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
