Cell Structure

Question 1

Function of cell surface membrane?

Answer 1

• Controls exchange of materials between internal cell environment and external environ
  -Partially permeable and formed from phospholipid
  bilayer

Question 2

Function of cell wall?

Answer 2

• in plant cells
• offer support and structure by the polysaccharide cellulose in plants

Question 3

Function of a nucleus?

Answer 3

Control cell activity
- Nucleus separated from cytoplasm by nuclear envelope - has pores
- pores important for allowing mRNA and ribosomes to travel out nucleus
- nucleus contains chromatin - material that makes up chromosomes

Question 4

Function of mitochondria and structure?

Answer 4

• Aerobic respiration in eukaryotes
• surrounded by double membrane with inner membrane folded - cristae
• matrix contains enzymes for respiration,to produce ATP

Question 5

Chloroplasts function and structure?

Answer 5

• Site of photosynthesis
• Surrounded by double membrane
  Compartments called thylakoids stack to form grana -these are joined together by lamellae (thin thylakoid membranes )

Question 6

Function of ribosomes?

Answer 6

• Composed of 2 subunits and where proteins are produced
• each ribosome consists of rRNA and proteins

Question 7

Structure and function of endoplasmic reticulum?

Answer 7

RER - series of flattened sacs in a membrane with ribosomes on the surface
- formed from continuous folds of membrane continuous with the nuclear envelope
- folds and processes proteins made on ribosomes

SER- membrane bound sacs
- produces and processes lipids

Question 8

Structure and function of Golgi apparatus?

Answer 8

• Fluid filled flattened and curved sacs with vesicles on the edges
• packages and modifies proteins and lipids
• produces lysosomes

Question 9

Function of large permanent vacuoles?

Answer 9

-a sac in plant cells surrounded by tonoplast

Question 10

Function of vesicles?

Answer 10

• In plant and animal cells
• membrane bound sac for transport and storage

Question 11

Function of lysosomes?

Answer 11

• Specialist form of vesicles - contain hydrolytic enzymes
• break down worn out organelles

Question 12

Function of centrioles ?

Answer 12

• Hollow fibres made of microtubules arranged at right angles to each other
• involved is cell division

Question 13

What is the cytoskeleton made up of?

Answer 13

2 types of protein fibres: microfilaments and microtubules
→ microfilaments - solid strands made from actin
- cause cell movement/ organelles

→ microtubules - tubular hollow strands made from tubulin
- organelles / other cell contents move along these fibres

Question 14

Importance of cytoskeleton?

Answer 14

Strength and support - maintains shape of cell/ keeps organelles in place
Intracellular movement - form tracks along which organelles can move/ movement of chromosomes when they separate in cell division due to contraction of microtubules in spindle
Cellular movement - enables cell movement e.g movement of cilia and flagella a used by cytoskeletal protein filaments that run through them

Question 15

How are prokaryotic cells different from eukaryote cells?

Answer 15

Prokaryotes have:
- cytoplasm that lacks membrane bound organelles
- smaller ribosomes (70S instead of 80S)
- no nucleus
- cell wall that contains MUREIN/peptidoglycan instead of cellulose and lignin
- SOMETIMES have PLASMIDS, CAPSULES and FLAGELLUM
- 0.5 - 5 um instead of 100um diameter
- cell division occurs by BINARY FISSION instead of mitosis and meiosis

Question 16

Purpose of plasmids?

Answer 16

→ small loops of DNA
→ contain genes that can be passer between prokaryotes

Question 17

Purpose of capsules?

Answer 17

→ final outer layer
→ protects bacteria from drying out / attack from immune system cells

Question 18

Purpose of flagellum?

Answer 18

→ long hair like structure that rotates, enabling prokaryote to move

Question 19

Difference between magnification and resolution?

Answer 19

Magnification - how many times bigger image produced is than the real life object
Resolution - ability to distinguish between objects

Question 20

How are light microscopes useful?

Answer 20

• max resolution of 200nm - used to observe eukaryotic cells/nuclei (maybe mitochondria and chloroplasts)
• max magnification is 1500x

Question 21

Ad and dis of transmission electron microscopes?

Answer 21

• beam of electrons are transmitted through the specimen - CAN SEE ULTRASTRUCTURE
  AD: high resolution images
• Can see smaller structures

DIS: can only be used with very thin specimens
- can’t use live specimens
- lengthy preparation of specimens
- not colour image

Question 22

Ad and dis of scanning electron microscopes?

Answer 22

• scan a beam of electrons across the specimen
• beam bounces off surface of specimen/electrons are detected - forms image

AD: can be used on thick/3D specimens
- allow external 3D structure o be seen

DIS : lower resolution than TEMS
- cannot be used to see live specimens
- not a colour image

Question 23

Ad and dis of laser scanning confocal microscopes?

Answer 23

Type of light microscope:
Use laser beams to scan a specimen that is tagged with fluorescent dye - laser causes dye to give off light
Detectors connected to computer - generates IMAGE

AD: used on thick/3D specimens
- allows external 3D structure to be seen
- clear images - high resolution

DIS : - slow
- laser can cause photo damage to cells

Question 24

PAG 1 : microscopy

Answer 24

1. Prepare slide :
   Using liquid specimen: ADD SPECIMEN TO SLIDE
   - cover liquid with coverslip (lower coverslip at an angle/use mounted needle) /press to remove air bubbles
   - add stain on edge of coverslip dab with paper towel drawing it under coverslip
   Using solid specimen : cut small sample from tissue /peel away thin layer of cells from tissue sample
   - apply stain /apply coverslip
   - add drop of water to specimen can prevent dehydration of tissue
   - Calibrate Graticule
   - start with lower power objective lens
   - by using the scale on the graticule lens/ stage micrometer , can work out the size of 1 division on eyepiece graticule
   Take repeat measurement/calculate mean if taking measurements

Question 25

How is the structure of mitochondrial membranes related to function of mitochondria?

Answer 25

- site of ATP synthesis - outer membrane is highly permeable to allow movement of molecules

Question 26

How to improve cell drawings?

Answer 26

- label - add scale - add title

Question 27

Role of RER membrane?

Answer 27

- Maintains **different conditions** between cytoplasm and RER (compartmentalisation) - separates proteins from cytoplasm

Question 28

How are organelles involved in protein synthesis?

Answer 28

1. Nucleolus manufactures ribosomes for proteins synthesis in RER 2) nucleus manufactures mRNA /attached to ribosome on RER 3) proteins in RER are sent in VESICLES to Golgi body 4) Golgi body processes proteins/sends them in vesicles to the PLASMA MEMBRANE 5) vesicles fuse with plasma membrane to secrete finished protein product

Question 29

Types of dyes used in microscopy and what are they used for?

Answer 29

**Acetic orcein** —> bind to DNA/stain chromosomes dark red **Eosin**- stains CYTOPLASM dark red/pink **Iodine** - stain starch blue-black **Iodine in potassium iodide solution** - stains CELLULOSE yellow **Haematoxylin** - stains RNA/DNA purple/blue **Methylene blue** - all purpose stain - blue

Question 30

Magnification formula?

Answer 30

Image size /actual size

Question 31

How is colorimeter calibrated? Why is it important to calibrate ?

Answer 31

Set to zero absorbance - using distilled water - values all measured to same standard

Question 32

Micrometers to cm?

Answer 32

10,000 micrometer = 1 cm

Question 33

Compare magnification and resolution of Light microscope, TEM and SEM?

Answer 33

Microscope type **LIGHT**. **TEM**. **SEM** **Resolution** 0.2 micrometers 0.0002 micrometers 0.002 micrometers **Magnification** X1500. >X1,000,000. < 500,000

Question 34

Stains used for electron microscopes?

Answer 34

Heavy metal compounds - absorb electrons well So no colour