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OCR A level Biology HJ > Communication and homeostasis > Flashcards

Communication and homeostasis Flashcards

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1
Q

define homeostasis

A

Homeostasis is the process which ensures a constant internal environment is maintained. This allows cells to function normally despite internal or external changes.

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2
Q

what benefit do animals that carry out homeostasis have ?

A

Animals that can carry out homeostasis can live in a greater variety of habitats as they are more independent of changes in the external environment.

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3
Q

why do environmental changes need to be monitered?

A

These environmental changes need to be monitored as can potentially put stress upon an organism.

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4
Q

what does the blood transport around the body?

A
  • Transports nutrients and oxygen to tissues
  • Transports urea, removed from the blood by the liver, to the kidneys
  • Removes waste products from tissues, preventing their accumulation
  • Redistributes heat around the body to prevent overheating or overcooling
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5
Q

why is it that at different times the requirements surrounding the transport of blood changes?

A

For example, during activity,greater amounts of CO2 must be removed whilst moreO2must be delivered to respiring tissue.

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6
Q

what methods does the body use to modify the activity of the heart to respond to changes in demand for CO2 and O2?

A
  • Changing the heart rate (number of beats per minute)
  • Changing the contraction strength of the ventricles
  • Changing the stroke volume (the volume of blood transported per beat)`
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7
Q

what is the muscle of the heart called?

A

cardiac muscle

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8
Q

what does myogenic mean??

A

the heart can contract by itself without receiving signals from nerves

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9
Q

what is the sinoatrial (SAN) and what does it do?

A

The sinoatrial node (SAN) is the heart’s pacemaker and it can override the myogenic action of cardiac muscle to control heart rate. It is a region of tissue that can initiate an action potential.

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10
Q

what is the sequence of events controlling the basic heart rate?

A
  1. The SAN produces a wave of electrical excitation which spreads across the atria causing them to contract. The wave of excitation travels through the atrioventricular node (AVN) and down Purkyne fibres to the walls of the ventricles, causing them to contract
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11
Q

how is the heart rate controlled at rest?

A

At rest, the SAN controls the heart rate by maintaining a set frequency of waves of excitation. (resting heart rate is typically 60-80 beats per minute).

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12
Q

what changes the frequency of excitation waves in response to a change in output?

A

The frequency of excitation waves can be changed in response to output from part of the medulla oblongata called the cardiovascular centre.

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13
Q

where do the parasympathetic and sympathetic nerves come from and what do they do?

A

Parasympathetic and sympathetic nerves from the cardiovascular centre can stimulate the SAN

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14
Q

what is the acceleran nerve and what does it do?

A

The accelerans nerve is a sympathetic nerve. When stimulated it releases noradrenaline (a neurotransmitter) at the SAN, this results in an increase in heart rate

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15
Q

what is the vagus nerve and what does it do?

A

The vagus nerve is a parasympathetic nerve. When stimulated it releases another neurotransmitter (acetylcholine)at the SAN. This results in a decrease in heart rate

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16
Q

other than noradrenaline, what else increases the heart rate?

A

Heart rate can also be increased by adrenaline, a hormone present in the blood to which the heart muscle directly responds.

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17
Q

what is the role of sensory neurones in controlling heart rate?

A

Sensory receptors detect changes in the environment and adjust the heart rate accordingly. These receptors feed into the cardiovascular centre, which coordinates sensory inputs, ensuring SAN output is the appropriate response to the detected environmental change.

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18
Q

where are chemoreceptors located?

A

-in the walls of the carotid arteries and aorta

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19
Q

what do chemoreceptors do?

A

monitor the pH in the blood

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20
Q

how do chemoreceptors work when exercising?

A
  1. Exercising increases the concentration of CO2in the blood. The CO2reacts with water to produce carbonic acid, lowering the pH
  2. Chemoreceptors detect this change and signal to the cardiovascular centre
  3. In turn, this centre sends more frequent impulses along the accelerans nerve to the SAN, increasing heart rate.Consequently, more CO2passes to the lungs and is removed by them
  4. As the concentration of CO2in the blood decreases, the chemoreceptors are stimulated less and the heart rate slows to normal
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21
Q

where are stretch receptors found?

A

in the carotid sinus

22
Q

what do the stretch receptors do?

A

The pressure of the blood needs to be maintained at a set level. Stretch receptors in the carotid sinus detect changes in blood pressure and send signals to the heart.

23
Q

what happens with the stretch receptors if the blood pressure drops?

A
  1. If the blood pressure drops, stretch receptors detect this change and send action potentials to the cardiovascular centre in the medulla oblongata.
  2. This centre sends more frequent impulses along the accelerans nerve to the SAN of the heart
  3. This leads to an increase in heart rate and, by extension, blood pressure
24
Q

what is the role of the stretch receptors in the limb muscles?

A

There are also stretch receptors in the limb muscles. These detect when exercise is occurring and send impulses to the cardiovascular centre to modify the heart rate accordingly.

25
Q

what is the mechanism employed by chemoreceptors and stretch receptors an example of?

A

NEGATIVE FEEDBACK

26
Q

why is it important to regulate body temperature?

A
  • changes in body temp impact cellular activity
  • increase temp=increase kinetic enegy for molecules=more frequent collision=increase chemical reaction
  • too high of a temp can alter tertiary structure of enzymes, causing them to denature so have to regulate temperature to ensure reactions can happen as efficiently as possible
27
Q

whats the difference between an ectotherm and an endotherm?

A

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

endotherm = An organism that relies on heat from metabolic reactions to regulate its body temperature.

28
Q

what receptors detect temperature changes and how?

A
  • temperature changes are detected by temperature changes in the thermoregulatory centre of the hypothalamus
  • the hypothalamus then sends out impulses to effectors in the skin and muscles to reverse these changes
29
Q

what happens with endotherms if the body is too cold?

-name 5 responses

A
  • Endotherms increase the rate of exergonic reactions such as respiration. These reactions release heat, increasing the internal body temperature
  • Hairs and feathers stand erect, trapping air which insulates the body
  • Capillaries near the extremities constrict (vasoconstriction), reducing blood flow near the surface of the skin. This minimises heat loss from the blood
  • Spontaneous muscle contractions (i.e. shivering) occur to generate heat from respiration
  • The rate of respiration increases in liver cells so more energy from food is released as heat
30
Q

what happens with endotherms if the body is too hot?

-name 3 responses

A

• Sweat glands secrete fluid onto the surface of the skin. This evaporates removing heat from the blood • Animals that can’t sweat pant instead, removing heat through the evaporation of saliva• Capillaries under the skin dilate (vasodilation), directing blood to the surface of the skin. This increases heat loss from the blood

31
Q

why are mechanisms that regulate temp in endotherms switched off?

A

These responses return the body temperature to normal. The mechanisms then switch off, preventing the system from overshooting and moving further from the optimum. This is an example of negative feedback.

32
Q

what do peripheral temperature receptors do?

A

There are also peripheral temperature receptors in the skin, which monitor temperature in the extremities and relay this information to the hypothalamus. This allows the hypothalamus to respond more quickly (before blood temperature has changed), minimising variation in the core body temperature.

33
Q

what are some examples of ectotherms?

A

reptiles, amphibians, and most fish

34
Q

what are some responses that ectotherms have to being too cold?

A
  • Move away from shade
  • Expose more surface area to the sun
  • Move to a warm surface
35
Q

what are some responses that endotherms have to being too hot?

A
  • Move away from sun
  • Expose less surface area to the sun
  • Move underground
36
Q

what are some advantages of endotherms?

A
  • Can maintain their temperature despite changes in external temperature
  • Can remain active at time during the day when temperatures are low and can inhabit colder parts of the world
37
Q

what are some disadvantages endotherms?

A
  • More likely to overheat in hot weather as they have their own internal source of energy
  • Use a lot of energy to maintain their body temperature, therefore require much food
38
Q

what are some advantages of ectotherms?

A
  • More energy and nutrients from food can be used for growth.
  • Need to find less food and can survive for longer periods without food
39
Q

what are some disadvantages of ectotherms?

A
  • Less active when temperatures are low, meaning they are more at risk to predators
  • Have a smaller range of habitats in which they can thrive.
40
Q

what are some conditions that homeostatis helps maintain?

A
  • body temp
  • pH
  • blood pressure
  • water potential
  • blood glucose concentration
41
Q

what is the standard response pathway?

A
  1. stimulus
  2. receptor
  3. co-ordinator
  4. effector
  5. response
42
Q

what is the role of the receptor?

A

• Receptors (also known as sensory receptors) — these detect changes in the internal and external environment and relay this information to effectors

43
Q

what is the role of the co-ordinators?

A

• Co-ordinators (or communication pathway) — transmit the information from receptors (input) to effectors (output)

44
Q

what is the role of the effector?

A

• Effectors (e.g. muscle or liver cells) — these bring about a response

45
Q

what is negative feedback?

A

The body’s mechanism for reversing a change so that it returns back to the optimum.

46
Q

what are the steps in the mechanism of negative feeback?

A
  1. The receptor detects a change away from the optimum and responds by sending a signal to a co-ordinator (input)
  2. The co-ordinator integrates information from different receptors to determine the appropriate response then signals to the correct effector to carry out this response (output)
  3. Effectors bring about a change returning the internal conditions closer to their optimum point, thus reducing the stimulus
  4. The receptor responds to the reduction in stimulus, and reduces its input to the coordination centre
  5. The output from the coordination centre is also then reduced, and in turn the effectors reduce their activity
47
Q

what is positive feedback?

A

Positive feedback is the opposite of negative feedback and describes any deviation from the optimum which causes changes resulting in an even greater deviation from the norm.

48
Q

what are the effects of positive feedback?

A

This brings about a large, unstable change in the body. Positive feedback is usually harmful, but it can be useful in some cases, for example during action potentials in neurones.

49
Q

give an example of when negative feedback is useful?

A

An initial influx of sodium ions causes more sodium channels to open, leading to a greater sodium influx.

50
Q

how do receptors and effectors communicate?

A

-cell signalling

51
Q

what are some differences between the neuronal and hormonal communication system?

A

Neuronal System:
• The neuronal system uses neurones to carry signals through the body
• Signals are passed from one neurone to the next through synapses
• The neuronal system carries signals around the body very rapidly and usually produces a short-term response
Hormonal System:
• The hormonal system uses blood to carry signals through the body
• Endocrine glands release hormones (a cell signalling molecule) into the blood, where they travel to cells with receptors for the hormones
• The hormonal system usually co-ordinates long-term responses

52
Q

what are some features of a good communication system?

A
  • Cover the whole body — ensures that all of the receptors can communicate with all of the effectors
  • Allow for specific communication — a specific stimulus results in a specific response
  • Communicate rapidly — allows for a response to be co-ordinated immediately
  • Produce long and short-term responses — the length of the response depends on the stimulus

OCR A level Biology HJ (23 decks)

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