cells

Question 1

what is the function of the rough ER?

Answer 1

-it synthesises proteins and transports them
-ribosomes cover the surface of it

Question 2

what is the function of the smooth ER?

Answer 2

-it synthesises carbohydrates and lipids

Question 3

what is the function of the golgi?

Answer 3

-it modifies molecules, specifically proteins and lipids

Question 4

what is the function of the golgi vesicles?

Answer 4

-they transport the modified molecules to the required places

Question 5

what is the function of mitochondria?

Answer 5

-respiration of the cell and the production of ATP
-has a folded double membrane called cristae, which increases the surface area

Question 6

what is the function of lysosomes?

Answer 6

-they remove bacteria and dead cells
-they can release lytic enzymes
-they are a type of golgi vesicle

Question 7

what is the function of the vacuole?

Answer 7

-it contains sugars and amino acids
-the membrane surrounding it is called a tonoplast
-the vacuole helps to maintain pressure in the cell, keeping it rigid

Question 8

what is the function of chloroplast?

Answer 8

-used for photosynthesis in plants
-they have a double membrane called thylakoid membranes
-these membranes stack up to form a grana

Question 9

how does prokaryotic DNA differ from eukaryotic DNA?

Answer 9

-it is circular
-it doesn’t have histones associated to it
-it doesn’t have a nucleus, so its free floating around the cell

Question 10

what is the structure of a virus?

Answer 10

-a virus is much smaller than prokaryotic and eukaryotic cells
-structure:
-capsid
-lipid envelope
-attachment proteins
-genetic material (RNA)
-matrix
-enzymes

Question 11

optical microscopes

Answer 11

-uses light to form the image
-has a worse magnification and resolution than an electron microscope
-it will not allow you to view organelles that are especially small, such as ribosomes and lysosomes

Question 12

scanning electron microscopes

Answer 12

-scans a beam of electrons over the specimen which forms the image
-can produce 3D images
-good microscope to use on thick specimens
-has a lower resolution than a transmission electron microscope

Question 13

transmission electron microscopes

Answer 13

-uses electromagnets to focus a beam of electrons which is transmitted through a specimen
-the densest parts of the specimen absorb more electrons which makes them look darker
-TEMs produce a high resolution image to see internal structure of organelles
-they can only be used on thin specimens

Question 14

how do view a specimen under a microscope

Answer 14

-pipette a drop of water onto the slide and use tweezers to place a thin section of the specimen on the drop
-add a drop of stain to highlight objects in the cell (e.g. eosin for cytoplasm, iodine in potassium iodine solution for starch grains in plant cells)
-add a cover slip (square of clear plastic) to protect the specimen
-stand the slip upright on the slide and tilt and lower it until the specimen is cover - making sure not to get any air bubbles under.

Question 15

what are the steps in cell fractionation?

Answer 15

-homogenisation
-filtration
-ultracentrifugation

Question 16

what occurs in homogenisation?

Answer 16

-the plasma membrane of the sample is broken up so that the organelles are released
-this can be done by vibrating the cells or grinding the cells
-the sample needs to be isotonic, ice cold and pH buffered

Question 17

why does the sample need to be isotonic, ice cold and pH buffered?

Answer 17

-ISOTONIC- this means that the same concentration of chemicals is used so that osmosis doesn’t occur to the organelles so that they aren’t damaged
-ICE COLD- the sample needs to be ice cold so that the rate of enzyme activity is reduced, meaning the organelles arent broken down
-pH BUFFERED- this means that a a pH buffer solution is added so that changes in pH don’t occur

Question 18

what happens during filtration?

Answer 18

-the homogenised cell solution is filtered through a gauze so that any large cell debris is removed from the sample
-organelles, which are much smaller, pass through the gauze so they don’t get filtered

Question 19

what happens in ultracentrifugation?

Answer 19

-cell fragments are poured into a tube and the tube is put into a centrifuge (a machine which separates material by spinning). -the solution is spun at low speed and the heaviest organelles, like nuclei, will get moved to the bottom by the centrifugal force.
-they form a thick sediment called the pellet and the rest of the organelles stay suspended in fluid above the sediment - this is called the supernatant.
-the supernatant is drained off and poured into another tube which is then spun at a higher speed in the centrifuge.
-the next heaviest organelles (the mitochondria) form a pellet and the supernatant is drained off and spun again at even higher speed.
-the whole process is repeated at higher and higher speeds until all of the organelles have been separated. Each time, the pellet at the bottom contains lighter and lighter organelles.