Q2

• What is the cell theory?

  Cell theory is accepted as aunifying conceptin biology- All living things are made up of cells, cells are thebasic units of structure, function and organisationin living things, new cells are produced from existing cells
• Organisation in complex organisms

  In animals and plants, cells are organised into tissues, tissues into organs and organs into organ systems

  - Makes an organism
• Describe the ultrastructure of prokaryotic/bacterial cells

  Bacteria are prokaryotic cells. They contain organelles common to all prokryotes

  - 70S ribosomes

  - Nucleoid with circular DNA in single chromosomes

  - Plasmids

  As well as this, bacteria cells contain

  - Cell surface membrane

  - Cell wall

  - Cytoplasm

  - Capsule

  - Pili

  - Flagellum
• Describe the structure of nucleoids


  Prokaryote cells have asingle, often circular, DNA molecule- Since prokaryotes do not have membrane bound organelles, its not called a nucleus- DNA folded into a reigion known as anucleoid- Can take up half of the cytoplasm
• Describe the structure of plasmids


  Plasmids are small, circular lengths of DNA- Plasmids oftencontain genes that aid in the bacterium's survival, such asantibiotic resistanceor genes fortoxin production
• Describe the structure of 70S ribosomes


  Ribosomes are the site on which proteins are made

  - S is a measurement of size, made up of a 50S and 30S subunit
• Describe the structure of the bacterial cell wall


  All bacterial cell walls are made ofpeptidoglycan- A polymer of sugar and amino acids
• What is the difference between gram positive bacteria and gram negative bacteria?


  Ingram positive bacteriathe peptidoglycancell wall is very thick and protective- Retains apurplestain, called gram stainIngram negative bacteriathecell wall is thin- Does not hold purple stain- they do hold a safranin counterstain and are stainedred- They have anadditional outer fatty/protein membrane(liposaccharide and protein)

  Both can act as pathogens
• How do gram positive and gram negative bacteria react to different antibiotics


  Gram negativebacteriaaremore resistantto antibiotics that act onwall formation- E.g.penecillinHowever, some antibiotics, such aspolymixins, areonlyeffectiveagainstgram negative bacteriabecause they interact with the outer membrane (fatty/protein)
• Eukaryotic cells


  Contain a nucleus and other organelles that are bound by membranes.

  
• What is the function of the nucleus?


  Stores DNA and controls the cell
• What is the function of the nucleolus?


  Makes ribosomes
• What is the function of the 80S ribosomes?


  Site of protein synthesis

  - Contrast in 70S ribosomes in prokaryotes
• What is the function of the rough endoplasmic reticulum?


  Ribosomes on the surface

  - Proteins made here
• What is the function of the smooth endoplasmic reticulum?


  Lipidsmade here
• What is the function of the mitochondria?


  Cellular respiration

  - Produces ATP
• What is the function of the centrioles?


  Centrioles are involved inspindleformation during cell division/replication- They are found only in animal cells
• What is the function of the lysosomes?


  Lysosomes contain digestive enzymes- destroy old orgenelles andpathogens(cell waste)
• What is the function of the Golgi apparatus


  Modifies and packs proteins in vesicles for transport to the RER
• What is the function of the cell wall?


  To protect and support the cell

  - They are found only in plant cells
• What is the function of the chloroplasts?


  Site of photosynthesis

  - They are found only in plant cells
• What is the function of the vacuole?


  Storing water and minerals

  - They are found only in plant cells
• What is the function of the tonoplast?


  It is the vacuolar membrane

  - Semi-permeable membrane surrounding the vacuole
• Magnification


  An increase in the apparent size of an object
• Resolution


  The ability to clearly distinguish the individual parts of an object-See two objects as distinct
• Magnification and resolution in light and electron miscroscopy


  Alight microsopecan resolve to about 0.2 μm and theelectron microscopeto 1nm or less-Any two objects closer together than this will look like one objectOnce you resolve it well it is worthmagnifyinga lot
• Why is it important to stain specimens in microscopy?


  Most structures are colourless in their natural state

  - Giving structures colour through a stain allows for identification
• Core practical 2:


  use of the light microscope, including simple stage and eyepiece micrometers and drawing small numbers of a cell from a specialised tissueFINISH
• What are the stages of mitosis?


  Prophase, metaphase, anaphase, telophase
• What happens in prophase?


  Chromosomes condenseCentriolesmove to opposite polesSpindleapparatusformed by microtubules
• What happens in metaphase?


  Chromosomes line up in the middle of the cell- They are attached to thespindleby their centromere
• What happens in anaphase?


  Sister chromatidssplit and move to either pole (Disjunction)
• What happens in telophase?


  Nuclear membrane reforms

  Chromosomes decondense
• What is cytokinesis?


  The division of the cytoplasm
• Why is mitosis important?


  It produces identical copies of the dividing cell forgrowthandrepairin animals and plants, as well as forasexual reproductionin some organisms.
• Mitosis in growth


  In plants, growth involves an increase in cell number and size- Mitosis causes doubling in cell number- Interphase the cells growIn animals growth occurs all over the bodyIn plants it only occurs atspecial growing pointscalledmeristemsat thetip of the stems and roots
• Mitosis in asexual reproduction


  -Binary fissionis where asingle microbesplits into two daughter cells-Budingoccurrs in other microbes when two daughter cells form that aredifferent sizes- In higher organisms like plants, asexual reproduction is calledvegetative reproduction- In animals, greenfly reproduce asexually throughout the summer
• Mitosis in repair


  Human cells need to be repaired and replaced, e.g. skin and red blood cells- Mitosis is needed in this process-Rapid mitosis occurs around a wound to regenerate skin and close the wound
• What are the stages of meiosis?


  Prophase I, Metaphase I, Anaphase I, Telophase I, Prophase II, Metaphase II, Anaphase II, Telophase II
• What is meiosis and why is it important?


  Meiosis is the process of two nuclear divisions, creating four haploid daughter cells from just one diploid cell

  - It reduces the number of chromosomes by half to avoid doubling in each generation

  - It results in genetic variation amongst gametes