biology paper 2

• Conscious response


  Signal goes from receptor through sensory neuron to relay neurons up the spinal cord to the brain, decision is made to act, signal goes back via relay and motor neurons to an effector
• Reflex arc


  Signal goes straight through the spinal cord to the motor neurons, bypassing the brain, action occurs before realizing what happened
• Stimulants


  Decrease reaction time or improve reactions, increase rate of neurotransmitter release across synapses
• Depressants


  Impair reactions, reduce amount of neurotransmitters crossing synapses
• Accommodation to focus on distant objects

  Ciliary muscles relax, suspensory ligaments tighten, lens becomes thinner, light refracts less
• Thermoregulation


  Ability of body to control internal temperature, an example of homeostasis
• Body response when hot

  Sweat glands produce sweat which evaporates, blood vessels dilate increasing blood flow to skin
• Body response when cold

  Vasoconstriction occurs, blood vessels get thinner reducing blood flow and heat loss, hairs stand on end trapping insulating air
• Glands


  Part of endocrine system, secrete hormones that affect other parts of the body
• Pituitary gland


  Master gland, found in the brain, responds to changes and secretes hormones that cause other glands to do the same
• Body response to high blood glucose

  Pancreas secretes insulin, causing glucose to enter cells for respiration, excess converted to glycogen
• Body response to low blood glucose

  Pancreas secretes glucagon, causing liver and muscles to convert glycogen back into glucose
• Kidneys


  Remove excess water from blood, mix with urea to form urine, filter out glucose and mineral ions
• ADH


  Anti-diuretic hormone from pituitary gland, causes kidneys to reabsorb water into bloodstream
• Thyroxin


  Controls metabolic rate, secreted by thyroid gland
• Adrenaline


  Increases blood flow and breathing rate, secreted by adrenal glands
• Hormones in menstrual cycle

  • FSH (follicle stimulating hormone)
  • Estrogen
  • LH (luteinizing hormone)
  • Progesterone
• FSH


  Causes egg to mature, causes ovaries to produce estrogen
• Estrogen


  Causes uterus lining to thicken, inhibits FSH
• LH


  Causes egg to be released
• Progesterone


  Maintains uterus lining
• Gibberellins


  Induce germination, promote flowering, increase fruit size
• Ethylene


  Promotes fruit ripening
• Auxins


  Growth hormones in plants, promote growth and elongation of cells, cause phototropism
• Stages of meiosis


  Chromosomes copied, homologous chromosomes pair up and genes swapped, cell divides twice to produce 4 genetically different haploid cells (gametes)
• DNA


  Double helix polymer, A-T and C-G base pairs, 3 bases code for 1 amino acid, sequence determines proteins synthesized
• Sexual reproduction


  Offspring can be better adapted to environment
• Asexual reproduction


  Produces clones
• Homozygous


  Two identical alleles for a gene
• Heterozygous


  Two different alleles for a gene
• Cloning an animal


  Take nucleus from cell, insert into egg cell of same species, insert into surrogate mother
• Estimating population size


  Use quadrats to sample 10% of area, count organisms, calculate average per square meter, multiply by total area
• Food chains and food webs

  Show direction of energy/biomass transfer between trophic levels
• Human impact on biodiversity

  Land use for building, quarrying, deforestation, peat extraction reduces biodiversity
• Pyramids of biomass get smaller going up trophic levels due to energy and biomass losses at each level