Topic 2 bio

• Chromosomes


  Genetic information found in the nucleus, containing coils of DNA
• Gene


  Short section of DNA that codes for a protein and controls a characteristic
• There are 23 pairs of chromosomes in each cell of the body, resulting in 46 chromosomes in total
• Sex cells (gametes) have half the number of chromosomes, resulting in 23 chromosomes in total
• Diploid number of chromosomes

  Amount found in body cells (46 in humans)
• Haploid number of chromosomes

  Half the diploid amount (23 in humans), found in gametes
• Cell cycle


  1. Interphase

  2. Mitosis

  3. Cytokinesis
• Interphase


  • Cell grows, organelles grow and increase, protein synthesis, DNA replication, energy stores increased
• Mitosis


  • Chromosomes line up at equator, cell fibres pull each chromosome to either side
• Cytokinesis


  • Two identical daughter cells form as cytoplasm and cell membranes divide
• Mitosis


  Cell division process that produces two genetically identical diploid daughter cells
• Cell division by mitosis in multicellular organisms is important for growth, development, and replacing damaged cells
• Mitosis is also a vital part of asexual reproduction, as it replicates the organism's own cells to produce offspring
• In animals, growth occurs via cell division and differentiation
• In animals, most specialised cells can make more of the same cell by undergoing mitosis
• In mature animals, cell division mostly only happens to repair or replace damaged cells
• In plants, growth occurs by cell division, differentiation, and elongation
• In plants, many types of cells retain the ability to differentiate throughout life
• Cancer


  Uncontrolled cell division resulting in a tumour
• Percentiles


  Charts used to measure the growth of an organism compared to others
• Stem cell


  Undifferentiated cell that can undergo division to produce more similar cells, some of which will differentiate
• Types of stem cells

  • Embryonic stem cells
  • Adult stem cells
  • Meristems in plants
• Embryonic stem cells


  • Form when egg and sperm fuse, can differentiate into any cell type, can be cloned and directed to differentiate
• Adult stem cells


  • Found in bone marrow, can form many cell types including blood cells
• Meristems in plants


  • Found in root and shoot tips, can differentiate into any plant cell type, can be used to make clones
• Therapeutic cloning


  Producing an embryo with the same genes as the patient to obtain embryonic stem cells
• Benefits of stem cell research

  • Can replace damaged/diseased body parts
  • Unwanted embryos from fertility clinics could be used
  • Research into differentiation process
• Problems of stem cell research

  • Differentiation process not fully understood, hard to control
  • Removal of stem cells destroys embryo
  • Religious/ethical objections
  • Risk of contamination and infection
• Central Nervous System


  • Brain and spinal cord, responsible for controlling consciousness, movements, thoughts, emotions
• Stem cells


  Can be used to replace damaged or diseased body parts
• Problems with stem cells

  • We do not completely understand the process of differentiation, so it is hard to control stem cells to form the cells we desire
  • Removal of stem cells results in destruction of the embryo
  • People may have religious or ethical objections as it is seen as interference with the natural process of reproduction
  • If the growing stem cells are contaminated with a virus, an infection can be transferred to the individual
  • Money and time could be better spent on other areas of medicine
• Nervous system response


  1. Receptor cells convert a stimulus into an electrical impulse

  2. Electrical impulse travels along sensory neurons to the central nervous system (CNS)

  3. Information is processed and the appropriate response is coordinated, resulting in an electrical impulse being sent along motor neurons to effectors

  4. Effectors carry out the response
• Reflex


  Automatic responses which take place before you have time to think, important to prevent the individual from getting hurt
• Reflex arc


  1. Stimulus is detected by receptors

  2. Impulses are sent along a sensory neuron

  3. In the CNS the impulse passes to a relay neuron

  4. Impulses are sent along a motor neuron

  5. The impulse reaches an effector resulting in the appropriate response
• Synapse


  The gaps between two neurons, where a chemical called a neurotransmitter is released into the synapse, diffuses across, and triggers the impulse to begin again in the next neuron
• Myelinated nerves


  Nerves surrounded by a myelin sheath, which allows nerve transmission (action potential) to travel faster
• Nervous system


  Allows us to react to our surroundings, and coordinate actions in response to stimuli
• Nervous system response


  1. Receptor cells convert a stimulus into an electrical impulse

  2. Electrical impulse travels along sensory neurons to the central nervous system (CNS)

  3. Information is processed and appropriate response is coordinated

  4. Electrical impulse sent along motor neurons to effectors

  5. Effectors carry out the response
• Reflex


  Automatic responses which take place before you have time to think, important to prevent the individual from getting hurt
• Reflex arc


  1. Stimulus detected by receptors

  2. Impulses sent along sensory neuron

  3. Impulse passes to relay neuron in CNS

  4. Impulses sent along motor neuron

  5. Impulse reaches effector resulting in appropriate response