Home / IB DP Biology B4.1 Adaptation to environment- FA 2015- IB Style Questions For SL Paper 2

IB DP Biology B4.1 Adaptation to environment- FA 2015- IB Style Questions For SL Paper 2

IBDP Biology Paper 2 - All Chapters

Question

Vinegar is a water-based solution of ethanoic acid. Acetobacter aceti is used in the production of vinegar. This bacterium has the ability to convert ethyl alcohol, \(\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}\), into ethanoic acid, \(\mathrm{CH}_3 \mathrm{COOH}\).
\( \mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}+\mathrm{O}_2 \rightarrow \mathrm{CH}_3 \mathrm{COOH}+\mathrm{H}_2 \mathrm{O} \)
In the generator method of ethanoic acid fermentation, Acetobacter aceti are grown over wood shavings in a fermenter to the point where they form a biofilm.

At the base of the fermenter oxygen is bubbled in, which then rises through the wood shavings. Ethanol drips through the wood shavings. At a suitable temperature the ethanol is converted to ethanoic acid, which is withdrawn from the bottom of the fermenter, and new ethanol is added at the top.

a.i. \(A\). aceti is a Gram-negative bacterium. If a Gram staining procedure were carried out on a sample of \(A\). aceti, predict the result that would be observed after decolourization. 
ii. \(A\). aceti is a Gram-negative bacterium. If a Gram staining procedure were carried out on a sample of \(A\). aceti, predict the result that would be observed after counterstaining. 
b.i. List two abiotic variables that would need to be monitored during this fermentation process. 
ii. Describe one way in which microorganisms in this fermenter could be limited by their own activities. 
iii. Distinguish between batch fermentation and continuous fermentation. 
c. Outline the concept of an emergent property. 

▶️ Answer/Explanation

a.

i. Result after decolourization:

  • As a Gram-negative bacterium, A. aceti has a thin peptidoglycan layer and an outer membrane.
  • After decolourization (alcohol wash), the crystal violet stain is lost, so the cells appear clear or colourless.

ii. Result after counterstaining:

  • After applying the counterstain (usually safranin), the bacteria take up the stain and appear pink under a microscope.

b.

i. Two abiotic variables to monitor:

  1. Temperature – to ensure optimal enzymatic activity.
  2. pH – ethanoic acid production lowers pH, which can affect bacterial function.

ii. One way microorganisms could limit themselves:

  • As A. aceti produces ethanoic acid, the pH of the medium drops, which can inhibit its own growth and enzyme activity if the acid concentration becomes too high.

iii. Distinction between batch and continuous fermentation:

FeatureBatch FermentationContinuous Fermentation
Input/outputAll nutrients added at the startNutrients added continuously
Product removalProduct removed only at the endProduct removed continuously
Growth phasesAll growth phases observed (lag, log, etc.)Maintained in log/exponential phase
EfficiencyLess efficient; downtime between batchesMore efficient; steady-state operation possible
c.
  • Emergent properties are characteristics or behaviours of a system that arise from the interaction of its parts, not evident when parts are isolated.
  • These cannot be predicted by examining individual components alone.
  • Example in microbiology:
    • Biofilm formation by bacteria like A. aceti: individual cells cannot form structured layers or protect themselves efficiently, but together they create a protective matrix, coordinate behaviour (e.g., quorum sensing), and form channels for nutrient transport—none of which occur in isolated cells.

Markscheme: 

a.i. the bacteria would be clear/colourless
a.ii. would stain pink
Do not accept “violet” or “lilac”.

b.i. Any two of:
   a. oxygen
   b. temperature
   c. \(\mathrm{pH}\) levels
   d. \(\mathrm{CO}_2\)

b.ii. Example responses:
   a. \(\mathrm{pH}\)
   b. lowered by ethanoic acid production.
OR
   a. increase in temperature
   b. due to metabolism.
OR
   a. increased population size/reproduction
   b. would limit resources.

b.iii. Key differences:
   – Batch fermentation: All materials added at start, products removed at end
   – Continuous fermentation: Materials continuously added, products continuously removed

c. Emergent properties:
   a. arise from the interaction of the elements of a system
   b. behaviours exhibited which are not shown by individuals
   Examples: quorum sensing, matrix production, water channels, antibiotic resistance

Question

The model describes the fundamental and realized niches of a species of microscopic marine arthropod in the Northern hemisphere with respect to two different factors (X and Y). The abundance of the species is shown over twelve months. The fundamental niche is separated into five zones ranging from critical to optimal conditions. The population of the species in its realized niche each month is represented by an oval. The size of each oval shows the population abundance.

a. Distinguish between fundamental niche and realized niche.

b. State the month where the population reaches its maximum.

c.i. Outline how factor \( Y \) affects the species from January to April.

ii. Suggest, with a reason, what factor \( Y \) could be.

▶️ Answer/Explanation

a.

  • Fundamental niche: The entire range of environmental conditions (Factor X and Factor Y) under which a species can potentially survive and reproduce.
  • Realized niche: The actual conditions under which the species lives, considering biotic interactions like competition, predation, and limited dispersal.

b.

  • April. The largest oval, representing the highest population abundance, appears in April and is located in the optimal zone of the fundamental niche.

c.i.

  • From January to March, the species remains in low to medium suitability zones—Factor Y appears to limit population growth.
  • In April, Factor Y changes such that conditions shift into the optimal zone, causing a rapid increase in population size.

c.ii.

  • Suggested factor: Temperature
  • Reason: In the Northern Hemisphere, temperatures rise from winter to spring (January to April). This warming could improve metabolic or reproductive conditions for the marine arthropod, making temperature a plausible Factor Y that enhances niche suitability in spring.

Markscheme:

a. Fundamental niche is all potential conditions a species could live in, whereas realized niche is the actual conditions under which the species lives.

b. April

c.i.

  • Limited effect on low/stable population size from January to March (OWTTE).
  • Large effect increases population size from March to April (OWTTE).
  • Niche conditions decrease from January to March.
  • Niche conditions improve from March to April.

c.ii.

  • Factor example: temperature.
  • Explanation: As temperature increases in spring (March to April), the conditions for the species become more favorable.
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