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Question 1Physiology of Plants

Which tissue in a dicot leaf is mainly responsible for capturing light energy for photosynthesis?

  1. Spongy mesophyll
  2. Palisade mesophyll Correct answer.
  3. Xylem
  4. Lower epidermis

Explanation

Palisade mesophyll cells are packed with chloroplasts and lie near the upper surface, so they receive the most light and carry out most photosynthesis. Spongy mesophyll has fewer chloroplasts and is more involved in gas exchange.

Question 2Physiology of Plants

Water and dissolved mineral ions move upward through a plant mainly in which structure?

  1. Xylem vessels Correct answer.
  2. Root hair cells
  3. Cambium
  4. Phloem sieve tubes

Explanation

Xylem vessels are dead, hollow tubes with lignified walls that form a continuous pipeline from root to leaf, carrying water and minerals upward. Phloem, by contrast, transports sugars and amino acids.

Question 3Physiology of Plants

Which process is the main driving force that pulls water up the xylem of a tall tree?

  1. Guttation from hydathodes
  2. Translocation in phloem
  3. Active transport in root hair cells
  4. Transpiration from leaves Correct answer.

Explanation

As water evaporates from leaf surfaces, it creates tension in the water column, and the cohesion of water molecules transmits this pull down to the roots. This transpiration pull is the dominant force in tall trees.

Question 4Physiology of Plants

A plant is kept in the dark for 48 hours and then a leaf is tested with iodine solution. What result is expected and why?

  1. Brown, because the leaf lost all its water
  2. Blue-black, because chlorophyll absorbs heat
  3. Brown, because no new starch was formed without light Correct answer.
  4. Blue-black, because starch was made in the dark

Explanation

Starch is only produced when photosynthesis occurs, and photosynthesis requires light. After 48 hours of darkness any stored starch is used up, so the iodine stays brown, showing no starch is present.

Question 5Physiology of Plants

Which mineral ion deficiency most directly causes yellowing of leaves because it is needed to make chlorophyll?

  1. Magnesium Correct answer.
  2. Phosphate
  3. Nitrate
  4. Potassium

Explanation

Magnesium is a central atom in every chlorophyll molecule, so a shortage leads to chlorosis, with leaves turning yellow between the veins. Nitrate is needed mainly for proteins and nucleic acids.

Question 6Physiology of Plants

Which tropism explains a plant shoot bending toward a light source coming from one side?

  1. Negative phototropism
  2. Positive geotropism
  3. Thigmotropism
  4. Positive phototropism Correct answer.

Explanation

Shoots grow toward unilateral light because auxin accumulates on the shaded side, stimulating greater cell elongation there. The result is a bend toward the light, which is positive phototropism.

Question 7Physiology of Plants

Which structure allows gases to enter and leave a leaf while limiting water loss?

  1. Lignified xylem wall
  2. Cuticle
  3. Stoma Correct answer.
  4. Palisade cell wall

Explanation

A stoma is a pore flanked by guard cells that can open and close, letting carbon dioxide in and oxygen and water vapour out. The cuticle is waxy and largely impermeable to gases.

Question 8Physiology of Plants

Which statement correctly describes the role of phloem in a flowering plant?

  1. It supports the plant by providing rigid lignified tubes.
  2. It absorbs mineral ions from the soil solution.
  3. It transports sucrose and amino acids to growing and storage regions. Correct answer.
  4. It carries water from roots to leaves.

Explanation

Phloem sieve tubes with companion cells carry organic solutes such as sucrose and amino acids from sources to sinks, including growing tips, roots and storage organs. Water movement upward is the job of xylem.

Question 9Physiology of Plants

Guard cells open a stoma when they become turgid. Which change in the guard cells produces this turgidity?

  1. The cell walls thicken on the inner side
  2. Water leaves and the cells shrink
  3. Water enters and the cells swell Correct answer.
  4. Potassium ions leave the guard cells

Explanation

When potassium ions are pumped into guard cells, water follows by osmosis, the cells become turgid and the stoma opens. Loss of water makes them flaccid and closes the pore.

Question 10Physiology of Plants

A student places a leafy shoot in a potometer and records the bubble moving 30 mm in 10 minutes. Which change would most reliably increase the rate of bubble movement?

  1. Covering the leaves with a plastic bag
  2. Placing the apparatus in still, humid air
  3. Removing all the leaves from the shoot
  4. Directing a fan at the leaves Correct answer.

Explanation

Moving air removes the humid boundary layer around leaves, increasing the water vapour gradient and therefore transpiration. A faster transpiration pull moves the potometer bubble further per unit time.

Question 11Physiology of Plants

Which sequence correctly traces the path of water from soil to the atmosphere in a herbaceous plant?

  1. Root hair → xylem → mesophyll cell → stoma → air Correct answer.
  2. Root hair → xylem → phloem → mesophyll → air
  3. Stoma → mesophyll → xylem → root hair → air
  4. Root hair → phloem → xylem → stoma → air

Explanation

Water is absorbed by root hair cells, passes through the root cortex into xylem, is drawn up to the leaf, enters mesophyll cells and evaporates into air spaces before diffusing out through stomata. Phloem is not part of this water pathway.

Question 12Physiology of Plants

Why is the rate of photosynthesis of a plant usually lower on a hot, dry afternoon than in the cooler morning, even though light is brighter?

  1. Respiration stops in the afternoon
  2. Roots absorb less magnesium at high temperature
  3. Chlorophyll is destroyed by bright light
  4. Stomata close to conserve water, limiting carbon dioxide entry Correct answer.

Explanation

In hot, dry conditions plants close stomata to reduce water loss, which restricts carbon dioxide diffusion into the leaf. Carbon dioxide then becomes the limiting factor, so photosynthesis slows despite strong light.

Question 13Physiology of Plants

In the light-dependent stage of photosynthesis, what is produced that is used in the light-independent stage?

  1. Carbon dioxide and water
  2. ATP and reduced NADP Correct answer.
  3. Sucrose and starch
  4. Glucose and oxygen

Explanation

The light-dependent reactions generate ATP and reduced NADP, which supply energy and hydrogen for reducing carbon dioxide in the Calvin cycle. Glucose and oxygen are overall products, not the carriers passed between stages.

Question 14Physiology of Plants

A root grows downward into soil while a shoot grows upward. Which explanation fits these responses to gravity?

  1. Auxin inhibits root growth on the lower side and shoot growth on the upper side
  2. Both organs respond only to light, not gravity
  3. Roots are positively geotropic and shoots are negatively geotropic Correct answer.
  4. Both root and shoot show positive geotropism

Explanation

Auxin accumulates on the lower side of both organs when they are horizontal. In roots the higher auxin concentration inhibits elongation so the root bends down, while in shoots the same accumulation promotes elongation so the shoot bends up.

Question 15Physiology of Plants

Which adaptation of a xerophyte most directly reduces water loss through transpiration?

  1. Brightly coloured petals
  2. Aerial roots exposed to air
  3. Large, thin leaves with many stomata
  4. Sunken stomata in pits on the leaf surface Correct answer.

Explanation

Stomata sunk in pits trap a layer of humid air, reducing the vapour gradient and therefore water loss. Large thin leaves with many stomata would increase transpiration.

Question 16Physiology of Plants

A plant is supplied with water containing a dissolved red dye. After several hours, which tissue shows the most intense red colour in a cross-section of the stem?

  1. The phloem sieve tubes
  2. The pith cells
  3. The xylem vessels Correct answer.
  4. The outer cortex

Explanation

The dye travels with the transpiration stream, which moves through xylem. Therefore the xylem vessels appear most strongly stained, showing that xylem is the water-conducting tissue.

Question 17Physiology of Plants

Which combination of conditions gives the fastest net uptake of carbon dioxide by a well-watered C3 plant?

  1. Low carbon dioxide and low temperature
  2. Low light intensity and high humidity
  3. Darkness and warm temperature
  4. High light intensity and normal carbon dioxide concentration Correct answer.

Explanation

At high light intensity with adequate carbon dioxide and water, photosynthesis proceeds near its maximum and net carbon dioxide uptake is greatest. Low light, darkness or low carbon dioxide all limit the rate.

Question 18Physiology of Plants

Which statement best explains why a wilting plant recovers after watering?

  1. Turgor pressure returns to the cells as water enters by osmosis Correct answer.
  2. Phloem transports water directly to the leaves
  3. Xylem vessels contract and pull water down
  4. Stomata permanently close, preventing further loss

Explanation

Watering restores the water potential gradient so water enters cells by osmosis, rebuilding turgor pressure that holds stems and leaves upright. Loss of turgor is what causes wilting.

Question 19Physiology of Plants

Which feature of insect-pollinated flowers is most directly linked to attracting specific pollinators?

  1. Large, brightly coloured petals and nectar Correct answer.
  2. Small, dull petals with no scent
  3. Light, dry pollen released in clouds
  4. Feathery stigmas hanging outside the flower

Explanation

Insect-pollinated flowers offer visual and chemical rewards, so large colourful petals, scent and nectar attract insects that transfer pollen. Wind-pollinated flowers instead show small dull petals and exposed stigmas.

Question 20Physiology of Plants

A potometer reading shows transpiration slowing sharply at midday on a very hot day. Which explanation is most consistent with this observation?

  1. Root hair cells have stopped absorbing minerals
  2. Stomata have closed to prevent excessive water loss Correct answer.
  3. Chlorophyll has absorbed too much carbon dioxide
  4. Xylem vessels have become blocked by lignin

Explanation

At very high temperatures and low humidity the plant risks desiccation, so guard cells lose turgor and stomata close. This reduces both transpiration and carbon dioxide uptake, explaining the midday slowdown.

Question 21Physiology of Plants

Two shoots are placed horizontally in darkness, one with its tip removed and one intact. After two days, which result is expected?

  1. Neither shoot shows any bending
  2. Only the intact shoot bends upward Correct answer.
  3. Only the tip-less shoot bends upward
  4. Both shoots bend upward equally

Explanation

The shoot tip produces auxin, which redistributes to the lower side and stimulates elongation, causing upward bending. Removing the tip removes the auxin source, so the tip-less shoot does not bend.

Question 22Physiology of Plants

In a leaf, air spaces in the spongy mesophyll are important because they

  1. prevent any water vapour from leaving the leaf
  2. conduct sugars away from the leaf
  3. increase the surface area for gas diffusion to mesophyll cells Correct answer.
  4. store starch grains for later use

Explanation

The interconnected air spaces bring carbon dioxide close to the surface of many mesophyll cells, maintaining a steep diffusion gradient. This improves gas exchange efficiency without the need for transport in liquid.

Question 23Physiology of Plants

A plant is grown in a solution lacking nitrate but with adequate magnesium. Which symptom is most likely, and why?

  1. Yellow leaves between veins, because chlorophyll cannot form
  2. Stunted growth with pale older leaves, because amino acids and proteins cannot be made Correct answer.
  3. Purple stems, because phosphate cannot be absorbed
  4. Brown leaf edges, because stomata cannot regulate water

Explanation

Nitrate supplies nitrogen for amino acids, proteins and nucleic acids, so deficiency stunts growth and causes pale older leaves as nitrogen is redistributed to new growth. Chlorosis from lack of chlorophyll is more typical of magnesium deficiency.

Question 24Physiology of Plants

Which observation would provide the strongest evidence that transpiration pull rather than root pressure drives water movement in a tall tree?

  1. Roots continue to absorb water after the stem is cut
  2. Water rises faster on a warm, windy day than on a cool, still day Correct answer.
  3. Water droplets appear at leaf margins at dawn
  4. Sap is forced upward when a root is pressurised

Explanation

If transpiration pull is the main mechanism, factors that increase evaporation such as warmth and wind should increase the rate of water movement. Root pressure would not explain this strong correlation with evaporative conditions.

Question 25Physiology of Plants

A plant's stomata are more numerous on the lower leaf surface than the upper. Which advantage does this arrangement give a terrestrial dicot?

  1. It speeds up translocation in the phloem
  2. It allows more carbon dioxide to enter the upper epidermis
  3. It increases light absorption by the palisade layer
  4. It reduces water loss because the lower surface is cooler and shaded Correct answer.

Explanation

The lower surface is shaded and cooler, so the diffusion gradient for water vapour is smaller, and fewer stomata there reduce total water loss. Light absorption is unaffected because stomata do not absorb light.

Question 26Physiology of Plants

Which tissue in a young dicot stem transports sucrose from a mature leaf to a developing root?

  1. Phloem sieve tubes Correct answer.
  2. Sclerenchyma fibres
  3. Xylem vessels
  4. Root hair cells

Explanation

Sucrose made in the leaf is loaded into phloem sieve tubes and carried in the direction of the sinks, such as developing roots. Xylem carries water and mineral ions upward, not sugars, so it cannot perform this role.

Question 27Physiology of Plants

Which mineral ion deficiency causes yellowing of older leaves first, because the element is mobile and is withdrawn from older tissue to supply new growth?

  1. Iron
  2. Boron
  3. Calcium
  4. Nitrogen Correct answer.

Explanation

Nitrogen is a mobile element, so when supply is short the plant recycles it from older leaves to young growing tissue, and chlorosis appears on older leaves first. Iron, calcium and boron are immobile, so their deficiencies show first on young leaves.

Question 28Physiology of Plants

A student measures the rate of transpiration of a leafy shoot under four sets of conditions. Which set should give the highest rate?

  1. Warm, dry, moving air Correct answer.
  2. Cool, humid, still air
  3. Cool, dry, moving air
  4. Warm, humid, still air

Explanation

Transpiration is driven by the diffusion gradient of water vapour between the moist air spaces inside the leaf and the surrounding air. Warm air holds more moisture, dry air keeps the external vapour concentration low, and moving air removes the humid boundary layer, so all three raise the gradient and the rate.

Question 29Physiology of Plants

Which statement describes the role of the Casparian strip in a root?

  1. It actively pumps water into the xylem by osmosis
  2. It forces water and ions entering the xylem to pass through cell membranes Correct answer.
  3. It allows water to move freely through the apoplast into the xylem
  4. It increases the surface area available for absorption of ions

Explanation

The Casparian strip is a waterproof band of suberin in the radial and transverse walls of endodermal cells. It blocks the apoplast pathway, so water and dissolved ions must cross a selectively permeable membrane before reaching the xylem, giving the root control over which solutes enter.

Question 30Physiology of Plants

In the light-independent stage of photosynthesis, carbon dioxide is combined with a five-carbon compound. What is the immediate product of this carbon fixation step?

  1. One molecule of ribulose bisphosphate
  2. One molecule of glucose
  3. Two molecules of glycerate 3-phosphate Correct answer.
  4. Two molecules of triose phosphate

Explanation

The enzyme rubisco attaches carbon dioxide to ribulose bisphosphate, a five-carbon compound, and the unstable six-carbon product immediately splits into two molecules of glycerate 3-phosphate. These are then reduced to triose phosphate using ATP and reduced NADP from the light-dependent stage.

Question 31Physiology of Plants

A leaf is kept in bright light with adequate carbon dioxide but at a temperature close to freezing. Which factor most directly limits the rate of photosynthesis under these conditions?

  1. Carbon dioxide concentration
  2. Light intensity
  3. Availability of chlorophyll
  4. Enzyme activity in the Calvin cycle Correct answer.

Explanation

Photosynthesis depends on enzyme-controlled reactions such as those catalysed by rubisco, and enzyme activity falls sharply at low temperature. Since light and carbon dioxide are already adequate, temperature acting through enzyme kinetics is the limiting factor.

Question 32Physiology of Plants

Which feature of a hydrophytic plant such as a water lily is an adaptation to living in water?

  1. Thick waxy cuticle on the upper leaf surface
  2. Leaves reduced to spines
  3. Large air spaces in the leaf and stem tissue Correct answer.
  4. Sunken stomata in deep pits

Explanation

Hydrophytes live in or on water, where buoyancy and gas exchange are the main problems, and extensive aerenchyma provides air spaces that keep tissues buoyant and allow oxygen to diffuse to submerged parts. Thick cuticles, sunken stomata and spine-like leaves are xerophytic features that reduce water loss.

Question 33Physiology of Plants

Which statement explains why a plant that has wilted in dry soil regains its rigidity after watering?

  1. Water replaces the cellulose in the cell walls, making them rigid
  2. Water enters the root cells and is drawn up to the leaves, making cells turgid again Correct answer.
  3. Water is actively pumped into leaf cells using ATP from respiration
  4. Water moves into the xylem and pushes the cell walls outward by root pressure alone

Explanation

When soil water is restored, root cells take up water by osmosis and the transpiration stream carries it to the leaves. Water entering the vacuoles of leaf cells increases turgor pressure against the cell walls, restoring rigidity.

Question 34Physiology of Plants

A plant is grown with its roots in a sealed chamber in which the air pressure is reduced, while the shoot is in normal air. Which observation would support the cohesion-tension theory of water movement?

  1. The rate of transpiration increases sharply
  2. The xylem vessels collapse and refill repeatedly
  3. Water continues to rise to the leaves at the same rate
  4. Water movement up the stem slows or stops Correct answer.

Explanation

The cohesion-tension theory states that water is pulled up the xylem under tension created by transpiration at the leaves. Reducing the pressure around the roots removes the push from root pressure, so if movement depends mainly on transpiration pull, it should continue, but if root pressure were the main driver it would fail; the standard test is that pull-driven flow depends on an intact, continuous water column. In this setup, reducing external pressure on the roots removes root pressure as a driving force, so any slowing shows that pull from the leaves is needed to sustain flow.

Question 35Physiology of Plants

Which change would most increase the rate of transpiration of a leafy shoot in a potometer?

  1. Lowering the temperature of the surrounding air
  2. Increasing the humidity of the surrounding air
  3. Coating the leaves with a thin layer of grease
  4. Increasing the air movement around the leaves Correct answer.

Explanation

Increasing air movement removes the layer of humid air close to the leaf surface, steepening the diffusion gradient for water vapour and increasing transpiration. Coating leaves, raising humidity and cooling the air all reduce the gradient or block stomata.

Question 36Physiology of Plants

Which statement describes the mechanism by which auxin causes a shoot to bend toward unilateral light?

  1. Auxin accumulates on the shaded side, where it stimulates cell elongation Correct answer.
  2. Auxin is transported equally to both sides but light destroys it in the tip
  3. Auxin accumulates on the illuminated side, where it inhibits cell elongation
  4. Auxin is destroyed on the illuminated side, so that side grows faster

Explanation

Auxin produced in the shoot tip is redistributed laterally so that its concentration is higher on the shaded side. In shoots, higher auxin concentration promotes elongation, so the shaded side grows faster and the shoot bends toward the light.

Question 37Physiology of Plants

A plant is placed in an airtight transparent chamber in bright light. The carbon dioxide concentration inside falls during the morning but stops falling and begins to rise around midday, although light intensity remains high. Which explanation is most consistent with these observations?

  1. The plant has used up all its chlorophyll during the morning
  2. Photosynthesis has stopped because the light-dependent stage has been switched off by darkness
  3. Respiration has stopped, so carbon dioxide is no longer produced
  4. Stomata have closed because of water stress, so carbon dioxide uptake has stopped Correct answer.

Explanation

At midday, high temperature and water loss can cause stomata to close to conserve water, which cuts off carbon dioxide supply and slows or halts photosynthesis. Respiration continues, releasing carbon dioxide, so the chamber concentration stops falling and then rises.

Question 38Physiology of Plants

Which statement correctly describes the role of magnesium in a plant?

  1. It is required for the transport of sucrose in phloem
  2. It is a component of proteins and nucleic acids
  3. It is a component of chlorophyll and is needed for normal leaf colour Correct answer.
  4. It is needed for the formation of middle lamella and cell walls

Explanation

Magnesium is a central atom in the chlorophyll molecule, so deficiency reduces chlorophyll synthesis and causes chlorosis, especially in older leaves because magnesium is mobile. Nitrogen is the element associated with proteins and nucleic acids, and calcium with the middle lamella.

Question 39Physiology of Plants

A student compares the rate of water uptake by a shoot in still air and in moving air, using a potometer. Which conclusion is best supported if the bubble moves faster in moving air?

  1. Water is absorbed by active transport in moving air
  2. The xylem vessels widen in moving air, allowing faster flow
  3. Transpiration pull increases when the humid layer around the leaf is removed Correct answer.
  4. Root pressure increases when air moves around the shoot

Explanation

Moving air removes the humid boundary layer around the leaf, increasing the water vapour gradient and the rate of transpiration. Greater transpiration increases the tension in the xylem, so the pull on water and the rate of uptake measured by the potometer rise.

Question 40Physiology of Plants

Which comparison of the apoplast and symplast pathways of water movement in a root is correct?

  1. The apoplast pathway passes through cell walls and intercellular spaces, while the symplast pathway passes through cytoplasm and plasmodesmata Correct answer.
  2. The apoplast pathway requires ATP, while the symplast pathway is passive
  3. Both pathways pass through the vacuole and are identical in route
  4. The apoplast pathway passes through cytoplasm, while the symplast pathway passes through cell walls

Explanation

In the apoplast pathway, water moves through the non-living cell walls and intercellular spaces, while in the symplast pathway it moves through the cytoplasm of cells connected by plasmodesmata. Both routes are passive, but the apoplast route is interrupted by the Casparian strip in the endodermis.

Question 41Cell Biology and Organisation

Which organelle is the main site of ATP synthesis in a eukaryotic cell?

  1. Lysosome
  2. Smooth endoplasmic reticulum
  3. Golgi apparatus
  4. Mitochondrion Correct answer.

Explanation

Mitochondria carry out oxidative phosphorylation, using the electron transport chain and ATP synthase on the inner membrane to produce most of the cell's ATP. The other organelles listed handle modification and packaging, digestion, or lipid synthesis and do not generate ATP on this scale.

Question 42Cell Biology and Organisation

A plant cell is placed in a solution whose solute potential is more negative than the cell sap. What is the expected immediate response?

  1. Water leaves the cell and the protoplast shrinks away from the wall
  2. Water enters the cell and the protoplast swells against the cell wall Correct answer.
  3. No net movement of water occurs across the membrane
  4. The cell wall dissolves and the cell bursts

Explanation

The external solution has a lower water potential than the cell sap, so water moves in by osmosis down the water potential gradient. Because the plant cell has a rigid wall, the protoplast swells and turgor pressure rises rather than the cell bursting.

Question 43Cell Biology and Organisation

Which feature distinguishes prokaryotic cells from eukaryotic cells?

  1. Presence of a plasma membrane
  2. Presence of ribosomes
  3. Absence of a membrane-bound nucleus Correct answer.
  4. Presence of DNA

Explanation

Prokaryotes keep their genetic material in a nucleoid region without a nuclear envelope, whereas eukaryotes enclose DNA within a double membrane. Plasma membranes, ribosomes and DNA are common to both cell types, so they cannot distinguish them.

Question 44Cell Biology and Organisation

An enzyme is added to a substrate solution at its optimum pH, but the reaction rate is low at 5 degrees Celsius. Which explanation is most consistent with enzyme kinetics?

  1. The substrate has been denatured by the cold
  2. The enzyme has been digested by the substrate
  3. The active site has permanently changed shape
  4. Low kinetic energy gives few successful enzyme-substrate collisions Correct answer.

Explanation

At low temperature molecules move slowly, so enzyme and substrate collide less often and with less energy, lowering the rate of reaction. The enzyme is not denatured by cold, and its activity recovers as temperature rises towards the optimum.

Question 45Cell Biology and Organisation

Which combination correctly describes the fluid mosaic model of the plasma membrane?

  1. A rigid layer of cellulose with protein pores
  2. A phospholipid bilayer with proteins embedded in or attached to it Correct answer.
  3. A double layer of protein with lipid channels through it
  4. A single layer of phospholipids with cholesterol on one side

Explanation

The model describes a bilayer of phospholipids whose hydrophobic tails face inward, with proteins floating within or attached to the bilayer. This arrangement accounts for membrane fluidity and selective permeability.

Question 46Cell Biology and Organisation

A student observes a cell with a large central vacuole, chloroplasts and a visible cell wall. Which conclusion is best supported?

  1. It is a plant cell Correct answer.
  2. It is a bacterial cell
  3. It is an animal cell
  4. It is a fungal cell

Explanation

A large permanent central vacuole, chloroplasts and a cellulose cell wall are characteristic features of plant cells. Animal cells lack walls and chloroplasts, bacteria lack these membrane-bound organelles, and fungi have walls but no chloroplasts.

Question 47Cell Biology and Organisation

Which process moves glucose into an intestinal epithelial cell against its concentration gradient?

  1. Simple diffusion through the phospholipid bilayer
  2. Active transport using ATP Correct answer.
  3. Osmosis through aquaporins
  4. Facilitated diffusion without energy input

Explanation

Movement against a concentration gradient requires energy, supplied by ATP, usually through a carrier protein. Simple diffusion and facilitated diffusion only move substances down their gradient, and osmosis applies to water only.

Question 48Cell Biology and Organisation

Which statement best explains why the rate of diffusion across a membrane increases when the surface area of the membrane increases?

  1. The particles gain more kinetic energy
  2. The concentration gradient becomes steeper
  3. More membrane is available for particles to cross per unit time Correct answer.
  4. The membrane becomes more permeable to large molecules

Explanation

Diffusion rate is proportional to surface area, so a larger membrane offers more routes for particles to cross in a given time. Surface area does not alter the concentration gradient, the kinetic energy of particles, or the permeability of the membrane.

Question 49Cell Biology and Organisation

Which organelle is directly responsible for modifying and packaging proteins for secretion?

  1. Rough endoplasmic reticulum
  2. Golgi apparatus Correct answer.
  3. Peroxisome
  4. Nucleolus

Explanation

The Golgi apparatus receives proteins from the rough endoplasmic reticulum, modifies them, and packages them into vesicles for secretion. The rough ER synthesises proteins, the nucleolus makes ribosomal RNA and ribosomes, and peroxisomes handle oxidative reactions.

Question 50Cell Biology and Organisation

A red blood cell is placed in distilled water. Which observation is expected?

  1. The cell shrinks and becomes crenated
  2. The cell becomes turgid but does not burst
  3. The cell maintains its shape because of its cell wall
  4. The cell swells and bursts by haemolysis Correct answer.

Explanation

Distilled water has a higher water potential than the cytoplasm, so water enters the cell by osmosis. Red blood cells lack a cell wall, so they swell and eventually burst, a process called haemolysis.