Carbohydrate questions

Cow's milk contains the sugar lactose. Many cats are unable to digest cow's milk because they are lactose intolerant. Cow's milk can be made suitable for these cats by treating it with the enzyme lactase to hydrolyse lactose. This makes the cow's milk lactose-free. Beads are coated with lactase and placed in a tube, as shown in the diagram below. Cow's milk flows over the beads and the lactose is hydrolysed.
Attaching lactase to the beads is a more efficient use of lactase than adding the lactase directly to cow's milk. Suggest three reasons why it is more efficient to attach lactase to the beads
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Cow's milk contains the sugar lactose. Many cats are unable to digest cow's milk because they are lactose intolerant. Cow's milk can be made suitable for these cats by treating it with the enzyme lactase to hydrolyse lactose. This makes the cow's milk lactose-free. Beads are coated with lactase and placed in a tube, as shown in the diagram below. Cow's milk flows over the beads and the lactose is hydrolysed.
Attaching lactase to the beads is a more efficient use of lactase than adding the lactase directly to cow's milk. Suggest three reasons why it is more efficient to attach lactase to the beads
Beads can be reused
No need to remove beads from milk
Enzyme is more stable
Monosaccharides and disaccharides taste sweet. The lactose-free milk made after hydrolysis with lactase tastes sweeter than the cow's milk containing lactose. Suggest why.
1. (Lactose hydrolysed to) galactose and glucose;
2. (So) more sugar molecules; 2. Idea of more sugars essential
3. (So) more / different receptors stimulated / sugars produced are sweeter (than lactose).
Give two ways in which the structure of starch is similar to cellulose
(Both)
1. Are polymers / polysaccharides / are made of monomers / of monosaccharides;
2. Contain glucose / carbon, hydrogen and oxygen; 3. Contain glycosidic bonds;
4. Have 1−4 links; Neutral: references to 'unbranched', insoluble, formed by condensation, flexible and rigid
5. Hydrogen bonding (within structure). Ignore reference to H bonds between cellulose molecules
Give two ways in which the structure of starch is different from cellulose.
(Starch) 1. Contains α / alpha glucose; forms α glycosidic bonds
2. Helical / coiled / compact / branched / not straight; 3. 1,6 bonds / 1,6 branching;
4. Glucoses / monomers same way up;
5. No H-bonds between molecules;
6. No (micro / macro) fibres / fibrils.
In plants, mass transport of sugars takes place through columns of sieve cells in the phloem. Other cells, called companion cells, transport sugars into, and out of, the sieve cells. The diagram shows the structure of the phloem.
Structures I and J allow the transport of sugars between cells. (i) Using the diagram, suggest and explain one other way in which sieve cells are adapted for mass transport.
1. No / few organelles / very little cytoplasm / cytoplasm at edge / more room / hollow / large vacuole / large space / thick walls; Accept strong walls for thick walls
2. (So) easier / more flow / (thick / strong walls) resist pressure. Easier flow may be expressed in other ways e.g. lower resistance to flow
Image: In plants, mass transport of sugars takes place through columns of sieve cells in the phloem. Other cells, called companion cells, transport sugars into, and out of, the sieve cells. The diagram shows the structure of the phloem. Structures I and J allow the transport of sugars between cells. (i) Using the diagram, suggest and explain one other way in which sieve cells are adapted for mass transport.
Using the diagram, suggest and explain one other way in which companion cells are adapted for the transport of sugars between cells.
1. Mitochondria release energy / ATP / site of respiration; Q Reject: 'produce energy' but accept produce energy in form of ATP
2. For active transport / uptake against concentration gradient. Note: no mark is awarded for simply naming an organelle
3. Ribosomes / rough endoplasmic reticulum produce(s) proteins; Concept of making proteins needed
4. (Proteins) linked to transport e.g. carrier proteins / enzymes
Starch and cellulose are two important plant polysaccharides. The following diagram shows part of a starch molecule and part of a cellulose molecule.
(a) Explain the difference in the structure of the starch molecule and the cellulose molecule shown in the diagram above.
1. Starch formed from α-glucose but cellulose formed from β-glucose;
2. Position of hydrogen and hydroxyl groups on carbon atom 1 inverted.
Image: Starch and cellulose are two important plant polysaccharides. The following diagram shows part of a starch molecule and part of a cellulose molecule. (a) Explain the difference in the structure of the starch molecule and the cellulose molecule shown in the diagram above.
Starch molecules and cellulose molecules have different functions in plant cells. Each molecule is adapted for its function.
Explain one way in which starch molecules are adapted for their function in plant cells.
1. Insoluble;
Don't affect water potential;
3. Helical; Accept form spirals
Compact;
Large molecule;
Cannot leave cell.
Explain how cellulose molecules are adapted for their function in plant cells
1. Long and straight chains;
2. Become linked together by many hydrogen bonds to form fibrils;
3. Provide strength (to cell wall).
.A student investigated the effect of chewing on the digestion of starch in cooked wheat. He devised a laboratory model of starch digestion in the human gut. This is the method he used.
1. Volunteers chewed cooked wheat for a set time. The wheat had been cooked in boiling water.
2. This chewed wheat was mixed with water, hydrochloric acid and a protein-digesting enzyme and left at 37 °C for 30 minutes.
3. A buffer was then added to bring the pH to 6.0 and pancreatic amylase was added. This mixture was then left at 37 °C for 120 minutes.
4. Samples of the mixture were removed at 0, 10, 20, 40, 60 and 120 minutes, and the concentration of reducing sugar in each sample was measured.
5. Control experiments were carried out using cooked wheat that had been chopped up in a blender, not chewed.
(a) What reducing sugar, or sugars, would you expect to be produced during chewing? Give a reason for your answer.
1. Maltose;
2. Salivary amylase breaks down starch
In this model of digestion in the human gut, what other enzyme is required for the complete digestion of starch?MaltaseWhat was the purpose of step 2, in which samples were mixed with water, hydrochloric acid and pepsin?(Mimics / reproduces) effect of stomach.In the control experiments, cooked wheat was chopped up to copy the effect of chewing. Suggest a more appropriate control experiment. Explain your suggestion.1. Add boiled saliva; 2. Everything same as experiment but salivary amylase denatured.The figure below shows the student's results. Explain what these results suggest about the effect of chewing on the digestion of starch in wheat.1. Some starch already digested when chewing / in mouth; 2. Faster digestion of chewed starch; 3. Same amount of digestion without chewing at end. Accept use of values from graphIn humans, the enzyme maltase breaks down maltose to glucose. This takes place at normal body temperature. Explain why maltase: • only breaks down maltose • allows this reaction to take place at normal body temperature.1. Tertiary structure / 3D shape of enzyme (means); Accept references to active site 2. Active site complementary to maltose / substrate / maltose fits into active site / active site and substrate fit like a lock and key; Idea of shapes fitting together 3. Description of induced fit; 4. Enzyme is a catalyst / lowers activation energy / energy required for reaction; Accept "provides alternative pathway for the reaction at a lower energy level" 5. By forming enzyme-substrate complex; Accept idea that binding stresses the bonds so more easily broken Do not award point 5 simply for any reference to E-S complexScientists have investigated the effects of competitive and non-competitive inhibitors of the enzyme maltase. Describe competitive and non-competitive inhibition of an enzyme.1. Inhibitors reduce binding of enzyme to substrate / prevent formation of ES complex; Max 3 if only one type of inhibition dealt with. Accept maltase and maltose as examples of enzyme and substrate (and others) Only once, for either inhibitor (Competitive inhibition), 2. Inhibitor similar shape (idea) to substrate; 3. (Binds) in to active site (of enzyme); Accept allows max rate of reaction to be reached / max product will eventually be formed Accept complementary to active site 4. (Inhibition) can be overcome by more substrate; (Non-competitive inhibition), 5. Inhibitor binds to site on enzyme other than active site; 6. Prevents formation of active site / changes (shape of) active site; Accept does not allow max rate of reaction to be reached / max product will not be formedMany sports drinks contain water, sodium chloride and carbohydrates. The manufacturers of the sports drinks claim that carbohydrates provide an energy boost. The sodium chloride is used to increase absorption of glucose in the small intestine. Scientists investigated the effect of a sports drink on the performance of runners in 5 km races. They recruited 100 runners who had previously run a 5 km race in similar times. During this race, Race 1, they had water they could drink. The scientists divided the runners into two equal groups, P and Q. Both groups ran a second 5 km race, Race 2. During this race: • group P had water available • group Q had the sports drink available. The scientists recorded the meantime for each group to complete this race. Figure 1 shows their results. Explain how a sports drink could provide an energy boost when running.1. (Drink) contains carbohydrates / sugars so High GI / (drink) contains carbohydrates / sugars so raises blood glucose concentration quickly; Each alternative requires both aspects for credit The second alternative requires a reference to speed eg 'quickly' or 'immediately' 2. Contains salt so glucose more rapidly absorbed; 3. Increases glucose to muscles for respiration; 4. More / faster respiration so more / faster energy release; Reject reference to energy production Accept more ATP produced