Prokaryotic and eukaryotic cellsEdexcel A-Level Biology B: Flashcards
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What does cell theory state?
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- What does cell theory state?
- Cells are the fundamental unit of structure, function and organisation of all living organisms.
- What is the nucleoid?
- The region of a prokaryotic cell containing the circular DNA, with no nuclear envelope.
- What is a plasmid?
- A small circular loop of DNA in bacteria that carries extra genes such as antibiotic resistance.
- What size are ribosomes in prokaryotes and eukaryotes?
- 70S in prokaryotes and 80S in eukaryotes.
- What is a Gram-positive cell wall like?
- Thick peptidoglycan with no outer membrane; stains purple.
- What is a Gram-negative cell wall like?
- Thin peptidoglycan with an outer membrane; stains pink.
- Why are Gram-negative bacteria often less affected by antibiotics such as penicillin?
- The outer membrane reduces the entry of the antibiotic to the peptidoglycan wall.
- What is the function of the nucleolus?
- It makes ribosomal RNA and assembles ribosomes.
- What do the rough ER and Golgi apparatus do?
- RER folds and transports proteins; the Golgi modifies them and packages them into vesicles.
- What is the function of lysosomes?
- They contain digestive enzymes to break down worn-out organelles and engulfed material.
- What is the function of the tonoplast?
- It is the membrane around the vacuole in plant cells.
- Difference between magnification and resolution?
- Magnification is how much larger the image is; resolution is the ability to see two close points as separate.
- Why does a TEM have a higher resolution than a light microscope?
- Electrons have a much shorter wavelength than light.
- How is a graticule calibrated?
- Compare its divisions with a stage micrometer of known length, at each objective lens.
- Formula for magnification?
- Magnification = image size ÷ actual size.
Exam questions on Prokaryotic and eukaryotic cells
- 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
- 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
- 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
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).