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Biology OCR A - A-level > Communication and homeostasis > Flashcards

Communication and homeostasis Flashcards

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1
Q

What is a change to an internal or external environment called?

A

Stimulus

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2
Q

What detects a stimulus?

A

Receptors

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3
Q

What are effectors?

A

Cells that bring a response to a stimulus (muscle cells)

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4
Q

What are photoreceptors?

A

Receptor cells that that connect to the nervous system

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5
Q

How do receptors and effectors communicate?

A

Cell signalling

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6
Q

What is the biological word for nearby?

A

Adjacent

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7
Q

What is homeostasis?

A

The maintenance of a constant internal environment

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8
Q

What happens to enzymes if the body temp is too high?

A

Become deantured - molecules vibrate too much - breaks hydrogen bonds - active site shape changes

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9
Q

What happens to enzymes if body temp is too low?

A

Enzyme activity reduced - Slows metabolic reactions

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10
Q

What is a humans optimum temperature?

A

37°c

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11
Q

What does the homeostatic system involve?

A

Receptors

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12
Q

What does the communication system involve?

A

Effectors

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13
Q

What type of feedback is the controlling of body temperature? Why?

A

Negative feedback - too hot/cold means effectors respond to decrease/increase temp

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14
Q

What is positive feedback useful for in protecting the body?

A

To rapidly activate something - blood clot after an injury

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15
Q

What are sensory neurones?

A

Transmitting nerve impulses from receptors to CNS

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16
Q

What is the CNS?

A

Central nervous system - brain and spine

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17
Q

What are motor neurons?

A

Transmit nerve impulses from CNS to effectors

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18
Q

What a relay neurones?

A

Transmit nerve impulses between sensory and motor neurones

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19
Q

What is the pathway of impulses? (5 steps)

A

1) Stimulus
2) Receptors
3) CNS
4) Effectors
5) Response

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20
Q

What do sensory receptors do?

A

Convert the energy of a stimulus into electrical energy

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21
Q

What does sensory receptors act as? And what is that?

A

Transducers - convert one form of energy into another

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22
Q

What is voltage known as?

A

Potential difference

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23
Q

What is the potential difference called when a cell is at rest?

A

Resting potential

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24
Q

What is the change in potential difference due to a stimulus called?

A

The generator potential

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25
Q

What does a bigger stimulus do?

A

Excites the membrane more, causes a bigger movement of ions and a bigger change in the potential difference

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26
Q

What happens if the generator potential is big enough?

A

It will trigger an action potential along the neuron

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27
Q

How is a generator potential being big enough determined?

A

If the generator potential reaches above the threshold level

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28
Q

What are pacinian corpuscles?

A

Mechanoreceptors - they detect mechanical stimuli and they are found in your skin

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29
Q

What is the sensory nerve of a pacinian corpuscle wrapped by?

A

Connective tissue called lamellae

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30
Q

Where is the cell body on a sensory neurone?

A

In the middle between the dendron and the axon

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31
Q

Where is the cell body on a motor neuron?

A

On the left of the axon

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32
Q

Where is the cell body on a relay neuron?

A

In the middle surrounded by an axon and dendrites

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33
Q

What charge is the outside of the membrane when a neuron is at a resting state?

A

Positively charged

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34
Q

What is the voltage of the membrane at resting potential?

A

-70 mV

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35
Q

How is the resting potential created?

A

By sodium-potassium pumps and potassium ion channels

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36
Q

What ions does the sodium-potassium pump transport?

A

Three sodium ions out and two potassium ions in

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37
Q

What ions does the potassium ion channel transport? and how?

A

Potassium ions out of the neuron by facilitated diffusion

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38
Q

What does a stimulus trigger to open?

A

Sodium ion channels to open

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39
Q

What is the 5 step sequence of an action potential?

A

1) Stimulus
2) Depolarisation
3) Repolarisation
4) Hyperpolarisiation
5) Resting potential

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40
Q

What is step 1 of an action potential and what happens in it?

A

Stimulus - this excites the neurone cell membrane and causes sodium on channels to open. Sodium ions diffuse into the neurone. Inside of the neurone becomes less negative.

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41
Q

What is step 2 of an action potential and what happens in it?

A

Depolarisation - if the potential difference reaches the threshold value Then voltage – gated sodium ion channels open. More sodium ions diffuse into the neuron.

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42
Q

What is the threshold value?

A

-55 mV

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43
Q

What sort of process is depolarisation?

A

Positive feedback

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44
Q

What is step 3 of an action potential and what happens in it?

A

Repolarisation - when potential difference is +30, sodium are on channels close. Voltage – gated potassium ion channels open. Potassium ions diffuse out and membrane it begins to return to its resting potential.

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45
Q

What sort of process is repolarisation?

A

Negative feedback

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46
Q

What is step 4 of an action potential and what happens in it?

A

Hyperpolarisation - Potassium ion channels are slow to close, so too many potassium ions diffuse out of the neuron. Potential difference becomes more negative negative than the resting potential.

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47
Q

What is step 5 of an action potential and what happens in it?

A

Resting potential - ion channels are reset. The sodium-potassium pump returns the membrane to its resting potential.

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48
Q

What is the period between the beginning of repolarisation and the beginning of the resting potential called?

A

The refractory period

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49
Q

Why can’t there be another action potential straight after one?

A

The refractory period is occurring

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50
Q

How does an action potential move along the neuron?

A

A wave of depolarisation- sodium ions diffuse sideways, meaning that ion channels in the next region open and causes a wave to travel along the neurone.

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51
Q

Describe the impulses of small and big stimulus’.

A

A small stimulus will have less frequent action, potentials, and a big stimulus would have more frequent action potentials

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52
Q

What do myelinated neurons do to action potentials?

A

Speed up the action potential

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53
Q

What is a myelin sheath?

A

An electrical insulator made up of Schwann cells

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54
Q

What are nodes of Ranvier?

A

Tiny patches of membrane where the myelin sheath isn’t present - sodium ion channels are located here

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55
Q

What is saltatory conduction?

A

Where the cytoplasm of myelinated neurones conducts enough electrical charge to depolarise the next node, so the impulse jumps from node to node very fast

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56
Q

Why are non-myelinated neurons slower?

A

Because the impulse travels along the whole length of the axon membrane

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57
Q

What is a synapse?

A

The junction between a neuron and another neuron

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58
Q

What is the gap between the cells at the synapse?

A

The synaptic cleft

59
Q

What part of the neuron contains vesicles?

A

The end of the pre-synaptic neuron - the synaptic knob

60
Q

When are neurotransmitters released into the synaptic cleft?

A

When an action potential reaches the end of a neuron

61
Q

What are the three outcomes of a neurotransmitter binding to a receptor?

A

1) trigger an action potential
2) cause muscle contraction
3) cause a hormone to be secreted

62
Q

Why doesn’t the response keep happening after the neurotransmitters have been secreted into the cleft?

A

Neurotransmitters are removed from the cleft by the pre-synaptic neuron and broken down

63
Q

What are the two examples of neurotransmitters?

A

Acetylcholine and noradrenaline

64
Q

What are signups is that use Acetylcholine called?

A

Cholinergic synapses

65
Q

What is the enzyme that breaks down acetylcholine called?

A

Acetylcholinesterase (AChE)

66
Q

What are three steps of neurotransmitters transmitting nerve impulses between neurons?

A

1) an action potential triggers a calcium influx
2) A calcium influx causes a neurotransmitter release
3) the neurotransmitter triggers an action potential in the post synaptic neuron

67
Q

How do calcium ions? Enter enter enter the pre and post synaptic neurons?

A

Voltage gated sodium ion channels

68
Q

What is an excitatory synapse?

A

Neurotransmitters depolarise the post synaptic membrane - this fires an action potential if the threshold is reached

69
Q

What is an inhibitory synapse?

A

Neurotransmitters bind to receptors on the post-synaptic membrane and hyper polarise it, preventing an action potential from being fired

70
Q

How do synapses allow information to be dispersed? What is this called?

A

One neuron connects to many neurons and disperses the message to different parts of the body - Synaptic divergence

71
Q

How do synapses allow information to be amplified? What is this called?

A

Many neurons connect to one neuron - synaptic convergence

72
Q

What is summation?

A

The effect of neurotransmitters can be combined

73
Q

What is spatial summation?

A

Neurons converge meaning the small amount of neurotransmitter released from each neuron can be enough altogether to reach the threshold

74
Q

What is temporal summation?

A

Two or more nerve impulses arrive in quick succession from the same neuron - action potential is more likely

75
Q

How do you signup is ensure impulses are only transmitted one way?

A

Receptors are only located on the post-synaptic membranes

76
Q

What are endocrine glands?

A

A group of cells that are specialised to secrete hormones

77
Q

What are hormones?

A

Chemical messengers, that are usually proteins, peptides or steroids

78
Q

When are hormones secreted?

A

When an endocrine gland is stimulated by either an electrical impulse or a change in the concentration of a specific substance

79
Q

Where do hormones go?

A

Directly into the blood and taken around the body by the circulatory system

80
Q

Where do hormones end up?

A

They bind to specific receptors found on the membranes of target cells

81
Q

What is the five step hormonal system?

A

1) stimulus
2) receptors
3) hormone
4) effectors
5) response

82
Q

What is the first messenger in the hormonal system? Why?

A

The hormone - it carries the message from the endocrine gland to the receptor on the target cell

83
Q

What happens when a hormone binds to its receptor?

A

It activates an enzyme in the cell membrane

84
Q

What does the enzyme released after a hormone bind to its receptor do?

A

Catalyses the production of a signalling molecule inside the cell

85
Q

What does a signalling molecule do?

A

Activates a cascade of events - carries the chemical message from the receptor to the other parts of the cell

86
Q

Describe the steps of the hormone adrenaline working.

A

1) adrenaline binds to specific receptors
2) this activates adenylyl cyclase
3) adenylyl cyclase catalyses the production of cAMP
4) cAMP activates a cascade of events to make more glucose available (glycogen to glucose)

87
Q

Where are adrenal glands located?

A

Above your kidneys

88
Q

What is the structure of an adrenal gland?

A

An inner part called the medulla and an outer part called the cortex

89
Q

What does the cortex of an adrenal gland do? Give an example

A

Secretes steroid hormones when you’re stressed - cortisol

90
Q

What does the medulla of an adrenal gland do? Give an example.

A

Secrets catecholamine hormones when you’re stressed - adrenaline and noradrenaline

91
Q

What type of responses do the steroid hormones from the cortex produce?

A

Short and long-term responses

92
Q

What type of responses do the hormones in the medulla produce?

A

Short term responses

93
Q

What type of gland is the pancreas?

A

And endocrine gland

94
Q

Describe how the pancreas functions.

A

Islets of langerhans Secrete hormones directly into the blood to help control blood glucose concentration

95
Q

What are the two cells that make up the islets of langerhans and what do they secrete?

A

Alpha cells that secrete glucagon hormone and beta cells that secrete insulin hormone

96
Q

How can you differentiate between alpha and beta cells?

A

If a special stain has been used to make them different colours

97
Q

Once the special stain is used, how can you tell apart alpha and beta cells?

A

Alpha cells are pink stained and beta cells are purple stained

98
Q

What are ectotherms?

A

Reptiles and fish that can’t control their body temperature internally

99
Q

What are endotherms?

A

Mammals and birds that can control their body temperature internally by homeostasis

100
Q

How do ectotherms control their temperature? Give an example.

A

By altering their behaviours - reptiles gain heat by basking in the sun

101
Q

How can endotherms control their body temperature? Give two examples.

A

Internally by homeostasis, but also by altering behaviour such as finding shade to cool down

102
Q

What is the metabolic rate of an ectotherm?

A

Variable and they generate little heat themselves

103
Q

What is the metabolic rate of an endotherm?

A

Constantly high and they generate a lot of heat from metabolic reactions

104
Q

What are the three mechanisms to reduce a mammal body temperature?

A

1) sweating
2) hairs lying flat
3) vasodilation

105
Q

How does sweating reduce body temperature?

A

The water in sweat evaporating takes heat from the body

106
Q

How does hair lying flat reduce body temperature?

A

Less air is trapped meaning that the skin is less insulated

107
Q

How does vasodilation reduce body temperature in mammals?

A

Arterioles near surface of the skin dilate - causes more blood to flow through capillaries in the surface layer of the dermis - resulting in heat loss from the skin by radiation

108
Q

What are the five mechanisms to increase the body temperature of mammals?

A

1) shivering
2) much less sweat
3) hairs stand up
4) vasoconstriction
5) hormones

109
Q

How does shivering increase body temperature?

A

More heat is produced from the increased respiration as a result of muscle spasms

110
Q

How does much less sweat increase body temperature?

A

Less sweat secreted means heat loss is reduced

111
Q

How does hair standing up increase body temperature?

A

Has standing up traps more air and prevents heat loss

112
Q

How does vasoconstriction increase body temperature?

A

Arterioles near the surface constrict so less blood flows through the capillaries and reduces heat loss

113
Q

How do hormones increase body temperature?

A

Adrenaline and thyroxine increase metabolism so more heat produced

114
Q

How do hairs stand up and lie flat?

A

Erector pilli muscles contact and relax

115
Q

What part of the brain is responsible for controlling body temperature in mammals?

A

The hypothalamus

116
Q

What is the name of the temperature receptors responsible for giving information to the hypothalamus?

A

Thermoreceptors

117
Q

What do firmer receptors in the hypothalamus detect?

A

Internal temperature - the blood

118
Q

What do Thermo receptors in the skin detect?

A

External temperature - temperature on the skin

119
Q

What are the thermoreceptors on the skin called?

A

Peripheral temperature receptors

120
Q

What happens to blood glucose concentration after eating food containing carbohydrates?

A

Blood glucose concentration rises

121
Q

What happens to blood glucose concentration after exercise?

A

Blood glucose concentration falls - glucose used in respiration

122
Q

What does insulin do?

A

Lowest the blood glucose concentration when it’s too high

123
Q

How does insulin lower blood glucose concentration?

A

1) defines two specific receptors on liver and muscle cells
2) increases permeability of cell so cell takes up more glucose
3) Cells store glycogen in the cytoplasm via glycogenesis

124
Q

How is glycogen formed?

A

By insulin activating glycogenesis to convert glucose to glycogen

125
Q

What does glucagon do?

A

Raises blood glucose concentration when it’s too low

126
Q

How does glucagon raise blood glucose concentration?

A

1) glucagon binds to specific receptors on the liver cells
2) glucagon, activates enzymes that breaks down glycogen to glucose
3) glycogenolysis occurs
4) Glucagon also promotes formation of glucose from glycerol and amino acids

127
Q

What is glycogenolysis?

A

The breaking down of glycogen to glucose

128
Q

What is the process of forming glucose from non-carbohydrates called?

A

Gluconeogenesis

129
Q

What occurs in gluconeogenesis?

A

Glycerol and amino acids are converted to glucose

130
Q

What type of feedback does insulin and glucagon trigger?

A

Negative feedback

131
Q

How do beta cells secrete insulin?

A

1) when blood glucose concentration is high, more glucose enters the beta cells
2) high glucose causes rate of respiration to increase - more ATP
3) Potassium ions can’t get through membrane, so they build up inside cell
4) inside of the cell becomes less negative (potassium positive) so membrane is depolarised
5) calcium ion channels open
6) vehicles containing insulin fuse with membrane and release by exocytosis

132
Q

What is diabetes?

A

A condition where blood glucose concentration can’t be controlled properly

133
Q

What is the main difference between type one diabetes and type two diabetes?

A

Type one is where the body attacks and destroys beta cells and type two is where beta cells can’t produce enough insulin or when the body doesn’t respond properly to insulin

134
Q

What age group does type one diabetes usually develop in?

A

Children or young adults

135
Q

What are the three treatment types for type one diabetes?

A

1) insulin therapy - injections
2) islet cell transplantation
3) monitoring their diet (balanced diet and regular exercise)

136
Q

What age group does type two diabetes usually develop in?

A

Later in life than type one

137
Q

Why don’t the body cells respond properly to insulin in type two diabetes?

A

Insulin receptors on their membranes don’t work properly so the cells don’t take up enough glucose

138
Q

What are the three treatment options for type two diabetes?

A

1) lifestyle changes
2) medication
3) insulin therapy - injections

139
Q

What sort of lifestyle changes would be required in type two diabetes?

A

Healthy eating and regular exercise

140
Q

What is the main example of a medicine that can be prescribed for type two diabetes? How does it work?

A

Metaformin - it acts on liver cells to reduce the amount of glucose they release into the blood and also increases the sensitivity of cells to insulin so more glucose can be taken up

141
Q

How did insulin used to be extracted?

A

From pancreases of pigs or cattle to treat type one diabetes

142
Q

How is insulin produced nowadays?

A

Genetically modified bacteria

143
Q

Why is using genetically modified bacteria to produce insulin better than extracting from animal pancreases?

A

• It is cheaper
• Larger quantities can be produced
• It is more ethical
• GM bacteria produces human insulin, which is more effective than pig or cattle insulin

144
Q

How could stem cells be used to cure diabetes?

A

Because stem cells are unspecialised and can develop into any type of cell, they could be grown into beta cells and then implanted into the pancreas of a person with type one diabetes

Biology OCR A - A-level (24 decks)

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