Communication and Homeostasis

• Explain why multicellular organisms need a communication system.

  Organisms need to respond to internal/external changes for survival. Different cells rely on others for materials/removal of waste and different organs work together to ensure homeostasis.
• List the factors that need keeping constant inside cells.

  Blood Glucose concentrationTemperatureWater potentialCell pH
• Explain why it is important to keep conditions inside cells relatively constant.

  Enzymes will only function properly under a small range of certain conditions, such as preferred pH and temperature. If any conditions are outside their specific range then the enzymes cannot function. This could cause the organism to die.
• Name the process by which cells communicate with each other.

  cell signalling
• Define the term "cell signalling"


  a complex system of intercellular communication
• Give two examples of systems whose purpose is cell signalling

  Transfer signals locally, eg. between neurones at synapses.Transfer signals across large distances, eg. using hormones
• Outline the process of cell signalling in these two systems

  Cell releases a chemical which has an effect on the target cell
• Compare the neuronal and hormonal systems of cell signalling

  
• Define the terms "negative feedback", "positive feedback" and "homeostasis".

  Negative Feedback- restores systems to their original levelPositive Feedback- when a change takes place systems in the body act to reinforce the changeHomeostasis- The maintenance of a dynamic equilibrium within narrow ranges in the body
• List 4 factors that need to be kept constant (within a narrow range) in animals.

  Blood Glucose levelsTemperatureBlood Water levels
• Draw a flow chart to outline the processes involved in negative feedback.

  
• Define the terms "effector" and "receptor" in relation to negative feedback.

  Effector- Responds to the changesReceptor- detects the changes
• Explain what is meant by "constant" in terms of homeostasis.

  The maintenance of a constant internal environment despite changes in internal and external conditions.
• Define endotherm


  Animals that rely on their metabolic processes to warm their bodies and maintain their core temperature.
• Define ectotherm

  Animals that use heat from their surroundings to heat their body eg. lizard
• Define thermoregulation

  control of core body temperature
• Define the term "core body temperature".

  Core body temperature is the temperature of the body's internal organs
• Explain why "warm-blooded" and "cold-blooded" are inappropriate terms for endotherms and ectotherms.

  "cold blooded" animals don't always have cold blood, their core body temperature depends greatly on the environment so if the external temperature is hot, their internal temperature will be hot as well.
• Explain why temperature needs to be maintained within a narrow range with cells.

  Enzymes work at an optimum temperature, therefore at too high a temperature the enzymes will denature an at too long a temperature the enzymes won't have enough kinetic energy to work. In both cases it results in metabolic processes stopping.
• Describe and explain 4 ways that heat is transferred between an organism and their environment.

  Radiation- organism gains heat by radiation from sunConduction- organism gains heat from hot surfacesConvection- organism loses heat by convection currents in the airEvaporation- organism loses heat by evaporation of water from the surface of the skin
• Describe how an organism generates heat internally.

  Vasoconstriction- arterioles near the surface of the skin constrict Decreased sweatingRaising body hairs- traps an insulating layer of warm hairShivering- muscles contract and relax generating metabolic heat
• Define the term "exothermic reaction"

  Reactions that release energy.
• Describe the advantages and disadvantages of being an ectotherm.

  Don't have to rely on metabolic processes to keep core temperature constant so less energy used however it does mean they have to rely greatly on external temperatures which can be unpredictable. They are less active in cooler temperatures and have to warm up in the morning sun before they are more active. This puts them at risk from predators. They are not capable of activity during the winter as they can't warm up enough. They have to have sufficient stores of energy to survive over winter without eating.
• Outline how an ectotherm regulates its internal temperature

  Dark colours absorb more radiation, so animals living in colder climates tend to be darker skinned. Some also alter their heart rate to increase or decrease the metabolic rate. They rely a great deal on behavioural responses such as; bask in the sun, orientate their bodies so maximum surface area is in the sun, pressing against the warm ground, shelter in the shade.
• Draw a table to show 6 adaptations for temperature regulation in ectotherms, and how they help regulate temperature. Give an example for each adaptation.

  black in morning/on side exposed to Sun- absorbs more energy so can get warmer pale grey away from Sun/at certain times of day- reflects light so reduces heat loss orientation of body sideways to Sun- maximise surface area available to absorb sunlight increased heart rate in cool morning increases metabolic rate, increasing temperature inflation/deflation of body- maximises/reduces surface area exposed to sun presses body to sand- allows animal to warm up by conduction heart rate slows down- reduces metabolic rate and so less warming panting during day / mouth open- cools by evaporation of water from surfaces and radiation from tissues holds away from desert surface- to allow cooling into air by conduction, radiation, etc
• List 4 different types of organism that are ectotherms.

  reptiles, amphibians, crabs, fish
• Describe the advantages and disadvantages of being an endotherm.

  Lots of energy required to maintain core body temperature so lots of food needed, however less dependent on the weather and external temperature so have the same energy day/night and summer/winter.
• Outline how an endotherm regulates its internal temperature.

  Thermoregulation. Receptors detect a change in body temperature. Vasoconstriction/vasodilation. Sweating, erect and relax erector pili muscles. Shivering. Also behavioural responses such as hibernating, putting more clothes on.
• Explain why a shrew has to eat almost its own body mass each day, but an elephant eats less than 1% of its body mass each day.

  Shrews have a larger SA:Vol ratio therefore lose a lot of heat to the environment and therefore has to eat a lot of food just to keep warm.- An elephant has a small SA:Vol ratio so less energy is lost to the environment so needs less food.
• Explain why Australian penguin species are often smaller than Antarctic penguin species.

  It is a hotter environment in Australia so they have a larger SA:V therefore lose a lot of heat from evaporation to the environment. It is colder in Antarctic so more heat has to be kept in so smaller SA:V means core body temperature maintained easier as less heat loss to environment.
• Draw a diagram to show the components of the negative feedback mechanism that allows thermoregulation in endotherms.

  
• State the part of the brain involved in thermoregulation and describe its role in this process.

  Hypothalamus- the temperature receptors in the hypothalamus control the responses that maintain the core body temperature in a dynamic equilibrium
• Explain the role of the peripheral temperature receptors in thermoregulation.

  Detect the changes in the surface temperature.
• Explain how core body temperature is increased if it drops below the optimum.

  Shivering- muscles contract and relax, metabolic heat from the exothermic reactions warm up the body. Erector pili muscles in the skin contract, traps an insulating layer of air and so reduces cooling through the skin.Vasoconstriction- arterioles near the surface of the skin constrict so less heat loss.Less Sweating- less sweat evaporated from skin so less heat loss
• Explain how core body temperature is decreased if it rises above the optimum.

  Vasodilation- arterioles near the surface of the skin dilate so more heat loss Increased sweating- sweat evaporates from the skin, heat is lost Erector pili muscles relax- hairs lie flat to the skin, avoids trapping a layer of insulating air.