Chapter 3- Cell Structure

Question 1

Magnification =

Answer 1

Size of image / size of real object

Question 2

What is resolution?

Answer 2

Minimum distance apart that two objects can be in order for them to appear as separate items

Question 3

What is cell fractionation?

Answer 3

Process where cells are broken up + organelles are separated out

Question 4

What are the 3 steps of cell fractionation?

Answer 4

1. Tissue is placed in a cold, buffered, same water potential solution
2. Homogenation
3. Ultracentrifugation

Question 5

Describe homogenation

Answer 5

-Cells broken up by homogeniser
-Releases organelles from cells
-Resultant fluid = homogenate -> filtered

Question 6

Describe ultracentrifugation

Answer 6

Ultracentrifugation = fragments in homogenate are separated in centrifuge
1. Filtrate placed in centrifuge + spun (slow speed)
2. Heaviest organelles (nuclei) spun to bottom of tube
3. Fluid at top (supernatant) removed (leaves nuclei sediment)
4. Supernatant -> other tube + spun at faster speed
5. Next heaviest organelles (mitochondria) forced to bottom
6. Process repeated at faster speed each time so each organelles is sedimented + separated

Question 7

What is a transmission electron microscope (TEM)?

Answer 7

-Parts of specimen absorb electrons + appear dark -Produces image on screen + photographed -> photomicrograph
-Resolving power = 0.1nm (limited by specimen preparation + electron beam damaged specimen)

Question 8

What are the limitations of the TEM?

Answer 8

-Must be in a vacuum - X observe living specimens
-Specimen needs complex staining process but image X in colour
-Specimen = extremely thin
-Produces a flat 2D image
-Image may have artefacts

Question 9

How does a scanning electron microscope (SEM) work?

Answer 9

-Specimens X need to be extremely thin - electrons don’t penetrate
-Directs electron beam onto specimen depending on contours of specimen
-Resolving power = 20nm

Question 10

What is an eyepiece graticule?

Answer 10

Placed in eyepiece of microscope + scale is etched onto it + then its calibrated for each objective lens then it can remain in place

Question 11

Structure + function of nucleus

Answer 11

-Nuclear envelope = double membrane, controlling entry/exit + contains everything
-Nucleolus = small spherical, assembles ribosomes
-Chromosomes = protein-bound, linear DNA
-Nucleoplasm = majority of nucleus, jelly-like
-Nuclear pores = allow passage of large molecules e.g. mRNA
-Function = Contains genetic info, control centre

Question 12

Structure + function of mitochondria

Answer 12

-Cristae = part of inner membrane, large SA (protein + enzyme attachement)
-Double membrane = controls entry/exit
-Matrix = contains proteins, lipids, ribosomes + DNA -> mitochondria can control protein production
-Function = aerobic respiration, ATP production

Question 13

Structure + function of chloroplasts

Answer 13

-Chloroplast envelope = double membrane, selective entry/exit
-Stroma = where 2nd photosynthesis stage happens
-Grana = stack of disc-like structures called thylakoids containing chlorophyll, where light absorption happens
-Granal membrane = large SA, chemical can attached for 1st photosynthesis stage
-Manufactures proteins for photosynthesis -> ribosomes + DNA

Question 14

Structure + function of ribosomes

Answer 14

-Two types -> 80S (eukaryotic) + 70S (prokaryotic cells, mitochondria, chloroplasts + are smaller)
-Function = site of protein synthesis

Question 15

Structure + function of endoplasmic reticulum

Answer 15

Rough (RER):
-Ribosomes present
-Functions: large SA -> protein synthesis, pathway for material transport through cell

Smooth (SER):
-No ribosomes
-Functions: synthesis/store/transport lipids + carbohydrates

Question 16

Structure + function of Golgi apparatus

Answer 16

-Cisternae = stack of membranes
Functions:
-Add carbohydrates to proteins -> glycoproteins
-Produce secretory enzymes
-Secrete carbohydrates
-Transport lipids
-Form lysosomes

Question 17

Structure + function of lysosomes

Answer 17

-Lysozymes -> hydrolyse cell wall of bacteria
Functions:
-hydrolyse material ingested by phagocytes
-release enzymes out of cell to destroy materials
-digest old organelles to reuse chemicals
-break down dead cells

Question 18

Structure + function of cell wall

Answer 18

-Middle lamella = boundary between adjacent cell walls
-Made of polysaccharides
Functions:
-Mechanical strength

Cell walls of fungi made of chitin

Question 19

Structure + function of vacuoles

Answer 19

-Single membrane around = tonoplast
Functions:
-supports plants = makes cells turgid
-sugars + amino acids = temporary food store
-pigments -> colour petals -> attract insects

Question 20

How do cells become specialised?

Answer 20

Only having some genes expressed at one time -> different genes switched on in different specialised cells -> makes it adapted to a particular function which it performs effectively to make an organism efficient

Question 21

What are tissues?

Answer 21

Collection of similar cells performing a similar function e.g. epithelial tissues -> often line organ surfaces as protection/to secrete

Question 22

What are organs?

Answer 22

Combination of tissues performing variety of functions, often having one predominant function e.g. animals = stomach, plants = leaf

Question 23

What is an organ system?

Answer 23

Organs working together to perform particular functions e.g. digestive = digest + process food

Question 24

Function of a cell wall in prokaryotes

Answer 24

Made of murein
Physical barrier to protect from substances + mechanical damage

Question 25

Function of a capsule

Answer 25

Mucilaginous slime, protection + so bacteria can stick together

Question 26

Ribosomes in prokaryotes

Answer 26

70S, synthesise proteins

Question 27

Cell-surface membrane in prokaryotes

Answer 27

Controls entry/exit of chemicals

Question 28

Circular DNA in prokaryotes

Answer 28

Genetic info for bacterial cell replication

Question 29

Plasmids in prokaryotes

Answer 29

Possesses genes aiding survival of bacteria in adverse conditions

Question 30

Flagellum in prokaryotes

Answer 30

Used for locomotion, may be >1

Question 31

Structure of viruses

Answer 31

-Acellular + non-living
-Contain nucleic acids (DNA/RNA) as genetic info but only multiply in host cells
-Have a capsid (protein coat)
-Attachment proteins = allow virus to identify + attach to host cell

Question 32

Process of binary fission

Answer 32

-Circular DNA replicates + both copies attach to cell membrane
-Plasmids replicate
-Cell membrane grows between 2 DNA molecules -> divides cytoplasm
-New cell wall between 2 DNA molecules = divides -> 2 identical daughter cells

Question 33

How do viruses replicate?

Answer 33

-Attach to host cell via attachment proteins -> inject nucleic acids into it -> genetic info provides ‘instructions’ for host cell’s metabolic processes to start producing viral components -> assembled into viruses

Question 34

What are the 3 stages of the cell cycle and what happens in each?

Answer 34

1. Interphase -> most of cell cycle, no division
2. Nuclear division -> either mitosis or meiosis, just nucleus dividing
3. Cytokinesis -> cytoplasm dividing, cell dividing

Question 35

How does cancer treatment treat cancer?

Answer 35

Blocks part of the cell cycle -> disrupts it (prevents replication, spindle formation) + ceases cancer growth

Question 36

What is cancer?

Answer 36

Uncontrolled growth + cell division -> tumour formation
-Mutation in gene causing mitosis -> uncontrolled mitosis -> surviving cells can divide to form clones -> tumours
Malignant tumour = cancerous