Biology Unit 1 Booklet 2

Question 0

Why electron microscope are better for viewing small objects (2)

Answer 0

Resolution is higher (1)

As electrons have shorter wavelengths (1)

Question 1

Not being able to see small organelles with optical microscope (2)

Answer 1

Resolution is too poor (1)

Wavelength of light is too long (1)

Question 2

Pros and cons of transmission microscopes (7)

Answer 2

Small objects can be seen (1)
High resolution (1)
As wavelengths of electrons are short (1)
Living cells cannot be seen (1)
Carried out in a vacuum (1)
Specimen has to be very thin (1)
Artefacts may be produced (1)

Question 3

Calculating the size of organelles when given magnification (2)

Answer 3

Measure the organelle in mm and convert to micrometers or nm (1)
Divide by the magnification (1)

Question 4

Calculating magnification with a given scale bar (2)

Answer 4

Measure the scale bar in mm and convert to micrometers or nm (1)
Divide by the given number on the scale bar (1)

Question 5

Estimating the size of a cell/ organelle when given no figures (2)

Answer 5

Measure length with eyepiece scale (1)
Calibrated against something of known and uniform length (1)
E.g. Red blood cell

Question 6

Use of ice cole, isotonic, buffer solution in cell fractionation (3)

Answer 6

Ice cold to slow down enzyme activity or prevent self digestion by enzymes in lysosomes (1)
Isotonic to prevent water movement by osmosis (1)
Buffer solution to prevent changes in pH that may affect protein structure (1)

Question 7

Explain why isotonic solution is used (2)

Answer 7

Prevents net movement of water in or out of the organelle by osmosis (1)
So organelle does not shrivel or burst (1)

Question 8

Why is tissue homogenised? (1)

Answer 8

To release cell contents (1)

Question 9

Osmosis (4)

Answer 9

Movement of water (1)
From an area of less negative water potential to an area of more negative water potential (1)
Across a selectively permeable membrane (1)
Down a concentration gradient (1)

Question 10

How to find water potential the same value as the tissue used (2)

Answer 10

Plot a graph of results and draw a line of best fit (1)

Find the concentration where the ratio is one or there is no change in mass (1)

Question 11

Deference between types of diffusion and active transport (3)

Answer 11

Diffusion is net movement of solutes from high to low concentration (1)
Facilitated diffusion is transport of large or charged particles through membrane protein (1)
Active transport is net movement of molecules against a concentration gradient that requires energy in the form of ATP and carrier proteins (1)

Question 12

Why some cells may have lots of mitochondria (3)

Answer 12

Mitochondria produce ATP (1)
By respiration (1)
Energy release is used for muscle contractions, active transport and nerve impulse (1)

Question 13

Describe how prokaryotes are different from eukaryotes (9)

Answer 13

Prokaryotes have a loop of DNA (no nucleus) (1)
No mitochondria (1)
No Golgi (1)
No endoplasmic reticulum  (1)
Have smaller 70 s ribosomes (1)
Have capsule (1) 
Have flagellum (1) 
Have plasmids (1) 
Have a cell wall made of murein (1)

Question 14

Mechanisms of cholera infection (6)

Answer 14

Bacteria enters body via contaminated water, some bacteria may survive the acidic conditions of stomach (1)
Bacterium propels through the lining of small intestine using flagellum (1)
Bacterium secretes a protein that binds to receptors on surface of epithelial cells (1)
Bacterium also secretes a toxic protein that interferes with chloride channels (1)
Chloride ions flood lumen making the water potential more negative (1)
Water moves from epithelial cells to lumen via osmosis causing diarrhoea (1)

Question 15

What is an exotoxins (1)

Answer 15

A toxic protein secreted by bacteria (1)

Question 16

Why cholera protein binds receptors on small intestine (2)

Answer 16

Protein is a complementary shape (1)

To the specific tertiary structure of the receptor protein (1)

Question 17

How cholera causes diarrhoea (3)

Answer 17

Water potential in lumen is more negative (1)
Water moves from epithelial calls into lumen (1)
By osmosis (1)

Question 18

Oral rehydration therapy (2)

Answer 18

Contains water to rehydrate the tissues (1)

Electrolytes to rebalance the osmotic potential (1)

Question 19

Explain why ORT replaces water lost (4)

Answer 19

Encourages cells to uptake sodium and glucose (1)
Water potential in cells becomes more negative (1)
Water moves from small intestines back into cell (1)
By osmosis (1)

Question 20

Molecules of transport (3)

Answer 20

Ions are transport by channel proteins (1)
Big molecules are transported by carrier protein (1)
Active transport uses only carrier protein (1)

Question 21

Fick’s law (2)

Answer 21

The rate if diffusion is proportional to surface area x concentration gradient (1)
Divided by thickness (1)