Biology Unit 2.10.3 Starch, glycogen and cellulose

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Question Answer
Name 3 important polysaccharidesStarch, glycogen and cellulose
Where is starch found and in what form?Starch is found in many parts of a plant in the form of small grains. Especially large amounts occur in seeds and storage organs, such as potato tubers.
What is starch in diets?Starch is the main energy source in most diets
What is starch made up of/formed from?Starch is made up of a chain of alpha glucose monosaccharides linked by glycosidic bonds that are formed by condensation reactions. The unbranched chain is wound into a tight coil that makes the molecule very compact.
What is the main role of starch?energy storage
What is starch suited for its main role?1.It is insoluble and therefore does not tend to draw water into the cells by osmosis. 2.Being insoluble, it does not easily diffuse out of cells 3.It is compact, so a lot of it can be stored in a small space. 4.When hydrolysed it forms alpha glucose, which is both easily transported and readily used in respiration
Is starch found in animal cells?Starch is never found in animal cells. Instead a similar polysaccharide, called glycogen, serves the same role
Structure of glycogen?Very similar in structure to starch but has shorter chains and is more highly branched.
What is glycogen to animals?Major carbohydrate storage product of animals
What is glycogen stored as in animals?Stored as small granules mainly in the muscles and the liver.
Why does glycogens structure suit its purpose and how is it better than starch?Structure suits its purpose for the same reasons given for starch. However, because it is made up of smaller chains, it is even more readily hydrolysed to alpha glucose.
Is glycogen found in animal cells?Glycogen is found in animal cells but never in plant cells.
How does cellulose differ from starch and glycogen?It is made up of monomers of beta glucose rather than alpha glucose
What does the difference in glucose mean for cellulose?Fundamental differences in the structure and function. In the Beta glucose units, the position of the -H group and the -OH group on a single carbon atom are reversed. In Beta glucose the -OH group is above, rather than below, the ring. This means that to form glycosidic links, each Beta glucose molecule must be rotated by 180 degrees compared to its neighbour. The result is that the -CH2OH group on each Beta glucose molecule alternates between being above and below the chain.
Describe the structure of cellulose.Rather than forming a coiled chain like starch, cellulose has straight, unbranched chains. These run parallel to one another, allowing hydrogen bonds to form cross-linkages between adjacent chains. While each individual hydrogen bond adds very little to the strength of the molecule, the sheer overall number of them makes a considerable contribution to strengthening cellulose.
What does cellulose do for plants?Cellulose is a major component of plant cell walls and provides rigidity to the plant cell. The cellulose cell wall also prevents the plant cell from bursting as water enters it by osmosis. It does this by exerting an inward pressure that stops any further influx of water. As a result, living plant cells are turgid and push against one another, making parts of the plant semi-rigid. This is important in maintaining stems and leaves in a turgid state so that they can provide the maximum surface area for photosynthesis.