🦠Biology Unit 2 Cells

• Cell theory

  Unifying concept that states that cells are a fundamental unit of structure, function and organisation in all living organisms
• In complex organisms, cells are organised into tissues, organs, and organ systems
• Organelles in eukaryotic cells

  • Nucleus
  • Nucleolus
  • 80S ribosomes
  • Rough and smooth endoplasmic reticulum
  • Mitochondria
  • Centrioles
  • Lysosomes
  • Golgi apparatus
  • Cell wall
  • Chloroplasts
  • Vacuole and tonoplast
• Prokaryotic cells


  Cells that do not have a nucleus, or any interior compartments
• Eukaryotic cells


  Cells that have a nucleus, and various other interior compartments, called organelles
• Cell membrane (or plasma membrane)

  • Thin, flexible layer round the outside of all cells made of phospholipids and proteins
  • Separates the contents of the cell from the outside environment
  • Controls the entry and exit of materials
• Nucleus


  • Largest organelle
  • Surrounded by a nuclear envelope
  • Contains nucleoplasm and chromatin
• Mitochondria


  Sausage-shaped organelle where aerobic respiration takes place and ATP is synthesised. Contains a double-membrane with cristae
• Chloroplast


  Organelle where photosynthesis takes place, found in photosynthetic organisms (plants and algae)
• Ribosomes


  Sites of protein synthesis, found either free in the cytoplasm or attached to the rough endoplasmic reticulum
• Endoplasmic reticulum (ER)


  • Series of membrane channels involved in synthesising and transporting materials
  • Rough ER is studded with ribosomes
  • Smooth ER does not have ribosomes and is used to process lipids
• Golgi body (or Golgi apparatus)


  Series of flattened membrane vesicles that transport proteins destined for extracellular use from the ER to the cell membrane for export
• Vacuoles


  • Membrane-bound sacs containing water or dilute solutions of salts and other solutes
  • Plant cell vacuoles help to keep the cell rigid or turgid
• Lysosomes


  Small membrane-bound vesicles containing digestive enzymes, used to break down unwanted materials
• Cytoskeleton

  Network of protein fibres extending throughout all eukaryotic cells, used for support, transport and motility
• Centrioles


  Two centrioles found near the nucleus, used in cell division to make the spindle fibres that move the chromosomes
• Cell extensions

  • Cilia
  • Flagella
  • Microvilli
• Cytoplasm (or cytosol)


  Solution within the cell membrane, containing enzymes and other materials needed for the cell to function
• Cell wall


  Thick layer outside the cell membrane, made of different materials in different cell types
• Magnification and resolution can be achieved using light and electron microscopy

  
• Staining specimens is important in microscopy as it increases contrast so intra-cellular structures are visible
• Types of passive transport

  • Diffusion
  • Facilitated diffusion (through carrier proteins and protein channels)
  • Osmosis
• Properties of molecules that affect transport

  • Solubility
  • Size
  • Charge
• Water potential

  Turgor pressure + osmotic potential
• Active transport


  Requires energy from the hydrolysis of ATP
• Endocytosis and exocytosis


  Processes for transporting large molecules into and out of cells through the formation of vesicles
• Flagella

  Longer than the cell, usually only one or two, used for motility (e.g. sperm)
• Microvilli


  Short extensions found in certain cells such as in the epithelial cells of the intestine and kidney, where they increase the surface area for absorption of materials
• Cytoplasm (or Cytosol)

  The solution within the cell membrane, containing enzymes for glycolysis (part of respiration) and other metabolic reactions together with sugars, salts, amino acids, nucleotides and everything else needed for the cell to function
• Cell Wall


  A thick layer outside the cell membrane, made of different materials in different cell types
• Materials cell walls are made of

  • Cellulose (plant)
  • Chitin (fungal)
  • Peptidoglycan (bacterial)
• Cell walls


  • Used to give strength and rigidity to cells and to resist osmotic lysis
  • Made of a network of fibres that give strength but are freely permeable to solutes (unlike membranes)
• Layers of plant cell walls

  • Middle lamella (outer layer, made of calcium pectate)
  • Primary cell wall (middle layer, thin, flexible cellulose microfibrils)
  • Secondary cell wall (inner layer, thick, network of cellulose, hemicellulose and pectin)

  
• Plant cell walls are usually studded with channels called plasmodesmata, which link the cytoplasms of adjacent cells, forming a symplast (a continuous cytoplasm)

  
• Tissue

  A group of similar cells performing a particular function
• Organ

  A group of physically-linked different tissues working together as a functional unit
• Organ system

  A group of organs working together to carry out a specific complex function
• Prokaryotic cells


  • Smaller than eukaryotic cells
  • Do not have a nucleus or membrane-bound organelles
• Main features of prokaryotic cells

  • Cytoplasm
  • Ribosomes
  • Nucleoid
  • DNA
  • Plasmid
  • Plasma membrane
  • Cell wall
  • Capsule
  • Flagellum

  
• Types of bacterial cell wall

  • Gram positive
  • Gram negative