7.2 Energy for Action

Question 1

Basal metabolic rate, BMR

Answer 1

The metabolic rate
of a person who is completely at rest but not
asleep. It is a measure of the energy required for
activities that go on all the time. Examples are
the beating of the heart, breathing, and the active
transport of substances into and out of cells.
Basal metabolic rate is usually measured in
kJ/m–2/h–1 or kJ/g/h. This takes into account the size of the
person and the time, making it easier to compare
figures.

Question 2

Respiration, Respire

Answer 2

The process by which cells
break down molecules such as carbohydrates to
transfer energy for use in the cell. This energy is
used to make ATP. The process is inefficient, so some energy is released and raises the
temperature of the cell. Glucose is only one of a number of substances that can be used for respiration. When oxygen is present aerobic respiration takes place. Respiration can also take
place in the absence of oxygen (anaerobic
respiration).

Question 3

Glycolysis

Answer 3

Part of the biochemical pathway of
respiration in which a six-carbon molecule of
glucose is broken down to produce two threecarbon
pyruvate groups. This reaction produces
a net gain of two molecules of ATP. Glycolysis
takes place in the cytoplasm of the cell and is
common to both aerobic and anaerobic
respiration.
yield a net gain of 2 ATP, 2 pairs of H atoms (2 red NAD), 2 molecules of pyruvate

Question 4

Pyruvate

Answer 4

A three-carbon compound formed from
glucose in glycolysis. In aerobic respiration
pyruvate enters the link reaction where it is
converted to acetyl coenzyme A. In anaerobic respiration it is converted either to lactate in animals or to ethanol and carbon dioxide in plants and microorganisms such as yeast.

Question 5

Coenzyme

Answer 5

An organic substance which plays an
essential part in an enzyme-catalysed reaction.
Examples of coenzymes are coenzyme A which
combines with pyruvate to produce acetyl
coenzyme A in the link reaction of respiration,
NAD and FAD, which are reduced in
respiration, and NADP, which is reduced in the
light-dependent reaction in photosynthesis.

Question 6

NAD, Nicotinamide adenine dinucleotide,Reduced NAD

Answer 6

A coenzyme that plays an
important part in respiration. Respiration is a
series of reactions in which glucose is oxidised
step by step. Hydrogens are transferred to NAD
which is reduced as a result. The reduced NAD
then transfers the hydrogens to the electron
transport chain.

Question 7

Substrate-level phosphorylation

Answer 7

The formation
of ATP as part of the respiratory pathway. For
example, when glucose is converted to pyruvate
in glycolysis there is phosphorylation of ADP
to form ATP. Unlike oxidative phosphorylation,
ATP synthesis is associated with the electron
transport chain.

Question 8

Link reaction

Answer 8

Part of the pathway of aerobic
respiration in which pyruvate is converted to
acetyl coenzyme A and a molecule of carbon
dioxide is released. The reaction links the
reactions of glycolysis with those of the Krebs
cycle. Acetyl coenzyme A essentially carries a
two-carbon fragment into the Krebs cycle.

Question 9

Decarboxylated

Answer 9

Decarboxylation reactions
break off carbon dioxide, e.g.
pyruvate > acetyl CoA + CO2.

Question 10

Dehydrogenated

Answer 10

A molecule that has lost

hydrogen in a chemical reaction.

Question 11

Acetyl coenzyme A, Acetyl CoA

Answer 11

An
intermediate product formed during respiration.
Acetyl coenzyme A is produced by the link
reaction when coenzyme A combines with a
two-carbon fragment formed from pyruvate.
Acetyl coenzyme A carries this fragment into
the Krebs cycle.

Question 12

Krebs cycle

Answer 12

A cycle of reactions which forms
part of the biochemical pathway of aerobic
respiration. Acetyl coenzyme A, produced in
the link reaction, carries a two-carbon fragment
into the Krebs cycle. Here it combines with a
four-carbon compound to form a six-carbon
compound. The six-carbon compound is then
broken down through a series of intermediate compounds to produce the four-carbon
compound again. During this process, ATP and reduced coenzymes are produced.

2 CO2 produced, 1 ATP (substrate level phosphorylation), 4 pairs of H atoms ( 3 NAd 1 FAD)

Question 13

FAD, Flavine adenine dinucleotide

Answer 13

A
coenzyme which takes up hydrogen released
during respiration. It therefore acts as a
hydrogen acceptor. In the Krebs cycle, FAD
accepts hydrogen and is reduced as a result.
Reduced FAD then transfers the electrons from
these hydrogens to molecules in the electron
transfer chain. Energy is released in this
process and used to make ATP.

Question 14

Electron transport chain

Answer 14

A series of electron
carrier molecules along which electrons are
passed in a series of oxidation and reduction
reactions, releasing energy in the process. This
energy is used to produce ATP. Electron
transport chains are important in both
photosynthesis and respiration.

Question 15

Chemiosmotic theory

Answer 15

A theory that explains
how ATP is synthesised in the electron transport chain. In simple terms, energy released as
electrons passing down the electron transport chain is used to pump protons across the inner
membrane of the mitochondrion into the intermembrane
space. The protons diffuse back
through protein channels and ATP is
synthesised.

Question 16

Electrochemical gradient

Answer 16

An electrochemical
gradient occurs when an imbalance in the
distribution of ions, for example sodium ions
either side of a membrane, results in an electrical
difference, typically measured in volts.

Question 17

ATP synthase

Answer 17

An enzyme that catalyses the
synthesis of ATP from ADP and phosphate.
ATP synthase is found embedded in the inner
mitochondrial membrane where it is involved in
ATP synthesis as a result of the movement of
hydrogen ions across the membrane.

Question 18

Oxidative phosphorylation

Answer 18

A method of
synthesising ATP from ADP in mitochondria
in which oxygen acts as the final carrier in the
electron transport chain.

Question 19

Lactate, Lactic acid

Answer 19

In humans and other
animals, the end product of anaerobic
respiration is lactate. Respiration makes energy
available to the cells of the body. If there is
insufficient oxygen present, cells respire
anaerobically. The pyruvate formed at the end
of glycolysis is reduced to lactate. Lactate forms
lactic acid in solution. The build-up of lactic
acid is one of the factors which contributes to
muscle fatigue during exercise. Lactic acid is
produced when heart muscle respires
anaerobically and causes angina.

Question 20

Oxygen debt

Answer 20

The increase in oxygen
consumption which follows the completion of a
period of strenuous exercise. Strenuous exercise
leads to anaerobic respiration. The waste
product of anaerobic respiration is lactate so this
accumulates during strenuous exercise. It can be
converted back to pyruvate or converted
directly to carbon dioxide and water but this
needs oxygen, hence the increase in oxygen
consumption immediately after a period of
strenuous exercise.

Question 21

Creatine, Creatine phosphate

Answer 21

A substance
derived from amino acids. It is naturally found
in meat and fish, and is made in the body from
the amino acids glycine and arginine. Creatine
phosphate in cells provides phosphate for the
immediate regeneration of ATP. The creatine
phosphate breaks down as soon as exercise starts
to form creatine and phosphate. Taking creatine
supplements has been reported to increase
creatine phosphate levels in the muscles.
Creatine phosphate is taken by some athletes to
increase their performance in high-intensity
short-duration sports, and to increase muscle
mass.