AP6

Question 1

What generates nitrogenous waste?

Answer 1

• Break down of protiens and nucleic acids
• In digestive system
• Amino group (NH2) is removed

Question 2

Why do we need to get rid of nitrogenous waste?

Answer 2

• Forms toxic ammonia
• Raises pH of body fluids
• Inhibits key enzymes

Question 3

What are 3 different organisms get rid of nitrogenous waste? and what organisms use which?

Answer 3

1) Ammonia- bony fishes, aquatic amphibians and invertebrates
2) Urea- mammals, most amphibians, cartilaginous fish
3) Uric acid- birds, insects, reptiles, some amphibians

Question 4

4 facts about ammonia excretion

Answer 4

1) Doesnt require energy
2) Small molecule so rapid diffusion
3) Very toxic
4) Highly soluble in water

Question 5

Where is urea produced and what from? It is less toxic than ammonia but at what cost?

Answer 5

• Produced in the liver
• From ammonia
• Requires energy to make

Question 6

What are the costs and benefits of uric acid?

Answer 6

Benefits:

• insoluble
• less toxic
• excreted as semi solid, conserves water
• useful if development takes place in an egg

Costs: requires 3x as much energy to make as urea

Question 7

What are generalised excretory organs for protozoa, amelids, insects, fish and birds?

Answer 7

Protozoa- contractile vacuole
Annelids- pores in skin
Insects- malpighian tubules
Fish- gills
Birds- nasal salt glands

Question 8

Describe how malpighian tubules work to produce uric acid

Answer 8

• Salts and nitrogenous waste actively transported into gut lumen through tubules
• Water follows by osmosis
• Valuable ions pumped back into hacnolymph and water follows
• Uric acid eliminated with faeces

Question 9

Describe the structure of malpighian tubules in insects and why they are useful

Answer 9

• Blind ended tubes
• Walls = one cell thick
• Open to hindgut
• Float in haemolymph

Useful because they are highly effective at conserving water

Question 10

What are the 4 main steps in the human excretory system (kidneys)?

Answer 10

1) Filtration
2) Re-absorption
3) Secretion
4) Excretion of filtrate

Question 11

What are 2 key features of the human excretory system?

Answer 11

1) Selectively permeable membranes

2) Blood in close contact with excretory structures

Question 12

What is the job of the renal cortex and renal medulla?

Answer 12

Renal cortex- ultrafiltration

Renal medulla- regulates water and salt in blood

Question 13

What is the nephron and its job?

Answer 13

• Single long tubule surrounded by a network of capillaries

- Constantly brings in waste products that need excreting

Question 14

Describe the process of ultrafiltration?

Answer 14

• High blood pressure in glomerulus forces fluid into bowman capsule
• All solutes are pushed into nephron
• Water and salt is reabsorbed in proximal tubule
• In descending limb water leaves filtrate increasing osmolates
• Salt leaves filtrate, water in ascending limb

Question 15

What is the countercurrent multiplier system?

Answer 15

Concurrent: tubule fluid in descending limb flows in opposite direction from ascending limb

Multiplier: creates steep osmotic gradient by increasing solute potential in surrounding fluid