Topic questions Biological molecules Carbohydrates
10 questions · 79 marks · about 2 hours
The image below shows representations of the structures of four polysaccharides.
Use the image to answer questions 10 and 11.
Which of the molecules contains the highest proportion of 1-6 glycosidic bonds?
A Amylopectin
B Amylose
C Cellulose
D Glycogen
The image below shows representations of the structures of four polysaccharides.
Use the image to answer questions 10 and 11.
Which of the molecules is not used for energy storage?
A Amylopectin
B Amylose
C Cellulose
D Glycogen
The element nitrogen is recycled within ecosystems.
Complete the sentences using the most appropriate terms.
When animals die microorganisms convert nitrogen-containing molecules in the animals’
bodies to ammonia in a process known as........ This ammonia is
converted into nitrites and nitrates by........ bacteria. The bacterium
........ converts ammonia to nitrites and the bacterium........
converts nitrites to nitrates. Nitrates can be absorbed by plants and converted to
........ Nitrogen gas is very unreactive but it can enter the nitrogen cycle by
being converted to ammonia by........ bacteria such as Rhizobium.
Use your knowledge of the nitrogen cycle to suggest and explain why plants do not grow well in soil with a low oxygen content.
Rhizobium forms nodules on the roots of certain plants. The Rhizobium receives a supply of glucose from the plant which the bacterium is able to use.
The diagram below shows an incomplete diagram of the structure of alpha glucose.
Write on the diagram to show the complete structure of alpha glucose.
Explain how the structure of glucose allows it to move from the plant to the bacterium.
Cellulose is the main component of plant cell walls.
Which option is not a property of cellulose?
A High tensile strength
B Inflexible
C Insoluble in water
D Resistant to digestion by enzymes
Your answer
Glycogen is a large polysaccharide.
Which option describes the structure and function of glycogen?
A 1–6 glycosidic bonds are more accessible to enzymes than 1–4 glycosidic bonds so energy can be released more quickly.
B Bonds between 
-glucose residues are easily broken by enzymes.
C Exposed OH groups mean glycogen is soluble.
D Short branches allow more energy storage in a small space.
Your answer
Also involves Culturing microorganisms
A student investigated the effect of different sugars on the respiration rate in yeast using the following procedure.
• Prepare a stock solution of yeast containing 10 g of dried yeast in 250 cm3 of pH5 buffer.
• Prepare solutions of each sugar containing 5 g of sugar in 250 cm3 of distilled water.
• Keep the yeast and sugar solutions in a water bath at 35 ºC until required.
• Set up the apparatus with a 250 cm3 conical flask connected by a rubber tube to a 100 cm3 gas syringe.
• Add 25 cm3 of yeast solution and 25 cm3 of sugar solution to the flask, immediately connect the flask to the gas syringe and start the clock.
• Record the volume of gas produced after 30 s and then every 30 s for 7 min.
• Repeat the experiment 5 times for each different sugar.
• Prepare a fresh yeast solution for each set of sugars.
Describe two precautions the student should take between each experiment to ensure repeatable results.
The student’s procedure did not include a negative control.
Describe one negative control that the student could have used.
The student calculated mean values for each sugar and plotted the results on a graph.
The graph is shown below.
Describe how the student could use the graph to calculate the rate of respiration for each type of sugar.
* The student concluded the following from the graph:
• The rates of respiration with glucose, maltose and sucrose were very similar.
• The yeast could not hydrolyse disaccharides.
Evaluate the student’s conclusions.
Additional answer space if required.
The student wanted to study the effect of the different sugars on the rate of growth of a yeast population.
They used a colorimeter to measure the absorbance of a culture of yeast cells.
The absorbance of the yeast culture is proportional to the concentration of yeast cells.
As the yeast multiplied, it was necessary to dilute the sample to obtain a reading on the colorimeter.
Describe how the student could use 1 cm3 pipettes and 10 cm3 measuring cylinders to (i) dilute the sample so that it was 10 000 times less concentrated.
A light microscope can be used to observe yeast cells.
State the equipment that would be needed, in addition to a microscope, to measure the average diameter of yeast cells.
The student prepared a starter culture using 2.5 × 10−3 g yeast cells in 1 dm3 nutrient (iii) broth.
The average mass of a yeast cell is 2.0 × 10−11 g.
Calculate the number of cells in the starter culture.
Give your answer in standard form.
The population of this yeast doubles every 90 minutes when growing under ideal conditions.
A different starter culture was prepared containing 1 × 107 cells.
Use the axes below to sketch the growth curve you would expect for the yeast culture over the first 15 h.
* Plants lose water by transpiration.
The rate of transpiration varies between different species of plant.
The rate of transpiration can be measured using a potometer.
Plan an investigation into the rate of transpiration in two species of plant that would allow valid data to be collected.
Details of how to set up a potometer are not required.
Plant cell walls are made of cellulose. Cellulose is a polymer of 
-glucose.
Give three properties of cellulose that make it suitable as the basis of plant cell walls.
Cellulose cannot be digested by animals. Some mammals have bacteria in their stomachs that produce enzymes that can digest cellulose.
Explain whether the action of these enzymes is intracellular or extracellular.
Honeypot ants belong to several different genera. Some specialised individuals are used as food storage vessels. These individuals have swollen abdomens that store various foods, which can be given to members of the colony when required.
One such individual is shown in Fig. 19.1.
An investigation was carried out into the respiratory substrate of three different genera of honeypot ant, by measuring oxygen uptake and carbon dioxide production.
The data are shown in Table 19.1.
Use the data in Table 19.1 to suggest the likely diet of each genus of honeypot ant.
Justify your answer.
| Genus | Diet | Justification |
| Camponotus | mainly carbohydrate | ................................................. ................................................. |
| Melophorus | ................................................. ................................................. | ................................................. ................................................. |
| Cataglyphis | ................................................. ................................................. | ................................................. ................................................. |
Chitin is a polysaccharide found in insects. It is used to form the hard outer casing of their bodies.
Fig. 19.2 shows the chemical structure of chitin.
Using information from Fig. 19.2, state two similarities and two differences between the structures of chitin and glycogen.
* Insects use glucose to generate ATP.
Outline the processes involved in the generation of ATP through chemiosmosis.
Which of the statements, A to D, about amylopectin is correct?
A it contains 1-4 and 1-6 glycosidic bonds between 
-glucose monomers
B it is an unbranched chain of 
-glucose monomers
C it contains 
1-4 and 
1-6 glycosidic bonds
D it is made up of -glucose monomers and is uncoiled
Your answer
Also involves Respiratory substrates and RQ
Fig. 20 shows the disaccharide lactose, which is found in milk.
Another disaccharide is maltose. Maltose and lactose both contain the same number of atoms of each element, C, H and O.
State two other structural similarities between lactose and maltose.
Complete the table below to identify differences between the structures of lactose and maltose. The first one has been completed for you.
One of the monomers of lactose is galactose.
The bacterium E. coli usually uses glucose as a respiratory substrate.
Under certain circumstances, E. coli is able to use galactose as a respiratory substrate by breaking down lactose into glucose and galactose and then using both glucose and galactose as respiratory substrates.
Explain how the structure of galactose allows it to be used as a respiratory substrate.
E. coli usually grows in conditions where the extracellular concentration of lactose is low. In such conditions lactose does not easily cross the bacterial cell surface membrane.
Suggest and explain why lactose is unable to cross membranes.
In order for lactose to enter the cytoplasm of E. coli a protein is required.
The E. coli living in the digestive system of young mammals are more likely to contain this protein than E. coli living in the digestive system of old mammals.
Suggest an explanation for this observation.
Lactose is a reducing sugar.
Benedict’s reagent can be used to detect the presence of lactose in a solution.
A colorimeter can be used to measure the concentration of lactose.
The colorimeter first needs to be calibrated.
Describe how a method that uses Benedict’s reagent and a colorimeter could be calibrated to measure the concentration of lactose in an unknown sample.
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