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Figure 6 shows the structure and actual size of red blood cells (erythrocytes) - Edexcel - GCSE Biology: Combined Science - Question 3 - 2021 - Paper 1
Question 3
Figure 6 shows the structure and actual size of red blood cells (erythrocytes).  (a) (i) Calculate the image size of the top view of this red... show full transcript
Worked Solution & Example Answer:Figure 6 shows the structure and actual size of red blood cells (erythrocytes) - Edexcel - GCSE Biology: Combined Science - Question 3 - 2021 - Paper 1
Step 1
Calculate the image size of the top view of this red blood cell if this cell is magnified 400×.
Answer
To calculate the image size, we use the formula:
Given:
- Actual Size = 7.5 µm (micrometers)
- Magnification = 400
Calculating:
Since 1 mm = 1000 µm, we convert:
Thus, the image size is 3 mm.
Step 2
Explain how the shape of a red blood cell is related to its function.
Answer
The shape of a red blood cell (RBC), which is biconcave, is crucial for its function of oxygen transport. This shape provides a larger surface area relative to volume, facilitating maximum gas exchange. The thinness of the membrane allows oxygen and carbon dioxide to diffuse quickly in and out of the cell. Furthermore, the biconcave shape helps RBCs to deform easily as they navigate through narrow capillaries, ensuring efficient circulation throughout the body.
Step 3
State the role of haemoglobin inside the red blood cell.
Answer
Haemoglobin is a protein in red blood cells that binds to oxygen. Its primary role is to transport oxygen from the lungs to the tissues and to carry carbon dioxide from the tissues back to the lungs. This ability to bind to oxygen is facilitated by the iron contained in the haem group of the haemoglobin molecule.
Step 4
Explain why red blood cells cannot be stored in pure water.
Answer
Red blood cells cannot be stored in pure water because it would create a hypotonic environment, causing water to enter the cells through osmosis. This influx of water would lead to swelling and potential bursting (lysis) of the red blood cells. To maintain their integrity and function, they are stored in solutions that are isotonic, such as those containing glucose and salt.