IB Biology HL A2.2 Cell structure questions

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Question 1

Multiple choiceMedium1 mark

A filamentous eukaryote has a cell wall containing chitin. Microscopy of one tube shows many nuclei in a continuous length of cytoplasm, with no cross-walls. Which interpretation accounts for both observations?

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Answer: B. Chitin is characteristic of fungal cell walls. The absence of cross-walls and presence of many nuclei in continuous cytoplasm identify an aseptate fungal hypha.

A: associates a cell wall with plants but overlooks that plant walls contain cellulose, not chitin.
C: matches the multiple nuclei but overlooks that skeletal muscle cells have no cell wall.
D: identifies a fungus from the chitin wall but contradicts the observation that there are no cross-walls.
Remember: aseptate fungal hyphae contain multiple nuclei in continuous cytoplasm.

Question 2

Paper 2Medium16 marks

A student makes a temporary mount of leaf epidermal cells and examines it using a light microscope. At the objective used, a length of 100 μm on a stage micrometer spans 40 eyepiece graticule divisions. One cell has a width of 24 eyepiece graticule divisions. A printed image of the same cell has a width of 6.0 mm. Assume that the printed image has not been resized.

(a)

Calculate the actual length represented by one eyepiece graticule division.

[2]
(b)

Calculate the actual width of the cell and the magnification of the printed image. State the length on the printed image of a scale bar representing 10 μm.

[5]
(c)

A fluorescent stain is used to make cell boundaries visible. To locate protein R, a fluorescently labelled antibody against R is used. Describe how immunofluorescence reveals the location of R and distinguish it from the use of the fluorescent stain.

[3]
(d)

In a further test, 100 cells were scored according to the location of the strongest detectable fluorescence signal.

PreparationPlasma membrane (%)Cytoplasm (%)No detectable signal (%)
Fluorescently labelled antibody against R70255
Fluorescently labelled non-specific antibody6787

Assess the claim that protein R is located exclusively at the plasma membrane, using the data.

[3]
(e)

Another team wants to investigate the internal surfaces of cell membranes and the detailed structure of a protein complex while preserving it close to its native state. Outline how electron microscopy and its developments can be used to address these aims.

[3]

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