Biology p2

• Nervous system

  Enables humans to react to their surroundings and to coordinate their behaviour - this includes both voluntary and involuntary actions
• Nervous system

  • Made up of the central nervous system (CNS) and a network of nerves
  • CNS comprises the brain and spinal cord
• Nervous system responses

  1. Stimulus (change in environment) detected by receptors

  2. Information from receptors passes along cells (neurones) to the CNS as electrical impulses

  3. CNS coordinates the body's response to the stimulus

  4. Effectors bring about a response, such as glands secreting hormones or muscles contracting

  5. Body responds to the stimulus
• Homeostasis

  Regulation of internal conditions (of a cell or whole organism) in response to internal and external changes, to maintain optimum conditions for functioning
• What homeostasis maintains in the human body

  • Blood glucose concentration
  • Body temperature
  • Water levels
• Homeostasis control systems

  • Receptor cells, which detect stimuli (changes in the environment)
  • Coordination centres (such as the brain, spinal cord, or pancreas), which receive and process information from receptors
  • Effectors (muscles or glands), which produce responses to restore optimum conditions
• Factors affecting reaction time

  • Tiredness
  • Distractions
  • Caffeine
  • Alcohol
• Reflex actions of the nervous system are automatic and rapid- they do not involve the conscious part of the brain
• Reflex actions are important for survival because they help prevent damage to the body
• Reflex arc

  • Sensory neurone
  • Relay neurone
  • Motor neurone
• Endocrine system

  Composed of glands that secrete chemicals called hormones into the bloodstream
• Pituitary gland

  Known as a 'master gland', it secretes several hormones into the blood which then act on other glands to stimulate the release of other hormones
• Roles of main hormones secreted from different endocrine glands

  • Pituitary (controls growth, stimulates thyroid)
  • Thyroid (controls metabolic rate)
  • Pancreas (controls blood glucose)
  • Adrenal (adrenaline, fight or flight)
  • Ovaries (female secondary sexual characteristics, menstrual cycle)
  • Testes (male secondary sexual characteristics, sperm production)
• Control of blood glucose levels

  1. Blood glucose concentration monitored and controlled by pancreas

  2. Insulin released, glucose moves from blood into cells

  3. Excess blood glucose converted to glycogen for storage
• Diabetes

  Non-communicable disease where body cannot produce or respond to insulin, leading to uncontrolled blood glucose concentrations
• Type 1 diabetes

  Caused by pancreas no longer producing insulin, early-onset, commonly treated with insulin injections, diet control and exercise
• Type 2 diabetes

  Arises when body doesn't respond to insulin produced, late-onset, commonly treated through carbohydrate controlled diet and exercise
• Hormones involved in menstrual cycle

  • Follicle stimulating hormone (FSH) (causes eggs to mature)
  • Luteinising hormone (LH) (stimulates release of mature eggs)
  • Oestrogen (causes uterus lining to thicken)
  • Progesterone (maintains uterus lining)
• Menstrual cycle

  1. If egg not fertilised, uterus lining breaks down and is shed as a period

  2. Hormones cause uterus lining to build up again
• Contraception methods

  • Hormonal (oral contraceptives, injections, implants, IUDs)
  • Non-hormonal (barrier methods, copper IUD, sterilisation, spermicides, abstinence)
• Variation

  Differences in the characteristics of individuals in a population
• Causes of variation

  • Differences in the genes they have inherited (genetic causes)
  • Differences in the environment in which they have developed (environmental causes)
  • Combination of genes and environment
• Mutation

  A change in a DNA sequence
• Mutations occur continuously
• Very rarely a mutation will lead to a new phenotype
• Most mutations have no or little effect
• If a new phenotype is suited to an environmental change

  It can lead to a relatively rapid change in the species (theory of evolution by natural selection)
• Selective breeding (artificial selection)

  The process by which humans breed plants and animals for particular genetic characteristics
• Process of selective breeding

  1. Choose parents with desired characteristic from a mixed population

  2. Breed them together

  3. Choose offspring with desired characteristic and breed them together

  4. Continue over many generations until all offspring show the desired characteristic
• Characteristics targeted in selective breeding

  • Usefulness
  • Appearance
• Examples of characteristics targeted in selective breeding

  • Disease resistance in food crops
  • Animals that produce more meat or milk
  • Domestic dogs with a gentle nature
  • Larger or unusual flowers
• Disadvantages of selective breeding include inbreeding and reduced variation
• Genetic engineering

  A process that involves changing the genome of an organism by introducing a gene from another organism to produce a desired characteristic
• Genetic engineering applications

  • Bacterial cells engineered to produce human insulin to treat diabetes
  • Plant crops engineered to be resistant to diseases, insects, or herbicides, or to produce bigger and better fruits and higher crop yields
• Benefits of genetic engineering

  • Potential to overcome some inherited human diseases
  • Can lead to higher value of crops as GM crops have bigger yields than normal crops
  • Crops can be engineered to be resistant to herbicides, make their own pesticides, or be better adapted to environmental conditions
• Risks of genetic engineering

  • Genes from GM plants and animals may spread to other wildlife, which could have devastating effects on ecosystems
  • Potential negative impacts on populations of wild flowers and insects
  • Ethical concerns, for example, in the future people could manipulate the genes of fetuses to ensure certain characteristics
  • Some people believe the long-term effects on health of eating GM crops have not been fully explored
• Sexual reproduction

  Cell division through meiosis, joining (fusion) of male and female sex cells (gametes), produces non-identical offspring that are genetically different to parents, results in wide variation within offspring and species
• Asexual reproduction

  Cell division through mitosis, produces offspring that are genetically identical to parent (clones), no mixing of genetic information
• Meiosis

  A type of cell division that makes gametes in the reproductive organs, halves the number of chromosomes in gametes, fertilisation restores the full number of chromosomes
• DNA

  Genetic material in the nucleus of a cell, made up of two strands forming a double helix, contained in structures called chromosomes