP and NADPH (energy-rich molecules that power the light-independent reactions)

This takes place in the thylakoid membrane (pigments) and the thylakoid lumen.

Question 9

Describe what happens in the light-independent reaction stage of photosynthesis and where it takes place.

Answer 9

ATP and NADPH generated during the light-dependent reactions is used to convert carbon dioxide (CO2) into glucose through the calvin cycle.

This takes place in the stroma.

Question 10

What are the reactants and products of light dependent reactions in photosynthesis?

Answer 10

Reactants: H2O + ADP + Pi + NADP+ + light pigments

Products: ↑O2 + ATP + NADPH

Question 11

What are the reactants and products of light independent reactions in photosynthesis?

Answer 11

Reactant: CO2 + ATP + NADPH + H+

Products: C3H6O3

Question 12

Describe the steps of the Calvin Cycle.

Answer 12

1. Carbon Fixation: Attachment of atmospheric CO2 with RuBP with the help of the enzyme Rubisco, producing two molecules of 3-PGA.
2. Reduction Phase: Plant uses ATP and NADPH to convert 3-PGA (unstable) into G3P (stable).
3. Regeneration of RuBP: Some of the G3P molecules produced in the reduction step are used to regenerate RuBP.

Question 13

What is a redox process?

Answer 13

The loss and gain of an electron. This transfer of electrons leads to changes in the oxidation states of the atoms involved.

Question 14

In a redox reaction, the substance that loses electrons is called the _______ ______ , and the substance that gains electrons is called the ________ ______.

Answer 14

reducing agent, oxidizing agent

Question 15

What allows plants to capture the energy of light in the thylakoid membrane?

Answer 15

The pigment.

Question 16

Why does a thylakoid need larger amounts of surface area?

Answer 16

To hold more pigment.

Question 17

Thylakoids may be stacked in columns called ____.

Answer 17

Grana.

Question 18

What is needed for the light dependent reactions to take place?

Answer 18

H20, ADP, Pi, NADP, and light pigments.

Question 19

What are the products from the light dependent reactions?

Answer 19

↑O2, ATP, NADPH.

Question 20

What is needed for the light independent reactions to take place?

Answer 20

CO2, ATP, NADPH, and H+

Question 21

What are the products from the light independent reactions?

Answer 21

C3H6O3

Question 22

Why are plants green?

Answer 22

Because thats the wavelength that absorbs the least.

Question 23

Trace the movement of electrons in linear electron flow.

Answer 23

1. Light energy is absorbed by chlorophyll molecules in Photosystem II (PSII), leading to the excitation of electrons.
2. Excited electrons are then transferred through a series of protein complexes in the thylakoid membrane called the electron transport chain (ETC). As the electrons move through the ETC, they release energy, which is used to pump protons across the membrane, creating a proton gradient.
3. The electrons eventually reach Photosystem I (PSI), where they are re-energized by another photon of light energy.
4. Finally, the energized electrons are transferred to NADP+ along with protons, reducing it to NADPH, which is used in the Calvin cycle to produce carbohydrates.

Question 24

Trace the movement of electrons in cyclic electron flow.

Answer 24

1. Light energy is absorbed by chlorophyll molecules in PSI, exciting electrons to a higher energy state.
2. These energized electrons are then transferred through a series of electron carriers within PSI, releasing energy along the way.
3. They return to the chlorophyll molecule in PSI, completing a cycle and generating ATP through the establishment of a proton gradient across the thylakoid membrane.

Question 25

Describe the similarities and differences between oxidative phosphorylation in mitochondria and photophosphorylation in chloroplasts.

Answer 25

Oxidative phosphorylation and photophosphorylation both involve the generation of ATP through chemiosmosis and electron transport chains, BUT they occur in different organelles (mitochondria vs. chloroplasts), use different energy sources (electron donors), and have different end products (water vs. oxygen).

Question 26

Describe the role of ATP and NADPH in the Calvin cycle.

Answer 26

ATP and NADPH produced during the light-dependent reactions of photosynthesis are used as energy and reducing power, respectively, in the Calvin cycle to convert CO2 into organic molecules such as G3P, which can be further processed to produce glucose and other carbohydrates.