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
Answer:
(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.
Outline the exchange of materials between capillaries and tissues.
Explain the structures and functions of arteries and veins.
Describe what happens in alveoli.
▶️Answer/Explanation
Markscheme
a. molecules move by diffusion / move down a concentration gradient
b. nutrients move into tissues
c. gas exchange / Oxygen and carbon dioxide exchange between tissues and blood/capillaries
d. (nitrogenous) wastes/excess water move from cells/tissues into blood/capillaries
e. hormones leave capillaries in target tissues/to attach to receptors on cells / (endocrine) organs/gland tissues release hormones into the bloodstream
a. arteries and veins have three layers in their walls
OR
walls of arteries and veins have tunica externa, media and intima
b. pressure is high in arteries/pressure is low in veins
c. arteries receive blood from ventricles/heart / carry blood away from heart
d. lumen of artery is small to keep pressure high
e. arteries have thick (muscular) walls (with elastic fibres) to withstand pressure
f. elastic fibres recoil in response to ventricle/heart contraction
g. muscle / elastic fibres help maintain pressure between heartbeats
OR
muscle / elastic fibres help propel blood toward capillary beds
h. veins receive blood from capillaries/capillary beds / carry blood to heart
i. large lumen of veins so there is less resistance to blood flow
j. valves in veins keep blood flowing toward heart/prevent backflow
a. gas exchange
b. oxygen diffuses from air to blood and carbon dioxide diffuses from blood to air
c. oxygen binds to hemoglobin in red blood cells
d. pressure inside/volume of alveoli increases/decreases / air enters/exits alveoli during inspiration/expiration/ventilation
e. blood flow through capillaries / concentration gradients of gases/oxygen/CO2 maintained
f. type II pneumocytes secrete fluid/surfactant / secretion of surfactant to prevent sides of alveolus adhering
Accept answer in a clearly annotated diagram.
Question
Draw a labelled diagram of the human heart showing the attached blood vessels.
Describe the action of the heart in pumping blood.
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
Markscheme
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 cave/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.
Remember, up to TWO “quality of construction” marks per essay.
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.
Remember, up to TWO “quality of construction” marks per essay.
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.[3]
(b) Describe how the small intestine is adapted for efficient absorption of nutrients.[5]
(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.[7]
▶️Answer/Explanation
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. [3]
(b) Describe how ATP is produced by Photosystem II in the light-dependent stage of photosynthesis.[5]
(c) Explain how carbohydrates are transported from plant leaves.[7]
Answer/Explanation
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;