AP bio quiz

What is the plasma membrane?

The selectively permeable boundary separating a cell's interior from its external environment.

What is the plasma membrane primarily made of?

A phospholipid bilayer with associated proteins and other molecules.

What does amphipathic mean?

Having both hydrophilic and hydrophobic regions, as phospholipids do.

What are the main parts of a phospholipid?

A polar phosphate-containing head, a glycerol backbone, and two nonpolar fatty acid tails.

Why is the phospholipid head hydrophilic?

Its phosphate-containing region is polar/charged and interacts with water.

Why are fatty acid tails hydrophobic?

Their mostly carbon-hydrogen bonds are relatively nonpolar and do not interact favorably with water.

How are phospholipids arranged in a bilayer?

Hydrophilic heads face the aqueous environments on both sides; hydrophobic tails point inward toward one another.

Why do phospholipids spontaneously form bilayers in water?

Their heads interact with water while their tails avoid water, producing a stable two-layer arrangement.

How does phospholipid structure cause selective permeability?

The nonpolar interior slows or blocks most ions and large polar substances, but small nonpolar molecules cross readily.

What does selectively permeable mean?

A membrane permits certain substances to cross more readily than others based on their properties and available transport proteins.

What is the fluid mosaic model?

A dynamic phospholipid bilayer in which lipids and many proteins can move laterally; it contains diverse components.

What does "fluid" mean in fluid mosaic?

Membrane components can move laterally and the membrane can bend and shift.

What does "mosaic" mean in fluid mosaic?

The membrane contains many different molecules, including proteins, lipids, and carbohydrates.

Why can membranes remain flexible?

Weak hydrophobic interactions allow phospholipids to move while the bilayer stays together.

What is the difference between saturated and unsaturated fatty acid tails?

Saturated tails lack carbon-carbon double bonds and pack more tightly; cis-unsaturated tails have double-bond kinks that disrupt packing.

How do unsaturated fatty acid tails affect fluidity in the cold?

Their kinks prevent tight packing and help the membrane stay fluid.

How does winter wheat tolerate cold through membrane composition?

It increases unsaturated phospholipids so kinked tails maintain fluidity at low temperatures.

How does cholesterol affect membrane fluidity at high temperature?

It restrains excessive phospholipid movement, reducing fluidity.

How does cholesterol affect membrane fluidity at low temperature?

It prevents tight phospholipid packing, helping the membrane avoid solidifying.

What overall role does cholesterol play in membranes?

It buffers membrane fluidity across temperature changes.

What membrane adaptation was noted for bacteria living in hot springs?

Specialized or unusual membrane lipids help maintain membrane stability in high heat.

What are integral membrane proteins?

Proteins embedded in the phospholipid bilayer; some cross the entire membrane.

What is a transmembrane protein?

An integral protein spanning the lipid bilayer at least once, contacting both sides of the membrane.

What are peripheral membrane proteins?

Proteins attached to the membrane surface rather than embedded in its hydrophobic core.

How do integral and peripheral proteins differ?

Integral proteins are embedded in the bilayer; peripheral proteins associate with its surface.

What determines whether a protein region is hydrophilic or hydrophobic?

The polarity or charge of its amino acid side chains (R groups).

Where are hydrophobic regions of a transmembrane protein typically located?

Facing the phospholipid fatty acid tails within the membrane interior.

Where are hydrophilic regions of a channel protein typically located?

Lining the water-filled pore and facing the aqueous environments.

Why can membrane transport fail if a protein folds incorrectly?

Its shape and pore or binding site may be altered, preventing normal movement of its target substance.

What are major functions of membrane proteins?

Transport, signaling, enzyme activity, cell recognition, cell adhesion, and attachment to the extracellular matrix.

How do membrane proteins function as enzymes?

They catalyze chemical reactions at or near the membrane.

How do receptor proteins help cell signaling?

They bind signals and trigger responses inside the cell.

How do membrane proteins help tissues form?

They connect neighboring cells or anchor cells to the extracellular matrix.

How does the extracellular matrix relate to membrane proteins?

Membrane proteins anchor cells to the matrix, helping maintain shape and tissue stability.

What are membrane carbohydrates mainly used for?

Cell-to-cell identification and recognition, including during development and immune recognition.

What is a glycolipid?

A membrane lipid bonded to a carbohydrate.

What is a glycoprotein?

A membrane protein bonded to a carbohydrate; glycoproteins are common in cell recognition.

Why are blood transfusions type-specific?

Red blood cells display surface antigens that the recipient's immune system can recognize as compatible or foreign.

What is one likely function of the labeled peripheral protein C?

Cell signaling or structural support.

What is one likely function of the labeled integral protein E?

Transporting specific substances across the membrane.

Which molecules cross the lipid bilayer most easily?

Small nonpolar molecules such as O2, CO2, and N2, and other hydrophobic molecules.

Why do gases such as oxygen and carbon dioxide diffuse through membranes?

They are small and nonpolar, so they can dissolve in the lipid bilayer.

Can large polar molecules cross the bilayer directly?

Generally no; they usually require membrane transport proteins.

Can charged molecules or ions cross the bilayer directly?

Not readily; the hydrophobic interior makes direct passage energetically unfavorable.

Can small uncharged polar molecules cross the bilayer?

Some, such as water, pass slowly; channels can greatly increase transport rates.

What do aquaporins do?

Provide channels that speed water movement across membranes.

Why are hydrophobic molecules relatively membrane-permeable?

They interact favorably with the bilayer's nonpolar interior.

What is simple diffusion?

Net movement down a concentration gradient directly through the membrane without ATP or transport proteins.

What is facilitated diffusion?

Passive movement down a concentration or electrochemical gradient through a channel or carrier protein.

What is active transport?

Energy-dependent transport of a substance against its concentration or electrochemical gradient.

Which processes do not directly require ATP: simple diffusion, facilitated diffusion, or active transport?

Simple and facilitated diffusion are passive; active transport requires an energy source.

What happens at diffusion equilibrium?

Molecules still move randomly in both directions, but there is no net movement.

What is a concentration gradient?

A difference in a substance's concentration across a distance or membrane.

Why are concentration gradients important?

They can drive passive movement, while cells use selective permeability and transport to maintain them.

In the "use only 5 ATP" glucose strategy, what was the principle?

Let glucose move down its gradient by passive transport as much as possible, and spend energy only on movement against the gradient; passive transport itself uses no ATP.

What is osmosis?

Net movement of water across a selectively permeable membrane toward the side with higher effective solute concentration.

What happens to an animal cell in a hypotonic solution?

Water enters; the cell swells and may lyse.

What happens to an animal cell in a hypertonic solution?

Water exits; the cell shrinks.

What happens in an isotonic solution?

Water moves both ways with no net movement or change in cell volume.

How do diffusion and osmosis differ?

Diffusion refers to particle movement down a gradient; osmosis specifically refers to water movement across a selectively permeable membrane.

Why do plant cells have cell walls?

They provide shape, support, protection, and resistance to osmotic swelling.

Which organisms in the notes have cell walls?

Plants, fungi, bacteria, and archaea; animal cells lack cell walls.

What is the main structural material of plant cell walls?

Cellulose.

How does a cell wall differ from a plasma membrane?

The wall is a rigid supportive layer outside the membrane; the plasma membrane is the main selectively permeable boundary.

What are plasmodesmata?

Channels through plant cell walls connecting adjacent cells' cytoplasm.

What is osmotic lysis?

Cell bursting due to excessive water entry; a cell wall helps resist it.

Why are most cells small?

Smaller cells have a higher surface-area-to-volume ratio and can exchange materials efficiently relative to their needs.

What is the surface-area-to-volume (SA:V) ratio?

Cell surface area divided by its internal volume.

How does SA:V change as a cell gets bigger?

It decreases because volume grows faster than surface area.

Why does volume increase faster than surface area?

For similar shapes, surface area scales with length squared while volume scales with length cubed.

What is the surface area of a cube with side length s?

SA = 6s².

What is the volume of a cube with side length s?

V = s³.

What is the SA:V ratio of a cube with side length s?

6s²/s³ = 6/s.

What is the surface area of a rectangular prism?

SA = 2(lw + lh + wh).

What is the volume of a rectangular prism?

V = l × w × h.

What is the surface area of a sphere?

SA = 4πr².

What is the volume of a sphere?

V = (4/3)πr³.

What is the SA:V ratio of a sphere?

3/r.

What happens to a cube's SA:V ratio when its side length is halved?

It doubles, because SA:V = 6/s.

Does a large cube have more total surface area than a small cube?

Yes, but its surface-area-to-volume ratio is lower.

Compared with a bacterium, how does a whale's surface area and SA:V ratio differ?

The whale has vastly more total surface area, but a much lower SA:V ratio.

Why does a high SA:V ratio improve nutrient and waste exchange?

There is more exchange surface for each unit of internal volume that needs resources and waste removal.

What happens if a cell's interior cannot get sufficient nutrients or remove wastes?

Its functions become impaired and it may die.

How do specialized folds improve exchange?

They increase membrane surface area without proportionally increasing internal volume.

What are microvilli and why are they useful?

Small surface projections that increase absorptive surface area, especially in intestinal cells.

How can eukaryotic cells function at larger sizes than many prokaryotic cells?

Compartmentalized organelles, membrane folds, specialized shapes, and transport systems improve cellular efficiency.

What is compartmentalization?

Membrane-bound organelles create specialized internal spaces for different cellular processes.

Why are intestinal cells shaped with many microvilli?

To maximize surface area for nutrient absorption.

How does the shape of a red blood cell help it function?

Its biconcave shape provides high surface area and a short diffusion distance for gas exchange.

How do nerve-cell shapes support signaling?

Long axons carry signals over distances, while branching dendrites receive input from many cells.

How do flattened skin cells support function?

Tightly packed flattened cells create a protective barrier that limits water loss.

How do stomach-lining cell specializations support function?

They enable secretion of mucus or digestive substances and help protect the stomach lining.

How do rod and cone cells' structures aid vision?

Membrane discs create more area for light-sensitive proteins that detect light and initiate signals.

How can large leaves support photosynthesis?

Their greater surface area can capture more sunlight, though water, CO2, and other conditions also matter.

How do mitochondrial membrane folds help cells?

They increase inner-membrane area for reactions involved in energy production.

Why can flatworms exchange gases without a specialized respiratory transport system?

Their thin, flattened bodies provide a high SA:V ratio and short diffusion distances.

What is metabolic rate?

The rate at which an organism uses energy.

Why do small warm-blooded animals often use more energy per unit mass?

Their high SA:V ratio causes relatively rapid heat loss, requiring more energy to maintain body temperature.

What is heat or thermal exchange?

Transfer of thermal energy between an organism and its surroundings.

Why do small organisms generally lose heat faster relative to body size?

They have more exposed surface area per unit volume.