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HSC Biology practice questions

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Question 1Cells as the Basis of Life

Which organelle is the primary site of ATP production in a eukaryotic cell?

  1. Mitochondrion Correct answer.
  2. Golgi apparatus
  3. Ribosome
  4. Lysosome

Explanation

Mitochondria carry out aerobic respiration, using the electron transport chain on their inner membrane to generate most of the cell's ATP. Other organelles perform different specialised roles and do not produce ATP on this scale.

Question 2Cells as the Basis of Life

A cell is placed in a solution and its volume decreases over time. Which description of the surrounding solution best explains this observation?

  1. Hypertonic, so water leaves the cell by osmosis Correct answer.
  2. Hypotonic, so water enters the cell by osmosis
  3. Isotonic, so water enters and leaves at equal rates
  4. Hypertonic, so solutes enter the cell by diffusion

Explanation

Osmosis moves water from a region of higher water potential to lower water potential. A hypertonic solution has lower water potential than the cytoplasm, so water exits the cell and volume falls.

Question 3Cells as the Basis of Life

Which statement best describes the fluid mosaic model of the plasma membrane?

  1. A double layer of proteins with lipid pores between them
  2. A single layer of phospholipids with fixed protein channels
  3. A phospholipid bilayer with embedded proteins that can move laterally Correct answer.
  4. A rigid protein layer covering a cellulose wall

Explanation

The fluid mosaic model describes a phospholipid bilayer in which proteins and other components are embedded and can move laterally, giving the membrane a fluid character. The varied protein arrangement produces the mosaic appearance.

Question 4Cells as the Basis of Life

Which process moves glucose into a cell down its concentration gradient using a specific carrier protein but without direct ATP consumption?

  1. Simple diffusion
  2. Facilitated diffusion Correct answer.
  3. Phagocytosis
  4. Active transport

Explanation

Facilitated diffusion uses membrane carrier or channel proteins to move a substance down its concentration gradient without energy input from ATP. Glucose is polar and needs such a protein to cross the hydrophobic bilayer.

Question 5Cells as the Basis of Life

Which structure is present in a prokaryotic cell?

  1. Golgi apparatus
  2. Membrane-bound nucleus
  3. Circular chromosomal DNA Correct answer.
  4. Mitochondrion

Explanation

Prokaryotes lack membrane-bound organelles and instead carry their genetic material as a circular chromosome in the nucleoid region. This distinguishes them from eukaryotic cells, which compartmentalise DNA and functions.

Question 6Cells as the Basis of Life

Which molecule stores the genetic instructions that are translated into proteins?

  1. Cholesterol
  2. mRNA Correct answer.
  3. Cellulose
  4. ATP

Explanation

Messenger RNA carries a copy of genetic information from DNA to the ribosome, where it directs the order of amino acids in a polypeptide. Other listed molecules serve energy, membrane or structural roles.

Question 7Cells as the Basis of Life

Which statement about enzymes is correct?

  1. They are consumed in the reactions they catalyse
  2. They change the equilibrium position of a reaction
  3. They increase the activation energy of a reaction
  4. They lower the activation energy of a reaction Correct answer.

Explanation

Enzymes are biological catalysts that speed reactions by lowering the activation energy required. They are not consumed and do not alter the overall equilibrium, only the rate at which it is reached.

Question 8Cells as the Basis of Life

A plant cell is placed in pure water. What is the most likely result?

  1. Water enters and turgor pressure rises Correct answer.
  2. The cell wall dissolves
  3. Water leaves and the cell plasmolyses
  4. No net water movement occurs

Explanation

Pure water has higher water potential than the cell's cytoplasm, so water enters by osmosis. The rigid cell wall resists expansion, causing turgor pressure to build up and keep the cell firm.

Question 9Cells as the Basis of Life

Which feature of the phospholipid bilayer allows small nonpolar molecules such as oxygen to cross readily?

  1. The presence of cholesterol
  2. The hydrophilic phosphate heads
  3. The hydrophobic interior of the bilayer Correct answer.
  4. The integral membrane proteins

Explanation

The fatty acid tails form a hydrophobic core that small nonpolar molecules can dissolve into and pass through. Polar and charged substances are repelled by this region and require transport proteins instead.

Question 10Cells as the Basis of Life

An enzyme-catalysed reaction is occurring at its optimum temperature. The temperature is then raised well above the optimum and the reaction rate falls sharply. What best explains this?

  1. The activation energy of the reaction increases
  2. The enzyme's active site changes shape as bonds break Correct answer.
  3. The enzyme begins to catalyse the reverse reaction
  4. The substrate concentration decreases suddenly

Explanation

Excess heat disrupts hydrogen and other bonds maintaining the enzyme's tertiary structure, so the active site loses its complementary shape and substrate binding is reduced. This denaturation is usually irreversible.

Question 11Cells as the Basis of Life

Which combination correctly matches a cell structure with its function?

  1. Lysosome - synthesis of lipids
  2. Smooth endoplasmic reticulum - production of ribosomal RNA
  3. Rough endoplasmic reticulum - synthesis of proteins for secretion Correct answer.
  4. Nucleolus - modification and packaging of proteins

Explanation

Rough endoplasmic reticulum bears ribosomes and synthesises proteins destined for secretion or membrane insertion. Each organelle has a distinct role, so matching structure to function requires careful distinction.

Question 12Cells as the Basis of Life

A student compares a 10 micrometre cell with a 100 micrometre cell of the same shape. Which statement about the surface area to volume ratio is correct?

  1. Both cells have the same surface area to volume ratio
  2. The ratio depends only on the shape, not the size
  3. The larger cell has a larger surface area to volume ratio
  4. The smaller cell has a larger surface area to volume ratio Correct answer.

Explanation

Surface area increases with the square of linear dimension while volume increases with the cube, so the ratio of surface area to volume falls as size increases. The smaller cell therefore has the greater ratio, aiding efficient exchange.

Question 13Cells as the Basis of Life

Which statement best explains why cells must regulate the movement of ions across the plasma membrane?

  1. Ions are too large to cross any membrane
  2. Ion movement has no effect on cell function
  3. Ions are nonpolar and dissolve in the bilayer
  4. Ion gradients maintain membrane potential and drive transport Correct answer.

Explanation

Unequal ion distribution across the membrane creates an electrical potential and stores energy used in processes such as nerve signalling and coupled transport. Regulating ion movement is therefore essential for cell function.

Question 14Cells as the Basis of Life

During aerobic respiration, which statement about the role of oxygen is correct?

  1. It is produced as a waste product of the Krebs cycle
  2. It acts as the final electron acceptor in the electron transport chain Correct answer.
  3. It donates electrons to NADH
  4. It is the initial substrate that enters glycolysis

Explanation

Oxygen accepts electrons and protons at the end of the electron transport chain, forming water and allowing the chain to continue. Without this terminal acceptor, ATP yield from aerobic respiration falls dramatically.

Question 15Cells as the Basis of Life

Which observation would provide the strongest evidence that a substance enters a cell by active transport rather than facilitated diffusion?

  1. Uptake continues when the external concentration is lower than the internal concentration Correct answer.
  2. Uptake is reduced when a channel protein is blocked
  3. Uptake stops when the temperature is lowered
  4. Uptake increases as the external concentration rises

Explanation

Active transport can move substances against their concentration gradient, which diffusion cannot achieve. Continued uptake when the internal concentration already exceeds the external concentration therefore indicates energy-dependent pumping.

Question 16Cells as the Basis of Life

Which statement about the relationship between organelles in the endomembrane system is correct?

  1. Vesicles from the endoplasmic reticulum fuse with the Golgi apparatus Correct answer.
  2. The Golgi apparatus exports DNA to the cytoplasm
  3. Ribosomes fuse directly with lysosomes
  4. The nucleus buds vesicles that become mitochondria

Explanation

Proteins made in the rough endoplasmic reticulum are packaged into vesicles that fuse with the Golgi apparatus for further modification and sorting. This vesicle traffic links the organelles of the endomembrane system.

Question 17Cells as the Basis of Life

A cell is treated with a drug that blocks ATP synthesis. Which process would be most rapidly affected?

  1. Simple diffusion of carbon dioxide out of the cell
  2. Active transport of sodium ions out of the cell Correct answer.
  3. Osmosis of water across the membrane
  4. Diffusion of oxygen into the cell

Explanation

Active transport depends on ATP to pump ions against their gradient, so blocking ATP synthesis stops it quickly. Simple diffusion and osmosis are passive and continue as long as a gradient exists.

Question 18Cells as the Basis of Life

Which statement correctly compares prokaryotic and eukaryotic ribosomes?

  1. Only eukaryotic ribosomes translate mRNA
  2. Prokaryotic ribosomes are membrane-bound while eukaryotic ones are free
  3. Both types assemble proteins, but prokaryotic ribosomes are smaller Correct answer.
  4. Prokaryotic ribosomes synthesise lipids rather than proteins

Explanation

Ribosomes in both cell types are the site of translation, but prokaryotic ribosomes are smaller and differ in composition from eukaryotic ribosomes. This difference is exploited by some antibiotics that target bacterial ribosomes.

Question 19Cells as the Basis of Life

Which statement best explains why the rate of an enzyme-controlled reaction increases with substrate concentration up to a plateau?

  1. The activation energy rises as more substrate is added
  2. All active sites become saturated so the enzyme is working at maximum rate Correct answer.
  3. The substrate begins to inhibit the enzyme at low concentration
  4. The enzyme is gradually denatured as substrate increases

Explanation

At low substrate concentration many active sites are empty, so adding substrate increases collisions and rate. Once every active site is occupied, further substrate cannot increase the rate because the number of enzymes is limiting.

Question 20Cells as the Basis of Life

A cell's membrane becomes more fluid than normal at body temperature. Which change to its phospholipids could explain this?

  1. An increased thickness of the phospholipid bilayer
  2. A higher proportion of unsaturated fatty acid tails Correct answer.
  3. A reduced number of phospholipid molecules
  4. A higher proportion of saturated fatty acid tails

Explanation

Unsaturated tails contain kinks that prevent tight packing, increasing membrane fluidity. Saturated tails pack closely and tend to make the membrane less fluid.

Question 21Cells as the Basis of Life

Which statement best describes the role of the nucleolus?

  1. It assembles ribosomal subunits from rRNA and proteins Correct answer.
  2. It synthesises ATP for the nucleus
  3. It packages proteins into secretory vesicles
  4. It replicates the cell's chromosomal DNA

Explanation

The nucleolus is a region within the nucleus where ribosomal RNA is transcribed and combined with proteins to form ribosomal subunits. These subunits then leave the nucleus for the cytoplasm.

Question 22Cells as the Basis of Life

A researcher measures the rate of water uptake by plant root hair cells in solutions of different solute concentration. Uptake is fastest in the most dilute solution. Which conclusion is best supported?

  1. Water potential difference drives osmosis into the root cells Correct answer.
  2. Root hair cells absorb solutes faster than water
  3. Water is moved by active transport against its gradient
  4. Solute particles are actively pumped into the root cells

Explanation

The dilute solution has the highest water potential, creating the largest gradient between the external solution and root cell contents. Osmosis rate increases with the size of this water potential difference, supporting the conclusion.

Question 23Cells as the Basis of Life

A cell is exposed to a metabolic poison that halts the electron transport chain but leaves glycolysis functioning. Which prediction about ATP yield from one glucose molecule is most accurate?

  1. ATP yield rises because fermentation is more efficient
  2. ATP yield is unchanged because glycolysis produces all the ATP
  3. ATP yield falls only slightly because the Krebs cycle supplies most ATP directly
  4. ATP yield falls sharply because most ATP comes from oxidative phosphorylation Correct answer.

Explanation

Most ATP from aerobic respiration is produced by oxidative phosphorylation driven by the electron transport chain. If the chain stops, the cell relies on glycolysis and fermentation, giving a much smaller net yield.

Question 24Cells as the Basis of Life

Two enzymes catalyse similar reactions but have different optimum pH values. Which explanation is most consistent with current understanding of enzyme structure?

  1. The enzymes differ only in their substrate concentration
  2. pH affects the substrate but never the enzyme
  3. Their amino acid sequences differ, altering how pH affects active site charge and shape Correct answer.
  4. One enzyme must contain DNA rather than protein

Explanation

An enzyme's amino acid sequence determines its three-dimensional structure and the ionisable groups in its active site. Because pH alters the charge on these groups, enzymes with different sequences can have different pH optima.

Question 25Cells as the Basis of Life

A single-celled organism living in fresh water has a contractile vacuole. Which explanation for this structure is best supported?

  1. It stores nutrients absorbed from the environment
  2. It produces ATP by aerobic respiration
  3. It expels excess water entering by osmosis to prevent the cell bursting Correct answer.
  4. It synthesises proteins for the cell membrane

Explanation

Fresh water has a higher water potential than the cytoplasm, so water continually enters the cell by osmosis. The contractile vacuole actively expels this excess water, maintaining cell volume and preventing lysis.

Question 26Cells as the Basis of Life

Which structural feature is common to the cells of bacteria, fungi, and plants?

  1. A rigid wall made of cellulose
  2. Membrane-bound organelles such as mitochondria
  3. A membrane-bound nucleus containing linear chromosomes
  4. A plasma membrane controlling exchange with the environment Correct answer.

Explanation

All cells, whether prokaryotic or eukaryotic, are bounded by a plasma membrane that is selectively permeable and regulates the movement of substances into and out of the cell. The other listed features are not universal: a nucleus and membrane-bound organelles occur only in eukaryotes, and cellulose walls occur only in plants and some algae.

Question 27Cells as the Basis of Life

A student views a cell and observes many mitochondria, an extensive rough endoplasmic reticulum, and numerous free ribosomes. Which conclusion about this cell is best supported?

  1. It is a prokaryote with a highly folded internal membrane system
  2. It is a mature red blood cell specialised for oxygen transport
  3. It is a dead cell, because living cells lack free ribosomes
  4. It has a high demand for energy and for protein synthesis Correct answer.

Explanation

Mitochondria supply ATP, while ribosomes on the rough endoplasmic reticulum and free in the cytoplasm synthesise proteins. A cell with abundant amounts of both structures is therefore likely to have high energy and protein requirements, for example a secretory cell such as a pancreatic cell.

Question 28Cells as the Basis of Life

Which statement correctly describes the arrangement of molecules in the fluid mosaic model of the plasma membrane?

  1. A single layer of phospholipids is coated on both sides by protein
  2. Phospholipids are embedded within a solid lattice of protein
  3. Carbohydrate chains form the continuous core of the membrane
  4. Proteins are embedded within or attached to a bilayer of phospholipids Correct answer.

Explanation

The model describes a phospholipid bilayer in which proteins float, partially embedded or attached at the surfaces, giving a mosaic pattern. The bilayer is fluid because phospholipids and proteins can move laterally, and carbohydrates occur only as short chains attached to proteins or lipids on the outer surface.

Question 29Cells as the Basis of Life

Which process moves water across a selectively permeable membrane without the input of cellular energy?

  1. Osmosis, the diffusion of water down its concentration gradient Correct answer.
  2. Endocytosis, which engulfs material in a vesicle
  3. Active transport, which uses carrier proteins and ATP
  4. Phagocytosis, which requires rearrangement of the cytoskeleton

Explanation

Osmosis is the passive diffusion of water through a selectively permeable membrane from a region of higher water concentration to one of lower water concentration. Because it is passive, it depends on the concentration gradient rather than ATP, unlike active transport and the vesicle-based processes of endocytosis and phagocytosis.

Question 30Cells as the Basis of Life

A reaction is catalysed by an enzyme. When the substrate concentration is kept constant and the enzyme concentration is doubled, the initial rate of reaction approximately doubles. Which explanation is most consistent with this observation?

  1. The activation energy of the reaction has been lowered further by the extra enzyme
  2. More active sites are available, so more substrate molecules can be converted per unit time Correct answer.
  3. The enzyme has been converted into a product, increasing the rate of the reverse reaction
  4. The substrate molecules now have a higher kinetic energy because of the added enzyme

Explanation

When substrate is plentiful, the rate is limited by the number of enzyme active sites available. Doubling the enzyme concentration doubles the number of active sites, so more substrate molecules can bind and be converted per unit time, roughly doubling the reaction rate.

Question 31Cells as the Basis of Life

A cell is placed in a solution that is hypertonic to its cytoplasm. Which change is most likely to occur in an animal cell?

  1. The cell wall prevents any change in cell volume
  2. Solutes move out of the cell until the concentrations become equal
  3. Water leaves the cell by osmosis and the cell shrinks Correct answer.
  4. Water enters the cell by osmosis and the cell swells

Explanation

In a hypertonic solution, the external solute concentration is higher, so the water concentration outside is lower than inside the cell. Water therefore moves out by osmosis, and because an animal cell lacks a rigid wall, it shrinks and may become crenated.

Question 32Cells as the Basis of Life

Which statement best explains why the rate of diffusion of a gas into a cell increases as the cell becomes smaller?

  1. The concentration gradient across the membrane becomes steeper as the cell shrinks
  2. The gas molecules move faster because the cell contains less cytoplasm
  3. The surface area to volume ratio increases, so relatively more membrane is available per unit of cytoplasm Correct answer.
  4. The membrane becomes thinner as the cell shrinks, shortening the diffusion distance

Explanation

As a cell becomes smaller, its surface area decreases in proportion to the square of its dimensions while its volume decreases with the cube, so the surface area to volume ratio rises. More membrane is then available relative to the cytoplasm that must be supplied, allowing more rapid exchange.

Question 33Cells as the Basis of Life

A protein that normally functions inside the cytoplasm is found in the extracellular fluid after a cell is treated with a drug. Which process most directly explains its release?

  1. Simple diffusion of the protein through the phospholipid bilayer
  2. Osmosis of water carrying the protein out of the cell
  3. Exocytosis, in which vesicles fuse with the plasma membrane Correct answer.
  4. Facilitated diffusion through a channel protein

Explanation

Large molecules such as proteins cannot cross the phospholipid bilayer directly. They are exported when vesicles containing them fuse with the plasma membrane and release their contents outside the cell, a process called exocytosis.

Question 34Cells as the Basis of Life

An enzyme is immobilised on a solid support inside a reaction vessel. Compared with the same enzyme free in solution, which outcome is most likely?

  1. The enzyme will be consumed more rapidly because it is exposed to the flowing substrate
  2. The enzyme will no longer be able to lower the activation energy of the reaction
  3. The enzyme will catalyse a completely different reaction because it is attached to a surface
  4. The enzyme can be recovered and reused, but its activity may change because its shape is constrained Correct answer.

Explanation

Immobilising an enzyme allows it to be separated from the product and reused, which is valuable in industrial processes. However, attachment to a support can restrict the enzyme's movement and alter its active site shape, so its activity may be reduced or its optimum conditions may shift.

Question 35Cells as the Basis of Life

Which statement best describes how the products of the light-dependent reactions of photosynthesis are used in the light-independent reactions?

  1. ATP and NADPH supply energy and reducing power to convert carbon dioxide into carbohydrate Correct answer.
  2. ATP and oxygen are used to synthesise proteins directly from nitrogen
  3. NADPH is used to generate light energy for the chloroplast
  4. Oxygen and water are used to split glucose into pyruvate

Explanation

The light-dependent reactions produce ATP and NADPH, which are then used in the light-independent reactions to reduce carbon dioxide and build carbohydrate. Oxygen is a by-product released to the environment, and light energy itself is absorbed by pigments rather than generated by the cell.

Question 36Cells as the Basis of Life

A plant cell and an animal cell are both placed in distilled water. Which explanation best accounts for the different outcomes?

  1. The plant cell shrinks because its wall excludes water, whereas the animal cell swells
  2. The animal cell becomes turgid because it lacks a wall that would limit water entry
  3. The plant cell becomes turgid because its cell wall resists expansion, whereas the animal cell may burst Correct answer.
  4. Both cells shrink equally because distilled water is hypertonic to both

Explanation

Distilled water is hypotonic to both cells, so water enters each by osmosis. The plant cell's cellulose wall is strong but slightly elastic, so it resists further expansion and builds turgor pressure that prevents bursting, while the animal cell has no wall and may lyse.

Question 37Cells as the Basis of Life

Which observation would best distinguish facilitated diffusion from simple diffusion across a plasma membrane?

  1. The substance passes through the membrane without the cell expending ATP
  2. The rate of transport increases as the temperature rises within the normal range
  3. The substance moves from a region of higher concentration to one of lower concentration
  4. The rate of transport levels off as solute concentration increases, indicating a limited number of carrier proteins Correct answer.

Explanation

Facilitated diffusion depends on a finite number of specific carrier or channel proteins, so once these are saturated the transport rate plateaus even if concentration rises further. Simple diffusion has no such protein limit and continues to increase with the concentration gradient.

Question 38Cells as the Basis of Life

A cell is treated with a drug that prevents the formation of the mitotic spindle. Which outcome is most likely?

  1. Proteins cannot be synthesised because ribosomes cannot assemble
  2. Chromosomes cannot be separated into two daughter nuclei, so cell division fails Correct answer.
  3. The cell cannot carry out glycolysis because ATP production stops
  4. DNA replication cannot occur during the S phase of the cell cycle

Explanation

The spindle is made of microtubules that attach to chromosomes and pull sister chromatids to opposite poles during mitosis. Without a functional spindle, chromosomes cannot be segregated accurately, so division stalls or produces daughter cells with abnormal chromosome numbers.

Question 39Cells as the Basis of Life

In a cell, a mutation changes a receptor protein so that it remains active even when its signalling molecule is absent. Which consequence is most consistent with this change?

  1. The cell responds continuously as though the signal were always present Correct answer.
  2. The cell stops responding to the signal because the receptor is permanently occupied
  3. The signalling molecule is produced in larger quantities to compensate
  4. The receptor is destroyed immediately because it cannot bind the signal

Explanation

Receptors normally become active only when their specific signalling molecule binds. If a mutation locks the receptor in its active conformation, downstream signalling continues without the ligand, so the cell behaves as if it is constantly receiving the signal.

Question 40Cells as the Basis of Life

Two cell types contain identical genes, yet one secretes large amounts of digestive enzyme while the other does not. Which explanation is most consistent with this difference?

  1. The non-secreting cell has lost the gene for the enzyme during division
  2. The secreting cell contains extra copies of the gene for the enzyme
  3. Different genes are expressed in each cell, so only one produces the mRNA for the enzyme Correct answer.
  4. The non-secreting cell translates all its mRNA into the same proteins as the secreting cell

Explanation

Cells of an organism generally contain the same genome, but selective gene expression determines which proteins are made. In the secreting cell, the gene for the digestive enzyme is transcribed and translated, whereas in the other cell it is switched off, so no mRNA for the enzyme is produced.

Question 41Organisation of Living Things

Which type of blood vessel carries blood away from the heart and has a thick muscular wall to withstand high pressure?

  1. Vein
  2. Capillary
  3. Artery Correct answer.
  4. Lymph vessel

Explanation

Arteries carry blood away from the heart, so they experience the highest hydrostatic pressure in the circulatory system. A thick muscular and elastic wall lets them stretch with each heartbeat and recoil to maintain pressure between beats.

Question 42Organisation of Living Things

Which structure in a flowering plant is the main site of photosynthesis?

  1. Phloem sieve tube
  2. Mesophyll cell Correct answer.
  3. Root hair
  4. Xylem vessel

Explanation

Photosynthesis occurs mainly in the mesophyll tissue of leaves, where cells contain many chloroplasts and are close to air spaces for gas exchange. Their position near the leaf surface also allows light to reach the chloroplasts efficiently.

Question 43Organisation of Living Things

Which component of blood is primarily responsible for transporting oxygen?

  1. Red blood cells Correct answer.
  2. Platelets
  3. White blood cells
  4. Plasma proteins

Explanation

Red blood cells contain haemoglobin, an iron-containing pigment that binds oxygen in the lungs and releases it in respiring tissues. Their biconcave shape and lack of a nucleus maximise surface area and space for haemoglobin.

Question 44Organisation of Living Things

What is the main function of the stomata on a leaf?

  1. To allow gas exchange and regulate water loss Correct answer.
  2. To absorb mineral ions from the soil
  3. To transport sugars to the roots
  4. To anchor the leaf to the stem

Explanation

Stomata are pores controlled by guard cells that open to let carbon dioxide in and oxygen out for photosynthesis. Opening also allows water vapour to escape, so guard cells must balance gas supply against transpirational water loss.

Question 45Organisation of Living Things

Which term describes the movement of water through a plant from roots to leaves in the xylem?

  1. Osmosis
  2. Active transport
  3. Transpiration stream Correct answer.
  4. Translocation

Explanation

The transpiration stream is the continuous column of water pulled up the xylem as water evaporates from leaf surfaces. Cohesion between water molecules and adhesion to xylem walls keep the column intact under tension.

Question 46Organisation of Living Things

Which chamber of the mammalian heart pumps oxygenated blood into the aorta?

  1. Right atrium
  2. Left ventricle Correct answer.
  3. Left atrium
  4. Right ventricle

Explanation

The left ventricle receives oxygenated blood from the left atrium and pumps it into the aorta for distribution around the body. Its thick muscular wall generates the high pressure needed for systemic circulation.

Question 47Organisation of Living Things

What is the main role of villi in the small intestine?

  1. To secrete bile
  2. To produce red blood cells
  3. To store undigested food
  4. To increase surface area for absorption Correct answer.

Explanation

Villi are finger-like projections that greatly increase the surface area of the small intestine, and each contains capillaries and a lacteal for absorbing nutrients. Their thin epithelium shortens the diffusion distance for absorbed molecules.

Question 48Organisation of Living Things

Which of the following best describes the role of guard cells in a leaf?

  1. They open and close the stomatal pore. Correct answer.
  2. They protect the leaf from herbivores.
  3. They carry sugars to the root system.
  4. They transport water up the stem.

Explanation

Guard cells change shape by taking up or losing water, which opens or closes the stomatal pore between them. This controls the balance between carbon dioxide uptake for photosynthesis and water loss by transpiration.

Question 49Organisation of Living Things

A student measures the rate of transpiration in a leafy shoot under three conditions: still air, moving air, and still air at high humidity. Which prediction follows from the mechanism of transpiration?

  1. Moving air will increase the rate, and high humidity will decrease it. Correct answer.
  2. Moving air will decrease the rate, and high humidity will increase it.
  3. Both moving air and high humidity will decrease the rate.
  4. Both moving air and high humidity will increase the rate.

Explanation

Transpiration depends on the water vapour concentration gradient between the moist leaf interior and the surrounding air. Moving air removes humid air from around the stomata, steepening the gradient and increasing the rate, while high humidity reduces the gradient and slows water loss.

Question 50Organisation of Living Things

A person has a condition in which the left ventricle wall becomes much thinner and weaker. Which immediate consequence is most likely?

  1. Increased rate of gas exchange in the alveoli
  2. Reduced ability to pump blood into the systemic circulation Correct answer.
  3. Reduced ability to send blood to the lungs
  4. Increased production of red blood cells

Explanation

The left ventricle must generate high pressure to force blood through the aorta and systemic circuit. A thinner, weaker wall reduces the force of contraction, lowering cardiac output to the body.