Meaning: 'Interrelated' means that things are connected or have a mutual relationship.

Wrong options:

• custom: 'Custom' refers to a traditional practice or norm, which does not fit the context of describing the relationship between biological branches.
• responded: 'Responded' is a verb that indicates an action taken in reply, which does not fit grammatically or contextually in this sentence.
• diversity: 'Diversity' refers to variety or differences, which does not convey the idea of connection between the subdivisions.
• phenomena: 'Phenomena' refers to observable events or occurrences, which does not describe the relationship between the branches of biology.
• sensitive: 'Sensitive' describes the ability to perceive or respond to stimuli, which does not fit the context of interconnection.

Correct answer: custom

Explanation: The word 'custom' refers to the established practice of separating the study of plants and animals, which is relevant in the context of how biology is organized. It fits grammatically as it serves as a noun that describes the practice of categorization.

Meaning: 'Custom' means a traditional and widely accepted way of doing something.

Wrong options:

• interrelated: 'Interrelated' describes a connection, but it does not fit here as it does not refer to a practice or method of separation.
• responded: 'Responded' is a verb that does not fit in this context as it does not describe a practice or method.
• diversity: 'Diversity' refers to variety, which does not relate to the concept of a practice or custom in the context of biological study.
• phenomena: 'Phenomena' refers to observable events, which does not describe a method or practice of separation.
• sensitive: 'Sensitive' describes a quality of perception, which does not fit the context of a customary practice.

Correct answer: phenomena

Explanation: The term 'phenomena' refers to observable events or occurrences in biology that all living things share, which fits the context of discussing common biological characteristics. It is grammatically correct as it serves as a noun that summarizes the shared biological aspects.

Meaning: 'Phenomena' means observable events or occurrences, particularly in a scientific context.

Wrong options:

• custom: 'Custom' refers to a traditional practice, which does not fit the context of describing shared biological characteristics.
• responded: 'Responded' is a verb that does not fit grammatically or contextually as it does not describe a biological characteristic.
• diversity: 'Diversity' refers to variety, which does not encapsulate the idea of shared biological occurrences.
• interrelated: 'Interrelated' describes a connection, but it does not fit as it does not refer to observable events or characteristics.
• sensitive: 'Sensitive' describes a quality of perception, which does not fit the context of shared biological phenomena.