A2.2 Cell Structure

Question 1

Function of Mitochondria

Answer 1

• Site of aerobic respiration (release energy)

Question 2

Function of ribosome

Answer 2

• Site of protein synthesis

Question 3

Function of cell membrane

Answer 3

• Controls movement of substances in and out of cell

Question 4

What is Cytology

Answer 4

Study of cells.

Question 5

Cell theory statements

Answer 5

• All organisms are made up of one or more cells.
• Cells are the smallest unit of life.
• All cells come from pre-existing cells.

Question 6

Cells and the microscope

Answer 6

• Microscopes with high magnification and resolution helps make cell visible as they are very small.
• Magnification: number of times larger an image is than the object.
• Resolution: minimum distance between two points which they can still be distinguished.
• Most common microscopes: light microscopes and electron microscopes.

Question 7

Difference between Light microscopes and Electron microscopes

Answer 7

• Light: Inexpensive; simple specimen prep; magnifies up to 2000; specimens can be dead or alive.
• Electron: Expensive; preparation of specimens is very complex; magnifies up to 500000; specimens have to be dead.

Question 8

Converting units

Answer 8

μm = 1000 x mm
nm = 1000 x μm

Question 9

Magnification calculation

Answer 9

Total magnification = Ocular x Objective
Magnification = Image size/ specimen size

Question 10

Example question: Object has been magnified x31000 and measures 43mm in length. What is its actual size in nm?

Answer 10

Object size = image / magnification
43/31000 = 0.001387
0.001387 x 1000 = 1.387μm

Question 11

Types of electron microscope

Answer 11

• Transmission electron microscope (TEM): beam of electron is transmitted through a specimen and focused to produce an image. Similar to light microscopy. Has excellent resolution (resolving power of 0.5nm). Has magnification of up to 500,000.
• Scanning electron microscope (SEM): a beam of electrons is sent across the surface of a specimen and the reflected electron are collected. Has good resolution (resolving power of 3-10nm). Has magnification of up to 100,000. Can produce 3D images.

Question 12

Explain what is meant by an Artefact

Answer 12

• Structures that are produced due to perpetration process, not actually a feature of the specimen.
• Can be found in light microscopy as well. Bubbles trapped under coverslip are artifacts.
• Artefacts are inevitable in electron microscopy. Experience allows scientists to distinguish between artefacts and actual structures.

Question 13

Explain Freeze-fracture

Answer 13

• A process of preparing a sample for electron microscopy: Specimen is rapidly frozen then physically broken apart.