A 2.2 CELL STRUCTURE - eukaryotic cell structure

• What is a Cell Wall?

  a rigid layer that surrounds the plasma membrane and is only found in some eukaryotic cells
• Function of a Cell Wall?

  protects and gives shape to the cell by providing mechanical support
• Where are cell walls found and what are they made of?

  plants and algae = cellulosefungi = chitin
• What are centrioles?

  hollow fibres made of microtubules (composed of the protein tubulin)
• How are centrioles found/arranged?

  found in pairs at right angles to each other to form a centrosome
• What is the function of centrioles?

  organises microtubules during cell division
• What is a chloroplast?

  an organelle with a double membrane which contains the pigment chlorophyll
• Describe the structure of chloroplasts?

  internal membranes called thylakoids stack to form structures called grana (which are joined together by lamellae)
• What is the internal fluid in chloroplasts called?

  the internal fluid in the chloroplast is called stroma
• is chloroplasts larger or smaller than mitochondria?

  larger
• what is the function of a chloroplast?

  site of photosynthesis
• What are the 2 stages of photosynthesis in chloroplasts?

  light-dependent stage which takes place in thylakoids light-independent stage (Calvin cycle) which takes place in stroma
• What else may be found in chloroplasts?

  circular pieces of DNA and ribosomes used to synthesise proteins needed in chloroplast replication and photosynthesis
• What is cilia?

  tiny hair-like projections made from microtubules which are present on the surface of many cells (often in groups)
• What is the function of cilia?

  can beat to allow cell movement of create a current in the fluid surrounding a cell to help the movement of substances over a cell surface
• Structure of cilia?

  contain a ring of 9 doubles microtubules plus 2 central ones
• What is the cytoskeleton?

  a network of fibres extending throughout the cytoplasm
• function of cytoskeleton

  Helps cell maintain shape, cell movement and intracellular organization
• What is a flagellum/flagella?

  a long, slender structures which enables a cell to swim (e.g. sperm cells)
• Where are flagella found?

  specialised cells
• Are flagella and cilia similar?

  have same structure but often occur individually
• structure of flagella?

  made of longer microtubules
• What is cytoplasm?

  region inside plasma membrane and outside nucleus where organelles are found
• Structure of cytoplasm?


  liquid part called cytosol and small fibres/rods called cytoskeleton
• Function of cytoplasm

  Where chemical reactions take place
• What is the golgi apparatus?

  a stack of flattened, membrane-bound sacs - continuously being formed - and are budded of as vesicles
• What are the flattened sacs of membrane called in golgi apparatus?

  cisternae
• function of golgi apparatus

  processes proteins brought from vesicles from rER and will be carried in vesicles to plasma membrane for secretion
• What happens to proteins that usually go through golgi apparatus


  usually exported (e.g. hormones), put into lysosomes (hydrolytic enzymes) or delivered to membrane bound organelles
• What is a lysosome?

  specialist forms of vesicles which contain hydrolytic enzymes
• What are hydrolytic enzymes?

  enzymes that break biological molecules down
• function of lysosomes

  breakdown/hydrolysis of macromolecules (e.g. digesting food, organelles or whole cells)
• where are lysosomes used?

  used extensively by cells of the immune system and in apoptosis (programmed cell death)
• What are microfilaments?

  narrowest fibres of the cytoskeleton made up of a protein called actin
• function of microfilaments

  help cell move and provide rigidity and shape for the cell
• What are microtubules?

  small hollow tubes made from tubulin proteins and are the widest components of the cytoskeleton
• function of microtubules

  helps cell resist compression, provide a track for vesicles to move along and help move chromosomes during cell division
• What is microtubules the structural element for?

  flagella, cilia and centrioles
• What is microvilli?

  finger-like projections on the free surfaces of epithelial cells
• What is an epithelial cell?

  cell that lines the external and internal surfaces of the body