2 - Cells and Control

• A gene is a short section of DNA that codes for a protein and controls a characteristic.
• Mitosis occurs to produce genetically identical cells for growth, repair and asexual reproduction.
• In interphase, before mitosis occurs, the DNA is replicated.
• In prophase, the chromosomes condense and become visible, breaking down the nuclear membrane.
• In metaphase, the chromosomes line up in the equator of the cell. Spindle fibres attach to the centromeres.
• In Anaphase, the chromatids are separated to opposite poles of the cell.
• In Telophase, two new nuclei form around the chromosomes on both sides.
• In cytokinesis, the cytoplasm divides into two daughter cells.
• Plants have specialised growing areas called meristems which contain stem cells that can differentiate, allowing the plant to grow for its whole life span.
• Plant cells also grow by cell elongation where it expands.
• Cancer occurs due to uncontrolled cell division, which forms a tumour.
• Adult stem cells are found in specific tissues and differentiate to repair the tissue.
• Embryonic stem cells can become any type of cell in the body as differentiation hasn't started in the embryo.
• The reasons for stem cell research is that it can be used to treat diseases, reduces the need to find donors, and less money will be wasted testing new drugs.
• The reasons against stem cell research is that it diverts resources away from treatments that really work, it is against certain religions to stop life developing and some embryonic stem cells are unstable and cause tumours.
• Embryonic stem cells vs adult bone marrow cells:

  Embryonic stem cells treat a wider variety of problems, is painless and is better than wasting ivf embryos.

  However it causes death to the embryo, is less tested and embryo can't give consent.
• Adult bone marrow cells vs Embryonic stem cells:

  Adult bone marrow cells are low risk and don't kill donor, is well tested and there is consent.

  However it is painful so people may not donate, treats fewer diseases and operation hazards still occur such as infection.
• The cerebral cortex is responsible for cognition, intelligence, emotion and sight.
• The cerebellum is responsible for balance and movement.
• The medulla is responsible for involuntary actions.
• The central nervous system is the brain and spinal cord.
• The process of responding has 4 steps:

  1. There is a change in the environment
  2. This stimulus is detected by a receptor
  3. The impulse is sent to the central nervous system by sensory neurons and the information is processed
  4. The motor neurone sends the impulse to the effector and the response is carried
• • The dendron carries impulses towards the cell body
  • The axon carries the impulse to the axon terminal
  • The myelin sheathe is an insulating fatty layer around the axon which speeds up impulses
  • The nerve muscle junction is where the impulse is carried to the effector
  • Dendrites go towards the cell body and pick up impulses from other neurons
• Relay neurons connect motor and sensory neurons together and protect us from harmful stimuli by allowing us to react rapidly.
• Steps in synaptic transmission:

  1. Electrical impulse travels to pre synaptic membrane
  2. This triggers the release of neurotransmitters
  3. They diffuse across the synaptic cleft
  4. They bind to receptors on the post synaptic membrane
  5. This stimulates another electrical impulse which travels to the next neurone
• The process behind a reflex action (6 marker):

  1. Receptor detects harmful stimulus and generates electrical impulse
  2. Sensory neuron conducts impulse to spinal cord
  3. Synaptic transmission occurs and the chemical stimulates an impulse in the relay neuron
  4. The impulse doesn't travel to the brain
  5. The impulse is sent to the motor neurone
  6. This is sent to the effector, causing the muscle to contract.
• PET scanners

  • PET scans use radioactive tracers which collect in areas where there is an increased blood flow
  • This includes the active regions within the brain as well as cancerous tissues which have a higher blood flow than healthy tissues
  • Neurologists can use the images to study the structure and function of the brain in real time
  • This has been useful in building understanding of specific diseases such as Parkinson's
• CT scanners

  • CT scans produce 3D images of the brain using X-rays which are fired at the brain from multiple different directions
  • A scan produced in this way shows physical structures of the brain and allows visualisation of any tissue damage
  • Symptoms caused by tissue damage can allow neurologists to work out which regions of the brain are responsible for which functions
  • CT scans are not recommended for pregnant patients or children due to the risks of exposure to the X-ray radiation, which is given at a higher level than in a normal X-ray
• The ciliary muscle moves the suspensory ligament which changes the shape of the lens
• The optic nerve sends sensory information from the retina to the brain by sensory neurons
• The cornea is the outermost lens which refracts light through the pupil
• Pupils dilate in a dark setting to let more light in
• Pupils constrict in bright setting so less light enters the eye avoiding damage
• When an object is near, the lens needs to be thicker to refract light more

  1. The ciliary muscles contract which loosens the suspensory ligament
  2. The more rounded lens enables light to focus correctly on the retina
• When an object is far, the lens needs to be thinner to refract light less

  1. The ciliary muscles relax which tightens the suspensory ligament
  2. The less rounded lens enables light to focus correctly on the retina
• Cataracts are when protein builds up in the lens and everything appears misty.

  This can be corrected by replacing the cloudy lens with a plastic lens.
• Long sightedness is when close objects are blurry and the light rays focus behind the retina because the cornea is not curved enough.

  Laser surgery or a converging lens can be used.
• Short sightedness is when far objects are blurry and the light rays focus in front of the retina because the cornea is too curved.

  Laser surgery or a diverging lens can be used.
• Colour blindness is when there are not enough cones so some wavelengths of light are not detected.

  There is no cure