Topic 3 Biology

• Until microscopes became powerful enough to view individual cells, no-one knew for certain what living organisms were made from
• Robert Hooke


  Thought to be the first person to view cells, using the term 'cell' to describe these newly discovered structures
• Matthias Schleiden and Theodor Schwann


  Scientists who studied animal and plant cells
• In 1837 they came up with the idea that all living organisms are made of cells
• Cell theory


  A unifying concept in biology, meaning that it is universally accepted
• Cell theory includes three main ideas

  • All living organisms are made up of one or more cells
  • Cells are the basic functional unit in living organisms
  • New cells are produced from pre-existing cells
• Cells of all living organisms share some common features

  • Cell surface membrane
  • Cytoplasm
  • DNA
  • Ribosomes

  
• Beyond these common features different cell types contain different structural elements and combinations of organelles
• Prokaryotic cells


  Have no internal membranes and smaller ribosomes

  
• Eukaryotic cells


  Have several internal membrane-bound organelles and larger ribosomes

  
• Cell ultrastructure refers to the internal structures of the cell
• Cells can become specialised for specific functions
• Examples of specialised cells

  • Epithelial cells in the small intestine
  • Red blood cells
  • Xylem cells in plants
• Tissue


  A group of cells that work together to perform a particular function
• Organ


  A group of tissues working together to perform a particular function
• Organ system


  A group of organs working together to perform a particular function
• Levels of Organisation


  • Cells
  • Tissues
  • Organs
  • Organ systems
• Cells can be divided into two broad types; eukaryotic and prokaryotic cells
• Eukaryotic cells


  Have a more complex ultrastructure than prokaryotic cells
• Eukaryotic cells


  Are larger than prokaryotic cells
• Eukaryotic cells


  Have membrane-bound organelles, including a nucleus

  
• Eukaryotic cells


  Have larger ribosomes known as 80S ribosomes

  
• Key differences between animal and plant cells

  • Animal cells contain centrioles and some have microvilli while plant cells do not
  • Plant cells have a cellulose cell wall, large permanent vacuoles, and chloroplasts while animal cells do not
• Cell surface membrane


  Controls the exchange of materials between the internal cell environment and the external environment
• Cell surface membrane


  Is formed from a phospholipid bilayer spanning a diameter of around 10 nm
• Nucleus


  Is relatively large and separated from the cytoplasm by a double membrane called the nuclear envelope, which has many pores

  
• Chromatin


  The material from which chromosomes are made
• Nucleolus


  The site of ribosome production

  
• Mitochondria


  The site of aerobic respiration within eukaryotic cells
• Mitochondria


  Are surrounded by a double-membrane with the inner membrane folded to form structures called cristae

  
• Mitochondrial DNA


  Small circular pieces of DNA found in the matrix of mitochondria

  
• Ribosomes


  Can be found as free organelles in the cytoplasm of all cells or as part of the rough endoplasmic reticulum in eukaryotic cells

  
• Ribosomes


  Are the site of translation

  
• Rough Endoplasmic Reticulum (RER)


  Its role is to process proteins made on the ribosomes

  
• Smooth Endoplasmic Reticulum (SER)


  Is involved in the production, processing and storage of lipids, carbohydrates and steroids

  
• Golgi apparatus


  Modifies proteins and lipids before packaging them into Golgi vesicles
• Lysosomes


  Contain hydrolytic enzymes that break down waste materials such as worn-out organelles
• Centrioles


  Are made of hollow fibres known as microtubules and organise the spindle fibres during cell division
• Formation of extracellular enzymes

  1. Nucleus - transcription of DNA code

  2. Ribosomes - translation to produce proteins

  3. Rough endoplasmic reticulum - proteins folded and processed

  4. Golgi apparatus - proteins modified and packaged into vesicles

  5. Cell surface membrane - proteins secreted out of the cell

  
• Golgi apparatus

  Processes and modifies proteins transported from the rough endoplasmic reticulum in vesicles, preparing them for secretion