3.3.3 Maintaining Water Balance

Question 1

Why must water levels in blood plasma remain constant?

Answer 1

• too much water = water will move into blood cells causing lysis (swell+burst)
• too little water/too much solute = water will diffuse out of blood cells = shrink

Question 2

When do water and salts enter body?

Answer 2

When consuming food + drink

Water created during respiration

Question 3

When are water + salts lost from body?

Answer 3

Sweat
Urine
Water evaporates out of body when exhaling

Question 4

What is excretion?

Answer 4

Removal of waste products

Question 5

What is urine?

Answer 5

A solution containing water, urea, and other waste substances

Question 6

What is urea?

Answer 6

Toxic, must be removed

Question 7

What happens to urea

Answer 7

Kidneys filter urea out of blood + produce urine constantly
—> urine trickles into bladder
—> bladder stores urine until urination

Question 8

First step of urine production

Answer 8

Small molecules (water, glucose, urea and salts) pass into tubes inside kidney. Blood cells are too big and stay inside capillaries

Question 9

Urine production part 2 SELECTIVE REABSORBTION

Answer 9

Kidneys put back any useful substances into blood, including all of glucose, salts body needs, some water

Question 10

If you are short of water/hot day…

Answer 10

Kidneys produce very little urine, water saved for body’s use
Produce small amount of dark yellow, concentrated urine

Question 11

If drink too much water/ quickly drink many drinks…

Answer 11

Kidneys produce lots of urine, excess water is lost from body
Produce large amount of dilute, almost colourless urine