In the summer of 2003, NASA’s Jet Propulsion Laboratory launched two Mars Exploration Rovers - Spirit and Opportunity - towards Mars. They landed on January 3rd and 4th, 2004. Their primary scientific goal was to study the geology of Mars and search for signs of water. Although they were expected to last only 3 months, they have been vigorously sending back data for over 2 years and are still going strong! In this activity, students receive simulated Martian soils and are given the task of designing 3 tests to determine whether the soil sample contains something alive or something that was once alive. They may use any of the tools from the previous lessons – agar plates, tests for organic molecules, microscopes, or something of their own design. This assignment allows students an opportunity to demonstrate what they have learned throughout the unit, both about scientific experimentation and about the special characteristics of living things.
Can describe the necessary characteristics of life.
Can categorize objects as alive or not alive using self-generated data.
Can demonstrate that all living things will grow and reproduce when provided with the proper nutrients and environmental conditions.
Can demonstrate that living things are made of organic molecules.
Can test for the presence of protein, glucose and starch.
Can design an experiment.
Can make observations and keep track of data over several days.
Can interpret the results of an experiment.
10 min introduction
20-30 min design experiments
35-50 min conduct experiments (some tests may need to be left overnight)
20-30 min discuss experiments
Groups of 2-3 students
For all tests:
For soil samples, enough for a class of 30 students in teams of 3:
For nutrient milkshake:
For agar plates (see Life Trap activity for ordering information):
For organic molecules tests (see Testing for Life activity for ordering information):
For microscope test:
Optional for introduction:
Mars, Blueberries, and Hematite
The Mars Exploration Rover mission provides the inspiration for exciting science experiences. These two rovers represent incredible feats of engineering and have contributed vast piles of data for geology and astrobiology research.
This lesson is built around the discovery of Martian “blueberries” by the rover Opportunity in Meridiani Planum. The blueberries aren’t really blue – they’re actually grey – nor are they the size of blueberries – they are only around 3 millimeters in diameter. When they were first observed scattered across the floor of Meridiani Planum, their composition was an enticing mystery.
What are they? Their uniformity and symmetrical shape calls to mind the bacterial and fungal colonies grown on agar plates. Could they once have been living things, now frozen or fossilized on the surface of Mars? What about the 3 fused berries in the picture? Does this capture the process by which berries reproduce? That is the question posed to students in this activity, however, this is not a theory supported by scientists. Scientists guessed that the blueberries were concretions, formed when water rich in minerals permeates into porous rock then evaporates, leaving behind the hardened minerals in the spaces. Although originally buried within the rock, as the surrounding rock weathered away, the concretions were freed and left to roll around on the Martian surface.
For several long weeks, the blueberries were too small and scattered to be analyzed accurately with Opportunity’s scientific instruments. Thus the scientists’ theory could not be confirmed. Finally the rover reached a spot nicknamed the “Berry Bowl”. There, enough blueberries had collected in one place for the rover to use its Mössbauer, thermal emission, and alpha particle X-ray spectrometers to decipher its chemical make-up. By comparing the berry cluster in the Berry Bowl with a berry-free patch nearby, scientists were able to determine that the blueberries are composed of hematite (or haematite).
Hematite is the mineral form of iron oxide (rust). It is very common on Earth and is generally found in places where there has been standing water or mineral hot springs. However, it may also be formed volcanically. So, does the hematite blueberries on Mars indicate the former presence of water or were the blueberries formed volcanically? The presence of fused blueberries, like the triplet berry near the center of the image strongly argues that these blueberries were formed through the action of liquid water. Volcanically formed beads are unlikely to fuse along a line in this fashion.
More information on the Mars Exploration Rover mission is available on the NASA/JPL website and specific links of interest to this lesson are provided in the Sources section.
Tips for Teachers
Be aware of several tips as you embark on this open-ended experiment.
The yeast will remain active when added to the nutrient milkshake for a few hours until they run out of nutrients to sustain their growth. Adding more milkshake will reinvigorate the culture.
For students to grow yeast on agar plates, the nutrient agar must include sugars for the yeast to digest. This differs from the agar plates described in the Life Trap activity in which no sugar was required. In addition, it is best to dissolve the yeast-soil sample in water first (approximately 1 part yeast-soil to 2 parts water) and seed the plates with a Q tip dipped in the solution. Dry yeast get too little moisture from the plates alone to grow effectively.
To test for organic molecules, it is important to dissolve the yeast-soil sample in water first (approximately 1 part yeast-soil to 2 parts water). Only the protein test will yield a positive result. If you want to increase the rate of positive results, add 2 tablespoons of flour to the yeast-soil mixture. This will make the starch test give a positive result as well without interfering with any of the other tests the students might conduct.
Students need a thorough understanding of the characteristics of life and must be equipped with several means of testing for life such as growing microbes on agar plates or nutrient-rich solutions, testing for organic molecules, observing cells under the microscope, etc. See the Life Trap, Testing for Life, and Seeing Cells activities.
For soil samples:
For nutrient milkshake: combine 500 ml distilled water, 85 g table sugar, and 85 g all purpose white flour in a 1 liter bottle or flask.
For agar plates: see Life Trap activity for directions on how to mix nutrient agar and pour plates.
For organic molecules tests: see Testing for Life activity for directions on how to set up test stations.
This lesson was inspired by a workshop by Steve Ribisi of the University of Massachusetts and Mission 10 from the Life in the Universe curriculum, published by the SETI Institute.
To learn more about the Mars Rovers, go to the NASA/JPL website. The following are some of the highlights from this site that may be used in conjunction with this lesson:
To learn more about blueberries and hematite, see:
5. Organisms in ecosystems exchange energy and nutrients among themselves and with the environment. As a basis for understanding this concept:
e. Students know the number and types of organisms an ecosystem can support depends on the resources available and on abiotic factors, such as quantities of light and water, a range of temperatures, and soil composition.
1. All living organisms are composed of cells, from just one to many trillions, whose details usually are visible only through a microscope.
Structure and Function in Living Systems
5. The anatomy and physiology of plants and animals illustrate the complementary nature of structure and function. As a basis for understanding this concept:
a. Students know plants and animals have levels of organization for structure and function, including cells, tissues, organs, organ systems, and the whole organism.
Chemistry of Living Systems (Life Sciences)
6. Principles of chemistry underlie the functioning of biological systems. As a basis for understanding this concept:
a. Students know that carbon, because of its ability to combine in many ways with itself and other elements, has a central role in the chemistry of living organisms.
b. Students know that living organisms are made of molecules consisting largely of carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur.
c. Students know that living organisms have many different kinds of molecules, including small ones, such as water and salt, and very large ones, such as carbohydrates, fats, proteins, and DNA.
Grades 9-12 Biology
1. The fundamental life processes of plants and animals depend on a variety of chemical reactions that occur in specialized areas of the organism's cells. As a basis for understanding this concept:
a. Students know cells are enclosed within semipermeable membranes that regulate their interaction with their surroundings.
b. Students know enzymes are proteins that catalyze biochemical reactions without altering the reaction equilibrium and the activities of enzymes depend on the temperature, ionic conditions, and the pH of the surroundings.
h. Students know most macromolecules (polysaccharides, nucleic acids, proteins, lipids) in cells and organisms are synthesized from a small collection of simple precursors.
Grades 9-12 Chemistry
Organic Chemistry and Biochemistry
10. The bonding characteristics of carbon allow the formation of many different organic molecules of varied sizes, shapes, and chemical properties and provide the biochemical basis of life. As a basis for understanding this concept:
a. Students know large molecules (polymers), such as proteins, nucleic acids, and starch, are formed by repetitive combinations of simple subunits.
b. Students know the bonding characteristics of carbon that result in the formation of a large variety of structures ranging from simple hydrocarbons to complex polymers and biological molecules.
c. Students know amino acids are the building blocks of proteins.
Investigation and Experimentation
7. Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students should develop their own questions and perform investigations. Students will:
a. Select and use appropriate tools and technology (including calculators, computers, balances, spring scales, microscopes, and binoculars) to perform tests, collect data, and display data.
e. Communicate the steps and results from an investigation in written reports and oral presentations.