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A-Level Biology > Homeostasis - 5.1.1 > Flashcards

Homeostasis - 5.1.1 Flashcards

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1
Q

Animal and plant responses?

A

To internal and external changes - through nervous or hormonal systems - must be COORDINATED to produce the required response in an organism

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2
Q

Why is coordination of cells needed?

A

Cells have become specialised - need to coordinate the functions of these different cells to operate effectively ; muscle cells must contract but cannot do so without oxygen from red blood cells

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3
Q

Flowering in plants coordination?

A

Needs to coordinate with the seasons and pollinators must coordinate with the plants

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4
Q

Homeostasis

A

Maintenance of a relatively constant internal environment - digestive organs and the endocrine pancreas/liver work together to maintain a constant blood glucose concentration

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5
Q

Cell signalling

A

Nervous and hormonal systems coordinate the activities of whole organisms - coordination relies on communication at a cellular level through cell signalling
One cell releasing a chemical which has an effect on the target cell

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6
Q

What can cells do as a result of cell signalling?

A

Transfer signals locally - between neurones at synapses, signal used is a neurotransmitter
Transfer signals across large distances - using hormones - cells of the pituitary gland secrete ADH, which acts on cells in the kidneys to maintain water balance in the body

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7
Q

What state must our body stay in?

A

A dynamic equilibrium

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8
Q

What is a dynamic equilibrium?

A

Small fluctuations over a narrow range of conditions - this is called homeostasis
Sensory receptors detect changes in internal/external environments and this is transmitted to the brain

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9
Q

How are impulses sent from the brain?

A

Through motor neurones to effectors - brings about changes to restore equilibrium in the body

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10
Q

What are effectors?

A

Muscles or glands that react to the motor stimulus to bring about a change in response to a stimulus - both receptors and effectors are vital, detecting change is no use without means to react and effectors cause chaos unless responding to a need

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11
Q

Negative feedback system

A

Small change detected by receptors and then effectors work to reverse the change, restoring conditions to their base level - reverse initial stimulus ; important in temperature control, water balance and blood sugar levels

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12
Q

Positive feedback system

A

Change in internal environment is detected by receptors, effectors are stimulated to reinforce that change and increase the response

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13
Q

Example of positive feedback system

A

Blood clotting cascade - when a blood vessel is damaged, platelets stick to the damaged region and they release factors that initiate clotting and attract more platelets - add to the positive feedback cycle and continues until a clot is formed

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14
Q

Positive feedback during childbirth

A

Head of body presses against cervix - stimulates production of hormone oxytocin which stimulates uterus to contract, pushing head of baby even harder against cervix and triggering the release of more oxytocin - continues until baby is born

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15
Q

What is thermoregulation?

A

Maintenance if a relatively constant core body temperature to maintain optimum enzyme activity

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16
Q

Convection

A

Heating and cooling by currents of air or water, warm air or water rises and cooler air or water sinks - setting up convection currents around an organism

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17
Q

Conduction

A

Heating as a result of the collision of molecules - air is not a good conductor of bear but ground/water are

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18
Q

Gain in heat

A

Waste heat from cell respiration

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19
Q

Losses of heat

A

Evaporation of water

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20
Q

Ectothermic

A

Use their surroundings to warm their body - heavily dependent on their environment (all invertebrates, fish, amphibians and reptiles)

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21
Q

Animals in water?

A

Water has a high SHC so temperature of environment does not change much so no need to thermoregulate

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22
Q

Ectotherms that live on land?

A

Temperature of air can vary dramatically over a short period of time - they have evolved a range of strategies that enable them to cool down/warm up

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23
Q

Endotherms?

A

Mammals and birds are endothermic - rely on their metabolic processes to warm up and they usually maintain a very stable core body temperature regardless of the temperature of the environment
So endotherms survive in a wide range of environments - keeping warm in cold conditions and cooling down in bit conditions are both active processes

24
Q

Metabolic rate of endotherms?

A

5 times higher than ectotherms - so need to consume more food to meet their metabolic needs than ectotherms of same size

25
Q

How can ectotherms not control their temperature?

A

Through metabolism

26
Q

Behavioural responses for ectotherms

A

Bask in the sun to warm up to a temperature at which metabolic reactions happen fast enough for them to be active - maximum SA exposed to the sun - lizards bask to get warm enough to move fast and locusts/butterflies orientate themselves for maximum exposure to the sun and spread their wings to increase the available SA to fly

27
Q

How else can ectotherms increase their body temperature?

A

Through conduction by pressing their bodies against the warm ground - also as a result of Exothermic metabolic reactions ; contract their muscles and vibrate increasing cellular metabolism and moths may vibrate their muscles before they take flight

28
Q

Behavioural responses to cool down - ectotherms?

A

Shelter from the sun by seeking shade - hiding in cracks in rocks or digging burrows
Press their bodies against cool, shady stones or move into water
Minimum SA exposed to the sun - minimise movement to reduce metabolic heat generated

29
Q

Physiological responses of ectotherms?

A

Dark colours absorb more radiation than light colours - lizards in cold climates are darker coloured
Alter heat rate to increase or decrease metabolic rate

30
Q

Advantage of ectotherms?

A

Can maintain a stable temperature by using physiological and behavioural responses - need less food than endotherms as they use less energy in homeostasis so they can survive in some very difficult habitats where food is in short supply

31
Q

How do endotherms detect a change in the internal environment?

A

Peripheral temperature receptors in the skin detect changes in surface temperature and temperature receptors in the hypothalamus detect the temperature of the blood deep in the body

32
Q

Endotherms sensitivity?

A

Combination of two receptors allows it to respond not only to actual changes in the temperature of the blood but to pre-empt possible problems that might result from changes in the external environment

33
Q

What is thermostats of the body?

A

Temperature receptors in the hypothalamus - control responses to maintain dynamic equilibrium 1 degrees within 37

34
Q

How do endotherms keep warm?

A

Using internal Exothermic metabolic activities

35
Q

How do endotherms cool down?

A

Energy-requiring physiological responses

36
Q

Behavioural responses of endotherms?

A

Similar to ectotherms - basking in the sun, pressing themselves to warm surfaces, wallowing in water and mud to cool down and digging burrows to keep warm or cool

37
Q

Hibernation?

A

Dormant through coldest weather

38
Q

Aestivation

A

Prolonged period of deep sleep in the summer/dry seasons to avoid heat stress

39
Q

Additional behavioural adaptations for humans?

A

Clothes/houses etc

40
Q

What do endotherms mainly rely on?

A

Physiological adaptations - peripheral temperature receptors, thermoregulatory centres of the hypothalamus, the skin and the muscles

41
Q

Cooling down

A

Vasodilation
Increased sweating
Reducing insulating effect of hairs

42
Q

Vasodilation

A

Arterioles near surface of skin dilate - arteriovenous shunt vessels (direct connection between arterioles and venules) - constricts, forcing blood through capillary networks close to the surface of the skin
Skin flushes and cools as a result of increased radiation

43
Q

If skin is pressed against cool surfaces?

A

Cooling results from conduction

44
Q

Sweating

A

Sweat spreads out across the skin - sweat evaporates from the surface, heat is lost, cooling blood below the surface
In some animals the sweat glands are restricted to less hairy surfaces like paws - these animals often open their mouths and pant, losing heat as water evaporates

45
Q

What do cats do?

A

Lick their front legs to keep cool in high temperatures

46
Q

Reducing insulating effect of hairs?

A

Body temperature increases - erector pili muscles in the skin relax, hairs lie flat and no insulating layer

47
Q

Endotherms anatomical adaptations?

A

Large SA:V to maximise cooling (large ears/wrinkly skin) and pale fur to reflect radiation

48
Q

Warming up

A

Vasoconstriction
Decreased sweating
Raising body hairs
Shivering

49
Q

Vasoconstriction

A

Arterioles near the surface constrict - arteriovenous shunt vessels dilate - little blood flows through capillaries near the skin
Skin = pale ; little radiation ; warm blood kept below surface

50
Q

Decreased sweating

A

Rates of sweating decrease and sweat production stops entirely - reduces evaporation of water from skin but some evaporation from lungs still continues

51
Q

Raising body temperature

A

Erector pill muscles contract - pulling hairs erect - traps an insulating layer of air which reduces cooling through skin and is very effective in reducing heat loss to environment in many animals
In humans this has little effect

52
Q

Shivering

A

Rapid involuntary contracting and relaxing of large voluntary muscles in the body - metabolic heat from the exothermic reactions warm up the body

53
Q

Anatomical adaptations in endotherms

A

Small SA:V (small ears) so less heat lost
Thick layer of insulating fat underneath the skin - blubber
Hibernate - build up fat stores, build a well insulated shelter

54
Q

Two control centres in thermoregulation

A

Heat loss centre
Heat gain centre

55
Q

Heat loss centre

A

When temperature of blood flowing through hypothalamus increases - sends impulses through AUTONOMIC motor neurones to effectors in the skin and muscles, triggering responses to lower the core temperature

56
Q

Heat gain centre

A

When temperature of blood flowing through hypothalamus decreases - sends impulses through AUTONOMIC nervous system to effectors in the skin and muscles, triggering responses to raise core temperature

57
Q

Interaction of what key components?

A

Sensory receptors, autonomic nervous system, effectors (NEGATIVE FEEDBACK) ; maintains a stable core temperature regardless of environmental conditions/activity levels

A-Level Biology (37 decks)

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