Core Biolody - Topic 2 Responses To A Changing Environment

• 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

• 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

• 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

• 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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• 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

• 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

• 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

• 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

• 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

• 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