cells

• -High resolution images are produced.

  -Thus, small objects can be displayed.

  Give two advantages of using TRANSMISSION ELECTRON MICROSCOPES.
• -Can only be used on thin specimens.

  -the microscope can only work with non-living specimens


  Give two drawbacks of using TRANSMISSION ELECTRON MICROSCOPES.
• how much bigger the image is than the specimen(sample observed).

  What is magnification?
• Size of image/size of real object


  What is the equation for magnification.
• milimetre(mm)= 1mm

  micrometre(μm)= 0.001mm

  nanometre(nm)= 0.000001mm


  Give the units for MM, μm, and NM.
• how detailed the image is. how well a microscope distinguishes between two points that are close together. however. increasing the magnification won't help if a microscope lens can't separate two objects.


  What is resolution?
• cell homogenisation breaks open cell walls.

  filter to remove large debris.

  use isotonic solution to prevent damage to mitochondria.


  Describe and explain how cell fractionation and ultracentrifugation can be used to isolate mitochondria from a suspension of animal cells.
• where the specimen is suspended in a drop liquid on the slide.


  what is a temporary mount?
• 1

  - begin by pipetting a small drop of water onto the centre of the slide.

  2

  - you will then need to place a thin section of your specimen on top of the water drop through using tweezers.

  3

  - add a drop of stain. stains are used to highlight objects in a cell.

  4

  -add a cover slip.

  -do this by standing the slide upright on the slide, next to the water droplet.

  -carefully tilt and lower so specimen is covered.

  -ensure no air bubbles are seen. they'll obstruct view of specimen.


  describe the steps to preparing a microscope slide using a temporary mount?
• a square of clear glass or plastic that protects the specimen.

  what is a cover slip?
• -can only be used on thin specimens.

  -non-living specimens can only be applied on as the microscope can only work with non-living specimens.


  give two disadvantages of using TRANSMISSION ELECTRON MICROSCOPES.
• -lower resolution images given.

  - only on non-living specimens, it can be used upon.

  give two disadvantages of using SCANNING ELECTRON MICROSCOPES.
• What are eyepiece graticules used for?


  Used to measure the size of objects
• What is standard deviation?


  A measure of how spread out the data is from its mean
• Why is standard deviation preferred over the range of a set of data?


  Standard deviation allows us to understand

  the data set's variability(inconsistency, lack of pattern, how it varies)

  It gives the variation of values from the mean

  of the data set (some values are closer to the mean than others)

  It provides better variability than the range, which

  only gives us the difference between the maximum and minimum value
• What is it useful for?

  when comparing consistency between different data sets
• What must be done before we can calculate the standard deviation?


  The mean must be calculated
• How do we calculate standard deviation?


  Step 1: Calculate the mean

  Step 2: Subtract the mean from each value(do this in a table)

  Step 3: Square each difference

  Step 4: Total the differences

  Step 5: Divide the total by (n-1) to get value A (n being the number of values)

  Step 6: Get the square root of value A
• What is the scale?


  Typically 10 mm long and divided into 100 sub-divisions
• Why can't eyepiece graticules be used to directly measure the size of objects?


  each objective lens will magnify to a different degree

  graticule must be calibrated for each different objective lens
• Calibrating the eyepiece graticule


  - use a stage micrometer - scale etched on it schools = 10 mm long and have 1 mm subdivisions and smallest of 0.1mm

  - line up eyepiece graticule scale and stage micrometer
• How to use - calibrating

  Place the micrometer on the stage

  Focus the microscope

  Line up micrometer with eyepiece graticule (0 part of micrometer aligned with 0 of graticule and that they are parallel)

  Find the scale, e.g. 50 eyepiece graticule = 1mm / 1 eyepiece graticule = 1/50

  For each magnification calibrate the eye piece again - the micrometer is magnified but the eyepiece graticule isn't so the scale will no longer work.

  
  

  You can now remove the micrometer and place sample to measure it and use the scale to work out actual length e.g. RBC measures 5 eyepiece graticule = 5x 1/50
• specialised


  having particular structure to serve a specific function.
• cells become specialised to


  perform a particular role, become specialsed to suit the role it will carry out
• how are cells produced

  mitotic divisions
• how does a cell become specialised

  Only some of the genes are expressed (switched on) in any one cell, at any one time. Different genes are expressed in different specialised cells. Rest of genes are switched off.
• tissue

  group of similar cells organised into structural unit that serves a particular function
• Structure - nucleus


  Surrounded by nuclear envelope

  Contains nucleolus and chromatin (genetic material)
• Function - nucleolus


  Ribosomes synthesised
• Function - nuclear envelope


  Separates nucleus

  Allows diffusion

  Has nuclear pores for larger substances
• Function - nucleus


  Control centre of cell

  Stores and transmits genes

  Instructs protein synthesis
• Structure - RER


  Membranes containing cisternae and is attached to nuclear membrane

  Has ribosomes
• Function - RER


  Synthesis and transport of proteins
• Structure - SER


  Membranes of cisternae

  No ribosomes
• Function - SER


  Synthesis and assistance in absorption of lipids and carbohydrates
• Structure - golgi apparatus


  Stack of membrane bound sacs and vesicles
• Function - golgi apparatus


  Modifies, packages and transports proteins (via vesicles), transports lipids
• Structure - mitochondria


  Double membrane

  Inner membrane - cristae

  Inner part is fluid filled matrix
• Function - mitochondria


  Site of ATP production (aerobic respiration)

  Highly abundant in cells requiring a lot of energy e.g. muscle and liver cells
• Structure - chloroplasts


  Double membrane

  Inner membrane continuous with thylakoid stacks (containing chlorophyll)

  Thylakoid stack - granum, surrounded by stroma (matrix)