Core Biolody - Topic 2 Responses To A Changing Environment

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  • Created by: Katie
  • Created on: 18-04-13 20:20


  • Internal environment - the conditions inside the body
  • Homeostasis - keeping the intenal environment stable
  • Osmoregulation - the control of water in the body
  • Thermoregulation - the control of body temperature
  • Blood glucose regulation - the control of glucose in the blood
  • Vasicibstriction -  narrows blood vessels closet to the surface
  • Vasofilation - when the bidy is hot and needs to lose heat
  • Body loses water through breathe, urine and sweat
  • Sweat glands in the skin produce sweat
    • a gland is a part of the body that makes substances and releases them
  • If body contains too much water kidneys produce more urine
  • If body doesn't have enough water kidneys produce little urine and brain responds by making you feel thirsty
  • Body controls concentration of materials e.g. glucose in blood
  • Hypothalamus reduces blood flow to the skin when its cold
  • Body temperature control is example of negative feedback
  • Maintaining the right level involves mechanisms working in differen directions
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Homeostasis Continued

  • Chemical reactions in the body work best at 37 degrees
  • Your hypothalamus in the brain constantly monitors temperature
    • receives info from nerve endings in the dermis of the skin
    • recieves info from blood about internal body temperature
  • Hypothalamus causes muscles to shiver if body temperature goes below 37 degrees
    • shivering releases heat to warm you up
  • Hypothalamus erector muscles in the dermis to contract
    • causing body hairs to stand upright
    • has little effect in humans
    • traps air and is insulation for other mammals
  • Oil from the sebaceous glands at the base of hairs keep skin lubricated
  • Also keeps bloodflow away from the skin avoiding heat loss to the air
  • Hypothalamus causes sweating if body temperature goes above 37 degrees
  • Sweat evaporates from skin cooling it down as heat energy is transferred from skin to surroundings
  • Allows bloodflow nearer to the surface of the skin - makes us look pink
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  • Stimulus - anything the body is sensitive to, changes detected in surroundings
  • Sense organs detect changes inside and outside body
  • 5 common senses - touch, sight, hearing, taste, smell
    • others - heat, cold, pain, balance, changes in positions
  • Sense organs contain receptor cells that detect stimulus
  • Receptor cells create electrical signals called impulses travel to brain
    • brain sends impulses to organs that alter the way the body works
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Sensitivity Continued

  • This transmission of impulses caled neurotrasmitter
  • Neurones have a cell body and long extensions to carry nerve impulses
  • Dendron has branches called dendrites
    • to recieve imoulses from receptor cells and neuornes
  • Impulses move along dendron to axon
  • Pass along axonto the ends where it passes across other neurones
  • Nerves - neurones packed together
  • Spinal chord - organ that connects to the brain, made of many nerves packed together
  • Together the brain and spinal chord form the central nervous system (CNS)
    • its the CNS that controls your body
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Responding To Stimuli


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  • Hormones - chemical messengers that travel in the blood
    • the parts of the body respond to their presence
  • Endocrine glands - produce and release hormones
  • An organ that responds to a certain hormone is a target organ
  • Most carbohydrates in food are digested into glucose
  • Concentration of glucose in your blood increases after a meal
    • pancreas releases insulin hormone when its a certain concentration
  • Insulin takes glucose out of the blook and converts in to glycogen
    • which is a store of glucose in the liver
  • Glucagon is a hormone released when glucose levels drop
    • the hormone causes liver cells to turn glycogen back into glucose
    • then its released back into the blood to increase levels
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  • Diabetes - a disease whereby blood glucose levels aren't controlled
    • Low blood glucose concentrations - unconsiciousness
    • High blood glucose concentrations - tiredness, organ damage e.g. eyes
  • Type 1 diabetes - pancreas does not produce insulin
    • body cannot bring down blood glucose levels when they get to high
    • between 5% and 10% of diabetics have it
    • most will inject insulin everyday
  • Must be injected into the fat layer beneath the skin - subcutaneous fat layer
    • easily absorbs insulin
    • spreads to blood vessels to be carried in the blood
  • Diabetics must balance the lowering and increasing factors
    • more exercise = less insulin
    • more insulin needed some days than others
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Diabetes Continued

  • Type 2 diabetes - when cells become 'resistant'/respond less to well to insulin being produced
  • Contributors to aquiring it are:
    • high-fat diets
    • lack of exercise
    • obesity
    • old age
  • Often controlled by changing diet and increasing amounts of exercise
  • Obesity - if a person's Body Mass Index (BMI) is over 30
  • BMI - estimate of how healthy your mass is for your height
  • weight in kilograms
  • height in metres2
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Plant Hormones

  • Tropism - responding to a stimulus by growing towards of away from it
  • Positive tropsism - growing towards a stimulus e.g. plant shoots
  • Negative tropism - growing away from a stimulus e.g. plan roots
  • Phototropism - a tropisim caused by light
  • Geotropism - a tropism towards the direction of gravity (positive gravitropism)
  • Photosythesis - positively phototrophic, to get light, to make food
  • Plant growth substances = plant hormones
  • Auxins - cause positive phototropism and positive gravitropism
  • Gibberellins - cause starch in a seed to be converted into sugars for growth energy
    • also stimulate flower/fruit production in some species
  • Germination - when roots and a shoot start to grow
    • gibberellins are released after this process
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Plant Hormones Continued

  • Auxins produced in the tip of a shoot
    • cause elongation of cells
  • Shoot grows towards light when
    • light coming from one direction
    • auxins move to shaded side of shoot
    • cells on shaded side elongate more
  • Auxins produced in root tips - opposite effect
    • causes cells to stop elongating
    • causes geotropism
  • Anchors the plant in place
    • and to reach moisture underground
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Uses Of Plant Hormones

  • Artificial auxin 
  • used as a seletive weedkiller
    • plants with broad leaves grow out of control and die e.g. dandilions, daisies
    • narrow leaved plants are unaffected e.g. grass, wheat
    • farmers can kill weeds without killing cereal crop
  • used in rooting powders
    • plant cuttings are dipped in rooting powders to increase root development
    • large numbers of plants can be produced quicker than growing seeds
  • Seedless fruits
    • flowers sprayed with hormones that cause fruits but not seeds to develop
    • naturally seedless but small fruits are sprayed with gibberellins to increase size
  • Fruit ripening
    • fruit trees sprayed with hormones to stop fruit falling and being damaged
    • also to speed up ripening to be picked all together
    • unripe fruit so it reaches shops in a 'just ripened' condition
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