AP Biology Exam Review: Cellular Energetics

During respiration, most ATP is formed as a direct result of the net movement of

Protons (hydrogen ions) down a concentration gradient

According to the chemiosmotic theory (chemiosmotic coupling), the energy required to move protons from the mitochondrial matrix to the intermembrane space against a concentration gradient comes most directly from

Electrons flowing along the electron transport chain

Where do high energy electrons come from in cell respiration?

NADH and FADH2

In what process is O2 released as a by-product of oxidation-reduction reactions

Light-dependent reactions of photosynthesis

What is photolysis?

The splitting of a water molecule using light energy

How is oxygen released in the beginning of the light-dependent reactions?

Through the stomata

In what process is CO2 released as a by-product of oxidation-reduction reactions?

The Krebs Cycle

In what process is carbon from CO2 incorporated into organic molecules?

Calvin cycle (light-independent reactions of photosynthesis)

How does cell respiration effect pH?

pH is more acidic (lower)

What is photophosphorylation?

Adding phosphate to a molecule using light

What is photosynthesis?

The process that converts solar energy into chemical energy

What are autotrophs?

Organisms that produce their own food

What are heterotrophs?

Organisms that obtain food by consuming other living things

Where do carbon dioxide and oxygen enter and exit a leaf?

The stomata

What is the stomata?

Small holes in a leaf that allow gas exchange to occur

How many chloroplasts does a typical mesophyll cell have?

30-40

Where is chlorophyll stored?

Thylakoid membrane

What is stroma?

Fluid portion of the chloroplast; outside of the thylakoids

What are thylakoids?

Saclike photosynthetic membranes found in chloroplasts

What is the equation for photosynthesis?

6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2

What is the equation for cellular respiration?

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + ATP

What does the splitting of water allow to happen?

Hydrogen electrons are incorporated into sugar molecules

What is a redox reaction?

A chemical reaction that transfers electrons

Photosynthesis is a redox process where what is oxidized and what is reduced?

Water is oxidized and carbon dioxide is reduced

What occurs in the light reactions of photosynthesis?

Water is split, oxygen is released, NADP+ is reduced to NADPH, and ATP is generated from ADP by photophosphorylation

Where does photosynthesis occur?

Chloroplast

Where does the Calvin Cycle occur?

Stroma of the chloroplast

How does the Calvin Cycle begin?

Carbon fixation, incorporating CO2 into organic molecules

What do the light reactions convert?

Solar energy to the chemical energy of ATP and NADPH

What is the electromagnetic spectrum?

The entire range of electromagnetic energy or radiation

Photosynthesis is a series of what kind of reactions?

Anabolic

Cell respiration is a series of what kind of reactions?

Catabolic

Is photosynthesis aerobic?

No

Is cell respiration aerobic?

Yes

What does glucose get oxidized into in photosynthesis?

6CO2

What does 6O2 get reduced into in photosynthesis?

6H2O

What is Chlorophyll a?

Main photosynthetic (light capturing) pigment

What are accessory pigments?

Chlorophyll b and carotenoids which absorb light and transfer it downward to the primary pigment (chlorophyll a) reaction center

What does chlorophyll b do?

Broadens the spectrum used for photosynthesis

What do caretenoids do?

Absorb excessive light that would damage chlorophyll

What is a photosystem?

A cluster of pigments and proteins that work together to capture light energy

What do light harvesting complexes in photosystems do?

Funnel energy from photons into reaction center

Explain the first step of the light reactions

1. A photosystem consisting of a reaction-center complex surrounded by light-harvesting complexes is present

2. The light-harvesting complexes (pigment molecules bound to proteins) funnel the energy of photons to the reaction center

3. A primary electron acceptor in the reaction center accepts an excited electron from chlorophyll a

4. An electron from a chlorophyll molecule is transferred via solar power to the primary electron acceptor

How does linear electron flow during the light reactions generate ATP and NADPH?

The passing of an electron from the primary electron acceptor of photosystem 2 to photosystem 1 puts out ATP, and the addition of electrons to NADP+ reduce it into NADPH

Where are the photosystems located?

Embedded in the thylakoid membrane

What is the concentration of H+ ions in the thylakoid space compared to the stroma?

The thylakoid has a high concentration of H+ ions while the stroma has a low concentration of H+ ions

Where do the ATP and NADPH produced during the light-dependent reactions go when the process is complete?

The Calvin Cycle

How is the Calvin Cycle similar to the Citric Acid Cycle

It regenerates its starting material after molecules enter and leave the cycle

What does the Calvin Cycle build?

Sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH

How is carbon converted during the Calvin Cycle?

It enters as CO2 and leaves as glyceraldehyde-3-phosphate (G3P)

How many times must the Calvin Cycle occur for net synthesis of 1 G3P?

3 times

What are the 3 phases of the Calvin Cycle?

-Carbon fixation (catalyzed by rubisco)

-Reduction

-Regeneration of the CO2 acceptor (RuBP)

What is photorespiration?

A respiratory process in many higher plants by which they take up oxygen in the light and give out some carbon dioxide, contrary to the general pattern of photosynthesis. (Oxygen is put into the Calvin Cycle rather than photosynthesis and CO2 is omitted without producing ATP or Sugar)

What does photorespiration limit?

Damaging products of light reactions that build up in the absence of the Calvin cycle

Why is photorespiration a problem for a plant?

It can drain as much as 50% of the carbon fixed by the Calvin Cycle

What is a C4 plant?

A plant in which the Calvin cycle is preceded by reactions that incorporate CO2 into a four-carbon compound, the end product of which supplies CO2 for the Calvin cycle ( Requires enzyme PEP carboxylase which has a higher affinity for CO2 than Rubisco, meaning it can fix CO2 even when CO2 concentrations are low)

When C4 plants go through photo respiration where are there 4 carbon compounds exported?

Bundle-sheath cells

What are CAM plants?

Plants that open their stomata during the night and close them during the day

What is fermentation?

A partial degradation of sugars that occurs without O2

What is aerobic respiration?

Consumes organic molecules and O2 and yields ATP

What is anaerobic respiration?

Consumes organic molecules and compounds other than oxygen and yields ATP

What does the transfer of electrons during chemical reactions do?

Release energy stored in organic molecules which is ultimately used to synthesize ATP

What is an electron donor called?

Reducing agent

What is an electron acceptor called?

Oxidizing agent

What becomes reduced in cell respiration?

Oxygen which forms CO2 and Water

What becomes oxidized in cell respiration?

"Fuel" (Glucose)

What are the 3 stages of cellular respiration?

-Glycolysis (breaks down glucose into two molecules of pyruvate)

-The citric acid cycle (completes the breakdown of glucose)

-Oxidative phosphorylation (accounts for most of the ATP synthesis)

What occurs in the link reaction?

Pyruvate loses a CO2 molecule and two hydrogens and becomes Acetate

Hydrogens accepted by NAD to form NADH.

Acetate combines with coenzyme A (CoA) to form acetyl CoA.

What accounts for almost 90% of the ATP generated by cellular respiration and where is the rest of the ATP formed?

Oxidative phosphorylation/smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation

What is glycolysis?

The breakdown of glucose into 2 molecules of pyruvate

What are the two major phases of glycolysis?

Energy investment phase and energy payoff phase

Where does glycolysis occur?

Cytoplasm

What is the net gain of glycolysis?

2 ATP, 2 NADH, 2 H2O, 2H+ ions, and 2 pyruvate molecules

Pyruvate enters the mitochondria only in the presence of what molecule?

Oxygen

What is pyruvate converted to before the citric acid cycle

Acetyl-CoA

What is produced in the link reaction?

2 NADH, 2 CO2, 2 Acetyl CoA

Where does the citric acid cycle take place?

Mitochondrial matrix

What compound is the final product of the electron transport chain?

Water

What molecule is phosphorylated during oxidative phosphorylation?

ADP

How many turns of the citric acid cycle occur for one glucose molecule?

2

Explain what occurs in the citric acid cycle

•The acetyl group of acetyl CoA joins the cycle by combining with oxaloacetate, forming citrate

•The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle

•The NADH and FADH2 produced by the cycle relay electrons extracted from food to the electron transport chain

What is produced with one turn of the citric acid cycle?

1 ATP, 3 NADH, and 1 FADH2

What is lost in the citric acid cycle?

2 CO2

What does NADH and FADH2 donating their electrons to the electron transport chain power?

ATP synthesis via oxidative phosphorylation

Where does the electron transport chain occur?

Cristae of mitochondria

Explain what occurs in the electron transport chain

Electrons are passed through multiple integral proteins, making the carriers switch between their oxidized and reduced states, eventually being passed to oxygen to form water. Electron transfer in the electron transport chain causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space. H+ then moves back across the membrane, passing through channels in ATP synthase which uses the exergonic flow of H+ to drive the phosphorylation of ATP

What does electron transfer in the electron transport chain cause?

Proteins to pump H+ from the mitochondrial matrix to the intermembrane space

What is the proton motive force?

The force provided by a transmembrane hydrogen ion gradient

How do chloroplasts and mitochondria generate ATP?

Chemiosmosis