RESPIRATION Flashcards
Q3- Describe how 6 carbon molecule of glucose is converted into pyruvate (6)
1- Glucose phosphorylated using molecule of ATP
2- This creates 1 glucose phosphate
3-and 1 ADP
4- ATP is used to add another phosphate to glucose phosphate’
5- forming hexose biphosphate
6- which is split into 2 TP’s
7- oxidised to form to form 2 pyruvate
8- NAD collects hydrogen ions , forming 2 reduced NAD
(c) Large areas of tropical forest are still found on some Caribbean islands. The
concentration of carbon dioxide in the air of these forests changes over a period of
24 hours and at different heights above ground.
Use your knowledge of photosynthesis and respiration to describe and explain how
the concentration of carbon dioxide in the air changes:
• over a period of 24 hours
• at different heights above ground.
(5)
c) 1. High concentration of / increase in carbon dioxide linked with respiration
at night / in darkness;
2. No photosynthesis in dark / night / photosynthesis only in light / day;
Neutral: less photosynthesis
3. In light net uptake of carbon dioxide / use more carbon dioxide than
produced / (rate of) photosynthesis greater than rate of respiration;
4. Decrease in carbon dioxide concentration with height;
More carbon dioxide absorbed higher up
Accept: less carbon dioxide higher up / more carbon dioxide
lower down
5. (At ground level)
less photosynthesis / less photosynthesising tissue / more respiration /
more micro-organisms / micro-organisms produce carbon dioxide.
Neutral: less leaves unqualified or reference to animals
Q2.(a) Describe how acetylcoenzyme A is formed in the link reaction.
(2)
- Oxidation of / hydrogen removed from pyruvate and carbon dioxide released;
- Addition of coenzyme A.
Accept: NAD reduced for oxidation
b) In the Krebs cycle, acetylcoenzyme A combines with four-carbon oxaloacetate to
form six-carbon citrate. This reaction is catalysed by the enzyme citrate synthase.
(i) Oxaloacetate is the first substrate to bind with the enzyme citrate synthase.
This induces a change in the enzyme, which enables the acetylcoenzyme A to
bind.
Explain how oxaloacetate enables the acetylcoenzyme A to then bind to the
enzyme. (2)
- Change (in shape) of active site / active site moulds around the
substrate;
Reject: reference to inhibitor
Accept: change in tertiary structure affecting active site - (Substrate / active site) now complementary.
Neutral: references to two active sites
(ii) Another substance in the Krebs cycle is called succinyl coenzyme A. This
substance has a very similar shape to acetylcoenzyme A.
Suggest how production of succinyl coenzyme A could control the rate of the
reaction catalysed by citrate synthase.
- Is a competitive inhibitor / attaches to active site;
Neutral: reference to inhibitor forming an enzyme-substrate
complex - Reduces / prevents enzyme-substrate / E-S complex forming.
Accept: Reduces / prevents acetylcoenzyme A binding to
enzyme / citrate synthase
(c) In muscles, pyruvate is converted to lactate during anaerobic respiration.
(i) Explain why converting pyruvate to lactate allows the continued production of
ATP during anaerobic respiration.
- Regenerates / produces NAD / oxidises reduced NAD;
- (NAD used) in glycolysis.
Accept: description of glycolysis
Accept: glycolysis can continue / begin
(ii) In muscles, some of the lactate is converted back to pyruvate when they are
well supplied with oxygen. Suggest one advantage of this. (1)
(ii) (Pyruvate used) in aerobic respiration / (lactate / lactic acid) is toxic /
harmful / causes cramp / (muscle) fatigue.
Accept: (pyruvate) can enter link reaction
Accept: reduces cramp / (muscle) fatigue
Neutral: ‘reduces muscle aches’
Q3.Researchers investigated the effect of cyanide on oxygen uptake by mitochondria. They
prepared a suspension of mitochondria from animal cells and a suspension of
mitochondria from plant cells. They placed the suspensions in separate flasks containing
isotonic solution, started the timer and began recording the concentration of oxygen in
each flask.
• After 5 minutes, they added a respiratory substrate and ADP to each flask.
• After 13 minutes, they added cyanide solution to each flask.
The graph below shows their results. From P to R the curves for animal and plant
mitochondria overlap
(a) Explain the line between P and Q.
3.(a) 1. No aerobic respiration / electron transfer / oxidative phosphorylation;
Reject reference to anaerobic respiration.
2. (Because) no (respiratory) substrate / nothing to respire;
Reject idea of ‘little’ or ‘less’ − this would result in a change
in oxygen concentration.
Accept the idea of no residual respiratory substrate in the
mitochondria.
(b) (i) Explain the line between Q and R. 2
(b) (i) (Oxygen concentration falls because)
1. Aerobic respiration (uses oxygen);
Accept ‘oxidative phosphorylation / electron transfer takes
place’.
2. Oxygen is terminal / electron acceptor;
3. (oxygen combines with) protons / H+ and electrons / eto form
water / H2O;
All aspects are required to gain mark.
(ii) The respiratory substrate and ADP added after 5 minutes (Q) were part of a
buffered isotonic solution.
What other substance would the buffer or solution have to contain?
………………
(1)
(ii) Phosphate (ions) / inorganic phosphate / PI;
Reject ‘phosphorus’ or ‘P’.
Accept ‘PO4’.
(c) Describe and explain the difference between line R to S (animal mitochondria) and
line R to T (plant mitochondria). (4)
(c) 1. Oxygen concentration continues to fall in plants but stays constant
in animals;
For ‘plants’ accept ‘line R to T’, for ‘animals’ accept ‘line R to S’.
MP1 and MP2. Accept answers in terms of ‘use’ of oxygen
rather than change in concentration.
2. (Oxygen concentration) falls more slowly in plants than before
cyanide added;
3. (Because aerobic) respiration continues in plant (mitochondria);
Accept (because aerobic) respiration stops in animal
(mitochondria).
4. (Because) electron transfer / oxidative phosphorylation continues in
plant (mitochondria);
Accept (because) electron transfer stops in animal
(mitochondria).
Accept for one additional mark
(up to 4 max) use of Resource A i.e: idea that plant
cytochrome oxidase is (more) resistant to cyanide
OR
idea that animal cytochrome oxidase not resistant to
cyanide.
Q4.The figure below shows the apparatus used for measuring the rate of oxygen consumption
in aerobic respiration by seeds.
(a) For the first 10 minutes, the tap attached to tube A was left open and the syringe
from tube B was removed.
Suggest three reasons why the apparatus was left for 10 min (3)
- Equilibrium reached.
Accept equilibrate - Allow for expansion / pressure change in apparatus;
- Allow respiration rate of seeds to stabilise.
Ignore seeds acclimatise
(b) Suggest and explain why the chosen temperature was 20 °C for this experiment. (2)
(b) 1. Optimum temperature / temperature for normal growth of seeds;
2. (Optimum temperature) for enzymes involved in respiration.
After 10 minutes, the tap attached to tube A was closed and the syringe was
attached to tube B. Every minute, the syringe plunger was moved until the levels in
the U-tube were the same. The reading on the syringe volume scale was then
recorded.
The results are shown in the table below.
Time / minutes Reading on syringe volume scale / cm3 0 0.84 1 0.81 2 0.79 3 0.76 4 0.73 5 0.70 6 0.68 7 0.66 8 0.63 9 0.62 10 0.58 (c) During the experiment, the coloured liquid in the tubing moved towards tube B (3)
(c) 1. Oxygen taken up / used by seeds;
2. CO2 given out is absorbed by KOH (solution);
3. Volume / pressure (in B) decreases.
(d) The mass of the seeds was 1.6 g. Use the information in the table above to
calculate the rate of oxygen consumption in cm3
g–1 hour–1 by the seeds.
Show your working.
Rate = cm3
g–1 hour–1
(2)
(d) 0.975 / 0.98
If incorrect,
0.26 × 6 / or incorrect numbers divided by 1.6 for 1 mark .
