Biology Lab 4

Question 1

What does a cell membrane control?

Answer 1

The movement of the chemicals into, or out of, the cell

Question 2

Name three nutrients a cell needs to take in.

Answer 2

1. Oxygen
2. glucose
3. amino acids

Question 3

All cells are surrounded by a?

Answer 3

Membrane

Question 4

Name something a cell must remove

Answer 4

Urea

Question 5

How is dialysis tubing similar to the cell membrane?

Answer 5

It is a selectively – permeable membrane

Question 6

What is a selectively – permeable membrane?

Answer 6

Something that allows the passage of some molecules, but restricts others, based on the size of the molecules.

Question 7

What is dialysis?

Answer 7

The movement of a solute through a selectively – permeable membrane

Question 8

What does dialysis solution contain?

Answer 8

1. Fructose
2. Starch
3. NaCl ( salt)

Question 9

What would you use Benedict’s reagent for?

Answer 9

To test for reducing sugar (fructose).

Question 10

What color would you expect to see if fructose were present?

Answer 10

Orange too dark brown

Question 11

What would you use silver nitrate to test for?

Answer 11

Chloride

Question 12

What would you use Lugol’s iodine (IKI) to test for?

Answer 12

Starch

Question 13

What is the chemical formula for silver nitrate

Answer 13

AgNO3

Question 14

Based on your results, which of the three substances: fructose, starch, and chloride can diffuse through the selectively – permeable membrane?

Answer 14

The substance which is detected both inside and outside the dialysis tubing set up – the chloride?

Question 15

What is osmosis?

Answer 15

The diffusion of water through a selectively – permeable membrane

Question 16

True or false? Water always moves from where it is more concentrated to an area of lower water concentration.

Answer 16

True

Question 17

The concentration of water depends on what?

Answer 17

The quantity of solutes that are dissolved in the water

Question 18

If a large quantity of sugar or salt is dissolved in water, the water concentration is____________?

Answer 18

Low

Question 19

Pure water, with nothing dissolved in it has the ____________

Answer 19

Highest water concentration

Question 20

A solution with a higher water concentration than a cell is

Answer 20

Hypotonic

Question 21

A solution with a lower water concentration than a cell is

Answer 21

Hypertonic

Question 22

How does temperature affect the rate of diffusion?

Answer 22

The rate of diffusion will be faster as the temperature increases. As the temperature increases the amount of energy available for diffusion is increased.

Question 23

From your results in the dialysis experiment, what can you predict about the size of the molecules of fructose, NaCl and starch?

Answer 23

The chloride molecules are the smallest. we can’t tell about the fructose or starch because they didn’t go through the dialysis tubing.

Question 24

Explain the results of the osmosis experiment.

Answer 24

On the slide with the water, the high water concentration outside of the cell causes the organelles to be spread widely apart. The hypotonic solution is going into the cell. When NaCl is added, the solution is hypertonic and water leaves the cell and the organelles become closer together.

Question 25

If animal cells are placed in pure water they swell up and burst. What part of a plant cell prevents it from bursting?

Answer 25

The cell wall.

Question 26

The water in your body comes partly from drinking water or other liquids. What is another source of water for humans or other animals?

Answer 26

Osmosis

Question 27

How do animals (and humans) get rid of excess water from the body?

Answer 27

Sweat, urine

Question 28

What are two ways that desert plants such as cactus reduce their water loss?

Answer 28

1. They don’t have leaves and lose water vapor like most plants. They produce food through photosynthesis in their stems.
2. They have ribs to shade parts of the plant to keep their temperature down. This slows the rate of diffusion.
3. They have a waxy substance on their skin to keep the cells from losing water to the areas of low water concentration surrounding the plant.

Question 29

Cells obtain nutrients by diffusion. Why is the body temperature of birds and mammals roughly 40°C and not 90°C?

Answer 29

If their temperature where 90°C, the diffusion rate would increase and they would need many more nutrients to survive.