The study of the interrelationship between living organisms and their physical and biological environment is called by which of the following terms?

Introduction / Context:
Understanding how living organisms interact with each other and with their surroundings is one of the central goals of biology. There is a specific branch of science that focuses on these interactions at many levels, from individuals and populations to communities and ecosystems. This question asks you to recall the term used for the study of relationships between organisms and their environment.

Given Data / Assumptions:

The focus is on interrelationships between living organisms and their environment. Options include plant geography, plant social science, ecology, ecosystem and biostatistics. We assume standard definitions used in environmental biology.

Concept / Approach:
Ecology is defined as the scientific study of interactions among organisms and between organisms and their environment. It examines how abiotic factors such as light, temperature, water and soil, and biotic factors such as other organisms, influence distribution, abundance and behaviour. Plant geography deals more specifically with the geographic distribution of plant species. The term ecosystem refers to a functional unit that includes a community of organisms and its physical environment, not the science itself. Biostatistics is the application of statistics to biological data. Therefore, the correct term for the branch of science that studies interrelationships between organisms and environment is ecology.

Step-by-Step Solution:
Step 1: Focus on the key phrase in the question: interrelationship between living organisms and their environment. Step 2: Recall the definition of ecology as the study of relationships between organisms and their environment. Step 3: Distinguish this from plant geography, which focuses mainly on where plant species occur spatially. Step 4: Recognise that ecosystem is the name of a structural and functional unit (for example, pond ecosystem), not the discipline that studies such units. Step 5: Conclude that ecology is the only option that exactly matches the wording and meaning of the question.

Verification / Alternative check:
You can verify your choice by recalling typical textbook chapter titles. Chapters that talk about food chains, food webs, energy flow, populations and communities are grouped under ecology. These chapters consistently define ecology as the study of interactions between organisms and their environment. Diagrams of ecosystems, biomes and trophic levels are usually labelled as part of ecology. None of the other listed terms is used in this broad and foundational way, confirming ecology as the correct answer.

Why Other Options Are Wrong:
Plant geography is a subfield that maps and explains the distribution of plant species across regions, but it does not necessarily cover all aspects of organism environment interactions. Plant social science is not a standard biological term and may be a distractor in this context. Ecosystem describes a system of living organisms and their physical environment functioning together, but it refers to the unit being studied, not the study itself. Biostatistics is a quantitative tool for analysing biological data, not a branch that focuses primarily on ecological relationships. These options therefore do not correctly name the field described in the question.

Common Pitfalls:
A common mistake is to choose ecosystem because the word itself suggests both organisms and environment, but it actually names the structure (for example, forest ecosystem) rather than the science of studying relationships. Another pitfall is confusion between ecology and environmental science; while they are closely related, the classical biologist term for the study of organism environment interactions is ecology. To avoid such errors, remember that ecology is the broad biological discipline, while ecosystem is a specific unit within ecology and environmental science.

Final Answer:
The study of the interrelationship between living organisms and their environment is called ecology.