2.1.1 structure of eukaryotic cells

• features of eukaryotic cells

  cytoplasm containing membrane-bound organelles

  so DNA enclosed in a nucleus
• general structure of eukaryotic cells

  cell-surface membrane

  mitochondrion

  nucleus

  ribosomes

  rough endoplasmic reticulum (RER)

  smooth endoplasmic reticulum (SER)

  golgi apparatus

  lysosome

  chloroplast (plant & algae)

  cell well (plant & algae)

  cell vacuole (plant & algae)
• structure of cell-surface membrane

  hydrophilic phosphate heads which point to/attracted to water

  hydrophobic fatty acid tails which point away/repelled from water
• function of cell-surface membrane

  selectively permeable → enables control of passage of substances in / out of cell

  molecules / receptors / antigens on surface → allow cell recognition / signalling
• structure of nucleus 


  nuclear envelope -> double membrane with nuclear pores

  nucleoplasm

  nucleolus (dense region)

  protein/histone-bound linear DNA -> chromatin (condensed) and chromosome (highly condensed)
• function of the nucleus 


  holds / stores genetic information which codes for polypeptides (proteins)

  site of DNA replication

  site of transcription (part of protein synthesis) producing mRNA

  nucleolus makes ribosomes / rRNA
• structure of a ribosome

  made of ribosomal RNA and protein (two subunits)

  not a membrane-bound organelle
• function of a ribosome 


  site of protein synthesis (translation)
• structure of rough endoplasmic reticulum

  ribosomes

  system of membranes
• structure of smooth endoplasmic reticulum

  system of membranes
• function of rough endoplasmic reticulum

  ribosomes on surface synthesise proteins

  proteins processed / folded / transported inside rER

  proteins packaged into vesicles for transport

  eg to golgi apparatus
• function of smooth endoplasmic reticulum

  synthesises and processes lipids

  eg cholesterol and steroid hormones
• structure of the Golgi apparatus

  flattened membrane sacs
• structure of golgi vesicles

  small membrane sac
• function of Golgi apparatus

  modifies protein eg adds carbohydrates to produce glycoproteins

  modifies lipids eg adds carbohydrates to make glycolipids

  packages proteins / lipids into Golgi vesicles

  produces lysosomes (a type of Golgi vesicle)
• function of golgi vesicles

  transports proteins / lipids to their required destination

  eg moves to and fuses with cell-surface membrane
• structure of lysosome 


  membrane

  hydrolytic enzymes
• function of lysosomes 


  release hydrolytic enzymes (lysozymes)

  to break down / hydrolyse pathogens or worn-out cell components
• structure of the mitochondria

  outer membrane

  cristae -> inner membrane fold

  matrix -> contains small (70s) ribosomes and circular DNA
• function of mitochondria 


  site of aerobic respiration

  to produce ATP for energy release

  eg for protein synthesis / vesicle movement / active transport
• structure of chloroplasts (plants & algae)

  double membrane

  stroma -> thylakoid membrane, small (70s) ribosomes, circular DNA, starch granules/lipid droplets

  lamella -> thylakoid linking grana

  grana -> stacks of thylakoid
• function of chloroplasts (plant & algae)

  absorbs light energy for photosynthesis

  to produce organic substances

  eg carbohydrates / lipids
• structure of cell wall (plants & algae)

  composed mainly of cellulose (a polysaccharide) in plants / algae

  composed of chitin (a nitrogen-containing polysaccharide) in fungi
• function of cell wall (plants & algae)

  provides mechanical strength to cell

  so prevents cell changing shape or bursting under pressure due to osmosis
• structure of cell vacuole (plants)

  tonoplast membrane

  cell sap
• function of cell vacuole (plants)

  maintains turgor pressure in cell (stopping plant wilting)

  contains cell sap → stores sugars, amino acids, pigments and any waste chemicals
• describe how eukaryotic cells are organised in tissues

  group of specialised cells with a similar structure working together to perform a specific function, often with the same origin
• describe how eukaryotic cells are organised in an organ

  aggregations of tissues performing specific functions
• describe how eukaryotic cells are organised in an organ system

  Group of organs working together to perform specific functions