topic 2 bio

• hi everyone and welcome to miss estrich biology this video is going to be the complete topic 2 which has been so highly requested on instagram that yes it is finally here now if you are new here my name is miss estrick and i've been teaching for 14 years now and i know just how challenging a level biology can be and preparing for exams and that's why i make lots of content to help you on youtube and instagram now if you do need even more help then check out my sponsor for today's video which is biosnip now i actually follow them anyway even though they are the sponsor because their content is so useful for a-level biology they will post different diagrams graphs content so you can test yourself and really get familiar with the exam technique as well as the daily quizzes that they post on their stories so go check out via snip for more extra daily help i'm also really excited to finally be able to tell you that my topics one to four which is the year 12 a.s content workbook is now out so if you haven't already got your copy of my active recall workbook then head to the link in the description and get your copy to help you with your revision consolidation and just generally ace in your a-level biology but for now let's get into topic two
• Key eukaryotic cell organelles

  • Nucleus
  • Endoplasmic reticulum
  • Golgi apparatus
  • Lysosomes
  • Mitochondria
  • Ribosomes
  • Vacuole
  • Chloroplasts
  • Cell wall
  • Plasma membrane
• Nucleus


  Where DNA replication occurs and site of transcription, contains DNA which is the genetic code for the cell
• Nucleolus


  Site of rRNA production and ribosome assembly
• Rough endoplasmic reticulum (RER)


  Site of protein synthesis due to ribosomes on the outside
• Smooth endoplasmic reticulum (SER)

  Site of lipid and carbohydrate synthesis and storage
• Golgi apparatus


  Modifies, packages and distributes molecules like glycoproteins, secretory enzymes, carbohydrates, lipids
• Lysosomes


  Bags of digestive enzymes involved in phagocytosis and exocytosis
• Mitochondria


  Site of aerobic respiration and ATP production, have their own DNA
• Ribosomes

  Site of protein synthesis, found in both prokaryotic and eukaryotic cells
• Vacuole


  Fluid-filled structure that provides support and stores substances in plant cells
• Chloroplasts


  Site of photosynthesis, have thylakoid membranes and stroma
• Cell wall


  Provides structural strength and prevents bursting in plant and fungal cells
• Plasma membrane


  Controls what enters and exits the cell, made of phospholipid bilayer
• Prokaryotic cells are much smaller, lack membrane-bound organelles, have a single loop of DNA, and may have additional features like flagella or capsules
• Viruses


  Acellular and non-living, consist of genetic material, capsid, and attachment proteins, replicate inside host cells
• Methods of studying cells

  • Microscopes
  • Cell fractionation and ultracentrifugation
• Magnification


  How many times larger the image is compared to the object
• Resolution


  Minimum distance between two objects where they can still be viewed as separate
• Optical microscopes


  • Use a beam of light, have lower resolution, can view living samples, produce color images
• Electron microscopes


  • Use a beam of electrons, have higher resolution, cannot view living samples, produce black and white images
• Cell fractionation


  1. Homogenization to break open cells

  2. Ultracentrifugation to isolate organelles by density
• Eukaryotic cells divide by mitosis or meiosis, prokaryotic cells replicate by binary fission, viruses replicate inside host cells
• Mitosis


  • One round of division, produces genetically identical cells, diploid cells
• Host cell


  The cell that uses the genetic material to replicate the virus particle
• Eukaryotic cell cycle


  1. Interphase

  2. Mitosis
• Interphase


  The longest stage of the cell cycle, includes G1, S, and G2
• G1


  Cell increases in size, organelles double
• S phase


  DNA replication happens
• G2


  Further growth, preparation for mitosis, error check stage
• Nuclear division


  Mitosis or meiosis
• Cytokinesis


  Cytoplasm divides to create two new cells
• Mitosis


  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase
• Mitosis


  • Only one round of division
  • Genetically identical cells created
  • Cells are diploid (two copies of every chromosome)
  • Used for growth and repair
• Specific example of mitosis


  • Clonal expansion of B cells
• Prophase


  1. Chromosomes condense and become visible

  2. Centriole pairs move to opposite poles, create spindle fibers
• Metaphase


  1. Chromosomes line up along the equator

  2. Spindle fibers attach to centromeres and chromatids
• Anaphase


  1. Spindle fibers retract, pulling chromatids to opposite poles

  2. Chromatids become chromosomes
• Telophase


  1. Chromosomes at poles become longer and thinner

  2. Spindle fibers disintegrate

  3. Nucleus reforms
• Mitotic index


  Percentage of cells in a field of view that are in a stage of mitosis