5.7 - Respiration

Question 1

What is respiration?

Answer 1

The process that occurs in living. ells and releases the energy stored in organic molecules such as glucose.

Question 2

What happens to the energy that is released from respiration?

Answer 2

Energy is immediately used to synthesise molecules of ATP from ADP and inorganic phosphate (Pi).

Question 3

What happens to ATP in cells?

Answer 3

Can be hydrolysed to release energy needed to drive biological processes.

Question 4

Which organisms all respire to obtain energy?

Answer 4

Microorganims (both eukaryotic microbes e.g. yeast, & prokaryotes e.g. bacteria), plants, animals, fungi & protoctists.

Question 5

Why do living organisms need energy?

Answer 5

When energy is released from organic molecules, via respiration, it can be used to make ATP to drive biological processes e.g.
> active transport
> endocytosis
> exocytosis (inc. secretion of large molecules from cells)
> DNA replication
> cell division
> synthesis of large molecules e.g. proteins, e.g. collagen, enzymes & antibodies

> movement - e.g. movement of bacterial flagella, eukaryotic cilia & undulipodia, & motor proteins that walk along cytoskeleton threads in cells, moving organelles.

> activation of chemicals - glucose is phosphorylated at the beginning of respiration so that it becomes more reactive & able to be broken down to release more energy.

Question 6

What are anabolic reactions?

Answer 6

Metabolic reactions where large molecules are synthesised from smaller molecules.

Question 7

What are catabolic reactions?

Answer 7

Metabolic reactions involving the hydrolysis of large molecules to smaller ones.

Question 8

Why is it important that cells, ions and molecules have kinetic energy?

Answer 8

This allows them to move.

e.g. when molecules diffuse down a concentration gradient, moving from one place to another, they use their kinetic energy to do so.

Question 9

What does a molecule of ATP consist of?

Answer 9

> adenosine: the nitrogenous base adenine plus the five-carbon sugar ribose
&
three phosphate (phosphoryl) groups

Question 10

List the four stages in aerobic respiration.

Answer 10

1) glycolysis
2) the link reaction
3) the Krebs cycle
4) oxidative phosphorylation

Question 11

Where do the four stages take place?

Answer 11

Glycolysis takes place in the cytoplasm of cells.

The other three stages take place in the mitochondria.

Question 12

Glycolysis definition.

Answer 12

First stage of respiration; a 10-stage metabolic pathway that converts glucose to pyruvate
(we only need to know the pathway in outline - so 3 stages).

Question 13

What are the three main stages of glycolysis?

Answer 13

1) Phosphorylation of glucose to hexose bisphosphate
2) Splitting each hexose bisphosphate molecule into two triose phosphate molecules
3) Oxidation of triose phosphate to pyruvate

Question 14

Is glycolysis aerobic or anaerobic?

Answer 14

Glycolysis is the first stage of both aerobic and anaerobic respiration. Doesn’t need oxygen to take place.
∴ it’s an anaerobic process.

Question 15

List the products of glycolysis.

Answer 15

From each molecule of glucose, at the end of glycolysis there are:
> two molecules of reduced NAD
> two molecules of pyruvate

> two molecules of ATP; four have been made, but two were used to ‘kick start’ the process, so net gain is TWO molecules of ATP

Question 16

What happens to pyruvate after it’s been produced during glycolysis?

Answer 16

• it is transported across the outer and inner mitochondrial membranes via
  a specific pyruvate-H+ symport =
  a transport protein that transports two ions or molecules in the same direction, and into the matrix.

THEN:
> pyruvate is converted to a two-carbon acetyl group during the link reaction
> the acetyl group is oxidised during the Krebs cycle.

Question 17

What happens in the link reaction?

Answer 17

Pyruvate is converted to Acetyl Coenzyme A.

Question 18

What happens in the Krebs cycle?

Answer 18

Reduced coenzymes and ATP are produced.

Question 19

What five things happen if oxygen is absent in respiration?

Answer 19

1) Oxygen cannot act as the final electron acceptor at the end of oxidative phosphorylation.
- protons diffusing through channels associated with ATP synthase are not able to combine with electrons and oxygen to form water.

2) The conc. of protons increases in the matrix & reduces the proton gradient across the inner mitochondrial membrane.
3) Oxidative phosphorylation ceases
4) Reduced NAD and reduced FAD are not able to unload their hydrogen atoms and cannot be reoxidised.
5) The Krebs cycle stops, as does the link reaction.

Question 20

How does an organism survive in conditions that have an absence of oxygen?

Answer 20

Glycolysis can take place, but the reduced NAD generated during the oxidation of triose phosphate to pyruvate must be reoxidised so glycolysis can continue.

> these reduced coenzyme molecules cannot be reoxidised at the electron transport chain, so another metabolic pathway must operate to reoxidise them.

Question 21

Eukaryotic cells have two metabolic pathways to reoxidise the reduced NAD:
&
Where do these pathways occur?

Answer 21

1) Fungi, such as yeast, and plants use the ethanol fermentation pathway.
2) Mammals use the lactate fermentation pathway.

Both take place in the cytoplasm of cells.