OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

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What is plasma in the context of blood composition?

A solid component that aids in clotting
A pale yellow liquid that transports substances
A type of red blood cell
A waste material produced by cells

The correct answer is: A pale yellow liquid that transports substances

In the context of blood composition, plasma refers to the pale yellow liquid component of blood that plays a crucial role in transporting various substances throughout the body. It constitutes about 55% of total blood volume and is composed primarily of water, but also contains proteins, glucose, electrolytes, hormones, and waste products. The proteins in plasma, such as albumin, globulins, and fibrinogen, serve important functions including maintaining blood pressure, immune response, and clot formation. Plasma is responsible for carrying nutrients from digestion to the cells, transporting hormones from glands to target organs, and helping to remove waste products from metabolic processes, which are then excreted by the kidneys. This fluid medium is essential for maintaining homeostasis as it ensures that cells receive necessary substances while also facilitating the removal of harmful byproducts.