Biology Lab 4 Flashcards
What does a cell membrane control?
The movement of the chemicals into, or out of, the cell
Name three nutrients a cell needs to take in.
- Oxygen
- glucose
- amino acids
All cells are surrounded by a?
Membrane
Name something a cell must remove
Urea
How is dialysis tubing similar to the cell membrane?
It is a selectively – permeable membrane
What is a selectively – permeable membrane?
Something that allows the passage of some molecules, but restricts others, based on the size of the molecules.
What is dialysis?
The movement of a solute through a selectively – permeable membrane
What does dialysis solution contain?
- Fructose
- Starch
- NaCl ( salt)
What would you use Benedict’s reagent for?
To test for reducing sugar (fructose).
What color would you expect to see if fructose were present?
Orange too dark brown
What would you use silver nitrate to test for?
Chloride
What would you use Lugol’s iodine (IKI) to test for?
Starch
What is the chemical formula for silver nitrate
AgNO3
Based on your results, which of the three substances: fructose, starch, and chloride can diffuse through the selectively – permeable membrane?
The substance which is detected both inside and outside the dialysis tubing set up – the chloride?
What is osmosis?
The diffusion of water through a selectively – permeable membrane
True or false? Water always moves from where it is more concentrated to an area of lower water concentration.
True
The concentration of water depends on what?
The quantity of solutes that are dissolved in the water
If a large quantity of sugar or salt is dissolved in water, the water concentration is____________?
Low
Pure water, with nothing dissolved in it has the ____________
Highest water concentration
A solution with a higher water concentration than a cell is
Hypotonic
A solution with a lower water concentration than a cell is
Hypertonic
How does temperature affect the rate of diffusion?
The rate of diffusion will be faster as the temperature increases. As the temperature increases the amount of energy available for diffusion is increased.
From your results in the dialysis experiment, what can you predict about the size of the molecules of fructose, NaCl and starch?
The chloride molecules are the smallest. we can’t tell about the fructose or starch because they didn’t go through the dialysis tubing.
Explain the results of the osmosis experiment.
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.
If animal cells are placed in pure water they swell up and burst. What part of a plant cell prevents it from bursting?
The cell wall.
The water in your body comes partly from drinking water or other liquids. What is another source of water for humans or other animals?
Osmosis
How do animals (and humans) get rid of excess water from the body?
Sweat, urine
What are two ways that desert plants such as cactus reduce their water loss?
- They don’t have leaves and lose water vapor like most plants. They produce food through photosynthesis in their stems.
- They have ribs to shade parts of the plant to keep their temperature down. This slows the rate of diffusion.
- 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.
Cells obtain nutrients by diffusion. Why is the body temperature of birds and mammals roughly 40°C and not 90°C?
If their temperature where 90°C, the diffusion rate would increase and they would need many more nutrients to survive.
