Movement of Substances : Excretion

Question 1

what do cells produce when carrying out chemical reactions?

Answer 1

• they constantly produce waste products, such as carbon dioxide

Question 2

what can waste products do?

Answer 2

• can damage the cells as they are toxic

Question 3

what happens to waste products?

Answer 3

• they are removed from the body
• through excretion

Question 4

what is excretion?

Answer 4

• the removal of metabolic waste

Question 5

what is the waste product of respiration and how is it removed?

Answer 5

• carbon dioxide
• removed via the lungs (in mammals and birds)
• removed through leaves in plants

Question 6

why do amino acids need to be removed from the body?

Answer 6

• humans cannot store excess amino acids like they can with carbohydrates and lipids (by storing them as fat tissue0
• therefore, excess amino acids need to be broken down
• however, what they are broken down into is toxic and therefore must be removed from the body

Question 7

where is carbon dioxide made, how is it made and where is it removed?

Answer 7

• respiring cells
• respiration
• removed in lungs via blood plasma

Question 8

name two excretory products.

Answer 8

• carbon dioxide
• urea

Question 9

where is urea made, how is it made and where is it removed?

Answer 9

• liver cells
• breakdown of amino acids (deamination)
• kidneys and skin

Question 10

describe how urea is formed.

Answer 10

1. amino acids are filtered into the liver, along with the rest of the blood via the hepatic artery and hepatic portal vein
2. excess amino acids cannot be stored and need to be broken down so they can be excreted, they ae broken down into carbohydrates and ammonia
3. ammonia is very toxic and must be converted into a slightly less toxic chemical called urea
4. amino acids that are needed and the urea are released back into the blood stream via the hepatic vein

Question 11

what does the kidney do?

Answer 11

• filters the blood and removes any excess materials and passes them to the bladder to be excreted

Question 12

label the diagram

Answer 12

*bio rev image

Question 13

label the diagram

Answer 13

*bio rev image

Question 14

what three sections does the kidney contain?

Answer 14

• around the outside and a lighter colour is the cortex
• in the middle are the triangular shaped medulla
• in the centre is the pelvis (the yellowy section)

Question 15

what does the kidney contain?

Answer 15

• the kidney contains millions of tiny structures called nephrons, these are the structures that filter the blood

Question 16

what are the stages of filtering the blood?

Answer 16

• ultrafiltration
• selective reabsorption
• water reabsorption

Question 17

describe ultrafiltration.

Answer 17

1. the diameter of the efferent arteriole at the exit of the glomerulus is smaller than the diameter of the afferent arteriole at the entrance
2. this pressure forces small molecules such as urea, water, glucose, amino acids and salts out of the capillaries of the glomerulus and into the Bowman’s capsule. this forms the glomerular filtrate.
3. larger molecules like proteins or red blood cells are too big to fit across the capillary walls and therefore stay in the blood

Question 18

label the diagram.

Answer 18

• bio rev image

Question 19

describe selective reabsorption.

Answer 19

1. the filtrate travels to the proximal convoluted tubule (PCT). however, it contains a lot of useful materials such as glucose which would be wasted unless they were recovered
2. there are specialised cells within the walls of the PCT. these move the useful materials back into the bloodstream. initially, molecules will move by diffusion, but some substances are also moved against a concentration gradient using ATP, called active transport.
3. ALL OF THE GLUCOSE AND AMINO ACIDS ARE REABSORBED ALONG WITH SOME SALTS AND 80% OF THE WATER!

Question 20

label the diagram

Answer 20

• bio rev image

Question 21

why does water reabsorption need to occur?

Answer 21

• although 80% of water is reabsorbed in the PCT, there is still some water needed to be reabsorbed.
• your kidneys will filter 180L of fluid a day but you will only produce 1.5L of urine per day

Question 22

which structures of the nephrons are involved in the water reabsorption stage?

Answer 22

• the loop henle
• the collecting duct

Question 23

describe the process of water reabsorption.

Answer 23

• the loop of henle concentrates the urine by transporting salt into the blood by active transport
• this causes water to diffuse into the blood by osmosis
• if you have lost a lot of water through sweating or perhaps you haven’t taken any in your body will try and reabsorb as much water from the filtrate as it can.
• this makes urine very concentrated, with a lower vol of water and therefore is a darker, browner colour
• the collecting duct responds to a hormone called ADH to vary how much water is reabsorbed. this is called osmoregulation.

Question 24

describe the process of osmoregulation.

Answer 24

• ADH is released depending on how much water your body is trying to reabsorb
• ADH creates holes in the walls of the collecting duct
• if you are dehydrated, your brain releases ADH -> creates holes so that more water in bloodstream and less coming out in your urine, making it a darker colour
• makes the collecting duct more permeable

Question 25

label this diagram

Answer 25

*bio rev image

Question 26

what are the adaptations of the PCT for selective reabsorption?

Answer 26

• many mitochondria -> respiration -> creates more energy -> used for active transport of glucose and amino acids and the active transport of harmful substances from the blood into the filtrate
• brush border made of many microvilli cells which have thin hair like projections to increase surface area which increases diffusion and active transport as there are more carrier proteins on the surface to aid active transport

Question 27

what is the glomerulus made of?

Answer 27

• capillaries

Question 28

what is urine?

Answer 28

• urea
• water
• salts

Question 29

what shouldn’t be in urine?

Answer 29

• protein
• red blood cells
• glucose