Outline the function of the stomach in food digestion.

State a mechanism by which the stomach destroys pathogens.

There are times when pathogenic bacteria infect the stomach, causing ulcers.

State a pathogenic bacterium that can cause stomach ulcers.

There are times when pathogenic bacteria infect the stomach, causing ulcers.

Explain how proton pump inhibitors (PPIs) reduce conditions that favour ulcer formation.

a. produces acid to break down molecules;

b. churns food for mechanical digestion;

c. produces proteases to digest proteins/peptides;

Allow pepsin.

Do not allow “acid kills bacteria”.

production of hydrochloric acid/HCl

Helicobacter pylori/H. pylori

a. acidity is achieved by a proton pump/H⁺, K⁺-ATPase;

b. exchange of H⁺ from the cytoplasm for K⁺ ions in the lumen;

c. PPIs bind irreversibly to the (proton) pump;

d. lowering amount of acid produced/H⁺;

Most candidates could outline at least one function of the stomach, and the strongest candidates provided complete answers.

This was done poorly, as most provided vague answers.

The majority of candidates could state Helicobacter pylori, some with minor distortion, but answers with other names were seen, including Escherichia coli and Vibrio cholerae.

Strong candidates distinguished themselves in this question, although most could state that their action lowered the volume of hydrochloric acid produced.

Samples from cardiac muscle were taken during autopsies from individuals who had coronary heart disease (CHD) and a control group. The histogram shows the relationship between the quantity of cardiac muscle cells and their diameter in the left ventricle in the two groups.

Distinguish between the distribution of cardiac muscle cell diameters in the CHD and control groups.

Describe how the structure of cardiac muscle cells allows them to transmit impulses.

Explain the reason for the delay between contractions of the atria and of the ventricles.

a. CHD has wider range/spread/more variation of diameter values / vice versa 

b. control has higher percentage/proportion/peak in middle values (accept numbers between 8–12)

Accept numerical statement supporting this

a. are branched/ have a Y-shape/ interconnected / connect to several neighbouring «cardiac» cells 

b. intercalated discs are special regions of/junctions between plasma membranes 

c. provide electrical coupling / enable rapid transmission of «electrical» impulses «between cells» 

d. ion channels in membranes 

e. «ease of» flow of ions allows action potentials to spread «between cardiac cells»
OR
«ease of» flow of ions allows rhythmic depolarization 

f. trigger action potentials without nervous input 

Accept annotated drawings.

a. impulses from atria do not pass directly to ventricles «due to layer of fibrous material» 

b. travel to ventricle via atrio-ventricular node/AVN in wall of right atrium 

c. impulses from AVN sent along Bundle of His /conducting fibres/Purkinje fibres 

d. ensures that the atria have ejected their blood into the ventricles first before the ventricles contract

On the diagram, label a

(i) second messenger. 

(ii) gene regulatory protein.

Outline one characteristic of steroid hormones that allows them to readily diffuse through cell membranes

Compare and contrast the mechanisms of action of peptide and steroid hormones.

(i) a. second messenger correctly labelled

(ii) b. gene regulatory protein correctly labelled

Do not accept steroid hormone/protein complex.

a. lipid-soluble/non-polar/hydrophobic molecules «that readily diffuse through cell membranes»

b. small enough to diffuse through membrane

Since the questions asks to “outline” a brief account is necessary to gain the mark.

Answers do not need to be presented as a table. Award marks for pairs of corresponding elements on the same line of this table.

Deduce from the results of the study whether HGH improves strength.

Suggest one reason that it is difficult to detect illegal use of HGH to enhance athletic performance.

HGH is a peptide hormone. Describe the mode of action of peptide hormones on target cells.

the drug does not appear to improve strength as less mass can be lifted «by arms and legs» ✔

a. occurs naturally so hard to tell whether it has been injected ✔ 

b. HGH has very short half life ✔

a. peptide hormones do not enter the cell ✔

b. they bind to receptors/proteins in the plasma membrane of the target cell ✔

c. a secondary messenger initiates the cell response ✔

d. causes a cascade of actions that changes the cell’s physiology ✔

e. cAMP is a common secondary messenger ✔

While this was generally done well, those who missed this mark chose to write about muscle growth rather than the mass being lifted.

Students were unable to state that the detection of illegal use of HGH was due it already being naturally present in the body.

Although a few students still confused peptide and steroid hormones, many were able to score 2 or 3 marks here. Most of these students stated that peptide hormones do not enter the cell due to their hydrophilic nature, that they do bind to receptors on the cell membrane, and that this binding initiates a secondary messenger and causes a cascade of reactions. This level of detailed knowledge was not seen elsewhere in the paper. One possible reason for this is that peptide and steroid hormones have appeared frequently on recent exam papers, and that the use of past papers remains the most common way for students to prepare for these exams.

Distinguish between the ECG trace of the patient with hypokalemia and the patient with hyperkalemia.

Outline the events that occur within the heart that correspond to the QRS complex.

Severe hypokalemia can lead to ventricular fibrillation. Describe the medical response to ventricular fibrillation.

Sometimes hyperkalemia occurs as a body tries to respond to low blood pH. State the normal range of blood pH in the human body.

Explain how low blood pH causes hyperventilation (rapid breathing).

a. hypokalemia has a flat T-wave whereas hyperkalemia has a heightened T-wave OWTTE
OR
hypokalemia S-T interval longer Accept vice versa

b. hypokalemia has narrower/faster QRS complex compared to hyperkalemia  Accept vice versa

c. hypokalemia trace/baseline «overall» lower than hyperkalemia Accept vice versa

a. arrival of signal at AV node 

b. transmission via conducting fibres/bundle of His/Purkinje fibres 

c. ventricles depolarize 

d. atrioventricular valves close
OR
semilunar valves open 

e. ventricular systole/contraction 

f. contraction begins at apex/base

a. use a defibrillator 

b. place electrodes on exposed chest of victim 

c. in a line with the heart in the middle of a diagonal line between the two paddles 

d. the device determines whether fibrillation is happening 

e. if it is, an electric discharge is given off to restore a normal heart rhythm

around 7.4 or 7.35 to 7.45

a. increased CO₂ lowers blood pH 

b. chemoreceptors in carotid/aorta detect lower pH 

c. signal/impulses to medulla «oblongata»
OR
signal/impulses to respiratory centre 

d. «from medulla/respiratory centre» to intercostal muscles/diaphragm 

e. ventilation rate increase occurs to expel CO₂

State the name of the bacterium that can cause stomach ulcers.

Compare and contrast the effect of adding antioxidants to nizatidine on the ulcer healing rate.

Components of gastric juice have been thought to aggravate the development of ulcers. Outline the role of nerves in the secretion of gastric juices.

Gastric juice production can be inhibited by the hormone secretin which is a polypeptide. Outline the mechanism by which a peptide hormone carries out its function.

Helicobacter pylori ✔

To award [1] full scientific name is required.

a. vitamin E and thioctic acid both improve healing rate «compared with nizatidine alone»
OR
all trials with antioxidant/three trials improve healing rate «compared to N alone» ✔

b. adding vitamin E increases healing rate more than adding thioctic acid
OR
adding both vitamin E and thioctic acid increases healing rate to highest level «but still less than 100 %» ✔

Giving values alone is not enough.

[Source: Effect of Helicobacter Pylori
Eradication Therapy and some Antioxidants
on Ulcer Healing Rates in Patients with
Helicobacter pylori-associated Duodenal
Ulcer, Ahmed M Ali, 2013, http://
www.rroij.com/open-access/effect-ofhelicobacter-
pylori-eradication-therapy-andsome-
antioxidants-on-ulcer-healing-rates-inpatients-
with-helicobacter-pylor-.php?
aid=34774, licensed under a Creative
Commons Attribution 4.0 International
License]

a. sight/smell of food stimulates brain ✔

b. food entering stomach stimulates chemoreceptors/stretch receptors to send impulses/signals to brain ✔

c. impulse/signal from brain causes cells in stomach lining/parietal cells to secrete acid/HCl/gastric juice ✔

d. brain sends impulses/signals «via vagus nerve» to endocrine cells in wall of stomach to release gastrin ✔

e. gastrin stimulates «more» production of acid/HCl/gastric juice ✔

a. bind to plasma membrane receptors of «target» cell ✔

b. results in activation/release/synthesis of a secondary messenger ✔

c. triggers a cascade of reactions ✔

d. leads to promotion/inhibition of enzymes
OR
causes activation of protein kinase «resulting in hormonal effect» ✔

A large number stated the complete binomial name, as expected; many provided only a partial name; a noticeable number wrote E. coli, something else irrelevant or left the box blank.

The majority could contrast the effect, but it was more difficult for some also to provide a comparison, that is, similarities; many had some difficulty organizing their answer, although correct.

The majority had a good idea about factors that would increase gastric juice secretion, but a large number bypassed the role of the brain or the nerves in their answer, limiting themselves to the various stimuli and responses.

Many candidates provided a correct, complete answer. Some nevertheless inverted the order of the production of a second messenger and the cascade of reactions, which occurs afterwards to cause the multiplying effect of the hormone. A noticeable number, especially in French, outlined the action of secretin in digestion instead of answering the question. A few confused peptide hormones with steroid hormones.

The electron micrograph shows a section through an alveolus showing blood in a capillary.

[Source: © International Baccalaureate Organization 2019]

Identify the cells found at X and Y.

X: 

Y:

Explain, with the aid of an annotated diagram, how physical exercise affects the affinity of hemoglobin for oxygen. 

a. X: «type I» pneumocyte ✔ 

b. Y: endothelial cells ✔

Accept endothelium/capillary wall

a. diagram showing normal oxygen dissociation curve ✔

b. diagram showing curve with increased CO₂ to the right ✔

c. both axes correctly labelled ✔

d. where tissues are respiring there is a higher concentration of CO₂ ✔

e. exercise increases the amount of CO₂ in the blood ✔

f. an increase in CO₂ lowers the pH of the blood ✔

g. a lower pH causes hemoglobin to release oxygen ✔

h. lower pH decreases hemoglobin affinity for O₂/changes hemoglobin conformation ✔

i. oxygen is released in tissue where it is required for respiration ✔

j. this is known as the Bohr effect/shift ✔

k. at the lungs the low concentration of CO₂ means oxygen attaches to hemoglobin ✔

l. «Bohr» effect particularly important during exercise ✔

Apply [4 max] if no diagram.

Many students did correctly identify that X was a pneumocyte I, but very few correctly identified cell Y as an endothelial cell. Many assumed that the second cell would be a pneumocyte II.

Students who did well on this question tended to achieve all marking points, including correct information on the graphs. These students also composed detailed explanations, including the role of reduced pH and its effect on affinity. Some students remain unsure about how, where and why CO₂ is produced and how this changes hemoglobin affinity for oxygen. Weaker students did not realise that the annotated diagram referred to in the question would be the dissociation curve; they often included caricatures of people exercising or attempts at drawing hemoglobin.

Compare and contrast the relationship between BMI and systolic blood pressure in males and females.

Outline the relationship between systolic blood pressure and hypertension.

State two effects hypertension can have on the circulatory system.

State how blood pressure and heart rate can be measured.

a. both males and females have higher «mean/range» SBP as weight increases
OR
both males and females have highest SBP for overweight BMI ✔

b. «SPB» males «slightly» greater than females in all BMIs ✔

c. similar values/no/little difference between underweight and normal weight in females but «visible/obvious» difference in males ✔

d. range of SBP narrower in «overweight» females than males ✔

«at rest/chronic/constant» higher than normal «120 mmHg» systolic blood pressure is an indicator of hypertension ✔
OWTTE

stroke ✔

thrombosis ✔

blood clot ✔

heart attack ✔

heart failure ✔

aortic aneurysms ✔

coronary heart disease/CHD ✔

peripheral arterial disease ✔

atherosclerosis ✔

Award up to [2 max] for the first two answers given

blood pressure:

sphygmomanometer/blood pressure monitor
OR
description how this is used ✔

heart rate:

taking pulse manually/using a blood rate monitor/stethoscope «to count the beats» ✔
OWTTE

Thyroxin is a hormone produced in the thyroid gland. State one function of thyroxin.

The action of thyroxin is similar to steroid hormones. Describe the action of steroid hormones.

The World Health Organization recommends that the iodine intake should be supplemented in pregnant women due to their increased requirements. Outline the need for iodine supplementation.

a. regulates the «basal» metabolic rate/BMR

b. controls body temperature

[Max 1 Mark]

a. steroid hormone passes through cell/plasma membrane

b. binds to receptor «proteins» in cytoplasm

c. receptor–hormone complex travels to nucleus

d. binds to DNA/chromatin

e. promotes/inhibits the transcription of specific genes

f. codes for/produces specific proteins

[Max 3 Marks]

a. iodine is an essential nutrient/cannot be synthesized by the body

b. iodine is required for thyroid hormones/thyroxin production

c. some areas in the world have iodine deficient soil/low iodine in their diet

d. supplementation will reduce stunted growth and mental development/cretinism in babies born to mothers associated with thyroid deficiency

e. thyroid deficiency will lead to health problems

[Max 2 Marks]

Describe the relationship between age and liver transplants due to cancers.

Describe the breakdown of hemoglobin in the liver.

Outline one other function of the liver.

State one material not produced by the human body that is egested from the digestive system.

as age increases liver transplant due to cancer increases ✔

a. hemoglobin taken up by Kupffer cells ✔ Do not accept confusion between erythrocytes and hemoglobin.

b. broken down into heme and globins ✔

c. globin hydrolysed/broken down to amino acids ✔

d. iron removed from heme group
OR
heme broken down to form bilirubin/bile pigment ✔

a. storage of nutrients ✔

b. regulation of blood glucose levels ✔ e.g. glucose to glycogen and vice versa.

c. production/secretion of bile ✔ Do not accept production of bile pigments from hemoglobin in the liver.

d. detoxification ✔

e. synthesis of plasma proteins e.g. albumin ✔

f. synthesis and regulation of cholesterol ✔

Accept only the first answer if more than one are provided.

cellulose/lignin/fibre
OR
bacteria ✔

Using the diagram, identify an organ containing an exocrine gland.

Using the diagram, identify a hormone involved in the development of a follicle.

Using the diagram, identify a steroid hormone.

State two effects of prolactin.

List two hormones produced by the posterior pituitary gland.

breast ✔

FSH ✔

estrogen
OR
progesterone ✔

a. growth and development of the breast/mammary gland ✔

b. lactation/synthesis of milk ✔

c. maintenance of milk secretion ✔

a. oxytocin ✔

b. antidiuretic hormone/ADH/vasopressin ✔

State one condition which would require the use of an artificial pacemaker.

Describe briefly how an artificial pacemaker works.

The structure labelled X in the micrograph is a junction between two cardiac muscle cells. Identify the structure labelled X.

Explain how the structure of cardiac muscle cells allows propagation of stimuli through the heart wall.

a. heartbeat too slow/fast/irregular/tachycardia/fibrillations ✔ 

b. sinoatrial node is malfunctioning ✔ 

c. pathway that conducts electrical impulses generated by the sinoatrial node is impaired ✔

Do not accept heart attack

a. a pacemaker contains a battery and pulse generator
OR
it is connected to the heart by wires/cables ✔

b. it detects that the heart’s natural rhythm is incorrect ✔

c. it sends electrical impulses to correct the heartbeat/it replaces sinoatrial node ✔

d. provide a regular impulse/constant rhythm ✔

intercalated disc ✔

a. branching provides larger surface area of contact between cells
OR
is branched to allow groups of cells to work together/synchronize ✔

b. intercalated disks hold cells together so they cannot separate
OR
intercalated discs allow easy transfer of electrical impulses between cells ✔

c. contain large numbers of mitochondria ✔

d. gap junctions «in intercalated discs» form channels that allow continuous flow of cytoplasm between cell ✔

For mpa, accept branching allows connection to multiple cells

This was generally well answered, with a few students identifying generic (and incorrect) medical problems such as heart attacks and hypertension.

A majority of the candidates stated that the pacemaker sends electrical impulses or replaces the SA node, and they achieved 1 mark. Few were able to state that the pacemaker is connected to the heart by wires or that it monitors the heart rate itself.

About half of the students correctly identified intercalated discs from the diagram, with the most common incorrect answer being Z-lines or another part of the sarcomere.

This question was yet another example where students lacked the subject-specific vocabulary to achieve the marks. The majority of candidates attempting this option were unable to identify structural features of cardiac muscle cells that help in the propagation of stimuli, instead writing about striation and the myogenic nature of cardiac tissue. Those who did write about gap junctions, Y-shaped cells or intercalated discs were unable to achieve marks because they did not explain how these structures affected the function of the cells.

State one function of the atrioventricular node.

Describe how the structure of cardiac muscle cells allows them to carry out their function.

a. relays signal from SAN to ventricles ✔

b. causes ventricular systole ✔

c. delays signal enabling both ventricles to contract simultaneously
OR
delays signal so the atria empty before ventricular systole ✔

Not necessary to present answer in a table.

Award [1] for each set of corresponding structure and function.

A large number could state one correct function of the atrioventricular node, mainly that it causes ventricular systole.

Many could provide a correct description including many elements, but many discussed the structure of the heart as a whole, rather than the cellular structure of cardiac muscle cells or discussed at length the myogenic nature of cardiac tissue.

Identify the structure labelled X.

Describe the unique properties of cardiac muscle cells.

State an early invention that led to improved knowledge of the heart.

intercalated disc

a. cells are myogenic/self-excitatory

b. cells are joined end to end

    OR

    cells are joined by intercalated disc

c. «intercalated discs» allow for faster propagation «of signal»

d. cells contract together for coordinated contraction

e. contain many mitochondria

f. cells are branching/Y-shaped

g. controlled by pacemaker/sinoatrial/SA and atrioventricular/AV nodes

[Max 4 Marks]

stethoscope

OR

electrocardiograph/ECG

Allow other valid example.

Cells on the surface of intestinal villi have microvilli, which provide a large surface area for absorption. State another structural characteristic of these villus cells that adapts them to the absorption of nutrients.

a. tight junctions 

b. protein channels / membrane pumps 

c. large number of mitochondria

Explain how the pH of blood is kept constant during exercise.

a. pH of blood is regulated to stay within a narrow range/7.35 to 7.45 ✔
If values provided, both required

b. increase in CO₂ produced during aerobic respiration «during exercise» ✔

c. CO₂ reacts with water to form carbonic acid ✔

d. chemoreceptors detect drop in blood pH «when CO₂ concentration rises»
OR
«increase in» CO₂ lowers blood pH ✔

e. carbonic acid dissociates to form hydrogen carbonate ions and hydrogen ions ✔
Allow formula

f. hydrogencarbonate is alkaline/increases pH/neutralizes H⁺ ions ✔
OWTTE

g. hydrogen ions bind to plasma proteins/hemoglobin ✔

h. stimulation of breathing centre/medulla oblongata
OR
ventilation rate increased ✔

i. faster diffusion/removal of CO₂ «in alveoli/lungs» ✔

A good marker of dietary intake of iodine is the urinary iodine level (UI). A study was carried out in the UK to establish urinary iodine levels and milk intake in schoolgirls aged 14–15 years.

Urinary iodine values from 50 to 99 μg dm^–3 are considered to be mild iodine deficiency. Deduce the effect of milk intake on the iodine status of schoolgirls in the UK.

Outline the need for iodine in the endocrine system.

Growth hormones are examples of peptide hormones. Explain the mechanism of action of peptide hormones.

a. the more milk taken in, the higher the iodine levels 

b. when no milk consumed all girls «in study» were iodine deficient 

c. in all cases median value is mildly deficient so milk may have no effect 

d. increase above 1 cup/day may have no/little effect

Accept answers in the converse.

a. iodine is absorbed/used/needed by the thyroid 

b. «needed» to synthesise thyroxin 

c. lack of iodine causes swelling of thyroid gland/goiter/hypothyroidism
OR
thyroxin used to regulate metabolic rate/generate heat

a. «peptide hormones» do not enter cells 

b. bind to «specific surface» receptors in plasma membrane 

c. leads to production /release of a secondary messenger inside cell 

d. triggers a cascade of reactions in the cytoplasm 

e. usually involves activating or inhibiting enzymes

Outline the role of the sinoatrial node in the contraction of the heart.

The graph shows the results of a study of the incidence of coronary heart disease (CHD) in different age groups of men participating in a study carried out by the National Heart, Blood and Lung Institute.

Comment on the claim that the bar chart proves that old age causes CHD.

Suggest one factor other than age and hypertension that is correlated with the incidence of CHD.

Hypertension has been suggested as a possible cause of CHD. Explain the possible causes of hypertension.

a. initiates action potentials / electrical impulses (at start of cardiac cycle) 

b. acts as pacemaker/ continuous beating without external stimuli 

c. signal spreads over atria / causes contraction of atria (systole) 

d. impulses transmitted to AV (atrioventricular) node / cannot pass directly to ventricles

a. data show correlation (increased chance of CHD with age) not causation

OWTTE.

sex / ethnic group / genetics / obesity / diet / life style / medical history / high cholesterol levels

Smoking / stress go under lifestyle.

a. deposition of fat in arteries thus losing elasticity/forming fibrous tissues 

b. deposition of fat/formation of plaque in arteries thus narrowing of lumen/causing a blockage 

c. high salt levels in diets thus retaining more fluids 

d. smoking because nicotine is a vasoconstrictor molecule 

e. prolonged high levels of stress thus causing vasoconstriction / exposure to stress hormones 

f. genetic predisposition makes it more likely that other factors will lead to hypertension

Do not accept a list.

From the diagram, deduce the effect of the disease polycythemia on the proportion of erythrocytes in total blood volume.

Suggest how high altitude could lead to polycythemia.

Suggest how changes in hemoglobin could help humans become better adapted to living at high altitude.

Outline the stages involved in the recycling of erythrocytes by the liver.

the proportion/percentage increases «from 45 % to 70%»

a. more erythrocytes/hemoglobin produced to compensate 

b. low oxygen «partial» pressure «at high altitude» 

c. lower oxygen saturation «of hemoglobin at high altitude» 

d. less oxygen carried to tissues/hypoxia

a. induced conformational change in the structure of the hemoglobin molecule occurs 

b. «this» hemoglobin has higher affinity for oxygen 

c. saturation curve shifted to the left «because of low O₂ levels»  

d. «this» hemoglobin becomes more saturated at lower partial pressures of oxygen 

e. increased hematocrit/concentration of hemoglobin/red blood cells to carry more O₂

Allow answers in an annotated diagram.

a. phagocytosis of erythrocytes by Kupffer cells 

b. hemoglobin is split into globin and heme group 

c. globin is re-used in protein synthesis 

d. heme group broken down into iron and bilirubin 

e. iron is carried back to the bone marrow «to produce new hemoglobin/erythrocytes»

Apart from the water temperature, state two other values to be measured at the start of the experiment.

1.

2.

The energy value calculated for avocado was 750 kJ 100 g^–1. The actual energy value of avocado is 840 kJ 100 g^–1. Suggest a source of error in the experiment.

Avocados are known to be a good source of dietary fibre and contain all the essential amino acids. State one health benefit of a diet high in fibre.

Avocados are known to be a good source of dietary fibre and contain all the essential amino acids. Distinguish between essential and non-essential amino acids.

a. mass/volume of water ✔ 

b. mass of avocado ✔

a. heat loss to the air ✔

b. heat transferred to the apparatus ✔ 

c. avocado may not be fully dried/incomplete combustion of avocado ✔

helps in movement of food along alimentary canal/peristalsis/decreases transit time
OR
regulates bowel action
OR
prevents cancer/constipation/heart attack ✔

essential amino acids must be included in the diet and the body cannot make them «whereas the body can synthesize non-essential amino acids» ✔

Many students missed these relatively simple marks by using language that lacked precision using terms, such as “amount” rather than mass or volume. This is the same problem that affects students when writing their individual investigations submitted for internal assessment.

While most students were able to identify loss of heat as the primary source of error, some were distracted by aspects of the diagram and therefore wrote answers such as “incorrect amount of oxygen.” As in the case of the individual investigations, students often erroneously identify mistakes; for example, they regard a misreading of thermometers as a source of error.

This was answered well although many students resorted to colloquialisms when referring to bowel action.

Credit required two pieces of information about synthesis of amino acids and whether or not they were necessary components in a balanced diet. Hence few candidates gained credit as they only included one of these in their responses.

State the importance of including vitamins in our diet.

Suggest one limitation of the information about vitamins shown on this label.

Distinguish between gastric juice and pancreatic juice using the table.

Describe the mode of action of steroid hormones.

Many animals, including humans, maintain strongly acidic conditions in part of their digestive systems. Explain two benefits of this to the animal.

are essential for health / cannot be synthesized by humans

Vitamin D is altered from a precursor.

does not mention whether the information is based on adults/children/age

OR

only two vitamins are shown/no quantities given for vitamins

OR

it does not take into consideration sex / pregnancy / activity levels

Accept other valid correct limitation.

Each row must be a distinction

a. steroid hormones enter cell / steroid hormones can pass through cell membranes 

b. steroid hormones bind to receptor in the cytoplasm 

c. the receptor-hormone complex interacts directly with genes/regulates gene expression 

d. example (e.g. oestrogen, testosterone, progesterone) 

a. provides ideal pH for stomach enzyme activity 

b. (acidic conditions) denature proteins /start breakdown of other organic substances 

c. (acidic conditions) convert pepsinogen (inactive) into pepsin 

d. (acidic conditions) destroy pathogens in ingested food

Identify which state had the smallest seasonal change in vitamin D levels.

Suggest one reason why people in Victoria show such a large seasonal change in vitamin D levels.

Outline one effect of lack of vitamin D.

Vitamins and minerals are both essential nutrients. Compare and contrast vitamins and dietary minerals.

Northern Territory ✔

less sun in winter than in summer
OR
colder in winter so cover up/indoors more
OR
skin has more exposure to sun in summer ✔

Accept other valid suggestions.

Accept vice versa.

a. «lack of vitamin D results in» calcium «ions» not absorbed from gut in sufficient quantities ✔

b. calcium salts not deposited or reabsorbed
OR
affects bone mineralization ✔

c. bones become softened/weakened ✔

d. can cause rickets «in children»/osteomalacia «in adults» ✔

Not necessary to present answer in a table.

Accept other valid similarities and/or differences.

Award marks for complete lines only.

The vast majority identified correctly Northern Territory, but some answered Queensland, which, although having a smaller value in summer, had a greater seasonal change.

Most could provide a valid reason for a large seasonal change in Victoria implying a decrease in sun exposure; some answers were nevertheless unclear or irrelevant.

The vast majority could list one effect of the lack of vitamin D, but it was more difficult for some to also include a cause in their outline.

An important number could provide a complete answer but the similarities and differences between vitamins and minerals are unclear for many; too many stated differences of different nature between the two.

Outline the main changes in the lungs that occur in patients with emphysema.

State a treatment for emphysema.

An increase in metabolic activity results in greater release of CO₂ into the blood. On the graph, draw the oxygen dissociation curve during intense exercise when the CO₂ concentration of the blood is high.

Explain how the increase in CO₂ concentration affects the release of oxygen to respiring cells.

a. air sacs/alveoli break down/rupture 

b. creating one larger air space instead of many small ones / reduces the surface area of the lungs 

c. loss of elasticity of lung tissue

supplemental oxygen / breathing techniques / bronchodilators / inhaled steroids / lung surgery to remove damaged tissue / lung transplant

curve has to be towards the right and starting together

Must start together but can finish slightly below the original curve.

a. increased levels of CO₂ lower the pH of the blood 

b. «which results in» decreased affinity of the hemoglobin for oxygen / greater release of oxygen 

c. this shifts the oxygen dissociation curve to the right/Bohr shift

Explain the process of erythrocyte and hemoglobin breakdown in the liver. 

a. erythrocytes rupture when they reach the end of their life span / after 120 days 

b. «erythrocytes» absorbed by phagocytosis 

c. Kupffer cells ingest/take in erythrocytes 

d. Kupffer cells in sinusoids in the liver 

e. hemoglobin split into globin and heme groups 

f. amino acids from the globin are recycled 

g. heme group is further broken down into iron and bilirubin / bile pigment 

h. iron stored in liver / transported to bone marrow/spleen 

i. bilirubin released into alimentary canal/becomes part of bile

Using the graph, explain the Bohr shift.

State two modes of transport of carbon dioxide in blood. 

1.

2. 

State the effect of carbon dioxide in blood on the rate of ventilation.

Describe what happens to the hemoglobin from old or damaged red blood cells that are broken down.

a. respiring tissues produce CO₂;

b. CO₂ leads to an increase in H⁺/decrease in blood pH;

c. increased acidity/decreased pH shifts the oxygen dissociation curve to the right;

d. affinity of the hemoglobin for oxygen is reduced;

e. greater release of oxygen from hemoglobin (at the same partial pressure of oxygen) in tissues;

a. dissolved/carried in plasma;

b. forms carbonic acid/H₂CO₃ (in plasma)
OR
as hydrogencarbonate (HCO₃-) ions (in plasma);

c. binds to hemoglobin in red blood cells;

increased carbon dioxide in blood increases the rate of ventilation
OR
positive correlation/relationship;

a. hemoglobin (from broken red blood cells) taken up by Kupffer cells (in the liver);

b. hemoglobin broken down into heme and globin;

c. globin hydrolyzed/broken down to amino acids;

d. iron removed from heme group
OR
heme broken down to form bilirubin/bile pigment;

Do not accept red blood cells broken down into heme and globin.

Most candidates did well in this question, but strongest candidates distinguished themselves with complete and very detailed answers. Although candidates did well, there were many inaccuracies in some answers. Bohr shift is the shift to the right of the oxygen dissociation curve in respiring tissues; it does not refer to the reverse process at lung level.

The majority of candidates did well also for this question, although some answers lacked accuracy.

Most candidates knew that CO₂ affects the rate of ventilation, but some did not specify that an increase in CO₂ caused an increase in ventilation rate, or vice versa.

The majority of candidates described the process correctly; some stated incorrectly that red blood cells, instead of hemoglobin, are broken down into heme and globin.

State the disease caused by Helicobacter pylori.

Outline how gastric acid is produced in the stomach.

Explain why proton pump inhibitors alleviate the symptoms of H. pylori infections.

stomach ulcer
OR
stomach cancer

a. sight/smell/«presence of» food in stomach stimulates nervous system 

b. nervous system/vagus nerve stimulates gastric glands «to produce gastric acid» 

c. gastrin controls release of gastric acid 

d. parietal cells «are stimulated to» release gastric/hydrochloric acid/HCl 

e. acidity maintained by the proton pump/H⁺/K⁺ ATPase

a. as proton pumps are inhibited less protons/H⁺ into stomach «lumen» 

b. «less protons/H⁺ in stomach» less hydrochloric acid produced 
OR
stomach «contents» become less acidic 
OWTTE.

c. stomach heals with higher pH

State the organ in the digestive system where this process is taking place.

Explain how components of bile are produced by the liver.

Outline a function of fats in the body.

Explain how epithelial cells in the gut are adapted for absorption.

In order to compare the absorption of fat and of glucose in the digestive system, state in the table, using yes or no, whether the processes occur.

small intestine ✔

a. hemoglobin «from red blood cells» broken down into heme and globin ✔

b. iron removed from heme ✔

c. «remainder of» heme group transformed to bilirubin ✔

d. «surplus» cholesterol is converted to bile salts ✔

e. bilirubin and bile salts form bile ✔

a. use as energy source «for cellular respiration»
OR
«long term» energy storage ✔

b. fat tissue for «heat» insulation ✔

c. protects axons by myelin sheath
OR
other function of fats ✔

Accept first function written only

a. microvilli/brush border to increase surface area ✔

b. numerous mitochondria for energy for active transport ✔

c. have transport proteins for specific nutrients ✔
eg: glucose, amino acids 

d. single layer of cells/short distance allowing for diffusion ✔

Explanation must be included for each characteristic

Award [1] for each correct row

Award the mark only for rows containing two correct answers, ie: no blanks accepted

Distinguish between essential and non-essential amino acids.

Using the data from the tables, suggest a reason for the differences in lysine concentration in the diets from the UK and India.

Explain the consequences of protein deficiency malnutrition.

List two dietary sources of vitamin D.

State one possible cause and one symptom of type II diabetes.

Cause:

Symptom:

Distinctive elements from the same line required to gain the mark.

Indian diet based on rice and wheat which have low levels of lysine
OR
low levels of meat/milk in Indian diet
OR
high levels of meat/milk in UK diet ✔

a. protein/muscle lost for energy ✔

b. lack of blood plasma proteins ✔

c. leading to tissue fluid retention/edema/swollen abdomen/kwashiorkor ✔

d. lethargic/little interest in surroundings ✔

e. thin muscles/flaky appearance of skin/sparse hair with lack of pigmentation ✔

f. physical/mental development retarded ✔

g. lack of menstrual cycle ✔

cod/fish liver oil
OR
oily fish «accept correctly named example» Check examples on the Internet if necessary.
OR
egg yolk
OR
«fortified/enriched» dairy product ✔ i.e. milk/cheese/yoghurt.

Allow any two sources for the mark. Mark only the first two.
Do not accept sunlight, as source has to be dietary, nor dietary supplements.
Reject fish alone.

Both one cause from left column and one symptom from right column required for the mark.
For the cause, do not accept risk factors, e.g. high sugar intake/obesity, lack of exercise, genetic predisposition, etc.

Other valid symptoms could be: slow-healing sores, dizziness, tiredness, red/swollen gums, kidney/back pain, nerve damage, erectile dysfunction.

Discuss the significance of the oxygen dissociation curves for adult hemoglobin and fetal hemoglobin.

a. oxyhemoglobin forms when partial pressure of oxygen is high
OR
oxyhemoglobin dissociates/breaks apart when partial pressure of oxygen is low ✔

b. respiring tissues have low partial pressure of oxygen ✔

c. sketch/statement of S-shaped «oxygen dissociation» curve ✔

d. axes of graph labelled correctly as percentage oxygen saturation of hemoglobin on y-axis AND partial pressure of oxygen on x-axis ✔ Both needed. Do not accept reverse axes.

e. «small» decrease in oxygen partial pressure over steep part of curve results in dissociation of oxyhemoglobin/oxygen release to tissues ✔

f. fetal hemoglobin is structurally different from adult/maternal hemoglobin ✔

g. fetal dissociation curve to left of adult dissociation curve ✔

h. fetal hemoglobin has greater affinity for oxygen than adult/maternal blood ✔

i. fetus obtains its oxygen from mother’s blood «at placenta» ✔

j. at any given partial pressure of oxygen fetus will take up oxygen from mother
OR
fetal hemoglobin always more saturated with oxygen than maternal blood ✔

Some of these points may be present in annotated diagrams.

Most candidates generally provided good, and many complete, thorough explanations including well annotated diagrams, but there were also answers lacking sufficient details or containing diverse inaccuracies or incorrect terminology (e.g. concentration instead of partial pressure). Some candidates ventured sometimes in long explanations of hemoglobin structure or gas exchange at lung level in adults, or description of Bohr shift, all irrelevant for this question which differed slightly from questions in past papers on similar topics.

Explain how steroid and peptide hormones exert their effect.

a. endocrine glands secrete hormones directly into the bloodstream;

Steroid hormones:
b. pass through the plasma membrane (of target cells);

c. bind to receptor proteins in the cytoplasm
OR
form a receptor–hormone complex;

d. (receptor–hormone complex) enters the nucleus;

e. promotes the transcription of specific genes;

Peptide hormones:
f. bind to receptors in the plasma membrane (of the target cell);

g. (binding of hormones to membrane receptors) activates a cascade of reactions;

h. (cascade of reactions) mediated by a second messenger (inside the cell);

i. (cascade results in) activation of enzymes;

The majority of candidates provided complete explanations, even if they did not specify plasma membrane; there are nevertheless some candidates having difficulty over the role of second messengers, the effect of peptide hormones on enzyme action or being able to outline the events in a correct sequence.

Using the graph, discuss the hypothesis that a high BMI in adolescence is more dangerous than a high BMI in adulthood.

State one factor, other than BMI, that increases the risk of CHD.

Hypothesis supported as:

a. all subjects with a high BMI «in Q5» in adolescence had a high risk of CHD «>6», even when BMI in adulthood was low «in Q2» 
OWTTE.

b. subjects with a high BMI in adulthood «Q4 and Q5» had a much higher risk of CHD if they also had a high BMI in adolescence 
OWTTE.

c. high BMI in both adolescence and adulthood increases risk

Accept any other valid answer based on the graph.

[Source: From The New England Journal of Medicine, A Tirosh et al, Adolescent BMI Trajectory and Risk of
Diabetes versus Coronary Disease, 364, 1315. Copyright © (2011) Massachusetts Medical Society.
Reprinted with permission from Massachusetts Medical Society]

increased triglycerides/cholesterol in the blood
OR
presence of plaque/atherosclerosis «in arteries»
OR
high blood pressure/hypertension
OR
sedentary lifestyle/lack of exercise
OR
genetic/hereditary factor
OR
smoking
OR
age
OR
diet

The figure below shows the average death rates from coronary heart disease in the UK.

[Source: Bhatnagar P, Wickramasinghe K, Wilkins E, et al, Trends in the epidemiology
of cardiovascular disease in the UK, Heart 2016; 102: 1945–1952.]

Suggest one reason for the general decrease in the incidence of coronary heart disease.

Outline the use of a defibrillator.

Explain the heart sounds.

improvement in medical care  Accept improvements in medication.
OR
healthier diet
OR
decrease in blood cholesterol/pressure
OR
decrease in cigarette smoking
OR
increase in exercise ✔

Accept other answers relating to greater awareness about health issues.

a. used in life-threatening cardiac conditions/arrythmia/ventricular fibrillation ✔

b. delivers therapeutic/small dose/shock of electrical energy ✔

c. depolarizes the heart muscle
OR
allows normal rhythm to be re-established ✔

a. «heart sounds» produced by the closing of the valves ✔

b. first sound «lub» is due to «closure of» the atrioventricular valves ✔ Accept bicuspid/mitral and tricuspid.

c. second sound «dub» is due to «closure of» the semilunar valves ✔ Accept pulmonary/aortic valves.

d. sequence of sounds from a healthy heart is lub dub «pause lub dub pause» ✔ OWTTE

The diagram shows the liver and its main blood vessels.

[Source: VectorStock]

Label the hepatic portal vein bringing blood to the liver.

Outline the circulation of blood through liver tissue.

Explain the breakdown of hemoglobin in the liver.

[Source: VectorStock]

Accept the vessel labeled (hepatic portal vein) as it ends in the liver and does not continue. A label anywhere on the vessel or pointing to the arrow underneath it is acceptable.

a. hepatic artery carries oxygenated blood (from the aorta) 

b. hepatic portal vein carries (deoxygenated) blood from digestive tract 

c. blood from hepatic portal vein and hepatic artery mixes 

d. flows through sinusoids 

e. hepatic vein carries blood away from liver/to heart

a. hemoglobin absorbed by phagocytes/Kupffer cells 

b. split into heme and globin 

c. globin hydrolysed/broken down to amino acids 

d. iron removed from heme group / heme broken down to form bilirubin/bile pigment

Athletes taking growth hormones show an increase in their sprinting capacity. This is not maintained after discontinuing the drug. Suggest one reason for the disappearance of the effect.

Distinguish between the mode of action of steroid hormones and peptide hormones.

Identify with reasons whether the pituitary gland is an exocrine or endocrine gland.

growth hormone/drug no longer present «in blood» OWTTE
OR
lack of hormones reduce «gained» muscle mass/strength ✔ 

Award [1 mark] for each complete row, up to [3 max].
Apply ECF the second time plasma is omitted and award the mark.

a. endocrine gland ✔

b. «ductless gland that» secretes hormones directly into the bloodstream ✔

Explain, using an oxygen dissociation curve, how hemoglobin supplies oxygen to respiring tissues and how the Bohr shift increases the supply.

How hemoglobin supplies oxygen to respiring tissues

a. properly labelled axes showing % saturation hemoglobin and partial pressure of oxygen

b. correct/sigmoid shape of «normal» oxygen dissociation curve

Do not accept concave curves. Curve should start at origin.

c. tissues use O₂ for «cellular» respiration thus lowering pO₂ at tissue level
OR
respiring tissues produce CO₂

d. O₂ dissociates more at lower pO₂ from Hb «than at higher pO₂» thus providing O₂ to «respiring» tissues/OWTTE

How Bohr shift increases the supply

e. CO₂ is converted to hydrogen carbonate ions/HCO₃⁻ and H⁺

f. increase in H⁺ lowers blood pH

g. H⁺ combines with Hb / conformational change in Hb «in red blood cell» freeing some O₂

h. shifts the oxygen dissociation curve to the right «Bohr shift»
OR
shift to the right shown on diagram labelled Bohr shift

i. oxygen dissociation curve steeper at lower pO₂ «corresponding to respiring tissues»

j. lowers the affinity of hemoglobin for oxygen

k. means less oxygen can be carried for same pO₂ «as normal»
OR
«even» more oxygen available for respiring tissues for same pO₂

Accept any of the marking points in a clearly annotated diagram. Values not required.

Jaundice causes a yellow discolouration of the skin, mucous membranes and sclera of the eyes. State the bile pigment causing this discolouration.

Explain how the normal production of bile pigments changes with the development of jaundice.

Distinguish between the structure of liver sinusoids and capillaries.

bilirubin

normal production: [2 max]

a. red blood cells/erythrocytes/hemoglobin broken down «in the liver»

b. hemoglobin/heme «from red blood cells» is converted to bilirubin/bile pigment

c. bilirubin/bile pigment transferred to bile and «normally» eliminated in the feces

change with jaundice:

d. «in jaundice» liver does not excrete/eliminate bilirubin/bile pigments

e. caused by immaturity/dysfunction/disease «of the liver»

    OR

    blockage of bile ducts

    OR

    increase in red blood cells breakdown

f. therefore bilirubin/bile pigment accumulates in the blood

[Max 4 Marks]

a. sinusoids have open pores/fenestrations/discontinuous endothelium and capillary endothelium is continuous/does not contain fenestrations

b. Kupffer cells are located inside sinusoids but not in capillaries

c. sinusoids larger in diameter/wider than capillaries

[Max 2 Marks]

Evaluate the effect of salt on blood pressure using the data in the graph.

State the instrument used by doctors to measure blood pressure.

Describe the mechanism by which the heartbeat is initiated.

a. systolic pressure increases with salt in diet during treatment;

b. diastolic pressure is slightly higher/no change with salt during treatment
OR
diastolic pressure only changes towards the end of the period;

c. (blood) pressure goes back to normal after treatment
OR
salt causes increased (blood) pressure;

d. standard deviation values overlap therefore not statistically significant;

sphygmomanometer/blood pressure monitor;

a. sinoatrial node/SAN initiates contraction of atria;

b. SAN sends messages to the atrioventricular/AV node;

c. AV node initiates ventricular contraction;

d. through conducting fibres;

The majority could evaluate that salt increased blood pressure, most comparing the effect on systolic and diastolic blood pressure.

Although strong candidates could state sphygmomanometer or blood pressure monitor, too many irrelevant or blank answers were seen.

Most candidates did well in this question, strongest candidates distinguishing themselves by complete and very detailed answers.

Outline one method that the researchers could have used to measure heart rate in this study.

Suggest reasons for the change in maximum heart rate with increasing age.

Outline the use of defibrillation to treat life-threatening cardiac conditions.

a. state the method/equipment 
eg take the pulse.

b. how method/equipment works 
eg count beats per minute. 

c. during exercise on treadmill/bicycle
OWTTE.

a. muscles become less elastic
OR
less muscle tone 

b. cells/mitochondria less efficient  

c. more fat deposits
OR
blood/oxygen supply to heart tissue reduced

Accept other valid documented answers. 

a. defibrillator is electrodes/a metal paddle/pad that is placed on the patient’s chest 

b. the device determines whether fibrillation is happening 

c. a series of electrical shocks are delivered through the electrodes 

d. electrical impulse is used to depolarize the heart muscle 

e. to re-establish the function of the SA node/natural pacemaker/natural rhythm «of the heart»

Describe how the liver regulates nutrient levels.

a. storage of glucose as glycogen
OR
breakdown of glycogen to glucose

Do not accept “sugar”.

b. deamination/breakdown of «excess» amino acids

c. storage/recycling of iron/copper

d. produces/eliminates cholesterol «as necessary»

e. storage of vitamin A/vitamin D/vitamin B12/vitamin K

A study was undertaken to determine the most effective method to delay the onset of type II diabetes in high-risk patients. Three groups were given either a placebo (control), a medicine that suppresses glucose production by the liver (anti-diabetic drug) or a lifestyle-modification program (lifestyle). The results for four years are shown in the graph.

Analyse the use of the anti-diabetic drug in delaying the onset of type II diabetes.

List features that would increase a person’s risk of developing diabetes.

a. less incidence of diabetes/more effective than placebo/control

b. but less effective than change in lifestyle

c. incidence nevertheless increases over the years

d. possibly ideal would be to combine both «anti-diabetic drugs and lifestyle»
OR
lifestyle and anti-diabetic drugs not tried together «so we do not know the outcome»

a. overweight patients
OR
obesity

b. sedentary lifestyle

c. high glucose diet
OR
high glucose level in blood

d. genetic predisposition

e. other valid risk factor

Discuss high altitude training for athletes.

benefits:

a. improved performance/endurance at lower oxygen levels

    OR

    improved performance/endurance when returning at low altitude

b. due to higher concentration erythrocytes/red blood cells/hemoglobin

c. more oxygen transported/circulating «due to increase in hemoglobin/RBC number»

d. improved metabolic/lung efficiency/gas exchange

e. increase in myoglobin/number of capillaries/mitochondria

risks:

f. altitude sickness/stroke/lower immunity

g. increased muscle tissue breakdown

h. effects are not immediate/not permanent/extended training at high altitude required

i. may be unfair to competitors who cannot train at high altitude

[Max 6 Marks]

Explain the role of receptors in mediating the action of both steroid and protein hormones.

a. receptors are proteins 

steroid hormones: [3 max]

b. steroid hormones cross plasma membrane 

c. bind to receptor «proteins» in the cytoplasm of the target cell 

d. to form a receptor–hormone complex 

e. «the receptor–hormone complex» promotes the transcription of specific genes 

peptide hormones: [3 max]

f. peptide hormones bind to receptors in the plasma membrane of the target cell 

g. binding of hormones to «membrane» receptors activates a cascade of reactions 

h. mediated by a second messenger inside the cell 

i. such as cAmp or Ca²⁺ calmodulin

Outline the possible consequences of a Helicobacter pylori infection of the stomach wall.

The bacterium secretes an enzyme that breaks down urea, resulting in an increase in pH. Outline how this would help the bacterium survive in the stomach.

Explain hormonal control of gastric secretion.

a. causes inflammation ✔

b. digestion of stomach lining by pepsin and HCl/gastric juice ✔ 

c. called «gastric» ulcer ✔

neutralizes the acid the stomach secretes that kills bacteria ✔

a. release of gastric juices stimulated by gastrin ✔

b. gastrin stimulates secretion of gastric hydrochloric acid ✔

c. from the parietal cells «of the stomach» ✔

d. gastrin release stimulated by presence of polypeptides/amino acids in stomach ✔

e. gastrin stimulates release of pepsinogen by chief cells «of the stomach» ✔

f. drop in pH/excess acid/secretion of secretin/somatostatin inhibits gastrin secretion ✔

Student answers revealed much confusion regarding how the bacteria affects the stomach, and again the quality of the responses was affected by lack of precision. Few could explain what caused the digestion of the stomach lining, and the most common marking point achieved was for simply stating that the bacterium causes ulcers.

While most students achieved this mark, many seem to think that “higher pH values” indicate greater acidity.

Of all the questions on this paper, this one seemed to encourage the most number of irrelevant statements. Students wrote about the role of the hypothalamus and the pituitary, pancreatic secretions and leptin almost as often as they outlined the role of gastrin. Even students who focused on gastric secretions often wrote more about control by the nervous system.

Describe a method that could be used to measure the energy content of a sample of food.

a. determine the initial and final/change in mass of the food sample 

b. determine initial and final/change in temperature of water 

c. ignite sample and place burning sample under a known volume/mass of water 

d. energy content is determined using formula

e. divide energy of water by mass of the food sample OWTTE

Using the R–R interval in this ECG, calculate the heart beats per minute (bpm) of this patient. Show your working.

Describe the electrical activity that occurs in the heart during the P wave.

Explain why the QRS wave has a larger amplitude than a P wave.

a. determining time of 1 beat = 0.46 «seconds»

b. correct calculation of heart rate/beats per minute = 130 «bpm»

Other possible calculations

eg:

23 «squares» × 0.02 «sec» = 0.46

OR

2.3 × 0.2 «sec» = 0.46

OR

atrial depolarization/electrical impulse travels from the sinoatrial/SA node to the atrioventricular/AV node

Accept atrial systole.

a. atrium has a small contraction requiring low electrical charge/OWTTE

b. the QRS complex shows the depolarization of the «right and left» ventricles 

Accept ventricular systole.

c. the ventricles have a large muscle mass compared to the atria, so the QRS complex has a larger amplitude than the P wave/OWTTE
OR
ventricle contraction needs more electricity than atrial contraction/OWTTE

Accept answers implying large muscle mass eg, stronger contraction, more pressure, etc.

Compare and contrast steroid and peptide hormone action.

a. both «peptide and steroid hormones» act on target organs/cells  

b. both «peptide and steroid hormones» travel through blood 

c. the effect of both «peptide and steroid hormones» lasts for a longer time «than neurotransmitters»
OR
both are effective at very low concentrations 

d. example of each type of hormone 

e. steroid hormones enter cell/cross plasma membrane while peptide hormones do not 

f. steroid hormones join receptor in cytoplasm while peptide hormones join receptor on membrane 

g. steroid hormone-receptor complex travels to nucleus whereas peptide hormone-receptor triggers a cascade reaction/second messenger 

h. steroid hormones activate genes while peptide hormones activate enzymes 

i. peptide hormone requires ATP, steroid hormone does not

Award [5 max] if no similarities are presented.

Explain how ventilation rate is changed during vigorous physical exercise.

a. exercise increases the rate of cellular respiration ✔

b. increases production of CO₂ ✔

c.  increased CO₂ causes increased acidity in blood
OR
decrease pH ✔

d. chemoreceptors in aorta/carotid artery/medulla oblongata detect change in pH ✔

e. impulse/signal/message to breathing centre
OR
impulse/signal/message to medulla oblongata ✔

f. impulse/signal/message to to diaphragm for more frequent contraction
OR
impulse/signal/message to intercostal muscles for more frequent contraction ✔

g. increase ventilation rate for more gas exchange ✔

h. long term effects of increased lung surface area
OR
vital capacity ✔

i. training decreases ventilation rate over time ✔

Outline how infection by Vibrio cholerae can lead to dehydration.

a. V. cholerae produces toxin 

b. «toxin» causes ions to be pumped into «small» intestine 

c. drawing water into the intestine 

d. through osmosis 

e. leading to water loss through diarrhea/vomiting
OR
leading to dehydration

Explain how an increase in cell respiration in a tissue causes increased release of oxygen by hemoglobin in the tissue.

a. cell respiration consumes O₂ / lowers O₂ partial pressure in tissues

b. (actively) respiring tissues release CO₂ / partial pressure of CO₂ increases 

c. CO₂ increases acidity / lowers pH of the blood 

d. decreases hemoglobin’s affinity for O₂ 

e. promotes the release of oxygen to respiring cells/tissues 

f. binding of hydrogen ions/ allosteric effect / conformational change in hemoglobin releases O₂ more readily 

g. more oxygen released at the same partial pressure 

h. this shifts the oxygen dissociation curve to the right/Bohr shift

These points can be presented in a graph.

diagram with correct labels:

i. partial pressure O₂ on x-axis and (percentage) saturation hemoglobin with O₂ on y-axis 

j. exponential shape curve at lower partial pressure/concentration of O₂ 

k. curve shifted to right (and lower) for higher partial pressure /concentration of CO₂ /lower pH