Communication and Homeostasis Flashcards
What is a stimulus?
Any change in the environment that causes a response
What is a response?
A change in the behaviour or physiology as a result of a change in the environment
Example of epithelial organs/tissues in animals and plants
Skin in animals and Bark in trees
4 things an enzyme needs to work efficiently
A suitable temperature
A suitable pH
An aqueous environment that keeps the substrates and products in solution
Freedom from toxins and excess inhibitors
A good communication system will…
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
What is cell signalling?
The process in which one cell will release a chemical that is detected by another cell
What two processes are involved in cell signalling?
The neural system
The hormonal system
Describe the neural system
An interconnected network or neurones that signal each other across across synapse junctions. these conduct signals very quickly and enable rapid responses to fast changing stimuli.
Describe the hormonal system
Uses blood to transport signals around the body. Cells in an endocrine organ release the signal (hormone) directly into the blood. This hormone is only recognised by specific target cells. This enables long term responses.
Define homeostasis
The maintenance of the internal environment in a constant state despite external changes.
Define negative feedback
A process that brings about a reversal of any change in conditions. It ensures that an optimum steady state can be maintained, as the internal environment is returned to its original set of conditions after any change. It is essential for homeostasis
Name the conditions in the body that must be kept constant
Temperature Blood glucose concentration Blood salt concentration Water potential of the blood Blood pressure Carbon dioxide concentration
What are sensory receptors?
These are receptors that monitor conditions inside the body such as temperature and blood glucose concentration. If a change is detected they will be stimulated to send a message.
Give an example of negative feedback
When body temperature gets too low so the body causes the muscles to contract and relax rapidly in order to produce more heat.
Define Positive Feedback
A process that increases any change detected by the receptors. It tends to be harmful and does not lead to homeostasis.
Give a beneficial example of positive feedback
At the end of pregnancy to bring about the dilation of the cervix. As the cervix stretches, signals tell the pituitary gland which is stimulated to produce oxytocin, hormone which increases uterine contractions causing the cervix to dilate further.
Give a damaging example of negative feedback
When the body gets too cold, enzymes involved in respiration are not able to work as efficiently, so respiration rate decreases, causing less heat to evolve from those reactions, causing the body to cool further. This can eventually lead to death if the body is not warmed fast.
Define ‘ectotherm’
An organism that relies on external sources of heat to regulate its body temperature. Commonly and incorrectly known as ‘cold blooded’.
Define ‘endotherm’
An organism that uses internal sources of heat to regulate it’s body temperature. Commonly and incorrectly known as ‘warm blooded’.
Advantages of being an ectotherm
They need less food for respiration, meaning they can focus more on growth.
They need less food overall to survive and so can survive for longer periods without food.
Disadvantages of being an ectotherm
Less active in colder temperatures and may need to warm up in the morning putting htem at a greter risk of predation.
If they are unable to go outsiede during colder months, they need to have sufficient storage of food to survive over this period.
Adaptations of ectotherms to regulate body temperature
Expose body to the sun so that more heat is absorbed.
Orintate body to the sun so that a larger surface area is available to absorb the heat ( and vice versa).
Hide in a borrow so that they can keep out of the sun and reduce the risk of overheating.
Increasing breathing movements evaporates more water and releases heat from the body.
Advantages of being an endotherm
Fairly constant body temperature whatever the external temperature is.
Activity is possible when external temperatures are cool.
They have the ability to inhabit colder parts of the planet.
Disadvantagse of being an endotherm
Significant part of energy intake is used to maintiain the body temperature.
More food is required to survive.
Smaller proportion of evergy is use in growth.
Components of endotherms body involved in temperature regulation
Sweat glands in the skin release sweat when B.T increases, which vapourises using the body’s heat.
The lungs, mouth and nose pant during increased B.T which causes more heat to be released through breathing.
The hairs of the skin stand on end when it is cold to form an insulating layer around the body and a partial wind break.
Arterioles undergo vasodilation when it is hot, and vasoconstriction when it is cold.
Liver cells increase rate of metabolism during cold times and decrease rate of metabolism during hot times.
Skeletal muscles are spontaneously contracted during cold times to produce heat through muscle contrations and increased respiration.
Behavioural mechansims of endotherms
Move into the shade or hide in a burrow when they are too hot to get out of the sun.
Orientate body to increase/decrease surface area exposed to the sun during cold/hot envirnoments.
They remain inactivein hot climates but move around more in cold climates.
What part of the brain regulates blood temperature?
The thermoregulatory centre
What helps the thermoregulatory monitor temperature?
The peripheral temperature receptors in the skin which feeds information tot he thermoregulatory centre in the hypothalamus.
What is a polarised membrane?
A membrane that has a potential difference across it. This is the resting potential.
REVISE CHAIN OF EVENTS TO CREATE AN ACTION POTENTIAL
Refer to pages 12-15
Define depolaristion
The loss of polarisation across the membrane. It refers to the period when sodium ions are entering the cell making the inside less negative with respect to the outside.
Define generator potential
A small depolarisation caused by sodium ions entering the cell.
Define action potential
Achieved when the membrane is depolarised to a value of about +40 mV. It is an all or nothing response. In the events leading up to an action potential, the membrane depolarises and reaches a threshold level, then lots of sodium ions enter the axon and an action potential is reached.
Define the resting potential
The potential difference or voltage across the neurone cell membrane while the neurone is at rest. It is about -60 mV inside the cell compared with outside the cell. Other cells may also maintain a resting potential that might change under certain circumstances.
Define Voltage-gated channels
Channels in the cell membrane that allow the passage of charged particles or ions. they have a mechanism called a gate which can open and close the channel. In these channels the gates respond to changes in the potential difference across the membrane.
