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Cells and microscopy

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Which observation directly supports the origin of cells from existing cells?

  1. One cell divides to produce two daughter cells.
  2. A purified enzyme still catalyses its reaction outside the cell.
  3. Ribosomes are smaller than nuclei.
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One cell divides to produce two daughter cells.

Division connects new cells to a pre-existing cell.

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Which feature best distinguishes rough endoplasmic reticulum from smooth endoplasmic reticulum?

  1. DNA enclosed in a double envelope
  2. Ribosomes attached to the cytosolic surface
  3. A surrounding phospholipid membrane
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Ribosomes attached to the cytosolic surface

Attached ribosomes give rough endoplasmic reticulum its characteristic appearance.

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Where would you expect an especially dense region of rRNA production?

  1. A smooth endoplasmic reticulum tubule
  2. A lysosome
  3. The nucleolus
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The nucleolus

The nucleolus is involved in rRNA production and ribosomal subunit assembly.

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Which structure is NOT surrounded by a double membrane?

  1. Lysosome
  2. Chloroplast
  3. Nucleus
  4. Mitochondrion
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Lysosome

A lysosome is bounded by a single membrane. The nucleus, mitochondria and chloroplasts each have an envelope of two membranes.

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Which comparison is correct?

  1. Bacterial and plant walls are both cellulose.
  2. Bacteria lack ribosomes because their cells are too small to hold them, so they use host ribosomes.
  3. A bacterial nucleoid is not enclosed by a nuclear envelope.
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A bacterial nucleoid is not enclosed by a nuclear envelope.

The DNA region is not a membrane-bound nucleus.

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Which statements describe a typical bacterial cell? 1: Its ribosomes are 70S. 2: Its DNA is enclosed in a nuclear envelope. 3: Its wall contains peptidoglycan. 4: It has no mitochondria.

  1. 1, 2, 3 and 4
  2. 1 and 3 only
  3. 1, 3 and 4 only
  4. 2, 3 and 4 only
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1, 3 and 4 only

Bacteria have 70S ribosomes, a peptidoglycan wall and no membrane-bound organelles. Their DNA lies in a nucleoid with no envelope, so statement 2 is false.

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50 divisions span 100 micrometres. What length is 15 divisions?

  1. 30 micrometres
  2. 7.5 micrometres
  3. 1500 micrometres
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30 micrometres

Each division is 2 micrometres, so 15 x 2 = 30.

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A scale bar 15 mm long represents 20 micrometres. A guard cell measures 28 mm on the same image. What is its actual length to 2 significant figures?

  1. 37 micrometres
  2. 1.9 micrometres
  3. 37.3 micrometres
  4. 21,000 micrometres
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37 micrometres

Magnification = 15,000 / 20 = x750, so actual length = 28,000 / 750 = 37.3, which is 37 micrometres to 2 significant figures.

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Question 1 of 7

Draw, calculate and compare

4 marks

A photomicrograph of a leaf epidermis has a scale bar 15 mm long labelled 20 micrometres. One guard cell is 28 mm long on the image. (a) Calculate the magnification and the actual length of the guard cell to 2 significant figures. (b) You draw the guard cell 90 mm long. Calculate the magnification of your drawing to 2 significant figures. (c) List four rules your drawing must follow. (d) Set out an observable-differences table comparing the guard cells with the other epidermal cells, with three rows. [4]

Convert mm to micrometres; divide image by actual; round at the end. Table: feature | guard cells | epidermal cells.

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