Studyledge

Transport in Animals: Question 6

Syllabus 9.4

Multiple choice Core 1 mark

A student studies gas exchange and transport in a mammal. They read that, in the lungs, a substance inside one type of blood cell combines with oxygen to form a compound called oxyhaemoglobin. This compound then travels around the body in the blood and, in respiring tissues where oxygen concentration is low, releases the oxygen again.

Which component of blood carries out this oxygen-carrying role?

Choose an answer to check it, then compare with the worked solution below.
Show worked solution Hide worked solution

Worked solution

Step 1: Identify what forms oxyhaemoglobin

The stem describes a substance inside a blood cell that combines with oxygen in the lungs to form oxyhaemoglobin, and later releases that oxygen in respiring tissues. This substance is haemoglobin, and it is found inside red blood cells.

Red blood cells are packed with haemoglobin. In the lungs, where oxygen concentration is high, haemoglobin combines with oxygen to form oxyhaemoglobin. As the blood reaches respiring tissues, where oxygen concentration is lower and is being used up in respiration, oxyhaemoglobin breaks down again, releasing oxygen to the cells. This is exactly the process described in the stem.

Step 3: Eliminate the other options

  • White blood cells defend the body against pathogens, by engulfing them (phagocytes) or producing antibodies (lymphocytes); they do not carry oxygen.
  • Platelets are cell fragments involved in blood clotting; they play no part in oxygen transport.
  • Plasma is the liquid part of blood and transports many dissolved substances, such as glucose, urea, hormones and carbon dioxide, but it is not the component that carries oxygen as oxyhaemoglobin; that role depends on the haemoglobin inside red blood cells.

Final answer

The component of blood that carries oxygen as oxyhaemoglobin is the red blood cell, option A.