5.2.1 - Excretion

Question 1

What is excretion?

Answer 1

The removal of metabolic waste from the body

Question 2

What is metabolic waste?

Answer 2

A substance that is produced in excess by the metabolic processes in the cells; it may become toxic

Question 3

What may happen if there is a build up of excess substances from chemical processes? (2 Points)

Answer 3

Inhibit enzyme activity or become toxic altering the pH.

Question 4

What are the main excretory products? (3 Points)

Answer 4

1) Carbon dioxide from respiration
2) Nitrogen-containing compounds such as urea (i.e nitrogenous waste)
3) Other compounds, such as the bile pigments found in faeces

Question 5

What are the 3 excretory organs?

Answer 5

1) Lungs
2) Liver
3) Skin

Question 6

How is the lung an excretory organ?

Answer 6

Carbon dioxide produced from respiration.
It is removed when the carbon dioxide passes from the cells of respiring tissues into the bloodstream, –> where it is transported to the lungs. The Carbon dioxide diffuses into the alveoli to be excreted as you breathe out

Question 7

How is the liver an excretory organ?

Answer 7

Pigment Bilirubin
Liver has many metabolic roles and some of the substances produced will be passed into the bile for excretion with the faeces.
Liver also involved in converting excess amino acids to urea. Deamination, nitrogen-containing part of the molecule is then combined with carbon dioxide to make urea

Question 8

How is the skin an excretory organ?

Answer 8

Urea, uric acid and ammonia which may be present in sweat.

Question 9

How is carbon dioxide transported in the blood?

Answer 9

As hydrogencarbondate ions

Question 10

How are H+ ions produced from hydrogencarbonate and where does this occur?

Answer 10

CO2+H2O–>H2CO3 (Carbonic Acid)

The Carbonic acid then dissociates to release Hydrogen ions

H2Co3–>H+ HCO3^-
This occurs in the red blood cells and blood plasma, under the influence of the enzyme Anhydrase.

Question 11

How are the H+ Ions and toxic

Answer 11

1) Affect the pH of the cytoplasm in the redblood cells
2) Hydrogen ions interact with bonds within haemoglobin, changing it’s 3D shape –> Reduces Affinity of haemoglobin for oxygen –> Affecting oxygen transport.
3) H+ Ions can form with haemoglobin to make Haemoglobinic Acid

Question 12

What happens to the carbon dioxide that is not converted to hydrogencarbonate ions

Answer 12

1. Combines directly with haemoglobin, producing carbanimohaemoglobin.
2. Carbaminoheamoglobin unable to combine with oxygen as normal –> Reducing oxygen transport further

Question 13

Excess hydrogen ions can reduce the pH of the blood plasma, why is maintaining the pH of the blood plasma essential?

Answer 13

1) Can alter the structure of the many proteins in the blood that help to transport a wide range of substances around the body. proteins in the blood act as buffers to resist the change in pH

Question 14

What happens if the change in pH is small in the blood plasma?

Answer 14

Extra hydrogen ions are detected by the respiratory

Question 15

What is respiratory acidosis?

Answer 15

Rapid heart rate and changes in blood temperature

Question 16

What can cause respiratory acidosis?

Answer 16

Diseases or conditions that affect the lungs themselves such as asthma or severe penuemonia. Blockage of the airway due to swelling, a foreign object or vomit can also induce acute respiratory acidosis

Question 17

Why are excess amino acids not excreted?

Answer 17

Amino acids contain almost as much energy as carbohydrates. Instead they are transported to the liver and the potentially toxic amino group is removed via Deamination

Question 18

What happens to excess amino acids

Answer 18

Amino group converted into something that is slightly less toxic called Urea which is then transported to the kidneys for excretion.
Remaining keto acid can be used directly in respiration to release its energy or it may be converted to a carbohydrate or fat for storage

Question 19

What is deamination?

Answer 19

Amino acids+ oxygen –> keto acid + ammonia

Question 20

How is urea formed?

Answer 20

Ammonia+Carbondioxide–> urea + water

2NH3 + Co2 –> (NH2)2CO + H2O