A is an example of a signal molecule that can bind to an intracellular receptor and thereby cause a gene to be turned on or off. a protein b glyceride c nucleic acid d steroid e carbohydrate

D. steroid

Explanation:

Intracellular receptors are a type of receptors located inside the cell, specifically in the cytoplasm or nucleus. When intracellular receptors are activated by ligands called SIGNALLING MOLECULES, they change shape and regulate genetic expression in the nucleus i.e. they induce turning on and off in a gene.

However, signalling molecules that activate intracellular receptors are usually hydrophobic hormones because they need to easily diffuse through the cell membrane and bind to the receptors located internally. Example of these hydrophobic signal molecules are STEROIDS.

air enters through the nose, moves through the nasal cavity, the pharynx, the larynx, enters the trachea, moves through the bronchi andbronchioles till the alveoli.