cells

• cell membrane

  phospholipid bilayer

  cholesterol- makes it rigid

  channel proteins
• nucleus

  controls cell growth and replication

  transcription
• chloroplasts

  in plants

  membrane- light dependent stage

  stroma- light independent stage

  thylakoids stack up to make grana
• golgi apparatus

  processes proteins from RER are transported in vesicles

  vesicles fuse with golgi, releasing proteins

  golgi modifies proteins
• lysosomes

  contain lysozymes

  digest pathogens
• ribosomes

  protein synthesis

  rRNA and proteins

  translation
• RER

  ribosomes on the surface produce proteins
• SER

  synthesises lipids
• cell wall (plants)

  cellulose

  in algae- chitin

  freely permeable
• cell vacuole (plants)

  cell sap

  maintains pressure
• prokaryotic cells


  cytoplasm lacks membrane bound organelles

  singular circular DNA molecule

  cell wall contains murein

  plasmids, capsule, flagellum
• viruses

  non cellular

  nucleic acid core

  capsid protein coat
• optical microscopes (light)

  low resolution and magnification

  can observe eukaryotic cells

  image is in colour

  specimens can be live
• transmission electron microscope

  high resolution and magnification

  specimen must be thin

  specimens can't be live as there's a vacuum

  image not in colour
• scanning electron microscope

  images can be 3D

  lower resolution

  specimen cannot be live

  image isn't in colour
• cell fractionation

  separating cell organelles from each other

  homogenisation, filtration, ultracentrifugation
• homogenisation

  breaking up of cells

  sample is placed in a cold, isotonic buffered solution

  placed in a homogeniser that grinds up the cells by breaking the meembrane
• cold, isotonic buffered solution

  cold- reduce enzyme activity that may break down organelles

  isotonic- prevents osmosis causing bursting of the cell

  buffered- pH, stops enzymes being denatured
• filtration

  the homogenate is filtered through a gauze

  the filtrate contains organelles
• ultracentrifugation

  centrifuge spins to separate out organelles

  nuclei, chloroplasts, mitochondria, lysosomes, endoplasmic reticulum, ribosomes
• mitosis

  interphase- G1-organelles replicated. S-DNA replicated. G2- cell keeps growing

  prophase- chromosomes condense. nuclear envelope disintegrates. centrioles move to poles and form spindle fibres

  metaphase- chromosomes line up along the equator. centromeres attach to spindle fibres

  anaphase- centromeres split and the chromatids move to the opposite poles of the cell

  telophase- chromosomes decondense. nuclear envelope reforms

  cytokinesis- cytoplasm divides. two genetically identical cells are formed
• binary fission

  a single, circular DNA molecules and any plasmids undergoes DNA replication

  the parent cell divides into 2 (cytoplasm roughly halved)

  the daughter cells contain a copy of the DNA molecule and a variable number of plasmids
• cell surface membrane

  partially permeable

  bilayer of phospholipids

  intrinsic or extrinsic proteins

  cholesterol and glycolipids
• simple diffusion


  the net movement of molecules from a high concentration to a low concentration

  down a concentration gradient
• facilitated diffusion


  large polar molecules and ions cannot diffuse through the cell membrane

  channel proteins and carrier proteins
• channel proteins


  water filled pores

  allows ions to diffuse through the membrane

  control exchange of ions
• carrier proteins

  can switch between 2 shapes

  down a concentration gradient
• diffusion factors

  temperature

  steepness of conc. gradient

  surface area

  no. of carrier/channel proteins
• osmosis

  net movement of water molecules from an area of high water potential to low water potential through a partially permeable membrane
• active transport


   movement of molecules and ions through a cell membrane from a lower concentration to a higher concentration using energy from respiration
• co-transport

  sodium ions are actively transported from epithelial cells into the blood

  Na conc. in cell is lower, conc. gradient between ileulm and epithelial cell established

  Na moved into the cell from the ileum by facilitated diffusion carrying glucose molecules with them

  glucose conc. in epithelial cell increases, glucose moves into the blood by facilitated diffusion
• antigen


  molecules on the surface of cells which triggers an immune response
• antigen variability 


  antigens change frequently due to genetic mutations

  surface receptors on lymphocytes and memory cells are no longer complementary so can't bind

  host suffers from the disease again
• phagocytes


  produced and stored in the bone marrow

  non-specific immune response

  neutrophils and macrophages
• phagocytosis

  antigen on phagocytes attract pathogens

  phagocyte engulfs the pathogen by endocytosis forming a phagosome

  phagosome and lysosome fuse to form a phagolysosome

  the lysosome releases lysozymes which hydrolyses the pathogen

  phagocyte absorbs digestive products and waste products leave by exocytosis
• t-lymphocytes


  have t cell receptors each specific to one antigen

  activated when in bound to their specific antigen

  activated t lymphocytes divide by mitosis

  t lymphocytes differentiate into helper t cells and cytotoxic t cells
• t helper cells 


  release chemicals to activated b lymphocytes
• t killer cells 


  destroy any cells that has been infected by a pathogen
• t regulatory cells


  suppress other immune cells and prevent them attacking host cells
• t memory cells


  remain in the blood in case of re-infection