Excretion

Question 1

Define excretion

Answer 1

Excretion is the removal of waste products from chemical reactions along with excess water and salts

Question 2

What are two waste products from plants and where are they removed from

Answer 2

Oxygen from photosynthesis
CO2 from respiration
They diffuse out of the stomata through gas exchange

Question 3

What are the three excretory organs

Answer 3

Kidney, skin and lungs

Question 4

What are the excretory products of the kidney, skin and lungs

Answer 4

Kidney- urea+salts
Skin- sweat
Lungs-carbon dioxide

Question 5

Describe the structure of the urinary system

Answer 5

Kidneys, ureters, bladder, urethra

Question 6

What vein and artery lead to and from the kidney

Answer 6

Renal artery and renal vein

Question 7

Describe the structure of the nephron

Answer 7

Bowman’s capsule, glomerulus, proximal convoluted tubule, loop of henle, distal convoluted tubule, collecting duct

Question 8

Describe ultrafiltration in the nephron

Answer 8

1. blood from the renal artery flows through the glomerulus
2. a high pressure is built up which squeezes water, urea, ions and glucose (small molecules) out of the blood and into the Bowman’s capsule
3. The membranes between the blood vessels in the glomerulus and the Bowman’s capsule act like filters, so big molecules like proteins and blood cells are not squeezed out and stay in the blood. the filtered liquid in the Bowmans’s capsule is known as the glomerular filtrate made up of water, urea, ions and glucose

Question 9

What is the composition of the glomerular filtrate

Answer 9

Glucose, water, urea, salt (sodium ions)

Question 10

describe reabsorption in the nephron

Answer 10

1. All the glucose is reabsorbed in the proximal convoluted tubule so that it can be used in respiration. The reabsorption of glucose involves the process of active transport against the concentration gradient.
2. Sufficient ions are reabsorbed. Excess ions are not.
3. Sufficient water is reabsorbed from the collecting duct into the bloodstream by osmosis

Question 11

What is selective reabsorption

Answer 11

As the filtrate flows along the nephron useful substances from the glomerular filtrate are selectively reabsrobed back into the blood

Question 12

What does urine contain

Answer 12

Water, urea, salt (ions)

Question 13

what are the three main roles of the kidneys

Answer 13

removal of urea from blood, adjustment of ion(salt) levels in the blood, adjustment of water content in the blood

Question 14

what is the glomerulus

Answer 14

a bundle of capillaries at the start of the nephron

Question 15

define active transport

Answer 15

the movement of particles against a concentration gradient, from an area of low concentration to an area of high concentration across a partially permeable membrane using energy released during respiration(ATP)

Question 16

describe the release of waste in the nephron

Answer 16

the remaining substances (including water, ions, urea) form urine. This continues out of the nephron, through the ureter and down into the bladder where it is stored before being released via the urethra

Question 17

what is osmoregulation

Answer 17

the body constantly balancing the water coming into the body against the water going out

Question 18

how do the kidneys adjust the body’s water content

Answer 18

1. water is taken into the body as food and drink and is lost from the body via sweating, breathing and weeing
2. this means the body must go through osmoregulation
3. the body can adjust the amount of water that is excreted by the kidneys in the urine. e.g is=f a person is sweating a lot or hasn’t drunk enough water, the kidneys can reabsorb more water during selective reabsorption so less is lost in the urine and the water balance is maintained
4. When the kidneys reabsorb more water the urine has a smaller volume and is more concentrated

Question 19

How does ADH help to control water content

Answer 19

1. The amount of water reabsorbed in the kidney nephrons is controlled by the anti-diuretic hormone (ADH). ADH makes the collecting ducts more permeable so more water is reabsorbed back into the blood
2. The brain monitors the water content of the blood and instructs the pituitary gland to release ADH into the blood according to how much is needed. If we are dehydrated more ADH is released, if we are too hydrated, less ADH is released
3. Th whole process of osmoregulation is controlled by a mechanism called negative feedback. This means that if the water content gets too high or too low a mechanism will be triggered that brings it back to normal