Introduction To Excretion

Question 1

What is excretion? (3 marks)

Answer 1

The removal of metabolic waste from the body.
Metabolic wastes are by products of normal cell processes.
Metabolic wastes are toxic if allowed to accumulate.

Question 2

What is secretion? (4 marks)

Answer 2

Release into the body of chemicals.
These useful cell products are produced by glands.
Endocrine glands secrete hormones into the bloodstream.
Exocrine glands secrete chemicals through ducts.

Question 3

What is egestion? (2 marks)

Answer 3

Removal of undefeated food by the process of dedication.
These substances have never been in cells and cannot be excreted.

Question 4

What do the sweat glands excrete? (3 marks)

Answer 4

Nitrogen containing compounds
Water
Electrolytes

Question 5

What do the lungs excrete? (2 marks)

Answer 5

Carbon dioxide
Water

Question 6

What does the kidney excrete? (4 marks)

Answer 6

Nitrogen containing compounds
Toxins
Water
Electrolytes

Question 7

What do the digestive organs (liver, large intestine, bladder) excrete? (3 marks)

Answer 7

Digestive waste
Bile pigments
Salts of heavy metals

Question 8

What are the two main things that need to be excreted due to build up? (2 marks)

Answer 8

Carbon dioxide
Nitrogen containing compounds (like urea)

Question 9

What is carbon dioxide secreted as? (1 mark)

Answer 9

Hydrogen carbonate ions

Question 10

How is carbon dioxide converted into hydrogen carbonate ions (inn two steps)? (2 marks)

Answer 10

Carbon dioxide + water —> H2CO3
H2CO3 —> H+ + HCO3-

Question 11

What effect do the H+ have on the haemoglobin’s affinity for oxygen, explain? (3 marks)

Answer 11

Reduces affinity.
Affects the pH of cytoplasm of red blood cells.
Interacts with the bonds within haemoglobin (changes the 3D shape).

Question 12

Can H+ react directly with haemoglobin, if yes what does it produce? (1 mark)

Answer 12

Yes
Haemoglobinic acid

Question 13

Can CO2 react directly with haemoglobin, if yes what does it produce? (1 mark)

Answer 13

Yes
Carbaminohaemoglobin

Question 14

What symptoms can excess CO2 cause, what is this known as? (4 marks)

Answer 14

Rapid heart rate
Fainting
Rapid breathing
Changes in blood pressure

Known as: respiratory acidosis

Question 15

What does the body do with amino acids, since it can’t store them? (2 marks)

Answer 15

They get deaminated in the liver.

Question 16

What is deamination? (2 marks)

Answer 16

The removal of the potentially toxic amino group.

Question 17

What does deamination initially form? (2 marks)

Answer 17

Ammonia and keto acid

Question 18

What is ammonia converted into and where does this chemical go? (2 marks)

Answer 18

Urea, it gets transported to the kidneys for excretion.

Question 19

What are the keto acids used in? (2 marks)

Answer 19

Respiration or stored as carbs/fats

Question 20

What is the chemical formula for urea? (1 marks)

Answer 20

(NH2)2CO

Question 21

What is the equation that forms urea? (2 marks)

Answer 21

Ammonia + carbon dioxide —> urea + water

Question 22

Why can fish excrete ammonia but mammals must convert it to urea? (6 marks)

Answer 22

• Ammonia is toxic and very soluble
• Fish can use lots of water to dilute ammonia so it is no longer toxic
• This dilute solution can be released all the time, through the gills, so it does not accumulate in body

• Mammals do not live in water so cannot release ammonia straight away, it must be stored before being released
• It is deaminated and stored as concentrated urea in urine in the bladder
• Urea is less toxic than ammonia, so it can be transported in the blood more safely and stored more safely in the bladder.

Question 23

What do reptiles and birds convert ammonia into? (1 mark)

Answer 23

Uric acid

Question 24

Why do reptiles and birds convert ammonia into uric acid instead of urea to be excreted? (2 marks)

Answer 24

Uric acid is insoluble
This saves water