2.1.1 Cells

Question 1

Structure and function of nucleus

Answer 1

• nucleolus - densest part of the cell (site of ribosome production)
  contains chromatin which makes up chromosomes ( wound around histones )
  surrounded by nuclear envelope (double membrane) which has nuclear pores to let mRNA and ribosomes through

Question 2

Structure of mitochondria

Answer 2

surrounded by double membrane
inner membrane folds to form cristae
cristae forms matric which contains enzymes needed for aerobic respiration
small mitochondrial DNA and ribosomes found in matrix

Question 3

Structure of chloroplasts

Answer 3

surrounded by double membrane
thylakoids (membrane bound compartments containing chlorophyll) stack to form grana
grana are joined by lamellae (thin and flat thylakoid membrane)

Question 4

Structure of ribosomes

Answer 4

found either freely in the cytoplasm or on the rough ER
80s in eukaryotic
70s in prokaryotic, mitochondria and chloroplasts

Question 5

Function of ribosomes

Answer 5

site of translation

Question 6

Structure of rough endoplasmic reticulum

Answer 6

formed from folds of membrane continuous with the nuclear envelope
surface covered in ribosomes

Question 7

Function of rough endoplasmic reticulum

Answer 7

processes proteins made by the ribosomes by folding primary structures into secondary and tertiary structures

Question 8

Function of smooth endoplasmic reticulum

Answer 8

synthesises, processes and stores lipids carbohydrates and steroids

Question 9

Structure of golgi apparatus

Answer 9

flattened sacs of fluid-filled membrane
has secretory vesicles to transport molecules
vesicles enter the cis face and leave via the trans face

Question 10

Function of golgi apparatus

Answer 10

modifies proteins and lipids
packages them into golgi vesicles
vesicles transport proteins out of the cell (exocytosis), or to membrane bound organelles

Question 11

Structure and function of vesicle

Answer 11

membrane-bound sac
used for transport and storage

Question 12

Structure and function of lysosome

Answer 12

specialist vesicle which contains hydrolytic enzymes (break biological molecules down)
used by immune system in phagocytosis

Question 13

Structure of centriole

Answer 13

hollow fibres made of microtubules
two centrioles at right angles to each other form a centrosome

Question 14

Function of centrioles

Answer 14

form centrosomes which organise spindle fibres in cell division

Question 15

Structure of microtubules

Answer 15

made of alpha and beta tubulin combined to form protofilaments
- 13 protofilaments in a cylinder make a microtubule

Question 16

What is a cytoskeleton made of

Answer 16

• microfilaments
• microtubules
• intermediate fibres

Question 17

Structure and function of microfilaments

Answer 17

made of actin
responsible for cell movement and contraction during cytokinesis

Question 18

Function of microtubules

Answer 18

acts as tracks for the movement of organelles around the cell
make up spindle fibres used for cell division

Question 19

Function of intermediate fibres

Answer 19

provide mechanical strength and help maintain integrity

Question 20

What is the cell wall made of

Answer 20

peptidoglycan in prokaryotes
cellulose in plants

Question 21

Organelles that are always present in prokaryotes

Answer 21

• cell wall
• cell membrane
• cytoplasm
• circular strand of DNA
• 70s ribosomes

Question 22

Organelles that are sometimes present in prokayotes

Answer 22

• flagellum
• slime capsule
• infolding of surface membrane
• plasmids
• pili

Question 23

Structure and function of flagellum

Answer 23

hair like structure with basal hook that attaches to cell membrane
rotates - mechanical motor

Question 24

Function of slime capsule

Answer 24

protects bacteria from drying out
protects from attack from immune system cells

Question 25

Function of plasmids

Answer 25

small loops of DNA that can be passed between bacterial cells
often contain genes for antibiotic resistance

Question 26

Describe the role of the nucleus in protein production

Answer 26

• ribosomes are produced in the nucleolus
• DNA is transcribed into mRNA which leaves the nucleus via the nuclear pore to a ribosome on the rough ER

Question 27

Describe the role of the rough ER in protein production

Answer 27

polypeptides move into the rough ER cisternae
primary structures are folded into secondary and tertiary structures
proteins are packaged into vesicles

Question 28

Describe the role of the golgi in production of proteins

Answer 28

vesicle fuses with cis face golgi and releases protein into golgi
protein is modified and packaged into secretory vesicle
vesicle leaves the trans face golgi and fuses to the cell membrane to release the protein through exocytosis

Question 29

What is the membrane surrounding the vacuole called

Answer 29

tonoplast

Question 30

What is resolution

Answer 30

the smallest distance that two points can be distinguished from each other

Question 31

Benefits of light microscopes

Answer 31

• cheap
• easy to use
• can view living organisms and cells

Question 32

Drawbacks of light microscopes

Answer 32

• maximum resolution - 0.2 micrometres
• maximum useful magnification - x1500
• therefore cannot be used to observe smaller organelles (rough ER etc)
• 2D images only

Question 33

How does a transmission electron microscope work

Answer 33

an electron beam is transmitted through the specimen
denser parts of the specimen absorb more electrons so appear darker

• specimen are dead and dipped in heavy metals (lead) to scatter electrons then embedded in wax

Question 34

Benefits of using a transmission electron microscope

Answer 34

• higher resolution - 0.5 nm
• higher magnification - over x500,000

Question 35

Drawbacks of using a transmission electron microscope

Answer 35

• black and white 2D images
• dead specimen due to vaccum
• lengthy treatment to produce very thin specimen

Question 36

How do scanning electron microscopes work

Answer 36

a beam of electrons hits the specimen and is scattered
electrons are detected, forming an image
- SEM’s can produce 3D images of the surfaces of specimens

Question 37

Benefits of scanning electron microscopes

Answer 37

• images of external, 3D structure can be observed
• maximum resolution of 3-10nm
• maximum magnification of x 500,000

Question 38

Drawbacks of scanning electron microscopes

Answer 38

• maximum resolution lower than TEM
• black and white images - can colour digitally
• dead specimen due to vaccum

Question 39

Benefits of staining specimen

Answer 39

increases the contrast - so different organelles can be visible e.g. nuclei
- so different biological molecules are visible e.g. starch grains

Question 40

What is the use of methylene blue

Answer 40

stains DNA blue

Question 41

What is the use of acetic orcein

Answer 41

stains DNA red

Question 42

What is the use of iodine

Answer 42

stains starch blue/black
stains cell walls brown/yellow

Question 43

What are the different types of sample preparation

Answer 43

• dry mount
• wet mount (specimen in liquid such as water or an immersion oil)
• squash slides
• smear slides

Question 44

Describe how to measure the size of X using a light microscope

Answer 44

use eyepiece graticule
calibrate the graticule using a stage micrometre
measure the length of X in eyepiece units
use calibrated epu to calculate the actual length of X