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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). 7.5 μm top view of red blood cell 2.5 μm side view ... 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
(i) 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 can use the magnification formula:
Substituting the actual size of the top view of the red blood cell (7.5 μm) and the magnification (400):
To convert μm to mm, we use the conversion factor (1 mm = 1000 μm):
Thus, the image size of the top view of the red blood cell is 3 mm.
Step 2
(ii) Explain how the shape of a red blood cell is related to its function.
Answer
The shape of a red blood cell (RBC) is a biconcave disk, which greatly enhances its functionality in several ways:
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Surface Area: The biconcave shape increases the surface area-to-volume ratio, allowing for more efficient gas exchange. This is crucial for transporting oxygen from the lungs to tissues and carbon dioxide from tissues back to the lungs.
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Flexibility: The flexible nature of RBCs allows them to deform as they pass through narrow capillaries, ensuring that blood circulation is unobstructed.
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Hemoglobin Localization: The shape aids in maximizing the space available for hemoglobin, the protein that binds oxygen, thereby facilitating improved oxygen transport in the bloodstream.
Step 3
(iii) State the role of haemoglobin inside the red blood cell.
Answer
The primary role of haemoglobin inside the red blood cell is to bind to oxygen molecules in the lungs, facilitating the transport of oxygen throughout the body. Hemoglobin also helps transport carbon dioxide from the tissues back to the lungs, ensuring efficient gas exchange.
Step 4
(b) Explain why red blood cells cannot be stored in pure water.
Answer
Red blood cells cannot be stored in pure water due to osmosis. When RBCs are placed in a hypotonic solution, such as pure water, water will enter the cells, causing them to swell and potentially burst (hemolysis). The correct storage solution for red blood cells includes 5.0% glucose and 0.9% salt, which maintains osmotic balance and prevents the cells from taking in excess water.