11.3

Question 1

what is excretion

Answer 1

removal of metabolic waste products

Question 2

what is osmoregulation

Answer 2

the maintenance of relatively constant water & solute concentration in an organism

prevents dehydration or over hydration

Question 3

three types of nitrogenous waste

Answer 3

ammonia (toxic): excreted by fish

urea (less toxic): excreted by mammals, amphibians

uric acid (not toxic): excreted by birds, insects

Question 4

excretion of nitrogenous waste depends on habitat and evolutionary history

Answer 4

habitat:
ammonia is very toxic and is excreted as a dilute solution so requires a habitat with abundant freshwater

urea is less toxic but requires some energy to make. it can be excreted as a more concentrated solution to conserve water

uric acid is not toxic but requires much energy to make. it is therefore excreted as a semi-solid paste to conserve even more water

evolutionary history:
marine mammals still excrete urea even though they live in aquatic environments where they don’t need to conserve as much water as terrestrial mammals

Question 5

over hydration and dehydration

Answer 5

• dehydration is the loss of water but not solutes from the body
• caused by exercise, excessive salt intake, diarrhoea
• body fluids become hypertonic
• symptoms include dark low volume of urine, inability to sweat, fatigue, death
• over-hydration is the gain of water but not of solutes
• caused by drinking excessive water (but not solutes)
• body fluids become hypotonic
• symptoms include blurred vision, nausea, seizures, death

Question 6

osmoconformer

Answer 6

organisms that maintain internal conditions that are equal to the osmolarity of their environment

Question 7

osmoregulator

Answer 7

organisms that maintain their body’s osmolarity constant regardless of their environment

Question 8

malpighian tubules

Answer 8

malpighian tubules in insects carry out osmoregulation and excrete nitrogenous waste

they excrete water and salts too and the body reabsorbs what it needs

Question 9

nephrons annotate

Answer 9

glomerulus: a knot of capillaries which filter blood at high pressure (ultrafiltration)

bowman’s capsule: collects the glomerular filtrate

PCT: useful molecules are selectively re absorbed

loop of henle: establishes a high solute concentration in the medulla so that water can be absorbed into the blood

DCT: adjusts pH of blood & reabsorbs useful ions

collection duct: where water is reabsorbed according to need (ADH)

Question 10

structure and function of ultrafiltration

Answer 10