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List 4 set of conditions enzymes need to work efficiently.
- suitable temperature
- suitable pH
- an aqueous environment that keeps the substrates and products in solution
- freedom from toxins and excess inhibitors
Why do living things need to maintain a certain limited set of conditions inside cells?
Becuase cellular activities rely on action of enzymes
Define stimulus and response.
- A stimulus is any change in the environment that causes a response.
- A response is a change in behaviour or physiology as a result of a change in the environment.
What 2 types of stimuli do organisms need to respond to?
- External (eg. outside temp)
- Internal (eg. CO2 conc in tissue fluid - too much could disrup action of enzymes by changing pH of environment around cell)
Composition of tissue fluid is maintained by ____. Therefore, need to monitor conc of ___ and other ____ in it.
Why is it important to have a good communication system in multicellular organisms in terms of homeostasis?
- Different cells (parts of body) are specialised to perform particular functions - forming tissues and organs.
- The cells that monitor blood may be well away from cells that release substances into blood or take away substances.
A good communication system will: (5)
- 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
Briefly explain what is meant by cell signalling.
Cells communicate with each other by this process, in which one cell release a chemical that is detected by another cell. The target cell will respond to the signal.
What are the 2 major systems of communication that work by cell signalling?
- The neuronal system - neurons signal each other across synapse junctions. Very quick signal and responses.
- The hormonal system - uses blood to transport its signals. Cells in endocrine organ release hormone into blood. Allows longer-term responses to be co-ordinated.
The maintenance of the internal environment in a constant state despite (external) changes.
List some examples of conditions that may need to be kept constant inside the body.
- body temp
- blood glucose conc
- blood salt conc
- water potential of blood
- blood pressure
- CO2 conc
Define negative feedback.
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.
- 2. Receptor
- 3. Communication pathway (cell signalling)
- 4. Effector
What are the 3 structures needed for negative feedback? With examples.
- Sensory receptors - eg. temp receptors or glucose conc receptors. Once they detect, they will be stimulated to send a message.
- Communication system - eg. nervous or endocrine. From receptor to effector. May or may not pass through coordination centre like brain.
- Effector cells - eg. liver or muscle cells.
Define positive feedback.
A process that increases any change detected by the receptors. It tends to be harmful and does not lead to homeostasis (although there are examples where it is helpful).
Give an example of harmful positive feedback and a beneficial one.
- Harmful: when body gets too cold, enzymes become less active, then less exergonic reactions that release heat. Body cools even further.
- Beneficial: at end of pregnancy, to bring about dilation of cervic. As cervix stretches, the change is signalled to anterior pituitary gland, stimulating it to secrete hormone, oxytocin. This allows more stretch. (ALSO, Anitgen production?)
Why do we need to maintain constant core body temperature?
- Changes in temp have effect on structure of proteins, eg. enzymes.
- Enzyme structure is very specific to its function, and so temp can greatly affect activity of enzymes and hence organism's ability to be active and survive.
What is an ectotherm?
- An organism that relies on external sources of heat to regulate its body temperature.
- (Not able to increase respiration rate to generate heat internally).
List advantages of being an ectotherm.
- Use less food in respiration.
- Need to find less food and may survive for long periods without eating. eg. snakes can for several weeks.
- Greater proportion of energy fro food can be used for growth.
List disadvantages of being ectotherm.
- Less active in cooler temps - puts them at greater risk of predation. And need to sunbathe etc.
- May not be capable of activity during winter, as they never warm up sufficiently. Means they must have sufficient stores of energy over winter without eating.
List some ways in which ectotherms regulate body temp.
- Expose body to sun
- Hide in shade
- Alter body shape
- Increase breathing movements.
An organism that can use internal sources of heat, such as heat generated from metabolism in the liver, to maintain its body temperature.
What name is given to a reaction that release energy in the form of heat? Example?
- Endotherms can increase rate of respiration in liver (exergonic reaction) simply to release heat.
List advantages of being endothermic.
- Fairly constant body temp (within a narrow range) whatever the temp is externaly.
- Activity (enzymes) possible when external temp are cool. (eg. night, winter)
- Ability to inhibit colder parts of planet (Larger range of habitats).
- No need to bathe in sun - less predation.
List disadvantages of being an endotherm.
- Significant part of energy intake used to maintain body temp in cold.
- Therefore, more food recquired.
- Less energy from food is used for growth/more food needed for growth.
List some of the physiological mechanisms to maintain body temp in endotherms. (Behavioural is similar to ectotherms)
- Sweat glands in skin (evaporation of water etc)
- Lungs, mouth and nose (evaporation of water from these surfaces)
- Hairs on skin (insulation)
- Arterioles leading to capillaries in skin [Vasodilation - sphincters open; Vasoconstriction - sphincters close] regulates heat being radiated from skin
- Liver cells - rate of metabolism
- Skeletal muscles - spontaneous contractions (shivering) generate heat as muscle cells respire more.
List the 3 components of negative feedback in body temp regulation in endotherms.
- Thermoregulatory centre in hypothalamus (monitor changes in temp in blood)
- Nervous system and hormonal system carry signals to...
- skin, liver and muscles
Explain role of peripheral temperature receptors.
These in the skin monitor the temp in the extremities. These give an early warning to the thermoregultory centre in hypothalamus, on whether the external environment is very cold or hot. The brain can then initiate behavioural mechanisms, enabling it to respons quickly and avoid too much variation in core body temp.
REMEMBER RON, questions with heat and maintaining body temp may often need you to think about...
- Surface-area-to-volume ratio.
- A smaller surface-area-to-volume ratio, like elephants, lose smaller proportion of body heat than those with larger S-A-T-V ratios, like a rat.