Topic 2 - Cells and control

• Diploid

  A cell that contains two sets of chromosomes (46 chromosomes)
• Haploid


  A cell that contains one set of chromosomes (23 chromosomes)
• Gametes


  The sex cells (sperm and egg cell)
• Sexual reproduction

  A type of reproduction that involves two parent cells to produce genetically different offspring
• Asexual reproduction

  A type of reproduction that produces clones (genetically identical copies) of one parent
• The cell cycle

  1. Interphase: A period of cell growth where the DNA replicates and new organelles are produced

  2. Mitosis: A period of nuclear division that results in the production of two identical diploid daughter nuclei

  3. Cytokinesis: A period of cell (cytoplasm) division that results in the production of two identical diploid daughter cells

  
• Mitosis

  1. Prophase: Chromosomes condense, nuclear membrane breaks down, spindle fibres form

  2. Metaphase: Chromosomes line up at the equator, spindle fibres attach to the centromere

  3. Anaphase: Spindle fibres contract and shorten, the chromatids get pulled apart to opposite poles of the cell

  4. Telophase: The nuclear membrane reforms, spindle fibres break down

  5. Cytokinesis: Cytoplasm of the cell splits, creates two genetically identical daughter cells
• Cancer cells are formed where there is rapid and uncontrolled cell division, a ball of cancer cells all undergoing this uncontrolled division is called a tumour, these can damage the body and result in cell death
• Meiosis

  Another type of cell division that results in the formation of the gametes, there are two rounds of cell division producing four non-identical haploid daughter cells
• Fertilisation

  The process when two haploid gametes fuse to make a diploid zygote
• Growth

  An increase in the size of cells, an increase in the length of cells (elongation) and the increase in the number of cells (mitosis)
• Animal growth

  Animals grow into their adult form by increasing the number of cells (mitosis), after an organism is a fully grown adult, cell division only continues to replace damaged cells and repair damaged tissues
• Plant growth

  Plants grow by increasing the number of cells and the cells elongate, this elongation occurs at the meristem which is found at the tip of the root and stem
• Differentiation

  The ability of unspecialised cells to develop into different types of specialised cells
• Stem cells

  Unspecialised cells that have the ability to differentiate into different types of specialised cells
• Types of stem cells

  • Totipotent stem cells - can differentiate into all different cell types
  • Pluripotent stem cells - can differentiate into almost all cell types
  • Multipotent stem cells - can differentiate into certain groups of cell types
• Embryonic stem cells

  Sourced from the blastocyst of embryos, are pluripotent so are useful in research and medicine, but there are ethical issues and risks of rejection
• Adult stem cells

  Sourced from adults, mostly from the bone marrow, are multipotent so their use in medicine is limited, but there is no risk of rejection
• Central nervous system (CNS)


  The brain and the spinal cord, which controls the body
• Peripheral nervous system (PNS)


  The nerves that extend from the spinal cord to the limbs
• Stimulus


  Anything the body is sensitive to, including changes inside the body and in the surroundings
• Receptor cells


  Cells in the sense organs that detect stimuli
• Neurone


  The cell that carries the electrical impulses around the body
• Myelin sheath


  Fatty layers that often surround the axons of neurones, insulating the electrical signal and speeding up transmission
• Synapse


  The gap between neurones, where information is sent between neurones by chemical substances called neurotransmitters
• Conscious motor movement


  Uses neurones in the brain and spinal cord to create actions that require thought
• Unconscious motor movement


  Does not use the brain, just the spinal cord to create actions that occur before you have thought about doing them
• Reflex arc


  Unconscious motor movements that use the neurones through the spinal cord to produce a response
• Types of neurone


  • Sensory neurone - carries an electrical impulse from the receptor to the relay neuron
  • Relay neurone - carries the electrical impulse to the motor neuron
  • Motor neurone - carries the electrical impulses to the effector
• Dendrite


  Part of the post-synaptic neurone
• There are only receptors on the post-synaptic neurone so impulses only travel in one direction
• Types of motor movement


  • Conscious
  • Unconscious
• Reflex arc


  1. Receptor cells detect stimulus

  2. Receptor cells activate sensory neurone

  3. Sensory neurone transmits impulse to relay neurone

  4. Relay neurone passes impulse to motor neurone

  5. Motor neurone activates effector
• Reflex actions are responses that are automatic, rapid and protect the body
• You can use a mnemonic to help remember the order of the reflex arc: Ronaldo Survives Reaching Mount Everest (Receptor, Sensory, Relay, Motor, Effector)