Home / IB DP Biology- C4.1 Populations and communities – IB Style Questions For SL Paper 1A

IB DP Biology- C4.1 Populations and communities - IB Style Questions For SL Paper 1A -New Syllabus

More DP Biology SL Paper 1 Questions..

Question

Which interspecific relationship has a negative impact on both individuals?

(A) Competition
(B) Mutualism
(C) Parasitism
(D) Pathogenicity
▶️ Answer/Explanation

Correct Answer: \( \boxed{\mathbf{A}} \)

In competition, two different species compete for the same limited resources, such as food, water, or space. As a result, both species are negatively affected because each has reduced access to the resources needed for survival and reproduction.

Question

A capture–mark–release–recapture study was conducted to estimate the population size of common periwinkles (Littorina littorea) on a rocky shore. Researchers used the Lincoln index formula, given by Population size estimate = (M × N) / R. The following data were collected:

DescriptionNumber
Individuals captured and marked initially100
Individuals recaptured50
Marked individuals recaptured10

What is the estimated total population size of Littorina littorea based on these results?

A. 160
B. 500
C. 1000
D. 5000

▶️ Answer/Explanation
Using the Lincoln index: \[ \text{Estimated population} = \frac{M \times N}{R} \] where: \( M = 100 \), \( N = 50 \), and \( R = 10 \). \[ \text{Estimated population} = \frac{100 \times 50}{10} = 500 \] Therefore, the estimated population size is 500 individuals.
✅ Answer: (B) 500

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: Fungus example

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. Fungi are classic examples of saprotrophs.

Answer Evaluation:

A. Correct – Fungi are saprotrophs. They release enzymes into the environment to break down complex organic materials (like dead plants), then absorb the simpler nutrients. This is the defining feature of saprotrophic nutrition.

B. Incorrect – The beetle ingests and digests food internally, which is typical of heterotrophic consumers, not saprotrophs.

C. Incorrect – This organism performs both photosynthesis and phagocytosis, making it a mixotroph, not a saprotroph.

D. Incorrect – A giraffe eats plants (autotrophs) and digests them internally. It is a herbivore, not a saprotroph.

More DP Biology SL Paper 1 Questions..
Scroll to Top