Lesson 4: Introduction to Cellular Respiration

Question 1

The Need for Energy

Answer 1

All organisms require energy and have evolved to take free energy from the
environment and convert it into usable forms

Autotrophs: create their own food (which will later be broken down into
usable energy).

Heterotrophs: must consume autotrophs or other heterotrophs in order to
gain energy.

Question 2

Autotrophs

Answer 2

Photoautotrophs:

Organisms that through
photosynthesis convert light
energy into chemical potential
energy in the form of glucose.

Ex: green plants
Chemoautotrophs:

Microorganisms that extract
energy from inorganic compounds
containing elements such as sulfur
and iron.

Usually found in extreme
environments such as volcanoes
and sulfur springs

Ex: archaebacteria

Question 3

Heterotrophs

Answer 3

Includes the majority of organisms (including all animals and
fungi, many protists and bacteria)

All organisms except chemoautotrophs use glucose (C6H12O6) as
their primary source of energy.

Question 4

Cellular Respiration

Answer 4

The process of extracting energy from organic,
nutrient molecules such as glucose and
converting it into a usable form (ATP) so the
cell can use it for energy-requiring activities.

Overall equation:

C6H12O6 + 6O2 6 CO2 + 6 H2O + 36
ATP

oxidized
reduced

Question 5

Adenosine triphosphate
(ATP)

Answer 5

Many cellular activities require ATP

The synthesis of molecules (such
as DNA, RNA, proteins)

Transports of molecules via active
transport (i.e. protein pumps such
as the Na+/K+ pump)

Movement of materials within the
cell

Muscle contractions

Question 6

ATP is Recycled

Answer 6

ATP is continuously produced and consumed

ATP ADP + Pi + Energy

It is broken down to release energy

ADP and a free phosphate are reconverted into ATP by cellular respiration.

Phosphorylation is attaching a phosphate group to a molecule to make the
molecule more unstable and therefore more reactive

Question 7

Three Goals of Cellular Respiration

Answer 7

Break the bonds between 6 carbon atoms (C6H12O6 ) to make 6 CO2
(convert organic carbon to inorganic carbon)

Move H atom electrons from C6H12O6 to O2 to make 6 H2O

Trap as much free energy as possible in ATP

Question 8

Cellular Respiration

Answer 8

In cellular respiration, several enzymes are used to
control the breakdown of glucose and to maximize
the amount of energy produced and retained in a
usable form.

Cellular respiration is a series of redox reactions.

Reduction – when a compound gains an
electron

Oxidation – when a compound loses an
electron.

During redox reactions, electrons are passed from
molecule to molecule in a sequence (moves to more
electronegative compounds).

This movement of electrons is a form of energy
(electrochemical energy) and it can be converted
into other forms.

Question 9

Aerobic Cellular Respiration

Answer 9

Cellular Respiration can be anaerobic or aerobic.

The human body uses both, however, aerobic is preferred due to greater
efficiency.

Aerobic Respiration occurs via 2 different energy transfer mechanisms

1. Substrate-Level Phosphorylation
2. Oxidative Phosphorylation

Question 10

Substrate Level
Phosphorylation

Answer 10

ATP is produced directly in an enzyme catalyzed
reaction.

The enzyme transfers a phosphate group from a
substrate molecule to ADP to make ATP.

Question 11

Oxidative Phosphorylation

Answer 11

ATP is formed indirectly.

It is more complex that substrate-level phosphorylation and makes much
more ATP.

ATP is formed via a series of redox reactions where O2 is the final electron
acceptor.

The energy released during the redox reactions is used to generate ATP by
phosphorylating ADP.

Question 12

Electron Carriers

Answer 12

Cellular Respiration relies on electron carrier molecules, also known as
co-enzymes

These are molecules can accept and give up electrons (so they a reduced and
oxidised)

In doing so, they remove electrons from glucose and move them to other
areas of the cell and to other more electronegative molecules.

The 2 important co-enzymes in cellular respiration are:

1. Nicotinamide adenine dinucleotide (NAD)
2. Flavin adenine dinucleotide (FAD)

Question 13

Reduction of NAD and FAD

Answer 13

NAD is reduced by accepting 2 atoms of hydrogen.

A hydrogen is made of 1 proton and 1 electron, therefore a hydrogen ion
(H+), is really just a proton

NAD+ + 2H + + 2é 🡪 NADH + H +

FAD is also reduced by the addition of 2 hydrogen atoms

FAD + 2H + + 2é 🡪 FADH2

The reduced co-enzymes NADH and FADH2 carry a lot of energy in those
gained electrons.

Most of that energy will be used to make ATP

Question 14

Four Stages Cellular Respiration

Answer 14

The stages of cellular respiration occur in each cell in both the cytoplasm and
the mitochondria.

Glycolysis – in cytoplasm

2) Pyruvate oxidation – in mitochondrial matrix

3) Krebs Cycle – in mitochondrial matrix

4) Electron Transport Chain (ETC) and Chemiosmosis – inner mitochondrial
membrane