2C

• Homeostasis is the regulation of internal conditions of a cell or organism to maintain optimum conditions
• All control systems include a receptor, a coordinator, and an effector
• What do receptors do?

  Receptors detect and respond to stimuli (changes in the environment)
• What do coordination centres do?

  Receive and process information from receptors
• Give 3 examples of a coordination centre

  Brain, Spinal cord, Pancreas
• What do effectors do?

  Bring about responses which restore optimum levels
• Information from receptors passes along neurones as electrical impulses.
• What is the order of neurones through the central nervous system?

  Stimulus -> Receptor -> Sensory neurone -> relay neurone ->motor neurone -> effector -> response
• Where two neurones meet there is a small gap called a synapse
• How does the electrical impulse cross the synapse?

  By diffusing over chemical transmitters (Neurotransmitters)
• The different glands in the Endocrine system are the pituitary gland, thyroid gland, adrenal glands, pancreas, ovary (female), Testis (male)
• The endocrine glands secrete different hormones directly into the bloodstream
• Endocrine effects are slower than the nervous system but they last for longer
• The pituitary gland is the 'Master gland' of the endocrine system and often creates hormones to stimulate hormone production in other glands.
• If blood glucose concentration is high, the pancreas produces insulin which moves glucose into cells and causes excess to be stored as glycogen.
• Type 1 diabetes is where the pancreas can no longer produce sufficient insulin causing uncontrolled high blood glucose levels and is often controlled by insulin injections.
• Type 2 diabetes means the body doesn't respond to insulin properly. Obesity is often a risk so exercise and a controlled diet are recommended.
• If blood glucose concentration is low, the pancreas will produce the glucagon hormone that causes the liver to convert glycogen into glucose.
• Oestrogen is the main reproductive female hormone from the ovary and Testosterone is the main male reproductive hormone from the testes that stimulates sperm production.
• FSH is the follicle-stimulating hormone which causes the maturation of an egg in the ovary.
• LH is the luteinising hormone that stimulates the release of an egg from the ovary.
• Oestrogen and progesterone are produced by the ovaries and are responsible for the menstrual cycle and maintaining the uterus lining.
• Sexual reproduction involves the fusion of female and male gametes to form a zygote.
• Sexual production also requires the mixing of genetic information from 2 parents which leads to variation in offspring
• Meiosis is the division of cells in reproductive organs to form gametes.
• When a cell divides to form gametes:

  -Copies of genetic information are made

  -The cell divides twice to form four gametes each with a single set of chromosomes

  -All gametes are genetically different from one another
• The genetic material in the nucleus of a cell is made of a chemical known as DNA
• DNA is a polymer made of two strands that form a double helix.
• The DNA is made of structures called chromosomes which code for a particular sequence of amino acids to make a specific protein.
• The genome of an organism is the entire set of genetic material in an organism.
• Gamete is a sex cell either a sperm or and egg in animals
• A gene is a section of a chromosome that codes for a particular protein.
• Heterozygous is a pair containing different alleles whereas homozygous is a pair containing the same allele.
• A genotype is a pair of alleles for a phenotype.
• A phenotype is a characteristic that is expressed by an organism as a result of its genotype and the environment.
• Dominant alleles are always expressed even if only a copy is present
• Recessive alleles are only expressed if two copies are present.
• Polydactyly (extra fingers or toes due to a dominant allele) and Cystic Fibrosis (a disorder in cell membrane due to a recessive allele) are examples of inherited disorders.
• Differences in the characteristics of individuals in a population is called variation.
• Mutations in DNA can very rarely lead to the formation of a new phenotype which if suited to the environment can cause to a rapid change in the species as the new advantage will make it easier for certain groups to survive and reproduce. Which then passes in the new gene.