cell biology

• Cells


  The basic unit of all living organisms
• Cells


  • Many different types of cells can be found within one organism
  • All with specific subcellular structures that enable them to perform their individual roles
• Prokaryotic cells


  Cells without a nucleus
• Eukaryotic cells


  Cells with a nucleus
• Prokaryotic cells tend to be much simpler and smaller than eukaryotic cells
• Eukaryotes


  Organisms made up of eukaryotic cells
• Prokaryotes


  Organisms that are prokaryotic
• Eukaryotes are often multicellular (made up of many cells) whereas prokaryotes are often single-celled (only one cell)
• Prokaryotic cells


  • Their genetic material is free in the cytoplasm
  • They have a main circular strand of DNA and occasionally additional small rings of DNA called plasmids
  • They do not contain chloroplasts or mitochondria
  • They have a cell wall, cell membrane and cytoplasm
  • They often have flagella, hair-like structures that help the bacteria move
• Eukaryotic cells


  • A nucleus that holds all the genetic material (including DNA) needed to control the cell's activities
  • Cytoplasm which is a jelly-like substance that contains nutrients, salts and enzymes required for chemical reactions to take place
  • A semi-permeable cell membrane that controls what comes in and out of the cell
  • Many mitochondria that contain enzymes needed for respiration, which releases energy for the cell to use
  • Ribosomes for the production of proteins
• Differentiation


  The process by which different types of cells develop their specific set of cell structures and become specialised
• The majority of differentiation in animal cells happens in the early stages of life, as the organism develops, however in most plants the ability to differentiate is never lost
• Stem cells


  Undifferentiated cells which means they have the ability to develop into different types of cells
• Sperm cells


  • The head contains all the genetic information ready for fertilisation and has enzymes that are able to digest the egg cell membrane
  • They have lots of mitochondria to provide the energy required for movement
  • They have a tail to help it swim
• Nerve cells


  • They have a long axon to carry the impulse over long distances
  • They are branched at both ends so they can connect and pass signals between one another
  • They are insulated in a fatty sheath which helps the impulse move along the nerve quickly
• Muscle cells


  • They contain lots of mitochondria to provide energy for the contraction
  • They have protein filaments that slide over to cause the muscle to contract
• Root hair cells


  • They are an exchange surface, specialised for absorbing water and nutrients from the soil
  • They have a vacuole full of cell sap that is more concentrated than soil water which creates a water potential gradient for efficient water absorption
  • They have lots of mitochondria to provide energy for the active transport of mineral ions from the soil
• Xylem cells


  • They are dead and hollow and do not have top and bottom cell walls, subcellular structures or cytoplasm
  • This allows water to be drawn upwards
• Phloem cells


  • They are joined end to end with sieve plates between them to allow the passage of substances
  • They are living despite also having very few subcellular structures
• Light microscope


  Uses light and lenses to create a magnified image of a specimen
• Light microscope


  • Their development enabled scientists to view individual cells and their larger subcellular structures such as nuclei
  • They have a maximum magnification of only ×1500 and resolutions of up to 0.2 μm
• Electron microscope


  Uses electron beams instead of light which have a much smaller wavelength
• Electron microscope


  • It has much greater magnification and resolving power than light microscopes
  • It allowed scientists to see cells in much more detail including the internal structures of mitochondria, chloroplasts and nuclei, and tiny structures like ribosomes and plasmids
• Magnification


  Actual size of object/Size of the image
• Using a light microscope to draw and label a cell with a magnification scale

  1. Prepare the slide

  2. View slide under the light microscope
• Chromosomes


  The genetic material called DNA which is coiled up into structures in the nucleus of eukaryotic cells
• Each chromosome contains a large number of genes which are sections of DNA that control the development of specific characteristics in an organism
• Human body cells usually have 23 pairs of chromosomes, one received from their mother and one from their father. This means they have 46 chromosomes altogether
• Before cells divide they must replicate their DNA so the new cells have their own copies
• The Cell Cycle and Mitosis

  1. Growth phase

  2. Mitosis
• Growth phase


  • The cell grows, then prepares for mitosis by replicating all of its subcellular structures
  • The cell also duplicates all of its DNA so each new cell will have a copy of the DNA
• Mitosis


  1. Nuclear membrane breaks down

  2. Chromosomes line up at the equator

  3. Fibres pull the arms of the chromosome to opposite ends of the cell

  4. Membranes form around the chromosomes

  5. Cytoplasm and cell membrane divide in cytokinesis
• Mitosis


  A vital stage of the cell cycle that produces 2 daughter cells that are identical to the original cell with the same number of chromosomes
• Mitosis is an essential process in organisms for growth and replacing damaged cells
• Newly fertilised egg cells (zygotes) must undergo several rounds of mitosis to increase the number of cells and develop into embryos
• Organisms that reproduce asexually divide by mitosis
• Binary fission


  The process by which prokaryotic cells, such as bacteria, divide and reproduce
• Binary fission


  1. The genetic material stored in the circular DNA and plasmids get replicated

  2. The cell starts to expand and the circular DNA moves to opposite poles of the cell

  3. The cytoplasm divides and cell walls form around the 2 new daughter cells
• The speed of binary fission division depends on conditions such as temperature and nutrient concentrations
• Some bacteria can divide as often as once every 20 minutes but if conditions are unfavourable binary fission will stop and cells will start to die