5.1 - Communication and Homeostasis Flashcards
State the conditions within a cell that need to be maintained.
Suitable temperature - this may not be 37°C.
Suitable pH.
An aqueous environment - to allow successful collisions between enzyme active sites and substrates, the maintenance of products in solution for transport etc; hydrolysis and condensation reactions.
Freedom from toxins and inhibitors - carbon dioxide, urea, etc.
Which external changes does an organism need to monitor?
Temperature, sunlight darkness, predator/prey.
These are all stimuli, they bring about a response.
Describe the features of an effective communication system.
Covers the whole body; allows cell to cell communication; specific; rapid; short and long term responses.
Describe how an organism coordinates a response to a stimulus.
Cell signalling. Hormonal signalling - uses endocrine system, hormone released into blood, targets cells with specific receptor, often slow acting, long lasting response. Electrical impulses - uses neurones, synapses and chemical messengers, rapid, short term response.
What is homeostasis?
The maintenance of an internal environment despite internal and external factors.
Explain the importance of maintaining body temperature and blood pH?
Temperature - too low enzymes work slowly and cellular metabolism drops, too high and enzymes denature.
Blood pH - too low or high and enzyme tertiary structure and active site disrupted, cellular metabolism drops.
Explain the importance of maintaining a constant blood glucose concentration.
Too high and the water potential of blood is reduced and water diffuses out of cells by osmosis, cells become crenated.
Too low and cellular metabolism drops as cells do not have enough glucose for respiration.
Describe the mechanism of homeostasis.
Stimulus> receptor> communication pathway/ cell signalling> effector> response.
Define a sensory receptor.
Cells/sensory nerve endings that detect/respond to a stimulus. Stimulus may be internal or external. An action potential or hormonal response is initiated.
Describe a communication pathway.
Neuronal or hormonal system.
Responds to receptor and transits message from receptor cells, input, to effector cells, output via coordination centre.
What is an effector?
Muscle - neuronal response.
Gland - hormonal response.
What is negative feedback?
An action that reverses the initial change in conditions. Effective response. Restores systems to their original level/an optimum. System stabilised. Usually beneficial e.g. blood glucose, body temperature.
What is positive feedback?
An increase to the initial change. Further increase away from original levels/an optimum. System destabilised. Usually harmful e.g. hypothermia, reduction in body temperature. Release of oxytocin is an example of beneficial positive feedback. Increase uterine contraction causing cervix to stretch. In turn stretching causes release of more oxytocin.
What is overshoot?
Overcorrection to the system that takes conditions past the optimum, away from the stimulus.
What is an ectotherm?
An organism that relies on external sources of heat to maintain body temperature e.g. lizard.