One process all multicellular organisms undergo is
development. Starting as a single haploid or diploid cell, they are
all the result of a complex series of events known as morphogenesis and
differentiation in which one becomes many and a simple fertilized egg divides
and multiplies into a mosaic of cells with structures and functions as
different from the original as they are from each other. You are
such an organism, growing from a zygote in your mother's womb to the full-sized
adult you are today, and along the way, your cells also left behind the
features of that first cell and took on those of the specialized
cells that make up human tissues like nerve and skin.
Plants too are multicellular organisms, and they undergo the morphogenic and differentiation process as well. There are many similarities between the way plants and animals like yourself do these tasks, and therefore, they make excellent creatures for you to study the cycle of growth and development.
Specifically, you will be looking at the relationship between the differentiating parts of a plant and their respective metabolic rates. All cells burn oxygen in reaction with sugar, creating CO2, H2O, and usable energy as by-products (C6H1206 + 02 --> C02 + H20 + ATP). Since energy production takes place in those parts of a plant where growth and development are taking place the most, measuring and comparing cellular respiration rates from these locations allows one to sequence the events taking place and, thus, to know what is occurring and where. Hence, you can study the developmental process in plants by testing differences in metabolic activity as determined by how much the cells in specific areas respire.
The way scientist do this is with a tool known as a respirometer. These are simply closed systems (most often a flask or test tube) that can be used to measure changes in either gas pressure or volume. Normally, if an organism is placed in such a situation, any carbon dioxide released during cell respiration essentially replaces the oxygen consumed, but if the CO2 is removed (usually by reacting with KOH to form non-gaseous K2CO3), then any additional O2 used up causes both the pressure (P) and volume (V) n the contained system to drop since as the ideal gas law informs us, mass (n) is directly proportional to pressure and volume (PV=nRT). These drops, in turn, are easily quantified.
Your assignment will be to choose one of the questions
below about plant development and hypothesize an answer to it based on
your current understanding of the life cycle of flowering plants.
You will need to design an experiment to test your hypothesis, and after
you perform it, collecting and interpreting your data, you will need to
determine whether your original hypothesis is valid. You may assume access
to the basic protocol system for respirometers described below when designing
your procedures as well as all the materials listed (your teacher will
tell you whether you will be using CBLs or the water-displacement apparatus).
But all other elements (controls, variable, etc.) are up to you. It is your experiment.
3 125-ml respirometers
3 600-ml beakers TI-82 or TI-83 calculator
1 100-ml graduated cylinder Venier Bio-Software Package or equivalent
1 250-ml graduated cylinder Venier Biology Gas Pressure Sensor
1 thermometer (0-10 kpasc) or equivalent
balances & weigh boat or:
non-absorbent cotton water-displacement apparatus
1-L 15% KOH
forceps or tweezers
an assortment of germinating seeds:
great northern beans
alaskan snow peas
C. Respirometer Construction:
Take a #4 rubber stopper containing a graduated pipette
and a 124-ml flask provided by your teacher and place a 2 cm layer
of absorbent cotton in the bottom of the flask. Use an eyedropper
to saturate the cotton with fresh 15% KOH and cover this layer with 2-3
cm of non-absorbent cotton to protect any living samples from the KOH.
Place the samples inside the flask and seal with the pipette-stopper.