Excretion

Question 1

Excretion in plants

Answer 1

Plants also excrete waste products of metabolism
In light, leaves produce oxygen from photosynthesis
In dark, plant excrete CO2 from respiration
Plant exchange these gases through pores in the leaf called stomata

Question 2

Excretion in humans

Answer 2

Unlike plants, humans have organs which are specialised for the removal of certain excretory products
Excretory organs in humans include lungs, kidney, skin

Question 3

Lungs, what it excretes, and explanation

Answer 3

Excretes Carbon dioxide during exhalation

Question 4

Kidneys, what it excretes, and explanation

Answer 4

Excretes excess water, excess salts and urea by producing urine

Question 5

Skin, what it excretes, and explanation

Answer 5

Excretes water, salts and urea through sweat glands in the skin. Not excreted as excess but rather to lower body temperature

Question 6

What are 2 main functions of the kidney and explain

Answer 6

Excretion- process by which waste products of metabolism are removed from the body
Osmoregulation- Control of water content in the blood plasma

Question 7

What is Homeostasis?

Answer 7

Keeping the conditions in the internal environment relatively constant, particularly blood together with another liquid called tissue fluid
Eg: Blood glucose level, blood water and salt, blood ph, body temperature, CO2 levels in blood
Homeostasis is important to cells, as cells will only function properly if they are bathed in tissue fluid, which contains optimum conditions. Otherwise, cells might not function efficiently and cause permanent damage

Question 8

Tissue fluid

Answer 8

Watery solution of glucose, salts, and other solutes surrounds the cells of the body forming a pathway for the transfer of nutrients between blood and the cells
Tissue fluid is formed by leakage from blood capillaries, it is similar to blood plasma but it lacks plasma proteins

Question 9

Urea

Answer 9

Formation takes place in Liver
It is the main excretory product of the human kidneys
Excess amino acids are broken down in the liver by a process called deamination into urea and passes to the blood
Amino acids cannot be stored in the body as it would be toxic to cells if built in blood
Urea rich blood is filtered out by kidney tubules/nephrons to form urine

Question 10

Composition of urine

Answer 10

Mainly urea
Water
Salt/Ions

Question 11

Structure of the kidney- 3 parts

Answer 11

Cortex-darker outer region. Contains many blood vessels, microscopic filtering units; kidney tubules or nephrons
Medulla- middle layer has bulges called pyramids; tubules run down through this region.
Pelvis- funnel like structure that urine emptying and it connects with the ureter carrying the urine to the bladder

Question 12

Nephron or kidney tubule

Answer 12

In kidney to to act as the filtering units of blood to form urine
Nephrons are very small structures that have their own blood supply branching off the renal artery and are responsible for filtering a small amount of blood
Nephron has a cup shaped structure, 2 coiled tubules separated by a U- shaped loop and it is joined to a collecting duct

Question 13

Function of Bowman’s capsule

Answer 13

Filters the different sized molecules in the glomerulus under pressure in to the capsule in a process known as ultrafiltration

Question 14

Function of Glomerulus

Answer 14

High pressure in the glomerulus forces fluid to filter through the capillary and capsule walls

Question 15

Function of first coiled tube

Answer 15

Reabsorb all glucose from filtrate back into blood by active transport in a process known as Selective reabsorption

Question 16

Function of Loop of Henle

Answer 16

Reabsorb water and salts from the filtrate back into the blood

Question 17

Function of collecting duct

Answer 17

Reabsorbs most of the water in the blood depending on the ADH levels in blood in a process called osmoregulation

Question 18

2 main stages in the process of urine formation

Answer 18

Ultrafiltration in Bowman’s capsule
Selective reabsorption

Question 19

Ultrafiltration in the Bowman’s capsule

Answer 19

Blood vessel that carries blood away from the glomerulus has a smaller diameter than the blood vessel carrying blood in the glomerulus, so pressure in blood in the glomerulus is high
This pressure forces fluid from the blood into the Bowman’s capsule through the capsule wall
This filtrate is called glomerular filtrate
Only small items such as water, ions, glucose and urea can filter through.
Blood cells and plasma proteins are too big to filter through

Question 20

Selective reabsorption

Answer 20

First coiled tube and second coiled tube are separated by a U-shaped loop that runs down into the medulla of the kidney called the Loop of Henle
99% of glomerular filtrate is reabsorbed by the blood and 100% of glucose is reabsorbed
Sodium ions and glucose are reabsorbed by active transport

Question 21

Loop of Henle

Answer 21

U-shaped tube that involves with concentrating the fluid by reabsorbing more water back to the blood
Some salts and ions are reabsorbed back to the blood

Question 22

Size of Loop of Henle in animals

Answer 22

Long LH- can make more concentrated urine so that desert mammals can conserve water
Short LH- animals who have easy access to water
Mixture of long and short- human

Question 23

Osmoregulation and ADH

Answer 23

Control of body’s water content
Changes to volume of urine are controlled by hormone ADH produced by the pituitary gland
ADH travels through the blood to the kidney and acts on the kidney tubules
Action of ADH follows the principle of Negative Feedback

Question 24

Action of ADH

Answer 24

ADH causes the collecting ducts to be more permeable to water so that more water is reabsorbed back into the blood
This makes urine more concentrated, so body loses less water and blood becomes more dilute

Question 25

When blood volume is less

Answer 25

More ADH is released by the pituitary gland
This causes collecting duct to be more permeable to water, so more water is reabsorbed from urine through osmosis
Volume of blood increases and concentration decreases

Question 26

When blood volume is less

Answer 26

Less ADH is secreted by the pituitary gland into the blood
Kidney tubules become less permeable to water
More water passes out the body in urine