Cells

• Eukaryotes

  • Animals
  • Fungi
  • Plants
  • Larger than prokaryotic cells
  • Contain membrane bound organelles
  • Contain a true, membrane bound nucleus
• Nucleus

  • Contains the genetic material in the form of protein bound linear chromosomes
  • Acts as the control centre for the cell through the production of mRNA and ribosomes
  • Has a double membrane which controls what enters and leaves the nucleus
  • Pores in the nucleus membrane allow large molecules including mRNA to pass out of the nucleus
• Mitochondrion

  • The site of ATP synthesis by aerobic respiration
  • Has a double membrane
  • The inner membrane is folded into cristae which increases surface area for the attachment of enzymes and other proteins involved in respiration
  • The matrix is where the link reaction and Krebs cycle of respiration occur
• Chloroplasts

  • The site of the reactions of photosynthesis
  • They have a double membrane
  • They contain dark areas called grana which are made of stacks of folded membranes called thylakoids containing chlorophyll
  • The stroma contains many enzymes involved in the LIS of photosynthesis along with large starch grains to store the products of photosynthesis
• Rough Endoplasmic Reticulum

  • A system of ribosome covered, sheet like membranes running through the cytoplasm
  • Rough ER provides a large surface area for the synthesis of proteins
• Smooth Endoplasmic Reticulum

  • A system of sheet like membranes running through the cytoplasm
  • There are no ribosomes attached to smooth ER
  • The site of synthesis and transport of lipids
• Golgi apparatus

  • It receives proteins and lipids from ER
  • It modifies proteins often attaching carbohydrates to them to form glycoproteins
  • Molecules are labelled in the golgi apparatus so that they can be transported to the right destination
  • Golgi apparatus packages proteins and other materials into golgi vesicles which transport substances around the cell
  • Golgi apparatus froms lysosomes
• Lysosomes

  • Larger vesicles produced by the golgi which contain enzymes - lysozymes
  • They hydrolyse materials ingested by phagocytic white blood cells
  • They digest worn out organelles and dead cells (autolysis)
• Ribosomes

  • Small granules made of rRNA and protein
  • Ribosomes have 2 subunits which lock together
  • Ribosomes are found in the cytoplasm or attacked to the surface of rough ER
  • Ribosomes are larger in eukaryotic cells (80s) than in prokaryotic cells (70s)
  • Ribosomes are involved in protein synthesis
• Plant cell wall

  • Made of strong microfibrils of cellulose
  • The cell wall provides mechanical strength to stop cells bursting when water enters by osmosis - causing turgor pressure - the cell becomes turgid
  • Fungal cell walls are made of chitin
  • Bacterial cell walls (prokaryote) are made of murein
• Plant cell vacuole

  • A large fluid filled sac surrounded by a membrane called tonoplast
  • Acts as a temporary store of sugars and amino acids
  • Helps to support the stems of non woody (herbaceous) plants by making them turgid
• Prokaryotic cells

  • 'Circular' loop of DNA
  • Plasmid (NAP)
  • 70s ribosomes
  • Slime capsule (NAP)
  • Cell wall made of murein
  • Cytoplasm
  • Cell membrane
  • Flagellum (NAP)
• Resolution


  The ability to distinguish between 2 points
• Magnification


  How much bigger the image of the object is than the actual size of the object
• Microscopes

  • Light/compound microscopes
  • TEM - Transmission Electron Microscope
  • SEM - Scanning Electron Microscope
• Cell differentiation

  • The process by which cells become specialised to carry out a particular function
  • All body cells are derived from a single fertilised egg cell (zygote) which undergoes mitosis, so all cells have exactly the same genes
  • Cells become differentiated when certain genes are switched on whilst others are switched off
• How do cells change during differentiation?

  • They change in size and shape
  • The type and number of organelles
• Palisade cell

  • Function - Photosynthesis
  • They are long and thin forming a continuous layer to absorb sunlight
  • They are packed with chloroplasts that collect sunlight
  • They have a large vacuole that pushes the chloroplasts to the edge of the cell
• Epithelial cell from small intestine

  • Function - Absorption of nutrients
  • Microvilli to increases surface area for absorption of nutrients
  • Many mitochondria to make ATP for active transport
  • Co-transporter proteins in membrane (transport glucose and sodium ions)
• Red blood cells (erythrocytes)

  • Shape - biconcave disc to increase surface area making diffusion of oxygen into and out of cells more efficient
  • Cytoplasm full of the red oxygen carrying pigment haemoglobin
  • Most organelles including the nucleus are removed making more room for haemoglobin
  • Flattened shape allows them to bend and squash against capillary wall reducing diffusion distance
• Sperm cell

  • Tail for swimming (locomotion)
  • Many mitochondria (in midpiece) produce ATP by aerobic respiration providing energy for movement of the tail
  • Nucleus - carrying only one copy of each chromosome (23 chromosomes in total)
  • Acrosome - large lysosome carrying enzymes to digest the jelly coat around the egg
• Root hair cell

  • Function - exchange surface for absorption of water and minerals from soil
  • Elongated to increase surface area
  • Many dissolved solutes and minerals in vacuole and cytoplasm create low water potential so water enters by osmosis
  • Many mitochondria to provide ATP for active transport
  • Many carrier proteins in the cell membrane to uptake minerals by active transport
• Xylem vessel

  • Function - transport water and minerals
  • Small elongated cells
  • Thick cell walls are reinforced and waterproofed by deposits of lignin (a woody material)
  • Ends of cells breakdown to form continuous tubes
  • Cytoplasm and organelles are removed from the cell
• Tissues


  A group of similar cells working together to perform a particular function
• Organs


  A group of different tissues working together to perform a particular function
• Systems


  A group of different organs working together to perform a particular function
• Epithelial tissues

  • Line all body surfaces
  • They form sheets which usually have a protective or secretory function or act as exchange surfaces
• Xylem tissues

  • Made of a number of similar cell types which work together to carry water and minerals through plants
• The stomach

  • Has muscle tissue to churn food
  • Epithelium to protect the stomach wall and produce secretions
  • Connective tissue to hold the different tissues together
• Leaf of a plant

  • Has palisade mesophyll tissue - to carry out photosynthesis
  • Epidermis - protects the leaf and carry out gas exchange
  • Phloem tissue - transports organic materials produced in photosynthesis away from the leaf
  • Xylem tissue - transports water and minerals to leaf
• Digestive system

  • Digests and processes food
  • Made up of: salivary glands, oesophagus, stomach, small and large intestine, pancreas and liver.
• Respiratory system

  For breathing and gas exchange is made up of: trachea, bronchi and lungs
• Circulatory system

  • Circulates blood around the body
  • Made up of: heart, arteries and veins
• Eukaryotic cells

  • Linear DNA
  • DNA associated with histone proteins
  • DNA contained in a true, membrane bound nucleus
  • DNA longer
  • Presence of introns
  • Larger
  • Membrane bound organelles
  • 80s ribosomes
  • No plasmids/slime capsule/flagellum
• Prokaryotic cells

  • Circular DNA
  • DNA not associated with histone proteins
  • DNA loose in the cytoplasm
  • DNA shorter (fewer genes)
  • No introns present
  • Smaller
  • Organelles not membrane bound
  • 70s ribosomes
  • Sometimes has flagellum/slime capsule/plasmids
• Actual size of an object using a scale bar

  Actual length = (image length ÷ bar scale length) x bar scale
• Artefact


  Something which appears in a prepared specimen which was not originally there but is only there as a result of the preparation
• Transmission Electron Microscope (TEM)

  • Electrons forced using electromagnets
  • Denser area of the specimen absorb more electrons and appear darker on the screen
  • This has the highest resolution as electrons have a shorter wavelength than light
  • The specimen is always dead due to the presence of a vacuum
  • There is much preparation of specimens so high chance of artefacts occurring and personnel have to be highly trained
  • Image produced is not in colour so needs to be added afterwards
• Scanning Electron Microscope (SEM)

  • Electrons are deflected off, or dislodged from, the specimen and are detected - forming an image
  • Lower resolution than TEM
  • Used to look at the surface of specimens eg viruses
  • Produces a 3D image
• Viruses

  • Non living
  • Acellular
  • HIV - RNA, capsid, attachment proteins, reverse transcriptase, phospholipid envelope