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| Question | Answer |
| What conditions do all living thing need to maintain their cells | • suitable temperature •suitable pH •aqueous environment that keeps substrates and products in solution •freedom from toxins and excess inhibitors |
| What happens to cells if they do not have the correct conditions | Cells will die and become inactive |
| Why do cells in multicellular organisms communicate | Cells are specialised and rely upon each other to coordinate their activites |
| What is the external environment for living organisms and what happens if it changes | •Air, water or soil around them •If it changes it may place stress on the living organisms |
| Give an example of a change in the external environement | •Environment becomes cooler •Leads to greater heat loss •The organsisms must monitor changes in the environemtn and change its behaviour or physiology in order to survive |
| Define stimulus | A change in the environment that brings about a response |
| Define response | The way in which the organisms changes its behaviour or physiology |
| What is the environment of cells | Tissue fluid bathes internal cells and tissues, not exposed to external environemtn |
| How do the activities of cells alter their own environment | •Cells undergo metabolic activities and create new products •These compounds can be unwanted or toxic and move out of cells into the surrounding tissue fluid •It would reduce the cell's activities so less waste is made |
| How is the tissue fluid maintained | •It is maintained by the blood •Blood flows throughout the body and transport substances to and from cells, waste products would be carried away and removed from the body by excretion |
| Why is it important to monitor the concentrations of waste products and substances | •So the body does not excrete too much of a useful substance •So the body removes enough of the waste products •So cells in the body are supplied with the substrates they need |
| Why is a good communication system required? | •So different parts of the body work together effectively •Cells that monitor blood may be in a different part of the body away from the source of the waste product |
| What will a good communication system do (5 points) | •cover the whole body •enable cells to communicate with each other •enable specific communication •enable rapid communication •enable both short-term and long-term response |
| Name the two major systems of communication | • Neuronal system •Hormonal system |
| What is the neuronal system | •Interconnected network of neurones that signal to each other across synapse junctions •Neurones can conduct a signal quickly and enable rapid responses to a stimuli |
| What is the hormonal system? | •System that uses blood to transport its signals •Cells in an endocrine organ releases the signal directly into the blood and is recognised by a specific target cells •Enables long term responses |
| Define homeostasis | Maintaining a constant internal environment despite changes in the external and internal factors |
| What is maintained by homeostasis? (6) | •Body temperature •Blood glucose concentration •Blood salt concentration •Blood Ψ •Blood pressure •Carbon dioxide concentration |
| What is the response pathway | Stimulus → receptor → communication pathway (cell signalling) → effector →response |
| What is the function of sensory receptors? Give an example | Sensory nerve endings that monitor changes in the internal or external environment of an organism and create action potentials Temperature receptors on the skin or in the brain |
| What is an effector? Give an example | •A cell, tissue or organ that brings about a response Liver cells or muscle cells |
| What is cell signalling? | •Can occur in adjacent or distant cells •Cells in the nervous system communicate via neurotransmitters •Cells in the hormonal system communicate via hormones |
| What are receptors? | •They detect stimuli and are specific •Different types of receptors detect different types of stimulus |
| What is negative feedback? | The mechanism that reverses a change, bringing the system back to the optimum |
| What is the mechanism for negative feedback | 1) Receptor detects stimulus and sends input to coordination centre 2)Coordination centre sends a output to the effectors 3)Effectors respond and brings about a change to bring system closer to optimum 4)As the system gets closer to optimum, the response is reduced |
| What are the limitations of negative feedback? | Only works within certain limits, there is variation around the optimum condition If the change is too big, the effectors cannot counteract it |
| How is temperature control maintained by negative feedback | The mechanism that increases a change, taking the system further away from the optimum Is less common and usually harmful |
| What is positive feedback? | The mechanism that increases a change, taking the system further away from the optimum Is less common and usually harmful |
| What is the mechanism of positive feedback? | 1)Receptor detects change and sends input to communication system 2)Communication system sends output to effector 3)Effector brings about a response that increases the change |
| Give an example of positive feedback | •Positive feedback is used for the dilation of the cervix at the end of a pregnancy •Cervix stretch causes PPG to secrete oxytocin •Oyxtocin increases uterine contraction which stretches cervix more •Birth ends the production of oxytocin |
| Why do we need to control body temperature? | •Too high can lead to enzymes denaturing •Too low can slow chemical reactions down •Too low can affect the individual's health (chemical reactions slow down etc) |
| Define Ectotherm | An organism that relies on external sources of heat to maintain body temperature |
| How do ectotherms regulate their temperature? | They rely on behavioural responses to alter that amount of eat exchanged with the environment When they are active muscle contraction will generate heat from increased respiration Can't control their temperature internally |
| How do ectotherms increase their temperature? | •Move into a sunny area •Lie on a warm surface •Expose a larger surface area to the sun |
| Give an example of an ectotherm trying to increase their temperature | •Snake can be found lying down exposed to the sun •Locust expose a large surface area to the sun in the morning but less at midday |
| How do ectotherms decrease their temperature? | •Move out of the sun •Move underground •Reduce body surface exposed to the sun |
| Give an example of an ectotherm trying to decrease their temperature | •A Locust increase the rate and depth of breathing when it is hot to cool the body •A lizard uses burrows to hide in during the hottest part of day and during the night •A horned lizard can change its shape by contracting/expanding its ribcage |
| What are the advantages of ectothermy? | •Do not use up energy to keep warm •Less of their food is used in respiration •More energy and nutrients gained from food can be converted to growth •Need to find less food •Can survive for long periods without food |
| What are the disadvantages of ectothermy? | •Less active in cooler temperatures •So at risk from predators while they are cold and unable to escape •Cannot take advantage of food that is available while they are cold |
| Define endotherm | An organism that uses heat from metabolic reactions to maintain body temperature |
| How do endotherms regulate their temperature? | Largely independent of external temperatures and controls their temperature to strict limits Use a variety of temperature regulation mechanisms (physiological and behavioural) |
| What physiological mechanisms are used by endotherms to maintain body temperature when hot and cold (5) | |
| What behavioural adaptations are used by endotherm to maintain body temperature? | |
| What are the advantages of |
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