Excretion

Question 1

what is excretion?

Answer 1

the removal of waste products of metabolism from the body

Question 2

what two waste products are produced by plants?

Answer 2

• oxygen from photosynthesis
• carbon dioxide from respiration

Question 3

how do plants remove waste products?

Answer 3

they diffuse out of the stomata, tiny pore-like openings on the underside of leaves that allow gas exchange

Question 4

label the parts of a leaf cross-section

Answer 4

GO TO ONENOTE

Question 5

when is more oxygen produced by a leaf and why?

Answer 5

• more oxygen is produced during the day (photosynthesis):
• the plant uses CO₂ and produces O₂
• there’s a net movement of CO₂ into the leaf (for photosynthesis)
• there’s a net movement of O₂ out of the leaf (as a waste product)

Question 6

when is more carbon dioxide produced by a leaf and why?

Answer 6

• more carbon dioxide is produced during the night (no photosynthesis):
• only respiration occurs → plant uses O₂ and makes CO₂.
• so there’s a net movement of O₂ into the leaf.
• and a net movement of CO₂ out of the leaf.

Question 7

name the four waste products in humans

Answer 7

• carbon dioxide
• water
• salts
• urea

Question 8

explain how carbon dioxide is produced and excreted by the body

Answer 8

• produced = waste products of respiration
• excreted = exhaled by the lungs after diffusing into alveoli from the bloodstream

Question 9

explain how water is produced and excreted by the body

Answer 9

• produced = waste product of respiration + ingested
• excreted = exhalation as water vapour by lungs + sweated off by skin + removed from blood by kidneys and urinated out of body

Question 10

explain how salts are produced and excreted by the body

Answer 10

• produced = ingested from foods
• excreted = removed from body by kidneys and urinated out of body + some goes into sweat

Question 11

explain how urea is produced and excreted by the body

Answer 11

• produced = amino acids which are not needed by body are converted into urea in the liver
• excreted = removed from blood by kidneys and urinated out of body + some is sweated off by skin

Question 12

name the excretory organs

Answer 12

• skin
• kidneys
• lungs
• liver

Question 13

name the excretory products of the skin

Answer 13

Excess water, salts and some urea is excreted by sweat glands as a form of thermoregulation

Question 14

name the excretory products of the kidneys

Answer 14

ALL urea, excess water and excess salts are excreted in the urine by filtration out the blood

Question 15

name the excretory products of the lungs

Answer 15

carbon dioxide and water vapour, waste products of respiration, are excreted by exhalation from the lungs

Question 16

name the excretory products of the liver

Answer 16

produces urea from excess amino acids, which get later filtered out of blood to make urine by kidneys

Question 17

briefly describe the structure of the urinary system

Answer 17

• each of the two kidneys is supplied with a renal artery where unfiltered blood enters at high pressure
• inside each kidney, the blood is filtered and then exits the kidney by the renal vein where it travels back to the heart
• each kidney also has a renal pelvis, in which urine from the collecting duct of nephrons travels towards, and connects to a ureter
• the ureter transports the urine away from the kidney and joins with the other ureter at the bladder, where urine is stored
• when you go to the toilet, urine is excreted from the bladder by the urethra

Question 18

label the urinary system, kidneys and nephron

Answer 18

GO ONENOTES AND DO IT

Question 19

briefly describe the structure of the kidneys

Answer 19

• renal artery and vein both branch out within the kidney around each medulla to supply the nephrons
• the dark exterior is the cortex, which is supplied with many capillaries from the renal artery for the glomeruli of nephrons
• there are microscopic filtration units called nephrons which sit between the cortex and the medulla
• the medulla is after the cortex and has many pyramid-like bulges that point towards the renal pelvis
• the renal pelvis is where urine is emptied from the collecting ducts of nephrons within the medullas
• the renal pelvis connects to the ureter which transports urine to the bladder from the kidneys

Question 20

why is osmoregulation important in terms of tissue fluid water potential?

Answer 20

• if the tissue fluid is hypotonic (high wp), then water will move into the cells, causing them to fill up and eventually burst - lysis
• if the tissue fluid is hypertonic (low wp) then water will move out of cells, causing them to shrivel - crenation - and it also would make the blood more viscous and thick which is harder to pump around the body
• if the tissue fluid isotonic (equal wp in+ out of cell) then no osmosis occurs

Question 21

briefly describe the structure of the nephron

Answer 21

• nephrons are microscopic filtration units located between base of the medullas and cortex
• the contents of the nephron (urine) drain into the renal pelvis by the collecting duct and go to the bladder by the ureter
• the afferent arteriole enters the glomerulus, a ball of capillaries within the bowman’s capsule, which is separated from the bowman’s capsule by a basement membrane
• the efferent arteriole exits the glomerulus
• then there is the proximal convoluted tubule, the loop of Henle, the distal convoluted tubule and finally the collecting duct

Question 22

what is function of the nephron?

Answer 22

remove all the urea from the blood, as well as excess water and salt thru ultrafiltration of the blood

Question 23

what are the two important functions of the kidney?

Answer 23

• homeostatic organ = maintains a constant blood water potential through osmoregulation
• excretory organ = removal of toxic urea as urine

Question 24

what is ultrafiltration?

Answer 24

small molecules are forced out of the blood in the glomerulus and into the filtrate in the bowman’s capsule under high pressure, and larger molecules remain in the blood

Question 25

why is it called ULTRAfiltration? how is this process sustained?

Answer 25

- it is called ultrafiltration as it occurs at high pressure - this is maintained as the afferent arteriole is wider than the efferent, creating a bottleneck effect - this allows high pressure to build up in the glomerulus, forcing smaller molecules (water, salts, glucose, urea etc) out of the blood through the basement membrane and into the bowman's capsule = ultrafiltration

Question 26

explain the process of ultrafiltration

Answer 26

- the blood enters the glomerulus through the wide afferent arteriole, and exits through a thinner efferent arteriole, creating high pressure within the glomerulus - this high pressure forces small molecules (water, glucose, salts, urea) through the walls of the capillaries in the glomerulus, through the basement membrane and into the bowman's capsule as a glomerular filtrate - molecules like RBCs and proteins are too large to be filtered out of the blood by ultrafiltration, so leave the glomerulus by the efferent arteriole - the glomerular filtrate then passes out of the bowman's capsule to the proximal convoluted tubule, where the selective reabsorption of essential small molecules (salts, water, glucose) occurs

Question 27

what small molecules are in the glomerular filtrate?

Answer 27

- glucose - water - salts - urea

Question 28

what is in the urine?

Answer 28

- water - urea - excess ions

Question 29

what is selective reabsorption?

Answer 29

where the kidneys will selectively return some of the small molecules in the glomerular filtrate back into the blood

Question 30

what molecules are selectively reabsorbed back into the blood from the glomerular filtrate?

Answer 30

- all of the glucose - as much water as the body requires - as many salts as the body requires

Question 31

why is selective reabsorption needed? by which process does it occur?

Answer 31

- many of the small molecules in the glomerular filtrate are essential to the body so the kidneys must reabsorb these whilst also allowing unneeded molecules like urea to pass out the body in urine - selective reabsorption occurs by active transport using ATP and osmosis for water

Question 32

what is selectively reabsorbed in the proximal convoluted tubule? how is it adapted for this? what would happen if a person was diabetic?

Answer 32

- all of the glucose, most amino acids, some water and most of the sodium and chloride ions are selectively reabsorbed at the proximal convoluted tubule - this process occurs by active transport (and osmosis for water), and the cells in the walls of the PCT contain many mitochondria to release energy for active transport of all glucose and most of the ions in the filtrate - diabetics have glucose in their urine as not all of the glucose is reabsorbed at the PCT

Question 33

what is selectively reabsorbed in the loop of Henle and, more importantly, the collecting duct?

Answer 33

- more ions and water is reabsorbed in the loop of Henle and mostly in the collecting duct - the water leaves the glomerular filtrate by osmosis whereas the ions would be actively transported

Question 34

what does ADH stand for? where is it produced and what does it do?

Answer 34

- ADH = anti-diuretic hormone - produced by the pituitary gland - causes the collecting ducts within nephrons to become more permeable to water, allowing more water to move across its partially permeable membrane by osmosis - this increase in the removal of water occurs when blood water potential drops slightly, causing more water to re-enter the blood - this causes urine to become more concentrated

Question 35

describe the negative feedback loop for low blood water potential

Answer 35

- low blood water potential stimulates the hypothalamus to transmit an electrical impulse to the pituitary gland to secrete more ADH - this travels in the bloodstream towards the kidneys, where it goes to the collecting duct in nephrons and makes their walls more permeable to water - this means that more water is reabsorbed into the blood by osmosis, returning the blood water potential levels to normal - this removal of water causes the glomerular filtrate (which is now urine) to become more concentrated and dark coloured - less urine is produced - blood becomes more watery as more water enters it from collecting duct

Question 36

describe the negative feedback loop for high blood water potential

Answer 36

- high blood water potential stimulates the hypothalamus to transmit an electrical impulse to the pituitary gland to secrete less ADH - less ADH in bloodstream makes the walls of collecting ducts less permeable to water - this means that less water is reabsorbed into the blood by osmosis, returning the blood water potential levels to normal - this causes the glomerular filtrate (which is now urine) to become less concentrated, more watery and lighter coloured - more urine is produced as the increase in water in glomerular filtrate increases volume - blood becomes thicker as less water enters it from collecting duct