IB DP Biology- B2.3 Cell specialization- IB Style Questions For HL Paper 1A -FA 2025
▶️ Answer/Explanation
Totipotent cells are present in the very early stages of embryonic development, such as in the zygote and first few cell divisions. These cells have the potential to develop into any cell type in the body, including both embryonic and extraembryonic tissues (like the placenta).
✅ Answer: (A) Totipotent
Question
Scenedesmus is a microscopic, unicellular green alga. However, it often exists as multicellular colonies of cells.
The magnification of the image is 500×. What is the length of one cell?
A. 10nm
B. 50 μm
C. 20 μm
D. 10mm
▶️Answer/Explanation
Answer: C. 20 μm
Explanation:
What is Magnification and How is Actual Size Determined?
Magnification is the number of times an object’s size is increased in an image. The actual size of the object can be calculated using the formula:
\text{Actual size} = \frac{\text{Image size}}{\text{Magnification}}
If we know the magnification but not the image size, we can still answer based on biological knowledge. Scenedesmus is a type of microscopic green alga. Individual cells typically measure between 10–30 micrometers (μm) in length.
Now, evaluate each option:
Option A. Incorrect – 10 nm
A nanometer (nm) is 1,000 times smaller than a micrometer (μm). 10 nm is the size of a virus or a protein, not a whole algal cell. This is far too small for any eukaryotic cell.
Option B. Incorrect – 50 μm
50 micrometers is possible for some large cells, but it is larger than the usual size of Scenedesmus cells. This value is slightly above the known typical range of 10–30 μm.
Option C. Correct – 20 μm
20 micrometers is within the normal size range for Scenedesmus cells. It is biologically accurate and fits the expected dimensions of these algae under 500× magnification.
Option D. Incorrect – 10 mm
10 millimeters equals 10,000 micrometers. This is far too large for any single algal cell and would be visible without a microscope. It is not realistic.