3.1.2 - carbohydrates

Question 1

what are monosaccharides?

Answer 1

• monomers of carbohydrates
• e.g. glucose (C6H12O6), galactose and fructose.

Question 2

how are disaccharides formed?

Answer 2

• formed by a condensation reaction between 2 monosaccharides.

Question 3

what type of bond is formed in between a disaccharide?

Answer 3

• a glycosidic bond.

Question 4

what is released in a condensation reaction?

Answer 4

• water is released.

Question 5

which two monosaccharides make up maltose disaccharide?

Answer 5

• two alpha glucose.

Question 6

which two monosaccharides make up sucrose disaccharide?

Answer 6

• alpha glucose.
• fructose.

Question 7

which two monosaccharides make up lactose disaccharide?

Answer 7

• beta glucose.
• galactose.

Question 8

how are polysaccharides formed?

Answer 8

• formed by the condensation of many monosaccharides.

Question 9

how can glucose be released from starch and glycogen?

Answer 9

• molecules of glucose can be released from starch and glycogen for respiration by a hydrolysis reaction, which uses water and breaks the glycosidic bond between monomers.

Question 10

what type of polysaccharide is within a plants cell wall?

Answer 10

• cellulose.
• it provides strength and support to plant cells.

Question 11

how do you test for starch?

Answer 11

• add iodine/potassium iodine solution.
• if starch is present is turns from orange/yellow to blue-black.

Question 12

what’s the test for reducing sugars? - all monosaccharides and maltose

Answer 12

• add Benedict’s reagent.
• heat to 80 degrees.
• if reducing sugar is present it turns from blue to brick red/orange/green.
• more precipitate (of red copper oxide) indicates higher concentration of reducing sugar.

(all monosaccharides and maltose)

Question 13

what’s the test for non-reducing sugars? - some disaccharides

Answer 13

• boil in hydrochloric acid (to hydrolyse the disaccharide into its monosaccharides).
• add hydrogen carbonate solution (to neutralise).
• add Benedict’s reagent.
• heat to 80 degrees.
• if reducing sugar is present it turns from blue to orange/green.

Question 14

what is the key thing to know about the disaccharide lactose?

Answer 14

that it is the main sugar in milk.

Question 15

what is the key thing to know about the disaccharide sucrose?

Answer 15

• carbohydrates in plants are transported as sucrose as it allows for more efficient energy transfer and increased energy storage.
• quick form of energy = broken apart quickly by a hydrolysis reaction.

Question 16

what is the key thing to know about the disaccharide maltose?

Answer 16

• it’s a reducing sugar.
• germinating seeds use maltose as an energy and food store.
• animals convert starch to maltose as it absorbs easier.

Question 17

where is the polysaccharide starch mainly found?

Answer 17

plants.

Question 18

where is the polysaccharide cellulose mainly found?

Answer 18

plants.

Question 19

where is the polysaccharide glycogen mainly found?

Answer 19

in animals, fungi and bacteria.

Question 20

what is the monomer of the polysaccharide amylose (starch)?

Answer 20

alpha glucose.

Question 21

what type of covalent bonds are in amylose (starch)?

Answer 21

alpha 1,4 glycosidic bonds.

Question 22

what is the structure of amylose (starch)?

Answer 22

• unbranched polymer.
• coiled/ helical = making it compact for storage.

Question 23

what is the function of amylose (starch)?

Answer 23

• storage of glucose for respiration.
• storage in plants.
• releases glucose over a long period of time.
• insoluble so doesn’t affect the water potential.

Question 24

what is the monomer of the polysaccharide amylopectin (starch)?

Answer 24

alpha glucose.

Question 25

what type of covalent bonds are in amylopectin (starch)?

Answer 25

alpha 1,4 glycosidic bonds and alpha 1,6 glycosidic bonds.

Question 26

what is the structure of amylopectin (starch)?

Answer 26

• branched polymer.
• branched chains have many terminals so glucose molecules can be rapidly broken off when energy is needed.
• crystalline structure.

Question 27

what is the function of amylopectin (starch)?

Answer 27

• releases glucose for cellular respiration rapidly when needed.

Question 28

what is the monomer of the polysaccharide glycogen?

Answer 28

alpha glucose.

Question 29

what type of covalent bonds are in glycogen?

Answer 29

alpha 1,4 glycosidic bonds and alpha 1,6 glycosidic bonds.

Question 30

what is the structure of glycogen?

Answer 30

• highly branched.
• spherical shape.

Question 31

what is the function of glycogen?

Answer 31

• can be broken down very quickly.
• high metabolic rate.
• storage in animals and fungi.
• insoluble so it doesn’t affect the water potential.

Question 32

what is the monomer of the polysaccharide cellulose?

Answer 32

beta glucose.

Question 33

what type of covalent bonds are in cellulose?

Answer 33

beta 1,4 glycosidic bonds.

Question 34

what is the structure of cellulose?

Answer 34

• linear chain.
• alternating orientation = each beta glucose is rotated 180 degrees allowing hydrogen bonds to form between the hydroxyl group of adjacent chains.
• hydrogen bonds form microfibrils.
• microfibrils = bundles into fibres providing high tensile strength.

Question 35

what is the function of cellulose?

Answer 35

• plant cell wall = structural molecule.
• high tensile strength = helps the cell maintain its shape and resist turgor pressure and chains overlap so there is no weak point.
• flexibility = allows the cell wall to expand as the cell grows.
• protection = protects cells from mechanical damage and pathogens.
• support = allows the plant to stand upright and grow.

Question 36

which type of glucose is the main substrate of respiration?

Answer 36

alpha glucose.