APES Unit 9
Name___________________________Date__________Period______
The Effects of Radiation on the Germination and Growth of Radish Seeds
INTRODUCTION:
Gamma radiation is a form of energy similar to X-rays, which, along with other forms of radiation,
is emitted from a variety of environmental sources. Two other kinds of radiation are beta radiation and
alpha radiation. Beta radiation consists of rapidly moving electrons, and alpha radiation consists of
rapidly moving particles that are composed of two protons and two neutrons. Atoms of the same element
that differ from one another in the number of neutrons present are called isotopes. Some isotopes of
atoms, such as Cobalt 60, are natural sources of gamma radiation. X-ray machines and nuclear power
reactors are also sources of gamma radiation. Radiation is of concern because, depending on its type,
total amount, or rate of delivery, radiation can cause changes in the genetic material (DNA) within cells,
or change the activities of cells. In very high doses, it kills cells directly.
Radiation dosage is measured in rads. A rad (radiation absorbed dose) is equal to 100 ergs of
energy absorbed by 1 gram of material. Most human radiation doses are measured in milliards (mrad =
1/1,000 of a rad). Another unit that is often used to quantify radiation dosages is the rem (roentgen
equivalent man). It is a slightly different way of measuring radiation, but for gamma radiation the rad and
rem are equivalent.
The following chart gives some idea of the amounts of radiation humans are likely to encounter.
Kind of exposure
Color television set
Upper limit allowable from a nuclear power facility
Chest X-ray
Brain scan X-ray
Natural background
Allowable maximum radiation exposure for general public
Barium enema X-ray
Allowable exposure for a worker in a nuclear power plant
Radiation treatment
Lowest exposure known to cause leukemia in Hiroshima survivors
Dose
(amount of exposure)
0.5 mrad/yr
5 mrad/yr
5.8 mrad/X-ray
100 mrad/X-ray
100-200 mrad/yr
500 mrad/yr
800-1,500 mrad/X-ray
5,000 mrad/yr
10,000 mrad/yr
20,000 mrad/yr exposure
Effects of exposure
(at dose shown)
None known
None known
None known
None known
None known
None known
None known
None known
Early embryo abnormal
Leukemia
Text and information courtesy of William Enger
In lab today you will begin to analyze the effects of different doses of radiation on the germination
and growth of radish seeds. The radish seeds that you will examine in lab have received the following
amounts of radiation from a Cobalt 60 source:
 Unirradiated
 Irradiated 50,000 rads
 Irradiated 150,000 rads
 Irradiated 500,000 rads
 Irradiated 4,000,000 rads
HYPOTHESIS:
In the space below, write a proper hypothesis for this lab:
PROCEDURE:
Day 1
1. Obtain five petri dishes with lids. Label the side of each dish with your period, group number, and
one of the five radiation treatments (Unirradiated, 50,000 rads, 150,000 rads, 500,000 rads, 4,000,000
rads).
2.
Cut out pieces of paper towel to fit each of the petri dishes.
3.
Thoroughly wet the pieces of paper towel and place them into the petri dishes.
4.
Place ten seeds of the appropriate kind in each of the petri dishes. They should be spread out on the
paper towel.
5.
Place another piece of wet paper towel on top of the seeds in each petri dish and return the lids to the
petri dishes. Bring the petri dishes to the spot on the counter designated for your class.
6.
Construct a data table that will allow you to record the number and percentage of seeds that have
germinated for each treatment. Construct a second data table that will allow you to record the
average length (in millimeters) of the roots and shoots that have sprouted for each treatment. Leave
an extra column in each data table for class data.
Day 2
1. After two days, record the number of seeds that have germinated and the average length of the roots
and shoots (in millimeters) for each treatment. Germinated seeds will have split the brownish seed
coat, and you should be able to see a whitish or yellowish part of the young plant protruding from the
seed coat. (Since some roots may be curved, you will need to take this into account when measuring
them.) When measuring roots and shoots, only use seeds that have germinated to calculate your
average. On a different note, do not use seeds that have not germinated in the calculation of your
averages for each treatment.
2.
Share your group’s data with other members of the class. Record the overall class averages in the
columns on your data tables labeled “Class Data”.
3.
Use the class data to construct two graphs. One should show the relationship between %
Germination and Radiation dose. The other should show the relationship between Average
Root/Shoot length and Radiation dose. Label the following information on the graphs
 Threshold dose for radiation on germination and/or root/shoot length (if it exists).
 LD-50 for germination
 ED-50 for root/shoot length
DATA:
100
GRAPHS:
Percentage of seeds germinate d
90
80
70
60
50
40
30
20
10
4,000
500
150
0
50
0
Log radiation dose (1,000 rads)
100
80
70
60
50
40
30
20
10
Log radiation dose (1,000 rads)
4,000
500
0
150
0
50
Average root/shoot length (millimeters)
90
CONCLUSION:
1. What is the effect of increased radiation on germination of radish seeds?
2. What is the effect of increased radiation on the root and shoot length of radish seeds?
3. Is there a threshold dose for radiation on either germination or root/shoot length?
4. What is the significance of the threshold dose? How do you identify the threshold?
5. What is the LD-50 for germination? What is the ED-50 for root/shoot length?
6. What is the significance of the LD-50/ED-50 dose?
7. Could this data be applied to humans in any way? Provide one argument for extending these toxicity
results to humans and one argument against doing so.