Cells and control

• Mitosis = cell division in BODY CELLS
• Inter phase = Cells grow and make extra organelles. Cells replicate DNA, making chromosome copies.
• Prophase: DNA in chromosomes condense, becoming more visible. The nuclear membrane breaks down + disappears and spindle fibres appear. Chromosomes move freely in the cytoplasm.
• Metaphase = The two chromatids line up on spindle fibres across the equator of the cell
• Anaphase = The two chromatids separate and pulled apart on spindle fibres to opposite cell poles.
• Telophase = New membranes form around each full chromosome set at each pole of the cell -> two nuclei are formed with identical chromosomes. Spindle fibres disappear.
• Cytokinesis = the cell splits into two. Cell surface membranes/cell walls form to separate the identical cells.
• • Mitosis is important in growth + repair as it produces identical cells.
  • Mitosis is important in asexual reproduction as there's only one parent. It produces clones, whose cells are IDENTICAL to the parent.
  • It is faster + doesn't need others.
• • Mitosis produces 2 DAUGHTER CELLS.
  • Mitosis results in the formation of 2 GENETICALLY IDENTICAL body cells.
  • These cells have identical sets of chromosomes in the nucleus to the parent cell.
• Cancer is a result of changes in cells this leads to uncontrolled cell division
• Cell division and differentiation in plants:

  • Growth occurs due to cell elongation (zone of elongation) due to intake in water (osmosis) in vacuoles.
  • Cells also differentiate into specialised cells which have particular functions (zone of differentiation): xylem/phloem, root hair cells.
  • Growth happens firstly in the MERISTEM at the end of shoots/roots due to rapid cell division
• Cell division and differentiation in animals:


  • Growth happens by cell division (mitosis) In younger animals, cell division is at a faster rate -> more growth.
  • In mature animals, cell division is mostly used for repair not growth.
  • Cells divided by mitosis eventually DIFFERENTIATE to become different types of SPECIALISED cell.
  • Most cells stop differentiating at early stages - specialised cells with nuclei divide by mitosis.
• Differentiation produces specialised cells, adapted/specialised to carrying out specific functions. They make up a whole multi-cellular organism + specialised cells make them work more effectively
• • EMBRYONIC STEM CELLS are cells taken from embryos at early stages of division. They can divide to produce any type of specialised animal cell.
  • Can replace/repair damaged: brain cells (treat Parkinson's); retina cells (treat blindness). Used to grow transplants/drug testing tissue.
• • ADULT STEM CELLS are taken from differentiated tissue in an animal (e.g. bone marrow). As the animal is fully developed, stem cells lose ability to produce other specialised cells - only produced surrounding tissue stem cells
  • Can treat leukaemia (bone marrow cancer) + potentially new tissues genetically matched to patients.
• • PLANT MERISTEM CELLS are taken from rapidly growing parts: root/shoot meristems. Can divide and differentiate to produce any type of specialised plant cell for as long as the plant lives.
  • Can produce cloned crop plants for farmers with desirable traits.
  • Can be used to clone rare plants to stop their extinction
• ALL STEM CELLS

  • Benefits: Replace faulty, diseased cells with healthy, specialised ones and stimulate their growth - scientific interest for cures if disease.
  • Drawbacks: REJECTION of cells from another person.
  • CANCER (stem cells don't stop dividing after replacing damaged ones)
  • Viruses inside cells can infect cells + if not spotted, could spread.
• EMBRYONIC STEM CELLS

  • Benefits: Easy to extract from embryos + produces any cell type.
  • Drawbacks: Embryos destroyed when cells are removed - some believe in right to life (ethical issue).
• ADULT STEM CELLS

  • Benefits: No embryo destroyed (no ethical/religious issue)Already used to treat disease by bone marrow transplants which can differentiate into specialised cells
  • Drawbacks: Produce a narrow range of cell types + only from the tissue around them.
• CEREBELLUM: responsible for balance, posture and muscle coordination as well as timing/fine control of muscles
• MEDULLA OBLONGATA: unconscious/automatic activities: breathing/ heart rate as well as reflex control: vomiting, sneezing+ swallowing
• CEREBRAL HEMISPHERES: Controls voluntary movement, sensory info , consciousness, language, memory and behaviour.
• CT scan: uses x-rays shows shapes of structures in the brain computers process uses information to build a 3D view of the brain in slices.
• PET scan: radioactive glucose injected into bloodstream more active cells take in more glucose to respire rapidly so gamma rays detect where the radioactive atoms are
• SPINAL CORD INJURY:

  Reduces flow of information between the brain + body parts.

  NO ADULT STEMS CELLS differentiate into neurons.

  The spine protects the spinal cord - hard to access it for surgery. Permanent/further damage could occur.
• BRAIN TUMOURS:

  Cancer cells divide rapidly to form tumours.

  Radiotherapy and Chemotherapy can kill cancer cells but this can damage healthy cells.

  Chemotherapy may not work due to the BLOOD-BRAIN BARRIER only allowing certain substances to pass (difficult for medicine to enter). The skull protects the brain - hard to access it for surgery.
• SENSORY NEURONES:

  • Carry impulses from receptor cells to the CNS. Dendrite branches collect impulses from receptor cells. Impulses passed into them are transmitted along a long dendron to the cell body in the middle of the neurone. A short axon transmits impulses away from the cell body to the series of axon terminals, passing impulses to other neurones.
• MOTOR NEURONES:

  Carry impulses from the CNS to effectors. Dendrite branches receive impulses from other/relay neurones and they pass nerve impulses to the cell body. The impulse is transmitted along a long axon from the cell body to a series of axon terminals, passing impulses to effector cells. (No dendrons).
• RELAY NEURONS:

  • Carry impulses from between neurons and makes up the tissue of the CNS. Dendrite branches pass nerve impulses from the sensory neurone to the cell body. The axon transmits impulses away from the cell body to axon terminals, passing impulses to other neurones. This can link sensory + motor neurons