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looking for life

Looking for Life

Overview

Materials

A pair of objects, one living (such as an insect or plant) and one non-living (any inanimate object, preferably one not made from once-living material such as wood or leather)

An outdoor area to investigate, or images of a variety of living and nonliving things

Criteria for Life Log Charts – download PDF

3 small containers per group of 3 students (clear beakers or cups, or 3-oz. paper dixie cups)

Clean play sand, 150 ml per group of 3 students (50 ml for each of 3 containers)

Sugar, 15 ml per group of 3 students (5 ml will be added to each container)

Instant active dry yeast, 5 ml per group of 3 students (added to container B)

1 fizzing antacid tablet crushed to a fine powder per group of 3 students (added to container C)

Warm tap water (enough to cover each soil sample)

Cup for holding the warm tap water ( 1 per group of 3 students)

Paper towels in case of spills

Management

  • Prior to teaching the lesson, locate an outdoor area that contains a variety of living and nonliving things for students to investigate. If an outdoor area is not available, gather images of a variety of living and nonliving things.
  • The day ahead of teaching the lesson, mix a batch of each soil sample (enough for the class) and store in airtight containers. Humidity will inactivate the yeast and cause the effervescent tablets to lose their fizz.
  • Right before the lesson p our samples into jars for each group
  • Be sure the water is not too hot. Yeast do well with warm tap water (about 50 C).

Background

  • Locomotion
  • Metabolic processes that show chemical exchanges, which may be detected in some sort of respiration, or exchange of gases or solid materials
  • Some type of reproduction, replication or cell division
  • Growth
  • Reaction to stimuli

Procedures

Part 1
  1. Ask students, “How do you know if something is alive?” and discuss the criteria students come up. Provide counterexamples as appropriate.

Example: Consider a bear and a chair— they both have legs, but one can move on its own and the other can’t; therefore, independent movement might be one characteristic that indicates life. Not every living organism needs legs or roots. But they do need a mode of locomotion or a way to get nutrients. Also, the bear breathes and the chair does not, another indication of life. Or consider a tree and a light pole. We know that a light pole cannot reproduce — it is made by humans — and we know that the tree makes seeds that may produce more trees. The tree also takes in nutrients and gives off gasses and grows. The light uses electricity and gives off light, but it is strictly an energy exchange and there is no growth or metabolic processes.

Part 2

  1. Just before class, prepare jars of soil samples for student groups of three to four students.
    • Place 50 ml of sand in each jar. (You will need 3 jars per team.)
    • Add 5 ml of sugar to each jar. Label one jar in each set of 3 “A” and set aside.
    • Add instant active dry yeast to the second jar in each set of 3 and label these jars “B.”
    • Add a powdered fizzing antacid tablet to the remaining jars. Label these jars “C.”
    • Give each group a set of three jars, a hand lens and Data Chart I.

  • Explain to the students that each team has been given a set of soil samples. No one knows if there is anything alive in them. The assignment is to make careful observations and check for indications of living material in the samples based on the fundamental criteria for life.
  • Ask students to observe all three samples for signs of life. They can smell and touch the samples, but not taste them. Encourage students to put a few grains on the circles on Data Chart 1 and observe them with a hand lens. Students should then record their data.
  • Give each group a cup of water. (Use hot tap water, about 50 C, for the best results. Do not kill the yeast.) Ask students to pour the water so that each sample is covered with water.
  • Repeat Step 2 and record the data on Data Chart II. Students should look for and record differences caused by adding water. After recording the first observations, have students go back and observe again. (After about 10 minutes, Sample B will show even more activity. Leave it for several hours or overnight and reproduction will be obvious.)
  • Discuss which samples showed indications of activity (Samples B and C). Does that activity mean there is life in Samples B and C and no life in Sample A? Are there other explanations for the activity in either B or C? (Note: Samples B and C exhibit a chemical reaction; Sample C activity stops; Sample B sustains long term activity; Sample A is a simple physical change in which sugar dissolves.)
  • Determine which sample(s) contain life by applying the fundamental criteria for life.
  • Tell students that Sample B contained yeast and Sample C contained an effervescent antacid tablet. Discuss how scientists could tell the difference between a nonliving chemical change (fizzy antacid) and a life process (yeast) which is also a chemical change.
  • Discuss which of the criteria for life would identify yeast as living and fizzy antacid as nonliving.
  • Discussion

    • Besides Mars, where else might there be life in our solar system?
    • Is it possible that there is life on a planet orbiting another star?
    • How do scientists look for life when they can’t visit another world themselves?
      Evidence of respiration, amino acids, etc.

    Assessment

    Extensions

    • Learn about astrobiology, the search for life on other worlds
    • “Exoplanets and the Search for Habitable Worlds” article and lesson
    • Learn about exoplanets, planets outside our solar system
    • Keep track of the current exoplanet discovery count
    • Download the Exoplanet Travel Bureau posters
    • Learn about exoplanet detection methods
    • Ask an astrobiologist
    • Life in the Extreme Activity Cards
    • Astrobiology Science Learning Activities for Afterschool

    Activity Details

    • Subjects:SCIENCE
    • Types:CLASSROOM ACTIVITY
    • Grade Levels:4 – 8
    • Primary Topic:ASTROBIOLOGY
    • Additional Topics:
      ENERGY
      LIFE SCIENCES
    • Time Required: 30 mins – 1 hr
    • Next Generation Science Standards (Website)

    Construct an argument that plants and animals have internal and external structures that function to support survival, growth, behavior, and reproduction

    Construct a scientific explanation based on evidence for how environmental and genetic factors influence the growth of organisms

    Conduct an investigation to provide evidence that living things are made of cells; either one cell or many different numbers and types of cells

    Construct and revise an explanation based on evidence for the cycling of matter and flow of energy in aerobic and anaerobic conditions

    Using the fundamental criteria for life, students examine simulated extraterrestrial soil samples for signs of life. ]]>