As Biology Unit 1 Notes

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AS Biology - Unit 1
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Metabolism
Metabolism is a term to describe all reaction which is taking place within a cell and is separated into two types which are * anabolic = compounds being built up
* catabolic = compounds being broken down

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Water
The water molecule is a molecule which is made up from 2 hydrogen atoms and 1 oxygen atom. It is bounded by 2 covalent bonds and has is polar. The reason why water molecules are important for living organisms are because: 1. They are important solvents since they are polar

2. Important coolants for excessive metabolic reactions
3. Important for insulation since they have high specific heat capacities 4. It is a very good mechanism for transport since they are highly cohesive 5. Important reagents for chemical reactions ( such as hydrolysis and photosynthesis )

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Carbohydrates
Separated into 3 types which are monosaccharides, disaccharides and polysaccharides Monosaccharides
* they are three main types of monosaccharides which you have to know in this level which are Pentoses - Such as ribose (with formula C5H10O5) and fructose Hexose - Such as alpha and beta glucoses

* All members of monosaccharides are reducing since they have the aldehyde groups, therefore they will cause a brick red precipitate to form when tested with Benedict’s solution.

Disaccharides
* You would need to know 3 types of disaccharides in this level which is 1. Lactose - Formed between glucose and galactose and is bounded by 1,4 glycosidic bonds (found in milk) 2. Maltose - Formed by 2 molecules of glucose and is bounded by 1,4 glycosidic bonds (found in starch after being hydrolysed) 3. Sucrose – Formed by a molecule of glucose and a molecule of fructose bounded by 1,2 glycosidic bonds (Found in most plant since it is used to transport sugary compounds) * The formation of bonds between 2 monosaccharides is called condensation and the breakage of these bonds are called hydrolysis. Hydrolysis of these bonds can be brought about by adding dilute HCl. * Both lactose and maltose are reducing but sucrose is not a reducing sugar. Therefore disaccharides can or cannot be reducing. It is not always a reducing agent.

Polysaccharides
* There are three types of polysaccharides that we need to know at this level which are

Starch
* A polymer of alpha glucose and is bounded by 30% amylose (1,4 glycosidic bonds) and 70% amylopectin (both 1,4 and 1,6 glycosidic bonds) * It is used as a food storage for plants and is built from the amyloplasts in the cytoplasm of plant cells. * Starch is an important storage molecule since it is compact, insoluble in water, inert to chemical reactions and is easily hydrolysed when required.

Glycogen
* A polymer of alpha glucose with 1,4 glycosidic bonds but even more 1,6 glycosidic bonds compared to starch since it is even more branched. * It is used as an energy store in animals and is also found in bacterias * Glycogen is an important storage molecule since it is compact, insoluble in water, inert to chemical reactions and is easily hydrolysed when required.

Cellulose
* A polymer of beta glucose and is by only 1,4-glycosidic bonds. Therefore it is not branched but arranged in a matrix which is bounded by hydrogen bonds * It is the constituent of cell walls and can be hydrolysed by ruminant animals by the action of cellulase enzymes. * All polysaccharides are non reducing sugars.

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Lipids
* Lipids are basically fats and oils that contain elements of carbon, hydrogen and oxygen * An example of a lipid would be the triglyceride which is formed by glycerol and fatty acids .The bond formed is catalysed by the process of condensation between the –OH groups of the glycerol and the...
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