Topic 2

• chromosomes: coiled up length of DNA molecules, which carries genes. They are found in the nucleas and normally in pairs in body cells.
• Cell cycle: a series of stages in which cell divide to produce new cells, which includes interphrases and mitosis and cytokinesis
• When a cell is not divind, it is in interphrase. It prepares for division:

  • grows in size
  • increase the amount of subcellular structures e.g. mitochondria and ribosomes
  • duplicates it's DNA
• Mitosis is the stage of the cell cycle where a cell divides into two identical daughter cells
• MItosis allow organisms to grow and replace cells that have been damaged. Some organisms use mitosis in asexual reproduction.
• calculate number of cells after mitosis = 2^n
• Plants and animal grow due to:

  • cell differentiation: a cell change to become specialise for it's job. Having specialisse cells help organism to work effectively
  • cell division: by mitosis
  • Cell elongation: plant cell expand and make the cell bigger and grow
• Animals:

  • growth happen by division
  • when young, cell divide at a fast rate. When old, cell is to repair
• Plant:

  • growth in height due to cell elongation, in tips of roots and shoots
  • plant grown continuously . They continue to differentiate to develop new parts
• Cancor:

  • rate of cell divide by mitosis is controlled by genes in DNA
  • change in genes = divide uncontrollably
  • mass of abnormal cell = tumour, if it destroy surrounding cell = cancer
• Percentille charts:

  • used to monitor a child's growth
  • 50th percentile = size 50% of baby will reach at a certain age
• Stem cell: undifferentiated cell that can divide to produce more stem cell by mitosis and differentiate into many types of cell.
• Stem cell found in:

  • human embryos: divide to any kind of human cell
  • adult: many kinds of cell e.g. blood cell, mainly to replace damaged cell
  • plant meristem: any kind of aimal cell, and generate as long as plant live
• Stem cell can be grow in a lab and made to differentiate. The specialised cell can be transferredinto people and used in medicine:

  pros: replace cells that have been damaged by disease or injury e.g. new cardic muscle cell to treat heart diseases

  cons:

  • tumour deveopment: stem cells divide quickly and scientist can't control the rate
  • Diseases tansmission: donor stem cell are infected by a virus
  • rejection: recognise cell as foreign and trigger immune response. But they can take drugs
• The brain

  A) Cerebral hemispheres

  B) Cerebellum

  C) Medulla oblongata

  D) hypothalamus

  E) SPinal chord

  
• Brian structure:

  • Cerebrum: divided into two halves called cerebral hemisphere. The right control movement on left body and the left control movement on the right body. Different part responsible for movement, intelligence, memory, language, vision
  • Cerebellum: muscle coordinate, balance
  • Medulla oblongata: unconcious activities like breathing etc.
• Central nervous system (CNS): consisit of the brain and the spinal cord. It is complex therefore difficult to treat

  • tumours can grow in parts of brain that are hard to access and remove surgically
  • operating on spinal chord can risk permanent damage
  • CNS tissue can't be repair
• Methods for studying the brain without surgery:

  • CT scanning: X-ray shows main structure of the brain, but doesn't show their function
  • Pet scanning: use radioactive chemicals to show which part of the brain are active. Very detail and can investigate both structure and function of brain in real time. Such as disorder
• Neurons: cells that carry information as electrical impulses in the nervous system. The nervous system means that human can react to their surroundings and coordinate their behaviour.

  Stimulus = sensory receptor = sensory neurone = CNS = motor neurone = effector = response
• Effector can be muscle (contract ) or glands ( secrets hormone )
• Synapse: the connection between 2 neurones. A nerve signal is transferred across a synapse by diffusion of neurotransmitters
• Neurons:

  • have cell bdy with a nucleus
  • dendrites and dendrons carry nerve impulses towards the cell body and axon carry nerve impulses away
  • myelin sheath act as an insulator which speed up electrical impulses
  • neurones are very long to speed up the impulses = connect with another neurons slows it down
• Sensory neurons: carries impulses from receptor cell to the CNS

  A) receptor cells

  B) dendron

  C) cell body

  D) Axon

  
• Motor neurone: carries impulses from the CNS to the effector cells

  • not all motor neurones have myelin sheaths, sensory and relay neurons can be myelined too

  A) dendrites

  B) cell body

  C) myelin sheath

  D) Axon

  E) effector cells

  
• Relay neurone: carries impulses from sensory neurones to motor neurons

  A) dendrites

  B) cell body

  C) axon

  
• Reflex arc: passage of information in a reflex, from receptor to effector
• Reflexes: rapid,automatic response to stimuli, which desn't involve concious part of the brain. It reduce the chance of injury
• Reflex arc:

  1. Stimulus detected by a receptor
  2. Impluses sent along a sensory neurone to a relay neurone in the CNS ( spinal chord or unconscious part of the brain)
  3. When impulses reach synapse between sensory and relay , they trigger neurotransmitter to be released
  4. same thing happen between relay and motor neurone.
  5. Impulses trave along motor neurone to an effector, show effective responds e.g. muscle then contract
• Structure of the eye:

  A) suspensory ligaments

  B) ciliary muscles

  C) cornea

  D) iris

  E) pupil

  F) lens

  G) optic nerves

  H) retina

  
• Function of the eye:

  • Lens: focuses light into retina
  • cornea: refracts light into eye
  • Iris: cntains muscle controlling pupil size
  • Retina: contains receptor muscles sensitive to light intensity (rods) and colour (cones)
  • Optic nerve: carries impulses from receptor cells to brain
• Rod cells are sensitive in dim light but can't sense colour

  Con cells are sensitive to different colour but not good in dim light
• Colour blindness: some cons don't work properly, can't tell the difference between colour. There's no cure as cone cell can't be replaced
• Cataracts: cloudy patch on the lens, which stop lights from entering the eye normally , which cause blurred vision. They might experience colour look less vivid and difficult to see in bright light. It is treated by replacing with artificial lenses
• To look at close objects:

  • ciliary muscle contracts and suspensory muscle relax
  • lens become a rounder shape and thicker
  • light is refracted more
• To look at distant objects:

  • Ciliary muscle relax and suspensory ligaments tighten
  • lens in less round shape and thinner
  • refracted less
• Long sightedness: unable to focus on near object

  • lens doesn't bend light enough or eyeball too short
  • Image of near object brought into fcus behind retina
  • fixed using convex lens
• Short sightedness: unable to focus distant object

  • lens bend light too much or eyeball too long
  • image of distant object brought into focus in front of retina
  • fixed using concave lens
• Which part of motor neurone is surrounded by myelin sheath?

  Axon
• Benefit of adult cell being able to programme into embryotic cell:

  • have the potential to produce any cell type
  • less chance of patients rejecting their own cell
  • no need to use mebrotic stem cells
• What happen in interphase?

  DNA is replicated

  metabollic activity