Which one of the following statements refers to Reductionist Biology?

The correct answer is: Physico-chemical approach to study and understand living organisms.

Detailed Explanation:
Reductionist biology (or reductionism in biology) is a scientific approach that aims to understand the complex nature of living systems by breaking them down into their simplest, most fundamental components. The core idea is that biological systems can be fully explained and understood by studying the physical and chemical properties and interactions of their constituent parts (such as DNA, RNA, proteins, lipids, and chemical reactions).
Therefore, reductionist biology relies heavily on a physico-chemical approach to analyze and explain life at the molecular and cellular levels.

Let's evaluate the options to see why this is the most accurate statement:
1. Physico-chemical approach: This is the correct choice because reductionism reduces biological phenomena to the fundamental laws of physics and chemistry.
2. Physiological approach: Physiology deals with the functions and mechanisms of organs and organ systems as a whole. While related, it operates at a higher level of organization compared to pure reductionism.
3. Chemical approach: Although chemical processes are a massive part of reductionist biology, studying physical principles (like molecular structures, thermodynamics, and cellular mechanics) is also essential. Thus, the combined "physico-chemical" term is more complete.
4. Behavioural approach: Behavior is a high-level, macroscopic property of whole organisms. Analyzing behavior as a whole is a holistic or organismal study, which is conceptually opposite to reductionist molecular biology.