Photosynthesis Lecture Notes Review

These flashcards cover essential concepts from the photosynthesis lecture, including the differences between autotrophs and heterotrophs, key equations, and processes within chloroplasts relevant to the study of photosynthesis.

What does photosynthesis convert into chemical energy?

Solar energy.

What are autotrophs?

Organisms that sustain themselves without eating anything derived from other organisms.

How do heterotrophs obtain their organic material?

From other organisms.

What is the equation for photosynthesis?

6CO2 + 6H2O + Light energy → 6O2 + C6H12O6.

Where do plants obtain the reactants for photosynthesis?

From air (CO2) and soil (H2O).

What are the products of photosynthesis used for?

In cellular respiration to make ATP.

What are chloroplasts associated with?

They are sites of photosynthesis in plants.

What pigment gives leaves their green color?

Chlorophyll.

Define the light reactions in photosynthesis.

They split H2O, release O2, reduce NADP+ to NADPH, and generate ATP from ADP.

What do the light reactions produce?

ATP and NADPH.

What happens to electrons in the light reactions?

They are transferred through an electron transport chain.

What is the role of rubisco in the Calvin cycle?

Catalyzes the initial fixation of CO2.

What are the three phases of the Calvin cycle?

Carbon fixation, reduction, and regeneration of RuBP.

What are C4 plants?

Plants that minimize photorespiration by incorporating CO2 into four-carbon compounds.

What does CAM stand for in plants?

Crassulacean acid metabolism.

Why do plants undergo photorespiration?

Because on hot, dry days, they close stomata, limiting CO2 access.

What are the by-products of splitting water in photosynthesis?

Oxygen gas and hydrogen ions.

What is the primary pigment involved in photosynthesis?

Chlorophyll a.

What is the main purpose of cyclic electron flow?

To generate surplus ATP without producing NADPH or releasing oxygen.

How does the Calvin cycle function?

It uses ATP and NADPH to convert CO2 into sugars.

What happens to excess sugar produced from photosynthesis?

It's stored as starch.

What are the disc-like sacs within chloroplasts?

Thylakoids.

Stacks of thylakoids are called?

Grana.

What is the fluid-filled space surrounding the thylakoids called?

Stroma.

Where do the light reactions occur within the chloroplast?

Thylakoid membranes.

Where does the Calvin cycle occur?

Stroma.

What is the space inside the thylakoid called?

Thylakoid lumen.

What are the two types of photosystems in the thylakoid membrane?

Photosystem II (PSII) and Photosystem I (PSI).

What is the reaction-center chlorophyll of PSII called?

P680.

What is the reaction-center chlorophyll of PSI called?

P700.

What happens to an electron when chlorophyll absorbs light energy?

It gets excited to a higher energy level.

What is the first step in the light reactions after light absorption?

Excited electrons are captured by a primary electron acceptor.

What is the primary pathway of electron flow in the light reactions?

Linear electron flow.

What replaces the electrons lost by P680 in PSII?

Electrons from the splitting of water (H_2O).

What replaces the electrons lost by P700 in PSI?

Electrons from the electron transport chain coming from PSII.

What is the process of ATP synthesis in the light reactions called?

Photophosphorylation.

How is ATP generated during the light reactions?

By chemiosmosis.

What is established across the thylakoid membrane to drive ATP synthesis?

A proton gradient.

What enzyme synthesizes ATP using the proton gradient?

ATP synthase.

What are accessory pigments?

Pigments that absorb light at different wavelengths and pass energy to chlorophyll a.

Give examples of accessory pigments.

Chlorophyll b and carotenoids.

What is the function of carotenoids?

Broaden the spectrum of colors that can drive photosynthesis and provide photoprotection.

What does an absorption spectrum show?

The range of a pigment's ability to absorb various wavelengths of light.

What does an action spectrum show?

The relative effectiveness of different wavelengths of light in driving photosynthesis.

What is the initial 3-carbon sugar produced in the Calvin cycle?

Glyceraldehyde-3-phosphate, or G3P.

How many molecules of CO_2 are required to produce one molecule of G3P?

3 molecules of CO_2.

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

9 ATP and 6 NADPH.

What molecule is regenerated in the final phase of the Calvin cycle?

RuBP - Ribulose-1,5-bisphosphate.

What is the enzyme that initially fixes CO_2 in C4 plants?

PEP carboxylase.

Where does CO_2 fixation occur in C4 plants?

Mesophyll cells.

Where does the Calvin cycle occur in C4 plants?

Bundle-sheath cells.

What is the main advantage of C4 photosynthesis in hot, arid climates?

Minimizes photorespiration and water loss.

How do CAM plants adapt to arid conditions?

Open stomata at night to take in CO_2, close during the day to conserve water.

When do CAM plants perform carbon fixation and the Calvin cycle?

Carbon fixation at night, Calvin cycle during the day.

What is the disadvantage of C3 plants in hot, dry conditions?

They undergo photorespiration and lose efficiency.

What are the two main stages of photosynthesis?

Light reactions and Calvin cycle.

What happens to light energy during photosynthesis?

It is converted into chemical energy in ATP and NADPH.

What is the role of stomata?

Pores on leaves through which CO2 enters and O2 exits, also water vapor release.

How does light intensity affect photosynthesis?

Up to a certain point, increased light intensity increases the rate of photosynthesis.

How does CO_2 concentration affect photosynthesis?

Increased CO_2 concentration increases the rate of photosynthesis, up to a certain saturation point.

What is visible light in the context of photosynthesis?

The segment of the electromagnetic spectrum that powers photosynthesis, ranging from 380 to 750 nm in wavelength.

What is a photon?

A discrete particle of light energy with a fixed quantity of energy.

What happens when a pigment molecule absorbs a photon?

One of the pigment's electrons is elevated to an orbital where it has more potential energy.

What is the primary function of the light-harvesting complex in a photosystem?

To capture light energy and transfer it to the reaction-center complex.

What is found at the reaction-center complex of a photosystem?

A pair of chlorophyll a molecules and a primary electron acceptor.

How is the energy from light transferred within a photosystem?

Pigment molecules transfer the energy of absorbed photons to the reaction-center chlorophyll a molecules.

What is released when an excited electron falls back to its ground state?

Heat and/or light (fluorescence).

What is the role of the primary electron acceptor in a reaction-center complex?

It captures the excited electron from the reaction-center chlorophyll a before it can fall back to its ground state.

What is the specific wavelength of light best absorbed by the reaction-center chlorophyll a of Photosystem II (PSII)?

680 nanometers (P680).

What is the specific wavelength of light best absorbed by the reaction-center chlorophyll a of Photosystem I (PSI)?

700 nanometers (P700).

What is the path of electrons in noncyclic (linear) electron flow?

From H_2O to PSII, then via electron transport chain to PSI, and finally to NADP+.

What is the final electron acceptor in the light reactions (linear electron flow)?

NADP+, which is reduced to NADPH.

What is an electron transport chain (ETC) in photosynthesis?

A series of protein complexes that transfer electrons between PSII and PSI, releasing energy used to pump protons.

Name the components of the electron transport chain between PSII and PSI.

Plastoquinone (Pq), a cytochrome complex, and plastocyanin (Pc).

What is the source of electrons for Photosystem II?

The splitting of water molecules (H_2O).

What happens to the oxygen atoms from split water molecules in the thylakoid lumen?

They combine to form O_2 gas, which is released.

Where do the protons (H^+) from water splitting accumulate?

In the thylakoid lumen, contributing to the proton gradient.

What is the difference in electron donors between cyclic and linear electron flow?

Linear flow uses electrons from water, while cyclic flow recycles electrons within PSI.

What is the primary output of cyclic electron flow?

ATP, but no NADPH or O_2 is produced.

Why might plants use cyclic electron flow?

To produce additional ATP needed for the Calvin cycle, as the Calvin cycle consumes more ATP than NADPH.

What drives the chemiosmosis for ATP synthesis in chloroplasts?

The diffusion of protons (H^+) from the thylakoid lumen to the stroma through ATP synthase.

What is the proton-motive force in the context of chemiosmosis in chloroplasts?

The energy stored in the form of a proton (H^+) electrochemical gradient across the thylakoid membrane.

In what way is ATP synthase similar in chloroplasts and mitochondria?

Both use the flow of protons down their concentration gradient to power ATP synthesis.

What is the initial product of carbon fixation in the Calvin cycle?

An unstable 6-carbon intermediate that immediately splits into two molecules of 3-phosphoglycerate (3-PGA).

In the reduction phase of the Calvin cycle, what molecules are used to convert 3-PGA to G3P?

ATP (for phosphorylation) and NADPH (for reducing power).

For every 3 molecules of CO_2 fixed, how many molecules of G3P are produced, and how many exit the cycle?

Six molecules of G3P are produced, but only one exits the cycle for sugar synthesis. The other five are used to regenerate RuBP.

What happens to the G3P molecule that leaves the Calvin cycle?

It is used to synthesize glucose, sucrose, or other organic compounds.

How is RuBP regenerated in the Calvin cycle?

Five molecules of G3P are rearranged into three molecules of RuBP, consuming ATP.

What is phosphoglycolate?

A two-carbon compound produced when rubisco binds O2 instead of CO2 during photorespiration.

Which organelles are involved in photorespiration?

Chloroplasts, peroxisomes, and mitochondria.

What is the main drawback of photorespiration for C3 plants?

It consumes ATP and releases CO_2 without producing sugar, thus reducing photosynthetic output.

What is the initial 4-carbon compound formed in C4 photosynthesis?

Oxaloacetate.

How do C4 plants concentrate CO_2 around rubisco?

They pump CO2 from mesophyll cells into bundle-sheath cells, maintaining high CO2 levels where the Calvin cycle occurs.

What transports the 4-carbon compound from mesophyll cells to bundle-sheath cells in C4 plants?

The 4-carbon compound (e.g., malate, aspartate) is transported.

What happens to the 4-carbon compound once it reaches the bundle-sheath cells in C4 plants?

It releases CO_2, which is then used by rubisco in the Calvin cycle.

How do CAM plants temporally separate carbon fixation and the Calvin cycle?

They fix CO2 into organic acids at night and release CO2 from these acids during the day for the Calvin cycle.

What is a key anatomical distinction of C4 plants that aids in their photosynthetic efficiency?

Their bundle-sheath cells are arranged in tightly packed sheaths around the veins of the leaf (Kranz anatomy).

What is an example of an organism that performs photosynthesis?

Plants, algae, cyanobacteria.

What are the major evolutionary advantages of photosynthesis?

Formation of oxygen atmosphere, basis of most food webs, and conversion of light energy to chemical energy.

What is the relationship between cellular respiration and photosynthesis?

Photosynthesis produces oxygen and glucose, which are inputs for cellular respiration, while cellular respiration produces carbon dioxide and water, which are inputs for photosynthesis.