Colloidal systems - such as gum, starch, proteins, cellulose, agar and gelatine - when placed in water, will absorb a large volume of water and swell up. These substances are called _______ .

imbibants

The correct answer is Option (4)-imbibants

The correct term for substances that absorb a large volume of water and swell up is imbibants.

Here's why the other options are incorrect:

• Porins: These are proteins that form channels in cell membranes, allowing passage of specific molecules.
• Apoplasts: This refers to the network of cell walls and intercellular spaces outside the living plant cells.
• Combustibles: These are substances that can readily burn.

The substances described, such as gum, starch, proteins, cellulose, agar, and gelatine, are referred to as imbibants. When placed in water, they have the ability to absorb a significant volume of water and swell up. This property is commonly observed in colloidal systems, where the imbibants form colloidal dispersions or gels upon hydration. The process of absorbing water and swelling is known as imbibition.