13 Excretion in humans

Question 1

Excretion

Answer 1

The removal of the waste products of metabolism, toxic materials and substances in excess of requirements from the body.

Question 2

Egestion

Answer 2

Process of passing out food that has not been digested or absorbed in the form of faeces.

Question 3

Urinary system

Answer 3

Organ system involved in excretion of urea, and excess salts and water. It includes the kidneys, ureters and urethra.

Question 4

Urea

Answer 4

Waste product from the breakdown of excess amino acids, coverted in the liver and excreted in urine.

Question 5

Urine

Answer 5

Waste product of urea and excess ions dissolved in excess water secreted by kidneys.
Urine is formed as a result of filtration in the glomerulus and selective reabsorption in the tubule.

Question 6

Ureter

Answer 6

Tube that transports urine from the kidneys to the bladder.

Question 7

Bladder

Answer 7

Organ that stores urine until it is released from the body.

Question 8

Urethra

Answer 8

A tube that allows the passage of semen and urine through the centre of the penis.

Question 9

Kidney

Answer 9

Filter waste products out of the blood to form urine

Question 10

The liver has many functions in the body, including:

Answer 10

assisting the body in taking up amino acids for cellular use
breaking down excess amino acids.
Producing bile

Question 11

Assimilation

Answer 11

The movement of digested food molecules into the cells of the body where they are needed.

Question 12

Deamination in the liver

Answer 12

It involves the removal of the nitrogen-containing (–NH 2 group) part of amino acid molecules

The –NH 2 group is converted to ammonia, NH 3 , after it is removed. High levels of ammonia in the bloodstream can have serious health consequences such as brain damage. It is important for your body to keep the ammonia levels low by converting it to urea, which is less toxic.

Question 13

Assimilation in the liver

Answer 13

The liver has a role in the assimilation of amino acids. It can convert them into proteins, including fibrinogen and other plasma proteins. Fibrinogen is involved in the blood clotting that prevents blood loss and entry of pathogens after wounding the skin

Question 14

Cortex

Answer 14

outer part where blood is filtered and some selective reabsorption happens

Question 15

Medulla

Answer 15

inner part where some selective reabsorption happens, and fluid is collected to form urine

Question 16

Selective reabsorption

Answer 16

The process in the kidney where the nephron reabsorbs only the molecules the body needs back into the bloodstream.

Question 17

Nephron

Answer 17

The functional unit of the kidney, consisting of a glomerulus and a tubule.

Question 18

Role of a nephron

Answer 18

Its role is to filter the blood, separating waste and returning substances that are needed back to the bloodstream. Each kidney has around a million of these structures.

Question 19

Glomerus

Answer 19

The glomerulus is a network of capillaries. The blood is filtered here under pressure (called ultrafiltration).
Water, glucose, urea and ions leave the capillaries and enter the tubule. Protein molecules are too large to leave the capillaries and so they stay in the blood.

Question 20

Tubule

Answer 20

Substances entering the tubule are selectively reabsorbed back into the blood:
All of the glucose
Most of the water
Some ions.

Urea is not reabsorbed but instead remains dissolved in the liquid inside the tubule. This liquid forms the urine.