Answers to Respiration worksheet (HL Questions)
1.
Explain the link reaction that occurs between glycolysis and the Krebs cycle.
pyruvate (from glycolysis) enters a mitochondrion;
enzymes in the matrix remove one carbon dioxide and hydrogen from
the pyruvate;
hydrogen is accepted by NAD/forms NADH;
removal of hydrogen is oxidation;
removal of carbon dioxide is decarboxylation;
the whole process/link reaction is oxidative decarboxylation;
the product is an acetyl group which reacts with CoA/coenzyme A;
acetyl CoA enters Krebs cycle;
Accept any of the above points in the form of a clearly drawn and
correctly labelled diagram.
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2. D
3. C
Core Questions:
1. B
2. There is, bizarrely, NO correct answer to this question!
3. Compare how pyruvate is used in human cells when oxygen is available and
when oxygen is not available.(5)
aerobic cell respiration if oxygen available and anaerobic if
unavailable;
pyruvate enters mitochondrion for aerobic respiration;
whereas pyruvate stays in the cytoplasm for processing under
anaerobic conditions;
pyruvate converted aerobically into carbon dioxide and water;
whereas pyruvate converted anaerobically to lactate;
large ATP yield when oxygen available/from aerobic cell
respiration;
no (further) ATP yield without oxygen;
5 max
4. Outline the process of glycolysis ( 5 marks)
occurs in cytoplasm;
hexose is phosphorylated using ATP;
hexose phosphate is split into two triose phosphates;
oxidation by removal of hydrogen;
(do not accept hydrogen ions/protons)
conversion of NAD to NADH (+H+);
net gain of two ATP / two ATP used and four ATP produced;
pyruvate produced at the end of glycolysis;
Accept glucose/fructose/6C sugar instead of hexose.
Accept 3C sugar/glyceraldehyde instead of triose.
DBQ:
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6.
(a)
90 (minutes)
1
(b)as temperature increases activity increases/positive correlation
1
(c) avoid predators / less competition for food
1
(d) as temperature increases metabolic rate decreases/negative correlation
(accept converse)
1
(e) metabolic rate of group mice is always less than single mice;
(accept converse)
both follow similar pattern of increases/decreases/fluctuations at
same time of day;
fluctuations greater in group mice;
both most active/higher metabolic rate during evening/21:00;
(accept any reference to times between 18:00 and 00:00)
(f) single mice need to produce more heat/have greater heat loss
because of greater surface exposed to air / group mice huddle
together to reduce the surface exposed to air
Allow any other reasonable answer.
(g)
oxygen is required for (aerobic) respiration;
respiration produces ATP/releases energy/heat in the mice;
metabolic rate is a measure of total energy released/consumed in
the body / oxygen consumption is proportional to energy released/
consumed in body/proportional to metabolic rate;
(h)
metabolic activity high when mice more active supports the hypothesis;
activity is normally correlated with energy consumption;
but another factor may be causing both to increase at the same time /
correlation does not always establish cause and effect;
grouping/environmental temperature also affect metabolic rate;
2 ma
1
2 max
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8. Explain the production of energy during aerobic respiration from pyruvate that
has been produced by glycolysis.
Krebs cycle:[3 max]
in matrix of mitochondrion;
decarboxylation;
oxidation / removal of hydrogen by NAD and FAD;
substrate level phosphorylation;
Electron transport chain:[5 max]
transfer of hydrogen to inner membrane carriers;
hydrogen ion pumped across inner membrane;
creates a concentration gradient;
electron transferred between carriers;
chemiosmosis;
hydrogen ion passes down concentration gradient;
through ATPase complex;
oxygen is final acceptor forming water;
8 max