Topic 2 - Cells and Control

• what does the nucleus contain

  genetic information
• genetic info is found in the form of

  chromosomes - contain coils of DNA
• a gene is

  section of DNA that codes for a protein - controls certain characteristic
• how many pairs of chromosomes are in each cell of body

  23 - in total 46
• gametes are

  sex cells - have 23 chromosomes in each cell
• diploid cells

  have two copies of each chromosome
• haploid cells

  half number of chromosomes
• cell cycle is

  series of steps that the cell has to undergo to divide

  when divides - mitosis
• mitosis - interphase

  • cell grows and increases amount of sub-cellular structures - mitochondria/ribosomes
  • duplicates its DNA so theres one copy for each new cell
• mitosis - prophase

  • chromosomes condense
  • membrane around nucleus breaks down
  • chromosomes are free in cytoplasm
• mitosis - metaphase

  • chromosomes line up at centre of cell / cell equator
• mitosis - anaphase

  • spindle fibres pull chromosomes apart
  • chromatids pulled to opposite ends of cell / poles
• mitosis - telophase

  • membranes form around each set of chromosomes
  • these become nuclei of two new cells
  • nucleus has divided
• mitosis - cytokinesis

  • before telophase ends
  • cytoplasm and cell membrane divide to form two separate cells
• what does mitosis produce

  two identical diploid daughter cells

  genetically identical to parent cell
• cell division by mitosis is important for

  • growth and development
  • replace damage cells
  • asexual reproduction
• growth for animals

  • via cell differentiation and cell division (mitosis)
  • cells can then differentiate to specialised forms that adapt to their function
  • most cells differentiate at an early stage
  • mature animals - cell division happens to repair or replace damage cells
• growth for plants

  • cell division, cell differentiation and elongation
  • elongation = plant cells grow longer in specific direction by absorbing water into their vacuoles - process controlled by auxins
  • many plants retain ability to differentiate through life
• cancer

  occurs as result of small changes in cells that lead to uncontrollable cell division

  group of cells that results from this called tumour

  tumour cells can break off and spread to other tissues - secondary tumours
• what are percentile charts

  tell us rate at which an organism is growing
• percentile charts

  • 50th percentile of mass - heavier than 50% babies
  • 25th percentile of mass - heavier than 75% babies
  • 75th percentile of mass - heavier than 25% babies
• what measurements are taken to make sure a baby is growing properly

  • length
  • mass
  • head circumference
• what are stem cells

  undifferentiated cell that can divide by mitosis to produce more similar cells

  will differentiate to perform a specific function
• types of stem cells

  • embryonic
  • adult
  • meristems
• embryonic stem cells

  • when sperm and egg fuse to form zygote
  • can differentiate into any type of cell in body
  • scientists can clone these (through culturing them) and direct them to differentiate into almost any cell in body
  • could potentially be used to: replace insulin-producing cells in those who have diabetes, new neural cells for Alzheimers, nerve cells for paralysed (spine cord injury)
• adult stem cells

  • arent as versatile
  • found in bone marrow
  • can form many types of cells like blood cells - replace damaged ones
• meristems - plants

  • in root and shoot tips
  • can differentiate into any type of plant - have this ability throughout life
  • can be used to clone plant - may be necessary if plan has desirable feature
  • can form specialised tissues like xylem and phloem
• therapeutic cloning

  • involves embryo being produced with same genes as patient
  • embryo produced can be harvested to obtain embryonic stem cells
  • could be grown into any cells the patient needs (new tissues or organs)
  • wouldnt be rejected - same genetic makeup
• research of stem cells - benfits

  • can be used to replace damaged/diseases body parts
  • unwanted embryos from fertility clinics could be used as they would otherwise be discarded
  • allow more research into process of differentiation
• research of stem cells - problems

  • we dont completely understand process of differentiation - hard to control stem cells to form ones we desire
  • removal results in destruction of embryo
  • people may have religious/ethical objections - interference with natural process of reproduction
  • if contaminated with virus - infection can be transferred to individual
  • money and time could be better spent in other areas of medicine
• what is the nervous system

  allows us to react to our surroundings and coordinate actions in response to stimuli
• how nervous system works

  • receptor cells convert stimulus to electrical impulse
  • electrical impulse travels along sensory neurones to CNS
  • in CNS - info is processed and response coordinated
  • results in electrical impulse being sent along motor neurones to effectors
  • effectors carry out response (may be muscles contracting/glands secreting horomones)
• sensory neurone

  • one long dendron carries nerve impulses from receptor cells to cell body (in middle of neurone)
  • one short axon carries nerve impulses from cell body to CNS
  • receptor - dendron - axon
• motor neurone

  • many short dendrites carry nerve impulses from CNS to cell body
  • one long axon carries nerve impulses from cell body to effector cells
  • myelin sheath around axon - allows nerve transmissions to travel faster
  • dendrites - axon - effector cells
• relay neurone

  • many short dendrites carry nerve impulses from sensory neurones to cell body
  • axon carries nerve impulses from cell body to motor neurones
• reaction time

  time it takes for your body to respond to a stimulus
• reflexes are

  automatic rapid responses to stimuli

  prevent injury - info travels down reflex arc allowing quick responses
• reflex arc

  • stimulus detected by receptors
  • impulses sent along sensory neurone
  • in CNS - impulse passes to relay neurone
  • impulses sent along motor neurone
  • impulse reaches effector resulting in appropriate response
• example of reflex arc

  pupils get smaller to avoid damage from bright lights

  • light receptors detect bright light
  • send message down sensory neurone to brain
  • then travels along relay neurone to motor neurone
  • tells muscles in iris to contract
• what are synapses

  connections/gaps between two neurones