Some Hypotheses For Biology Labs
In each of the following examples, the dependent variable is red while the
independent variable is blue. These variables are identified in the if clause only,
however, you might want students to treat the variables in the same way in the then clause. Also,
each example given can be composed in a variety of ways. For example, there is nothing incorrect
with reversing the order of the independent and dependent variables. I just do it one way for
consistency. As far as the independent variable is concerned, it can be varied by increasing,
decreasing or removing it entirely. Finally, the two variables in question do not actually have to be
related. Observations from testing the independent variable will reveal the nature of the relationship
such as direct, indirect, limited range, or no relationship at all (as in the first example).
If the pigments responsible for fall colors of leaves are related to chlorophyll by-products, then
separating pigments of green leaves (summer/spring) will reveal only green pigments.
If chlorophyll is related to food making in plants, then non-green appearing plants such as purple
plum will contain green as well as purple pigments.
If food making is related to chlorophyll, then starch will be found only in the green portions of a
If photosynthesis is related to light, then portions of a leaf shaded from light will test negative for starch.
If the rate of photosynthesis is related to wavelength of light (or concentration of carbon dioxide, or
temperature) then varying the color of light will vary the rate of oxygen production.
If animal metabolism is related to temperature, then increasing ambient temperature will increase
animal metabolism (carbon dioxide gas production).
If animal metabolism is related to plant metabolism, then isolating plants from animals will result
in decline in animal metabolism.
If effectiveness of disinfectants is related to exposure time (or concentration), then the longer the
exposure (or the higher the concentration) the less bacterial growth will result.
If rigidity of herbs is related to turgor pressure, then increasing the water content of cells will result
in firmer plant tissue.
If stomate density is related to rate of water loss, then drought resistant plants will have a lower
density of stomates on their leaves than will non drought resistant plants.
If transpiration is related to humidity (light or temperature or wind velocity), then increasing
humidity will decrease water loss.
If root growth is related to gravity, then roots will always turn toward the earth regardless of a
If shoot growth is related to gravity, then shoots will always grow upward even in the absence of
If hatching of brine shrimp is related to salinity (or temperature), then the greater the salt
concentration, the higher the hatching rate.
If enzyme activity is related to temperature (or pH or quantity), then increasing the temperature will
increase the products of an enzymatic reaction.
If diffusion efficiency is related to the ratio of surface to volume, then decreasing the S/V
(increasing volume of a cell mass) will decreasing the rate of diffusing into a cellular mass
If the thickness of annual growth rings in trees is related to annual rainfall, then examining wood
samples will reveal correlations in the growth rings to the historical records for rainfall in its
Physical & Earth Science Examples