Cells

• Define the terms eukaryotic and prokaryotic cells?

  Eukaryotic : DNA is contained in a nucleus and contains membrane bound organelles

  Prokaryotic: DNA is free in cytoplasm and no organelles
• Describe how optimal microscopes work?

  Lens focus ray of light and magnify a thin specimen

  Different structures absorb different wavelengths of light
• Outline how a student could prepare a temper or y mount of tissue for an optical microscope?

  Obtain a thin specimen of tissue

  Add drop of water

  stain tissue to make organelles visible

  lower down cover slip with mounted needle
• Suggest advantages and limitations of using an optical microscope ?

  Advantages:

  Produce colour image

  Can show living structures

  Disadvantages:

  2D image

  Low resolution
• Describe how a TEM microscope works?

  Pass a high energy beam of electrons though thin slice

  more dense structures appear darker since they absorb more electrons

  Focus onto fluorescent screen
• Suggest advantages and disadvantages of using a tem microscope?

  Advantages:

  High magnification

  High resolution

  Disadvatages:

  2D image

  Requires a vacuum - no living species

  artefacts

  no colour image
• Describe how a scanning electron microscope work ?

  Focus beam of electrons onto a specimen

  Refelcted electrons hit a collecting device
• Suggest the advantages and disadvantages of using a SEM microscope?

  Advantages:

  3D image

  high resolution

  Disadvantages:

  vacuum - no living structrues

  no colour images

  outer surface
• Define magnification an resolution ?

  Magnification ; factor by which the image is larger than teh actual specimen

  Resolution ; smallest separation distance by which two separate structure can be distinguished from one another
• Outline what happens during cell fractionation and ultracentrefutation?

  Homogenise tissue to break open cell and release debris

  filter to remove debris

  spin homogenise in a centrifuge

  most dense in mixture form a pellt

  filter of and spin again at higher speeds
• Explain why fractionated cells are kept in a cold , buffered isotonic solution?

  cold: slow action of enzymes

  buffered : maintain constant ph

  isotonic: prevent the shrinking or bursting of cells
• State what the cell cycle is and outline its stages ?

  cycle of division with intermediate growth periods

  Interpahse

  mitosis

  cytokenisis
• State the purpose of mitosis ?

  Produces two genetically identical daughter cells

  cell growth

  cell repair

  asexual reproduction
• Outline what happens during prophase ?

  Chromosomes condense becoming visible
• Outline what happens during metaphase ?

  Sister chromatids line up at the cell equator attracted to the spindle fibres at the centromere
• Outline what happens during anaphase?

  Spindle fibres contract an centromeres divide

  Pulled to opposite poles of the cell
• Outline what happens during telophase?

  Chromosomes decondense becoming invisible again

  nucleus envelopes form around each set of chromosomes
• Why is the roots tip only used when calculating a mitotic index ?

  Cells in the root tip are activley undergoing mitosis
• How do prokaryotic cells replicate?

  DNA loop replicate

  Plasmids replicate

  celle elongates separating 2 dna loops

  cell membrane contracts and splits
• Outline how viruses replicate ?

  Attachment protiens bind onto receptors on host cell

  release RNA into cytoplasm

  Host ell uses genetic information to synthesise new viral proteins

  components of viral particle assemble
• Describe the fluid mosaic model of membranes?

  fluid phospholipid bilayer which has a flexible shape
• Explain the role of cholesterol and glycolipids in the membranes ?

  Cholestra ; reduces fluidity to provide stability

  glycolipids - cell signalling and recognition
• Define osmosis?

  Water diffuses across semi permeable membrane from an area of high water potential to an area of low water potential
• Define simple diffusion ?

  Net movement of small , lipid soluble molecules from an area of high concentration to an area of low concentration

  down a concentration gradient
• Define facilitates diffusion ?

  Passive movement of molecules across a cell membrane with the help of transport proteins.
• Explain how channel and carrier protiens work?

  Channel : hydrophilic channels bind to specific ions

  Carrier : Bind to complementary molecule
• Name 5 factors that affect the rate of diffusion?

  Temeprature

  Distance

  Surface area

  Size of molecule

  Steep of concentration gradient
• How are cells adapted to maximise the rate of transport across their memebrane?

  folded membrane increase surface area

  many carrier / channel proteins
• Define active transport?

  Movement of molecules across a cell membrane that requires ATP
• Compare and contrast active transport and facilitated diffusion?

  Both involve carrier protiens

  Facillitated may also involve channel

  Active transport requires atp
• Define co transport ?

  The simultaneous transport of two substances across a cell membrane, where the movement of one substance is coupled to the movement of another substance.
• Explain how co-transport is involved in the absorption of glucose/amino acids in the small intestine?

  Na+ activley transported out which lowers the concentration

  Na+ can now move in brining glucose / amino acid with it via facilitated diffusion
• What is an antigen?

  A cell surface molecule that triggers an immune response.
• How does phagocytosis destroy pathogens?

  Phagocte moves towards a pathogens toxins

  phagocyte engulfs pathogen to form a phagosome

  phagosome fuses with lysosome

  lysozymes digest pathogen
• Explain the role of antigen presenting cells?

  macrophage display antigens from pathogen on its surface and enhances recognition by helper T cells.
• Name the 2 types of speecific immune response ?

  Cell-medicated

  humoral
• outline the process of the cell mediated response ?

  Complementary helper t cell binds to forgein antigen

  releases cytokenes that stimulate

  clonal expansion become memory cell or tigger humoral response

  cytotoxic T cells
• Outline the process of the humoral response ?

  Complementary t helper cell bind to forge in antigen

  stimulate b cells to divide via mitosis

  b cells differentiate into plasma cells.

  plasma cells secrete antibodies with complementary variabe region to antigen.
• What is an antibody?

  Protiens secreted by plasma cells
• How do antibodies lead to the destruction of a pathogen?

  formation of antigen-antibody complex results in agglutination which enhances phagocytosis