BIO PAPER 2

• homeostasis = maintaining a stable internal environment
• Negative feedback counteracts change, and it is an automatic process
• stimulus = change in the environment
• Central nervous system (CNS)


  In vertebrates, consists of the brain and spinal cord only. Connected to the body by sensory neurones and motor neurones
• sensory neurones

  carry information as electrical impulses from receptors to the CNS
• motor neurones

  carry electrical impulses from the CNS to the effector
• effectors

  all your muscles and glands which respond to nervous impulses
• CNS coordinates the response
• gamete


  a sex cell e.g. sperm, ovums
• DNA


  large and complex polymer, which is made up of two strands forming a double helix
• chromosomes


  contained inside the cell's nucleus. These are long threads of DNA, which are made up of many genes.
• gene


  small section of DNA on a chromosome that code for a particular sequence of amino acids, to make a specific protein
• alleles


  different versions of the same gene - for example the gene for eye colour has an allele for blue eye colour and an allele for brown eye colour
• genotype

  collection of alleles that determine characteristics and can be expressed as a phenotype
• Dominant alleles are represented by a capital letter, for example, A.
• A dominant allele is always expressed, even if one copy is present
• a recessive allele is only expressed if the individual has two copies and does not have the dominant allele of that gene
• • Homozygous alleles are both identical for the same characteristic, for example AA or aa.
• heterozygous alleles are both different for the same characteristic, for example Aa
• human body cells have 23 pairs of chromosomes in the nucleus
• twenty two pairs are known as autosomes and control characteristics
• one pair carries genes that determine sex - whether offspring are male or female
• Cystic fibrosis is an inherited disorder of cell membranes that mainly affects the lungs and digestive system. They can become clogged with lots of thick, sticky mucus as too much is produced
• cystic fibrosis is caused by a faulty recessive allele on chromosome 7
• To be born with cystic fibrosis, a child has to inherit two copies of this faulty gene - one from each of their parents. Their parents will not usually have the condition themselves, because they will only carry one faulty gene and one that works normally.
• Polydactyly is an inherited condition in which a person has extra fingers or toes. It is caused by a dominant allele of a gene. This means it can be passed on by just one allele from one parent if they have the disorder.
• Someone who is homozygous (PP) or heterozygous (Pp) for the dominant allele will develop polydactyly.
• when the body's temp is above 37.5:

  • sweat
  • vasodilation
  • hairs lie flat
• when the body's temp is below 37.5:

  • no sweat
  • vasoconstriction
  • hairs rise up
• water level control is called osmoregulation
• nervous system - fast responses and short-term
• pituitary gland - in the brain. produces growth hormones
• thyroid - in the throat. produces thyroxine
• adrenal glands - located above the kidneys, produce adrenaline
• insulin - pancreas - increases conversion of glucose into glycogen for storage
• Low thyroxine levels in the bloodstream stimulate the hypothalamus to release TRH and this causes the pituitary to release TSH so the thyroid releases more thyroxine
• 1. Normal thyroxine levels in the bloodstream inhibit TRH release from the hypothalamus and this inhibits the release of TSH from the pituitary, so normal blood levels are maintained.
• when adrenaline is released into the bloodstream:

  • increases breathing rate, heart rate, and conversion of glycogen to glucose
  • diverts blood away from areas towards the muscles
• Type 1 diabetes is a disorder in which the pancreas fails to produce enough insulin. This can be detected from an early age. It is characterised by uncontrolled high blood glucose levels and it can be controlled by injecting insulin.
• in type 2 diabetes the person's body cells no longer respond to insulin produced by the pancreas. It is more common in older people. It can be controlled by a carbohydrate controlled diet and an exercise regime.