Biology-111 Unit 2 Exam Key Terms

What is the fluid mosaic model?

The cell membrane is a flexible phospholipid bilayer with proteins embedded in it.

Why is it called “fluid”?

Phospholipids and some proteins can move sideways within the membrane.

Why is it called a “mosaic”?

Because the membrane contains various proteins and lipids that create a diverse and patchwork-like appearance.

Who proposed the fluid mosaic model, and when?

The fluid mosaic model was proposed by S.J. Singer and Garth Nicolson in 1972.

What is the cell membrane mainly made of?

A phospholipid bilayer and proteins.

What are the two parts of a phospholipid?

Hydrophilic head (attracted to water) and hydrophobic tails (repelled by water).

What do membrane proteins do?

Transport substances, receive signals, identify cells, and help cells attach.

What is simple diffusion?

Movement of molecules from high to low concentration directly through the membrane.

Does simple diffusion require energy?

No

What is facilitated diffusion?

Movement from high to low concentration through a membrane protein.

Does facilitated diffusion require energy?

No

What is the difference between simple and facilitated diffusion?

Simple diffusion passes through the lipid bilayer; facilitated diffusion uses a protein.

What do channel proteins do?

Form passageways that allow specific substances to cross the membrane.

What do carrier proteins do?

Bind to specific substances and change shape to move them across the membrane.

What is osmosis?

The net movement of water across a selectively permeable membrane.

What is a selectively permeable membrane?

A membrane that allows some substances through but restricts others.

What is passive transport?

Movement across a membrane without cellular energy, usually down a concentration gradient.

What is active transport?

Movement against a concentration gradient using energy.

What is the main energy source for active transport?

ATP

What is the difference between passive and active transport?

Passive transport does not require energy; active transport does.

What is bulk transport?

Movement of large materials into or out of a cell using vesicles.

What is endocytosis?

The cell brings materials in by forming a vesicle from its membrane.

What is exocytosis?

A vesicle fuses with the cell membrane and releases materials outside the cell.

What is a vesicle?

A small, membrane-bound sac that transports or stores materials.

What is a hypotonic solution?

Lower solute concentration outside the cell than inside; water tends to enter the cell.

What happens to an animal cell in a hypotonic solution?

It swells and may burst.

What is a hypertonic solution?

Higher solute concentration outside the cell than inside; water tends to leave the cell.

What happens to an animal cell in a hypertonic solution?

It shrinks.

What is an isotonic solution?

Equal solute concentrations on both sides; there is no net water movement.

What happens to an animal cell in an isotonic solution?

It generally stays the same size.

How does water move during osmosis?

Toward the side with the higher solute concentration, assuming the solute cannot cross the membrane.

What is a prokaryotic cell?

A cell without a nucleus or other membrane-bound organelles.

What is a eukaryotic cell?

A cell with a nucleus and membrane-bound organelles.

Which organisms are prokaryotes?

Bacteria and archaea.

Which organisms are eukaryotes?

Animals, plants, fungi, and protists.

Where is DNA found in a prokaryotic cell?

In the nucleoid region of the cytoplasm.

What is the endosymbiotic theory?

Mitochondria and chloroplasts originated from bacteria that were engulfed by an ancestral cell and lived inside it.

What evidence supports endosymbiotic theory?

Both organelles have their own DNA, ribosomes, and double membranes; they also divide in ways similar to bacteria.

What is the main function of mitochondria?

Produce most of a eukaryotic cell's ATP through cellular respiration.

What is the main function of chloroplasts?

Convert light energy into chemical energy during photosynthesis.

Which cells typically contain chloroplasts?

Plants and algae.

What are cristae?

Folds of the inner mitochondrial membrane where the electron transport chain and ATP synthase are located.

What is the mitochondrial matrix?

The innermost compartment of a mitochondrion, where pyruvate oxidation and the citric acid cycle occur.

What is the stroma?

The fluid inside a chloroplast where the Calvin cycle occurs.

What are thylakoids?

Membrane sacs inside chloroplasts where the light-dependent reactions occur.

What is a granum?

A stack of thylakoids.

What is ATP?

The cell's main energy-carrying molecule.

What happens when ATP is converted to ADP?

A phosphate is removed, releasing usable energy.

What is oxidation?

Loss of electrons.

What is reduction?

Gain of electrons.

What is a redox reaction?

A reaction in which electrons are transferred; oxidation and reduction occur together.

What is NADH?

An electron carrier that delivers high-energy electrons to the cellular respiration electron transport chain.

What is FADH₂?

An electron carrier that delivers high-energy electrons to the electron transport chain.

What is the role of oxygen in cellular respiration?

It is the final electron acceptor in the electron transport chain.

What happens to energy during cellular respiration?

Energy from glucose is transferred into ATP, with some energy released as heat.

What is cellular respiration?

The process of breaking down fuel molecules, such as glucose, to produce ATP.

What is the overall equation for aerobic cellular respiration?

Glucose + oxygen → carbon dioxide + water + ATP.

What are the three main stages of cellular respiration?

Glycolysis, citric acid cycle, and oxidative phosphorylation.

Where does glycolysis occur?

Cytoplasm (cytosol).

What happens during glycolysis?

One glucose molecule is split into two pyruvate molecules.

What are the net products of glycolysis per glucose?

2 pyruvate, 2 ATP, and 2 NADH.

Does glycolysis require oxygen?

No

What happens between glycolysis and the citric acid cycle?

Pyruvate is converted to acetyl-CoA, producing NADH and releasing CO₂.

Where does pyruvate oxidation occur in eukaryotes?

Mitochondrial matrix.

Where does the citric acid cycle occur?

Mitochondrial matrix.

What happens during the citric acid cycle?

Acetyl-CoA is broken down, releasing CO₂ and producing electron carriers and a small amount of ATP.

What are the products of the citric acid cycle per glucose?

4 CO₂, 6 NADH, 2 FADH₂, and 2 ATP (or equivalent GTP).

Where does oxidative phosphorylation occur?

Inner mitochondrial membrane.

What are the two parts of oxidative phosphorylation?

Electron transport chain and chemiosmosis.

What does ETC stand for?

Electron transport chain.

What does the electron transport chain do?

Uses energy from electrons to pump protons across the inner mitochondrial membrane.

What happens to NADH and FADH₂ in the ETC?

They donate electrons and are converted back into NAD⁺ and FAD.

What is chemiosmosis?

Protons flow down their electrochemical gradient through ATP synthase, helping produce ATP.

What does ATP synthase do?

Uses the energy of proton flow to make ATP from ADP and phosphate.

Why is oxygen necessary for aerobic respiration?

It accepts electrons at the end of the ETC, allowing electron flow to continue.

What happens when oxygen is unavailable?

The aerobic ETC cannot continue normally; cells may use fermentation or other pathways, depending on the organism.

What is fermentation?

A process that regenerates NAD⁺ so glycolysis can continue without relying on an oxygen-powered ETC.

What are the two common types of fermentation?

Lactic acid fermentation and alcoholic fermentation.

What does lactic acid fermentation produce?

Lactate and regenerated NAD⁺; it yields no additional ATP beyond glycolysis.

What does alcoholic fermentation produce?

Ethanol, CO₂, and regenerated NAD⁺; it yields no additional ATP beyond glycolysis.

What is anaerobic respiration?

Respiration that uses an electron transport chain with a final electron acceptor other than oxygen.

How is anaerobic respiration different from fermentation?

Anaerobic respiration uses an ETC; fermentation does not.

How much ATP is made per glucose in aerobic cellular respiration?

Commonly about 30–32 ATP in eukaryotic cells, though the exact yield can vary.

What is photosynthesis?

The process of converting light energy into chemical energy stored in sugars.

What is the overall equation for photosynthesis?

Carbon dioxide + water + light energy → sugar + oxygen.

Where does photosynthesis occur?

In chloroplasts in plants and algae.

What are the two main stages of photosynthesis?

Light-dependent reactions and the Calvin cycle.

What does it mean to harvest photons?

Pigments absorb packets of light energy.

What is chlorophyll?

A pigment that absorbs light energy for photosynthesis.

What is chlorophyll a?

The primary photosynthetic pigment that directly participates in the reaction-center energy conversion.

What is chlorophyll b?

An accessory pigment that absorbs additional wavelengths and transfers energy to chlorophyll a.

Where do the light-dependent reactions occur?

Thylakoid membranes.

What happens during the light-dependent reactions?

Light energy drives electron movement, water is split, oxygen is released, and ATP and NADPH are produced.

Why is water split during photosynthesis?

To supply electrons and protons; oxygen is released as a byproduct.

What are the products of the light-dependent reactions?

ATP, NADPH, and O₂.

What is photolysis?

The splitting of water using light energy during photosynthesis.

What is the role of ATP in photosynthesis?

Supplies energy for the Calvin cycle.

What is the role of NADPH in photosynthesis?

Supplies high-energy electrons for sugar production.

What is carbon fixation?

Incorporating inorganic CO₂ into an organic molecule.

What is the Calvin cycle?

A series of reactions that uses CO₂, ATP, and NADPH to produce G3P, a molecule used to build sugars.