cell structure

Question 1

cell-surface membrane (eukaryotic cells)

Answer 1

• phospholipid bilayer
• function –> extracellular substances enter & waste leaves the cell (sometimes requires active transport or membrane proteins)

Question 2

smooth endoplasmic reticulum

Answer 2

• (membrane forms flattened sacs –> called cisternae)
• site of lipid synthesis, toxin modification & glycogenesis

Question 3

rough endoplasmic reticulum

Answer 3

• (membrane forms flattened sacs –> called cisternae)
• has large no. of ribosomes attached to the surface
• folds & processes proteins made on the ribosomes

Question 4

nucleus
(eukaryotic cells)

Answer 4

• nuclear envelope has a double membrane & nuclear pores to export mRNA n ribosomes into cytoplasm
• contains chromatin –> consists of DNA bound to histone proteins
• contains nucleolus –> site of ribosome production

Question 5

ribosomes

Answer 5

-either free or on R.E.R
-eukaryotes have 80s ribosomes –> consists of 2 subunits, 60s & 40s
-70s ribosomes found in prokaryotes, mitochondria & chloroplasts
-site of translation (during protein synthesis)

Question 6

golgi apparatus
(eukaryotic cells)

Answer 6

• stack of membrane-bound flattened sacs
• proteins modified in cis-face
• role in ‘packaging’ & ‘secretion’ of proteins
• digestive enzymes placed into lysosomes

Question 7

golgi vesicles
(eukaryotic cells)

Answer 7

export modified proteins to fuse with the cell membrane (leave through trans-face)

Question 8

mitochondria
(eukaryotic cells)

Answer 8

• site of aerobic respiration
• double membrane
  >inner membrane folds to form cristae (gives it large S.A –> increases rate of aerobic resp.)
• small circular pieces of DNA found in the matrix

Question 9

centrioles
(eukaryotic cells)

Answer 9

• hollow cylinders
• produce spindle fibres for cell division

Question 10

lysosome
(eukaryotic cells)

Answer 10

• small, membranous vehicle
• has hydrolytic enzymes –> destroys pathogens/gets rid of unwanted cells & organelles

Question 11

vacuoles (only in plant cells)

Answer 11

• membrane-bound organelle found in all plant cells
• surrounded by tonoplast
• turgid –> helps cells stay rigid

Question 12

chloroplasts (only in plant cells)

Answer 12

• site of photosynthesis (light-dependant stage takes place in the thylakoid membranes, light-independant stage takes place in the stroma)
• membrane-bound thylakoids containing chlorophyll stack to form grana
  –> grana joined tg by lamellae

Question 13

plant cell wall

Answer 13

• provides structural support (made of cellulose)
• plasmodesmata (narrow threads of cytoplasm) connect the cytoplasm of neighbouring plant cells)

Question 14

epithilial cell

(specialised eukaryotic cell)

Answer 14

• villi increase S.A for absorption
• mitochondria releases energy to waft things away/transport digested food molecules

Question 15

erythrocyte

(specialised eukaryotic cell)

Answer 15

no nucleus & biconcave disc shape –> maximises S.A –> can carry more oxygen

Question 16

sperm cell

(specialised eukaryotic cell)

Answer 16

• acrosome enzyme to penetrate egg
• long midpiece –> lots of mitochondria –> releases lots of energy for swimming

Question 17

how is bacteria digested?

(exam q)

Answer 17

lysosomes fuse with the vesicle & release hydrolytic enzymes

Question 18

organelles in prokaryotic cells

Answer 18

1) plasma membrane
2) peptidoglycan cell wall
3) capsule (outer gel coating)
* flagella
* pili (for attachment to other cells, involved in reproduction)
* plasmid DNA
* circular DNA
* ribosomes (not membrane bound!!)

Question 19

what is the name for the types of organelles eukaryotic cells contain but prokaryotic cells don’t contain?

Answer 19

membrane-bound organelles!

Question 20

difference between DNA in eukaryotes & DNA in prokaryotes

Answer 20

• eukaryotes –> linear, long, associated w histone proteins, contains introns
• prokaryotes –> circular, short, not associated w histone proteins, no introns

Question 21

parts of virus particle

Answer 21

-attachment proteins
-genetic material
-capsid

Question 22

process of viral replication

Answer 22

1. virus injects nucleic acid into host cell
2. infected host cell replicates the virus

Question 23

process of binary fission

Answer 23

1. circular DNA & plasmids replicated in bacterial cell
2. circular DNA & plasmids move to opp. poles of cell
3. cytoplasm divides
4. two daughter cells prod. –> each contains 1 copy of circular DNA (but can have multiple plasmids)

Question 24

define ‘resolution’

Answer 24

minimum distance at which 2 very close objects can be distinguished

Question 25

light microscope --> *preparation*

Answer 25

* cut **thin** layer of specimen * add drop of water & **potassium iodide**/stain onto specimen * put coverslip on top

Question 26

light microscope --> *pros*

Answer 26

* images are **colourful** * living tissue can be viewed

Question 27

light microscope --> *cons*

Answer 27

* long wavelength of light makes resolution low * max. magnification only **x1500**

Question 28

**scanning** electron microscope

Answer 28

* beam of electrons **scatters** across surface of specimen, **knocking** electrons off --> electrons form **3D image** * **lower** resolution than TEM (but higher than optical)

Question 29

**transmission** electron microscope

Answer 29

* beam of electrons **passes through** specimen --> areas that absorb electrons = **darker** on micrograph --> internal image prod.

Question 30

electron microscopes --> *cons*

Answer 30

* in **vacuum** environment --> living objects can't be viewed * specimens must be very **thin** * specimens must be **dehydrated** & stained w heavy metals * complex staining process may intorduce **artefacts**

Question 31

why do electron microscopes have a vacuum environment?

Answer 31

so particles in the air don't **deflect** electrons **out** of the beam alignment

Question 32

define **'cell fractionation'**

Answer 32

technique which separates organelles according to their **density**

Question 33

stages of cell fractionation

Answer 33

1. homogenisation 2. filtration 3. ultracentifugation

Question 34

*homogenisation*

Answer 34

place cells in **cold, isotonic & buffered** solution --> **blend** to release organelles * ***cold*** --> reduces enzyme activity as some enzymes may break down organelles * ***isotonic*** --> solution needs same w.p as organelles so **osmosis** doesn't occur (organelles would burst/shrink) * ***buffered*** --> maintains **constant** pH (proteins in organelles can be denatured by change in pH)

Question 35

*filtration*

Answer 35

removes any tissue debris

Question 36

*ultracentrifugation*

Answer 36

* filtrate spun at diff. speeds * **heaviest** organelles sink to bottom of tube, forming **pellet** * fluid above the supernatant is removed and spun **again** in centrifuge at **higher** speed * process continues until desired organelle is obtained (nuclei would be 1st, ribosomes would be last)

Question 37

stages of cell division

Answer 37

1. interphase 2. mitosis 3. cytokinesis

Question 38

*interphase*

Answer 38

* G1 --> protein synthesis * S --> DNA replication * G2 --> DNA checked over

Question 39

*mitosis*

Answer 39

* ***prophase*** --> chromosomes **condense** & become visible, spindle fibres form, nuclear membrane breaks down * ***metaphase*** --> chromosomes line at up **equator** & attach to the spindle fibres via centromere * ***anaphase*** --> spindle fibres contract, centromere splits, sister chromtids pulled to opp. poles of cell * ***telophase*** --> nucleus begins reforming

Question 40

*cytokinesis*

Answer 40

2 gentically identical, diploid cells produced

Question 41

what is mitosis used for?

Answer 41

* growth & repair * asexual reproduction