Biology Paper 2

• Homeostasis


  The regulation of the internal conditions of either a cell or whole organism to maintain the optimum conditions for function in response to internal and external changes
• Homeostasis mechanism


  1. Receptor detects stimulus

  2. Coordination centre (brain, spinal cord, pancreas) responds

  3. Effector (muscle, gland) produces response
• Negative feedback loop


  Body makes enough of a hormone or enzyme until it is inhibited and stops being made
• Examples of homeostasis regulation

  • Blood glucose concentration
  • Body temperature
  • Water levels
• Nervous system


  Uses nerves/neurons to transfer electrical impulses, provides fast but short-lived responses
• Endocrine system


  Uses hormones released from glands, provides slower but longer-lasting responses
• Reflex reaction


  1. Stimulus detected by receptor

  2. Sensory neuron transmits impulse

  3. Relay neuron in spinal cord

  4. Motor neuron transmits impulse to effector (muscle)

  5. Effector responds
• Reflex reactions are rapid automatic reactions that don't involve the conscious part of the brain
• The first required practical in biology paper 2 is investigating the effect of a factor like caffeine or tiredness on reflex reaction time
• Endocrine glands


  • Pituitary
  • Pancreas
  • Thyroid
  • Adrenal
  • Ovaries (females)
  • Testes (males)
• Pituitary gland


  Master gland that controls other endocrine glands by secreting hormones
• Thyroid gland


  Produces thyroxine hormone that stimulates basal metabolic rate
• Adrenal glands


  Produce adrenaline hormone that leads to fight-or-flight response
• Blood glucose regulation


  1. Blood glucose rises

  2. Pancreas secretes insulin

  3. Insulin stimulates glucose uptake by cells

  4. Blood glucose falls

  5. Pancreas secretes glucagon

  6. Glucagon stimulates liver to release glucose
• Type 1 diabetes


  Pancreas doesn't make enough insulin, leads to uncontrolled high blood glucose
• Type 2 diabetes


  Cells no longer respond to insulin, can often be controlled by diet and exercise
• Menstrual cycle


  1. FSH causes egg maturation

  2. LH triggers ovulation

  3. Ovaries produce estrogen and progesterone

  4. Progesterone levels fall, uterus lining shed (menstruation)
• Fertility treatment


  1. FSH and LH drugs to stimulate egg maturation

  2. IVF - eggs fertilised in lab, embryos inserted into uterus
• Sexual reproduction


  Involves fusion of genetically unique gametes to produce genetically unique offspring
• Asexual reproduction


  Produces genetically identical clones without gametes
• Mitosis


  1. DNA doubles

  2. Cell divides once to produce two genetically identical diploid cells
• Meiosis


  1. DNA doubles

  2. Cell divides twice to produce four genetically unique haploid gametes
• Gene


  Length of DNA that codes for a particular protein
• Allele


  Different variants of the same gene
• Genotype


  The alleles an organism has
• Phenotype


  The observable characteristics of an organism
• Homozygous


  Having two of the same alleles
• Heterozygous


  Having two different alleles
• Recessive allele


  Only expressed when homozygous
• Expressed


  What is actually seen, the phenotype
• Genotype


  The genetic makeup of an organism, determined by the alleles it possesses
• Homozygous


  Having two of the same allele
• Recessive allele


  An allele that is only expressed when in the homozygous state
• Dominant allele


  An allele that is expressed even when only one copy is present (in the heterozygous state)
• The genetic material of a eukaryotic cell is contained in the nucleus and is made of DNA
• DNA is a long molecule made of two polymer chains forming a double helix
• Human cells have 23 pairs of chromosomes
• Genome


  The entire genetic material of an organism, including all genes and non-coding DNA
• The Human Genome Project sequenced the human genome


  1986-2003
• Sex chromosomes


  The X and Y chromosomes that determine biological sex