1.4- STARCH, GLYCOGEN AND CELLULOSE Flashcards
What is starch?
a polysaccharide found in many parts of a plant in the form of small grains
Where do especially large amounts of starch occur?
in seeds and storage organs, such as potato tubers
Why is starch an important component of food?
major energy source in most diets
What is starch made up of?
chains of α-glucose monosaccharides linked by glycosidic bonds
How are glycosidic bonds formed?
by condensation reactions
How can the chains of starch be?
branched or unbranched
What happens to the unbranched chains of starch?
wound into a tight coil that makes the molecule very compact
What is the main role of starch?
energy storage
How is starch being insoluble helpful?
doesn’t affect water potential, so water is not drawn into the cells by osmosis
How is starch being large and insoluble helpful?
does not diffuse out of cells
How is starch being compact helpful?
so a lot of it can be stored in a small space
How is when starch is hyrdrolysed it forms α-glucose helpful?
easily transported and readily used in respiration
How does the starch with branched forms having many ends helpful?
the ends can be acted on by enzymes simultaneously meaning that glucose monomers are released very rapidly
Where is starch never found?
in animal cells
What similar polysaccharide similar to starch serves the same role?
glycogen
Where can glycogen be found?
in animals and bacteria but never in plant cells
Glycogen is very similar to the structure of what?
the structure of starch but glycogen has shorter chains and is more highly branched
Why is glycogen sometimes called “animal starch”?
as it is the major carbohydrate storage product of animals
How is glycogen stored in animals?
as small granules mainly in the muscles and the liver
Why is the mass of carbohydrates that is stored relatively small?
as fat is the main storage molecule in animals
How is glycogen being insoluble helpful?
does not tend to draw water into the cells by osmosis
does not diffuse out of cells
How is glycogen being compact helpful?
so a lot of it can be stored in a small space
How is glycogen being more highly branched than starch and having more ends make is helpful?
it can be acted on simultaneously by enzymes. Therefore more can be rapidly broken down to form glucose monomers, which are used in respiration
Why is glycogen being broken down into glucose important?
it’s important to animals which have a higher metabolic rate and therefore respiratory rate than plants because they are more active
In what major aspect does cellulose differ from starch and glycogen?
it is made of monomers of β-glucose rather than α-glucose
How does cellulose being made up of β-glucose monomers make it differ from starch and glycogen?
in structure and function of this polysaccharide
How are celluloses’ chains?
straight and unbranched rather than forming a coiled chain like starch
How are the cellulose chains arranged?
run parallel to one another
What does cellulose chains running parallel allow?
allows the hydrogen bonds to form cross-linkages between adjacent chains
What is the effect of the cross-linkages between each individual bond in cellulose?
the sheer overall number of them makes a considerable contribution to strengthening cellulose, making it the valuable structural material it is
What does cellulose molecules grouped together form?
microfibrils
How is microfibrils arranged?
in parallel groups called fibres
Why is cellulose a major component of plant cells walls?
provides rigidity to the plant cell
What does the cellulose cell wall prevent?
prevent the cell from bursting as water enters it by osmosis
How does the cellulose cell wall prevent the cell from bursting?
by excreting an inward pressure that stops any further influx of water
What is the result of cellulose cell walls being able to prevent cells from bursting?
living plant cells are turgid and push against one another, making non-woody parts of the plant semi-rigid
Why is this especially important for plant cells to be turgid?
in maintaining stems and leaves in a turgid state so that they can provide the maximum surface area for photosynthesis
How is cellulose being made up of β-glucose helpful?
form long straight, unbranched chains
How is cellulose molecular chains running parallel to each other and being cross linked by hydrogen bonds helpful?
add collective strength
How is cellulose molecules being grouped to form microfibrils which in turn are grouped to form fibres helpful?
provide yet more strength
