cell biology

• animal and plant cells are eukaryotic cells
• bacteria cells are prokaryotic cells which are much smaller
• animal and plant cells contain:

  • a cell membrane
  • a cytoplasm
  • a nucleus
• bacteria cells contain:

  • cell wall
  • cell membrane
  • cytoplasm
  • single circular strand of DNA
  • plasmids
• conversions:

  • centi - 0.01
  • milli - 0.001
  • micro - 0.000001
  • nano - 0.000000001
• organelles in animal and plant cells:

  • nucleus - contains DNA coding for a particular protein
  • cytoplasm - chemical reactions occur, contains enzymes
  • cell membrane - controls what enters and leaves the cell
  • mitochondria - where aerobic respiration occurs, creating energy
  • ribosomes - site of protein synthesis
• structures only in plant cells:

  • chloroplasts - where photosynthesis occurs to make food, contains green chlorophyll which harvests light
  • permanent vacuole - contains cell sap and improves cell rigidity
  • cell wall - made from cellulose, provides strength
• the cell wall in a bacteria cell is made up of peptidogylcan
• cells specialise by undergoing differentiation where new sub-cellular structures are gained to perform its role
• cells can differentiate early on or have the ability to differentiate their whole life, these are called stem cells
• sperm cells (specialised cell in animals):

  • specialised to carry male DNA to egg for reproduction
  • streamlined head and long tail for swimming
  • many mitochondria to supply energy for movement
  • acrosome (top of head) has digestive enzymes which break down the membrane of the egg cell
• nerve cells (specialised cells in animals):

  • specialised to transmit electrical signals quickly from areas
  • long axon so impulses can be carried long distances
  • lots of dendrites creating connections to other nerve cells
  • mitochondria on nerve endings supply energy to make neurotransmitters which allows the impulse to pass along cells
• muscle cells ( specialised cells in animals):

  • specialised to contract quickly to move bones causing movement
  • special proteins slide over each other causing muscles to contract
  • lots of mitochondria providing energy for contraction
  • store glycogen used by mitochondria for respiration
• root hair cells (specialised cells in plants):

  • specialised to take up water via osmosis and mineral ions via active transport from the soil as they are found in root tips
  • large surface area due to root hairs so more water moves in
  • large permanent vacuole affects speed of water movement from soil to the cell
  • mitochondria provide energy for the active transport of mineral ions into the root hair cell
• xylem cells (specialised cells in plants):

  • specialised to transport water and mineral ions from roots to shoots
  • lignin is deposited causing cells to die
  • they become hollow and join so water and mineral ions can move through
  • lignin deposited in spirals which help cells cope with pressure of water
• phloem cells (specialised cells in plants):

  • specialised to carry products of photosynthesis to parts of the plant
  • cell walls of each structure form sieve plates when they break down, allowing movement of substances from cell to cell
  • energy for these cells to be alive is supplied by mitochondria of companion cells
• in animals, cells differentiate at an early stage then lose this ability
• in animals, specialised cells can make the same cells by undergoing mitosis
• red blood cells cannot divide and are replaced by adult stem cells
• in mature animals, cell division only occurs to replace or repair damaged cells
• in plants, many cells differentiate throughout their life, but only when they reach their final position but can re-differentiate when moved to another position
• the electron microscope allows us to view sub-cellular structures by forming an image
• a light microscope produces a magnified image through the objective lens which is then magnified and directed into the lens by the eyepiece lens
• electron microscopes have both a higher resolution and magnification than light microscopes
• magnification of light microscope:

  magnification of eyepiece lens x magnification of objective lens
• size of an object:

  • size of image $\div$ magnification
• microorganisms are very small, so to study them they must be cultured in a lab
• the culture medium contains carbohydrates for energy, minerals, proteins and vitamins
• microorganisms can be grown by a nutrient broth solution:

  • involves making a suspension of bacteria to be grown
  • mixed with sterile nutrient broth (culture medium)
  • flask stoppered by cotton wool to prevent air contamination
  • shake regularly to provide oxygen for growing bacteria
• microorganisms can be grown on an agar gel plate:

  • agar acts as a culture medium and bacteria on it forms colonies on the surface
• how to make an agar plate:

  • hot, sterilised agar is poured into a petri dish and left to cool and set
  • inoculating loops are dipped in a solution of microorganism and spread over the agar evenly
  • lid is taped on and plate is incubated for a few days so microorganisms can grow
• agar practical:

  • petri dish and culture sterilised by an oven to stop contamination and prevent new pathogens being created
  • inoculating loop is sterilised on a flame to kill unwanted microorganisms
  • lid of petri dish loosely sealed with tape to stop airborne microorganisms from contaminating culture but not all the way so anaerobic bacteria cannot grow
  • petri dish stored upside down to prevent condensation landing on agar affecting growth
  • incubated at 25 degrees at optimum temperature to prevent harmful bacteria
• if there is a supply of nutrients and a suitable temperature, bacteria can multiply by binary fission
• if microorganisms are bacteria they can be used to test the effects of different antibiotics and disinfectants
• antibiotic practical:

  • soak paper disks in different concentrations of antibiotics and place on agar gel spread evenly with bacteria
  • one control disk soaked in water to show type of antibiotics have different inhibition zones
  • leave plate at 25 degrees for 2 days
  • zone of inhibition is measured, the bigger it is the more bacteria killed so it is more effective
• the nucleus contains genetic information
• chromosomes are found in the nucleus and contain coils of DNA
• a gene is a short section of DNA that codes for a protein and controls characteristics
• gametes, also known as sex cells, have 23 chromosomes in total in each cell
• there are 46 chromosomes in a human body cell