Communication and Homeostasis

Question 1

Why do multicellular organisms need a communication systems?

Answer 1

Need to respond to changes in internal environment such as temperature, pH, toxins blah blah
Need to respond to changes in external environment to reduce external stress e.g. cold
Need to co-ordinate the activities of different organs

Question 2

How do cells communicate?

Answer 2

Cell signalling

Question 3

Give some examples of cell signalling

Answer 3

Neuronal and hormonal

Question 4

Define negative feedback

Answer 4

The process that brings about a reversal of any change in conditions. It ensures that an optimum steady state can be maintained, as the internal environment is returned to its original set of conditions after any change. It is essential for homeostasis.

Question 5

Define positive feedback

Answer 5

The process that increases any change detected by teh receptors. It tends to be harmful and doesn’t lead to homeostasis. Examples include secretion of labour hormone oxytocin and opening of sodium ion channels in nerves.

Question 6

Define homeostasis

Answer 6

The maintenance of the internal environment in a constant state despite external changes

Question 7

What is the general process of negative feedback in the context of maintaining an internal environment?

Answer 7

Change away from optimum conditions
Receptors detect change
Communication system informs effectors 
Effector reacts to reverse change
Return to optimum conditions

Question 8

Define ectotherm

Answer 8

An organism that relies on external sources of heat to regulate its body temperature

Question 9

How do ectotherms regulate their body temperature?

Answer 9

Warming up: bask in sun
Cool down: hide in burrow
Can orientate themselves to either face sun, or be side on
Can alter surface area to increase heat exchange
Can increase breathing rate to increase water loss

Question 10

Define endotherm

Answer 10

An organism that can use internal sources of heat, such as heat generated from metabolism in the liver to maintain its body temperature

Question 11

What physiological mechanisms to endotherms employ to regulate body temperature?

Answer 11

Sweat glands in skin release more/let sweat
Panting to increase water evaporation if too hot
Hairs lie flat so not much insulation if too hot
Arterioles leading to capillaries vasodilate if too hot to increase heat exchange
Liver cells adjust rate of metabolism (respiration produces heat)
Skeletal muscles will contract (shivering) generating heat

Question 12

What behavioural mechanisms do endotherms employ to regulate body temperature?

Answer 12

Seek shade/sunlight
Orientate body to change surface area exposed to sun
Adjust how much you are active

Question 13

How is the body temperature controlled in endotherms?

Answer 13

Change in core temperature; thermoregulatory centre in hypothalamus detects change; nervous and hormonal system carry signals to skin, liver and muscles; less/more heat generated and more/less heat lost; return to optimum temperature

Question 14

What is the role of sensory receptors?

Answer 14

They are energy transducers: they convert energy from one type to electrical energy, sending off an impulse.

Question 15

What are the differences in appearance between sensory and motor neurones?

Answer 15

Sensory neurones have cell body to one side; motor neurones have it in the line of impulse
Sensory neurones have a long dendron; motor neurones have very short/non-existant dendrons
Sensory neurones have a short axon; motor neurones have a longer axon

Question 16

Describe the structure and function of a generic nerve cell

Answer 16

Long, so can transmit impulses over long distances
Many gated ion channels to control entry and exit of ions such as sodium
Have Na/K pumps that use ATP to maintain resting potential
Often surrounded by Schwann cells for insulation
Have gaps called nodes of Ranvier in Schwann cells so impulse can be transmitted
Cell body contains many mitochondria for ATP, and ribosomes for protein synthesis
Many dendrites so can connect and pass info to lots of different nerves

Question 17

How is the resting potential of a nerve cell maintained?

Answer 17

Sodium/Potassium pumps use ATP to pump 3Na out of the cell and 2K into the cell.
Potassium ions then diffuse out again through potassium ion leak channels - the membrane is more permeable to potassium
In this way, the interior of the cell is more negative than the exterior: the membrane is polarised at about -70mV

Question 18

How is an action potential generated?

Answer 18

If some sodium ions enter the cell, the potential changes, Voltage-gated sodium ion channels detect this change and open, allowing sodium to flood in down its electrochemical gradient, depolarising the membrane
The VG channels will only respond to a large change in potential, so depolarisation must be big enough to reach threshold potential: all or nothing response

Question 19

What occurs during an action potential?

Answer 19

Once the depolarisation has reached the threshold value (around -50mV), all the voltage gated sodium ion channels open, allowing sodium ions to flood in down their electrochemical gradient. The cell becomes positively charged compared to the outside. The membrane potential reaches +40mV
VG sodium channels close, and VG potassium ion channels open, and potassium ions diffuse out of cell, down their electrochemical gradient. Cell becomes negatively charged again, repolarising the membrane. The VG K channels close slowly, so the cell becomes hyperpolarised. The Na/K ATP pumps restore the resting potential

Question 20

How does an action potential travel down a myelinated neurone?

Answer 20

Under the myelin sheath, there are no ion channels, as the Schwann cells insulate the membrane (waste of bioresources)
Therefore, movement of ions occurs at the nodes of Ranvier in the gaps between the Schwann cells
At one node of Ranvier, an action potential occurs, meaning sodium ions diffuse into the cell
That part of the cell becomes positively charged with a high conc. of Na+, whilst at the next node, the cell is negatively charged with a low conc. of Na+, so Na+ ions move down to next node in local currents
This sets of the action potential at the next node, called saltatory conduction

Question 21

What is the significance of the frequency of impulse transmission?

Answer 21

The brain can’t determine the intensity of a stimulus by one action potential: they are all the same. However, a more intense stimulus will cause action potentials to be fired more frequently, from which the brain can determine the intensity of the stimulus.

Question 22

Describe the structure of a cholinergic synapse

Answer 22

The synaptic knob contains many mitochondria, a lot of smooth ER, vesicles containing the chemical acetylcholine
The presynaptic membrane contains voltage gated calcium ion channels
The postsynaptic membrane has specialised sodium ion channels with 5 peptide subunits that respond to the presence of acetylcholine. 2 signalling molecules need to bind for the channel to open

Question 23

How are action potentials transmitted across a cholinergic synapse?

Answer 23

An action potential arrives at the synaptic knob
Voltage gated calcium ion channels open; calcium ions diffuse in
Calcium ions cause synaptic vesicles containing acetylcholine to move towards and fuse with the presynaptic membrane
Acetylcholine is released by exocytosis
Acetylcholine diffuses across the synaptic cleft
AC binds with sodium ion channels, causing them to open and sodium to flood in
An excitatory postsynaptic potential is generated
If potential change is sufficient, an action potential begins
Acetylcholinesterase breaks down acetyl choline into ethanoic acid and choline, closing the sodium channels

Question 24

What is the neurotransmitter and enzyme associated with cholinergic synapses?

Answer 24

Acetylcholine and Acetylcholinesterase

Question 25

What is the role of synapses in the nervous system?

Answer 25

If presynaptic neurones converge to one postsynaptic neurone, different parts of the nervous system can create the same response
If one presynaptic neurone diverges to many postsynaptic neurones, one bit of info could be transmitted to brain and muscle and other
Ensures signals only go in one direction
Can filter out low level signals
Low level signals can be amplified by summation if it is persistent or several presynaptic neurones release the same signal
If a synapse runs out of vesicles, no longer transmits action potential: acclimatisation
Creates specific pathways within the nervous system: basis for thought and memory

Question 26

Define endocrine gland

Answer 26

A gland that secretes hormones directly into the blood. Endocrine glands have no ducts

Question 27

Define exocrine gland

Answer 27

A gland that secretes molecules into a duct that carries the molecules to where they are used

Question 28

Define hormone

Answer 28

Molecules that are released by endocrine glands directly into the blood. They act as messengers, carrying a signal from the endocrine gland to a specific target organ or tissue

Question 29

Define target tissue

Answer 29

Tissues that possess a specific receptor on their plasma membrane. The shape of the receptor is complementary to the shape of the hormone molecule.

Question 30

Explain the meaning of the term first messenger

Answer 30

The hormone that transmits a signal around the body. Adrenaline is an example of a first messenger

Question 31

Explain the meaning of the term second messenger

Answer 31

The molecule that transmits a signal inside the cell. For example, adrenaline is protein based, and therefore can’t enter a cell, so it binds to a receptor that, when adrenaline attaches to it, activates a molecule of cAMP (made from ATP), which makes changes in a cell through enzyme action

Question 32

What are the functions of the adrenal glands?

Answer 32

In the centre, is the adrenal medulla. This makes and releases adrenaline as a response to stress.
The adrenal cortex produces several steroid hormones from cholesterol. These have a variety of functions such as helping to control the concentrations of Na and K in the blood and controlling the metabolism of carbohydrates and proteins

Question 33

Describe the effects of adrenaline

Answer 33

Relaxed smooth muscle in bronchioles
Increased stroke volume and heart rate
Vasoconstriction to raise blood pressure
Conversion of glycogen into glucose
Dilate pupils
Increase mental awareness
Inhibit action of gut
Erect body hair

Question 34

Describe the histology of the pancreas

Answer 34

The acinar cells are found in small groups at the end of tiny tubules into which they secrete digestive enzymes such as amylase, trypsinogen, lipase. The tubules join up to form the pancreatic duct. The fluid also contains sodium hydrogencarbonate to make it alkaline
The islets of Langerhans contain alpha and beta cells that secrete insulin and glucagon directly into the blood. They are well supplied with blood capillaries

Question 35

How is the concentration of blood glucose regulated?

Answer 35

Rise/fall of glucose concentration detected by beta cells in islets of Langerhans; beta/alpha cells secrete insulin/glucagon; insulin/glucagon detected by chemoreceptors on liver and muscle/liver cells; liver and muscle cells remove glucose from blood and convert it to glycogen/liver cells convert glycogen to glucose which is released into the blood; return to optimum concentration.

Question 36

What happens when insulin is released?

Answer 36

Insulin binds specific, complementary receptors on target cells in liver, muscles and some brain cells. This activates adenyl cyclase which converts ATP to cAMP which activates some enzyme-controlled reactions.
More glucose channels are placed into plasma membranes
More glucose enters cells
Glucose is converted to glycogen, fats and used in respiration

Question 37

How is insulin secretion controlled?

Answer 37

Beta cell membranes contain calcium and potassium ion channels. The K channels are usually open; the Ca channels are closed
K diffuses out of the cell, making the inside more negative; resting potential of -70mV
If glucose concentration is high, glucose diffuses into the cell
Glucose is metabolised to produce ATP
ATP causes the potassium ion channels to close
The potential difference across the membrane changes
Voltage gated calcium ion channels open
Calcium ions enter the cell, and cause vesicles containing insulin to move to the plasma membrane and fuse with it, releasing insulin by exocytosis

Question 38

What is type-I diabetes?

Answer 38

The result of an autoimmune response/viral issue in which your immune system/a virus attacks the beta cells, meaning the body can’t produce insulin and store excess glucose as glycogen

Question 39

What is type-II diabetes?

Answer 39

When the body can still produce insulin, but the target cells become less sensitive to the hormone. This is due to receptors declining and/or decreased levels of insulin release. Contributing factors include obesity, high sugar diet and family history

Question 40

How can diabetes be treated?

Answer 40

Type-II: careful monitoring of diet, matching carbohydrate intake to use. Insulin injections may boost this as well as other drugs that slow down the absorption of glucose from the digestive system
Type-I: insulin injections. Blood glucose conc. is monitored, and correct dosage of insulin is administered to maintain a stable concentration

Question 41

How can insulin be produced for diabetes treatment?

Answer 41

It was extracted from pigs, but the fit wasn’t so great, and was expensive and space-using etc…
Now can be made from genetically engineered bacteria

Question 42

What are the advantages of using insulin from genetically engineered bacteria?

Answer 42

Exact copy of proper shape (faster acting; more effective)
Less chance of developing tolerance
Less chance of immune system rejecting it
Lower risk of infection
Cheaper
Process more adaptable to demand
Less moral objections

Question 43

What are the potential uses of stem cells in treating diabetes?

Answer 43

Could be a treatment for type-I diabetes. If can find precursor cells in human pancreas (like in mice) could be made to produce new beta cells for patients

Question 44

How is our heart rate controlled?

Answer 44

Heart muscle is myogenic
Nerves from cardiovascular centre in medulla oblongata in brain help regulate the frequency of contraction
Receptors in cardiovascular centre detect things like blood pressure (carotid sinus) and pH and muscle stretch receptors and respond by adjusting impulses sent down accelerator nerve and vagus (decelerator) nerve.
Adrenaline also has an effect on the heart rate