Cells And Magification

Question 1

equation

Answer 1

Magnification= size of image/ size of object
size of object = size of image/ magnification

Question 2

Magnification

Answer 2

is a value that tells us how much larger an image is when compared to the original object.

Question 3

Microscopes

Answer 3

light microscopes how they work: light passes up through the specimen and is focused by the objective and eye piece lens. Sometime staining is required.

Advantages of light microscopes: cheap and portable and you can view living specimens.

Disadvantages of light microscopes: lower resolution than electron microscopes. Resolution is limited by the wavelengths of visible light. Lower maximum magnification of (x1500)

How transmission electron microscopes (TEM’s) work: electromagnet focuses on a beam of electron through the specimen. Denser parts absorb more electrons, so they appear darker. The tissue is fixed in a resin then sliced thinly.

How scanning electron microscopes (SEM’s)work: A beam of electrons ‘scans’ over the surface of the specimen. Reflected electrons form image. 3D images produced on computer screen.

Advantages of electron microscopes: higher maximum magnification approx. X500000. Higher maximum resolution approx. 1-5nm (0.0001µm)

Disadvantages of electron microscopes: specimen material must be dead as it is placed in a vacuum. Image produced is black and white although it can be artificially coloured by a computer

Question 4

Resolution

Answer 4

is the ability to see individuals as separate entities.

Question 5

Why electron microscopes’ resolution is better than a light microscope’:

Answer 5

electron microscopy offers a better resolution than light microscopes and can reveal the structure of smaller objects not usually seen by the latter. This is because the wavelength of electrons is up to 100,000 shorter than visible light photons.

Question 6

Cellular ultrastructure

Answer 6

Eukaryotic cells-contain a nucleus and other organelles that are bound by membranes

Plasma membrane- a selectively permeable membrane phospholipid bilayer forming the boundary of the cells.

Cytoplasm-a jellylike fluid inside the cell in which the organelles are suspended, chemical reactions occur there.

Nucleus – surrounded by a nuclear envelope has nuclear pores to allow movement of molecules through it. The nucleus contain chromatin. The function is to regulate cellular activity.

Nucleolus-found inside the nucleus and produces ribosomes

Rough endoplasmic reticulum (RER)- the region of the endoplasmic reticulum that is studded with ribosomes and engages in protein modification.

Smooth endoplasmic reticulum (SER)- an endo membrane system where lipids are synthesised, calcium levels are regulated, and toxic substances are broken down

Golgi apparatus: a system of membranes that modifies and packages proteins for export by the cell.

Vesicles- small membrane sacs that specialise in moving into out of and within a cell.

Lysosomes – An organelle containing digestive enzymes

‘8OS ribosomes- larger ribosomes found in eukaryotes. Site of protein synthesis.

Mitochondria-site of aerobic respiration, two membranes, cristae matrix.

Centrosomes and centrioles- organelles responsible for forming and anchoring the spindle fibre.