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Biology OCR AS Level > Homeostasis > Flashcards

Homeostasis Flashcards

1
Q

What conditions in the cell need to be maintained?

A
  • A suitable temperature
  • A suitable PH
  • An aqueous environment that keeps the substrates and products in solution
  • Freedom from toxins and excess inhibitors
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2
Q

Why do cells needs certain conditions to be maintained?

A

This is because cell metabolism relies on enzymes that require specific conditions to work efficiently or else they will die.

*Cells are specialised and rely upon one another therefore they must be able to communicate in order to coordinate their activities.

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3
Q

All organisms have an external environment, when this changes it may place stress on the living organism. What is a stimulus?

A

A change in the environment that brings about a response (the behavioural or physiological change in an organism due to the stimulus). Responses can be gradual or rapid.

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4
Q

What is the external environment of cells? (This is known as the internal environment of humans)

A

The extracellular fluid in which cells and tissues are bathed in. Extracellular fluid circulates constantly within the blood and lymphatic system. In the blood, that would be plasma. In the tissue that would be tissue fluid.

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5
Q

How can the external environment of cells change?

A

The activities of a cell can change their own environment. As they undergo metabolic activities, substrates are used up and new products are made. These products can be toxic or unwanted. For example, when CO2 is made, it diffuses into the tissue fluid. If it accumulates, PH of tissue fluid changes affecting enzyme activity.

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6
Q

What is the stimulus when CO2 accumulates in the tissue fluid?

A

When CO2 accumulates, it causes a change in the PH. This change in PH is the stimulus.

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7
Q

What is the response to the change in PH of the blood due to accumulation of CO2?

A

Accumulation of CO2 = PH changes (becomes more acidic) – stimulus = Breathing activity increases to expel accumulated CO2 – response.

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8
Q

How may the waste products (such as CO2) have a direct effect on the cell?

A

May stimulate the cell to produce less of the waste product, by reducing activity – may have a negative impact on cell.

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9
Q

How is the internal environment in tissues maintained?

A

The internal environment of the tissues is the tissue fluid, the composition of tissue fluid is maintained by blood. Any waste or toxic products accumulating in the tissue fluid, move into the blood. To prevent the waste products from accumulating in the blood, it is transported to the correct organs to be removed.

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10
Q

Why does the concentration of waste products in the blood need to be monitored apart from the fact that it will cause a change in the internal environment that may affect enzyme activity and affect the functioning of cells?

A

Concentration of waste products are monitored to ensure that the body does not excrete too much of any useful products but still removes enough waste products to maintain good health (waste products and useful substances are removed at the same time) – ensures that cells in the body are supplied with the substrates they need.

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11
Q

Why are multicellular organisms more efficient than single-celled organisms?

A

Cells are differentiated - different cells are specialised to perform a particular function. Cells performing similar functions form tissues and organs. Different groups of tissues carry out different roles – rather than one cell doing all of the functions.

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12
Q

Why is a communication system required in the body?

A

As different cells are specialised to carry out different roles, they may be located in different parts of the body i.e. those that produce waste products may be in a different place to those remove the waste products. Therefore in order for these different parts of the body to work together, a communication system is needed (something that tells it do what and when).

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13
Q

A good communication system will…?

A
  • Cover the whole body
  • Enable cells to communicate with each other
  • Enable specific communication
  • Enable rapid communication
  • Enable both short-term and long-term responses
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14
Q

How do these different cells (at different parts of the body) communicate?

A

Via cell signalling – where one cell will release a chemical (e.g.neurotransmitters + hormones) that will be detected by another cell that responds appropriately.

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15
Q

Which two communication systems work by cell signalling?

A
  • Neuronal system

- Hormonal system

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16
Q

What is the neuronal system?

A

An interconnected network of neurones that signal each other across synapse junctions. They allow for rapid responses to stimuli as they conduct and transfer signals rapidly.

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17
Q

What is the hormonal system?

A

A system that uses the blood to transport its signal. Cells in the endocrine organ release a hormone into the blood. This is detected by target organs which coordinate a response

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18
Q

What is Homeostasis?

A

This is maintaining a constant internal environment despite changes in external and internal factors.

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19
Q

When maintaining a constant internal environment, which internal conditions are maintained?

A
  • Body temperature
  • Blood glucose concentration
  • Blood salt concentration
  • Water potential of the blood
  • Blood pressure
  • Carbon dioxide concentration
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20
Q

What is the standard response pathway for maintaining this condition?

A

Stimulus –> receptor –> communication pathway (cell signalling) –> effector –> response

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21
Q

For the standard response pathway to work a number of specialised structures are needed like?

A
  • Sensory receptors
  • A communication system
  • Effector cells
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22
Q

What are sensory receptors?

A

Cells/sensory nerve endings, that respond to a stimulus in the internal or external environment of an organism and can create action potentials.

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23
Q

Examples of sensory receptors?

A
  • External temperature receptors in the skin – monitors changes in external environment
  • Internal temperature receptors in the brain – monitors changes in the internal environment
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24
Q

Example of communication system, to coordinate a response to a stimulus?

A

The neuronal or the hormonal system – transmits a message from the receptor cells to the effector cells.

25
Q

What are the messages that travel to the coordination centre from the receptor known as?

A

The input

26
Q

What are the messages that travel from the coordination centre to the effector known as?

A

The output

27
Q

What is an effector/effector cells?

A

A cell tissue or organ that brings about a response.

28
Q

Examples of effector cells?

A

Liver or muscle cells

29
Q

What is negative feedback?

A

The mechanism that reverses a change, bringing the system back to the optimum.

*When maintaining a constant internal environment, there will be some variation around the optimum. So as long as the variation is not too great, the conditions will remain acceptable, even after negative feedback is applied.

30
Q

When effectors bring about a change, what happens to the stimulus, the input and the output and response?

A
  • System moves closer to optimum + stimulus decreases
  • Therefore, input to coordination centre decreases
  • Thus, output from coordination centre decreases
  • Effectors reduce their activity and thus the response is reduced.
31
Q

For negative feedback to work, a number of processes must occur:

A

1) Stimulus (change in environment) must be detected
2) Change must be signalled to other cells
3) There must be an effective response that reverses the change in conditions.

32
Q

What is positive feedback?

A

The mechanism that increases the change, taking the system further away from the optimum. So acts to increase the change rather than minimise it. This destabilises the system and is usually harmful.

33
Q

An example of positive feedback?

A

End of pregnancy to bring about dilation of the cervix: As cervix stretches, the posterior pituitary gland to secrete the hormone oxytocin. This increases the uterine contraction which stretch the cervix more, which in turn causes the secretion of more oxytocin. Once the cervix is fully dilated, the baby can be born. The bird ends the production of oxytocin.

34
Q

Why is it important to maintain body temperature?

A

Too hot = enzymes become denatured (i.e. tertiary structure unravels and changes) = shape of active site (specific and complementary in shape to a particualr susbtrate) changes = can no longer bind to the particular substrate as easily = less ESCs can form = less EPCs = less product molecules form = rate of enzyme-controlled reactions decreases/stops.
Too cold = substrates and enzyme have a lack of kinetic energy = move slower = less ESCs form = less EPCs = less product molecules form = rate of enzyme-controlled reactions decreases/stops.

35
Q

What are ectotherms?

A

An organism that relies on external sources of heat to maintain body temperature.
They control their temperature by changing their behaviour.

36
Q

What are endotherms?

A

An organsim that uses heat from metabolic reactions to maintain body temperature.
They control their temperature by homeostatis (internal) and they also change their behaviour.

37
Q

Which organisms, ectotherms or endotherms, control their body temperature more effectively?

A

Endotherms because the temperature of ectotherms varies with the external conditions (less control over body temp) unlike endotherms, which can control it internally. Behavioural changes allow ectotherms to control their body temp and thus their metabolic rate.

38
Q

Are humans endotherms or ectotherms?

A

Endotherms

39
Q

How do ectotherms increase body temperature when it is low? State the behavioural responses.

A

They absorb more heat from environment:

  • Move into a sunny area
  • Lie on warm surface
  • Expose a large SA to the sun (e.g. expanding ribcage)
  • Increase rate of breathing and depth of breathing movements (in insects. As a result, more water evaporates from tracheal system = body cools)

*They don’t use internal energy sources, however when active muscle contractions will generate heat due to increased respiration.

40
Q

How do ectotherms decrease body temperature when it is high? State the behavioural responses.

A

The avoid gaining heat from the environment + increase heat loss by:

  • Moving out of the sun
  • Move underground (into burrows which are cooler and have a more stable temp than air).
  • Decrease SA exposed to the Sun.
41
Q

Advantages of ectotherms?

A

Use ecternal source of heat therefore, less energy is used to keep them warm. Therefore:

  • Less of their food is used in respiration
  • More of the energy and nurtrients from food are converted to growth.
  • They need to find less food
  • They can survive long periods of time without food
42
Q

Disadvantages of ectotherms?

A
  • Less active in cooler temperatures = this means that they are at a greater risk from predators = unable to escape
  • Less active in cooler temperatures = cannot take advantage of food in cooler temperatures (cannot catch prey easily)
43
Q

As we discussed, endotherms control their bdoy temp internally by homeostasis but can also change their behaviour. What type of changes describe changes in homeostasis?

A

Physiological changes (dealing with the functions and activities of living organisms and their parts, including all physical and chemical processes).

44
Q

If a reaction is exergonic what does that mean?

A

Reactions which releases energy as heat

45
Q

Example of an exergonic reaction?

A

Respiration

*Why tho? It releases energy in the form of ATP, not heat (not directly anyway).

46
Q

Physiological responses by skin to increased and decreased body temp?

A

Increased body temp:

  • Increased sweating - more sweat produced by sweat glands. Heat from blood used as latent heat of vapourisation of the water in the sweat, so when it evapourates, cools body.
  • Hairs lie flat to reduce insulation + allow greater heat loss.
  • Vasodilation of arterioles + percapillary sphinctters, directing blood to skin surfaceso more heat can be radiated away from the body (You can use this point for the skin)

Decreased body temp is exactly the opposite:
Less sweating = less evapouration = less heat loss
Hairs stand erect = traps air = this insualtes body
Vasoconstriction of arterioles + sphincters = blood directed away from surface

47
Q

Physiological responses by gaseous exchange system to increased and decreased body temp?

A

Increased body temp:
Some animals pant, increasing evapouration from surface of lungs and airways. Evapouration uses heat from the blood as the latent heat of vapourisation.

How does panting cause increased evapouration???

Decreased body temp:
Less panting = less heat lost

48
Q

Physiological responses by liver to increased and decreased body temp?

A

Increased body temp:
Body temp is already high, so liver cells, reduce the amount of respiration in order to not contribute to already high temp.

Decreased body temp:
Increased respiration - increased release of energy.

49
Q

Physiological responses by skeletal muscles to increased and decreased body temp?

A

Increased body temp:
Fewer skeletal muscle contractions = less respiration taking place = less heat released.

Decreased body temp:
Increased skeletal muscle contraction = more respiration = more heat released

50
Q

Physiological responses by blood vessels to increased and decreased body temp?

A

Increased body temp:
- Dilation to direct blood to the extremities (limbs, arms and legs, particularly the fingers and toes) so that more heat can be lost

Decreased body temp:
- Constriction to limit blood flow to the extremities, so blood is not cooled too much - this can lead to frostbite, in extreme conditions.

51
Q

Behavioural responses by body if too hot?

A
  • Move out of the sun or into a burrow
  • Orientate body to reduce SA exposed to sun.
  • Remain inactive + spread limbs to enable greater heat loss due to increased SA.
  • Wet skin to use evapouration to cool body. (lick yourself or pour water on yourself).
52
Q

Behavioural responses if body too cold?

A
  • Move into sun
  • Orientate body towards sun to increase SA exposed to Sun.
  • Be active so muscles generate heat + decrease SA, by rolling into a ball, to reduce heat loss.
  • Remain dry
53
Q

Advantages of endotherms?

A
  • They can maintain a fairly constant body temperature, regardless of the temperature outside (unless extreme)
  • Remain active at low external temp = take advantage of prey available + escape from predators
  • Inhabit colder parts of the plant
54
Q

Disadvantages of endotherms?

A
  • Use signficant part of energy intake to maintain body temp
  • Require more food
  • Less energy + nutrients used for growth
  • May overheat in hot weather.
55
Q

In the homeostatic process of temperature control in the body (thermoregulation), what detects change in temp (stimuli)?

A
  • Thermoreceptors in the hypothalamus detect internal temperature (temp of blood) Thermoreceptors in the skin (aka peripheral temeprature receptors) detect external temperature (temp of skin).
56
Q

Homeostatic response to increase in body temp?

A

1) Thermoreceptors in hypothalamus detect rise in body temp (stimuli)
2) Hypothalamus sends impulses and signals through the nervous and hormonal system to the effectors (muscles and gland)
3) Effectors respond: vasodilation occurs, sweating occurs, hairs lie falt, fewer skeletal muscle contraction/less shivering, no adrenaline or thyroxine released to reduce rate of metabolic, exergonic reactions.

57
Q

Homeostatic response to decrease in body temp?

A

1) Thermoreceptors in hypothalamus detect fall in body temp (stimuli)
2) Hypothalamus sends impulses and signals through the nervous and hormonal system to the effectors (muscles and gland)
3) Effectors respond: vasoconstriction occurs, less sweating, hairs stand erect, more shivering, adrenaline and thyroxine released to increase rate of exergonic metabolic reactions.

58
Q

If thermoreceptors cause a homeostatic response, what is the peripheral temeprature receptors for?

A

Peripheral temperature receptors monitor the temperature in the extremities. This info is fed to the thermoregulatory centre in the hypothalamus which causes the brain to initiate behavioural mechanisms for maintaining body temp. It also helps the hypothalamus recieve an early warning that core body temp might change, so that it can quickly respond to any changes to minimise it when it happens.

Biology OCR AS Level (10 decks)

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