Transport in Animals: Question 1
Syllabus 9.4
A veterinary science student separates a small blood sample from a goat and studies its components under a microscope. She finds that most of the sample's volume is a pale yellow liquid, which is not made of cells. This liquid carries the blood cells themselves, together with dissolved food molecules, urea, hormones and carbon dioxide, around the goat's body.
Which component of blood is being described?
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Worked solution
Step 1: Recall what plasma does
Plasma is the pale yellow liquid part of blood. It is not made of cells; instead, it is the liquid in which the blood cells float. Plasma’s job is to transport the blood cells themselves, plus dissolved substances such as digested food molecules, urea, hormones and carbon dioxide, around the body.
Step 2: Match the description to a component
The stem describes a pale yellow liquid, not made of cells, that carries blood cells and dissolved substances including food molecules, urea, hormones and carbon dioxide. This matches the description of plasma exactly.
Step 3: Eliminate the other options
- Red blood cells and white blood cells are themselves cells, not a liquid, so neither can be the non-cellular liquid described in the stem; instead, they are carried within the plasma.
- Platelets are small cell fragments involved in clotting, not a transport liquid, so they do not match the description either.
Final answer
The component described is plasma, option A.