All multicellular organisms start as a single cell.
You yourself came from such a cell when an egg from your mother was fertilized
by an egg from your father to from the zygote that was the first cell of
your body. Dividing over and over again, this cell underwent a complex
sequence of events that created new kinds of cells that were very different
from that first one. That is why your body now has the specialized
muscle cells that help make you move and nerve cells that help you think
even though that first cell could not do any of these things. Biologists
call the process of a single cell multiplying and growing into a many celled
Plants too are multicellular organisms, and they also undergo development. There are many similarities between the way plants and animals grow from single cell zygotes to adults, including the way their cells differentiate to do separate tasks just as the fertilized egg you came from turned into nerves, muscles, and other things. Thus, plants make excellent creatures to study the cycle of growth and development, and you will be using them to perform an experiment to see how it works.
Specifically, you will be looking at the relationship between the parts of a plant as they develop and how much energy they use. Because energy production takes place in those areas of a plant where cells are dividing and specializing the most, measuring and comparing energy use in the different parts of a plant helps scientists like you to figure out what takes place as seeds turn into mature plants. Such knowledge could be important because the more we understand how seeds function, the better we might be able to grow crops to feed hungry people.
You will be studying the seed, then, and how it develops in its early stages. You will be trying to discover which part of the seed develops first and to know why that might be the case. You will be looking at the difference in oxygen consumption in the different parts of the growing plant. All cells consume oxygen to produce usable energy and give off carbon dioxide (C6H1206 + 02 --> C02 + H20 + energy). Since plants make more energy where they are growing the most, measuring and comparing rates of oxygen consumption from various regions of the plant let you know where the plant is developing the most. Hence, you can study plant developmental by testing differences in respiration rates (oxygen consumption).
The way scientist do this is with a tool known as a respirometer. Respirometer use a chemical called potassium hydroxide (KOH) to remove carbon dioxide gas when organism respire. That way, when the oxygen is consumed by the organism, there will not be as much gas in the respirometer, lowering the pressure just like when a balloon releases air. This change in pressure is easy to measure.
3 125-ml respirometers (see sample
3 600-ml beakers absorbent cotton
1 100-ml graduated cylinder glass beads
1 thermometer forceps
CBL unit with link calculator marker
Biology Gas Pressure Sensor eyedropper
30 germinated great northern beans 25 ml of 15% KOH
a graphing calculator with biology sensor software
1. Put your goggles on and then collect the materials from your teacher.
2. Fill the 600-ml beakers a little less than half full of water (the amount does not need to be precise) and set them at your table or work bench.
3. Prepare your respirometers by marking one flask "A" and one flask "B" and one flask "C".
4. Place a 2 cm layer of absorbent cotton in the bottom of each 125-ml and use an eyedropper to saturate the cotton with fresh 15% KOH, being careful not to get any on the sides of the flask. KOH can burn you; so if any gets on your skin, wash the area immediately and inform your teacher.
5. Cover this layer with 2-3 cm of non-absorbent cotton in each flask to protect your plant samples and set the respirometers aside.
6. Carefully use a pair of dissecting scissors to snip off the radicle from each bean and lay them on a damp paper towel.
7. Use a balance to mass the total number of beans minus their radicles and record this number in table 1. Repeat this step for the radicle alone.
8. Fill a 100-ml graduated cylinder to the 50 ml mark and record initial volume in table 1.
9. Next add the 30 radicle-less beans to the graduated cylinder, being sure to make sure that none are floating on the top of the water.
10. Record the difference between the 50 ml mark and the new reading. This is the volume of your beans and you should record this number in table 1.
11. Remove the beans from the graduated cylinder and set them aside on a moist paper towel.
12. Repeat step 6 and then add the radicles to the graduated cylinder. Look at the new reading and then add glass beads to the cylinder until the volume in the cylinder reads the same as it did when the beans were in there. Make sure that the difference between the new reading and the 50 ml mark give the same volume as the one you wrote down for the beans, and record your new value in table 1.
13. Remove the radicles with the beads and place them on a damp paper towel.
14. Repeat step 11 only this time only add glass beads until the volume
of beads is the same as the volume of the beans and record your volume
in table 1.
15. Now, carefully place the glass beads into flask A, the beans into one flask B, and the radicles into flask C so that they rest on top of the non-absorbent cotton only.
16. Tightly seal each flask with the #4 rubber stopper containing the graduated pipette to assemble your respirometers and then attach a biology gas pressure sensor to the open tip of each pipette.
17. Place the completed respirometers into the 600-ml beakers until the water comes up and covers the flasks' sides and allow them to sit and equilibrate for 10 minutes. Record the temperature of all three flasks.
18. Connect the biology gas pressure sensors to the CBL unit as follows: the one connected to flask A into channel 1; the one connected to flask B into channel 2; and the one connected to flask C into channel 3. Be sure to OPEN the stop cocks to the sensors to allow gas pressures to equalize.
19. Firmly attach the CBL to your calculator with the link cable and turn on both the CBL and the calculator. Follow the directions your teacher gives for programming the calculators. You will be using the method described in Biology with CBL by Masterman and Holman, and you will be selecting the biology gas sensor probe to collect 40 readings, one every 30 seconds. Be sure to program the calculator to time graph the data as it collects it. Your experiment will run for approximately 20 minutes.
20. After you have finished collecting the data, one member of your group should disconnect the calculator from the CBL unit and perform a linear regression on the data to obtain the rate of oxygen consumption (the slope of the line). Or you can graph the raw data on a sheet of graph paper and determine the rate by computing the slope of the line.
21. Next, take the stoppers out of the flasks and carefully remove the beans, radicles, and glass beads with the forceps, being sure not to dump the contents out to avoid burning yourself with the KOH.
22. Throw the beans away and return the beads to your teacher. Wash the flasks and set them out to dry.
23. Now complete table 2 and then answer the lab conclusion questions.
C. Analysis and Conclusions
|Flask||Initial Vol.||Final Vol.||Vol. of Tissue||Mass (in g)||Mass (in kg)|
|Type of Tissue||Rate of Respiration||Temperature|
| Bean minus radicle
| Radicle alone
1. How was your experiment controlled?
2. What was a tight seal needed around each connection point in the experimental device?
3. Draw a picture of your sprouting bean seedling, label its primary parts and show where the highest respiration rates were and explain why.
4. What two structures or factors did you compare in your investigation?
5. What was the difference in respiration rates between the two structures you compared and what about their respective developmental patterns would explain this difference?
6. If the respiration rate increases, what happens to the gas pressure? Explain your answer.
7. Begin with a dormant seed and describe the life cycle of the plant, explaining the purpose of each stage for the development and success of the plant.
8. Does the germinating seed contain a zygote or an embryo?
9. Which stage of animal development is the seed analogous to?
10. What is morphogenesis, and how is it different in plants and animals?
11. Where was(were) the meristematic tissue(s) of the developing plant you tested?
12. What role does meristematic tissue play in the plant's growth and
development (i.e. why would the respiration rates be highest there even
when the plant is mature)?
Carbon dioxide probes record the concentration of CO2 molecules in a
closed system instead of the pressure of the gas. If you had used
this kind of sensor instead of a gas pressure probe in the experiment you
just performed, what kinds of data would you have expected to collect?
Graph these hypothetical results and explain what these results mean and
why you would have gotten them.