OCR AS BIOLOGY F211 COMPLETE NOTES

1.1.1 Cells

(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:

Nucleus

Houses all of the cell’s genetic material in the form of DNA, which contains the instructions for protein synthesis

Largest organelle.

Darkened patches= chromatin

Nucleolus-

Makes ribosomes and RNA which pass into the cytoplasm and are used in protein synthesis

Dense spherical structure in nucleus

Nuclear envelope

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

Golgi apparatus

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

Ribosomes

Site of protein synthesis.

Tiny, some are in cytoplasm some bound to RER

Mitochondria

Where ATP is made.

 

Spherical or sausage shape, double membrane

Lysosomes

Contain digestive enzymes that are used to break down material

Spherical sausage shape,  single membrane

Chloroplasts

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

Phospholipid bilayer

…