Biology AS AQA
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1-1-biological-molecules-carbohydrates11 主题
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1-1-1-biological-molecules-key-terms
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1-1-2-biological-molecules-reactions
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1-1-3-monosaccharides
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1-1-4-glucose
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1-1-5-the-glycosidic-bond
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1-1-6-chromatography-monosaccharides
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1-1-7-disaccharides
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1-1-8-starch-and-glycogen
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1-1-9-cellulose
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1-1-10-biochemical-tests-sugars-and-starch
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1-1-11-finding-the-concentration-of-glucose
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1-1-1-biological-molecules-key-terms
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1-2-biological-molecules-lipids3 主题
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1-3-biological-molecules-proteins5 主题
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1-4-proteins-enzymes12 主题
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1-4-1-many-proteins-are-enzymes
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1-4-2-enzyme-specificity
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1-4-3-how-enzymes-work
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1-4-4-required-practical-measuring-enzyme-activity
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1-4-5-drawing-a-graph-for-enzyme-rate-experiments
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1-4-6-using-a-tangent-to-find-initial-rate-of-reaction
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1-4-7-limiting-factors-affecting-enzymes-temperature
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1-4-8-limiting-factors-affecting-enzymes-ph
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1-4-10-limiting-factors-affecting-enzymes-enzyme-concentration
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1-4-11-limiting-factors-affecting-enzymes-substrate-concentration
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1-4-12-limiting-factors-affecting-enzymes-inhibitors
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1-4-14-control-of-variables-and-uncertainty
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1-4-1-many-proteins-are-enzymes
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1-5-nucleic-acids-structure-and-dna-replication8 主题
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1-5-2-nucleotide-structure-and-the-phosphodiester-bond
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1-5-3-dna-structure-and-function
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1-5-4-rna-structure-and-function
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1-5-5-ribosomes
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1-5-6-the-origins-of-research-on-the-genetic-code
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1-5-8-the-process-of-semi-conservative-replication
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1-5-9-calculating-the-frequency-of-nucleotide-bases
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1-5-10-the-watson-crick-model
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1-5-2-nucleotide-structure-and-the-phosphodiester-bond
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1-6-atp-water-and-inorganic-ions4 主题
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2-1-cell-structure7 主题
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2-2-the-microscope-in-cell-studies4 主题
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2-3-cell-division-in-eukaryotic-and-prokaryotic-cells8 主题
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2-4-cell-membranes-and-transport9 主题
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2-4-1-the-structure-of-cell-membranes
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2-4-3-the-cell-surface-membrane
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2-4-4-diffusion
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2-4-5-osmosis
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2-4-7-osmosis-in-animal-cells
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2-4-9-required-practical-investigating-water-potential
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2-4-10-active-transport-and-co-transport
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2-4-11-adaptations-for-rapid-transport
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2-4-13-required-practical-factors-affecting-membrane-permeability
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2-4-1-the-structure-of-cell-membranes
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2-5-cell-recognition-and-the-immune-system7 主题
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2-6-vaccines-disease-and-monoclonal-antibodies6 主题
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3-1-adaptations-for-gas-exchange6 主题
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3-2-human-gas-exchange14 主题
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3-2-5-the-alveolar-epithelium
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3-2-1-the-human-gas-exchange-system
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3-2-2-dissecting-the-gas-exchange-system
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3-2-3-microscopy-and-gas-exchange-surfaces
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3-2-4-investigating-gas-exchange
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3-5-5-investigating-heart-rate
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3-5-6-blood-vessels
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3-5-7-capillaries-and-tissue-fluid
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3-5-8-cardiovascular-disease-data
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3-2-10-risk-factor-data
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3-2-11-correlations-and-causal-relationships
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3-2-6-ventilation-and-gas-exchange
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3-2-8-the-effects-of-lung-disease
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3-2-9-pollution-and-smoking-data
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3-2-5-the-alveolar-epithelium
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3-3-digestion-and-absorption5 主题
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3-4-mass-transport-in-animals6 主题
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3-5-the-circulatory-system-in-animals4 主题
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3-6-mass-transport-in-plants6 主题
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4-1-dna-genes-and-chromosomes10 主题
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4-2-dna-and-protein-synthesis3 主题
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4-3-genetic-diversity-mutations-and-meiosis7 主题
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4-4-genetic-diversity-and-adaptation6 主题
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4-5-species-and-taxonomy4 主题
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4-6-biodiversity9 主题
2-3-6-investigating-plant-root-tips
Exam code:7401
Mitotic index
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The mitotic index is the proportion of cells (in a group of cells or a sample of tissue) that are undergoing mitosis
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The mitotic index can be calculated using the formula below:
mitotic index = number of cells with visible chromosomes ÷ total number of cells
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The answer can be multiplied by 100 if the mitotic index is required as a percentage
Worked Example
A student who wanted to observe mitosis prepared a sample of cells. They counted a total of 42 cells in their sample, 32 of which had visible chromosomes.
Calculate the mitotic index for this sample of cells (give your answer to 2 decimal places).
mitotic index = number of cells with visible chromosomes ÷ total number of cells
mitotic index = 32 ÷ 42
mitotic index = 0.76
Worked Example
The table below shows the number of cells in different stages of mitosis in a sample from a garlic root tip. Calculate the mitotic index for this tissue (give your answer to 2 decimal places).
mitotic index = number of cells with visible chromosomes ÷ total number of cells
mitotic index = (prophase + metaphase + anaphase + telophase) ÷ total number of cells
mitotic index = (14 + 5 + 3 + 6) ÷ (36 + 14 + 5 + 3 + 6)
mitotic index = 28 ÷ 64
mitotic index = 0.44
Worked Example
The micrograph below shows a sample of cells from an onion root tip. Calculate the mitotic index for this tissue (give your answer to 2 decimal places).
Number of cells with visible chromosomes (green) = 20
Total number of cells (green + red) = 20 + 55 = 75
mitotic index = number of cells with visible chromosomes ÷ total number of cells
mitotic index = 20 ÷ 75
mitotic index = 0.27
Calculating the size of root tip cells
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The images (micrographs) taken of slides containing root tip cells can be used to calculate the actual size of root tip cells
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The magnification equation can be used:
actual size = size of image ÷ magnification
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The size of cells is typically measured using the micrometre (μm) scale, with cellular structures measured in either micrometres (μm) or nanometers (nm)
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When doing calculations, all measurements must be in the same units
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It is best to use the smallest unit of measurement shown in the question
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To convert units, multiply or divide depending if the units are increasing or decreasing
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Magnification does not have units
Examiner Tips and Tricks
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There are 1000 nanometers (nm) in a micrometre (µm)
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There are 1000 micrometres (µm) in a millimetre (mm)
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There are 1000 millimetres (mm) in a metre (m)
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