Home / IB DP Biology B3.2 Transport- FA 2015- IB Style Questions For SL Paper 2

IB DP Biology B3.2 Transport- FA 2015- IB Style Questions For SL Paper 2

IBDP Biology Paper 2 - All Chapters

Question

The diagram shows the structure of the human heart.

(a) Annotate the diagram by adding arrows to show how deoxygenated blood enters the heart.

(b) Identify the blood vessel labelled X.

(c) Explain the function of the left ventricle.

▶️ Answer/Explanation

(a)

(b)

  • X is the aorta.
  • It is the largest artery in the body.
  • It carries oxygenated blood from the left ventricle to the rest of the body.

(c)

  • The left ventricle is responsible for pumping oxygen-rich blood to the entire body.
  • When it contracts, it creates a high pressure that pushes blood through the aorta.
  • It receives oxygenated blood from the left atrium, which gets it from the lungs via the pulmonary veins.
  • The contraction of the left ventricle is controlled by electrical impulses from the atrioventricular (AV) node.

Markscheme:

(a) Arrows added to the diagram to show how deoxygenated blood enters the heart:

(b) Aorta;

(c)
a. Contracts to generate high pressure / pumps blood at high pressure;
b. Pump blood (through the aorta) to all parts of the body (apart from the lungs);
c. Receives blood from the left atrium;
d. Contraction is stimulated by the AV node;

Question

The human circulatory system is structured to serve the organs and tissues of the body efficiently.

a. Outline the exchange of materials between capillaries and tissues.
b. Explain the structures and functions of arteries and veins.
c. Describe what happens in alveoli. 
▶️ Answer/Explanation

a.

  1. Diffusion of substances: Materials move between blood and tissues by diffusion, following concentration gradients.
  2. Nutrient delivery: Glucose, amino acids, and oxygen diffuse from capillaries into tissue cells.
  3. Gas exchange:

    • Oxygen moves from blood to cells.

    • Carbon dioxide moves from cells into the blood.

  4. Waste removal: Metabolic wastes like urea and excess water diffuse from cells into capillaries.
  5. Hormone transport:

    • Hormones exit capillaries at target tissues to bind to cell receptors.

    • Glands release hormones into blood at capillaries.

b.

Arteries:

  • Function: Carry blood away from the heart (usually oxygenated).
  • Pressure: Blood flows under high pressure from the ventricles.
  • Structure:
    • Thick muscular walls: To withstand and maintain pressure.
    • Elastic fibers: Allow stretching and recoil with each heartbeat.
    • Narrow lumen: Helps maintain high pressure.

Veins:

  • Function: Return blood to the heart (usually deoxygenated).
  • Pressure: Blood flows under low pressure.
  • Structure:
    • Thinner walls: Less muscle and fewer elastic fibers due to lower pressure.
    • Wider lumen: Reduces resistance to blood flow.
    • Valves: Prevent backflow and ensure unidirectional flow toward the heart.

c.

  1. Gas exchange site: Oxygen and carbon dioxide are exchanged between alveolar air and blood.
  2. Oxygen movement: Oxygen diffuses into the capillaries and binds with hemoglobin in red blood cells.
  3. Carbon dioxide movement: CO₂ diffuses from blood into alveolar air to be exhaled.
  4. Ventilation support: Air moves in and out due to pressure changes during breathing.
  5. Surfactant secretion: Type II pneumocytes produce surfactant, reducing surface tension and preventing alveolar collapse.
  6. Efficient exchange: Thin walls and close contact with capillaries maintain steep gas concentration gradients.

 

Markscheme:

a. Exchange of materials between capillaries and tissues:

  • Molecules move by diffusion / move down a concentration gradient.
  • Nutrients move into tissues.
  • Gas exchange / Oxygen and carbon dioxide exchange between tissues and blood/capillaries.
  • (Nitrogenous) wastes/excess water move from cells/tissues into blood/capillaries.
  • Hormones leave capillaries in target tissues/to attach to receptors on cells / (endocrine) organs/gland tissues release hormones into the bloodstream.

b. Structures and functions of arteries and veins:

  • Arteries and veins have three layers in their walls OR walls of arteries and veins have tunica externa, media, and intima.
  • Pressure is high in arteries/pressure is low in veins.
  • Arteries receive blood from ventricles/heart / carry blood away from the heart.
  • Lumen of artery is small to keep pressure high.
  • Arteries have thick (muscular) walls (with elastic fibers) to withstand pressure.
  • Elastic fibers recoil in response to ventricle/heart contraction.
  • Muscle/elastic fibers help maintain pressure between heartbeats OR muscle/elastic fibers help propel blood toward capillary beds.
  • Veins receive blood from capillaries/capillary beds / carry blood to the heart.
  • Large lumen of veins so there is less resistance to blood flow.
  • Valves in veins keep blood flowing toward the heart/prevent backflow.

c. What happens in alveoli:

  • Gas exchange.
  • Oxygen diffuses from air to blood and carbon dioxide diffuses from blood to air.
  • Oxygen binds to hemoglobin in red blood cells.
  • Pressure inside/volume of alveoli increases/decreases / air enters/exits alveoli during inspiration/expiration/ventilation.
  • Blood flow through capillaries / concentration gradients of gases/oxygen/CO2 maintained.
  • Type II pneumocytes secrete fluid/surfactant / secretion of surfactant to prevent sides of alveolus adhering.

Accept answer in a clearly annotated diagram.

Question

a. Draw a labelled diagram of the human heart showing the attached blood vessels. 
b. Describe the action of the heart in pumping blood. 
c. Nerves connecting the brain and heart contain neurons that control heart rate. Explain how a nerve message passes from one neuron to another neuron. 
▶️ Answer/Explanation

a.

b.

  • Atria fill with blood from the veins:
    • Right atrium receives deoxygenated blood from the vena cavae.
    • Left atrium receives oxygenated blood from the pulmonary veins.
  • SA node (sinoatrial node) in the right atrium generates electrical impulses:
    • Triggers atrial contraction (atrial systole), pushing blood into the ventricles.
    • AV valves open to allow flow into ventricles.
  • After a short delay, ventricles contract (ventricular systole):
    • AV valves close to prevent backflow into atria.
    • Semilunar valves open, allowing blood to exit:
      • Right ventricle → pulmonary artery (to lungs)
      • Left ventricle → aorta (to body)
  • Ventricles relax (diastole):
    • Semilunar valves close to prevent backflow from arteries.
    • The cycle then repeats with the next impulse from the SA node.

c.

  1. When a nerve impulse reaches the end of the presynaptic neuron, it causes depolarization.
  2. This opens calcium channels in the membrane, and Ca²⁺ ions diffuse into the neuron.
  3. The influx of calcium triggers neurotransmitter-containing vesicles (e.g., with acetylcholine) to move to and fuse with the presynaptic membrane.
  4. Neurotransmitters are released into the synaptic cleft by exocytosis.
  5. They diffuse across the cleft and bind to receptors on the postsynaptic membrane.
  6. This causes ion channels to open, allowing sodium (Na⁺) to enter the postsynaptic neuron.
  7. The membrane becomes depolarized, triggering a new action potential in the postsynaptic neuron.
  8. Neurotransmitter is then broken down by enzymes or reabsorbed into the presynaptic neuron to reset the synapse.

Markscheme: 

a. Diagram of the Human Heart

Remember, up to TWO “quality of construction” marks per essay.

NB: Drawings must be correctly proportioned and clearly drawn showing connections between structures. The drawing may show the heart without contraction or in any stage of contraction. Award [1] for any correctly labelled part that has been drawn to the stated standards.

a. atria/right atrium/left atrium – shown above the ventricles and must not be bigger than ventricles;

b. ventricle/left ventricle/right ventricle – shown below the atria, must have thicker walls than atria;

c. vena cava/superior vena cava/inferior vena cava – connected to right atrium;

d. pulmonary artery – shown from right ventricle (to lungs);

e. pulmonary vein(s) – shown (from lungs) to left atrium;

f. aorta – shown as large artery from left ventricle out of heart;

g. AV valves/atrioventricular valves / mitral/bicuspid and tricuspid – named correctly and shown between both atria and ventricles and labelled at least on one side;

h. semilunar valves – shown in aorta/pulmonary artery;

Valves need to open in correct direction.

b. Action of the Heart in Pumping Blood

a. (both) atria collect blood (from veins);

b. sinoatrial/SA node sends impulses to muscle/fibres initiating contraction;

c. blood is pushed to ventricles by contraction of atria/atrial systole;

d. AV (atrioventricular) valves are open (as atria contract);

e. semilunar valves are closed so that ventricles fill with blood;

f. ventricles contract / ventricular systole;

g. AV (atrioventricular) valves close (and preventing backflow);

h. blood is pushed out through the semilunar valves/into pulmonary artery and aorta;

i. when ventricles relax/diastole, semilunar valves close preventing backflow of blood;

Do not accept the description of blood flow without a clear action.

Do not accept general statements such as systole = heart contraction and diastole = heart relaxation.

[4 max] if suggests that left and right sides are contracting at different times or simultaneous contraction not indicated.

c. Nerve Message Transmission Between Neurons

a. nerve impulse reaches the end of the presynaptic neuron;

b. (depolarization causes) calcium channels in membrane (to) open;

c. calcium diffuses into the presynaptic neuron;

d. vesicles of/containing neurotransmitter move to and fuse with presynaptic membrane;

e. (neurotransmitter) released (by exocytosis) into synaptic space/cleft;

f. (neurotransmitter) diffuses across the space/synapse;

g. (neurotransmitter) attaches to receptors on postsynaptic neuron;

h. receptors cause ion channels to open and sodium diffuses into the postsynaptic neuron;

i. the postsynaptic neuron membrane is depolarized;

j. (depolarization) causes a new action potential;

k. (neurotransmitter) on postsynaptic membrane is broken down;

l. (neurotransmitter) is reabsorbed into the presynaptic neuron;

Question

Humans ingest food which provides energy and nutrients to carry out life processes.

(a) Outline how starch in the diet is modified for absorption in humans.

(b) Describe how the small intestine is adapted for efficient absorption of nutrients.

(c) Blood transports nutrients to all tissues of the body. Explain the initiation of the heartbeat and how blood flow is controlled in the heart. 

▶️ Answer/Explanation

 (a)

Starch, a complex carbohydrate, must be broken down into simpler sugars before it can be absorbed by the body:

  1. Enzyme action: Starch is broken down by the enzyme amylase, which begins the digestion process.
  2. Sources of amylase: Amylase is secreted by the salivary glands (acting in the mouth) and the pancreas (acting in the small intestine).
  3. Digestion site: Most starch digestion occurs in the duodenum, the first part of the small intestine.
  4. Conversion: Amylase breaks starch into smaller molecules like maltose and eventually into glucose.
  5. Absorption-ready: These resulting monomers are small and soluble, allowing them to be easily absorbed through the intestinal wall into the bloodstream.

(b)

The structure of the small intestine is highly specialized to maximize nutrient absorption:

  1. Length: It is very long, providing a large surface area for absorption over time.
  2. Villi and microvilli: The lining contains finger-like projections called villi, and the epithelial cells of each villus have even smaller projections called microvilli, massively increasing the surface area.
  3. Thin walls: The epithelial layer is only one cell thick, minimizing the diffusion distance.
  4. Rich blood supply: Each villus contains capillaries and lacteals to quickly transport absorbed nutrients into the bloodstream and lymphatic system.
  5. Mitochondria in cells: The cells lining the villi contain many mitochondria to produce energy for active transport of nutrients.
  6. Transport proteins: Membranes contain specific proteins to carry out facilitated diffusion and active transport of nutrients like glucose, amino acids, and ions.

(c)

  1. The heart beats automatically and keeps blood flowing in the correct direction due to electrical signals and valve mechanisms:

  2. Myogenic initiation: The heart’s contraction is myogenic, meaning it begins within the heart muscle itself, not from nerves.

  3. Pacemaker region: The sinoatrial (SA) node, located in the right atrium, acts as the natural pacemaker by generating regular electrical impulses.

  4. Impulse conduction: These impulses cause the atria to contract and are then relayed to the ventricles, causing ventricular contraction.

  5. Autonomic control: Heart rate can be adjusted by the medulla oblongata via sympathetic and parasympathetic nerves, and hormones like adrenaline can increase heart rate during stress or activity.

  6. Valves regulate flow:

    • Atrioventricular (AV) valves prevent blood from flowing back into the atria when ventricles contract.

    • Semilunar valves (in the aorta and pulmonary artery) prevent blood from flowing back into the ventricles after ejection.

  7. One-way system: These valves ensure blood flows in one direction only, maintaining efficient circulation throughout the body.

Markscheme:

(a)
a. starch is broken down by the enzyme amylase;
b. (amylase) secreted by the pancreas/salivary glands;
c. acts in the duodenum/small intestine/mouth;
d. starch is broken down into monomers/maltose/glucose;
e. products of digestion are smaller/more soluble molecules for absorption

(b)
a. small intestine is very long;
b. small intestine contains villi/microvilli;
c. the epithelial cells of villi have microvilli;
d. these increase the surface area for absorption;
e. the cells of the small intestine contain (a large number of) mitochondria;
f. these provide energy for active transport;
g. the walls contain proteins for active transport/facilitated diffusion;
h. the villi have a rich blood supply/lacteals;
i. the walls of the villi are thin so less distance for diffusion;

(c)
a. the contraction of the heart is myogenic / heart beat initiates within the heart tissue itself;
b. heart beat initiates in the sinoatrial node OR SA acts as a pacemaker;
c. the SA node is located in the right atrium;
d. electrical impulses pass over the atria then the ventricles;
e. nerves from the medulla can control the rate of heart beat/blood flow;
f. epinephrine/adrenaline can increase the rate of the heart/blood flow;
g. contraction of heart/cardiac muscle causes blood to flow;
h. ventricles send blood to the organs/cells of the body;
i. the direction of flow is controlled by valves/valves prevent backflow OR when the heart/named chamber contracts the valves/named valve open;
j. AV valves prevent backflow from ventricles/into atria;
k. semilunar valves prevent blood returning/backflow to the heart/ventricles.

Question

A wide variety of organic compounds are used by living organisms.

(a) Draw a diagram to show the ring structure of D-ribose. 

(b) Describe how ATP is produced by Photosystem II in the light-dependent stage of photosynthesis. 

(c) Explain how carbohydrates are transported from plant leaves. 

▶️ Answer/Explanation

(a)

(b) 

ATP production in the light-dependent reactions occurs in the thylakoid membranes of chloroplasts:

  1. Light absorption: Light is absorbed by Photosystem II, exciting electrons in chlorophyll.
  2. Electron transport: Excited electrons are passed along the electron transport chain (ETC) through a series of electron carriers.
  3. Proton pumping: The energy from electrons is used to pump protons (H⁺) into the thylakoid lumen, creating a proton gradient.
  4. Proton gradient: A high concentration of protons builds up inside the thylakoid space.
  5. ATP synthesis: Protons flow back into the stroma through the enzyme ATP synthase, which uses the energy to phosphorylate ADP into ATP.
  6. Process name: This ATP production is called photophosphorylation, driven by chemiosmosis.

(c)

Carbohydrate transport from leaves (sources) to storage or growing tissues (sinks) occurs through the phloem in a process called translocation:

  1. Sucrose loading: Sugars like sucrose are actively transported into phloem sieve tubes by companion cells.
  2. Osmosis: The high solute concentration in the phloem draws water in by osmosis from nearby xylem, increasing pressure.
  3. Pressure flow: This generates high hydrostatic pressure at the source end.
  4. Flow to sink: Sap moves down the pressure gradient to the sink (roots, fruits, seeds), where sugars are removed and used or stored.
  5. Sieve elements: Phloem sieve tubes with sieve plates and no nuclei allow unimpeded flow of the sugary sap.

Markscheme:

(a)
a. ring with four carbons and one oxygen atom;
b. \(\mathrm{CH}_2 \mathrm{OH}\) attached to \(\mathrm{C} 4\);
c. \(\mathrm{OH}\) and \(\mathrm{H}\) attached by single bonds to \(\mathrm{C} 1, \mathrm{C} 2\) and \(\mathrm{C} 3\) with \(\mathrm{OH}\) facing downwards on \(\mathrm{C} 2\) and \(\mathrm{C} 3\);

(b)
a. light (energy) absorbed by pigments/chlorophyll/photosystems;
b. excited electrons passed to electron carriers/electron transport chain;
c. protons/hydrogen ions pumped into thylakoid (space);
d. proton gradient/high proton concentration generated;
e. protons pass via ATP synthase to the stroma;
f. ATP synthase phosphorylates ADP/ATP synthase converts ADP to ATP;
g. photophosphorylation/chemiosmosis;
h. ATP synthase/electron carriers/proton pumps/photosystems/pigment are in the thylakoid membrane;

(c)
a. translocation/movement by mass flow;
b. in phloem sieve tubes;
c. sieve plates/pores in end walls/lack of organelles allows flow (of sap);
d. carbohydrates (principally) transported as sucrose;
e. (sucrose/glucose/sugar/carbohydrate) loaded (into phloem) by active transport;
f. loading/pumping in (of sugars) by companion cells;
g. high solute concentration generated (at the source);
h. water enters by osmosis (due to the high solute concentration);
i. hydrostatic pressure increased/high hydrostatic pressure generated;
j. pressure gradient causes flow (from source to sink);
k. leaves are a source because carbohydrates are made there;
l. transport to the sink where carbohydrates are used/stored;

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