Section 5 exam questions Flashcards
Why must the apparatus for the respirometer be airtight
To prevent air entering/leaving the apparatus
This would change the volume and therefore the pressure
This would affect the movement of the liquid
Explain the purpose of the soda-lime in the respirometer apparatus
To absorb CO2 produced in respiration
This allows the volume of O2 absorbed by the maggots to be measured
Explain why the liquid in the respirometer moves towards the left
Respiring maggots take in oxygen during respiration in the experimental tube
The carbon dioxide produced in respiration is absorbed by the soda lime
Volume of gas in the experimental tube decreases, causing a decrease in pressure
The pressure in the experimental tube is comparitively lower than the control tube
The coloured liquid moves towards the experimental tube
If the coloured liquid moved 50mm in 5 mins what would the rate of respiration be? The diameter of the manometer is 3mm and 5g of maggots are in the experimental tube. Give the units
Rate= Volume/massxtime
Rate=353.43/5x5
rate=14.13
units= mm3min-1g-1
Malonate inhibits a reaction in the Krebs cycle.
Explain why malonate would decrease the uptake of oxygen in a respiring
cell
Less/no reduced NAD/Coenzymes
Oxygen is the final/terminal electron acceptor
Explain why a log scale is used to record the number of cells
Large range/difference/increase in numbers
Respirometer experiment with yeast
Many yeast cells die during the death phase.
Suggest one reason why
Decrease/no glucose
Competition for glucose
Increase in ethanol/CO2/acidity
Heat stress decreases the light-dependent reaction of photosynthesis.
Explain why this leads to a decrease in the light-independent reaction.
Less/no) ATP;
(Less/no) reduced NADP;
A decrease in the activity of the enzyme rubisco would limit the rate of
photosynthesis.
Explain why.
Less/no) carbon dioxide (reacts) with RuBP;
(Less/no) GP;
The student evaluated the effectiveness of different chemicals as
weed-killers by assessing their ability to prevent the decolourisation of
DCPIP in chloroplast suspensions.
He added different concentrations of each chemical to illuminated
chloroplast suspensions containing DCPIP. He then determined the IC50 for
each chemical. The IC50 is the concentration of chemical which inhibits the
decolourisation of DCPIP by 50%.
Explain the advantage of the student using the IC50 in this investigation.
Provides a standard / reference point
OR
Can compare different chemicals/weed-killers
OR
Can compare different concentrations of chemicals / weed-killers;
A student isolated chloroplasts from spinach leaves into a solution to form a
chloroplast suspension. He used the chloroplast suspension and DCPIP solution
to investigate the light-dependent reaction of photosynthesis. DCPIP solution is
blue when oxidised and colourless when reduced.
The student set up three test tubes as follows:
* Tube 1 – 1 cm3 of solution without chloroplasts and 9 cm3 of DCPIP
solution in light.
* Tube 2 – 1 cm3 of chloroplast suspension and 9 cm3 of DCPIP solution in
darkness.
* Tube 3 – 1 cm3 of chloroplast suspension and 9 cm3 of DCPIP solution in
light.
The student recorded the colour of the DCPIP in each of the tubes at the start
and after the tubes had been left at 20 °C for 30 minutes.
Explain why the student set up Tube 1.
To show light does not affect DCPIP;
To show chloroplasts are required;
Explain the results in Tube 3.
Reduction of DCPIP by electrons;
(From) chlorophyll / light dependent reaction;
Freshwater marshes have one of the highest rates of gross primary production
(GPP) and net primary production (NPP) of all ecosystems.
Carbon use efficiency (CUE) is the ratio of NPP:GPP. Freshwater marshes have
a high CUE.
(a)
(b)
Use your knowledge of NPP to explain why freshwater marshes have a
high CUE and the advantage of this.
Do not refer to abiotic factors in your answer.
Explanation;
low respiration/ Less energy lost in respiration
advantage;
so more growth/biomass
The student used the equation above; however, she substituted height for
biomass. This was because she did not want to destroy the plants to measure
their biomass.
State the assumption the student has made and suggest why this
assumption might not be valid.
assumed height is directly proportional to biomass
height does not include the roots/ plants may put biomass into (other named aspect of growth)
some increase in height results from water gain
Describe the role of saprobionts in the nitrogen cycle.
use enzymes to decompose proteins/RNA/DNA/urea
Releasing ammonia/ ammonium
