Cell structure and division

Question 1

What is the limitation of a light microscope?

Answer 1

Cannot distinguish two objects less than 0.2 um apart

Question 2

How can an electron microscope overcome this?

Answer 2

Beams of electrons have shorter wavelengths

Question 3

In terms of magnification, define ‘object’

Answer 3

The material put under the microscope

Question 4

Define ‘image’

Answer 4

The way the material appears when viewed through the microscope

Question 5

Define ‘magnification’

Answer 5

How many times bigger the image of an object is compared to its actual size

Question 6

How do you find out magnification of an object?

Answer 6

Size of image/ Size of object

Question 7

Define ‘resolution’

Answer 7

The minimum distance apart 2 objects must be in order to be distinguished from each other

Question 8

What is cell fractionation?

Answer 8

Where cells are lysed and the contents separated

Question 9

Why must the tissue be placed in cold, isotonic, buffered solution?

Answer 9

Cold - to reduce enzyme action

Isotonic - to prevent damage to organelles by osmosis

Buffered - to keep pH constant

Question 10

What is used to break up cells?

Answer 10

Homogeniser

Question 11

The fluid obtained is called:

Answer 11

Homogenate

Question 12

How are the organelles in the homogenate separated?

Answer 12

By using an ultracentrifuge

Question 13

What organelles are heaviest?

Answer 13

Nuclei

Question 14

Where in the centrifuged tube are the heaviest cell components found?

Answer 14

At the bottom, in the sediment

Question 15

What is the fluid at the top of the tube called?

Answer 15

Supernatant

Question 16

What are the 2 main advantages of an electron microscope?

Answer 16

1. Short wavelength

2. Beam can be focused using electromagnets

Question 17

What special conditions must an electron microscope operate in?

Answer 17

Near vacuum

Question 18

Why is this?

Answer 18

Molecules in the air can absorb electrons

Question 19

2 types of electron microscopes are:

Answer 19

1. Transmission electron microscope

2. Scanning electron microscope

Question 20

How is the beam focused in a TEM?

Answer 20

A condenser electromagnet

Question 21

Does the beam pass through the specimen?

Answer 21

Yes

Question 22

Why do some parts of the specimen appear dark?

Answer 22

They absorb electrons

Question 23

Limitations:

Answer 23

Vacuum

Process is complex and image is not coloured

Specimen must be very thin

Artefacts

Question 24

In a SEM, does the electron beam come from above or below?

Answer 24

Below

Question 25

When using a light microscope, how do we measure the size of an object?

Answer 25

With an eyepiece graticule

Question 26

What is used for calibration?

Answer 26

Stage micrometer

Question 27

Summarise how the calibration is done

Answer 27

line up the eyepiece graticule scale with the stage micrometer scale

Find how many units on the micrometer scale are equivalent to how many units on the graticule scale

If one unit on the stage micrometer equals 10 um, each unit on the graticule scale = 10 divided by the number of equivalent units on the graticule scale

Question 28

The two classes of cells are:

Answer 28

Eukaryotic

Prokaryotic

Question 29

2 features of eukaryotic cells:

Answer 29

1. Distinct nucleus

2. Membrane-bound organelles

Question 30

Function of nucleolus

Answer 30

Ribosomal RNA manufactured here. Assembles ribosomes

Question 31

What is chromatin?

Answer 31

The form that chromosomes take when the cell is not dividing

Question 32

Functions of the nucleus:

Answer 32

To control protein synthesis

To contain the cell’s genetic material

Manufactures ribosomes and ribosomal RNA

Question 33

Function of cristae:

Answer 33

To provide a large surface area for respiration

Question 34

Functions of ER:

Answer 34

Surface area for protein and glycoprotein synthesis

Transport pathway