SL Paper 3
The oxygen consumption rate of the fish Oplegnathus insignis was examined in a respirometer at three different water temperatures and at four different body masses.
Suggest how the oxygen consumption rate is determined using this apparatus.
State the relationship between body mass and the oxygen consumption of fish.
Predict the effects of global warming on aerobic respiration in fish.
Markscheme
a. the data logger measures the differences in oxygen concentration
OR
the oxygen concentration is measured before and after the water passes through the respirometer
b. over time
c. the mass of fish needs to be measured
greater body mass, less consumption of oxygen
OR
indirect/negative relationship
a. higher temperature, more oxygen consumption
b. «more oxygen consumption» is due to more respiration/metabolism
c. less oxygen can dissolve in warmer water so less «aerobic» respiration
OR
more carbon dioxide dissolved so less oxygen for respiration
Examiners report
White sage (Salvia apiana) is a native Californian shrub. Slender oat (Avena barbata) is a grass, originally from the Mediterranean, which was introduced to California. The map shows the distribution of the two species in relation to one another in an area near Santa Ynez, California.
Using the scale bar, determine the area of quadrat A1, giving the units.
Outline how chi-squared can be used to test for an association between the distributions of the two species.
Markscheme
9.0 m2 / 9 m2
Units required for the mark.
a. in each quadrat determine the presence/absence «of plants» of each type
b. null hypothesis is that the presence of one is random/independent in relation to the presence of the other plant
OR
alternate hypothesis is that the presence of one is associated with the presence or absence of the other
c.
Equation may be written out in words.
d. accept alternative hypothesis / reject null hypothesis if the difference between observed and expected is statistically significant / p<0.05 /calculated X2 higher than tabulated X2 / critical value
OR
it supports the association between the two species if the difference between observed and expected is statistically significant / p<0.05 /calculated X2 higher than tabulated X2 / critical value
Examiners report
When feed for animals is stored, moisture levels need to be kept low to prevent the growth of fungi. Feed was exposed to 15 % moisture and placed into a respirometer. O2 consumption was monitored using the respirometer over a period of six days.
[Source: © International Baccalaureate Organization 2019]
Outline how O2 consumption is measured using a respirometer.
Suggest one conclusion that can be drawn from the results shown in the graph.
Other than humidity, suggest a variable that would need to be controlled in this experiment.
Outline the role of fungi in nutrient cycling.
Markscheme
a. a CO2 absorber/KOH is added ✔
b. a bubble/starting water level is measured ✔
c. «the rate of» movement of the bubble/pressure reduction is a measure of O2 consumption ✔
a. as fungus grows, the rate of oxygen consumption increases ✔
b. around day 4/5 fungus begins to grow/no growth in days 1–3 ✔
c. the rate of fungus growth/rate of respiration is highest after 5 days ✔
temperature/amount or type of feed «in the respirometer»/amount of CO2 absorber
OR
other reasonable suggestion ✔
Do not accept light
a. act as saprotrophs/decomposers ✔
b. rot/feed on/break down organic matter/food/organisms
OR
return nutrients trapped in organic matter to the cycle/soil ✔
Do not accept detritivores
Examiners report
Very few candidates achieved a mark. Some confused a respirometer with a spirometer; others mentioned data logging probes. Credit was given for mention of a water column. Only the highest scoring candidates understood that a carbon dioxide absorber is required to allow pressure changes to be measured.
Many candidates described what was shown by the graph rather than making a conclusion related to the growth of fungi. Thus “oxygen consumption increased after day 4” or references to the feed respiring were common answers.
Often more than one answer was given but only the first was marked. Temperature and amount of feed were the most common answers.