Metabolism and Survival, KA 1-4

Question 1

What are metabolic pathways?

Answer 1

Metabolic pathways are integrated and controlled pathways of enzyme-catalysed reactions within a cell.
Metabolic pathways can have reversible steps, irreversible steps and alternative routes.

Question 2

Anabolic and catabolic reactions

Answer 2

Reactions within metabolic pathways can be anabolic or catabolic.
Anabolic reactions build up large molecules from small molecules and require energy.
Catabolic reactions break down large molecules into smaller molecules and release energy.

Question 3

What are embedded in membranes?

Answer 3

Protein pores, pumps and enzymes are embedded in membranes.

Question 4

What are metabolic pathways controlled by?

Answer 4

Metabolic pathways are controlled by the presence or absence of particular enzymes and the regulation of the rate of reaction of key enzymes.

Question 5

Induced fit

Answer 5

Induced fit occurs when the active site changes shape to better fit the substrate after the substrate binds.

Question 6

Affinity (chemical attraction)

Answer 6

The substrate molecule(s) have a high affinity for the active site and the subsequent products have a low affinity, allowing them to leave the active site.

Question 7

What drives a sequence of reactions in a particular direction?

Answer 7

Some metabolic reactions are reversible and the presence of a substrate or the removal of a product will drive a sequence of reactions in a particular direction.

Question 8

Activation energy

Answer 8

The activation energy is the energy needed to break chemical bonds in the reactant chemicals.
The presence of an enzyme lowers the activation energy.

Question 9

What is an inhibitor?

Answer 9

An inhibitor is a substance that decreases the rate of an enzyme controlled reaction.
There are three types of inhibition: competitive, non-competitive and feedback.

Question 10

Competitive inhibition

Answer 10

Competitive inhibitors bind at the active site preventing the substrate from binding.
Competitive inhibition can be reversed by increasing substrate concentration.

Question 11

Non-competitive inhibition

Answer 11

Non-competitive inhibitors bind away from the active site but change the shape of the active site preventing the substrate from binding.
Non-competitive inhibition cannot be reversed by increasing substrate concentration.

Question 12

Feedback inhibition

Answer 12

Feedback inhibition occurs when the end-product in the metabolic pathway reaches a critical concentration. The end-product then inhibits an earlier enzyme, blocking the pathway, and so prevents further synthesis of the end-product.

Question 13

Stages in aerobic respiration

Answer 13

1. Glycolysis - occurs in the cytoplasm.
2. Citric acid cycle - occurs in the matrix of the mitochondria.
3. Electron transport chain - occurs on the inner mitochondrial membrane.

Question 14

What is glycolysis?

Answer 14

Glycolysis is the breakdown of glucose to pyruvate in the cytoplasm.

Question 15

Energy investment phase

Answer 15

This is the first phase of glycolysis.

ATP is required for the phosphorylation of glucose and intermediates in this stage.

Question 16

Energy pay-off phase

Answer 16

This is the second phase of glycolysis.
The phosphorylation of glucose and intermediates during the first stage of glycolysis leads to the generation of more ATP during this stage and results in a net gain of ATP.

Question 17

What happens to the pyruvate if oxygen is present?

Answer 17

In aerobic conditions, pyruvate is broken down to an acetyl group that combines with coenzyme A forming acetyl coenzyme A.

Question 18

Citric acid cycle

Answer 18

In the citric acid cycle the acetyl group from acetyl coenzyme A combines with oxaloacetate to form citrate.
During a series of enzyme-controlled steps, citrate is gradually converted back into oxaloacetate which results in the generation of ATP and release of carbon dioxide.

Question 19

What occurs in both glycolysis and the citric acid cycle?

Answer 19

Dehydrogenase enzymes remove hydrogen ions and electrons and pass them to the coenzyme NAD, forming NADH.
The hydrogen ions and electrons from NADH are passed to the electron transport chain on the inner mitochondrial membrane.

Question 20

What is the electron transport chain?

Answer 20

The electron transport chain is a series of carrier proteins attached to the inner mitochondrial membrane.

Question 21

ATP synthesis

Answer 21

Electrons are passed along the electron transport chain releasing energy.
This energy allows hydrogen ions to be pumped across the inner mitochondrial membrane.
The flow of these ions back through the membrane protein ATP synthase results in the production of ATP.
Finally, hydrogen ions and electrons combine with oxygen to form water.

Question 22

Fermentation

Answer 22

In the absence of oxygen, fermentation takes place in the cytoplasm.
In animal cells, pyruvate is converted to lactate in a reversible reaction.
In plants and yeast, ethanol and CO2 are produced in an irreversible reaction.
Fermentation results in much less ATP being produced than in aerobic respiration.

Question 23

What is the role of ATP in the transfer of energy?

Answer 23

ATP is used to transfer energy to cellular processes which require energy.

Question 24

How can metabolic rate be measured?

Answer 24

Metabolic rate can be measured using respirometers, oxygen probes, carbon dioxide probes and calorimeters.

Question 25

How do we compare metabolic rates?

Answer 25

Measurement of oxygen consumption, carbon dioxide and heat production allow us to compare metabolic rates.

Question 26

Metabolic rate in different groups of animals

Answer 26

Birds and mammals have higher metabolic rates than reptiles and amphibians, which in turn have higher metabolic rates than fish.

Question 27

What do organisms with high metabolic rates require?

Answer 27

Organisms with high metabolic rates require more efficient delivery of oxygen to cells.

Question 28

Complete double circulatory system

Answer 28

Birds and mammals have a complete double circulatory system.
The heart consists of two atria and two ventricles.
There is no mixing of oxygenated and deoxygenated blood.

Question 29

Incomplete double circulatory system

Answer 29

Amphibians and most reptiles have an incomplete double circulatory system.
The heart consists of two atria and one ventricle.
The oxygenated and deoxygenated blood mix in the ventricle.

Question 30

Single circulatory system

Answer 30

Fish have a single circulatory system.

The heart consists of one atrium and one ventricle.

Question 31

Which circulatory system is most efficient and why?

Answer 31

Complete double circulatory systems enable higher metabolic rates to be maintained.
There is no mixing of oxygenated and deoxygenated blood and the oxygenated blood can be pumped out at a higher pressure.
This enables more efficient oxygen delivery to cells.

Question 32

What affects the ability of an organism to maintain its metabolic rate?

Answer 32

The ability of an organism to maintain its metabolic rate is affected by external abiotic factors.

Question 33

What are abiotic factors?

Answer 33

Non-living factors such as pH, salinity and temperature.

Question 34

Conformers

Answer 34

Conformers’ internal environment is dependent upon external environment.
They have low metabolic costs and a narrow range of ecological niches.
Conformers use behavioural responses to allow them to tolerate variation in their external environment to maintain optimum metabolic rate.

Question 35

Regulators

Answer 35

Regulators maintain their internal environment regardless of external environment.
Regulators use metabolism to control their internal environment, which increases the range of possible ecological niches.
This regulation requires energy to achieve homeostasis.
This increases their metabolic costs.

Question 36

What is the hypothalamus and where is it located?

Answer 36

The hypothalamus is the temperature monitoring centre and it is located in the brain.

Question 37

Thermoregulation by negative feedback

Answer 37

Information is communicated by electrical impulses through nerves to the effectors, which bring about corrective responses to return temperature to normal.

Question 38

Corrective responses to an increase in body temperature

Answer 38

Sweating: body heat used to evaporate water in the sweat, cooling the skin.
Vasodilation of blood vessels: increased blood flow to the skin increases heat loss.
Decreased metabolic rate: less heat produced.

Question 39

Corrective responses to a decrease in body temperature

Answer 39

Shivering: muscle contraction generates heat.
Vasoconstriction of blood vessels: decreased blood flow to skin decreases heat loss.
Hair erector muscles contract: traps layer of insulating air.
Increased metabolic rate: more heat produced.

Question 40

Why is thermoregulation important?

Answer 40

Regulating temperature is important for optimal enzyme activity and high diffusion rates to maintain metabolism.