Biology AS OCR
-
1-1-practical-skills-written-assessment AS7 主题
-
1-2-practical-skills-endorsement-assessment AS16 主题
-
1-2-1-practical-ethical-use-of-organisms as
-
1-2-2-practical-aseptic-techniques as
-
1-2-3-practical-dissection-of-gas-exchange-surfaces-in-fish-and-insects as
-
1-2-4-drawing-cells-from-blood-smears as
-
1-2-5-practical-investigating-biodiversity-using-sampling as
-
1-2-6-practical-data-loggers-and-computer-modelling as
-
1-2-7-practical-investigating-the-rate-of-diffusion as
-
1-2-8-practical-investigating-water-potential as
-
1-2-9-practical-factors-affecting-membrane-structure-and-permeability as
-
1-2-10-biochemical-tests-reducing-sugars-and-starch as
-
1-2-11-biochemical-tests-lipids as
-
1-2-12-biochemical-tests-proteins as
-
1-2-13-chromatography as
-
1-2-14-serial-dilutions as
-
1-2-15-practical-investigating-the-rate-of-transpiration as
-
1-2-16-practical-using-a-light-microscope as
-
1-2-1-practical-ethical-use-of-organisms as
-
2-1-cell-structure AS9 主题
-
2-1-2-using-a-microscope as
-
2-1-3-drawing-cells as
-
2-1-4-magnification-and-resolution as
-
2-1-5-eukaryotic-cells as
-
2-1-6-eukaryotic-cells-under-the-microscope as
-
2-1-7-organelles-and-the-production-of-proteins as
-
2-1-8-the-cytoskeleton as
-
2-1-9-prokaryotic-and-eukaryotic-cells as
-
2-1-1-studying-cells as
-
2-1-2-using-a-microscope as
-
2-2-biological-molecules AS17 主题
-
2-2-1-properties-of-water as
-
2-2-2-monomers-and-polymers as
-
2-2-3-monosaccharides as
-
2-2-4-the-glycosidic-bond as
-
2-2-5-polysaccharides as
-
2-2-6-biochemical-tests-reducing-sugars-and-starch as
-
2-2-7-lipids-and-ester-bonds as
-
2-2-8-lipids-structure-and-function as
-
2-2-9-biochemical-tests-lipids as
-
2-2-10-amino-acids-and-peptide-bonds as
-
2-2-11-protein-structure as
-
2-2-12-globular-proteins as
-
2-2-13-fibrous-proteins as
-
2-2-14-inorganic-ions as
-
2-2-15-biochemical-tests-proteins as
-
2-2-16-finding-the-concentration-of-a-substance as
-
2-2-17-chromatography as
-
2-2-1-properties-of-water as
-
2-3-nucleotides-and-nucleic-acids AS8 主题
-
2-4-enzymes AS9 主题
-
2-4-1-the-role-of-enzymes as
-
2-4-2-enzyme-action as
-
2-4-3-enzyme-activity-ph as
-
2-4-4-enzyme-activity-temperature as
-
2-4-5-enzyme-activity-enzyme-concentration as
-
2-4-6-enzyme-activity-substrate-concentration as
-
2-4-7-enzyme-activity-enzyme-inhibitors as
-
2-4-8-coenzymes-cofactors-and-prosthetic-groups as
-
2-4-9-practical-measuring-enzyme-activity as
-
2-4-1-the-role-of-enzymes as
-
2-5-biological-membranes AS9 主题
-
2-5-1-the-cell-surface-membrane as
-
2-5-2-membrane-structure-and-permeability as
-
2-5-3-diffusion-and-facilitated-diffusion as
-
2-5-4-practical-investigating-the-rate-of-diffusion as
-
2-5-5-active-transport as
-
2-5-6-endocytosis-and-exocytosis as
-
2-5-7-osmosis as
-
2-5-8-osmosis-in-animal-and-plant-cells as
-
2-5-9-practical-investigating-water-potential as
-
2-5-1-the-cell-surface-membrane as
-
2-6-cell-division-cell-diversity-and-cellular-organisation AS11 主题
-
2-6-1-the-cell-cycle as
-
2-6-2-the-stages-of-mitosis as
-
2-6-3-identifying-mitosis-in-plant-cells as
-
2-6-4-the-significance-of-mitosis as
-
2-6-5-the-stages-of-meiosis as
-
2-6-6-the-significance-of-meiosis as
-
2-6-7-specialised-cells as
-
2-6-8-the-organisation-of-cells as
-
2-6-9-stem-cells as
-
2-6-10-stem-cells-in-animals-and-plants as
-
2-6-11-the-use-of-stem-cells as
-
2-6-1-the-cell-cycle as
-
3-1-exchange-surfaces AS7 主题
-
3-2-transport-in-animals AS12 主题
-
3-2-1-the-need-for-transport-systems-in-animals as
-
3-2-2-circulatory-systems as
-
3-2-3-blood-vessels as
-
3-2-4-tissue-fluid as
-
3-2-5-the-mammalian-heart as
-
3-2-6-practical-mammalian-heart-dissection as
-
3-2-7-the-cardiac-cycle as
-
3-2-8-cardiac-output as
-
3-2-9-heart-action-initiation-and-control as
-
3-2-10-electrocardiograms-ecgs as
-
3-2-11-the-role-of-haemoglobin as
-
3-2-12-adult-and-fetal-haemoglobin as
-
3-2-1-the-need-for-transport-systems-in-animals as
-
3-3-transport-in-plants AS11 主题
-
3-3-1-the-need-for-transport-systems-in-plants as
-
3-3-2-the-xylem-and-phloem as
-
3-3-3-the-xylem as
-
3-3-4-the-phloem as
-
3-3-5-transverse-sections-stems-roots-and-leaves as
-
3-3-6-the-process-of-transpiration as
-
3-3-7-transpiration-in-plants as
-
3-3-8-practical-investigating-the-rate-of-transpiration as
-
3-3-9-translocation as
-
3-3-10-the-mass-flow-hypothesis as
-
3-3-11-the-adaptations-of-xerophytic-and-hydrophytic-plants as
-
3-3-1-the-need-for-transport-systems-in-plants as
-
4-1-communicable-diseases-disease-prevention-and-the-immune-system AS16 主题
-
4-1-1-common-pathogens-and-communicable-diseases as
-
4-1-2-transmission-of-communicable-pathogens as
-
4-1-3-plant-defences-against-pathogens as
-
4-1-4-non-specific-immune-responses as
-
4-1-5-phagocytes as
-
4-1-6-blood-cells as
-
4-1-7-the-t-lymphocyte-response as
-
4-1-8-the-b-lymphocyte-response as
-
4-1-9-primary-and-secondary-immune-responses as
-
4-1-10-antibodies as
-
4-1-11-opsonins-agglutinins-and-anti-toxins as
-
4-1-12-types-of-immunity as
-
4-1-13-autoimmune-diseases as
-
4-1-14-principles-of-vaccination as
-
4-1-15-sources-of-medicine as
-
4-1-16-antibiotics as
-
4-1-1-common-pathogens-and-communicable-diseases as
-
4-2-biodiversity AS10 主题
-
4-2-1-biodiversity as
-
4-2-2-sampling-to-determine-biodiversity as
-
4-2-3-practical-investigating-biodiversity-using-sampling as
-
4-2-4-measuring-species-richness-and-species-evenness as
-
4-2-5-simpsons-index as
-
4-2-6-genetic-diversity as
-
4-2-7-factors-affecting-biodiversity as
-
4-2-8-reasons-for-maintaining-biodiversity as
-
4-2-9-methods-of-maintaining-biodiversity as
-
4-2-10-conservation-agreements as
-
4-2-1-biodiversity as
-
4-3-classification-and-evolution AS15 主题
-
4-3-1-classification-of-species as
-
4-3-2-binomial-system as
-
4-3-3-classification-of-the-three-domains as
-
4-3-4-classification-of-the-five-kingdoms as
-
4-3-5-classification-and-phylogeny as
-
4-3-6-evidence-of-evolution as
-
4-3-7-types-of-variation as
-
4-3-8-standard-deviation as
-
4-3-9-variation-t-test-method as
-
4-3-10-variation-t-test-worked-example as
-
4-3-11-spearmans-rank-correlation as
-
4-3-12-adaptation as
-
4-3-13-natural-selection as
-
4-3-14-evolution-of-resistance as
-
4-3-15-consequences-of-resistance as
-
4-3-1-classification-of-species as
2-2-7-lipids-and-ester-bonds as
Exam code:H020
Lipids
Lipids
-
Lipids are macromolecules that contain carbon, hydrogen and oxygen atoms. Unlike carbohydrates, lipids contain a lower proportion of oxygen
-
Lipids are non-polar and hydrophobic (insoluble in water)
-
There are two groups of lipid that you need to know:
-
Triglycerides (the main component of fats and oils)
-
Phospholipids
-
-
Lipids play an important role in energy yield, energy storage, insulation and hormonal communication
Triglycerides
-
Triglycerides are non-polar, hydrophobic molecules
-
The monomers that make up triglycerides are glycerol and fatty acids
-
Glycerol is an alcohol (an organic molecule that contains a hydroxyl group bonded to a carbon atom)
-
Fatty acids contain a methyl group at one end of a hydrocarbon chain known as the R group (chains of hydrogens bonded to carbon atoms, typically 4 to 24 carbons long) and at the other is a carboxyl group
-
The shorthand chemical formula for a fatty acid is RCOOH
-
-
Fatty acids can vary in two ways:
-
Length of the hydrocarbon chain (R group)
-
The fatty acid chain (R group) may be saturated (mainly in animal fat) or unsaturated (mainly vegetable oils, although there are exceptions e.g. coconut and palm oil)
-
-
Unsaturated fatty acids can be mono or poly-unsaturated
-
If H atoms are on the same side of the double bond they are cis-fatty acids and are metabolised by enzymes
-
If H atoms are on opposite sides of the double bond they are trans-fatty acids and cannot form enzyme-substrate complexes, and therefore are not metabolised. ‘Trans-fat’ is linked with coronary heart disease
-
Examples of different types of fatty acids with the functional groups and presence of double bonds highlighted
Phospholipids
-
Phospholipids are a type of lipid, therefore they are formed from the monomers glycerol and fatty acids
-
Unlike triglycerides, there are only two fatty acids bonded to a glycerol molecule in a phospholipid as one has been replaced by a phosphate ion (PO43-)
-
As the phosphate is polar it is soluble in water (hydrophilic)
-
The fatty acid ‘tails’ are non-polar and therefore insoluble in water (hydrophobic)
Phospholipids are the major components of cell surface membranes. They have fatty acid tails that are hydrophobic and a phosphate head, that is hydrophilic, attached to a glycerol molecule.
-
Phospholipids are amphipathic (they have both hydrophobic and hydrophilic parts)
-
As a result of having hydrophobic and hydrophilic parts, phospholipid molecules form monolayers or bilayers in water
In the presence of water due to the hydrophobic and hydrophilic parts phospholipids will form monolayers or bilayers
Phospholipids v Triglycerides Table
Examiner Tips and Tricks
Ensure that you are familiar with the structure of a triglyceride and that you can recognise whether the fatty acids are saturated or unsaturated and know the difference between phospholipids and triglycerides!
The Ester Bond
-
Triglycerides contain three ester bonds between the fatty acids and the glycerol molecule
-
An ester bond forms when a hydroxyl (-OH) group from the glycerol bonds with the carboxyl (-COOH) group of the fatty acid
-
An H from glycerol combines with an OH from the fatty acid to make water
-
The formation of an ester bond is a condensation reaction
-
For each ester bond formed a water molecule is released
-
Three fatty acids join to one glycerol molecule to form a triglyceride
-
Therefore for one triglyceride to form, three water molecules are released
-
-
The ester bonds can break during breakdown of the triglyceride molecule (e.g. during digestion)
-
This process is a hydrolysis reaction and three water molecules are taken in the reverse reaction to the condensation
-
Responses