What is excretion? (1.1)

Question 1

Define excretion.

Answer 1

Excretion is the removal of waste products from the body, eg water, carbon dioxide and nitrogenous waste from metabolic reactions.

Question 2

Metabolic reactions =

Answer 2

All the reactions taking place in the body.

Question 3

What would happen if all the waste in your body accumulated?

Answer 3

Certain of these waste products, if they were to accumulate, would become highly toxic (poisonous) and cause damage to body tissues. Others, such as water, are not poisonous but an accumulation of excess water would disrupt homeostasis and lead to all sorts of complications.

Question 4

Define homeostasis.

Answer 4

Maintaining the internal environment of the body in a ‘steady state’ so that cells can function properly.

Question 5

Define internal environment.

Answer 5

Tissue fluid and blood make up the internal environment of the body.

Question 6

True or false

The liver is not an excretory organ.

Answer 6

True.

Question 7

Name the nitrogenous waste formed by the liver. (3)

Answer 7

• Urea
• Uric acid
• Creatinine

Question 8

Name the non-nitrogenous waste formed by the liver. (3)

Answer 8

• Toxins and drugs

- Alcohol

Question 9

How is urea formed?

Answer 9

It is formed from excess amino acids. Amino acids are first broken down into ammonia (toxic) and then into urea through a process called deamination. Urea is the main nitrogenous waste by the kidneys.

Question 10

How is uric acid formed?

Answer 10

Formed from the breakdown of nucleic acids.

Question 11

How is creatinine formed?

Answer 11

Found in skeletal muscle cells and is formed from creatinine phosphate.

Question 12

Name other excretory products formed in the liver and explain how they are formed? (2x2)

Answer 12

• Bile pigments are formed from the breakdown of red blood cells
• Cholesterol is formed from the breakdown of bile salts.

Question 13

Why is alcohol bad?

Answer 13

Causes permanent damage to liver cells (cirrhosis of liver) if it is drunk over a long period.

Question 14

Why is it important to get rid of waste?

Answer 14

To maintain homeostasis, it is important to get rid of the waste products which continually diffuse into the blood stream. They are then carried to the excretory organs from where they are removed from the body in a process called excretion.

Question 15

What are the four excretory organs?

Answer 15

• Kidneys
• Lungs
• Skin
• Gut/Colon

Question 16

What do the kidneys do?

Answer 16

The kidneys excrete all of the nitrogenous waste formed in the liver, most of which is urea. The kidney’s also excrete non-nitrogenous such as carbon dioxide, excess water, ions, hormones, poisons and drugs, which may come from all over the body.

Question 17

What do the lungs do excretion wise?

Answer 17

The carbon dioxide released from cellular respiration is carried to the lungs in the blood and is exhaled from the lungs when we breathe out. A little water and heat is also excreted this way.

Question 18

How does the skin excrete?

Answer 18

Water, salts and small amount of urea are released onto the surface of the skin in the form of sweat from the glands. As the water in sweat evaporates, heat is lost and the body is cooled. Sweat therefore is an excretion as it gets rid of waste and it is also a secretion as it helps to maintain body temperature.

Question 19

Define secretion.

Answer 19

The release of useful substances, such as hormones from specialised cells in the body.

Question 20

How do the guts/colon excrete?

Answer 20

Bile pigments and cholesterol, formed in the liver pass into the small intestine and are finally excreted from the colon in the faeces. A little mucus and bacteria are excreted in the faeces.

Question 21

Define defaecation or digestion.

Answer 21

The removal of undigested and unabsorbed food material, the faeces, from the gut.