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Practical Skills and Mathematical Requirements

Estimates, symbols and biological calculations

  • 3 things to know
  • Components 01, 02 and 03

Overview

Recall questions on estimating results and orders of magnitude, the symbols <, >, ≪, ≫, ∝ and ~, offspring probabilities, microbial population growth, magnification, and surface area to volume ratios.

What you need to know

Answer each one before you reveal it.

Your recallNot started
Process

State the formulae for the circumference and area of a circle.

Process

State the formulae for the surface area and volume of a sphere.

Process

Calculate the number of bacteria after 2 hours when N₀ = 250 cells and the generation time is 20 minutes.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Why should the answer to a biological calculation be estimated first?

    Model answer

    A rough estimate made with rounded numbers shows whether the calculated answer is sensible, catching mistakes such as multiplying instead of dividing.

  2. 2

    A student calculates the actual length of a cell as 14 400 mm from an image 24 mm long at a magnification of ×600. How does an order of magnitude check show the error?

    Model answer

    Cells are about 10 to 100 µm long, so 14 400 mm is roughly a million times too large; the student multiplied, and the correct size is 24 ÷ 600 = 0.04 mm (40 µm).

  3. 3

    What is an order of magnitude?

    Model answer

    A power of ten: a quantity one order of magnitude larger is about ten times bigger, and three orders of magnitude larger is about a thousand times bigger.

  4. 4

    How many orders of magnitude larger is a cell 10 µm across than a virus 100 nm across?

    Model answer

    Two: 10 µm = 10 000 nm, and 10 000 ÷ 100 = 100 = 10².

  5. 5

    What do the symbols < and > mean?

    Model answer

    < means less than and > means greater than.

  6. 6

    What do the symbols ≪ and ≫ mean?

    Model answer

    ≪ means much less than and ≫ means much greater than, for example the diameter of a ribosome ≪ the diameter of a nucleus.

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Cell Structure
Biological Molecules
Nucleotides and Nucleic Acids
Enzymes

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Centrioles consist of .
microtubuleschromosomesribosomes

Blank Blitz consolidates the facts

Rapid timed gap-fills on the terms and numbers you need to recall without thinking.

AA phospholipid contains one glycerol molecule.
BTwo fatty acids bond to the glycerol molecule.
COne phosphate group replaces the third fatty acid.

Build It trains answer structure

Assemble a full-mark answer from its marking points, in the order an examiner wants them.

Habitat means the physical place where an organism lives.
TrueFalse

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Spot the fault in a statement. The traps are the mistakes students actually make.

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