(a) State the resolution and magnification that can be achieved by a light microscope, a transmission electron
Microscope and a scanning electron microscope;
Light microscope - 200nm x1, 500
Transmission Electron Microscope- 0.1nm x500, 000
Scanning Electron Microscope- 0.1nm X100, 000
(b) explain the difference between magnification and resolution;
Magnification is the degree to which the size of an image is larger than the image itself.
Resolution is the degree to which it is possible to distinguish between two objects that are very close together.
Total magnification of a light microscope = objective lens x eyepiece lens
1mm = 100um
Animal cells- 20-24 um long
Cell surface membrane- 7- 10um with
Ribosomes- 20nm diameter
Viruses- 40-100nm diameter
(c) Explain the need for staining samples for use in light microscopy and electron microscopy;
· Most biological material isn’t coloured, so it’s difficult to distinguish between different features.
· Coloured stains - stain specimens for use with the light microscope. Chemicals bind to other chemicals in the specimen, which allows it be to seen.
· Some bind to specific structures, e.g. Acetic orcein staining DNA red.
· Electron micrographs start off black and white, with false colour being added by a specialised computer program afterwards.
(d) Calculate the linear magnification of an image;
Image size =Actual size x Magnification
(e) Describe and interpret drawings and photographs of eukaryotic cells as seen under an electron microscope and be able to recognise the following structures:
Houses all of the cell’s genetic material in the form of DNA, which contains the instructions for protein synthesis
Darkened patches= chromatin
Makes ribosomes and RNA which pass into the cytoplasm and are used in protein synthesis
Dense spherical structure in nucleus
A double membrane with nuclear pores/ allows large molecules through.
Surrounds nucleus, made of 2 membranes with fluid between them.
Rough endoplasmic reticulum-
Transports proteins made by the attached ribosomes.
ER has flat sacs called cisternae, they are continuous with the outer nuclear membrane. RER is studded with ribosomes and SER is not.
Smooth endoplasmic reticulum
Involved in the making of lipids
Modifies proteins received from the Rough ER and then packages them into vesicles so they can be transported and secretes lysosomes
Stack of membrane flattened sac
Site of protein synthesis.
Tiny, some are in cytoplasm some bound to RER
Where ATP is made.
Spherical or sausage shape, double membrane
Contain digestive enzymes that are used to break down material
Spherical sausage shape, single membrane
Site of photosynthesis
2 membranes separated by fluid filled space. Inner membrane is continuous with an elaborate network of flattened sacs called thylakoids, (piles of plates) 1 stack is a granum. Chlorophyll is on thylakoid membranes and interrgranal membranes
Plasma (cell surface) membrane
Controls the entry and exit of substances into and out of the cell