Biology Paper 2

• Homeostasis


  An organism's ability to regulate internal conditions even when external conditions change
• Importance of homeostasis


  • Allows crucial chemical reactions involving enzymes to happen at an Optimum rate
  • Regulates blood glucose concentration, temperature, and water levels
• Nervous system regulation of homeostasis

  1. Receptor detects change

  2. Electrical signal travels to spine through sensory and relay neurons

  3. Signal travels across synapse by neurotransmitter

  4. Signal goes to brain

  5. Conscious decision to act

  6. Signal goes back to effector via relay and motor neurons
• Reflex

  Signal bypasses the brain and goes straight through the spine to the effector
• Effectors

  Glands that produce specific chemicals the body needs
• Investigating reaction time


  1. Hold ruler between finger and thumb

  2. Drop ruler without warning

  3. Measure distance fallen before caught

  4. Repeat multiple times and take mean average
• Parts of the brain


  • Cerebral cortex - responsible for higher level functions like memory, speech, and problem solving
  • Cerebellum - responsible for motor skills, movement, balance, and coordination
  • Medulla oblongata - controls unconscious actions like heart rate and breathing
• MRI scans

  Magnetic resonance imaging - way of seeing brain activity safely
• Accommodation in the eye


  For far objects: Ciliary muscles relax, suspensory ligaments tighten, lens becomes thin

  For near objects: Ciliary muscles contract, suspensory ligaments slacken, lens becomes fatter
• Pupil


  Hole in the iris that can change size depending on light intensity
• Retina


  Contains rods (detect light intensity) and cones (detect colour)
• Myopia

  Shortsightedness - can't focus on far objects
• Hyperopia


  Longsightedness - can't focus on near objects
• Thermoregulation


  Brain senses blood temperature

  Sends nervous and hormonal signals to effectors

  Effectors cause body to lose or retain heat
• Conscious response


  Signal goes from receptor through sensory neuron to relay neurons up the spinal cord to the brain, decision is made, 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 realisation
• Stimulants


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


  Impair reactions, reduce amount of neurotransmitters crossing the synapse
• Accommodation (focusing 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 to heat

  Sweat glands produce sweat, blood vessels dilate
• Body response to cold

  Vasoconstriction, hairs stand on end
• Glands


  Part of endocrine system, secrete hormones
• Pituitary gland


  Master gland, responds to changes and secretes hormones
• Body response to high blood glucose

  Pancreas secretes insulin, glucose enters cells, excess converted to glycogen
• Body response to low blood glucose

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


  Remove excess water, filter glucose and ions, affected by ADH
• Thyroxin


  Controls metabolic rate, secreted by thyroid
• Adrenaline


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

  • FSH
  • Estrogen
  • LH
  • Progesterone
• FSH


  Causes egg maturation, ovary estrogen production, inhibits itself
• Estrogen


  Causes LH production, thickens uterus lining
• LH


  Causes egg release
• Progesterone


  Maintains uterus lining
• Gibberellins


  Induce germination, promote flowering, increase fruit size
• Ethylene


  Promotes fruit ripening
• Auxins


  Growth hormones, promote shoot growth, cause phototropism
• Stages of meiosis


  Chromosomes copied, homologous pairs form, genes swapped, two diploid cells formed, then four haploid cells
• DNA structure


  Double helix polymer, A-T and C-G base pairs, three bases code for amino acid
• Sexual reproduction advantage


  Offspring can be better adapted to environment