communication and homeostasis

• what is cell signalling?

  the way in which cells communicate with eachother
• most multicellular organisms have a range of tissues and organs. Many of the cells and tissues are not exposed to the external environment, they are protected by epithelial tissues and organs. In many animals, the internal cells and tissues are bathed in tissue fluids. This is the environment of the cells.
• All living organisms have an external environment that consists of the air, water and soil around them. This external environment changes which may place stress on the living organism. E.g. a cooler environment will cause greater heat loss. If the organism is to remain active and survive, the changes in the environment must be monitored and the organism must change its behavior or physiology in response.
• The environment may change slowly as the seasons pass. These changes elicit a gradual response. E.g. the arctic fox has a much thicker white coat in the winter and a thinner grey brown coat in the summer. The change in the coat provides greater insulation and camouflage in the winter- this ensures that the animal can survive but in the summer the animal doesn't overheat.
• as cells undergo their various metabolic processes, they use up substrates and create new products. some of these compounds are unwanted and or toxic. these substances move out of the cells into the tissue fluid and thus the activities of the cells will alter their environment.
• The composition of the tissue fluid is maintained by the blood. Blood flows through the body and transports substances to and from cells. Any waste or toxins accumulating in the tissue fluid will likely enter the blood and will be carried away. In order to prevent the accumulation, they need to be removed from the body via excretion.
• How does cell signalling work?

  One cell will release a chemical that is detected by the other cell. The second will respond to the signal from the first
• What are the two types of communication that work via cell signalling?

  Neuronal communications and Hormonal communications
• What is the neuronal system?

  An 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 change quickly.
• What is the hormonal system?

  A system that uses the blood to transport its signals. Cells in an endocrine organ release the signal directly into the blood. The hormone is transported throughout the body but is only recognized by the specific target cells. The hormonal system enables longer term responses to be coordinated.
• what is an effector?

  A cell, tissue, or organ that brings about a response
• What is homeostasis?

  The process to maintain a constant internal environment despite changes in external and internal factors
• What is meant by negative feedback?


  The mechanism that reverses a change, bringing about the system to back to the optimum
• What is positive feedback?

  The mechanism which increases a change, taking the system further away from the optimum.
• what are sensory receptors?

  Cells and/or sensory nerve endings that respond to a stimulus in the internal or external environment of an organism and can create action potentials
• what is the standard response pathway?

  Stimulus

  Receptor

  Communication pathway

  Effector

  Response
• what are endotherms?

  Organisms which are able to control their body temperature within very strict limits. They use a variety of mechanisms to control body temperatures and are largely independent of external temperatures.
• What are ectotherms?

  Organisms which are not able to control their body temperature when they are cold. They rely on external sources of heat and their body temperature will fluctuate with the external temperature
• what can ectotherms do if they are cold in order to absorb more heat from the environment?

  Move into a sunny area

  Lie on a warm surface

  Expose a larger surface area to the sun
• what can ectotherms do if they are too hot in order to increase heat loss into the environment?

  Move out of the sun

  Move underground

  Reduce surface area exposed to the sun
• what are the main advantages of ectothermic animals?

  Less food is used in respiration

  More energy and nutrients that is gained from food can be used for growth

  Less food needs to be found

  Can last for a long time without food
• what is the main disadvantage of ectothermic animals in terms of predators?

  Because they are less active in cooler temperatures, ectotherms are at higher risk from predators and as such are unable to escape.
• what does temperature regulation in endotherms rely on and why?

  Temperature regulation relies on the skin because of the effectors that are inside. The skin is the organ in contact with the external environment, therefore many of the physiological adaptations to control body temperature involve the kin. Thus, the changes that take place in the skin will alter the amount of heat being lost to the environment.
• in an endotherm, what do the sweat glands do if the organism is too hot?

  Sweat glands will secrete fluid onto the skin surface as this evaporates- it will use heat from the blood as the latent heat of evaporation.
• in an endotherm, what do the sweat glands do if the organism is too cold?

  Less sweat is secreted so less heat is lost.
• in an endotherm with hair or feathers, what happens if they are too hot?

  Hairs and feathers will lay flat to reduce insulation and allow greater heat loss.
• in an endotherm with hair or feathers, what happens if they are too cold?

  Hairs and feathers stand erect to trap air, insulating the body
• What do arterioles and precapilliary sphincters do in an endotherm if they are too hot?

  Vasodilation of arterioles and precapiliary sphincters direct blood to the skin surface so more heat can be radiate away from the body
• what do arterioles and precapilliary sphincters do in an endotherm if they are too cold?

  Vasoconstriction of arterioles and precapilliary sphincters leading to the skin surface. Blood will be diverted away from the skin surface and less heat is lost.
• in terms of the gaseous exchange system, what do some endotherms do if they are too hot?

  Some endotherms will pant, this increases evaporation of water from the surface of the lungs and airways. The evaporation uses heat from the blood as the latent heat of evaporation.
• in terms of the gaseous exchange system, what do some endotherms do if they are too cold?

  Endotherms that pant will pant less, so less evaporation of water from the surface of the lungs and airways occurs and less heat is lost.
• In terms of the liver, what do endotherms do if they are too hot??

  They will respire less, so less heat is released
• In terms of the liver, what do endotherms do if they are too cold?

  There will be increased respiration in the liver cells, so more energy from food is converted into heat.
• in terms of the skeletal muscles, what do endotherms do if they are too cold?

  They will contract their muscles more, so that they shiver and release heat.
• in terms of the skeletal muscles, what do endotherms do if they are too hot?

  They will contract their muscles less, so less heat is released
• what are the advantages of endothermic aniamls?

  Maintain a fairly constant body temperature, regardless of the external temperatures.

  They can remain active even when external temperatures are low, which means they can take advantage of prey that may be available or escape from predators.

  Endotherms are able to inhabit colder parts of the planet
• what are the main disadvantages of endothermic animals?

  They use a significant part of their energy intake to maintain body temperature in the cold

  They need more food

  Less energy and nutrients from food is used for growth

  They may overheat in hot weather
• which gland in the brain detects temperature changes of an ectotherm?

  hypothalamus