Biology Gcse

• Nerve cell


  • Long
  • Thin
  • Lots of branch connections to either end
  • Adapted to carry electrical impulses from one point to another
• Synapse


  Connection between nerve cells where electrical impulses are converted to chemical signals to pass between cells
• Nerve cell communication

  1. Electrical impulse hits end of nerve

  2. Causes release of chemicals

  3. Chemicals diffuse across gap to next nerve cell

  4. Triggers another electrical impulse

  5. Electrical impulse continues along new neuron
• Central nervous system


  • Made up of brain and spinal cord
  • Where 'thinking' takes place
  • Takes in sensory information, decides what to do, sends out orders to the body
• Sensory neurons


  Carry information from receptors all over the body to the central nervous system
• Motor neurons


  Carry impulses from the central nervous system to effectors (muscles or glands)
• Reflex arc


  Nerve pathway that underlies unconscious reflexes
• Reflex arc


  1. Stimulus detected by receptor cells

  2. Sensory neuron carries impulse to spinal cord

  3. Relay neuron transfers impulse to motor neuron

  4. Motor neuron carries impulse to effector (muscle) to cause movement
• Stem cells


  • Can divide by mitosis to form more cells
  • Can differentiate into specialized cells
• Human life starts


  1. Sperm cell fertilizes egg cell

  2. Forms a single cell called a zygote

  3. Zygote divides by mitosis over and over again

  4. Forms a small group of cells called an embryo

  5. Embryonic stem cells can differentiate into any type of cell
• Embryonic stem cells


  Stem cells found in the embryo that can differentiate into any type of cell
• Plant stem cells


  Stem cells found in plant tissues called meristems that can differentiate into all the cells and tissues the plant needs
• Stem cells


  Cells that can divide by mitosis to produce more cells and can differentiate into different types of specialized cells
• Types of stem cells


  • Embryonic stem cells
  • Adult stem cells
• Embryonic stem cells


  • Found in the early embryo
  • Can differentiate into any type of specialized cell
• Adult stem cells


  • Found in the bone marrow
  • Can only differentiate into different types of blood cells
• Using stem cells to treat conditions


  1. Extract stem cells

  2. Grow them in a lab

  3. Stimulate them to differentiate into desired cell type

  4. Transplant into patient
• Conditions that could be treated with stem cells


  • Diabetes
  • Paralysis
  • Sickle cell anemia
• Drawbacks of using embryonic stem cells


  • Limited supply
  • Ethical issues
  • Risk of rejection by patient's immune system
• Advantages of using adult stem cells


  • Easy to obtain
  • No risk of rejection
• Limitations of adult stem cells

  • Can only differentiate into blood cells
• Potential risks of using stem cells

  • Virus transmission
  • Tumor development
• Some people object to using embryonic stem cells on religious or moral grounds as they have the potential for human life
• Embryos used for research are usually unwanted ones from fertility clinics that would otherwise be destroyed
• Embryonic stem cell research is tightly regulated in the UK with strict rules for scientists to follow
• Animals

  • Multicellular
  • Heterotrophs
  • Reproduce sexually
  • Estimated 5-10 million species
• Plants

  • Multicellular
  • Autotrophs (get energy from sun via photosynthesis)
  • Estimated 300,000 species
• Fungi

  • Some are multicellular, some are unicellular
  • Heterotrophs (get energy from other organisms)
  • Many use saprotrophic nutrition (secrete digestive enzymes outside body)
  • Some have a mycelium body made of hyphae
• Protists

  • Nearly all are unicellular
  • Some are plant-like (have chloroplasts, photosynthesize)
  • Some are animal-like (consume other organisms)
  • Some are pathogens that can cause disease
• Bacteria

  • Single-celled organisms
  • Some can photosynthesize but don't have chloroplasts
  • Most feed off other living or dead organisms
  • Estimated to have more species than all other kingdoms combined
  • Some are pathogens that can cause disease, but most are harmless or helpful
• Viruses

  • Tiny particles, not cells
  • Have a protein coat surrounding genetic material (DNA or RNA)
  • Can only reproduce by infecting and using other living cells
  • All are considered pathogens as they cause harm to host organisms
• Viruses, bacteria, protists, fungi, plants, and animals are the 6 groups of life, with viruses being the only non-living group
• Eukaryotic cells have DNA in chromosomes and a nucleus, while prokaryotic cells have loose DNA and no nucleus
• Sexual reproduction


  Involves the fusion of two gametes like a sperm and an egg, leads to genetically different offspring
• Asexual reproduction


  Uses mitosis to form an identical clone of the parent organism
• Advantages of asexual reproduction


  • Only one parent is needed
  • The process is very quick
• A single organism reproduces asexually


  It can quickly colonize an entire new area
• Asexual reproduction can happen within just a couple of days in the right conditions
• Asexual reproduction can happen in some plants, e.g. a single seed getting blown into a new habitat
• Disadvantages of asexual reproduction


  • No genetic variation, so all offspring are susceptible to the same diseases
  • Less chance of adapting to new conditions like changes in climate or new competitors