1.2 carbohydrates Flashcards
Explain how a sports drink could provide an energy boost when running. (3)
- (Drink) contains carbohydrates / sugars so High GI / (drink) contains carbohydrates /
sugars so raises blood glucose concentration quickly;
2. Contains salt so glucose more rapidly absorbed;
3. Increases glucose to muscles for respiration;
4. More / faster respiration so more / faster energy release;
In 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.
- Tertiary structure / 3D shape of enzyme (means);
- Active site complementary to maltose / substrate / maltose fits into active site / active site and substrate fit like a lock and key;
- Description of induced fit;
- Enzyme is a catalyst / lowers activation energy / energy required for reaction;
- By forming enzyme-substrate complex;
Scientists have investigated the effects of competitive and non-competitive
inhibitors of the enzyme maltase.
Describe competitive and non-competitive inhibition of an enzyme. (5)
- 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;
7. Cannot be overcome by adding more substrate;
(i) Give two ways in which the structure of starch is similar to cellulose.
- Are polymers / polysaccharides / are made of monomers / of monosaccharides;
- Contain glucose / carbon, hydrogen and oxygen;
- Contain glycosidic bonds;
- Have 1−4 links;
Neutral: references to ‘unbranched’, insoluble, formed by
condensation, flexible and rigid
Are made of the monomer glucose = MP 1 and 2 = 2 marks - Hydrogen bonding (within structure).
Give two ways in which the structure of starch is different from cellulose.
- Contains α / alpha glucose;
- Helical / coiled / compact / branched / not straight;
- 1,6 bonds / 1,6 branching;
- Glucoses / monomers same way up;
- No H-bonds between molecules;
- No (micro / macro) fibres / fibrils.
(3)
- (Lactase / beads) can be reused / not washed away;
- Accept lactase / beads not wasted
- Less lactase used is insufficient
- No need to remove from milk;
- Accept lactase not present in milk.
- Allows continuous process;
- The enzyme is more stable;
- Avoid end-product inhibition.
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. (2)
- (Lactose hydrolysed to) galactose and glucose;
- (So) more sugar molecules;
- Idea of more sugars essential
- (So) more / different receptors stimulated / sugars produced are sweeter
(than lactose).
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 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. (2)
(ii) Using the diagram, suggest and explain one other way in which companion
cells are adapted for the transport of sugars between cells. (2)
(i) 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.
(ii) 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
OR:
3. Ribosomes / rough endoplasmic reticulum produce(s)
proteins;
Concept of making proteins needed
4. (Proteins) linked to transport e.g. carrier proteins / enzymes.
Raffinose is a trisaccharide of three monosaccharides: galactose, glucose
and fructose. The chemical formulae of these monosaccharides are:
* galactose = C6H12O6
* glucose = C6H12O6
* fructose = C6H12O6
Give the number of carbon atoms, hydrogen atoms and oxygen atoms in a
molecule of raffinose.
C = 18, H = 32, O = 16;
(2)
(b) 1. Filter and dry (the precipitate);
2. Find mass/weight;
- A = glucose and B = maltose;
- Because more sugar/precipitate after hydrolysis/maltase action;
Use of a colorimeter in this investigation would improve the repeatability of
the student’s results.
Give one reason why.
- Quantitative
OR
(Colour change is) subjective;
Accept: accurate/precise - Standardises (the) method;
Name the monomers from which a maltose molecule is made.
Glucose (and glucose);
Name the type of chemical bond that joins the two monomers to form
maltose.
(α1,4) Glycosidic;
A student wanted to produce a dilution series of a maltose solution so he could
plot a calibration curve. He had a stock solution of maltose of concentration 0.6
mol dm−3 and distilled water. He made a series of dilutions from 0.1 to 0.6 mol
dm−3.
(c) Complete the table below by giving all headings, units and the
concentration of the maltose solution produced.
- Headings correct – mol dm–3 and volume of water / cm3;
- Concentration correct. ie 0.2;
The student performed the Benedict’s test on six maltose solutions ranging from
0.1 mol dm−3 to 0.6 mol dm−3. He placed a sample of each solution in a
colorimeter and recorded the light absorbance.
His results are shown in the graph below. (2)
Line of best fit drawn;
Read off value at 0.45.
In mammals, in the early stages of pregnancy, a developing embryo exchanges
substances with its mother via cells in the lining of the uterus. At this stage, there
is a high concentration of glycogen in cells lining the uterus.
(a) Describe the structure of glycogen. (2)
- Polysaccharide of α-glucose;
OR
polymer of α-glucose;
2. (Joined by) glycosidic bonds
OR
Branched structure;
During early pregnancy, the glycogen in the cells lining the uterus is an
important energy source for the embryo.
Suggest how glycogen acts as a source of energy.
Do not include transport across membranes in your answer. (2)
- Hydrolysed (to glucose);
- Glucose used in respiration;
- Ignore ‘Broken down’
- ‘Energy produced’ disqualifies mp2
In Test 1, the student used a measuring cylinder to measure 15 cm3 of solution
from a beaker. The measuring cylinder gives a volume with an uncertainty of ±1
cm3. She used a graduated syringe to measure 5.0 cm3 of Benedict’s solution.
The graduated syringe gives a volume with an uncertainty of ± 0.5 cm3. She
mixed these volumes of liquid to do the biochemical test.
(e) Calculate the percentage error for the measurements used to obtain a 20
cm3 mixture of the solution from the beaker and Benedict’s solution. Show
your working.
Lactulose is a disaccharide formed from one molecule of galactose and
one molecule of fructose.
Other than both being disaccharides, give one similarity and one difference
between the structures of lactulose and lactose.
Similarity
1. Both contain galactose / a glycosidic bond;
Ignore references to hydrolysis and / or
condensation
Difference
2. Lactulose contains fructose, whereas lactose contains glucose;
Glycogen and cellulose are both carbohydrates.
Describe two differences between the structure of a cellulose molecule
and a glycogen molecule.
- Cellulose is made up of β-glucose (monomers) and glycogen is
made up of α-glucose (monomers);
2. Cellulose molecule has straight chain and glycogen is
branched;
3. Cellulose molecule has straight chain and glycogen is coiled;
4. glycogen has 1,4- and 1,6- glycosidic bonds and cellulose has
only 1,4- glycosidic bonds;
Starch is a carbohydrate often stored in plant cells.
Describe and explain two features of starch that make it a good storage
molecule. (2)
- Insoluble (in water), so doesn’t affect water potential;
- Branched / coiled / (α-)helix, so makes molecule compact;
OR
Branched / coiled / (α-)helix so can fit many (molecules) in
small area; - Polymer of (α-)glucose so provides glucose for respiration;
- Branched / more ends for fast breakdown / enzyme action;
- Large (molecule), so can’t cross the cell membrane
