cell structure

Question 1

what are the advantages and disadvantages of using a compound light microscope?

Answer 1

it provides an image in the samples original colour, the sample does not have to be dead when it is being viewed under the microscope, it is also a lot cheaper than an electron, microscope. however due to the wavelength of the light rays it can’t distinguish between objects that are within 0.2 micrometers apart.

Question 2

how do you calculate magnification?

Answer 2

size of image/size of real object

Question 3

what is the resolution of a microscope?

Answer 3

the resolution is the minimum distance that two objects can be in order for them to appear as separate items.

Question 4

what is cell fractionation?

Answer 4

cell fractionation is the process in which a cell is broken up into the different organelles that they contain.

Question 5

before cell fractionation what must happen to the sample?

Answer 5

it must be placed into a cold, buffered solution with the same water potential as the tissue. it needs to be cold to reduce enzyme activity that may break down the organelles. the water potential needs to be the same to stop the organelles from shrinking or bursting. having a buffer means that the pH won’t fluctuate.

Question 6

what are the two process of cell fractionation?

Answer 6

homogenisation and ultracentrifugation.

Question 7

what is the process off ultracentrifugation?

Answer 7

it is the process by which the fragments in the filters homogenate are separated out in a machine called a centrifuge, this spins the homogenate at a very high speed in order to create a centrifugal force.

Question 8

how is the process of ultracentrifugation carried out for animal cells?

Answer 8

the homogenate is primarily spun at low speeds forcing the heaviest organelles (the nuclei) to the bottom to form a thin sediment, the liquid on top called the supernatant is removed and put back in at a higher speed removing the next heaviest organelles. this process is then continued.

Question 9

what is the best resolving power of an electron microscope?

Answer 9

0.1nm

Question 10

what are the two different types of electron microscope?

Answer 10

transmission and scanning.

Question 11

why can’t the optimum resolution not alwase be achieved on an TEM?

Answer 11

difficulties in preparing the specimen, a higher energy electron beam is required and this may destroy the specimen.

Question 12

what are the limitations of using an TEM?

Answer 12

the whole thing must be in a vacuum so therefore living specimens can’t be observed; a complex staining process is required and even then the image is not in colour; the specimen must be ultra thin; the specimen may also contain artefacts

Question 13

what are artefacts?

Answer 13

artefacts are things that result fro the way that the specimen is prepared, there are not part of the natural specimen.

Question 14

what is the resolving power of an SEM?

Answer 14

it is much lower than that of a TEM of 20nm

Question 15

how do you calibrate an eyepiece graticule?

Answer 15

you need to use a stage micrometer, this slide has a scale edged onto it. usually the micrometer is 2mm long and has divisions at 1mm intervals.

Question 16

what are prokaryotic and eukaryotic cells?

Answer 16

prokaryotic cells are smaller and similar than eukaryotic cells e.g. bacteria. Eukaryotic cells are complex and include all animal and plant cells as well as algae and fungi.

Question 17

what is the ultrastructure of a cell?

Answer 17

the ultrastructure of a cell is the internal structure that makes the cell suited for its job.

Question 18

what is the nucleus made out of?

Answer 18

the nuclear envelope, nuclear pores, the nucleoplasm, chromosomes and the nucleolus.

Question 19

what are the functions of the nucleus?

Answer 19

to act as a control centre of the the cell through production of mRNA and tRNA and hence protein synthesis; to retain the genetic information of the cell in the form of DNA and chromosomes; manufacture ribosomal RNA and ribosomes.

Question 20

what do mitochondria do?

Answer 20

mitochondria are the site of the aerobic stages of respiration within the cell. they are therefore responsible fro the production of the energy carrier molecule called ATP from respiratory substances such as glucose.

Question 21

how are chloroplasts adapted to their function?

Answer 21

they have a small, flattened structure and are surrounded by a double cell membrane it also has membranes inside called thylakoid membranes. these membranes are stacked up in some parts of the chloroplast to form grant. these are linked together to form lamellae.

Question 22

what is the grana?

Answer 22

the grana are stacks of disc like structures containing things called thylakoids. these contain chlorophyll which carry out photosynthesis.

Question 23

what are chloroplasts made from?

Answer 23

the chloroplast envelope, the grana, the stroma.

Question 24

what is the rough endoplasmic reticulum?

Answer 24

the RER has ribosomes present on the outer surface of the membranes. it functions to - provide a large surface area for the synthesis of proteins and glycoproteins.
to provide a pathway for the transport of materials, especially proteins, through the cell.

Question 25

what is the smooth endoplasmic reticulum?

Answer 25

the SER lacks ribosomes on its outer suave and is often more tubular in its appearance. its functions are to:
synthesis, store and transfer lipids
synthesis, store and transport carbohydrates.

Question 26

what does the golgi apparatus look like?

Answer 26

the golgi body is similar to the SER its is formed out of a stack of membranes that form flattened sacks called cisternae with small round hollow structures called vesicles

Question 27

what are the functions of the golgi apparatus?

Answer 27

add carbohydrates to proteins to form glycoproteins
produce secretory enzymes, such as those recreated by the pancreas
secrete carbohydrates, such as those used in making cell walls in plants
transport, modify and stor lipids
to store lysosomes.

Question 28

what are the functions of lysosomes?

Answer 28

the functions of lysosomes are to:
hydrolyse material ingested by phagocytic cells
release enzymes to the outside of the cell in order to destroy material around the cell
digest workout organelles so that the useful chemicals they are made of can be re-used
completely break down cells after they have died.

Question 29

what are the two different types of ribosomes in cells?

Answer 29

80s is found in eukaryotic cells and has a diameter of about 25nm
70s is found in prokaryotic cells along with mitochondria and also chloroplasts. it is smaller than 80s.

Question 30

what features do cell walls have?

Answer 30

cell walls consist of a number of polysaccharides
there is a thin layer, called the middle lamella, which marks th boundary between adjacent cell walls and cements adjacent cells together

Question 31

what are the functions of the vacuole?

Answer 31

they support herbaceous plants, and herbaceous parts of wooded, by making cells turgid
the sugars and amino acids may act as a temporary food store
the pigments may colour to attract pollenating insects.

Question 32

what is a supernatant?

Answer 32

the liquid found on top after a solution has gone through the centrifuge.