| Date | May 2017 | Marks available | 8 | Reference code | 17M.2.SL.TZ1.6 |
| Level | Standard level | Paper | Paper 2 | Time zone | Time zone 1 |
| Command term | Explain | Question number | 6 | Adapted from | N/A |
Question
James Beard, a famous chef, once said “Food is our common ground, a universal experience.”
Explain how the small intestine moves, digests and absorbs food.
Distinguish between the structures of the different types of fatty acids in food.
Outline how leptin controls appetite.
Markscheme
a. contraction of muscle «layers»/peristalsis helps move food
OR
circular muscle contraction prevents backward movement of food
OR
longitudinal muscle contraction moves food along gut
b. peristalsis/muscle contractions mix food with intestinal enzymes
c. enzymes digest macromolecules into monomers
Accept an example for mp c
d. pancreatic enzymes/amylase/lipase/endopeptidase «chemically» digest food in«lumen of» small intestine
e. «pancreatic» amylase digests starch
OR
lipases digest lipids/fats/triglycerides
OR
endopeptidases/dipeptidases digest proteins/polypeptides
f. bile/bicarbonate secreted into the small intestine creates favorable pH for enzymes
OR
bile emulsifies fat
g. some final digestion into monomers is associated with epithelial cells/epithelium «of small intestine»
h. mucosa layer/inside surface/lining of small intestine contains villi/finger-like projections
i. villi/microvilli increase surface area for better absorption
j. villi absorb products of digestion/monomers/mineral «ions»/vitamins
k. glucose/amino acids enter blood «capillaries»
OR
lipids enter lymph vessels/lacteals
l. absorption involves active transport/diffusion/facilitated diffusion
m. different nutrients are absorbed by different transport mechanisms
a. fatty acids can be saturated or unsaturated
b. unsaturated can be monounsaturated or polyunsaturated
c. saturated fats have no double bonds/have maximum number of hydrogen atoms
OR
unsaturated fatty acids have «at least one» double C=C bond
OR
polyunsaturated fatty acids have more than one double bond / OWTTE
d. cis-form has hydrogen atoms on same side of carbon double bond
OR
cis-form has bend at carbon double bond
e. trans-form has hydrogens on opposite sides of carbon double bond
OR
trans-form makes a straight carbon chain
f. length of hydrocarbon chain can vary
OR
position/number of carbon double bonds can vary
Accept labeled diagrams that illustrate these marking points
a. leptin suppresses/inhibits appetite
b. is secreted by adipose tissue/fat «storage» tissue
c. level is controlled by amount of adipose tissue/«ongoing» food intake
d. leptin targets cells in hypothalamus/appetite control centre in brain
e. causes hypothalamus/control centre in brain to inhibit appetite
f. if amount of adipose tissue increases, blood leptin concentration rises
| Date | May 2017 | Marks available | 1 | Reference code | 17M.2.SL.TZ1.1 |
| Level | Standard level | Paper | Paper 2 | Time zone | Time zone 1 |
| Command term | Estimate | Question number | 1 | Adapted from | N/A |
Question
Native oyster populations are decreasing where rivers meet the ocean along the northwest coast of North America. These oyster populations are being attacked by a gastropod.
It is known that oysters and gastropods have hard parts composed of calcium carbonate and that ocean acidification is increasing. Studies were carried out using juvenile oysters and gastropods to investigate the effects of acidification on the decrease in the population of oysters.
The first step was to raise oysters in two different mesocosms. One had seawater at a normal concentration of CO2 and the other had sea water with a high concentration of CO2. Gastropods were raised in two further mesocosms with normal and high CO2 concentrations respectively.
A juvenile gastropod will attack a juvenile oyster by using its tongue-like structure (radula) to drill a hole through the oyster shell. Once the hole has been drilled, the gastropod sucks out the soft flesh. Researchers investigated the shell thickness at the site of the drill hole in relation to the size of the oyster. The results are seen in this graph.
Equal numbers of oysters raised in seawater with a normal CO2 concentration and in seawater with a high CO2 concentration were then presented together to the gastropod predators in seawater with a normal CO2 concentration. The same numbers of oysters from the two groups were also presented together to the gastropods in seawater with a high CO2 concentration. The bar charts show how many of the oysters were drilled by the gastropods and the mean size of drilled oysters.
Outline how acidified sea water could affect the shells of the oyster.
Outline the trends shown in the data in the graph.
Estimate how much smaller drilled oysters raised in seawater at a high CO2 concentration were than drilled oysters raised in seawater at a normal CO2 concentration.
Deduce from the data in the bar charts which factors were and were not correlated significantly with the number of oysters drilled by the gastropods.
Suggest reasons for the differences in the numbers of oysters drilled, as shown in the bar charts.
The radula in a gastropod is hard but not made of calcium carbonate. Outline how this statement is supported by the drilling success of the gastropods in seawater with normal or high CO2 concentrations.
Using all the data, evaluate how CO2 concentrations affect the development of oysters and their predation by gastropods.
Markscheme
Shells might dissolve/deteriorate / become smaller/thinner/weaker / OWTTE
OR
shell formation reduced / more difficult
a. positive correlation between shell thickness and shell size
OR
as shell thickness increases, shell size «also» increases
b. (positive correlation) occurs at two different CO2 concentrations / both high and normal concentrations
c. trend for thickness is «slightly» lower with high CO2
«approximately» 0.2 mm2
OR
«approximately» 40 % «smaller»
unit required
a. significant factor: concentration of CO2 in which oysters were raised
b. insignificant factor: concentration of CO2 at which oysters were presented to gastropods
a. (because) shells are thinner/smaller when the oyster is raised in high CO2/lower pH
OR
«because» lower pH/higher acidity prevents/reduces deposition of calcium carbonate
b. gastropods target smaller/thinner-shelled oysters more
c. gastropods can eat/drill thin-shelled/smaller oysters at a faster rate (and move onto another)
d. eating smaller oysters «from high CO2 environments» means given population of gastropods require more oysters for same food intake
a. data shows that similar numbers are drilled regardless of conditions
b. since radulas are not affected by acidification
OR
radulas not made of calcium carbonate so (remain) strong/successful at drilling
a. the data/trend lines indicate that a higher CO2 concentration diminishes the shell thickness, making gastropod predation more successful
OR
the bar graphs suggest that oysters raised in a higher CO2 concentration are smaller, making gastropod predation more successful
b. CO2 concentrations «during feeding» do not change the occurrence of drilling/predation «by gastropods»
c. «limitation» no information about how exaggerated the CO2 concentrations were
OR
«limitation» no information about numbers of gastropods used «in each setting»
| Date | November 2017 | Marks available | 3 | Reference code | 17N.2.SL.TZ0.05 |
| Level | Standard level | Paper | Paper 2 | Time zone | TZ0 |
| Command term | Discuss | Question number | 05 | Adapted from | N/A |
Question
State one disaccharide and the two monomers from which it can be synthesized.
Disaccharide:
1:
Monomers:
1:
and 2:
Discuss the roles of the enzymes secreted by the pancreas during digestion.
Compare and contrast cis-fatty acids and trans-fatty acids.
Markscheme
a. disaccharide name
eg: lactose, glucose and galactose
b. both monomers that make up mpa
eg: maltose, glucose and glucose
eg: sucrose, glucose and fructose
a. amylase breaks down/catalyzes/hydrolyses starch to maltose
b. lipase breaks down/catalyzes/hydrolyses fats to fatty acids and glycerol
c. proteases/peptidases break down/catalyze/hydrolyze proteins into smaller
polypeptides/dipeptides/amino acids
Award [2] if all three enzymes and substrates named correctly and one further mark for all three products named
correctly.
Allow specific enzymes
a. both are unsaturated fatty acids
OR
both have two carbon atoms joined by a double bond
b. in cis-fatty acids the two H atoms are on the same side while in trans-fatty acids they are on opposite sides
OR
cis-fatty acids are healthier than trans-fatty acids
OR
cis-fatty acids have a lower boiling/melting point than trans
OR
cis-fatty acids have a kink «in the chain» but trans do not
Accept answer in an annotated diagram
| Date | November 2015 | Marks available | 2 | Reference code | 15N.2.SL.TZ0.4 |
| Level | Standard level | Paper | Paper 2 | Time zone | TZ0 |
| Command term | Draw | Question number | 4 | Adapted from | N/A |
Question
Draw a labelled diagram showing the interconnections between the liver, gall bladder, pancreas and small intestine.
Outline the role of glucagon in homeostasis of glucose.
List two examples of polysaccharides.
Markscheme
a. pancreas linked to small intestine by (pancreatic) duct (pancreas and small intestine both must be labelled);
b. gall bladder shown associated with liver and linked to small intestine by (bile) duct, (gall bladder and small intestine must be labelled);
c. showing (bile and pancreatic) ducts joined together before discharging in small intestine;
Ducts are to be drawn as double line structures.
a. (glucagon) released in response to low blood glucose levels;
b. (glucagon) increases blood glucose levels;
c. glucagon leads to conversion of polysaccharides/glycogen (in the liver) to glucose;
Do not accept implication that glucagon directly converts glycogen to glucose.
starch / glycogen / cellulose
Award [1] for any two polysaccharides.
| Date | May 2013 | Marks available | 4 | Reference code | 13M.2.SL.TZ2.5 |
| Level | Standard level | Paper | Paper 2 | Time zone | Time zone 2 |
| Command term | State | Question number | 5 | Adapted from | N/A |
Question
State the source, substrate, products and optimal pH condition for lipase in the human digestive system.
Outline the use of named enzymes in gene transfer using plasmids.
Explain the effect of changes of pH, substrate concentration and temperature on enzyme activity.
Markscheme
eg source: pancreas;
substrate: triglycerides / lipids / fats / oils;
product: glycerol and (three) fatty acids; (both needed)
optimal pH: 8; (accept answers in the range of 7 to 8)
Accept other correct examples.
a. plasmids are removed/obtained from bacteria;
b. endonuclease/restriction enzymes cut the plasmids at target sequences;
c. DNA fragments of other organism are cut with the same restriction enzymes;
d. in both DNA and plasmid, complementary sticky ends/staggered cut are produced;
e. DNA segment added to the opened plasmid;
f. spliced together by ligase;
g. reverse transcriptase makes DNA copies of mRNA / DNA polymerase to increase the amount of DNA;
h. recombinant plasmids inserted into new/host cells;
i. cultured/cloned to produce the new genes/more genetically modified cells;
Award [3 max] if no specific enzyme names are given.
Do not accept the word “enzyme” on its own.
pH:
a. enzymes have an optimal pH/work best at a given pH;
b. activity increases as pH gets closer to optimal pH;
c. extreme pH denatures enzymes;
d. by breaking bonds / changing enzyme shape/structure / active site shape/structure;
substrate:
e. as substrate concentration increases, activity increases;
f. as substrate concentration increases, the collisions between substrate and enzyme increase;
g. up to a maximal level of action / reaching a plateau;
h. all active sites are saturated/occupied;
temperature:
i. enzymes have an optimal temperature (where they work most effectively);
j. activity increases as it gets closer to optimal temperature;
k. high temperatures stop enzyme activity due to irreversible changes in structure / denaturation;
l. by breaking bonds / changing enzyme shape/structure / active site shape/structure;
Award any of the above points in an annotated graph.
Award up to [8] if all three addressed and [6 max] if only two addressed.
| Date | May 2012 | Marks available | 6 | Reference code | 12M.2.SL.TZ1.5 |
| Level | Standard level | Paper | Paper 2 | Time zone | Time zone 1 |
| Command term | Describe | Question number | 5 | Adapted from | N/A |
Question
Outline, with examples, the types of carbohydrate found in living organisms.
Describe the importance of hydrolysis in digestion.
Explain the flow of energy between trophic levels in ecosystems.
Markscheme
(mono-, di- and polysaccharides) consist of one, two and many units;
example of monosaccharide (e.g. glucose/ribose/galactose/fructose);
example of disaccharide (e.g. maltose/lactose/sucrose);
example of polysaccharide (e.g. starch/glycogen/cellulose);
digestion is the breakdown of large molecules into small molecules;
to allow diffusion / to make food soluble;
so foods can be absorbed into the bloodstream/body;
so foods can move from bloodstream into cells;
small molecules can be joined to form the organism’s (unique) macromolecules;
hydrolysis is aided by enzymes;
hydrolysis requires water;
polysaccharides (hydrolysed) to disaccharides/monosaccharides/specific example;
proteins/polypeptides (hydrolysed) to amino acids;
fats/lipids/triglycerides (hydrolysed) to fatty acids and glycerol;
sunlight is the initial source of energy for (most) ecosystems;
sunlight (energy) is converted (through photosynthesis) into chemical/potential energy by producers/plants/autotrophs;
energy escapes from an ecosystem (as heat) / is not recycled;
flow of energy through an ecosystem can be represented as a pyramid of energy; (allow a suitable diagram)
energy flow in an ecosystem is measured as energy per unit area/volume, per unit time, for example kJ m–2 yr–1/ kJ m–3 day–1 / other valid unit;
(chemical) energy is passed along the food chain/trophic levels;
primary consumer/herbivores obtain energy from plant food;
secondary/tertiary consumer/carnivores obtain energy by eating other (animals);
energy transfer between trophic levels is not 100 % efficient / is only about 10% efficient;
some energy is lost as heat through respiration;
decomposers obtain energy from waste products/dead bodies/leaf litter;
| Date | May 2009 | Marks available | 7 | Reference code | 09M.2.SL.TZ1.6 |
| Level | Standard level | Paper | Paper 2 | Time zone | Time zone 1 |
| Command term | Explain | Question number | 6 | Adapted from | N/A |
Question
Draw a labelled diagram to show the structure of a membrane.
Outline how vesicles are used to transport materials secreted by a cell.
Explain how the structure of a villus in the small intestine is related to its function.
Markscheme
Award [1] for each of the following clearly drawn and correctly labelled.
phospholipid bilayer – double row of opposing phospholipids, tails to inside;
phospholipid – with head and two tails;
hydrophilic/phosphate/polar (heads) and hydrophobic/hydrocarbon/fatty acid/non-polar (tails) labelled;
integral protein – embedded in the phospholipid bilayer;
protein channel – integral protein showing clear channel/pore;
peripheral protein – on the surface;
glycoprotein – with carbohydrate attached on one side;
cholesterol – shown embedded in bilayer;
vesicles formed from rER transport proteins to Golgi apparatus;
these vesicles fuse with membranes of Golgi apparatus;
proteins are processed as they move through Golgi apparatus;
(transport) vesicles bud off/leave Golgi apparatus;
vesicles move through cytoplasm;
(vesicles) fuse with plasma membrane;
contents released to outside of cell / exocytosis;
cells use vesicles to secrete substances such as hormones/digestive enzymes/other appropriate example;
vesicles may contain cell products other than proteins;
Credit drawings which fully explain the points above.
To achieve [1] answer must name the structure and relate it to its function.
the villus has a large surface area to volume ratio;
microvilli increase surface area for absorption;
thin surface (epithelial) layer so products of digestion can pass easily through;
channel proteins located in plasma membrane used for facilitated diffusion;
network of capillaries inside each villus (so only short distance) for movement of absorbed products;
capillaries transport absorbed nutrients/sugars and amino acids away from small intestine;
blood flow in capillaries maintains concentration gradient;
central lymph vessel/lacteal to transport absorbed fats/fatty acids away from small intestine;
large number of mitochondria provide ATP needed for active transport;
protein pumps in membrane (of microvilli) carry out active transport;
pinocytosis occurs at surface (epithelial) layer;
Accept any of the points above shown in a drawing.
| Date | May 2010 | Marks available | 4 | Reference code | 10M.2.SL.TZ1.7 |
| Level | Standard level | Paper | Paper 2 | Time zone | Time zone 1 |
| Command term | Explain | Question number | 7 | Adapted from | N/A |
Question
Plants are a diverse group of eukaryotic organisms. Describe the different characteristics of the bryophyta, filicinophyta, coniferophyta and angiospermophyta.
Plants store carbohydrate in the form of starch. Explain the reasons for starch being digested by the human digestive system.
Compare the structure of prokaryotic and eukaryotic cells.
Markscheme
(At least one characteristic from each group is needed for maximum credit.)
bryophyta have no roots / only have rhizoids;
bryophyta have simple leaves/stems / only a thallus;
bryophyta produce spores in capsule;
byrophyta are nonvascular;
bryophyte exhibit (pronounced) alternation of generations / a significant gametophyte generation;
filicinophyta have roots, stems and leaves;
filicinophyta (often) have divided/pinnate leaves;
filicinophyta produce spores in sporangia/spores on the undersides of leaves;
filicinophyta exhibit alternation of generations;
filicinophyta have primitive vascular tissue / no true xylem and phloem;
coniferophyta have woody stems;
coniferophyta (often) have narrow leaves/needles/scales;
coniferophyta produce seeds in cones/unenclosed seeds;
angiospermophyta have flowers;
angiospermophyta have ovules in ovaries;
angiospermophyta produce seeds (with hard coats) in fruits;
starch is a large molecule;
large molecules/starch cannot be absorbed by the intestine/villi/epithelial cells;
glucose produced by digestion of starch can be absorbed;
starch/glucose is a useful source of energy;
starch is not used in humans;
glucose is stored as glycogen not starch;
starch is not soluble/could not be transported by blood;
(In the table below, information from both boxes on same line is needed for 1 mark.)
Differences [max 4]:
Similarities: (Award 1 mark for any combination of two different items [max 2])
cytoplasm/plasma membrane/contains DNA/contains ribosomes
| Date | May 2010 | Marks available | 1 | Reference code | 10M.2.SL.TZ2.1 |
| Level | Standard level | Paper | Paper 2 | Time zone | Time zone 2 |
| Command term | Identify | Question number | 1 | Adapted from | N/A |
Question
Male Lepidoptera (butterflies and moths) commonly drink from pools of water or from moist soil. This behaviour, called puddling, was investigated in an undisturbed area where male tiger swallowtails, Papilio glaucus, had been seen puddling.
Four successive sets of experiments were performed under similar conditions of temperature and humidity. In each set, equal samples of sand were spread out evenly on trays and then treated differently. Except for one dry sample (in the first set), all others were saturated with a different liquid. Results of the observations are given in the table below.
Study of the male moth Gluphisia septentrionis revealed that their puddling behaviour can last for hours. Though drinking results in the uptake of hundreds of gut-loads of fluid, this fluid becomes rapidly expelled from the digestive system through frequent anal ejections. In this experiment, the ion concentration change was calculated by subtracting ions ejected from ions taken in. The following data was collected from males drinking laboratory solutions and from natural puddles.
Identify the dissolved element always present in the three samples with most puddling time.
Discuss the relationship between sampling visits (V) and puddling time (T) in experiments 1, 2 and 3.
Analyse the results for experiment 4.
Identify which ion the moths are retaining in their body from the laboratory solutions.
Compare the gain and loss of ions in the male moths which have drunk from laboratory solutions with the changes in those that have drunk from natural puddles.
The diagram below shows the digestive system anatomy of the male and female moth.
Using the diagram above, evaluate the hypothesis that male moths are better adapted than female moths to benefit from puddling behaviour.
Markscheme
sodium/Na
unclear correlation between V and T;
depends on the nature of the substrate and its concentration;
sometimes high V with low T (e.g. experiment 1 for sucrose) / sometimes high V with high T (e.g. experiment 2 for NaCl);
higher salt/NaCl concentrations increase T and V;
increase in puddling with increase in salt/NaCl;
no clear relationship between the number of visits and the concentration of salt/NaCl;
sodium/Na
retention of sodium/Na from laboratory solutions and natural puddles;
definite loss of potassium from laboratory solutions but loss/gain uncertain from natural puddles;
slight loss of magnesium from laboratory solutions and uncertain gain/loss from natural puddles;
calcium uncertain in both cases / variation in data for calcium;
more conclusive results in laboratory solutions / conditions more reliable in laboratory solutions / greater variation in natural puddles;
Accept reference to error bars/ranges in data in place of uncertainty.
males have longer/wider digestive tracts for greater absorption of fluid;
ileum of males has greater surface area;
which allows faster/more absorption in males than in females;
| Date | May 2010 | Marks available | 8 | Reference code | 10M.2.SL.TZ2.5 |
| Level | Standard level | Paper | Paper 2 | Time zone | Time zone 2 |
| Command term | Explain | Question number | 5 | Adapted from | N/A |
Question
Outline the role of hydrolysis in the relationships between monosaccharides, disaccharides and polysaccharides.
Describe the use of biotechnology in the production of lactose-free milk.
Explain the importance of enzymes to human digestion.
Markscheme
monosaccharides are single sugars and disaccharides are two sugars and polysaccharides are multiple sugars;
hydrolysis is the addition of water to split a molecule into smaller fragments;
–OH and –H are added to the fragments;
disaccharides are split/digested into two single sugars;
polysaccharides are broken/digested into smaller fragments (e.g. diasaccharides);
process depends on enzyme control (in organisms);
a particular yeast (growing in natural milk) contains lactase;
biotechnology companies can grow/culture the yeast;
lactase (an enzyme) is extracted from the yeast;
natural milk contains lactose/milk sugar;
when added directly to milk, lactase converts lactose into simpler forms;
same effect when milk is passed past immobilized (on surface or beads) lactase;
simpler forms of sugar (glucose and galactose) are easily absorbed (in the small intestine);
a commercial market exists for lactose-free milk / lactose-free milk is example of biotechnology’s economic impact;
some people are lactose intolerant/cannot digest lactose in milk/have lost lactase activity in intestinal cells;
consuming lactose-free milk allows lactose intolerant people to be nourished by milk without discomfort (abdominal cramps and diarrhoea);
many Asians are lactose intolerant whereas less common among other groups (northern Europeans and some Africans);
biotechnology produced in one part of world is more useful in another;
food must be in a small enough form to leave the gut and enter the bloodstream;
physical breakdown is not enough / chemical breakdown is necessary;
enzymes are required for the chemical breakdown of food;
enzymes increase the rate of digestion;
enzymes are biological catalysts;
enzymes allow digestion to occur at body temperature;
enzymatic digestion is a sequential process e.g. from protein to peptide to amino acid;
specific location for each reaction with specific conditions/environments e.g. stomach high acidity;
most enzymes work extracellularly / some enzymes work intracellularly;
variations in pH throughout digestive tract promote the activity of different digestive enzymes / different enzymes have different optimal pHs;
amylases digest carbohydrate to monosaccharides;
proteases digest proteins to amino acids;
lipases digest fats to fatty acids and glycerol;
| Date | November 2011 | Marks available | 1 | Reference code | 11N.2.SL.TZ0.2 |
| Level | Standard level | Paper | Paper 2 | Time zone | TZ0 |
| Command term | Label | Question number | 2 | Adapted from | N/A |
Question
The structure of part of the digestive system is shown in the diagram below.
Label the diagram to show the structure that is involved in digestion of proteins in acid conditions (using the letter A).
Label the diagram to show the structure where most absorption of water to prevent dehydration occurs (using the letter B).
Label the diagram to show the structure where most absorption of nutrients occurs (using the letter C).
Explain how the structure of veins is adapted to their function.
Cells defend the body against pathogens. Outline how some of these cells ingest pathogens in the blood and in body tissues.
Markscheme
Award [1] for each of the following correctly labelled.
stomach (labelled A)
Award [1] for each of the following correctly labelled.
large intestine (labelled B)
Award [1] for each of the following correctly labelled.
small intestine / ileum (labelled C)
valves to avoid backflow;
thin wall allows them to be pressed flat by muscles to move/carry blood under low pressure;
wide lumen (for a given blood vessel diameter) for slow flowing blood;
attraction to foreign protein/pathogen / chemotaxis;
membrane invaginates / engulfs foreign matter / phagocytosis/endocytosis;
formation of vacuole/vesicle;
(phagocytes) can squeeze out of walls of capillaries;
Accept clearly annotated diagrams.
| Date | November 2012 | Marks available | 6 | Reference code | 12N.2.SL.TZ0.5 |
| Level | Standard level | Paper | Paper 2 | Time zone | TZ0 |
| Command term | Describe | Question number | 5 | Adapted from | N/A |
Question
Outline the role of condensation and hydrolysis in metabolic reactions involving carbohydrates.
Metabolic reactions are catalysed by enzymes. Explain how enzymes catalyse reactions and how a change in pH could affect this.
Describe the digestion of food in the human digestive system.
Markscheme
condensation is joining together molecules with the release of water;
(in general) two monosaccharides join to form a disaccharide / many mono-saccharides/disaccharides form polysaccharides;
example; (eg. two glucose from maltose)
hydrolysis is the breaking down of molecules with the addition of water;
(in general) disaccharides break into monosaccharides / polysaccharides break into disaccharides/monosaccharides;
example; (eg. maltose forms two glucose)
enzymes speed up the rate of chemical reactions;
lock and key model;
substrate fits into active site;
enzyme-substrate specificity;
enzymes work best at optimal pH/different enzymes have different optimal pHs;
increase/decrease from optimum pH decreases activity;
change in pH changes structure/charge of active site;
changing three-dimensional structure of enzyme/protein;
not allowing substrate to fit in active site;
enzymes can be denatured if change is extreme;
denaturing is loss of its biological properties;
sketch graph showing pH versus enzyme activity;
chewing food makes smaller particles/increases surface area of food;
starch digestion (begins) in the mouth/by saliva/(salivary) amylase/ptyalin;
digestion of proteins in stomach;
acid condition in stomach provides optimum pH for enzymes;
stomach muscle contraction causes mechanical digestion;
enzymes in small intestine complete digestion;
alkaline condition in small intestine provides optimum pH for enzymes;
bile salts help to emulsify fats;
example of amylase with source, substrate and products;
example of protease with source, substrate and products;
example of lipase with source, substrate and products;
| Date | November 2010 | Marks available | 1 | Reference code | 10N.2.SL.TZ0.3 |
| Level | Standard level | Paper | Paper 2 | Time zone | TZ0 |
| Command term | Explain | Question number | 3 | Adapted from | N/A |
Question
List two functions of membrane proteins.
Explain why digestion of large food molecules is essential.
Outline why antibiotics are effective against bacteria but not against viruses.
Outline the use of polymerase chain reaction (PCR) to copy and amplify minute quantities of DNA.
Markscheme
a. hormone binding sites / receptors;
b. (immobilized) enzymes;
c. cell adhesion;
d. cell (to cell) communication;
e. passive transport/channels;
f. active transport/pumps;
g. facilitate diffusion;
h. carry electrons;
a. many molecules are too large to be absorbed (by the villi) / small molecules are soluble and can be absorbed;
b. large food molecules are broken down so they can be reorganized/rearranged;
a. antibiotics block/inhibit specific metabolic pathways/cell functions found in bacteria;
Accept specific examples of inhibition such as cell protein synthesis, cell wall formation
b. viruses must use host/eukaryotic cell metabolism / viruses do not have their own metabolic pathways;
c. host/eukaryotic cell metabolism/pathways not blocked/inhibited by antibiotics;
a. strands of DNA (fragments) split/denatured with heat;
b. complementary nucleotides added to split stands (when cooling);
c. with the use of (DNA) polymerase (and primers);
d. process/heating and cooling cycle is repeated (until enough DNA is obtained);
Accept example of PCR application e.g. paternity cases or forensic investigations.
| Date | November 2009 | Marks available | 2 | Reference code | 09N.2.SL.TZ0.3 |
| Level | Standard level | Paper | Paper 2 | Time zone | TZ0 |
| Command term | Outline | Question number | 3 | Adapted from | N/A |
Question
Researchers extracted an enzyme from the human digestive system and tested its activity at different pH values on proteins extracted from the blood of cows. The results are shown in the graph below.
Deduce from where in the human digestive system this enzyme was extracted.
Outline the need for enzymes in the digestive system.
State one function of the large intestine.
Explain how the structure of the villus is adapted for absorption.
Markscheme
stomach
enzymes speed up the digestive processes;
(chemical) break down of food/food particles/large molecules;
make soluble products/molecules small enough to be absorbed;
to (re)absorb water/vitamins(s) (e.g. K and B12) / temporary storage of feces
N.B. for each marking point, function should accompany structure.
shape of villus has large surface area to improve absorption / microvilli increase surface area to improve absorption;
thin walls/epithelium to allow fast diffusion;
capillaries/rich blood supply (nearby) to absorb digested food products/ maintain concentration gradient;
lacteal in villus to absorb fatty acids/fats (and carry them away from small intestine);
protein pumps in membrane to carry on active transport / channel proteins in membrane to facilitate diffusion;
large number of mitochondria provide ATP for active transport;