Cell division, cell diversity and cellular organisation

• what type of cell division do eukaryotic cells take place in?

  mitosis and meiosis in the cell cycle
• what type of cell division do prokaryotic cells undergo?

  binary fission
• what type of cell division do viruses go through?


  they do not undergo cell division as they are non living
• what are the key stages in the cell cycle?


  Interphase (G1, S, G2)

  Nuclear division (mitosis or meiosis)

  Cytokinesis
• what happens in G1?

  • protein synthesis occurs to make proteins involved in synthesising organelles
  • the organelles replicate
  • cell is checked that it is the correct size and has the nutrients to grow and there is no damage to the DNA,
  • if it does not pass these checks the replication will stop
• what happens in the S phase?

  DNA is replicated
• what happens in G2 phase? 


  cell continues to grow, energy stores increase and the newly replicated DNA is checked for copying errors
• what are the 4 key stages of mitosis?

  • prophase
  • metaphase
  • anaphase
  • telophase
• what is mitosis?


  creates two identical diploid cells and is used for growth, tissue repair and asexual reproduction
• what happens in prophase ?

  • chromosomes condense and become visible
  • centrioles separate and move to opposite sides of the cell
  • centrioles create spindles fibres (spindle apparatus)
  • these will attach to the centromere and chromatids on the chromosome later
• what happens in metaphase?

  • chromosomes align in the middle of the cell
  • spindle fibres attach to the centromere
  • spindle assembly checkpoint to ensure every chromosome is attached to a spindle fibre
• what happens in anaphase?

  • chromosomes separate and move to opposite poles of the cell.
  • causes the centromere to divide
  • ATP is required
• what happens in telophase?

  • chromosomes become longer and thinner
  • spindle fibres disintegrate
  • Chromosomes decondense and nuclear envelopes reform.
• what happens in cytokinesis?

  • the cytoplasm splits in two genetically identical cells
  • animals (cytoskeleton draws in cell membrane until cell splits)
  • plants ( cell membrane splits into two new cells due to fusing of vesicles from Golgi apparatus)
• miotic index equation


  the number of cells in mitosis/ x 100

  the total number of cells
• what is meiosis?


  two nuclear divisions which result four genetically different haploid daughter cells.

  ( two rounds of divison meiosis I or meiosis II)
• haploid (n)


  on copy of each chromosome
• Diploid (2n)


  two copies of each chromosome
• crossing over

  • happen in prophase I
  • the homologous chromosomes pair form bivalents
  • parts of the chromatids are exchanged between homologous pairs
  • new combination of alleles in the resulting gamete
• independent assortment 


  during metaphase I the homologous pairs of chromosomes line up opposite each other on wither side of the equator and it is random

  • this results in each gamete receiving different combinations of the maternal and paternal chromosome
• cells - tissue - organ - organ system - entire organism
• erythrocytes

  • biconcave shape = increase SA for diffusion
  • increase flexibility to fit through capillaries
  • no nucleus more space to hold haemoglobin = increase transport of oxygen
• Neutrophils

  • loved nucleus and granular cytoplasm
  • flexible = able to surround + engulf pathogens
  • contain lysosomes (hydrolytic enzymes, lysozyme)
  • made from stem cells in bone marrow
• Sperm cells

  • flagellum contain mitochondria = energy to move forward to egg
  • head contains digestive enzymes to digest egg cell so sperm can penetrate and fertilise egg
• Palisade cell

  • located in the mesophyll tissue layer of leaves
  • rectangular + tightly packed contains many chloroplasts to absorb light energy for photosynthesis
  • thin wall = short diffusion pathway for CO2
• Guard cells

  • flexible walls more so on one side than the other
  • causes to bending when turgid to open stomata and the closing when flaccid
  • this control water loss by transpiration
• squamous epithelial cells

  • single layer of flat cells
  • in contact with basement membrane of the epithelium
  • this provides short diffusion distance e.g. lining in the lungs
• Ciliated epithelial cells

  • hair like projections that sway substances such as mucus out of the lungs
  • goblet cells are also located with the epithelium there release mucus + trap molecules such as trapping dust in the trachea
• Cartilage

  • connective tissue that firm and flexible (located in the outer ear, nose and the end of bones
  • provides structure support and it prevent the bones rubbing together
  • it made of elastin and collagen fibres and chondrocytes cells
• Muscle

  • composed of tissue that can contract and relax to create movement
  • skeletal muscle cause the skeleton to move and are made up of myofibrils + proteins actin + myosin
  • smooth muscle located in organs + cardiac muscles
  • muscle have multiple fibres connecting with connective tissue
• xylem

  • part of the vascular bundle
  • responsible for transporting water and mineral ions
  • made form elongated, hollow dead cells with lignin in the walls = strength + waterproof
  • made from stem cells (meristem)
• Phloem

  • part of the vascular bundle
  • transporting organic substances made in photosynthesis
  • made from sieve element cells (lack most organelle to make transporting sugars easier)
  • contain companion cells which contain organelle to provide resources to the sieve tube elements
  • sieve tubes made from stem cells (meristem)
• Totipotent

  • cell can divide and produce any type of body cell
  • there only occur for a limited time in early mammalian embryos
• Pluripotent

  • found in embryos and can become almost any type of cell
  • they are used in research to treat human disorders
• multipotent cells

  • found in bone marrow
  • can differentiate into a limited number of cells e.g lung, pancreas, heart
• Unipotent 


  can only differentiate into one type of cell
• potential stem cells

  • repairing damaged tissues
  • treatment of neurological conditions such as Alzheimer's and Parkinson's
  • research into developmental biology