b1 - cell biology

• eukaryotic cells

  plant and animal cells

  all have cell membrane, cytoplasm and genetic material enclosed in nucleus
• prokaryotic cells

  bacteria cells

  all have cytoplasm, cell membrane, cell wall

  no nucleus, single DNA loop

  may be small rings of DNA - plasmids
• bacteria cells

  approximately 10 times smaller than eukaryotic cells

  contains: cell wall, cytoplasm, loop of DNA, plasmid, flagellum
• nucleus

  contains DNA - controls activities of the cell
• mitochondria

  site of aerobic respiration
• ribosomes

  site of protein synthesis
• cell membrane

  controls which substances enter/leave the cell
• cytoplasm

  site of most chemical reactions
• chloroplast

  site of photosynthesis
• cell wall

  supports and strengthens the cell
• vacuole

  contains cell sap
• unique to plant cells

  chloroplast, permanent vacuoles and cell wall
• nerve cells

  long - to carry electrical impulses long distances in the body

  branched ends - to connect to other nerves
• muscle cells

  lots of mitochondria - to release energy through respiration, allows them to contract
• sperm cells

  lots of mitochondria - to release energy through respiration

  flagellum - to allow cell to swim to egg
• root hair cell

  absorbs water and minerals from soil

  long hair - increases the surface area

  lots of mitochondria - to release energy through respiration for active transport
• xylem vessels

  long and thin - to transport water and minerals ions up the plant

  made of dead cells in a tube

  strengthened with lignin
• phloem vessels

  transports sugars all over the plant (translocation)

  pores in end walls - allows cell sap and sugars to diffuse through

  mitochondria - to release energy through respiration
• osmosis 


  the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
• formula for percentage change in mass

  (final mass - initial mass/ initial mass) x 100
• active transport

  1. moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient). requires energy from respiration
  2. allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil. plants require ions for healthy growth
  3. allows sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration. sugar molecules are used for cell respiration
• specialised cells


  cell that differentiate to carry out a certain function
• object 


  real object or sample you are looking at
• image

  the image that we see when we look down the microscope
• magnification


  how many times larger the image is than the object
• magnification equation


  magnification = image size / object size
• resolution


  shortest distance between two points on an object, that can still be distinguished as two separate entities
• light microscopes


  easy to use

  relatively cheap

  rely on light to work

  has a wavelength of 0.2 micrometres so resolution is limited to 0.2 micrometres

  any details less than 0.2 micrometres will be blurry
• electron microscopes


  hard to use

  very expensive

  rely on electrons to work

  has wavelength of 0.1 nanometres so maximum resolution is 0.1 nanometres

  2000x better than light microscopes

  can be used to study sub-cellular structures
• chromosomes


  found in nucleus

  carries many genes

  found in pairs
• cell division (mitosis) stages


  stage 1: cell grows. increases number of subcellular structures (mitochondria and ribosomes) DNA replicates - two copies of each chromosomes

  stage 2: one set of chromosomes is pulled to each end of the cell. the nucleus divides

  stage 3: cytoplasm and cell membranes divide - forms two genetically identical cells
• diffusion


  spreading out of particles from an area of higher concentration to an area of lower concentration

  examples: gas exchange of oxygen and carbon dioxide, urea
• factors which affect the rate of diffusion


  1. difference in concentrations - higher difference = faster rate of diffusion
  2. temperature - higher temperature = faster rate of diffusion
  3. surface area of the membrane - larger surface area = faster rate of diffusion
• the effectiveness of an exchange surface is increased by: 


  1. having large surface area
  2. a membrane that is thin - short diffusion pathway
  3. having an efficient blood supply - to maintain a concentration gradient
• embryonic vs adult stem cells


  embryonic stem cells - can be cloned and made to differentiate into most different types of human cells

  adult stem cells - comes from bone marrow, can differentiate into only some different types of cells
• therapeutic cloning


  embryo is produced with the same genes as the patient. these stem cells are used for medical treatment

  advantages - cells has same DNA as patient so it won't be rejected

  disadvantages - can transfer viruses. embryos have a right to life
• plant stem cells


  from meristem

  can differentiate into any time of plant at any point in plant's life

  can be used to produce clones quickly and economically

  rare species can be cloned to protect from extinction