Section 2

• Microscopes • Cell fractionation and ultracentrifugation

. Use convex glass lenses . Uses wavelengths of light which can only resolve images 0.2 micrometres apart

Magnification= image size / actual size

The minimum distance apart that two objects can be distinguished as separate objects in an image

• Transmission electron microscope (TEM) • Scanning electron microscope (SEM)

A beam of electrons are focused by using electromagnets inside a vacuum. Electrons pass through a thin slice of specimen and areas that absorb the electrons and appear dark on the image produced.

Beams of electrons are focused using electromagnets inside a vacuum and they pass across the surface of the specimen and scatter. The pattern of scattering builds up a 3D image.

• Electron beam has a very short wavelength so the microscope has a high revolving power • Electrons are negatively charged so the beam can be focused using electromagnets

• A vacuum must be used so living specimens cannot be observed • The staining process is very complicated so may introduce artefacts into the sample • The SEM has a lower resolving power than TEM however both have a higher resolving power compared to light microscopes

Cell fractionation is the process in which different parts and organelles of a cell are separated so they can be studied in detail

• Place tissue in a: - cold = to reduce enzyme activity and prevents damage to organelles - buffered = to maintain a constant pH to prevent enzymes denaturing - isotonic = prevent change in water potential so organelles don’t shrink or burst via osmosis • Cells are homogenised to burst the cells and release the organelles in a fluid called the homogenate • Homogenate if filtered to remove any large debris or complete cells to produce the filtrate • Filtrate is then placed in a centrifuge and spun at a low speed where the heaviest organelle (the nucleus) forms a pellet at the bottom • The liquid at the top is the supernatant which is poured into a new tube, placed in a centrifuge and spun at a higher speed • The next heaviest organelle forms a pellet at the bottom (the mitochondria) and the process continues

A nucleus and membrane bound organelles

• Nucleus • Rough endoplasmic reticulum • Smooth endoplasmic reticulum • Golgi apparatus • Mitochondria • Lysosomes • Ribosomes • Centrioles

A double membrane called the envelope containing nuclear pores which control what enters and leaves. It contains the chromatin and a nucleolus which is the sight of ribosome production. The nucleoplasm is a jelly like material which makes up the bulk of the nucleus.

Series of flattened sacs which are enclosed by a membrane covered in ribosomes. It folds and processes proteins made on the ribosomes. It also provides a pathway for the transport of materials throughout the cell.

System of membrane bound sacs. It synthesises stores and transports lipids and carbohydrates.

Series of fluid flattened sacs with vesicles surrounding the edges. The Golgi modifies the lipids produced by the SER and transports them to their correct place. It also produces lysosomes and adds carbohydrates to proteins to make glycoproteins.

Oval shaped, bound by a double membrane called the envelope. The inner membrane is folded to form the cristae with a matrix on the inside containing all the enzymes needed for respiration.

Hollow cylinders containing microtubules arranged at right angles to each other. They’re involved in making spindle fibres for cell division.

Ribosomes in eukaryotic cells are made of two sub units and are the site of protein synthesis. The two sub units contain RNA and protein.

Murein

• Growth= all cells produced are genetically identical so organisms can grow • Repair= all cells produced are identical so organisms can replace dead or damage tissues • Reproduction= single celled organisms reproduce by dividing into two identical new organisms

Cell division which produces two genetically identical daughter cells which have the same number of chromosomes as the parent and each other.

Cell division which produces 4 daughter cells each with half the number of chromosomes than the parent cells ( 4 haploid cells produced )