2.6 Cell Division

• steps which occur in cell division:

  interphase

  mitosis / meiosis (nuclear division)

  cytokinesis
• what are the three main stages in the interphase stage?

  G1 - growth of cell

  S - synthesis of DNA/ DNA replication

  G2 - growth
• G1 phase - this is the firsg growth phase, this is also the longest stage. the cell increases the number of organelles and protein synthesis occurs to create spindle fibres
• G2 phase - this is a short gap before mitosis. here, the cell grows and there is an increase in the number of organelles in the cell. The protein synthesis occurs so spindle fibres can begin to form, for cell division
• S phase - DNA is replicated here, so that the daughter cells can have the same / identical DNA
• Cytokinesis - this is where the two cells divide
• G0 checkpoint - this occurs after mitosis. A cell would only enter G0 if:

  1. it has become fully differentiated e.g. Erythocyte
  2. The DNA in the cell is damaged, so the cell will try to repair the DNA
• G1 checkpoint - this occurs between the G1 and S phase, and checks that the cell is ready to proceed to the next phase. If not, then the cell would enter G0 where it would try to repair those issues
• G2 checkpoint - this occurs between G2 and mitosis, where the cell would check for an DNA mutations which may have occurred in the S phase. The daughter cells must receive the full identical genetic information, so that the proteins can functions properly. If not then the cell would enter G0
• metaphase checkpoint: Metaphase can not occur until all of the chromosomes have attached to a spindle fibre
• mitosis is used for:

  asexual reproduction

  repair damaged tissues

  growth of an organism
• during prophase:

  1. nuclear membrane breaks down
  2. chromosome condenses and are at random in the cell
  3. centrioles form on opposite poles, and spindle fibres form
• during metaphase:

  1. chromosomes / sister chromatids line up along the equator of the cell
  2. spindle fibres attach to the centromere of chromosmes
• During anaphase:

  1. sister chromatids are pulled to oppsite poles of the cell
  2. spindle fibres from the cytoskeleton contracts
  3. centromere breaks / divides
• During telophase:

  1. Cytokinesis occurs as the cell membrane begins to separate
  2. new nuclear enevlope forms
  3. the chromosome would uncoil and decondense becoming long and thin
  4. the spindle fibres break down
• stem cell- an undifferenciated cell, that can differenciate into any type of cell by mitosis
• totipotent cell - a stem cell that can differenciate into ANY type of body cell

  e.g) zygote/ the early stages of life
• multipotent cell - a stem cell that can differenciate into FEW types of cells

  e.g) RBC, WBC, Platelets - found in adults
• pluripotent cell - a stem cell that can differenciate into ANY type of body cell, apart from extra embryonic cells ( placenta, umbilical cord )
• erythocytes and neutrophils derive from the bone marrow
• to form an erythocyte-

  stem cells would have to differenciate to remove their nuclei, and create a lot of the protein haemoglobin
• to form a neutrophil-

  stem cells would have to differenciate to change the shape of their nuleus to 'multi-lobed', and produce a lot of lysosomes, to contain hydrolytic enzymes
• xylem vessels and phloem tubes are formed from meristems
• the stem cells in plants come from the cambium / meristem cells
• xylem vessel features:

  • The walls are filled with lignin, to provide strength against negative pressure; It is also waterproof.
  • It is made of dead xylem cells
  • It is a hollow tube - continuous column
  • Allows adhesion to take place - moves water up the plant
  • Pits - allow the flow of water
  • Transpiration
• phloem tube features:

  • made from live cells
  • have sieve tube elements and companion cells
  • companion cells provide ATP & proteins
  • contains plasmodesmata
  • allows assimilates (e.g sucrose and amino acids) to be transported up and down the plant
  • Translocation
• erythrocyte features:

  • no nuclei, mitochondria, golgi apparatus, rough ER
  • lots of haemoglobin
  • bioconcave - increases the surface area, so more efficient gas exchange
  • transport large volume of oxygen around the body
• neutrophil features:

  • multi-lobed nucleus = very flexible
  • granular cytoplasm - due to many lysosomes
  • lysosomes conatin a large volume of hydrolytic enzymes
  • englufs and breaks down pathogens
• Squamous epithelial cell features:

  • flattened / thin sacs
  • lines blood vessles
  • increase the rate of diffusion due to the short diffusion distance, from the thin structure
• ciliated epithelial cell features:

  • column shaped cells
  • found in trachea and bronchi
  • contain goblet cell - sectret mucus to trap pathogens
  • contain cilia, to ''waft'' mucus (with pathogen) up the trachea, to be coughed out / swallowed
• why do some smokers have a bad cough?

  the cilia on the cells are damaged, so they are unable to 'waft' the mucus that captures the pathogens, out and away from the lungs
• sperm cell features:

  • many mitochondria to provide ATP for movement
  • lysosomes in acrosome, to penetrate and fertilise the eggs
  • Flagellum moving in a propella-like action, in order to move cell
  • contains half the number of chromosomes
• palisade cell features:

  • they are long, thin and tightly packed
  • they have a lot of chloroplasts to absorb photons of sunlight for photosynthesis
• Guard cell and Stomata features:

  • allow gas exchange
  • guard cells open when water moves into the cell via osmosis, making them become turgid, and create a stomata
  • the stomata colses when the cells becomes flaccid
  • They have thin outer walls and thick inner walls
• Root hair cell features:

  • they have an increased surface area for the uptake of water and mineral ions
  • they have thin walls for efficient exchange
  • cytoplasm contains extra mitochondria for ATP for active transport
• tissue - groups of cells working together to carry out a particular function
• organ - groups of different tissues working together to carry out a particular function
• organ system - group of different organs that work togther to carry out different functions
• organism - is a group of different organ systems working together to carry out functions for your body
• squamous and ciliated epithelium work together in the lungs to aid the diffusion of gases/ to clear airways