Communication & Homeostasis

Question 1

What is the role of receptors?

Answer 1

receptors detect stimuli- they are specific and only detect one particular stimulus e.g. pressure, light or glucose concentration

Question 2

What are the different types of receptors?

Answer 2

some receptors are cells e.g. photoreceptors: they connect to the nervous system. Some are proteins on cell surface membranes e.g. glucose receptors are proteins found in the cell membranes of some pancreatic cells

Question 3

What are effectors?

Answer 3

they are cells that bring about a response to a stimulus to produce an effect. These include muscle cells and cells found in glands.

Question 4

What happens during cell signalling?

Answer 4

nervous system- cells communicate by secreting neurotransmitters which sends signals to adjacent cells e.g. nerve cells
hormonal system- cells release hormones which act as signals to distant cells; receptors allow cells to recognise the chemicals in cell signalling

Question 5

What are the three different neurones and what do they do?

Answer 5

Sensory neurones- transmit nerve impulses from receptors to the CNS
Motor neurones- transmit nerve impulses from the CNS to effectors
Relay neurones- transmit nerve impulses between sensory neurones and motor neurones

Question 6

What is the structure of the neurones?

Answer 6

have a cell body with a nucleus. the cell body has dendrites and dendrons that carry nerve impulses towards the cell body (dendrites are smaller branches of a dendron) axons carry nerve impulses away from the cell body.

Question 7

What is myelination?

Answer 7

an electrical insulator
allows the impulses to transmit faster as electrical impulses jump from one node of Ranvier to the next.
the cells also provide nutritional support

Question 8

What is the structure of a sensory neuron?

Answer 8

have short dendrites and one long dendron to carry nerve impulses from receptor cells to the cell body, and one long axon that carries nerve impulses from the cell body to the CNS

Question 9

What is the structure of a motor neuron?

Answer 9

have many short dendrites that carry nerve impulses from the CNS to the cell body, and one long axon that carries nerve impulses from the cell body to effector cells

Question 10

What is the structure of a relay neuron?

Answer 10

have many short dendrites that carry nerve impulses from sensory neurones to the cell body, and one axon that carries nerve impulses from the cell body to motor neurones

Question 11

What happens during nervous communication?

Answer 11

stimulus is detected
a nerve impulse is sent along a sensory neurone
when the nerve impulse reaches the end of a neurone, chemicals take the information across the synapse to the next neurone
the CNS processes the information & decides what to do about it
sends impulses along motor neurones to an effector

Question 12

Why are sensory neurones described as transducers?

Answer 12

the nervous system only sends information in the form of electrical impulses
sensory receptors convert the energy of a stimulus (light, kinetic, chemical) into electrical energy

Question 13

What is resting potential?

Answer 13

when nervous system receptors are in resting state (not being stimulated) . There’s a difference in charge between the inside and outside of a cell- the inside is negatively charged relative to the outside. This is achieved by an imbalance in concentrations of Na + and K + achieved by active transport. This means there’s a voltage/potential difference across the membrane and it is said to be polarised.

Question 14

What happens during resting potential?

Answer 14

sodium-potassium pumps use active transport to move 3 sodium ions out of the neurone for every 2 potassium ions moved in. Potassium ion channels allow the facilitated diffusion of potassium ions out of the cell. Voltage gated potassium and sodium ion channels are closed. In total, more positive ions move out than in making the outside +vely charged compared to the inside

Question 15

What happens during generator potential?

Answer 15

When a stimulus is detected, the cell membrane is excited and becomes more permeable.
allows ions to move in and out of the cell, altering the potential difference. Stimulus excites the membrane more causing a bigger movement of ions therefore, a bigger change in potential difference.

Question 16

What happens during the action potential?

Answer 16

if a generator potential is big enough it may reach the threshold level and trigger an action potential. An action potential is how impulses travel along a neurone.

Question 17

What is the pacinian corpuscle?

Answer 17

Its skin tissue (mechanoreceptor) that detects pressure and vibrations. When it’s stimulated e.g. by a tap on the arm, the lamellas is deformed and press on the sensory nerve ending. This causes deformation of stretch-mediated sodium channels in a sensory neurones cell membrane. The Sodium ion channels open and sodium ions diffuse into the cell creating a generator potential. If the generator potential reaches a threshold it triggers an action potential.

Question 18

What is the hormonal system?

Answer 18

It sends information as chemical signals and is made up of endocrine glands and hormones

Question 19

What are endocrine glands?

Answer 19

groups of cells that are specialised to secrete hormones.
Many hormones are proteins or peptides e.g. insulin.
Some hormones are steroids e.g. progesterone
They are secreted when an endocrine gland is stimulated. This could be due to a change in concentration of a specific substance or by electrical impulses

Question 20

What happens during hormonal communication?

Answer 20

Hormones diffuse directly into the blood then they’re taken around the body by the circulatory system.
They diffuse out of the blood and each hormone would bind to a specific receptor for that hormone found on the membrane of some cells called target cells.
Tissues that contain target cells are called target tissue. The hormones trigger a response in the target cells (effectors)

Question 21

What is the first and the second messenger in the action of hormones?

Answer 21

A hormone is called a first messenger because it carries the chemical message the first part of the way from the endocrine glands to the receptor on the target cells.
When it binds to its receptor it activates an enzyme in the cell membrane which catalyses the production of a signalling molecule.
This molecule signals other parts of the cell to change how the cell works.
The signalling molecule is called a secondary messenger because it carries the chemical message the second part of the way from the receptor to other parts of the cell.
Second messengers activate a cascade i.e. chain of reactions inside the cell.

Question 22

Describe the process of the action of adrenaline on the body?

Answer 22

Adrenaline is secreted from your adrenal glands when there’s a low concentration of glucose in your blood, when you’re stressed and when you’re exercising.
It gets the body ready for action by making more glucose available for muscles to respire.
Adrenaline is a first messenger. It binds to specific receptors in the cell membrane of many cells, activating an enzyme in the membrane called adenylyl cyclase. Activated adenylyl cyclase catalyses the production of a second messenger called cyclic AMP (cAMP) from ATP. This activates a cascade of enzyme reactions which makes glucose more available to the cell by catalysing the breakdown of glycogen into glucose (glycogenolysis)

Question 23

What is the structure of adrenal glands?

Answer 23

Each adrenal gland has an outer part called the cortex and an inner part called the medulla. The cortex and the medulla have different functions and hormones they secrete produce different responses to prepare for fight or flight

Question 24

Describe the function of the cortex.

Answer 24

It secretes steroid hormones e.g. cortisol and aldosterone when you’re stressed. Their effects include:
stimulating the breakdown of protein and fats into glucose, this increases the amount of energy available so the brain and muscles can respond to a situation
increasing blood volume and pressure by increasing the uptake of sodium ions and water by the kidneys
suppressing the immune system

Question 25

Describe the functions of the medulla.

Answer 25

It secretes catecholamine hormones e.g. it secretes adrenaline and noradrenaline when you’re stressed. They act to make more energy available in the short-term by increasing heart and breathing rate causing cells to break down glycogen into glucose and constricting some blood vessels so the blood is diverted to the brain and muscles

Question 26

What is the structure of a pancreas?

Answer 26

It’s a gland that contains endocrine tissue that is called islets of Langerhans. they’re found in clusters around blood capillaries and they secrete hormones directly into the blood. The two types of cells are:
alpha cells- secrete a hormone called glucagon (increases BGL)
beta cells- secrete and hormone called insulin (decreases BGL)

Question 27

What Is homeostasis?

Answer 27

the maintenance of a constant internal environment

Question 28

what is the effect of temperature on the body?

Answer 28

the rate of metabolic reactions increases when the temperature is increased more kinetic energy so molecules move faster substrate molecules more likely to collide with the enzymes active site energy of these collisions also increases which means each collision is more likely to result in a reaction
if temperature is too high the reaction stops.
rise in temperature makes the enzymes vibrate more the vibrations break some of the hydrogen bonds that hold the enzyme in its 3D shape.
active site changes shape no longer fit together and enzyme is denatured. if body temperature too low enzyme activity is reduced slowing metabolic rate reactions

Question 29

What is negative feedback?

Answer 29

when receptors detect when a level is too high or too low and communicate this to the effectors. The effectors respond to counteract the change bringing the level back to normal. It works with certain limits- if the change is too big then nf may not be able to counteract it

Question 30

What is positive feedback?

Answer 30

It amplifies the change- the effectors respond to further increase the level away from the normal level. it’s not involved in homeostasis because it doesn’t keep your internal environment constant. it’s useful to rapidly activates processes in the body

Question 31

What are ectotherms?

Answer 31

they can’t control their body temperature internally, they control their temperature by changing their behaviour. The internal temperature of ectotherms depends on the external temperature.
They have a variable metabolic rate because they can’t keep the internal temperature constant and generate very little heat themselves.
they are more active at higher temperatures and less active at lower temperatures

Question 32

What are endotherms?

Answer 32

They control their body temperature internally by homeostasis as well as by altering their behaviour. The internal temperature of endotherms is less affected by the external temperature. have a constantly high metabolic rate because they can keep their internal temperature constant.
They generate a lot of heat from metabolic reactions. level of activity is largely independent of the external temperature

Question 33

What are some mechanisms to reduce body temperature?

Answer 33

sweating- the water in sweat evaporates from the surface of the skin
hairs lie flat- have a layer of hair that provides insulation by trapping air. when it’s hot, the erector pili muscles relax so the hairs lie flat. less air is trapped so the skin is less insulated and heat can be lost more easily
vasodilation- when it’s hot, arterioles near the surface of the skin dilate more, blood flows through the capillaries in the surface layers of the dermis, this means more heat is lost from the skin by radiation and the temperature is lowered

Question 34

What are some mechanisms to increase body temperature?

Answer 34

shivering- when it’s cold, muscles contract in spasms, this makes the body shiver and more heat is produced from increased respiration
hormones- the body releases adrenaline and thyroxine- increase metabolism and so more heat is produced
much less sweat- is secreted from sweat glands when it’s cold reducing the amount of heat loss
hair stand up- erector pili muscles contract when it’s cold which makes the hair stand up. this trap small air and so prevents heat loss
vasoconstriction- when it’s cold arterioles near the surface of the skin constrict so less blood flows through the capillaries in the surface layers of the dermis- this reduces heat loss

Question 35

how does the hypothalamus control body temperature?

Answer 35

hypothalamus receives information about both internal and external temperature from thermoreceptors. thermoreceptors send impulses along sensory neurones to the hypothalamus which sends impulses along motor neurones to effectors.
the effectors respond to restore the body temperature back to normal

Question 36

what is the role of insulin in lowering blood glucose concentration?

Answer 36

insulin and glucagon act on effectors which respond to restore the blood glucose concentration to the normal level.
Insulin lowers the blood glucose concentration- when it’s too high it binds to specific receptors on the cell membranes of liver & muscle cells and increases the permeability of cell membranes to glucose- cells take up more glucose
it activates enzymes that converts glucose into glycogen, allowing them to store glycogen in their cytoplasm as an energy source (glycogenesis)
also increases the rate of respiration of glucose especially in muscle cells

Question 37

what is the role of glucagon in raising blood glucose concentration?

Answer 37

it binds to specific receptors on the cell membranes of liver cells and activates enzymes that break down glycogen into glucose (glycogenolysis)
it promotes the formation of glucose from glycerol and amino acids (gluconeogenesis)
glucagon decreases the rate of respiration of glucose in cells

Question 38

how do negative feedback mechanisms regulate blood glucose concentration?

Answer 38

when there is a rise in blood glucose concentration the beta cells secrete insulin and alpha cells stop secreting glucagon
receptors on the liver and muscle cells (effectors) respond to decrease the blood glucose concentration e.g. glycogenesis is activated
when there is a fall in blood glucose concentration the alpha cells secrete glucagon and the beta cells stop secreting insulin. glucagon binds to receptors on liver cells
they respond to increase the blood glucose concentration e.g. glycogenolysis is activated

Question 39

how is insulin secretion controlled by the beta cells?

Answer 39

beta cells contain insulin stored in vesicles they have k+ and Ca 2+ ion channels in their membrane
when the blood glucose concentration is around the normal level the k + channels are open and the Ca 2 + channels are closed
k+ ions diffuse out of the cell through the open k + channels which makes the inside of the cell membrane more negatively charged compared to the outside t(there are more positive ions outside the cell than inside) the membrane is polarised

Question 40

what happens when the Beta cells detect a high blood glucose concentration?

Answer 40

more glucose enters the beta cells by facilitated diffusion causing the rate of respiration to increase making more ATP
rise and ATP triggers the k+ ion channels in the plasma membrane to close
k+ ions can’t get through the membrane so they build up inside the cell
inside less negative because they’re more positively charged k+ ions inside the cell- plasma membrane of the b-cell is depolarised
depolarisation triggers Ca 2+ion channels in the membrane to open so Ca 2+ ions diffuse into the beta cell
causes the vesicles to fuse with the b-cell plasma membrane, releasing insulin by exocytosis

Question 41

what is type 1 diabetes?

Answer 41

autoimmune disease in which the body attacks and destroys the B cells in the islets of Langerhans
don’t produce any insulin
after eating, blood glucose concentration rises and stays high
kidneys can’t reabsorb all the glucose so some of it is excreted in the urine
usually develops in children or young adults
risk of developing is increased if there’s a close family history of the disease

Question 42

How do you treat Type 1 diabetes?

Answer 42

insulin therapy- having regular insulin injections throughout the day by using an insulin pump continuously delivers insulin into the body via tube inserted beneath the skin
transplantation- received healthy Islet cells from a donor so their pancreas can produce them insulin
need to think about diet and level of activity regular exercise

Question 43

what is type 2 diabetes ?

Answer 43

don’t produce enough insulin or when the body cells don’t respond properly to insulin because insulin receptors on their membranes don’t work properly so the cells don’t take up enough glucose
blood glucose concentration is higher than normal
usually acquired later in life than type 1
often linked with obesity
risk of developing is increased in people from certain ethnic groups e.g. African & Asian and people with close family history of the disease

Question 44

how do you treat type 2 diabetes?

Answer 44

managed through eating a healthy balanced diet getting regular exercise and losing weight if needed
medication may be prescribed:
Metformin- acts on liver cells to reduce the amount of glucose that they release into the blood & increases the sensitivity of cells to insulin so more glucose can be taken up with the same amount of insulin
Sulfonylureas- stimulate the pancreas to produce more insulin
Thiazolidinedione- also make the body cells more sensitive to insulin

Question 45

How is insulin extracted from GM bacteria?

Answer 45

insulin used to be extracted from animal pancreases (pig, cattle) to treat people with type 1 diabetes.
nowadays, human insulin can be made by genetically modifying bacteria
this is much better for many reasons:
it’s cheaper than extracting it from animal pancreases
larger quantities of insulin can be produced using GM bacteria
human insulin is more effective than using animal insulin- less likely to trigger an allergic response or be rejected by the immune system
it may be preferred for ethical or religious e.g. vegetarians may object to the use of animals and religious people may object to the use of using insulin from pigs

Question 46

Name a way in which we can cure diabetes

Answer 46

using stem cells could potentially cure diabetes
stem cells could be grown into b-cells which would then be implanted into the pancreas of a person with type 1 diabetes
the person will be able to make insulin as normal, curing people with type 1 diabetes