bio mod 2 exam

What is a cell?

The smallest unit that can carry out the basic functions of life.

What are the four main ideas of cell theory?

1. Cells are the fundamental units of life. 2. All living organisms are made of cells. 3. All cells come from preexisting cells. 4. Modern cells evolved from a common ancestor.

What are the four basic features shared by all cells?

1. Cell membrane - separates inside from outside. 2. Cytoplasm - interior contents excluding the nucleus in eukaryotes. 3. Ribosomes - build proteins. 4. Genetic material - stores biological instructions, usually in DNA.

Why are most cells small?

As cells get bigger, their volume increases faster than their surface area, limiting their ability to exchange materials.

What is the surface area-to-volume ratio?

The ratio that determines how efficiently a cell can exchange materials; calculated as SA/V.

What happens to the surface area-to-volume ratio as cell size increases?

Increasing cell size decreases the SA:V ratio, leading to less membrane surface per unit of cell volume.

What are the four major functions of the cell membrane?

1. Acts as a selectively permeable barrier. 2. Maintains a stable internal environment. 3. Receives signals and enables communication. 4. Helps cells attach to neighboring cells.

What does selectively permeable mean?

The membrane allows some substances to cross more easily than others.

What is the fluid mosaic model?

A description of the cell membrane as a fluid structure with various proteins and lipids that can move laterally.

What are phospholipids?

Molecules that form the cell membrane, consisting of a hydrophilic head and hydrophobic tails.

What does amphipathic mean?

A molecule that has both a water-attracting region and a water-avoiding region.

Which molecules can cross the lipid bilayer easily?

Small, nonpolar molecules like O2, CO2, and N2.

What types of molecules generally need transport proteins to cross the membrane?

Ions and large polar molecules such as Na+, Ca2+, and glucose.

What factors influence membrane fluidity?

Temperature, fatty acid tail unsaturation, tail length, and cholesterol.

How does lower temperature affect membrane fluidity?

It decreases fluidity as phospholipids move less and pack more tightly.

How does higher temperature affect membrane fluidity?

It increases fluidity as phospholipids move more freely.

What is the role of ribosomes in a cell?

They build proteins.

What is cytoplasm?

The interior contents enclosed by the membrane, excluding the nucleus in eukaryotic cells.

What is the genetic material in cells?

It stores biological instructions, usually in the form of DNA.

What is the significance of the cell membrane's asymmetry?

The inner and outer layers have different compositions, affecting membrane function.

Why do cells need to maintain a stable internal environment?

To ensure proper functioning and homeostasis.

What is the relationship between cell size and efficiency in material exchange?

Smaller cells have a higher SA:V ratio, allowing for more efficient exchange of materials.

What is the main role of cholesterol in the cell membrane?

To help maintain membrane fluidity.

What are the two regions of a phospholipid?

Hydrophilic head (attracted to water) and hydrophobic tails (repel water).

What is the importance of the endomembrane system?

It organizes various cellular functions and compartments within eukaryotic cells.

What is the function of aquaporin proteins?

They facilitate the movement of water across the cell membrane.

What is the significance of the evolutionary ancestry of modern cells?

It indicates that all modern cellular life shares a common origin.

What effect does higher temperature have on phospholipids?

It increases their movement.

How do cis double bonds in fatty acid tails affect membrane fluidity?

They increase fluidity by preventing tight packing.

What is the effect of longer fatty acid tails on membrane fluidity?

It usually decreases fluidity due to stronger interactions.

How do saturated fatty acid tails affect membrane fluidity?

They decrease fluidity because they pack tightly together.

What role does cholesterol play in cell membranes?

It acts as a fluidity buffer, reducing excessive fluidity at high temperatures and preventing rigidity at low temperatures.

What distinguishes the inner and outer leaflets of a membrane?

They differ in phospholipid types, cholesterol content, carbohydrates, and membrane proteins.

What are the main functions of membrane proteins?

Transporting substances, receiving signals, acting as enzymes, attaching to the cytoskeleton, helping cells join, and recognizing other cells.

What are integral membrane proteins?

Proteins that are at least partly embedded in the hydrophobic interior of the bilayer.

What are transmembrane proteins?

A type of integral protein that spans the entire membrane.

What are peripheral membrane proteins?

Proteins that associate with the membrane surface or with integral proteins through noncovalent interactions.

What are lipid-anchored proteins?

Proteins covalently linked to lipids that anchor them to the membrane.

How do carbohydrates function in cell membranes?

They act as identification labels, helping cells recognize and interact with each other.

What is diffusion?

The net movement of particles from a region of higher concentration to a region of lower concentration.

What is a concentration gradient?

A difference in concentration between two regions.

What factors affect the rate of diffusion?

Molecular size, solubility, concentration gradient, solution density, surface area, and temperature.

What is passive transport?

The movement of substances down their concentration gradient without energy input from the cell.

What is active transport?

The movement of substances against their concentration gradient, requiring energy input.

What is simple diffusion?

The direct movement of small, uncharged molecules through the phospholipid bilayer.

What is osmosis?

The net movement of water across a selectively permeable membrane.

What is facilitated diffusion?

The process that requires a transport protein but no energy to move substances down their concentration gradient.

What is primary active transport?

Transport that requires a protein and usually direct ATP use.

What is secondary active transport?

Transport that requires a protein and uses energy stored in an ion gradient.

What is tonicity?

Tonicity compares the concentration of relevant solutes in two solutions separated by a membrane.

What happens to a cell in a hypertonic solution?

Water tends to leave the cell, causing it to shrink.

What happens to a cell in a hypotonic solution?

Water tends to enter the cell, causing it to swell and potentially burst.

What is the effect of an isotonic solution on a cell?

There is no net movement of water, so the cell generally maintains its size.

How do plant cells respond in a hypotonic environment?

Water enters, and the cell becomes firm as the cell wall resists expansion.

What is the role of channel proteins in facilitated diffusion?

They form a hydrophilic passage through the membrane, allowing specific ions or small polar molecules to cross.

What is the difference between ligand-gated and voltage-gated channels?

Ligand-gated channels open or close in response to a chemical signal, while voltage-gated channels respond to changes in electrical potential.

How do carrier proteins function?

A specific molecule binds to the carrier, causing it to change shape and release the molecule on the opposite side.

What is saturation in the context of carrier proteins?

Saturation occurs when all carriers are occupied, and the transport rate plateaus.

What is an electrochemical gradient?

It combines the concentration difference of an ion across a membrane with the electrical attraction or repulsion caused by charge differences.

What does the sodium-potassium pump do?

It moves 3 sodium ions out of the cell and 2 potassium ions into the cell, using energy from one ATP molecule.

What is a symporter?

A transport protein that moves two or more substances in the same direction.

What is a uniporter?

A transport protein that transports one type of substance in one direction.

What is an antiporter?

A transport protein that transports two or more substances in opposite directions.

What does pH measure?

pH measures the hydrogen ion concentration of a solution.

What does a pH below 7 indicate?

It indicates an acidic solution with a higher concentration of hydrogen ions.

What does a pH equal to 7 indicate?

It indicates a neutral solution in the standard pure-water reference.

What does a pH above 7 indicate?

It indicates a basic solution with a lower concentration of hydrogen ions.

How does a decrease of one pH unit affect hydrogen ion concentration?

Each decrease represents a tenfold increase in hydrogen ion concentration.

What is the pH range for acidic solutions?

Below 7

What pH value indicates a neutral solution?

Equal to 7

What is the pH range for basic solutions?

Above 7

What happens to hydrogen ion concentration as pH decreases?

It increases; each decrease of one pH unit represents a tenfold increase in (H^+) concentration.

What process uses a hydrogen ion gradient to transport sucrose?

Secondary active transport

What is the main difference between prokaryotic and eukaryotic cells?

Prokaryotic cells lack a nucleus and membrane-enclosed organelles.

What occupies the region called the nucleoid in prokaryotic cells?

The main chromosome

What is a plasmid?

A small DNA molecule, often circular, separate from the main chromosome.

What is the function of a capsule in prokaryotic cells?

It helps prevent drying out and protects bacteria from immune defenses.

What is the primary function of a flagellum in bacteria?

It helps the cell move.

What is the role of the cell wall in prokaryotic cells?

It provides structural support and helps maintain cell shape.

What is compartmentalization in eukaryotic cells?

The presence of membrane-enclosed organelles that allow different processes to occur in different locations.

What is the nucleus's primary function?

It contains most of the cell's DNA and is the site of DNA replication and transcription.

What is nucleoplasm?

The material inside the nucleus.

What is chromatin?

DNA associated with proteins.

What is the nuclear envelope?

A double membrane surrounding the nucleus.

What is the endomembrane system?

A group of membranes and organelles that work together to process, modify, and transport proteins and lipids.

What is the function of the rough endoplasmic reticulum (RER)?

Protein synthesis by attached ribosomes, protein folding, and initial protein modifications.

What is the function of the smooth endoplasmic reticulum (SER)?

Lipid synthesis, detoxification, glycogen breakdown, and calcium ion storage.

What are the three main regions of the Golgi apparatus?

Cis face (receives materials), medial region (intermediate processing), trans face (sorts and ships materials).

What modifications does the Golgi apparatus perform on proteins?

Glycosylation, phosphorylation, and proteolysis.

Where does transcription occur in eukaryotic cells?

In the nucleus.

Where does translation occur in eukaryotic cells?

In the cytoplasm or on the rough endoplasmic reticulum.

What is proteolysis?

The process of cutting a protein or polypeptide to activate it or remove a signal peptide.

What is the role of nuclear pore complexes (NPC)?

They regulate transport across the nuclear envelope.

What is the significance of compartmentalization in eukaryotic cells?

It separates incompatible processes and allows for regulation and efficiency in cellular activities.

What is the primary structural component of the bacterial flagellum?

The protein flagellin.

What is the function of lysosomes?

Lysosomes contain digestive enzymes that break down macromolecules into smaller units.

What is the pH level of lysosomes?

The interior of lysosomes is acidic, with a pH around 5.

How do primary lysosomes become secondary lysosomes?

A primary lysosome fuses with material to be digested, becoming a secondary lysosome where digestion occurs.

What is a vesicle?

A vesicle is a small membrane-enclosed sac containing fluid and/or transported materials.

What is endocytosis?

Endocytosis is the process of taking external material into the cell by enclosing it in a vesicle formed from the plasma membrane.