12 Excretion

Question 1

Function of kidney

Answer 1

Excretes urea and excess water and ions

Question 2

Cortex

Answer 2

The tissue making up the outer layer of the kidney

Question 3

Medulla

Answer 3

The tissue making up the inner layers of the kidney

Question 4

Nephron

Answer 4

One of the tiny microscopic tubes in a kidney, where urine is formed

Question 5

Glomerulus

Answer 5

A small network of blood capillaries where blood is filtered in the kidney

Question 6

What substances are filtered from the blood in the glomerulus?

Answer 6

Water, glucose, urea, and ions

Question 7

Define excretion

Answer 7

the removal of waste substances of metabolism from organisms

Question 8

Outline the process in which urine is formed

Answer 8

1. Blood from the renal artery enters the glomerulus
2. The glomerulus filters water, glucose, urea, and ions from the blood into the renal capsule
3. The nephron reabsorbs all the glucose, most of the water and some of the ions back into the blood
4. The remaining urea and excess water and ions form urine. Urine flows out of the kidneys through the ureters into the bladder where it is temporarily stored before being excreted out of the body through the urethra

Question 9

Functions of the liver

Answer 9

• assimilates amino acids into proteins
• converts excess amino acids into carbohydrates and urea through deamination
• regulates blood glucose concentration with the help of insulin and glucagon
• synthesises plasma protein such as fibrinogen, from amino acids
• breaks down harmful substances such as alcohol
• produces bile for emulsification of fats

Question 10

Define deamination

Answer 10

the removal of nitrogen containing parts of amino acids to form urea

Question 11

How is urea formed?

Answer 11

1. Protein in food enters the alimentary canal
2. Protein molecules are broken down into amino acids during digestion
3. The amino acids are absorbed into the blood and taken to the liver through the hepatic portal vein
4. Amino acids that are needed by the body are converted into proteins in the liver through assimilation or released into blood to be assimilated by body cells
5. Amino acids that are not needed by the body are deaminated into carbohydrates and ammonia
6. The carbohydrates are used or stored in the liver. Ammonia is converted into urea
7. Urea to be excreted and amino acids to be used by the body are taken away by blood