Question
Which organism can best be described as a saprotroph?
A. A fungus that digests its food externally and absorbs the products of digestion
B. A beetle that feeds by ingesting the dung of other animal species and digesting its food internally
C. A single-celled eukaryote that is able to photosynthesize and consumes smaller organisms by endocytosis
D. A giraffe that feeds by ingesting leaves from an acacia tree
▶️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 outside its body (external digestion) and then absorbing the broken-down nutrients. This method of nutrition is typical of fungi, such as molds and mushrooms.
Fungi release enzymes onto dead material, digest it externally, and then absorb the simple nutrients this is a key part of their ecological role as decomposers.
Option Evaluation:
A. Correct – This describes a fungus, which is the classic example of a saprotroph. It digests food externally and then absorbs nutrients matching the definition perfectly.
B. Incorrect – This beetle is a detritivore, not a saprotroph. Detritivores ingest dead material and digest it internally.
C. Incorrect – This describes a mixotroph or a heterotrophic protist (like Euglena), which uses endocytosis. It’s not a saprotroph because it ingests its food.
D. Incorrect – A giraffe is a herbivore, not a saprotroph. It feeds on living plant material and digests it internally.
Question
Which is not essential in a viable mesocosm?
A. Light source
B. Autotroph
C. Saprotroph
D. Herbivore
▶️Answer/Explanation
Answer: D. Herbivore
Explanation:
A mesocosm is a small, controlled ecosystem used to study interactions between organisms and their environment. For a mesocosm to be viable (able to sustain life over time), it needs certain essential components to maintain energy flow and nutrient cycling.
Option Evaluation:
A. Incorrect – A light source is essential because it provides energy for photosynthesis, allowing plants or other autotrophs to produce food.
B. Incorrect – An autotroph (like plants or algae) is essential because it produces organic material from light or chemical energy, forming the base of the food chain.
C. Incorrect – A saprotroph (like fungi or bacteria) is important for breaking down dead organic matter, recycling nutrients back into the system.
D. Correct – An herbivore is not essential in a simple mesocosm. While herbivores consume autotrophs, a mesocosm can function without them if the focus is on energy production and nutrient recycling. Herbivores add complexity but aren’t always required.
Question
The Venus flytrap (Dionaea muscipula) is a photosynthetic plant. It obtains nitrogen but not energy by digesting captured insects.
Which term describes this plant?
A. Secondary consumer
B. Autotroph
C. Primary consumer
D. Saprotroph
▶️Answer/Explanation
Answer: B. Autotroph
Explanation:
The Venus flytrap is a photosynthetic plant, meaning it produces its own energy through photosynthesis using sunlight. This makes it an autotroph because autotrophs create organic compounds (energy) from inorganic sources.
However, it also digests insects to obtain nitrogen, an essential nutrient often limited in its environment. This carnivorous behavior helps with nutrition but does not mean it gets energy from insects.
Option Evaluation:
A. Incorrect – A secondary consumer eats primary consumers (herbivores). Venus flytraps don’t rely on insects for energy, so this term doesn’t fit.
B. Correct – It is an autotroph because it makes its own energy through photosynthesis.
C. Incorrect – A primary consumer eats plants (producers) for energy; the Venus flytrap produces its own energy instead.
D. Incorrect – A saprotroph digests dead organic matter externally, which the Venus flytrap does not do.
Question
Which row of the table describes a type of nutrition?
▶️Answer/Explanation
Answer: C. Mixotrophic
Explanation:
Mixotrophic organisms can get energy and carbon in two ways:
- They can use sunlight to make their own food through photosynthesis (like plants do).
- They can also ingest organic molecules to get energy and carbon (like animals do).
That’s why:
- Their energy source is both sunlight and organic molecules.
- Their carbon source is carbon dioxide (from photosynthesis) and organic molecules (from ingestion).
- Their method of acquiring energy is photosynthesis and ingestion.
This matches row C perfectly.
Question
Outline the role of fungi in nutrient cycling.
▶️Answer/Explanation
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
Question
The pie chart shows the modes of nutrition of fungi in Huahu Lake wetland in China.
What is the most common mode of nutrition of fungi in this wetland?
A. Heterotrophic fungi that feed on living organisms by ingestion
B. Autotrophic fungi that obtain organic nutrients from detritus by internal digestion
C. Fungi that have either an autotrophic or heterotrophic method of nutrition
D. Heterotrophic fungi obtaining nutrients from dead organisms by external digestion
▶️Answer/Explanation
Answer: D. Heterotrophic fungi obtaining nutrients from dead organisms by external digestion
Explanation:
- The pie chart shows that 62% of fungi in the Huahu Lake wetland are saprotrophs.
- Saprotrophs are a type of heterotrophic organism.
- They feed on dead organic matter.
- They release enzymes outside their bodies to digest food externally, then absorb the nutrients.
So, the correct description of saprotrophic nutrition is given in option D.
Key terms to remember:
- Heterotroph – An organism that gets food from other organisms.
- Saprotroph – A heterotroph that feeds on dead material by external digestion.
- External digestion – Enzymes break down food outside the organism’s body.