Cells as the Basic Units of Living Organisms – CIE AS Biology

Question-and-answer flashcards covering key structures, functions, and comparisons of eukaryotic cells, plant vs animal cells, ATP, prokaryotes, and viruses.

What does the term “ultrastructure” refer to in cell biology?

The detailed internal structure of a cell as revealed by electron microscopy.

Which type of membrane surrounds all cells and what is its primary function?

The cell surface membrane; it separates the cell from its surroundings and controls the exchange of materials.

Why is the cell surface membrane described as partially permeable?

Because it allows some substances to pass through while restricting others.

What is the basic structural component of the cell surface membrane?

A phospholipid bilayer about 10 nm thick.

Where is genetic material stored in eukaryotic cells?

Inside the nucleus as DNA arranged into chromosomes.

What are chromatin, and of what are they composed?

The complex of DNA and proteins that makes up chromosomes.

Name the double membrane surrounding the nucleus and state its key feature.

The nuclear envelope; it contains numerous nuclear pores.

What is the function of nuclear pores?

They allow mRNA and ribosomes to exit the nucleus and permit enzymes and signalling molecules to enter.

Which nuclear region is responsible for ribosome production?

The nucleolus.

How is the rough endoplasmic reticulum (RER) structurally distinguished?

It has continuous membrane folds studded with ribosomes and is connected to the nuclear envelope.

What is the main role of the rough endoplasmic reticulum?

Processing and folding proteins synthesised by its ribosomes.

How does the smooth endoplasmic reticulum (SER) differ from the RER?

The SER lacks ribosomes and is involved in lipid and steroid hormone synthesis.

What is the overall function of the Golgi body?

To modify proteins and package them into vesicles for transport.

Why do mitochondria have highly folded inner membranes called cristae?

The folds provide a large surface area for the enzymes and proteins involved in aerobic respiration.

Besides enzymes, what two key components are found inside the mitochondrial matrix?

Small circular mitochondrial DNA and 70S ribosomes.

What is the primary role of mitochondria?

They are the site of aerobic respiration and ATP production in eukaryotic cells.

Where are 80S ribosomes found and what is their function?

In the cytoplasm of eukaryotic cells (and on the RER); they are the site of translation during protein synthesis.

Which ribosome type is found in prokaryotes, mitochondria, and chloroplasts?

70S ribosomes.

What are vesicles and what do they do?

Small membrane-bound sacs that transport and store substances inside cells.

What distinguishes lysosomes from other vesicles?

They contain hydrolytic enzymes for breaking down waste, old organelles, pathogens, and cell debris.

What cellular structures form a centrosome and what is its role?

Two centrioles at right angles; they organise spindle fibres during cell division.

Of what protein are microtubules composed and what do they form in the cell?

Tubulin; they form part of the cytoskeleton, providing support and enabling movement.

Give one example of a cell type that uses cilia and state its function there.

Ciliated epithelial cells in the airways use cilia to waft mucus away from the lungs.

How do microvilli aid absorption?

By increasing the surface area of the cell surface membrane.

What polysaccharide provides structural support in plant cell walls?

Cellulose.

Why are plant cell walls described as freely permeable?

Because they do not control the movement of substances into or out of the cell.

Which organelle contains thylakoids, grana, and photosynthetic pigments?

The chloroplast.

What is the function of plasmodesmata?

They are cytoplasmic bridges that allow substances to move directly between neighbouring plant cells.

State two functions of a large permanent vacuole in plant cells.

Storing cell sap and providing additional structural support (turgor).

Which two structures are unique to animal cells and absent from plant cells?

Centrioles and microvilli.

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

Cellulose cell wall, large permanent vacuoles, and chloroplasts (also plasmodesmata).

Why is ATP called the universal energy currency?

Because all living organisms use ATP to transfer energy for every energy-requiring process.

How is energy released from ATP?

By hydrolysing ATP to ADP and inorganic phosphate.

List three major differences between prokaryotic and eukaryotic cells.

Prokaryotes have circular naked DNA in the cytoplasm, no membrane-bound organelles, and 70S ribosomes, whereas eukaryotes have linear DNA in a nucleus, membrane-bound organelles, and 80S ribosomes.

What polymer composes prokaryotic cell walls?

Peptidoglycan (murein).

How do prokaryotes reproduce compared with eukaryotes?

Prokaryotes divide by binary fission without spindle fibres; eukaryotes divide by mitosis or meiosis with spindle fibres.

Identify the two main structural components common to all viruses.

A nucleic acid core (DNA or RNA) and a protein coat called a capsid.

Why are viruses considered non-living particles?

They cannot reproduce independently and rely on infecting living cells to replicate.

What role do viral attachment proteins play in infection?

They bind to specific receptors on host cells, enabling viral entry.