Exam code: 7401
ATP is an important source of energy for cellular reactions.
Outline how energy is released from ATP to fuel cellular processes.
State the biochemical pathway in which ATP is produced from the oxidation of substrates.
List two processes within cells that utilise the energy released from the hydrolysis of ATP.
ATP is described as a phosphorylated nucleotide. Name another common molecule in cells that fits this description.
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List the molecules ADP, AMP and ATP in increasing order of the number of phosphate groups that they possess.
Aerobic respiration of one molecule of glucose generates roughly 38 separate molecules of ATP. Suggest one cellular advantage of releasing energy in small packages of ATP, rather than one single, large energy release.
Explain the process by which ATP can be recycled in the cell.
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State the type of bonding that forms between hydrogen and oxygen atoms within a molecule of water.
State the property of the bonds between hydrogen and oxygen within a water molecule that gives water many of the properties that make it an ideal medium for life.
Four adjacent liquid water molecules are shown in Figure 1.
Figure 1
Identify the kind of bond labelled X in Figure 1.
Explain how the distribution of charge shown in Figure 1 gives water the ability to fulfil its role as a universal solvent.
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Water is recognised as having a high specific heat capacity. Explain how this allows aquatic habitats to maintain stable conditions.
Identify the property of water that allows it to form long, unbroken columns of water as it rises up xylem vessels in plants as they transpire.
Inorganic ions play a vital role in biology. List three important inorganic ions that form part of biological systems.
Table 1 shows the roles of selected inorganic ions in biological systems.
Table 1
Inorganic ion | Animal / Plant systems | Biological role(s) |
Iron / Fe2+ | Animal | Haemoglobin |
| Animal | Co-transport of glucose in the small intestine |
| Plant | Constituent of chlorophyll |
Phosphate / PO43- | Animal / plant | Important constituent of nucleotides |
Use your knowledge of mineral ions in biology to complete the empty boxes in Table 1.
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Name the inorganic ion that forms part of the important proteins, haemoglobin and cytochrome c.
Identify two types of biological molecules in which phosphorus (phosphate) plays a role.
State a way in which calcium ions (Ca2+) are used in biological systems.
Table 1 shows the concentrations of typical mineral ions in a sample of a person's blood plasma.
Table 1
Mineral ion | Concentration in plasma / mmol dm-3 |
Na+ | 142.0 |
K+ | 5.0 |
Mg2+ | 1.5 |
Calculate how many times more sodium ions there are compared to potassium ions in the blood.
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Water plays a very important role within the cytoplasm of cells. State two properties of water that make it an important part of the cytoplasm of cells. For each property, explain why this makes water important for the cytoplasm.
Give two similarities between the processes by which inorganic ions and water molecules enter cells.
The relatively high specific heat capacity of water is of great biological significance to organisms. Give one example of how this property is biologically important.
With reference to bonding, explain how the relatively high specific heat capacity of water enables it to buffer temperature changes.
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Name two products created when ATP is hydrolysed by water.
Name the enzyme that catalyses the reaction between ATP and water.
Cells hydrolyse ATP to provide energy for other reactions or to add phosphate to other substances, making them more reactive. However, ATP needs to be resynthesised.
Describe how this occurs.
Identify the structures labelled X, Y and Z that make up ATP in Figure 1.
Figure 1
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Sodium ions are of great biological significance in living organisms. State the chemical formula for this ion and give one example of its biological importance.
Name two other inorganic ions and for each one, give an example of their biological importance in a cell.
Cubes of potato were placed in a solution containing sodium ions. The concentration of oxygen in air bubbled through the solution was changed and the rates of respiration and uptake of sodium ions were measured. The results are shown in Table 1.
Table 1
Concentration of oxygen / % | Rate of respiration / arbitrary units | Rate of uptake of sodium ions / arbitrary units |
3.8 | 43 | 54 |
15.6 | 56 | 76 |
24.7 | 62 | 87 |
32.9 | 89 | 90 |
Describe the link between oxygen concentration, rate of respiration and rate of uptake of sodium ions.
Explain the link between oxygen concentration, rate of respiration and rate of uptake of sodium ions shown by the results in Table 1.
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Give two properties of ATP that make it advantageous as an energy-storage molecule within a cell and two properties of ATP that make it advantageous as a source of energy for biological processes.
State the equation to show how adenosine triphosphate is synthesised from adenosine diphosphate.
Humans continuously synthesise ATP. Explain why we need to do this
If ATP solution is added to a strip of muscle tissue, the strip of muscle tissue shortens in length. Table 1 shows the results of a study in which increasing concentrations of ATP solution were added to strips of muscle of the same starting length. The strips of muscle were left for 10 minutes before the final length was recorded
Table 1
Concentration of ATP solution added to muscle tissue / arbitrary units | Final length of muscle tissue / mm |
10 | 51 |
20 | 42 |
30 | 37 |
40 | 33 |
50 | 26 |
Explain the results shown by the data in Table 1.
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Identify the properties (A, B, C) that explain the ability of water to dissolve solutes.
Property A: Polarity of water molecules
Property B: High specific heat capacity of water
Property C: Hydrogen bonding
Describe the properties of water that make it a useful component of blood.
A group of students wanted to investigate the thermal properties of water. To do this,they poured hot water into two thin plastic cups and measured the rate of cooling of each cup. The sides of one cup were covered with tissue paper soaked in hot water. The sides of the other cup were left uncovered. The temperature of the water in each cup was recorded with a thermometer every 2 minutes for 10 minutes. The result are shown in the graph in Figure 1 below.
Figure 1
Other than the starting temperature of the water, give two conditions that must be kept the same for each cup throughout the experiment.
With reference to the thermal properties of water, explain how the experiment in part c) can demonstrate how humans respond to overheating.
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Sucrose is formed from a molecule of glucose bonded to a molecule of fructose. Explain the role played by water in the synthesis and digestion of sucrose.
Water is described as a polar molecule. Define the term ‘polar’ and describe how this property manifests itself in the structure of a water molecule.
Astronomers looking for evidence of life on other planets and moons often look for signs of water existing or having existed on those bodies. Use your knowledge of the properties of water to explain why.
Figure 1 shows the structures of water (H2O) and hydrogen sulfide (H2S). Oxygen and sulfur are both members of Group 6 of the Periodic Table. Those elements, and their compounds, have some analogous properties.
Figure 1
Despite the structural similarities shown in Figure 1, there are several significant differences between the properties of the two molecules, as set out in Table 1.
Table 1
H2O | H2S |
Boiling point 100°C | Boiling point -60°C |
Non-toxic - necessary for life | Highly toxic |
High electronegativity | Low electronegativity |
Requires channel proteins to pass through cell membranes | Can easily diffuse through cell membranes |
Use your knowledge of the structure of water to explain the large differences in boiling points between water and hydrogen sulfide.
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The total volume of water on Earth is estimated to be 1.4 x 1021 dm3
The number of molecules in one mole of a substance (Avogadro’s number) is 6.02 x1023;
A teaspoon measures 5 cm3 of liquid;
The atomic mass of hydrogen is 1; the atomic mass of oxygen is 16;
1 cm3 of water has a mass of 1.0 g
Calculate whether the number of water molecules in one teaspoon of water is greater than or less than the number of teaspoonfuls of water on Earth. Show your calculations to back up your claim.
Identify the components that condense together to form ATP
A researcher carried out an experiment to examine the effect of substrate concentration on the activity of ATP hydrolase, which catalyses the hydrolysis of ATP. He dropped ATP solutions of varying concentrations onto fresh muscle tissue cut into narrow strips of 63 mm length. He measured the length of each strip of muscle tissue after 3 minutes. His results are shown in Figure 1
Figure 1
Suggest why the strips of muscle in zero concentration ATP solution grew in length (by 2 mm), rather than contracted. Ignore sources of measurement error.
Hydrolysis of a solution of ATP of concentration 0.1 mol dm-3 releases 3,050 J of energy per dm3. 58% of the energy released from the hydrolysis of ATP is released as heat; the remainder is used for muscle contraction. The researcher used 50 μl of ATP solution of concentration 8 x 10-6 mol dm-3 for one of the experiments of his investigation.
Calculate the energy transferred to the muscle tissue in this experiment.
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Water has one of the highest known latent heat of vaporisation values of any substance. Define this term and explain how water’s high value benefits organisms.
Aquatic habitats such as seas, oceans and large lakes often experience greater temperature stability than terrestrial ones. Use your knowledge of the properties of water to explain this phenomenon.
Describe and explain the structural feature of water that gives it the two properties outlined in part (a) and (b).
Most substances are denser as solids than in their liquid states. Use your knowledge of the structure of water to explain why water does not obey this rule. Explain the advantages to aquatic life that this provides.
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Outline the differences between adenine and adenosine.
The level of ATP in cells can be used as a marker for the viability of tissue. ATP can be assayed using an enzyme-controlled reaction that generates light in proportion to the concentration of ATP present in that tissue.
Suggest why the level of ATP is a measure of cell viability.
Research has shown that the ratio of daily ATP usage in the human body to body mass is approximately 1:1. Considering that at any one moment, a human body will contain a total of approximately 100 g of ATP, explain the very large mass of ATP being consumed.
Glucose has an energy content of 917 kJ mol-1. In aerobic respiration, each glucose yields ATP, which has an energy content of 30.5 kJ mol-1, when hydrolysed to ADP and inorganic phosphate.
Explain why the respiration of glucose transfers small amounts of energy into each ATP molecule.
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Inorganic ions play a vital role in many biological processes. Define the term, ‘inorganic ion’.
The pH inside a cell is a function of the hydrogen ion concentration [H+]. Describe the nature of this relationship and outline the consequences of a change in pH inside a cell.
Figure 1 shows a porphyrin ring structure found in certain biological molecules. This structure can have an inorganic ion at its centre, which gives the molecule its unique function.
Figure 1
Identify two inorganic ions that can associate with this kind of structure, and in each case, name the molecule and describe its function.
Describe the role of an inorganic ion required for the absorption of important food molecules in the small intestine. Name the substances concerned.
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