topic 2 cell and control

• Diploid - a cell that contains two sets of chromosomes
• Haploid - a cell that contains one set of chromosomes
• Gametes - the sex cells
• Somatic cells - all body cells (with the exception of the gametes)
• Sexual reproduction - involves two parent cells to produce genetically different offspring
• Asexual reproduction - produces clones (genetically identical copies) of one parent
• The cell cycle is the sequence of events by which cells grow and divide for growth, repair, and asexual reproduction in some organisms
• Three main phases within the cell cycle:

  • INTERPHASE: period of cell growth where DNA replicates and new organelles are produced
  • MITOSIS: period of nuclear division resulting in two identical diploid daughter nuclei, made up of Prophase, Metaphase, Anaphase, and Telophase
  • CYTOKINESIS: period of cell (cytoplasm) division resulting in two identical diploid daughter cells
• Mitosis is a process with four stages:

  • Prophase: chromosomes condense, nuclear membrane breaks down, spindle fibres form from the poles
  • Metaphase: chromosomes line up at the equator, spindle fibres attach to the chromosomes
  • Anaphase: spindle fibres contract and shorten, chromatids get pulled apart to opposite poles of the cell
  • Telophase: nuclear membrane reforms around the chromatids at each pole, spindle fibres break down
• Cytokinesis: cytoplasm of the cell splits, cell membrane fuses to create two separate daughter cells
• Meiosis is a type of cell division that results in the formation of gametes, with two rounds of cell division producing four non-identical haploid gametes
• Fertilisation is the process when two haploid gametes fuse to make a diploid zygote
• Growth and differentiation:

  • Growth is an increase in cell size, length, and number
  • Animal growth involves increasing cell number through mitosis
  • Plant growth involves increasing cell number and elongation at the meristem
  • Differentiation is the ability of unspecialised cells to develop into different types of specialised cells
• Neurones are cells that carry electrical impulses around the body
• Neurones have dendrites where impulses start, axons where impulses travel, and axon terminals where impulses are sent to surrounding neurones
• Myelin sheath surrounds axons, insulating electrical signals and speeding up neurotransmission
• Synapses are gaps between neurones where information is sent by neurotransmitters
• Neurotransmitters diffuse across the synapse and bind to receptors on the post synaptic neurone, triggering a new electrical impulse
• Conscious motor movements involve the brain and spinal cord, while unconscious motor movements only involve the spinal cord
• Reflex arcs are unconscious motor movements using sensory, reflex, and motor neurones through the spinal cord to produce a response
• Types of neurones:

  • Sensory neurone carries impulses from the receptor to the reflex neurone in the spinal cord
  • Relay neurone in the spinal cord carries impulses to the motor neurone
• Reflex Arc:

  • Reflex actions are automatic, rapid responses that protect the body
  • Steps of the reflex arc:

  1. Receptor cells in the hand detect a stimulus

  2. Receptor cells activate the sensory neurone to transmit an electrical impulse to the relay neurone in the spinal cord

  3. Relay neurone passes the electrical impulse to the motor neurone

  4. Motor neurone activates an effector, causing a response
• Brain:

  • Composed of millions of neurones
  • Divided into sections controlling different body mechanisms
  • Sections include the spinal cord, medulla oblongata, cerebellum, and cerebrum
• Spinal Cord:

  • Long column of neurones relaying information between the brain and spinal cord
  • Responsible for unconscious actions like breathing, heart rate, vomiting, sneezing, and swallowing
• Medulla Oblongata:

  • Mass of neurones connecting the brain to the spinal cord
  • Responsible for unconscious actions like breathing, heart rate, vomiting, sneezing, and swallowing
• Cerebellum:

  • Found at the base of the brain, responsible for balance, posture, and coordinating muscle activity
• Cerebrum:

  • Makes up 80% of the brain, split into two cerebral hemispheres
  • Responsible for conscious actions like movement, memory, language, and vision
• Brain Imaging:

  • CT Scans used to show brain structures
  • PET scans show brain activity by injecting radioactive glucose
• Brain and Spinal Cord Problems:

  • Spinal cord damage reduces information flow between body parts and the brain
  • Brain tumours can be treated with surgery, radiotherapy, or chemotherapy
• Eye:

  • Contains receptor cells sensitive to visible light
  • Key structures include cornea, iris, retina, optic nerve, lens, ciliary muscles, and pupil
• Retina:

  • Layer of cells at the back of the eye
  • Contains cone cells sensitive to color and rod cells sensitive to light intensity
• Problems with the Eye:

  • Short-sightedness and treatment with a diverging lens
  • Long-sightedness and treatment with a converging lens
  • Cataracts treated by replacing the clouded lens
  • Colour-blindness results from faulty cones and has no treatment
• Stem cell: an unspecialised cell that can differentiate into different types of specialised cells
• Types of stem cells:

  • Totipotent stem cells: can differentiate into all 216 different cell types
  • Pluripotent stem cells: can differentiate into almost all cell types
  • Multipotent stem cells: can differentiate into certain groups of cell types
• Sources of stem cells:

  • Embryonic stem cells: sourced from the blastocyst of embryos, pluripotent
  • Adult stem cells: sourced from adults, mostly from the bone marrow, multipotent
• Embryonic stem cells:

  • Useful in research and medicine as they can differentiate into almost every cell type needed in the body
  • Ethical issues: termination of embryos, rejection by the immune system, risk of cancer, need for immunosuppressants
• Adult stem cells:

  • Limited in use as they can only differentiate into certain cell types
  • Beneficial for the person they were taken from as there is no chance of rejection
• CT (Computed Tomography) Scans:

  • Used to show structures in the brain
  • Differences in structures between individuals help us to understand functions
  • X-ray beam rotates around the head and a detector measures X-ray absorption
  • Produces a series "slices"
• PET (Positron Emission Tomography) scan:

  • Shows brain activity
  • Patient injected with radioactive glucose
  • More active cells will take in more glucose than less active cells
  • Radioactive atoms release gamma rays which the scanner detects
• Brain and Spinal Cord Problems:

  • Brain imaging can be used to identify brain diseases
  • Used during brain surgery to attach electrodes to areas of the brain and apply electrical currents to neurones
  • Surgeons can understand brain areas better by observing patient responses