biology experiment 2

Learning Objectives

  • Write hypothesis statements based on knowledge of biological principles
  • Identify experimental variables such as the independent, dependent and control variables
  • Distinguish between qualitative and quantitative data
  • Determine the presence of amino acids, proteins, glucose, and starch using indicator solutions
  • Discuss how different biological molecules interact with distinct chemical test reagents
  • Discuss the functional aspects of different chemical functional groups in biological molecules
  • Recognize and identify chemical function groups in biological molecules

Conducting Experiments

The foundation of science knowledge is based on experimentation. Experiments are carefully designed to assure that results can be clearly interpreted. In conducting experiments, it is extremely important that all variables be very precisely defined, measured and controlled. In the laboratory experiments in this course, you will need to identify, measure and control specific variables like a scientist would do.

The first step of an experiment is to come up with a question based on an observation. For example, you might ask “Does the amount of nitrogen in the soil in my garden have an impact on the number of tomatoes on the vine?”. You would then develop a testable hypothesis statement. For example, “I hypothesize that the number of tomatoes in my garden will be low when the content of nitrogen in the soil is low.”

Independent variable

You will set the value of this variable (for example, the amount of nitrogen in the soil) it can be set to different values (for example, nitrogen levels could be low, medium, and high).

Dependent variable

The value of the variable will vary depending the value of the independent variable (for example, the number of tomatoes on the vine will be high when the amount of nitrogen is medium, but the number of tomatoes on the vine will be low when the amount of nitrogen is low and high). The value of this variable is the main experimental result. As part of a hypothesis statement, you would state how the independent variable will impact the dependent variable.

Control variable

You will set these values so that they do not change. By keeping these variables constant, you assure that they do not impact either the independent variable or the dependent variable (for example, if you set up three different test gardens for low, medium and high nitrogen soil levels, you will want to make sure that all three gardens receive the same amount of water and sunlight. In this case, water and sunlight would be the variables that you control.).

Experimental results

Experimental results can be either qualitative or quantitative. In the example above, the experimental result is quantitative because you can count the number of tomatoes; that is, you can quantify the result. If, for example, we defined the dependent variable as the appearance of blotches on the tomatoes then this could be regarded as a qualitative result because we are not quantifying the number of blotches nor the number of tomatoes with blotches. We are simply checking for the presence of blotches. Essentially, we are evaluating the quality of the result.

Biological Molecules

All matter is made of atoms; thus, living beings are also made of atoms and we speak of the chemistry of life. An examination of the periodic table of elements reminds us that chemical elements in certain groups on the left side of the periodic table interact with certain other elements on the right side of the periodic table; for example, sodium chloride NaCl (salt).

Interaction of the elements that form the basis of living organisms is also important. Biological molecules form the basis for the organelles, cells, tissues and organs and interact with elements and other biological molecules through arrangements of elements called functional groups. See the image below of a biomolecule with representative amino and carboxyl functional groups. Note that “R” represents a group of atoms attached to the functional groups; the R group is referred to as a “side chain.”

Sugars (saccharides) have hydroxyl functional groups and aldehyde functional groups. These aldehyde group of saccharides interacts with chemicals in a test solution called Benedict reagent. This test results in a change in color when a specific kind of sugar (called a reducing sugar) is present. Monosaccharides, such as glucose and fructose, are reducing sugars.

Proteins are composed of polymers of amino acids called peptides. There can be many amine/amino functional groups in proteins. These groups interact with chemicals in a test solution called Biuret Test reagent. Note that some peptides function as long-strand molecules rather than as proteins. The amino groups in long strands of peptides can also interact with chemicals in the Biuret Test solution.

Nutritionally speaking, we categorize the macromolecules as carbohydrates (sugars), lipids (fats), and proteins.

Note: Benedict and Biuret testing solutions are mentioned above only as examples. You will in fact use entirely different testing solutions for your lab work.

Orientation to the Biomolecules Lab Activities

Procedure I Overview

Group 1: Known Sample Solutions – In this procedure you will observe the reaction (color change) when different test solutions are added to a set of known sample solutions. This information will be used in the next procedure to determine the types of biomolecules present in a set of unknown sample solutions.

Procedure II Overview

Group 2: Unknown Sample Solutions – In this procedure you will observe the reaction (color change) when different test solutions are added to a set of unknown sample solutions. Using information from the previous procedure you will be able to identify the type of biomolecule present in each unknown sample solution.

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