Cell Biology, Transport, Biomolecules & Enzymes – Lecture Review

A comprehensive set of question-and-answer flashcards covering cell structures, specialised cells, transport mechanisms, biological molecules and enzymes from the provided lecture notes.

What is the primary function of the cell surface (plasma) membrane?

It is a partially permeable barrier that controls the movement of substances into and out of the cell.

What is the plant cell wall made of and name two of its functions.

It is made of cellulose; it protects against injury, gives a regular shape, and prevents bursting when excess water enters.

Which organelle controls cellular activities and contains chromatin?

The nucleus.

List the main components of a nucleus.

Nuclear envelope, nucleoplasm, nucleolus and chromatin.

Which organelle generates energy for the cell through cellular respiration?

The mitochondrion.

Which tiny round organelles synthesise proteins from mRNA?

Ribosomes.

What structural feature distinguishes rough ER from smooth ER?

Rough ER has ribosomes attached to its surface; smooth ER does not.

State two functions of the rough endoplasmic reticulum.

Synthesises proteins on its ribosomes and transports them to the Golgi body for modification and secretion.

Give two functions of the smooth endoplasmic reticulum.

Synthesises fats and steroids and detoxifies harmful substances.

What is the role of the Golgi body?

It stores, modifies and packages proteins into vesicles for secretion.

Define cytoplasm.

The cytosol plus all the organelles suspended in it, where numerous metabolic reactions occur.

How do vacuoles in plant and animal cells differ?

Plant cells contain one large permanent vacuole with cell sap; animal cells have many small temporary vacuoles.

Which pigment is found in chloroplasts and what process occurs there?

Chlorophyll; photosynthesis.

Describe one structural adaptation of red blood cells and its benefit.

Their biconcave shape increases surface area-to-volume ratio for faster oxygen exchange (they also lack a nucleus to store more haemoglobin).

Why do root hair cells contain numerous mitochondria?

To supply energy for active transport of mineral salts from the soil.

How do xylem vessels enable unobstructed water flow?

They are long hollow tubes without cross-walls and have lignified walls for support.

In which form do animals store carbohydrate?

Glycogen.

In which form do plants store carbohydrate?

Starch.

Name three structures present in plant cells but absent in typical animal cells.

Cell wall, chloroplasts and a large central vacuole.

Define diffusion.

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

What is a concentration gradient?

The difference in concentration between two regions.

How does a steeper concentration gradient affect diffusion rate?

It increases the rate of diffusion.

Name three small molecules that diffuse freely across cell membranes.

Oxygen, carbon dioxide and water.

Define osmosis.

The net movement of water molecules from a region of higher water potential to a region of lower water potential across a partially permeable membrane.

Which term describes a solution with lower solute concentration than another?

Hypotonic.

What happens to plant cells placed in a concentrated solution?

They lose water, become plasmolysed and the cell membrane pulls away from the cell wall.

What occurs when red blood cells are placed in a concentrated solution?

Water leaves the cells and they crenate (shrink with spiky surfaces).

What happens to red blood cells in pure water?

Water enters, the cells swell and may burst (haemolysis).

Why don’t plant cells burst in pure water?

The rigid cell wall withstands the internal turgor pressure.

What is turgor pressure?

The pressure exerted by water in the vacuole against the cell wall of a turgid plant cell.

Give two factors (other than concentration gradient) that affect diffusion rate.

Diffusion distance and surface area-to-volume ratio.

Explain how microvilli aid nutrient absorption in the small intestine.

They greatly increase surface area, enhancing diffusion and active transport of digested molecules.

Define active transport.

The movement of particles across membranes from lower to higher concentration using energy via membrane transport proteins.

Where does the energy for active transport come from?

ATP produced during cellular respiration in mitochondria.

Give an example of active transport in humans.

Absorption of glucose from the intestinal lumen into blood when blood glucose is already higher.

Give an example of active transport in plants.

Uptake of mineral salts by root hair cells from the soil solution.

Contrast diffusion, osmosis and active transport regarding energy requirement.

Diffusion and osmosis are passive and require no energy; active transport requires energy.

Which elements compose carbohydrates?

Carbon, hydrogen and oxygen.

Differentiate monosaccharide, disaccharide and polysaccharide.

Single sugar unit; two monosaccharides joined; many monosaccharide units joined.

Name one common monosaccharide.

Glucose.

How is maltose formed?

By condensation of two glucose molecules with the removal of a water molecule.

State two reasons starch and glycogen are good energy stores.

They are insoluble so don’t affect water potential and are compact, occupying little space.

Which extra element is present in proteins but not in carbohydrates or fats?

Nitrogen (sometimes sulfur).

What are the basic units of proteins and how are they linked?

Amino acids joined by condensation reactions to form polypeptide chains.

Which reaction forms fats from glycerol and fatty acids?

Condensation, producing a fat molecule and water.

List two biological functions of fats.

Long-term energy store and thermal insulation (also protect organs, dissolve fat-soluble vitamins, form membranes).

Define an enzyme.

A biological catalyst (usually a protein) that speeds up a reaction without being consumed.

How do enzymes increase reaction rate?

They provide an alternative pathway with lower activation energy.

Describe the lock-and-key hypothesis.

A substrate fits precisely into the enzyme’s active site forming an enzyme-substrate complex that enables the reaction.

Why are enzymes highly specific?

The unique 3-D shape of their active site is complementary only to a particular substrate.

What is the approximate optimum temperature for most human enzymes?

About 37 °C.

What happens to enzymes at temperatures above their optimum?

They denature, losing their 3-D structure and active site conformation, decreasing activity.

Define optimum pH for an enzyme.

The pH value at which that enzyme’s activity is greatest.

How do extreme pH changes affect enzymes?

They denature enzymes, altering active site shape and reducing activity.

Differentiate anabolic and catabolic enzyme reactions with an example each.

Anabolic build larger molecules (e.g., DNA polymerase synthesising DNA); catabolic break down molecules (e.g., lipase hydrolysing fats).

Why are only minute amounts of enzyme needed in reactions?

Because enzymes remain unchanged and can be reused repeatedly.

How does enzyme concentration affect reaction rate when substrate is abundant?

Increasing enzyme concentration increases the reaction rate until substrate becomes limiting.

Name the three main classes of digestive enzymes and their substrates.

Carbohydrases (carbohydrates), proteases (proteins), lipases (fats).

Why can’t large molecules like glucose diffuse directly through the lipid bilayer?

They are too large and therefore require transport proteins or channels.

What is the purpose of Benedict’s test in food analysis?

To detect the presence and approximate amount of reducing sugars.