BN02 · Quiz — Cell Biology | Olive Defence NDA

Question 1 of 20

Which scientist first observed cells using a self-made microscope and coined the term 'cell'?

AAntonie van Leeuwenhoek BRobert Hooke (1665, Micrographia) CRudolf Virchow DMatthias Schleiden

Robert Hooke (1665) observed cork under his compound microscope and saw small box-like compartments he called 'cells' (resembling monks' rooms). Leeuwenhoek first observed living microorganisms. Schleiden (plants) and Schwann (animals) formulated cell theory.

Question 2 of 20

The fluid mosaic model of the cell membrane describes it as:

AA rigid double layer of cellulose fibres embedded with protein channels BA fluid phospholipid bilayer with embedded proteins that can move laterally CA solid protein matrix surrounding and containing lipid molecules DA single phospholipid layer with proteins anchored only on the outer surface

The Fluid Mosaic Model (Singer and Nicolson, 1972): the membrane is a fluid phospholipid bilayer (two layers of phospholipid molecules, tails inward) with proteins embedded throughout (mosaic). Proteins can move laterally within the fluid lipid layer.

Question 3 of 20

Osmosis is defined as the movement of water molecules:

AFrom high solute concentration to low solute concentration through a semipermeable membrane BFrom low solute concentration to high solute concentration through a semipermeable membrane CAgainst the concentration gradient using ATP energy DAcross any membrane, powered by active transport proteins

Osmosis: movement of water molecules from a region of higher water concentration (lower solute = hypotonic) to lower water concentration (higher solute = hypertonic) across a semipermeable membrane. No energy required — it is passive transport.

Question 4 of 20

During interphase of the cell cycle, the cell primarily:

ADivides its cytoplasm into two daughter cells BCondenses its chromosomes for cell division CGrows, replicates DNA, and prepares for division DUndergoes apoptosis (programmed cell death)

Interphase is the longest phase of the cell cycle, divided into G1 (growth), S (DNA synthesis/replication), and G2 (preparation for mitosis). The cell grows, duplicates its organelles, and replicates its entire DNA during interphase before entering mitosis.

Question 5 of 20

A cell placed in a hypertonic solution (more concentrated than cytoplasm) will:

ASwell and may burst (plasmolysis) BShrink — water leaves the cell by osmosis CRemain unchanged — equilibrium is already established DTake in water through active transport to compensate

Hypertonic solution has higher solute concentration than the cell's cytoplasm → water moves OUT of the cell by osmosis → animal cells shrink (crenation); plant cells undergo plasmolysis (cytoplasm pulls away from cell wall). The cell loses turgor.

Question 6 of 20

The endoplasmic reticulum (ER) serves as a transport system within the cell. Which statement is CORRECT?

ASER has ribosomes for protein synthesis; RER synthesises lipids and detoxifies BRER has ribosomes on its surface (protein synthesis); SER lacks ribosomes (lipid synthesis) CBoth SER and RER synthesise proteins with equal efficiency in all cells DER is found only in plant cells; animal cells rely on the Golgi apparatus

RER has ribosomes → protein synthesis and transport. SER lacks ribosomes → lipid and steroid synthesis, drug/toxin detoxification (important in liver cells). Both are continuous with the nuclear envelope and form a network throughout the cytoplasm.

Question 7 of 20

Mitochondria are described as semi-autonomous organelles because they:

AThey can freely migrate between adjacent cells through plasmodesmata channels BThey have their own circular DNA, 70S ribosomes, and can partially self-replicate CThey are enclosed by a single membrane like lysosomes and vacuoles DThey produce all the cell's ATP independently with no nuclear gene involvement

Mitochondria have their own circular DNA (mitochondrial genome — inherited maternally), 70S ribosomes (like bacteria), and can partially self-replicate. This supports the endosymbiotic theory — mitochondria were once free-living alpha-proteobacteria engulfed by ancestral eukaryotes.

Question 8 of 20

During metaphase of mitosis, chromosomes are:

ACondensing from chromatin for the first time BAligned at the metaphase plate (cell equator) by spindle fibres CSeparating to opposite poles of the cell DDecondensing to form two new nuclei

Metaphase: chromosomes reach maximum condensation and align at the metaphase plate (equatorial plane) attached to spindle fibres at their centromeres. This is the best stage to count chromosomes and prepare a karyotype. Metaphase chromosomes are most clearly visible.

Question 9 of 20

Apoptosis (programmed cell death) is important because it:

AIs always a sign of disease or injury to the organism BRemoves damaged, infected CResults in inflammation and immune activation DOnly occurs in cancer cells as a protective mechanism

Apoptosis is controlled, programmed cell death — essential for: embryonic development (finger formation by removing webbing), immune function (killing infected cells), cancer prevention (removing mutated cells). Distinguished from necrosis (uncontrolled death) — apoptosis is tidy; necrosis causes inflammation.

Question 10 of 20

The sodium-potassium pump (Na⁺/K⁺ ATPase) in nerve cells is an example of:

APassive diffusion (no energy needed) BOsmosis across a semipermeable membrane CActive transport DFacilitated diffusion through channel proteins

The Na⁺/K⁺ pump uses ATP to actively transport 3 Na⁺ ions OUT and 2 K⁺ ions IN against their concentration gradients. This maintains the resting membrane potential essential for nerve impulse transmission. Active transport moves substances against the concentration gradient — requiring energy.

Question 11 of 20

Which organelle is responsible for the modification, sorting and packaging of proteins for secretion?

ARough endoplasmic reticulum BLysosome CGolgi apparatus (Golgi body) DMitochondria

The Golgi apparatus receives proteins from the RER, modifies them (adds sugars, phosphate groups), sorts them, and packages them into vesicles for secretion outside the cell or delivery to specific cellular locations (lysosomes, plasma membrane). Called the 'post office' of the cell.

Question 12 of 20

Telomeres are repeated DNA sequences at the ends of chromosomes. Their significance is:

AThey code for essential structural proteins BThey protect chromosome ends from degradation and CThey are the sites where DNA replication begins DThey contain the centromere for spindle attachment

Telomeres (repetitive TTAGGG sequences) cap chromosome ends, protecting them from degradation and preventing chromosomes from fusing with each other. Each cell division shortens telomeres slightly — this contributes to cellular ageing. Telomerase enzyme extends telomeres in cancer cells and stem cells.

Question 13 of 20

Cytokinesis in animal cells differs from plant cells because animal cells:

AUse a cell plate (phragmoplast) to divide the cytoplasm BForm a cleavage furrow by constriction of an actin-myosin ring CDivide by binary fission like bacteria DDo not undergo cytokinesis — only mitosis occurs

Animal cells: cleavage furrow — an actin-myosin contractile ring pinches the cell membrane inward to divide cytoplasm. Plant cells: cell plate — vesicles from Golgi fuse at the cell equator to form a new cell wall (phragmoplast). Plant cells cannot constrict because of their rigid cell wall.

Question 14 of 20

The inner mitochondrial membrane is highly folded into structures called:

AThylakoids BCristae CGrana DLacunae

Cristae are the folds of the inner mitochondrial membrane. They dramatically increase the surface area for the electron transport chain (ETC) and ATP synthase — maximising ATP production. The matrix (inside the inner membrane) contains mitochondrial DNA, ribosomes, and Krebs cycle enzymes.

Question 15 of 20

Which type of RNA carries the genetic code from DNA in the nucleus to the ribosome?

AtRNA (transfer RNA — carries amino acids) BrRNA (ribosomal RNA — structural component of ribosome) CmRNA (messenger RNA — carries genetic code) DsnRNA (small nuclear RNA — involved in splicing)

mRNA (messenger RNA) carries the genetic code (as codons — triplet nucleotide sequences) from DNA in the nucleus to ribosomes in the cytoplasm, where it serves as the template for protein synthesis (translation). tRNA brings specific amino acids; rRNA forms the ribosome structure.

Question 16 of 20

The concept of 'contact inhibition' in normal cells means that:

ACells stop dividing when they make contact with neighbouring cells BCells migrate away from areas of contact to new locations CCells inhibit the growth of bacteria through antibiotic secretion DCells stop producing hormones when in contact with target cells

Normal cells stop dividing when they come into contact with adjacent cells (contact inhibition). This prevents uncontrolled overgrowth. Cancer cells LOSE contact inhibition — they continue to divide even when crowded, leading to tumour formation.

Question 17 of 20

A mutation in a proto-oncogene can convert it into an oncogene. This is significant because:

AIt causes the cell to enter permanent G0 phase (non-dividing) BIt leads to uncontrolled cell proliferation — a hallmark of cancer CIt activates apoptosis pathways in the affected cell DIt causes the cell to differentiate into a specialised cell type

Proto-oncogenes normally regulate cell division. Mutations can convert them into oncogenes (overactive versions) that stimulate continuous cell division. Examples: Ras oncogene (mutated in ~30% of human cancers). Tumour suppressor genes (e.g., p53, Rb) normally inhibit division — their loss also contributes to cancer.

Question 18 of 20

Endocytosis and exocytosis are forms of bulk transport that differ because:

AEndocytosis uses ATP; exocytosis is passive BEndocytosis brings materials INTO the cell CExocytosis works only in plant cells; endocytosis in animal cells only DBoth transport only small molecules across the membrane

Endocytosis: cell membrane engulfs external material → forms vesicle inside cell (phagocytosis for solids; pinocytosis for liquids). Exocytosis: vesicles fuse with plasma membrane → release contents outside. Both require energy (ATP) and are forms of active, bulk transport.

Question 19 of 20

The G2 checkpoint in the cell cycle checks for:

ASufficient cell size and nutrient availability before S phase BCorrect and complete DNA replication before entering mitosis CProper chromosome attachment to spindle fibres during metaphase DCompletion of cytokinesis before re-entering G1

G2 checkpoint: verifies that DNA replication (during S phase) is complete and accurate, and that the cell is large enough and has sufficient energy to proceed into mitosis. If DNA damage is detected, the checkpoint halts the cycle to allow repair — preventing mutations from being passed to daughter cells.

Question 20 of 20

Plasmodesmata in plant cells are:

APores in the nuclear envelope for mRNA transport BCytoplasmic channels connecting adjacent plant cells through their cell walls CProtein channels in the plasma membrane for ion transport DStructures that anchor the cytoskeleton to the cell membrane

Plasmodesmata are narrow cytoplasmic channels that penetrate adjacent plant cell walls, directly connecting the cytoplasm of neighbouring cells. They allow transport of water, nutrients, and signalling molecules between cells — forming the symplast pathway. Analogous to gap junctions in animal cells.

BN02 — Cell Biology