5.1 Homeostasis Flashcards
How do cells in the nervous system communicate?
By secreting neurotransmitters to adjacent cells
Why must organisms respond to changes in their external environment?
To ensure their survival
Why must organisms respond to changes in their internal environment?
To ensure the conditions are always optimal for their metabolism
What is a stimulus?
Any change in the internal or external environment
How do distant cells communicate?
The hormonal system, where chemicals travel in the blood and signal distant cells.
What do cell surface receptors do?
They allow cells to recognise chemicals involved in cell signalling
What is homeostasis?
Maintenance of an internal environment, kept within a narrow range- roughly constant
What is positive feedback?
When a change acts to further increase the change, away from the normal level
When is positive feedback useful?
When something needs to be rapidly activated, e.g. a blood clot
What is negative feedback?
When a response acts to counteract a change or stimulus. It keeps things at a normal level
Why is negative feedback useful?
Maintains a relatively normal level e.g. body temperature at 37C
Why is cell signalling important?
It insures organ activity is coordinated, and that messages can be sent between receptors and effectors
The activity of neurones relies on _________ feedback.
Positive
What hormone promotes uterine contractions during birth?
Oxytocin
How is cervical dilation an example of positive feedback?
- As cervix begins to stretch, oxytocin is released
- Oxytocin increases contractions which cause the cervix to dilate more which increases the amount of oxytocin secreted
What is an ectotherm?
An organism that relies on external sources of heat to maintain its body temperature
Why is temperature control important?
Enzyme controlled reactions are temperature sensitive, too hot and they denature, too cold and they are too slow
What is Q10 rule?
As the temperature increases by 10 degrees, the rate of enzyme controlled reactions doubles
Why do ectotherms lie on their side in the sun when they feel cold?
To warm up they expose a larger surface area of their skin to the sun
How do ectotherms cool down?
By increasing heat loss to the environment: like moving to shade, into burrows etc
In terms of energy, what is an advantage of ectothermy?
Because they rely on external heat sources, they do not use their energy on keeping warm- so they can live longer without food
What are disadvantages of ectothermy?
- Less active in cold
- Risk from predators when cold
Why do locusts ‘breathe’ deeper in the heat?
An increased depth of breathing movements allows more water to evaporate from the tracheal system, cooling the body
Why do locusts climb to the top of plants at midday?
To escape the hot soil surface and cool down
How can horned lizards warm up?
By expanding their rib cage they increase the SA of their skin so more heat can be absorbed
Why do ectotherms like to have burrows?
Burrows tend to have a more stable temperature than the air outside- it will be colder inside when it’s hot outside and warmer inside when it’s cold outside
What do lizards do to maintain their body temperature?
Hide in burrows or crevices in between rocks
How do snakes warm up?
Basking in the sun to absorb its heat
What is an endotherm?
An organism that maintains its body temperature by homeostasis and generates its own heat
What is a disadvantage of endothermy, in terms of energy?
A significant part of our energy intake is used on body temperature maintenance, meaning more food is needed to survive
What monitors changes in external skin temperature?
Peripheral skin receptors
What monitors the blood temperature/core temperature?
Thermoregulatory centre in the hypothalamus
Why would an organisms hairs/feathers lie flat on the skin?
To reduce insulation and allow greater heat loss
What is vasodilation?
Arterioles directing blood to the skin and extremities
Why is vasodilation useful?
It allows blood to the skins surface allowing greater heat loss
Why does panting cool an animal down?
It increases evaporation from the lungs and airway surface
Why do we shiver when cold?
Spontaneous muscle contraction and respiration release heat
Why do people get frostbite in extreme cold conditions?
Vasoconstriction limits blood flow to the extremities
Why do hairs/feathers stand erect when cold?
To trap air in the gaps which insulates the skin, reducing heat loss
Why are peripheral temperature sensors useful in maintenance of body temperature?
They can act as an early warning sign that the body temperature may drop, allowing the hypothalamus to respond more quickly
What are the advantages of endothermy?
- Can remain active when cold
- Can escape predators when cold
- Can inhabit colder habitats
What muscle makes hair stand up?
Erector pili muscle
What hormones increase metabolism and allow more heat to be produced?
Adrenaline and thyroxine
