Cell structure

Question 1

Cell wall - what is it made of in plants and in bacterial cells? What is it made of structurally?

Answer 1

Plants - cellulose
Bacteria - peptidoglycan

Narrow threads of cytoplasm called plasmodesmata connect to neighbouring plant cells.

Question 2

Nucleus - parts and what do they do?

Answer 2

Nuclear envelope, double membrane

Nuclear pores (in the membrane) - channels for allowing mRNA and ribosomes to travel out of nucleus + allowing enzymes to enter.

Contains chromatin - to produce chromosomes

Nucleolus - dark stained region sites of ribosome production.

Question 3

What are chromosomes made of?

Answer 3

linear DNA tightly wound around histone protiens

Question 4

Mitochondria - structure and function

Answer 4

Site of aerobic respiration in eukaryotic cells.
Double membrane - inner folded - cristae

matrix formed by the cristae contains enzymes for aerobic resparation producing ATP.

Small circular pieces of DNA and ribosomes also found in the matrix

Question 5

Chloroplast - structure and function

Answer 5

Double membrane

thylakoids - membrane bound component containing chlorophyll stacked to form grana

grana joined by lamellae

chloroplasts are the site of photosynthesis
- light dependent stage - thylakoids
- light-independent stage - stroma

small circular DNA and ribosomes to synthesise proteins in chloroplast replication and photosynthesis.

Question 6

Ribosome structure and function.

Answer 6

Found freely in the cytoplasm of all cells or as part of the Rough ER in eukaryotic cells

made of Ribosomal RNA and proteins

80S - eukaryotic
70S - Prokaryotic

site of translation - protein synthesis

Question 7

Endoplasmic reticulum - structure and function.

Answer 7

Rough endoplasmic reticulum:
surface covered in ribosomes

Formed from continuous folds of membrane continuous with the nuclear envelope.

Processes proteins made by the ribosomes.

Smooth Endoplasmic reticulum:

Does not have ribosomes on surface
Involved in the processing and storage of lipids, carbohydrates and steroids.

Question 8

Golgi apparatus - structure and function

Answer 8

Flattened sacs of membrane similar to the smooth ER

Modifies proteins and lipids before packaging them into Golgi vesicles.

vesicles transport the proteins and lipids to their required destination.

Proteins that go through the Golgi apparatus are usually exported, put into lysosomes or delivered to membrane-bound organelles.

Question 9

Large permanent vacuole

Answer 9

sac in plant cells
surrounded by the tonoplast (selectively permeable membrane

Question 10

Vesicle

Answer 10

Membrane-bound sac for transport and storage.

Question 11

Lysosome

Answer 11

Specialist forms of vesicle
contains hydrolytic enzymes
lysozymes fuse to vesicle
breaks down waste materials such as:
worn out organelles (used a lot by the immune system) and in apoptosis (programmed cell death)

Question 12

Centriole

Answer 12

Hollow fibres made of microtubules
2 centrioles at right angles to each other forms a centrosome
this organises spindle fibres during cell division

not found in flowering plants and fungi

Question 14

What is the main component of a cell surface membrane an a cell wall?

Answer 14

Phospholipids - cell surface membrane
Murien or peptidoglycan glycoprotiens - cell wall.

Question 15

How do prokaryotic cell walls differ from eukaryotic cells in cell walls.

Answer 15

Prokaryotes - Glycoprotien called murien
Plant cells - polysaccharide called cellulose
Fungal cells - chitin
Animal cells - no cell wall, (air I guess)

Question 16

What limits the resolution of an optical microscope?

Answer 16

The wavelength of light

Question 17

TEM advantages

Answer 17

high resolution
internal structures within cells can be seen

Question 18

Disadvantages of TEM

Answer 18

Only used on very thin specimins
Cannot be used to observe live specemins (vacuum inside TEM, all water must be removed from specimen.)
The treatment to prepare specimines is long, artifacts can look like real structures if done wrong.
No colour in image.

Question 19

SEM advantages

Answer 19

Can be used on thick or 3D specimines
they allow the 3-D structure of specimines to be observed

Question 20

Disadvantages of SEM

Answer 20

give lower resolution images than TEM
cannot be used to observe live specimines
do not produce a colour image

Question 21

How does a TEM generate an image?

Answer 21

sends a beam of electrons through the specimen.

measuring how many electrons are absorbed by different parts of the specimen/denser parts of the specimen absorb fewer electrons and appear lighter.

Question 22

How does a SEM work?

Answer 22

Light bounces off a surface (rather to passing through)