excretion and osmoregulation

Question 1

definition of excretion

Answer 1

removal of metabolic waste products, toxic substances and substances in excess of the body’s requirements

Question 2

consequences of excess mineral salts in body

Answer 2

blood potential in plasma may be lowered, causing water to pass out of tissue cells into the bloodstream via osmosis. tissue cells would then become dehydrated and shrink

Question 3

consequences of excess water in body

Answer 3

water potential in plasma may increase, causing water to enter tissue cells via osmosis. they may then swell and burst

Question 4

structures inside a nephron

Answer 4

afferent arteriole, efferent arteriole, glomerulus, bowman’s capsule, proximal convoluted tubule, loop of henlé, distal convoluted tubule, collecting duct

Question 5

how do the afferent and efferent arteriole facilitate the ultrafiltration process

Answer 5

afferent arteriole is wider in diameter than the efferent arteriole, creating a high blood pressure in the glomerulus. this forces out water and small soluble substances like amino acids, urea and glucose to form the glomerular filtrate

Question 6

adaptations of glomerulus

Answer 6

1. knot of blood capillaries provides larger surface area for ultrafiltration process
2. capillary walls are one-cell thick and have tiny pores to allow substances to pass through easily
3. capillaries have thin partially permeable membrane to only allow small soluble molecules to pass through while remaining impermeable to blood cells, platelets and proteins

Question 7

what happens during selective reabsorption

Answer 7

as glomerular filtrate passes along nephron, useful substances are reabsorbed into surrounding capillaries. this includes most water, all glucose and amino acids and some mineral salts

Question 8

definition of osmoregulation

Answer 8

the control of water potential and solute concentration to maintain a constant water potential in the body

Question 9

how is amount of water in blood plasma regulated

Answer 9

antidiuretic hormone

Question 10

osmoregulation when water potential of blood plasma increases

Answer 10

hypothalamus in brain detects the stimulus, pituitary gland releases less ADH into the bloodstream, causing the cells in the walls of the collecting ducts to become less permeable to water and less water to be reabsorbed. more urine is produced and the water potential of blood decreases back to normal

Question 11

osmoregulation when water potential of blood plasma decreases

Answer 11

hypothalamus in brain detects stimulus, pituitary gland releases more ADH into bloodstream, causing cells in walls of collecting ducts to become more permeable to water and more water to be reabsorbed. less urine is produced and water potential of blood increases to normal

Question 12

process of dialysis

Answer 12

• needs to be undergone when someone is suffering from kidney failure
• dialysis machine has a similar function to kidneys and helps to remove metabolic waste substances from the blood

Question 13

features of dialysis machine

Answer 13

1. fluid contains same concentration of substances as healthy blood (ensures essential substances do not diffuse into dialysis fluid and substances can diffuse out of dialysis fluid if body lacks them)
2. fluid does not contain metabolic waste products (sets up concentration gradient that allows waste products to diffuse into the fluid and remove waste substances from the blood)
3. tubing is long narrow and coiled (increases surface area to volume ratio to speed up rate of exchange of substances between blood and fluid
4. direction of blood flow is opposite to flow of fluid (maintains concentration gradient for removal of waste products