chapter 14

Question 1

Define homeostasis.

Answer 1

Homeostasis is the maintenance of a
constant internal environment by the
biological systems of the body.

Question 2

Why is homeostasis necessary?

Answer 2

Homeostasis ensures that the cells and tissues
of the body have the correct environment to
function e.g. optimum temperature and pH,
enough glucose for energy.

Question 3

Define negative feedback.

Answer 3

Negative feedback is a response of a biological
system. When a change from the optimum is
detected, the system that produced the change
is turned off to return the variable to its optimum
level.

Question 4

Which component of a biological system detects a stimulus?

Answer 4

A receptor.

Question 5

Describe the role of a coordination system in homeostasis.

Answer 5

A coordination system (e.g. nervous system,
endocrine system) receives information about
stimuli from receptors and determines what the
response should be by sending instructions to
effectors.

Question 6

In homeostasis, what are effectors?

Answer 6

Effectors are components of a homeostatic
mechanism that produce a response to a
stimulus. Muscles and glands are effectors.

Question 7

Describe the ways in which the body can
conserve heat in a cold environment.

Answer 7

● Shivering
● Vasoconstriction of blood vessels to prevent
heat loss from the blood
● Raising hairs to trap a layer of insulating air next
to the skin

Question 8

Describe the ways in which the body can
rapidly lose heat in a warm environment.

Answer 8

● Vasodilation of blood vessels to increase heat
loss from the blood
● Increase in sweating - as the sweat
evaporates, it cools the skin.

Question 9

Define osmoregulation. Why is it
important?

Answer 9

The regulation of the water potential of the
blood. It is important because cells may shrink
or burst if the water potential of the blood is
too high or low, due to movement of water by
osmosis.

Question 10

Where and how is urea formed?

Answer 10

Urea is produced in the liver from the deamination (removal of the amine group) of excess amino acids.

Question 11

Outline the gross structure of the kidney

Answer 11

https://ibb.co/FsHPnw9

Question 12

What is a nephron?

Answer 12

A nephron is one functional unit of the
kidney.

Question 13

Name the structures of the nephron. https://ibb.co/qFw0r0c

Answer 13

https://ibb.co/K9j1Pnb

Question 14

Outline the blood vessels associated
with a nephron.

Answer 14

An afferent arteriole from the renal artery forms the
glomerulus. The efferent arteriole takes blood away from the glomerulus.
The efferent arteriole branches to form the capillaries that surround the nephron tubules. These combine to form the renal vein which drains the kidney.

Question 15

Describe the process of ultrafiltration.

Answer 15

Within the glomerular capillaries, there is hydrostatic
pressure. This filters the blood, forcing water, glucose,
urea and ions into Bowman’s capsule to form the
glomerular filtrate.
Proteins and cells are too big and are not filtered into
Bowman’s capsule; they stay in the blood.

Question 16

Describe how the structure of Bowman’s
capsule and the glomerular capillaries is
suited to its function.

Answer 16

● The capillary endothelial wall is one cell thick, and there are gaps between cells to allow substances to pass through
● The renal capsule has podocytes, which have spaces in between them to allow the filtrate to pass into the renal capsule
● The connective tissue between the capillaries and renal capsule prevents larger molecules, like proteins and red blood cells, leaving the blood

Question 17

In which part of the nephron does
selective reabsorption occur?

Answer 17

In the proximal convoluted tubule.
Water, glucose and ions are reabsorbed
back into the blood.

Question 18

Describe the process of selective
reabsorption of glucose.

Answer 18

Co-transport of glucose with Na+ ions into the cells of the proximal convoluted tubule. Glucose diffuses out of the cell and into the blood.
Active transport of Na+ ions out of the cells is required to ensure there is a low concentration. This maintains the Na+ diffusion gradient.
The presence of glucose and Na+ ions in the cells reduces the water potential, which draws water out of the tubule by osmosis.

Question 19

What happens in the loop of Henle in the
nephron?

Answer 19

In the ascending limb, Na+ and Cl- are actively transported into the medulla. The water potential of the medulla is very low, which draws water out of the
descending limb by osmosis. The water potential of the
surrounding tissue is much lower at the bottom of the
loop than at the top.

Question 20

Describe what happens in the distal
convoluted tubule and collecting duct.

Answer 20

In the collecting duct, Na+ ions are actively transported out of the tubule, resulting in water reabsorption.
The collecting duct moves through the medulla tissue
which has a lower water potential from the loop of Henle. This results in further water reabsorption.

Question 21

What is the role of the hypothalamus in
osmoregulation?

Answer 21

It contains osmoreceptors which detect
the water potential of the blood. If the
water potential is low, the hypothalamus
releases antidiuretic hormone (ADH).

Question 22

Where is ADH released into the blood?

Answer 22

ADH from the hypothalamus is transferred to the
posterior pituitary gland where it is secreted into the
blood.

Question 23

Explain how ADH increases the water
potential of the blood.

Answer 23

ADH binds to receptors on the cells of the distal convoluted tubule and collecting duct. It increases the number of aquaporins in the membrane of the cells in this part of the nephron. This increases permeability to water, which increases absorption and therefore the water potential of the blood.

Question 24

What happens to the secretion of ADH
once the water potential of the blood has
been restored?

Answer 24

Secretion is reduced to prevent too much
water reabsorption, which would make the
water potential of the blood too high. This is
an example of negative feedback.

Question 25

What are the effects of hypoglycaemia
and hyperglycaemia?

Answer 25

● Hypoglycaemia - not enough glucose for respiration in cells. The cell cannot function normally.
● Hyperglycaemia - the high glucose concentration in the blood decreases the water potential. Water leaves the cells, preventing normal functioning.

Question 26

How is the pancreas involved in the
regulation of blood glucose?

Answer 26

● The pancreas contains islets of Langerhans, which consist of α-cells and β-cells
● The α-cells produce the hormone glucagon, whereas β-cells produce the hormone insulin
● The pancreas also has receptors to detect the blood glucose concentration

Question 27

When is insulin released?

Answer 27

Insulin is secreted into the blood when
the blood glucose concentration is high.

Question 28

Describe how insulin decreases the
blood glucose concentration.

Answer 28

● Insulin increases uptake of glucose into cells from the
blood by increasing the number of carrier proteins in the membrane
● Insulin stimulates the conversion of glucose into
glycogen in muscle and liver cells

Question 29

Which hormone is released from the
pancreas if the blood glucose
concentration is too low?

Answer 29

Glucagon

Question 30

Describe how glucagon increases the
blood glucose concentration.

Answer 30

● Glucagon stimulates liver cells to convert glycogen to
glucose (glycogenolysis)
● Glucagon stimulates liver cells to synthesise glucose
from non-carbohydrate sources such as amino acids
and lipids (gluconeogenesis)

Question 31

What effect does adrenaline have on
blood glucose concentration?

Answer 31

Adrenaline increases the concentration
of glucose in the blood by glycogenolysis, similar to glucagon.

Question 32

Outline the second messenger model in
the stimulation of liver cells by
adrenaline.

Answer 32

● Adrenaline binds to a receptor on the membrane of a liver cell
● Results in a conformational change in the receptor protein, which activates a G protein
● G protein stimulates an adenylyl cyclase enzyme in the cell
● Adenyl cyclase converts ATP into cyclic AMP
● Cyclic AMP is the second messenger; it binds to protein kinase A and activates it. The protein kinase phosphorylates other enzymes to amplify the signalling cascade
● Finally, the enzyme responsible for glycogenolysis is activated

Question 33

The presence of glucose and ketones in
the urine is indicative of which disease?

Answer 33

Diabetes mellitus

Question 34

Describe how a dipstick can measure the
concentration of glucose in an urine
sample.

Answer 34

The glucose oxidase on the stick reacts with glucose in the urine to form gluconolactone and hydrogen peroxide. Hydrogen peroxide reacts with the chromogen chemical on the stick, catalysed by peroxidase. The colour produced is compared against a chart to obtain a measurement of glucose concentration.

Question 35

Name and explain a method of
measuring the blood glucose
concentration.

Answer 35

A biosensor.
The strip from a biosensor contains glucose
oxidase, which reacts with the glucose in the
blood to produce gluconolactone. An electric
current is produced, which is measured by an
electrode.

Question 36

What may be the cause of protein in the
urine?

Answer 36

● Diseases affecting the glomeruli
● An infection of the kidney or urinary tract
● Congestive heart failure

Question 37

Which cells regulate the opening and
closing of stomata?

Answer 37

Guard cells

Question 38

In what conditions do stomata open and
close?

Answer 38

Stomata are open when there is high light intensity (to
allow diffusion of CO2 for photosynthesis).
Stomata may close during the night, during low humidity, high temperature and water stress to limit water loss by transpiration.

Question 39

Explain the mechanism by which guard
cells open the stomata.

Answer 39

The water potential of the guard cells drives the opening and closing of the pore. When the cell is turgid, the pore opens; when the cell is flaccid, the
pore closes.
The guard cells drive H+ ions out of the cell via proton pumps, using ATP. This activates K+ channels, leading to a high concentration of K+ in the cell. This reduces water potential, leading to osmosis of water into the cell and turgidity

Question 40

Explain the mechanism by which guard
cells close the stomata.

Answer 40

The guard cell membrane becomes depolarised as
ions (such as Cl-) leave the cell. This causes the
release of K+ ions, which increases water potential
of the cell. Water leaves by osmosis and the cell
becomes flaccid, closing the pore.

Question 41

What is abscisic acid?

Answer 41

A plant hormone released during water
stress.

Question 42

What effect does abscisic acid have on
stomata?

Answer 42

Abscisic acid causes the closure of
stomatal pores.

Question 43

Explain how abscisic acid brings about
the closure of stomata.

Answer 43

● Abscisic acid binds to receptors on the cell membrane of guard cells. This inhibits the proton pumps, causing a rise in pH. It also stimulates movement of Ca2+ ions into the cell
● The Ca2+ ions act as a second messenger, opening channels to allow anions and K+ ions to leave the cell
● This increases the water potential and causes water to leave the guard cells by osmosis, closing the stomata