Microscopy and cells

Question 1

What is the equation for magnification?

Answer 1

Maginfcation=size of image/actual size of object

Question 2

Define magnification

Answer 2

The magnification of a microscope refers to how many times larger the image is compared to the object

Question 3

Define resolution

Answer 3

The resolution of a microscope is the minimum distant between two objects which they can still be viewed as seperate.

Question 4

Light microscope resolution

Answer 4

Limited to 0.2um and 200nm

Question 5

Light microscope advantages

Answer 5

Can see living specimens.
Easier specimen preparation.
Variety of coloured stains.

Question 6

Light microscope disadvantages

Answer 6

Low resolution so organelle detail / smaller components not visible.

Question 7

TEM electron microscope resolution

Answer 7

0.1 nm but not always achieved as difficult specimen prep. / high energy beam can destroy specimen.

Question 8

TEM electron microscope advantages

Answer 8

Very high resolution at high magnification.

Detailed organelle / sub-organelle structure.

Question 9

TEM electron microscope disadvantages

Answer 9

Specimens are not alive i.e. in a vacuum.
Difficult prep. e.g. very thin specimens / complex staining.
Black and white image.
Artefacts can spoil image.

Question 10

SES microscope resolution

Answer 10

20nm

Question 11

SES microscope advantages

Answer 11

3D images show structural formation.

Totally sic pics.

Question 12

SES microscopes disadvantages

Answer 12

Specimens are not alive.
Difficult prep.
Vacuum.
Black and white image.

Question 13

Describe the structure of a nucleus

Answer 13

Surrounded by a nuclear envelope, a semi-permeable double membrane
nuclear pores allow substance to exit/entry
Dense nucelous made of RNA and proteins assemble ribosomones

Question 14

Functions of the nucleus

Answer 14

Acts as the control centre of the cell - controls the cell’s activities
Controls synthesis of proteins
Contains the organism’s genetic material (in the form of DNA)
Manufactures ribosomes from ribosomal RNA

Question 15

Structure of a mitochondria

Answer 15

Double membrane - controls the entry and exit of material
Inner membrane is highly folded to form cristae - this is where respiration (oxidative phosphorylation) takes place and the folds provide a large surface area for increased respirations
Fluid matrix contains mitochondrial DNA, enzymes, lipid and proteins
Usually rod-shaped and around 1-10 micrometers long

Question 16

Function of mitochondria

Answer 16

Site of aerobic respiration
Produce the energy-carrier molecule ATP during respiration
Therefore, cells with a high level of metabolic activity that require a lot of ATP (muscle cells) have lots of large mitochondria with many cristae

Question 17

Structure of chloroplasts

Answer 17

Vesicular plastids with double membrane
Thylakoids flattered discs stack to form grana; contains photosytems with chlorophyll
Intergranal lamellae, tubes attach thlyakoids in adjacent grana
stroma- fulid-filled matrix

Question 18

Functions of chloroplast

Answer 18

Functions:
Carries out photosynthesis (converts light energy to chemical energy)

Question 19

Structure of Endoplasmic Reticulum (ER)

Answer 19

A 3D system of membranes that spreads throughout the cytoplasm of a cell
The membranes form a network of tubules and flattened sacs called cisternae
It is continuous (attached to) the outer nuclear membrane
There are two types of ER:
Rough ER (RER)
SmoothER (SER)

Question 20

Functions of ER

Answer 20

Rough ER - has ribosomes on its surface
Provides a large surface area for the synthesis of proteins
Provides a pathway for the transport of proteins throughout the cell
Smooth ER- lipid synthesis

Question 21

Structure of Gogi apparatus

Answer 21

A stack of membranes that form flattened sacs, called cisternae
Cis face - where vesicles from the ER fuse
Trans face - where golgi vesicles pinch off regularly from the cisternae

Question 22

Function of Gogi apparatus

Answer 22

Collects, modifies and transports molecules around or out of the cell
Proteins, lipids and carbohydrates produced in the ER enter and are passed through the golgi apparatus
Proteins are modified
The proteins are also ‘labelled’, allowing them to be sorted and then sent to their correct destination
Once sorted, the modified proteins and lipids are transported in golgi vesicles to their destination

Question 23

Lysosomes structure

Answer 23

Form when vesicles that bud off the golgi apparatus contain hydrolytic enzymes for breaking things down (eg. proteases, lipases or lysozymes)

Question 24

Lysosomes function

Answer 24

Hydrolyse material taken up by cells (phagocytic cells)
Release enzymes to the outside of the cell (exocytosis) in order to destroy external material
Digest old, worn out organelles for recycling
Break down of cells that have died

Question 25

Structure of ribosomes

Answer 25

Small granules found in all cells Occur in large numbers (can be almost 25% of the dry mass of the cell) They may either be found in the cytoplasm or be attached to the rough ER 2 types: 80S (found in Eukaryotic cells) - larger 70S (found in Prokaryotic cells, mitochondria and chloroplasts) - smaller

Question 26

Function of a ribosomes

Answer 26

the site of protein synthesis

Question 27

Structure of vacuole

Answer 27

A fluid-filled sac with a single membrane Usually a single large vacuole in plant cells Contains a solution of minerals, sugars, amino acids, wastes and sometimes pigments

Question 28

Function of vacuole

Answer 28

They support herbaceous plants (non-woody/soft) or herbaceous parts of woody plants by making cells turgid/rigid Storage of substances Sugars & amino acids - temporary food stores Pigments - give colour in petals to attract pollinating insects

Question 29

Structure of centroiles

Answer 29

Small hollow cylinders A centrosome = 2 centrioles (oriented at right-angles to each other) Form a network of fine fibres in the cytoplasm called the cytoskeleton made out of microtubules and filaments

Question 30

Function of centrolie

Answer 30

Supports the cell’s shape Organises and moves organelles During cell division the pair separate to opposite ends of the cell and form the spindle

Question 31

Structure of cell wall

Answer 31

Found in plant cells Made of cellulose micro-fibrils - very strong so supports the functions Fungi also have Cell walls (chitin) Algae also have cell walls (cellulose or Glycoproteins or both)

Question 32

Functions of cell wall

Answer 32

Providing the cell with strength to prevent it bursting due to osmosis Providing strength and support to the whole plant

Question 33

Cytoplasm

Answer 33

Contains enzymes, site of many reactions and dissolve solutes and adds supports to the cell

Question 34

plamaisa membrane

Answer 34

bi-layer of lipids and proteins channel it allows certain molecules and charged molecules to enter and exist the cell as it is semi-permeable.

Question 35

Role of plasimds

Answer 35

small ring of DNA that carries non-essential DNA can be exchanged between bacterial cells via conjunction

Question 36

Role of the flagellum

Answer 36

Roating tail propels organism

Question 37

Role of collapse

Answer 37

Prevent desiccation and chemical attack

Question 38

Pilus

Answer 38

Transfer of material between bacteria

Question 39

Describe the first stage of cell fractionation and ultracentrifugation.

Answer 39

Homogenisation: This breaks open the cells to release the organelles. Vibrating the cells, or grinding them up in a blender.

Question 40

Why use a ice-cold solution

Answer 40

cold to slow down and stop organelle activity, particularly the hydrolytic enzymes in lysosomes

Question 41

Why is it buffered

Answer 41

to prevent changes in pH levels so organelle proteins are not damaged.

Question 42

Why use the same water potential or isotonic

Answer 42

isotonic to prevent the movement of water in and out of organelles by osmosis.

Question 43

Describe stage two of cell fractionation and ultracentrifugation.

Answer 43

Filter the solution through a gauze to remove debris e.g. large cell debris or tissue debris.

Question 44

Describe stage three of cell fractionation and ultracentrifugation.

Answer 44

Ultracentrifugation: Spin the solution in a centrifuge at a low speed. The heaviest organelles (nuclei, chloroplasts) fall the to the bottom. The rest of the organelles stay suspended in the fluid above this sediment. This is the supernatant. The supernatant is drained off, poured into another tube, and spun again at a very high speed. This time, organelles like mitochondria and lysosomes fall to the bottom. Again, the supernatant is drained off, poured into another tube and spun at a higher speed. Finally, the lightest organelles remain. Material is separated on the basis of mass / density.

Question 45

Detail viral replication

Answer 45

Requires a host cell Complementary attachment proteins bind to cell surface receptors Viral genetic material injected / enters host cell Viral genes transcribed and viral proteins produced e.g. capsid Viral genome replicated many times New viruses assembled Exit cell via cell surface membrane e.g. budding

Question 46

What are the key features of viruses?

Answer 46

Acellular, non-living (NOT cells!) 20-300 nm Contain DNA or RNA nucleic acids (genome) Enclosed within a protein coat - capsid Surface attachment proteins Require a specific host cell to enter and replicate no metabolism no membrane