Cell Biology

• Eukaryotic cells are complex and include all animal and plant cells


  Prokaryotic cells are smaller and simpler- single celled organisms
• Animal cells contain a nucleus, cytoplasm, cell membrane, ribosomes, and mitochondria


  Plant cells contain a nucleus, cytoplasm, cell membrane, ribosomes, mitochondria, cell wall, permanent vacuole, and chloroplasts
• Nucleus


  contain genetic material that controls the activity of the cell
• Cytoplasm


  gel-like substance where most chemical reactions happen. contains enzymes to control these reactions
• cell membrane


  holds the cell together and controls what goes in and out
• ribosomes


  where proteins are made
• rigid cell wall


  made of cellulose, supports and strengthens the cell
• mitochondria


  where most of the reaction for aerobic respiration takes place. respiration transfers energy that the cell needs to work
• permanent vacuole


  contains cell sap, a weak solution of sugar and salts
• chloroplasts


  where photosynthesis occurs, contain green substance called chlorophyll, which absorbs the light
• Bacteria are smaller


  Don't have a nucleus, single circular strand of Dna

  one or more of Dna called plasmids

  no chloroplasts or mitochondria
• Light microscopes use light and lenses to magnify an image. Can see individual cells and large subcellular structures


  Electron microscopes use electrons to form an image. they have a higher magnification and resolution. Can see smaller things in more detail, like the internal structure of mitochondria and chloroplasts
• magnification


  image size/real size
• Slide Preparation


  add a drop of water

  cut an onion and separate it into layers-peel off epidermal tissue and place on slide

  add a drop of iodine solution- stain, highlights objects in a cell

  place a cover slip without air bubbles
• Parts of a microscope

  eyepiece, coarse adjustment knob, lenses, light, fine adjustment knob
• cell differentiation


  differentiation is the process by which a cell changes to become specialised for its job
• Sperm cells


  long tail + streamlined head- help it swim

  lot of mitochondria- to provide energy needed

  carries enzymes- digest egg cell membrane
• Nerve cells- to carry electrical signals

  long- to cover more distance

  have branched connections- connect to other nerve cells
• Muscle cells- to contract 


  long- to have space to contract

  contain lots of mitochondria- to generate energy needed
• Root hair cells- to absorb water + minerals


  grow into long hairs- to have a large surface area for absorbing water and mineral ions
• Xylem cells- to transport substances

  hollow + few subcellular structures- so that stuff can flow through them
• Stem cells


  Undifferentiated cells (stem cells) can differentiate into different types of cells

  found in early human embryos + adult bone marrow
• Stem cells can cure disease

  can replace faulty blood cells

  diabetes, nerve cells
• Therapeutic cloning


  an embryo could have the same genetic information as the patient. the stem cells would contain the same genes and so wouldn't be rejected.
• Embryo stem cells shouldn't be used for experiments because they take away human life. 


  People who exist already are suffering more than the embryos

  Embryos unwanted
• In plants, stem cells are found in meristems


  throughout the plant's entire life, the cells can differentiate into any type of plant cell. can be used to produce clones of plants quickly and cheaply. used to grow more of rare plants. used to grow identical plants for farmers- disease resistance
• Chromosomes contain genetic information

  chromosomes are coiled up lengths of dna

  each chromosome carries a large number of genes

  genes control the development of characteristics

  body cells have two copies of chromosomes- one from the mother, one from the father

  have 23 chromosomes
• Cell cycle

  body cells in multicellular organisms divide to produce new cells.

  the stage in the cell cycle where the cell divides is called mitosis
• In a cell that is not dividing, DNA is spread out in long strings

  Before division, the cell has to grow and increase the amount of subcellular structures- mitochondria + ribosomes

  It duplicates it's DNA so that each new cell has a copy
• Mitosis


  The chromosomes line up in the centre of the cell, cell fibres pull them apart, and the two arms of each chromosome goes to opposite ends of the cell

  Membranes form around each of the sets of chromosomes

  The nucleus divides

  The cytoplasm and cell membrane divides

  The cell now has two identical daughter cells
• Binary fission


  The circular DNA and plasmids replicate

  The cell gets bigger, and the circular DNA strands move to opposite ends (poles) of the cell

  The cytoplasm begins to divide and new cell walls form

  The cytoplasm divides and two daughter cells are produced

  Each have one copy of the DNA but can have varying numbers of plasmids
• Number of bacteria in a population

  Both times in the correct units

  Divide the total time by the mean division cells- this gives you the number of divisions

  2 to the power of the number of divisions to find the number of cells
• Bacteria can be grown in a lab

  bacteria are grown in a "culture medium" which contains the carbohydrates, minerals, proteins, and vitamins needed for them to grow. the culture medium can be a nutrient broth or a solid agar jelly. bacteria grown on agar plates will form visible colonies on the surface
• Making an agar plate


  hot jelly is poured into a shallow round dish called a petri dish.

  when the jelly is cooled and set, inoculating loops can be used to transfer microorganisms to the medium

  the microorganisms then mulitply
• in a lab at a school the microorganisms are stored at 25C


  harmful pathogens are more likely to grow at temperatures higher than 25C. In industrial conditions cultures are incubated at higher temperatures so that they can grow a lot faster
• Uncontaminated organisms


  The petri dishes and culture medium must be sterilised- to kill unwanted microorganisms

  If an inoculating loop is used, it should be sterilised first by passing it through a hot flame

  After transferring the bacteria, the lid of the Petri dish should be lightly taped on- to stop microorganisms from the air from getting in

  The Petri dish should be stored upside-down- to stop drops of condensation falling onto the agar surface
• Antibiotics on Bacteria Growth

  1. Place paper discs soaked in different types (or concentrations) of antibiotics on the agar plate that has even covering of bacteria

  2. Antibiotics should diffuse into the agar jelly

  3. Antibiotic resistant bacteria will continue to grow on the agar around the paper discs but non-resistant strains will die
• Inhibition zone


  A clear area where the bacteria have died
• Control


  • Paper disc soaked in sterile water
• The more effective the antibiotic is

  The larger the inhibition zone will be