Biology

• All living things are made of cells, which share some common structures. They all contain DNA and have plasma membranes.
• Prokaryote


  One of the two types of cells, the other being eukaryote
• Eukaryote


  One of the two types of cells, the other being prokaryote
• Light microscopes are limited in what they can allow us to see of cells, because the wavelength of light is the limiting factor.
• Electron microscopes have a much shorter wavelength than beams of light and allow much more detail to be seen, but can only examine dead material.
• Structures seen with a light microscope

  • Plasma membrane
  • Nucleus
  • Nucleolus
• Structures seen with an electron microscope (ultrastructure)

  • Organelles
  • Plasma membrane
  • Nucleus
  • Nucleolus
  • Rough endoplasmic reticulum
  • Smooth endoplasmic reticulum
  • Ribosomes
  • Vesicles
  • Nuclear envelope
  • Centrioles
  • Mitochondria
  • Lysosomes
  • Golgi apparatus
• Eukaryotic cells contain organelles, which are structures in cells with specialised functions enclosed by a membrane.
• Prokaryotic cells do not have membrane-bound organelles.
• Eukaryotic cells have 700-800 ribosomes, while prokaryotic cells have 70S ribosomes.
• The plasma membrane, nucleus and nucleolus are visible under the light microscope.
• Organelles are not always the same, for example some cells have 700 ribosomes, while others have 800.
• The cytoplasm contains many molecules dissolved in solution (enzymes, sugars, amino acids, fatty acids) and is the site of many metabolic processes.
• Mitochondria are surrounded by a double membrane, with the inner membrane folded into finger-like projections called cristae.
• Lysosomes are enclosed by a single membrane and contain digestive enzymes that destroy old organelles and pathogens.
• The Golgi apparatus is a series of single, curved sacs enclosed by a membrane, where proteins are modified and packaged into vesicles for transport.
• The rough endoplasmic reticulum is a series of single, flattened sacs enclosed by a membrane, the site of protein synthesis.
• The smooth endoplasmic reticulum is a series of single, flattened sacs enclosed by a membrane, involved in the movement of substances in and out of cells.
• Centrioles are two hollow cylinders arranged at right-angles to each other, which help form the spindle in cell division.
• The nuclear envelope is a double membrane with pores, surrounding the nucleus.
• Plant cells differ from those of other eukaryotes
• Plant cells


  • More complex than other eukaryotic cells
  • Contain additional organelles like plastids and a large central vacuole
• Organelles in plant cells

  • Plastids
  • Centrioles
  • Vacuole
  • Tonoplast
  • Cell wall
  • Amyloplasts
  • Middle lamella
  • Plasmodesmata
  • Pits
• Vacuole stores water and other substances
• Tonoplast


  Controls movement of molecules to and out of the vacuole
• Cell wall provides support and protection
• Amyloplasts


  Store starch
• Middle lamella


  Sticks cells together
• Plasmodesmata and pits


  Allow communication between cells
• A generalised plant cell can be seen through a low power electron microscope
• Organelles visible in electron micrographs

  • Mitochondria
  • Endoplasmic reticulum
  • Golgi apparatus
• Palisade mesophyll cells


  • Cylindrical shape to pack tightly in leaf
  • Contain many chloroplasts to capture light energy for photosynthesis
  • Have a large vacuole to maintain cell and leaf structure
• Root hair cells


  • Fine protrusion to increase surface area for water and mineral absorption
  • Thin cell wall to facilitate water absorption
  • Many mitochondria to provide energy for active transport of minerals
• The main function of palisade mesophyll cells is to capture energy transferred by light
• Root hair cells are adapted to absorb water and dissolved minerals from the soil
• Mammalian blood cells (red, white) are specialised for their functions
• White blood cells


  • Large nucleus, often with protrusions
  • Made in bone marrow and lymph nodes
  • Different types with function to fight pathogens
  • Can move through capillary walls to sites of infection
• Red blood cells


  • No nucleus or organelles, more room for haemoglobin
  • Small, round, biconcave discs to optimise surface area to volume ratio
  • Made in bone marrow, cannot divide
• Structural differences between human sperm and egg cells
• Columnar epithelial cells


  • Found in upper airway, have many mitochondria
  • Cilia to move particles out of lungs
  • Goblet cells produce mucus