cell biology

• Eukaryotic cells


  Cells that contain their genetic material enclosed in a nucleus
• what is in Eukaryotic cells

  • Contain a nucleus
  • Contain a cell membrane
  • Contain cytoplasm
• Prokaryotic cells


  Cells where the genetic material is not enclosed in a nucleus

  much smaller than eukaryotic cells
• what is in Prokaryotic cells

  • Do not have a nucleus
  • Have a cell membrane
  • Have a cell wall
  • Contain cytoplasm
  • May have plasmids
• Micrometer (μm)

  One millionth of a meter
• Size of objects

  • Typical human cell is 10-20 μm in size
• Nano

  One billionth
• Nanometer (nm)

  One billionth of a meter
• How to determine order of magnitude

  Count the number of zeros - each zero represents 1 order of magnitude
• Nucleus

  Encloses the genetic material
• Cytoplasm

  where chemical reactions take place
• Cell membrane

  Controls what enters and leaves the cell
• Mitochondria


  • Where aerobic respiration takes place
• Ribosomes


  • Sites of protein synthesis
• Ribosomes are too small to be seen using a light microscope, an electron microscope is required
• structures inside animal cell:

  cell membrane

  cytoplasm

  nucleus

  ribosomes

  mitochondria
• structures inside plant cell:

  cell membrane

  nucleus

  cytoplasm

  ribosomes

  mitochondria

  chloroplast

  cell wall

  vacuole
• chloroplast contains chlorophyll and are sites of protein synthesis
• cell wall is made from cellulose which strengthens the cell
• a vacuole is filled with cell sap and gives the plant cell its shape
• how a sperm cell is specialized

  has a long tail allowing it to swim to egg cell

  contain alot of mitochondria which provide the energy for swimming

  contain enzymes which allow them to digest outer layer of egg
• how a nerve cell is specialised

  axon - carries impulses from one part of the body to another

  dendrites - increase surface area so other nerve cells connect easily

  myelin - speeds up transmission of nerve impulses

  synapse - allows the impulse to pass from one nerve cell to another
• how phloem cell is specialised

  has 2 different types of cells: phloem vessel cell and companion cell

  end walls of phloem vessel cells have pores called sieve plates which allow dissolved sugars to move through cell

  each phloem vessel cell has a companion cell connected by pores
• how a muscle cell is specialised

  has lots of mitochondria which provide energy for movement

  contain protein fibres so muscle cell can change their shape
• how a root hair cell is specialised

  has thin walls so water can move through easily

  has no chloroplast because theres no light underground

  has root hair to increase surface area
• how a xylem cell is specialised

  has no top or bottom walls to form continuous tubes

  has thick walls to support the plant

  has no internal structures to allow flow of water
• what is differentiation

  when a cell becomes specialised
• how to use a microscope (required practical)

  1)clip slide onto stage

  2)make sure lower power objective lens is over the slide

  3)use coarse adjustment knob to bring slide and objective lens close

  4)look down eyepiece and use coarse adjustment knob to move stage downwards. stop when image is roughly focussed

  5)use fine adjustment knob to bring image into focus
• light microscopes

  have limited magnification

  can see large subcellular structures eg. vacuole
• electron microscopes

  have much higher magnification and resolution than light microscopes

  can see smaller subcellular structures eg. mitochondria
• equation for magnification

  image size/ actual size
• binary fission

  one bacterial cell splitting into 2 bacterial cells
• how many times do bacteria cells carry out binary fission

  every 20 min if they have enough nutrients and suitable temperature
• how to prepare an uncontaminated culture using aseptic technique

  1)sterilise petri dishes, bacterial nutrient broth and agar to kill unwanted microorganisms

  2)bacteria is transferred into the culture using inoculating loop

  3)sterilise inoculating loop by passing it through a flame

  4) put lid on petri dish using adhesive tape then store upside down
• what is the temperature bacteria is normally incubated at in school laboratories

  25 degrees celcius. this reduces chances of harmful bacteria growing
• required practical: effect of antibiotics on bacterial growth

  1)clean the bench with disinfectant solution to kill microorganisms

  2)sterilise an inoculating loop by passing it through a flame

  3)open a sterile agar gel plate near the flame so the flame kills bacteria in the air

  4)use the loop to spread the chosen bacteria evenly over the plate

  5)place sterile filter paper discs containing antibiotic onto the plate

  6)incubate the plate at 25 degrees celcius
• chromosomes

  -found in the nucleus

  -made up on DNA

  -body cells contain 23 pairs of chromosomes

  -carry genes which determine our features
• cell cycle

  stage 1: cell grows and number of subcellular structures increase. then DNA replicates to form 2 copies of chromosomes

  stage 2 (mitosis): one chromosome from each set is pulled to each end of the cell and the nucleus divides

  stage 3: cytoplasm and cell membrane divide to form 2 identical daughter cells
• why is mitosis important

  for growth and repair
• what is differentiation

  when a cell becomes specialised