Prokaryotic and eukaryotic cellsEdexcel A-Level Biology B: Mind map

Exam questions on Prokaryotic and eukaryotic cells

1. A hospital laboratory identifies two species of bacteria from patient samples. Species 1 stains purple with the Gram stain and species 2 stains pink. Penicillin, which stops the cross-links in peptidoglycan from forming as a bacterial cell wall is built, kills species 1 at a low concentration, but species 2 is affected only at a much higher concentration.
   Suggest why species 2 is much less affected by penicillin than species 1.2 marks
2. A student observes human cheek cells stained with methylene blue under a light microscope. She then looks at a transmission electron micrograph (TEM) of a similar cell in a textbook. In the TEM, mitochondria show their internal folds and ribosomes appear as tiny dark dots, but neither is clear in the light microscope.
   The image of one mitochondrion in the TEM is 45 mm long. The magnification of the image is ×15 000. Calculate the actual length of the mitochondrion in micrometres (µm).2 marks
3. A student is using a light microscope to measure cheek cells. A stage micrometer is a slide with a scale 1 mm long divided into 100 equal divisions. Using the ×40 objective, she finds that 4 divisions of the stage micrometer line up exactly with 25 divisions of the eyepiece graticule. She then finds that one cheek cell spans 35 eyepiece divisions.
   Calculate the actual length of the cheek cell in micrometres (µm). Show your working.3 marks