ATP, Water & Inorganic Ions (AQA A Level Biology)

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.

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   

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

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.

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.

Write an 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

Explain the results shown by the data in Table 1.

Which properties (A, B, C) 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.

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

Use your knowledge of the structure of water to explain the large differences in boiling points between water and hydrogen sulfide. 

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. 

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.  

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, account for 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. 

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.