AS OCR Biology-Cells and Organelles

Microscopes:

Light Microscope:

Disadvantages:

1. Magnification only up to X1500

2. Low Resolution

Advantages:

1. Live Specimen may be observed

2. Colours May be Observed

Electron Microscope:

1.Transmission Electron Microscope:

Electron beams passes through a very thin prepared sample and since the electrons passes through the denser parts less easily there is a contrast. The final image produced is 2D. has the highest Magnification up to X500000

2. Scanning Electron Microscope

Electron beams directed onto the sample but don't pass through it and Instead 'bounces off' the sample. The final image produced is 3D but magnification is only up to X100000.

Advantages of Electron Microscope:

1.Resolution is X2000 more than light microscope- therefore can produce detailed images of structures(organelles) inside cells.

2.Scanning Electron Microscope produces 3D images- therefore details of contours and cellular or tissue arragement may be observed.

Disadvantages/limitations of Electron Microscopes:

1. Electron beams are deflected by the molecules in air, so samples needs to be placed in vacuum.

2. Extremely Expensive

3.Preparing Specimen needs a high degree of skill and may require training.

Formula for working out magnification:

Magnification= Measure size / actual size ( MAGMA)

Cells and Organelles:

Cytoskeleton-network of proteins found within cells that gives structure and shape to the cell, also moves organelles around inside cells.

MEMBRANE BOUND ORGANELLES

Nucleus- This is the largest organelle. It is surrounded by nuclear envelope which consists of a double membrane with holes called nuclear pores. There is a dense spherocal structure called the nucleolus inside the nucleus. The Nucleus nearly all the cell's genetic materials. The nucleolus makes RNA and ribosomes.

Endoplasmic Reticulum- Consists…