AQA - 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 stimulus

  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, problem solving
  • Cerebellum - responsible for motor skills, movement, balance, 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)
• Thermoregulation


  Brain senses blood temperature

  Sends nervous and hormonal signals to effectors

  Effectors cause body to lose or retain heat
• Endocrine system


  System of glands that produce hormones that travel to effectors via the blood
• Pituitary gland


  Main or master gland that produces hormones in response to stimuli
• Insulin


  Hormone produced by the pancreas that causes glucose to move from blood into cells
• Glucagon


  Hormone produced by the pancreas that causes the liver and muscles to convert glycogen back into glucose
• Type 1 diabetes


  Pancreas can't produce enough insulin
• Type 2 diabetes


  Cells no longer absorb glucose properly
• Water and nitrogen balance

  Body loses water through exhaling, sweating, urinating

  Kidneys remove excess water from blood and mix with urea to form urine

  Antidiuretic hormone (ADH) regulates water reabsorption by kidneys
• Menstrual cycle


  FSH causes egg maturation and estrogen production

  LH causes egg release

  Progesterone maintains uterus lining
• IVF


  In vitro fertilization - eggs harvested and fertilized in lab, then implanted
• Adrenaline


  Hormone that increases heart and breathing rate in stressful situations
• Thyroxin


  Hormone secreted by thyroid that controls metabolic rate
• Plant hormones


  Gibberellins - promote seed germination, flowering, fruit growth

  Ethylene - induce fruit ripening

  Auxins - control shoot and root growth, phototropism, geotropism
• Meiosis


  Chromosomes copied, paired, genes swapped, cell divides twice to form haploid gametes
• Asexual reproduction


  Daughter cells genetically identical to parent
• Genome


  All the genetic material in an organism
• Gene


  Section of DNA that codes for a specific protein
• Human Genome Project


  Mapped out what every gene is responsible for coding
• Genotype


  Genetic code stored in DNA
• Phenotype


  How the genetic code is expressed in characteristics
• Nucleotides


  Monomers that make up DNA
• Asexual reproduction


  Only one parent is needed, e.g. a plant on its own can still reproduce to ensure species survival
• Parasite that causes malaria

  Can reproduce both sexually and asexually
• Genome


  The term given to all the genetic material in an organism
• DNA


  A two-stranded polymer in a double helix shape that stores the genetic code
• Gene


  A section of DNA that codes for a specific protein
• The Human Genome Project completed its initial goal in 2003 when scientists mapped out what every gene is responsible for coding
• Genotype


  The code stored in your DNA specifically
• Phenotype


  How the genotype is expressed in your characteristics and physiology