IB DP Biology- B4.2 Ecological niches - IB Style Questions For SL Paper 1A -FA 2025
▶️ Answer/Explanation
An abiotic factor is a non-living component of the environment that influences living organisms. Examples include temperature, salinity, light intensity, and pH.
The salinity surrounding marram grass on a sand dune is a physical, non-living condition, making it an abiotic factor.
In contrast, the other options involve biological interactions, which are biotic factors.
✅ Answer: (C)
▶️ Answer/Explanation
Answer: A. A fungus that digests its food externally and absorbs the products of digestion
Explanation:
A saprotroph is an organism that feeds on dead or decaying organic matter by secreting digestive enzymes externally and then absorbing the nutrients after breakdown. This process is characteristic of fungi, such as molds and mushrooms, which act as decomposers in ecosystems.
Fungi release enzymes onto dead material, digest it outside their bodies, and then absorb the resulting simple nutrients — this external digestion defines saprotrophic nutrition.
Option Evaluation:
A. Correct — Fungi are classic examples of saprotrophs, performing external digestion followed by absorption.
B. Incorrect — The beetle is a detritivore, as it ingests and digests dead material internally.
C. Incorrect — This describes a mixotroph or heterotrophic protist (e.g., Euglena), which uses endocytosis to ingest food, not external digestion.
D. Incorrect — A giraffe is a herbivore that feeds on living plants and digests food internally, not a saprotroph.
▶️ Answer/Explanation
Answer: D. Herbivore
Explanation:
A mesocosm is a small, controlled ecosystem designed to study interactions among living organisms and their environment. For a mesocosm to be viable — capable of sustaining life over time — it must include key components that maintain energy flow and nutrient cycling.
Option Evaluation:
A. Incorrect — A light source is necessary to supply energy for photosynthesis, enabling autotrophs to produce food.
B. Incorrect — An autotroph (such as plants or algae) is essential, as it forms the base of the food chain by producing organic matter from light or chemical energy.
C. Incorrect — A saprotroph (like fungi or bacteria) decomposes dead material, recycling nutrients back into the ecosystem for reuse.
D. Correct — A herbivore is not essential in a simple mesocosm. While herbivores consume autotrophs, the system can function without them if it includes producers and decomposers to maintain energy and nutrient cycles.