Biology - HOT Science Lab

Teacher
After
activity:
3. Fill a test tube with Iodine in order for student‘s to see it‘s original color.
Iodine acts as an indicator. Chemical indicators change color when the
substance you are testing for is present. Iodine (starch indicator) turns
blue-black when starch is mixed with iodine and remains amber
(orange-brown) when starch is not present.
What the teacher will do:
a. Have each group share their observations.
b. Lead discussion that focuses on questions in the investigations.
c. Record each group‘s data for each investigation on the board or
transparency, discussing each set of results as you record them.
d. Identify the meaning of diffusion, permeable, semi-permeable, and
impermeable as they apply to cell membranes.
e. Identify impermeable as a membrane that will not allow any diffusion across
a membrane.
f. Show a visualization such as the following and discuss why materials have
to pass into and out of the cell:
1. Diffusion animation: http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_
works.html
2. Osmosis animation: http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_
works.html
g. Answer Key for Results/Conclusion:
Activity 1: Diffusion of Starch
1. Sketch the experiment, use arrows to show the way the diffusion was
occurring. Answers will vary. Students should illustrate that the starch
inside the Ziploc bag is moving through the semi-permeable membrane
(bag)
2. Observing the diffusion process in real cells is difficult because they are
too small to be seen easily. In this activity you created a giant model of
a cell so that you can observe the effects of diffusion through a
membrane. In your cell model describe the role of each of the following
parts:
a. Ziploc bag: cell‘s membrane
b. contents of the bag: cell‘s cytoplasm
c. area outside the bag: cell's environment
Activity 2: Potato Osmosis
1. In this experiment, why was it important that the potato cores were the
same length In order for this to be a controlled experiment the core
samples must be the same size. If not, any change in the core sample
after placing them in the different solutions could be attributed to the
different size not the concentration of salt.
2. Why was it important to cover each beaker with a piece of aluminum
foil To minimize the rate of evaporation.
3. Into which of the potato cores did water flow From which of the potato
cores did water flow How can you tell
Surrounding the potato cell with a HYPOTONIC solution, such as 100%
water, will result in the net movement of water INTO the potato cells.
Biology HSL Page 159
Curriculum and Instruction