AQA Unit 1.6 (ATP), 1.7 (Water), 1.8 (Inorganic ions)

Question 1

ATP is a nucleotide derivative. Name the components of ATP.

Answer 1

1. Adenine nucleotide base
2. Ribose sugar
3. Three phosphate groups

Question 2

What is the name of the reaction in which ATP is synthesised from ADP and inorganic phosphate?

Answer 2

Condensation

Question 3

What is the name of the reaction when ATP is broken down with water to release energy?

Answer 3

Hydrolysis

Question 4

What is the name of the enzyme that catalyses the formation of ATP from ADP and inorganic phosphate?

Answer 4

ATP synthase

Question 5

What is the name of the enzyme the catalyses the hydrolysis of ATP?

Answer 5

ATP hydrolase

Question 6

The hydrolysis of ATP produces ADP and inorganic phosphate.

1. How does the cell use the inorganic phosphate released in this reaction?
2. What effect does this have?

Answer 6

1. Used to phosphorylate other compounds e.g. enzymes, receptors.
2. Phosphorylation usually makes a compound more reactive.

Question 7

Why can a cell not use glucose directly as the source of energy? (3 marks)

Answer 7

1. The break-down of glucose is a long and complex process, energy cannot be released quickly.
2. Glucose break down occurs in the mitochondria, which can be far away from where energy is needed.
3. Gucose releases very large amounts of energy, which is too much for most reactions.

Question 8

Explain why ATP is useful as a direct source of energy for the cell? (3 marks)

Answer 8

1. ATP can be easily broken down by hydrolysis to relase energy quickly.
2. It can diffuse out to different parts of the cell where hydrolysis of ATP can be coupled to energy-requiring reactions.
3. ATP contains small amounts of energy that is more manageable for the cell.

Question 9

ATP can be re-synthesised by the condensation of ADP and inorganic phosphate.

Name the 2 processes in which this can happen?

Answer 9

1. Respiration
2. Photosynthesis

Question 10

Name 4 biological processes which require ATP

Answer 10

1. Movement - e.g. muscle contraction
2. Active transport
3. Secretion
4. Metabolic processes - building macromolecules

Question 11

Why can ATP not be used for long-term storage of energy?

Answer 11

The phosphate bond in ATP is unstable and breaks down easily. It must be used quickly.

Question 12

Give examples of how water is involved in metabolic reactions (3 marks)

Answer 12

1. Water is released in condensation reactions when a bond is formed between 2 molecules e.g. carbohydrate, amino acid, ATP synthesis.
2. Water is in hydrolysis reactions to break bonds between molecules e.g. hydrolysis of ATP, peptide bonds.
3. Water is a raw material used in photosynthesis.

Question 13

Water is a polar molecule. Explain how this property makes water a good solvent for charged and partially charged (polar) molecules. (3 marks).

Answer 13

1. Negatively charged (or partially negatively charged) molecules are attracted to the partial positive charge on the hydrogen atom in water.
2. Positively charged (or partially positively charged) molecules are attracted to the partial negative charge of the oxygen atom in water.
3. As water surrounds the molecules, they dissolve.

Question 14

Explain how the properties of water allow it to provide a cooling effect for living organisms.

(2 marks)

Answer 14

1. Water has a high latent heat of vaporisation/ a lot of energy is required to break the hydrogen bonds in water for it to evaporate.
2. This allows animals to lose excess body heat through the evaporation of water from sweating or bathing.

Question 15

Explain why water is a good temperature buffer.

(2 marks)

Answer 15

1. Water has a high specific heat capacity (amount of energy required to raise the temperature of water).
2. This means it takes a lot of energy to raise the temperature of water.

Question 16

Why does water have a high specific heat capacity?

Answer 16

The hydrogen bonds in water can absorb a lot of energy.

Question 17

High specific heat capacity Vs High latent heat of vaporiasation

Answer 17

1. High specific heat capacity - amount of energy required to raise the temperature of a set mass of water by 1 degrees Celcius. Ability of hydrogen bonds to absorb heat energy.
2. High latent heat of vaporisation - amount of energy required to break the hydrogen bonds between water molecules so that it will evaporate (liquid to gas).

Question 18

How does the high specific heat capacity of water benefit living organisms? (2 marks)

Answer 18

1. Aquatic organisms wont need to worry about sudden changes in temperature.
2. Water inside organisms helps to maintain a stable internal temperature.

Question 19

With relation to water molecules, what is cohesion?

Answer 19

The tendency of water molecules to stick to each other.

Question 20

What is surface tension?

Answer 20

The ability of a liquid to resist a force trying to break through it’s surface. It is a result of the cohesive forces between water molecules at the air-water interface.

Question 21

What makes water molecules cohesive?

Answer 21

The hydrogen bonds between water molecules gives water it’s cohesive property.

Question 22

Give 3 examples of how cohesion and high surface tension of water are useful for living organisms?

Answer 22

1. Allows water to be pulled up the xylem vessels and allows plants to absorb water from the soil.
2. Allows organisms to float on the surface of water.
3. Allows insects and other organisms to to carry droplets of water.

Question 23

Where can inorganic ions be found in living organisms? (2 marks)

Answer 23

1. Cytoplasm
2. Body fluids

Question 24

What is an inorganic ion?

(2 marks)

Answer 24

A charged atom or molecule, that does not contain carbon (specifically carbon bonded to hydrogen)

Question 25

What is the main function of Iron ions in the body?

Answer 25

Iron ions (Fe2+) are necessary for the function of haemoglobin in red blood cells.

The iron ion is responsible for binding oxygen.

Question 26

Explain how sodium ions facilitate the transport of glucose and amino acids in the intestines.

Answer 26

Glucose and amino acids are transported into cells alongside sodium ion (Na+) via co-transporters.

Note: Other roles of sodium ions will be covere in year 2: action potential in neurons, water absorption in the kidneys.

Question 27

What is the main function of hydrogen ions (H+) in the body? Give 3 specific examples of the role of hydrogen ions.

Answer 27

Maintaing pH

1. Maintains correct pH for enzymes
2. Maintains the pH of blood at 7.4
3. Maintains a low pH in gastric juices

Note: Other roles of hydrogen ions will be covered in year 2: role in respiration and electron transport chain.

Question 28

What are the main roles of phosphate ions?

(2 marks)

Answer 28

1. Inorganic phosphate is combined with ADP to form ATP. Energy is stored in the phosphate bond.
2. Phosphate groups in RNA and DNA allow nucleotide units to join up to form polynucleotides.