Homeostasis and Excretion Flashcards
Why do we need communication systems for survival and activity
-cell metabolism relies on enzymes and enzymes need specific set of conditions in which to work efficiently
-all living things need to maintain: suitable temperature, suitable pH, aqueous environment keeping substrate and products in solutions, freedom from toxins and excess inhibitors
-without these conditions, cells become inactive and die
-in multicellular organisms, cells specialised to rely on one another therefore must be able to coordinate activities via communication
How do immediate changes in external environments act as a threat
-when the external environment including air, water, or soil changes, this puts stress on organism
-for instance, cooler environment will cause greater heat loss - organism must change behaviour or physiology to reduce stress
-the environment change is a stimulus and way which organism changes behaviour or physiology is response
-the animal may have to escape a predator or move from burrow to sunlight for heat
How do seasonal changes elicit response
-as seasons change, the environment will change eliciting a gradual response
-for example, the Arctic fox has a much thicker and whiter coat in winter and in summer its thinner and grey/brown
in winter it provides camouflage and insulation and in summer it allows the fox to not overheat
What is the internal environment
-most multicellular organisms have a range of tissues and organs
-many of the cells and tissues are not exposed to the external environment-protected by epithelial tissues and organs such as skin or bark
-in many animals, the internal cells and tissues are bathed in tissue fluid - this is the environment
How can internal environments change
-as cells undergo various metabolic activities, they use up substrates and create new products
-some of these compounds may be unwanted or toxic
-these substances move out of cells into tissue fluid therefore activities of cells alter own environment
Describe the change of CO2 in internal environments
-carbon dioxide is a waste product that if allowed to build up in tissue fluid outside cells, it will alter pH of tissue fluid and could disrupt action of enzymes and other proteins
-accumulation of excess waste or toxins in this internal environment must act as stimulus to cause removal of these waste products to ensure cells survive
-in this case, reduced pH of blood stimulates greater breathing activity that expels CO2 from body
How is internal environment maintained
-the composition of tissue fluid is maintained by blood
-blood flows throughout body and transports substances to and from cells
-any wastes or toxins accumulating in tissue fluid are likely to enter blood and be carried away
-to prevent accumulation in the blood, must be removed from body via excretion
What is the importance of monitoring
-it is important concentrations of wastes products and other substances in blood are monitored closely
-this ensures body does not excrete too much of any useful substances but removes enough waste products to maintain good health
-it also ensures that cells in the body are supplied with substrates they need
Why is the activity of organs required to be coordinated
-multicellular organism more efficient than single celled because its cells are differentiated
-this means that its cells are specialised to perform particular functions - groups of cells specialised to perform particular functions form tissues and organs
-the cells that monitor the blood may be in a different part of body well away from source of waste product
-they may also become distance from tissue or organ specialised to remove waste from the body
-therefore a good communication system required to ensure these different parts of body work together effectively
Describe a good communication system
-cover whole body
-enable cells to communicate with each other
-enable specific communication
-enable rapid communication
-enable both short term and long term responses
Describe cell signalling
-cells communicate with each other by process of cell signalling
-this is process in which one cell will release a chemical that is detected by another cell
-the second cell will respond to the signal released by first
-signals are specific by involving molecules with specific, complementary shape to cell surface receptor
Describe the neuronal system
-interconnected network of neurones that signal to each other across synapse junctions
-the neurones can conduct a signal very quickly and enable rapid responses to stimuli that may be changing quickly
-elicit rapid responses, uses action potentials, across synapses and neurone transmitters
Describe the hormonal system
-system that uses blood to transport its signals
-cells in an endocrine organ release the signal (a hormone) directly into the blood
-the hormone is transported throughout the body, but is only recognised by specific target cells
-the hormonal system enables longer term responses to be coordinated
Define effector
a cell, tissue or organ that brings about a response
Define homeostasis
Maintaining constant internal environment despite changes in internal and external factors
Define negative feedback
mechanism that reverses a change, bringing system back to optimum
Define positive feedback
mechanism that increases a change, taking system further away from optimum
Describe homeostasis
-homeostasis used in many living organisms to maintain conditions inside the body, despite external and internal factor changes
aspects maintained by homeostasis include: body temperature, blood glucose concentration, blood salt concentration, water potential of blood, blood pressure and carbon dioxide concentration
Define sensory receptors
sensory nerve endings that respond to a stimulus in the internal or external environment of an organism and can create action potentials
Describe the mechanism of homeostasis
-any response to changes in the environment requires complex mechanism which may involve series of tissues and organs that are coordinated through cell signalling
-stimulus - receptor -communication pathway - effector - response
Describe sensory receptors
-these receptors may be on surface of body such as temperature receptors on skin
-they monitor changes in external environment
-other receptors are internal to monitor conditions inside the body, for example, temperature receptors in brain
-when one receptor detects change it will be stimulated to send message to effector
Describe communication systems
-such as neuronal or hormonal system
-this acts by signalling between cells
-it is used to transmit a message from receptor cells to effector cells via coordination centre usually in brain
-the messages from receptor to coordination centre known as input
-messages sent to effectors known as output
Describe effector cells
-such as liver or muscle cells
-bring about response
Describe feedback
-when the effectors respond to the output from coordination centre, they bring about response that will change conditions inside body
-such changes will be detected by receptors
-this will have effect upon response pathway
-in effect, the input will change
Describe negative feedback
-in order to maintain constant internal environment, any change away from optimum must be reversed
-in this way, conditions inside body will be returned to optimum
-when conditions change, receptors detect this stimulus and send input to coordination system
-the coordination centre sends output to effectors and effectors respond
-they bring about a change that reverses initial change in conditions so the system moves it closer to optimum and stimulus reduced
-receptors detect reduction in stimulus and reduce input to coordination centre
-output from coordination centre to effectors also reduced so effectors reduce activity
-as system get closer to optimum, response it reduced
Summarise negative feedback
change away from optimum - receptor detects change -(input)-communication system informs effector -(output)- effectors reacts to reverse change - return to optimum condition - optimum condition
What are the requirements for negative feedback to work
- change to the internal environment must be detected
- change must be signalled to other cells
- must be effective response that reverses in change of conditions
Describe how internal environments constantly maintained
-negative feedback system can maintain a reasonably constant set of conditions
-however conditions will never remain perfectly constant; there will be some variation around optimum conditions
-when stimulus occurs may take time to respond and response may cause slight overshoot - however as long as this variation not too great, conditions will remain acceptable
-when negative feedback applied to living systems, the condition inside living organisms will remain within narrow range
-the conditions will remain warm enough to allow enzymes to continue functioning efficiently but cool enough to avoid damage to proteins
Describe positive feedback
-positive feedback less common than negative feedback
-when positive feedback occurs, the response is to increase original change
-this destabilises the system and is usually harmful
-for example, below certain core body temperature enzymes become less active and exergonic reactions that release heat are slower and therefore release less heat
-this allows body to cool further and slows enzyme controlled reactions more - causes body temperature to spiral downwards (hypothermia)
Describe oxytocin positive feedback
-there are some occasions where positive feedback is beneficial
-an example is seen at end of pregnancy to bring about dilation of cervix
-as cervix begins to stretch this causes posterior pituitary gland to secrete hormone oxytocin - this increases uterine contractions which stretch cervix more, which causes more secretion of oxytocin
-once cervix fully dilated baby can be born -t this birth ends production of oxytocin
-the activity of neurones also relies on positive feedback
Describe ectotherm
-organism that relies on external sources of heat to maintain body temperature
-they are able to control their body temperature as effectively as endotherms
-however, using various behavioural mechanisms some endotherms are able to control their body temperature in all but most extreme conditions
Describe endotherms
-organism that uses heat from metabolic reactions to maintain body temperature
-they control their body temperature within very strict limits and are largely independent of external temperatures
Why does body temperature need to be controlled
-changes in body temperature can have dramatic effect upon activity of cell processes
-as temperature rises molecules have more kinetic energy - they move about more quickly and collide more frequently
-this means essential chemical reactions occurs more quickly - however in cooler conditions opposite occurs and chemical reactions slow down
Why does body temperature need to be controlled - proteins
-the structure of proteins can also be affected by changes - especially increases
-many proteins have metabolic function; for example enzymes increase rate of biological reactions
-enzymes are globular proteins and have very specific tertiary structure giving them a specific 3D shape
-in case of enzymes, the shape of active site is complementary to shape of substrate and any change in shape will affect ability to function
-if temperature is allowed to increase too much, enzymes change shape and their function is lost
Describe how enzymes are very sensitive to temperature change
-some enzymes are very sensitive to temperature change
-if body temperature drops by 10 degrees the rate of enzyme controlled reactions falls by half
-many reactions in cells release heat, which can help maintain temperature but if temperature drops and reactions slow less heat is released
-this allows body to cool further - form of positive feedback
-as body cools, organism less able to function normally
-on the other hand, if temperature rises just a few degrees above optimum, enzymes may denature and cease to function
Why is core temperature an important factor
-the core temperature is an important factor as all vital organs found in centre of body
-peripheral parts of body may be allowed to increase or decrease in temperature to some extent without affecting survival of organism
Describe temperature control in ectotherms
-ectotherms do not use internal energy sources to maintain their body temperature when cold - however once they are active their muscle contractions will generate some heat from increased respiration
-temperature regulation relies upon behavioural responses that can alter amount of heat exchanged with environment
-for example they may try absorb more heat from environment via: lying on warm surface, expose more surface area to sun etc
Give behaviour adaptation of snakes and its benefits
-bask in sun - absorb heat directly from sun
Give behaviour adaptation of locust and its benefits
-in early morning, sit side on to sun exposing large surface area but at midday sit head on to sun, exposing smaller surface area. Also climb to top of plant at midday to get away from soil surface - cool morning they absorb more heat but at midday when sun hotter, absorb less heat. Also avoid heat radiating from soil at midday
-increase both rate of breathing and depth of breathing movements when its hot - more water evaporates from tracheal system cooling the body
Give behaviour adaptations of lizards and their benefits
-many lizards use burrows or crevices between rocks. During hottest part of day and coolest part of night, lizards hide in burrows - underground burrows tend to have more stable temperature than air. In day burrow will be cooler than air but at night, burrow will be warmer than air outside
Give behaviour adaptations of the horned lizard and its benefits
-can change shape by expanding or contracting ribcage - expanding ribcage exposes larger surface area to sun so more heat can be absorbed
Advantages of ectothermy
-rely on external sources of heat and do not use up energy to keep warm therefore:
-less food used in respiration
-more energy and nutrients gained from food converted to growth
-need to find less food
-can survive for long periods without food
Disadvantages of ectothermy
-less active in cooler temperatures
-at risk from predators whilst cold and unable to escape
-cannot take advantage of food available while cold
Describe temperature regulation mechanisms in endotherms
-temperature regulation relies on effectors in skin and muscles
-the skin is the organ in contact with external environment
-therefore any physiological adaptations to control body temperature involve the skin
-the changes that take place in skin alter amount of heat being lost to environment
-many chemical reactions in body are exergonic - release energy in form of heat
-endotherms can increase respiration in muscles and liver to release heat
-also have other physiological mechanisms that are useful
PHYSIOLOGICAL RESPONSE - skin
HOT
-sweat glands secrete fluid onto skin surface; as this evaporates it uses heat from blood as latent heat of vaporisation
-Hairs and feathers lie flat to reduce insulation and allow greater heat loss
-vasodilation of arterioles and precapillary sphincters directs blood to skin surface so more heat can be radiated away from body
COLD
-if too cold, less sweat is secreted so less heat is lost
-Hairs and feathers stand erect to trap air which insulates body
-vasoconstriction of arterioles and precapillary sphincters leading to skin surface, blood is diverted away from skin surface so less heat is lost
PHYSIOLOGICAL RESPONSE - gaseous exchange system
HOT
-some animals pant, increasing evaporation of water from surface of lungs and airways. Evaporation uses heat from blood as latent heat of vaporisation
COLD
-less panting so less heat is lost
PHYSIOLOGICAL RESPONSE -liver
HOT
-less respiration takes place so less heat it released
COLD
-increased respiration in liver cells means that more energy from food is converted to heat
PHYSIOLOGICAL REPSONSE - skeletal muscles
HOT
-fewer contractions means that less heat is released
COLD
-spontaneous muscle contractions (shivering) release heat
PHYSIOLOGICAL RESPONSE - blood vessels
HOT
-dilation to direct blood to extremities so that more heat can be lost
COLD
-constriction to limit blood flow to the extremities so blood is not cooled too much - this can lead to frostbite in extreme conditions
BEHAVIOURAL RESPONSES - hot
-hide away from sun in shade or in burrow
-orientate body to reduce surface area exposed to sun
-remain inactive and spread limbs out to enable greater heat loss
-wet skin to use evaporation to help cool body - cats lick themselves and elephants spray water over their bodies
BEHAVIOURAL RESPONSES -cold
-lie in sun
-orientate body towards sun to increase surface area exposed
-move about to generate heat in muscles or in extreme conditions roll into ball shape to reduce surface area and heat loss
-remain dry
