Biology Paper 2

• Nervous system


  • One of the ways that different parts of our body communicate with each other
  • Consists of the central nervous system (brain and spinal cord) and the peripheral nervous system (cranial nerves and other nerves throughout the body)
• How nerves work


  1. Receptor (sensory organ) detects stimulus

  2. Sensory neuron transmits signal to relay neuron

  3. Relay neuron transmits signal to brain

  4. Brain sends signal back through motor neuron

  5. Effector (muscle or gland) responds to stimulus
• Neuron


  • Main body, axon (long tail), dendrites (hair-like connections to other neurons)
  • Axon covered in myelin sheath to speed up signal transmission
• Synapse


  Gap between neurons where neurotransmitters transmit signals
• Stimulants and depressants


  Drugs that speed up or slow down neurotransmitter transmission
• Reflex


  Reaction that bypasses the brain, going directly from receptor to effector
• Measuring reaction time


  1. Grab ruler when dropped

  2. Repeat with different stimuli (audible, distractions)

  3. Repeat after drinking sugary drink
• Brain


  • Different parts control different functions (cerebral cortex for motor, cerebrum for movement, medulla oblongata for reflexes)
  • Can be imaged using CT scans or MRI scans
  • Nerves cross over as they enter the brain (contralateral control)
• Eye


  • Light hits cornea, pupil, lens, focused on retina
  • Rods detect black/white, cones detect colour
  • Optic nerve transmits signal to brain
• Accommodation


  Lens thickens/thins to focus on distant/close objects
• Endocrine system


  Glands secrete hormones that affect bodily functions
• Important endocrine glands


  • Pituitary
  • Thyroid
  • Pancreas
  • Ovaries
  • Testes
  • Adrenal
• Insulin regulation


  1. Pancreas secretes insulin

  2. Insulin tells liver to store excess glucose
• Diabetes


  Pancreas can't make enough insulin, leading to high blood glucose
• Menstrual cycle


  1. FSH stimulates egg maturation and estrogen production

  2. LH triggers egg release

  3. Empty follicle secretes progesterone
• Thermoregulation


  • Controlling internal body temperature of 37°C
  • Sweating, hair standing on end, blood vessel dilation/constriction
• Water control


  Kidneys remove urea and control water levels, producing urine
• Contraception methods


  • Physical
  • Hormonal (pill, patch)
• Fertility treatments


  Artificial insemination, IVF, FSH/LH therapy, surrogacy, egg donation
• Plant hormones


  Auxins promote/inhibit growth, ethene ripens fruit, gibberellins promote flowering and fruit size
• Reproduction


  Asexual (cloning) and sexual
• Auxin


  A chemical that can make cells elongate or stop them from elongating, used as a herbicide and rooting powder
• Ethene


  A chemical that can be used to ripen fruits
• Gibberellins


  Chemicals that promote flowering and make fruit size bigger
• How auxin works


  1. If in the shoot, light destroys it so it collects on the bottom side, making the stem grow upwards (positive phototropism)

  2. If in the root, it collects on the bottom side, inhibiting growth and making the root bend downwards
• Methods of reproduction


  • Asexual
  • Sexual
• Asexual reproduction


  A cell is cloned, no genetic variation between parents and offspring (mitosis)
• Sexual reproduction


  Gametes (haploid cells) join to form a diploid cell, genetic variation created through meiosis
• DNA


  A polymer with 4 bases (A, T, C, G) that codes for proteins
• Protein synthesis


  DNA is unzipped, RNA copies the code and takes it to the ribosome, ribosome assembles amino acids into a protein
• Genome


  All the DNA in an organism
• Gene


  Part of DNA that codes for a specific protein
• Alleles


  Different forms of the same gene
• Genotype


  The genes an organism has
• Phenotype


  The observable characteristics of an organism
• Genotypes for eye colour


  • Big B Big B
  • Big B little b
  • little b little b
• Dominant alleles (like Big B) are expressed in the phenotype, even if the recessive allele (little b) is also present
• Homozygous


  Having two of the same alleles
• Heterozygous


  Having two different alleles
• Some genetic disorders can be passed down, like cystic fibrosis