cell biology

Question 1

importance/function of plasma membrane (3)

Answer 1

• separate contents of cell from environment and control exchange of substances between the 2
• receptor sites for recognising external stimuli eg. hormones
• reactions can occur there, eg. light dependant reaction

Question 2

facilitated diffusion

Answer 2

polar and large molecules move across membrane with aid of channel and carrier proteins

Question 3

how does active transport work

Answer 3

• molecules bind to carrier protein and ATP attached to membrane protein on inside of cell/organelle
• binding of phosphate ion causes protein to change shape so that access for the molecule is open to the inside of the membrane but closed to the outside

Question 4

isotonic

Answer 4

2 solutions have sae water potential

Question 5

hypertonic

Answer 5

when a cell has a HIGHER water potential then its surroundings (net loss of water)

Question 6

hypotonic

Answer 6

when a cell has a LOWER water potential then its surroundings (net gain of water)

Question 7

2 main methods of cell fractionation

Answer 7

• homogenisation

- centrifugation

Question 8

μm in 1m

Answer 8

1000, 000

Question 9

μm in 1cm

Answer 9

10, 000

Question 10

μm in 1mm

Answer 10

1,000

Question 11

max resolution of scanning electron microscope

Answer 11

20nm

Question 12

max resolution of transmission electron microscope

Answer 12

0.1nm

Question 13

advantages of electron microscope

Answer 13

high resolving power = produces a very detailed imagine

Question 14

disadvantages of electron microscope

Answer 14

• specimen must be dead as vacuum needed
• artefacts may be produced
• expensive

Question 15

size of chloroplast

Answer 15

3-10 μm

Question 16

size of mitochondria

Answer 16

2.5 μm

Question 17

prokaryotes

Answer 17

smaller then eukaryotes, and have no nucleus or nuclear envelope

Question 18

how to prokaryotes differ from eukaryotes (6)

Answer 18

• smaller
• no nucleus/nuclear envelope
• smaller ribosomes
• no membrane-bound organelles
• single circular loop of DNA which is not associated with any histone proteins
• has a cell wall containing murein

Question 19

prokaryotes may also have… (3)

Answer 19

• 1+ plasmid
• a capsule surrounding the cell
• 1+ flagella

Question 20

how do channel proteins work

Answer 20

• water filled channels across the membrane
• allow specific water-soluble ions to pass through
• selective - each open in presence of specific ion
• ion binds to protein, causing it to change shape in a way that opens to one side of the membrane and closes to the other

Question 21

how to carrier proteins work

Answer 21

molecule binds with protein, changing its shape so that it is open to one side of the membrane and closed to the other

Question 22

how do prokaryotic cells replicate?

Answer 22

binary fission

Question 23

stages of binary fission

Answer 23

• circular DNA molecule replicates and both copied attach to cell membrane
• plasmids replicate
• cell membrane begins to grow between 2 DNA molecules and pinches inwards - dividing cytoplasm in 2
• new cell wall forms between 2 molecules of DNA

Question 24

how to viruses replicate?

Answer 24

• attach to host cell using attachment proteins
• inject nucleic acid into host cell
• nucleic acid contains ‘instructions’ for host cell’s metabolic processes to produce viral components (eg. enzymes and structural proteins)
• these are then assembled into new proteins

Question 25

why aren’t viruses ‘cells’ (3)

Answer 25

• no metabolism
• cannot-self reproduce
• no cytoplasm

Question 26

role of capsid in viral cells

Answer 26

• protect nucleic acid from degradation

- surface sites enable viral particle to bind to/enter host cell