Cell Structure (A2.2)

Question 1

Define cell theory (3)

Answer 1

all organisms made up of one or more cells

cells = smallest unit of life

all cells come from pre-existing cells

Question 2

Formation of carbon compounds on Earth

Answer 2

comets + asteroid brough H2O to earth

methane + ammonia released in collisions + volcanic eruptions

2 gases + water vapor + CO2 formed earth’s atmosphere

Question 3

Define magnification

Answer 3

number of times larger an image is than an object

Question 4

Define resolution

Answer 4

minimum distance between 2 points at which they can still be distinguished

Question 5

millimetre

Answer 5

0.001metres

Question 6

Define transmission electron microscopes (3)

Answer 6

beam of electrons transmitted through specimen + focused to produce image

has excellent resolution (resolving power of 0.5nm)

magnification of 500,000

Question 7

Define scanning electron microscopes (4)

Answer 7

beam of electrons sent across specimen surface + reflected electron collected

good resolution (3-10nm)

magnification of 100,000

can produce 3-D image

Question 8

Define freeze-fracture in microscopy (4)

Answer 8

preparing sample for electron microscopy

specimen rapidly frozen

then physically broken apart

reveals plan through sample