Cell biology

• prokaryotic cell


  A type of cell lacking a membrane-enclosed nucleus and membrane-enclosed organelles; found only in the domains Bacteria and Archaea.
• Eukaryotic cells


  Contain a nucleus and other organelles that are bound by membranes.
• Mitochondria


  An organelle found in large numbers in most cells, in which the biochemical processes of respiration and energy production occur. Releases energy for cell to use
• cell membrane


  A cell structure that controls which substances can enter or leave the cell. A semi permeable membrane.
• Cytoplasm


  A jellylike/gel like substance which contains enzymes and nutrients for chemical reaction to take place inside the cell
• Nucleus


  A part of the cell containing DNA and RNA and responsible for growth and reproduction. Controls the activity of cell
• Ribosomes


  Makes proteins (protein synthesis)
• cell wall


  A rigid structure that surrounds the cell membrane and provides support to the cell. Made up of Murein in bacteria, chitin in fungus and cellulose in plant cells(xylem cells)(algal cells have cell wall)
• Chloroplast


  An organelle found in plant and algae cells where photosynthesis occurs. It contains chlorophyll,a green pigment that absorbs the light and specific enzymes required for photosynthesis to occur and food to be produced.
• Permanent vacuole


  Filled with cell sap to help keep the cell turgid
• Plasmids


  small circular strands DNA molecules that replicate separately from the bacterial chromosome
• Slime capsule


  Found on the outside of bacteria to protect it
• Flagella


  whiplike tails found in one-celled organisms to aid in movement
• Diffusion


  The net spreading out/movement of particles from an area of higher concentration to an area of lower concentration down a concentration gradient
• rate of diffusion


  how much substance is diffused in a given time.
• Factors affecting rate of diffusion

  1. concentration gradient

  2. Surface area

  3. Temperature

  4. Surface area:volume ratio
• surface area to volume ratio


  used to measure how easily substances can move in and out of an organism.
• active transport


  Is the net movement of particles from an area of lower concentration to an area of higher concentration. This requires energy from respiration.

  
  

  Humans sometimes use active transport to absorb nutrients (such as amino acids and glucose) from the small intestine. If the concentration of nutrients in the intestinal cells is higher than the concentration of nutrients in the small intestine, they can't diffuse across passively. Active transport allows nutrients to be absorbed into the walls of the intestine against the concentration gradientso they can enter the blood and can be transported around the body to be used for respiration.
• turgid


  swollen
• Flacid


  lacking firmness
• Crenation


  Happens in hypertonic solution, water moves out of cell and causes it to shrivel
• Plasmolysis


  Collapse of a walled cell's cytoplasm due to a lack of water
• Lysis (animal cell)


  Water moves into cells which may cause in to burst(in hypotonic solution)
• Chromosomes


  The nucleus of eukaryotic cells contains genetic material called DNA which is coiled up into structures called chromosomes.

  Each chromosome contains a large number of geneswhich are sections of DNA that control the development of specific characteristics in an organism.

  Different species have different numbers of chromosomes. Human body cells usually have 23 pairs of chromosomes, one received from their mother and one from their father. This means they have 46 chromosomesaltogether.

  Before cells divide they must replicate their DNA so the new cells have their own copies.
• Mitosis


  Eukaryotic cells divide in a process called mitosis which is a vital stage of the cell cycle. Mitosis produces 2 daughter cells that are identical to the original cell with the same number of chromosomes.
• Cell cycle


  The first portion of the cell cycle is the growth phase.

  The cell grows, then prepares for mitosis by replicating all of its subcellular structures like mitochondria and ribosomes.

  The cell also duplicates all of its DNA so each new cell will have a copy of the DNA. When not dividing, the DNA is spread out in long strings but when copied ready for mitosis, it forms X-shaped chromosomes with both sides of the cross containing the same DNA.

  
  

  The other part of the cell cycle is mitosis and is where the cell divides into 2 identical cells.

  It begins with the nuclear membrane breaking down and the chromosomes lining up at the equator (centre) of the cell.

  Fibres then pull the arms of the chromosome to opposite ends of the cell.

  Membranes form around the chromosomes which creates the nuclei for the new cells.

  Finally, the cytoplasm and cell membrane divide in a process called cytokinesis, producing 2 identical daughter cells that contain the same DNA as each other and the parent cell.

  
• Importance of mitosis


  Mitosis is an essential process in organisms.

  Multicellular organisms need to carry out mitosis in order to grow and replace damaged cells.

  Newly fertilised egg cells (zygotes) must undergo several rounds of mitosis to increase the number of cells and develop into embryos. Embryos then go through many more rounds of mitosis and differentiation to create fully formed foetuses.

  Organisms that reproduce asexually divide by mitosis.
• Binary fission


  Binary fission is the process by which prokaryotic cells, such as bacteria, divide and reproduce. The speed of this division depends on conditions such as temperature and nutrient concentrations. Some bacteria can divide as often as once every 20 minutes but if conditions are unfavourable binary fission will stop and cells will start to die.

  The process of binary fission is as follows:

  The genetic material stored in the circular DNA and plasmids get replicated

  The cell starts to expand and the circular DNA moves to opposite poles of the cell

  The cytoplasm divides and cell walls form around the 2 new daughter cells. Each daughter cell will contain a copy of the circular DNA and a variable number of plasmids.
• Mean division time


  The mean division time is the average time it takes for one bacterial cell to divide once.

  Mean division time can be used to work out how many times a cell has dividedand therefore the number of cells produced.

  Number of divisions =Time spent dividing/mean division time​

  Number of cells produced =2^Number of Divisions

  Example: A cell has a mean division time of 20 minutes. How many cells will it have produced after 3 hours.

  3(hours)×60=180 minutes3(hours)×60=180 minutes

  Number of divisions =180/20=9

  Number of cells producedNumber of cells produced =2^9=512 cel;s
• Aseptic techniques


  Bacteria can be grown in labs in petri dishes that contain a growth medium. The growth medium contains all the molecules needed for the cells to grow and can either be a nutrient broth solution or solid agar jelly. Bacteria grown on agar gel plates will often form colonies on the surface.

  As bacteria are found all around, it is important to reduce contamination when studying bacterial growth to prevent unwanted pathogens forming that can affect your investigations. these unwanted pathogens can also pose a risk to your health.

  The lid of the petri dish must be taped on and opened as little as possible to prevent contamination from microorganisms in the air.
• How should Petri dish be stored

  The petri dish should be stored upside down to stop condensation falling on to the agar.
• Temp of incubation and why

  The dish should incubated at 25°C to restrict the growth of harmful pathogens.
• More aseptic techniques


  Wash your hands and work surfaces before beginning to prevent contamination.

  Growth media must be heated before use to kill any bacteria living in it.

  Growth media must be added to a sterile petri dish.

  
  

  Inoculating loops used to transfer microorganisms to the media must be sterilised by passing them through a flame

  ○ Kill any microorganism existing on the loop

  ○ Avoid contamination
• Why use Bunsen


  All work should be done in the presence of a Bunsen burner on a yellow flame to create a convection current above the bench and prevent contamination from the air.

  The Bunsen burner can also be used to sterilise equipment such as the inoculating loop that is used to transfer bacteria. Passing it through the flame will kill any bacteria.
• How to close lid and why

  The lid of the petri dish must be taped on and opened as little as possible to prevent contamination from microorganisms in the air.
• Light microscopes


  Light microscopes use light and lenses to create a magnified image of a specimen. Their development enabled scientists to view individual cells and their larger subcellular structures such as nuclei. Light microscopes have been further developed, with improved magnification and resolution, but typically have a maximum magnification of only ×1500×1500 and resolutions of up to 0.2 μm0.2 μm. This means that the amount of detail that can be seen via a light microscope is limited.
• electron micropscopes


  Electron microscopes have much greater magnificationand resolving power because they use electron beams instead of light which have a much smaller wavelength. The development of the electron microscope allowed scientists to see cells in much more detail including the internal structures of mitochondria, chloroplasts and nuclei, and tiny structures like ribosomes and plasmids.
• How to microscope


  Prepare the slide

  1.Add a drop of water to a clean slide.

  2.Carefully extract the cells of interest and place them on the slide, in the water - common choices are human cheek cells (animal) and onion epidermal cells (plant).

  3.Highlight the cells using an appropriate stain (Iodine for onion cells and methylene blue for cheek cells).

  4.Finally, place a cover slipover the top of the specimen.

  
  

  
  

  View slide under the light microscope

  Carefully place the slide onto the stage and clip it in place.

  Select the objective lenswith the lowest power and therefore lowest magnification.

  While looking down the eyepiece, move the stage up and down using the coarse adjustment knobuntil the image becomes more focussed.

  Use the fine-adjustment knob to further focus the image until it is clear.

  Switch to a higher powered objective lens and refocus if greater magnification is required.
• What are sperm cells and their specialization?

  Sperm cells are specifically designed for the effective transport of male DNA to the female DNA for sexual reproduction. The head of the sperm contains all the genetic information ready for fertilisation and has enzymesthat are able to digest the egg cell membrane. They also have lots of mitochondria to provide the energy required for movement and a tail(flagellum) to help it swim.
• What are muscle cells and their specialization

  Muscle cells must be able to contract quickly so they contain lots of mitochondria to provide energy for the contraction and have protein filaments that slide over to cause the muscle to contract.