6. Cell Energy - Bubbling Plants

Elodea nuttallii: Image courtesy of Christopher Fischer.Elodea nuttallii: Image courtesy of Christopher Fischer.Summary
Students often believe that only animals “breathe”, but all things exchange gases with their environment. It’s just that the process is not so obvious in plants. Elodea is a very common water plant that can be found in aquarium stores. As photosynthesis occurs, oxygen is produced as a by-product. Elodea releases bubbles of oxygen as it photosynthesizes. In fact, the number or volume of bubbles in a certain amount of time can be used as a rough measure of photosynthetic rate.

6. Cell Energy - Plant Pigments

Chlorophyll extractionChlorophyll extractionSummary
Chlorophyll is the pigment in plants that captures sunlight energy and uses it to drive photosynthesis. While chlorophyll does give plants their characteristic green color, chlorophyll actually comes in many colors and subtypes ranging from green to yellow to orange to red. In this experiment, students use paper chromatography to separate the many pigments from one another. First the pigments are extracted from the plants by simply crushing the plant cells open on the filter paper with the edge of a penny. When the filter paper is then immersed in rubbing alcohol, the pigments are carried upwards through capillary action. The smallest pigments travel more quickly and thus separate from the larger pigments that remain closer to the origin line.

6. Cell Energy (photosynthesis and respiration)

Here you will find a toolbox full of inquiry investigations on photosynthesis and respiration. Rather than the detailed lesson plans provided elsewhere at My Science Box, each experiment only contains a short background, materials, procedure, and going further section. It is up to you to decide which of the many experiments you wish to try with your students and how to sequence them. You will find everything from descriptions for how to extract chlorophyll, discover that plants “breathe”, recreate the experiments of Priestly and Ingenhousz, detect carbon dioxide production, and measure the rate of yeast respiration. None of these experiments require expensive equipment such as metabolism chambers or oxygen meters although those are great tools if you can afford them.

5. Slimy cells

To solidify students’ conceptualization of cells, students build a model of a cell in a ziplock bag using polyvinyl alcohol slime as cytoplasm. So far, students’ experience with cells has been 2 dimensional – diagrams and microscopic slides. The 3 dimensional nature of cells comes to life as students use everyday objects to represent the many parts of a cell. In addition, students can use this activity to develop a sense of scale, calculating how big a human would be if the ziplock bag cell model were really the size of a cheek cell.

4. Seeing Cells

The invisibly small world of the cell comes to life as students look at plant and animal cells through a microscope. Students create wet-mount slides of onion skin, elodea leaf, and human cheek cells. They learn some of the gross differences between plant and animal cells (cell walls are present in plant but not in animal cells), and even some of the differences between different plant cells (chloroplasts are found in the leaves but not in the roots). It is suggested that this lesson take place after students learn the parts of a cell and their functions. Resources for good cell diagrams are provided in the Sources section. This lesson may be used in conjunction with the Pond Water activity for students to get a sense of the diversity of microscopic life, both single celled and multi-celled.

Assessment - Life on Mars

Mars Exploration Rovers: This special-effects image combines a model of the Mars rover Opportunity and 46 photogrpahs that Opportunity took of "Burns cliffs" near the edge of "Endurance Crater". Image courtesy of NASA/JPL-Caltech/Cornell.Mars Exploration Rovers: This special-effects image combines a model of the Mars rover Opportunity and 46 photogrpahs that Opportunity took of "Burns cliffs" near the edge of "Endurance Crater". Image courtesy of NASA/JPL-Caltech/Cornell.

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.

Organic molecule
Biuret solution
Benedict’s solution

3. Testing for Life's Molecules

All known life is made out of a small group of chemical compounds called organic molecules. Common organic molecules include proteins, glucose, starch, lipids, and nucleic acids. This lesson plan asks students to conduct tests for proteins, glucose, and starch. At the beginning of the activity, they choose 3 items to test: one known to be “never alive”, one known to be “once was alive”, and one mystery item. In addition, each station includes a positive control. By the end of the experiment, students should be familiar with some of the major organic molecules and should recognize that living things, and substances derived from them, are made of organic molecules. In addition, this is a chance to bring in topic surrounding nutrition, health, and digestion. Since our bodies are made up of organic molecules, we need each of these molecules as nutrients in our food.

2. Life Traps

Life trapsLife trapsAs part of recognizing the characteristics of life that all organisms share, students grow microbes on nutrient agar plates. Students swipe surfaces with a sterile Q tip swab and seed plates resulting in a wide range of colorful and prolific bacteria and fungi colonies. Other plates may be simply opened to the air to catch life floating in the air. Through these experiences, students learn that all living things, even those so small and invisible as to be floating in the air, grow and reproduce when provided with the proper nutrients and water. Teachable moments abound since the “dirtiest places”, like the toilet rim, often result in the least bacterial growth while presumably “clean” places, like the surface of your skin, have the most. A fun extension of this activity (see the Going Further section) is to start a sourdough culture from wild yeast in the air and make sourdough bread.

1. Is it alive?

What does it mean to be alive? Is a cactus alive? Is a seed alive? Is the air we breathe alive? What are the necessary characteristics? To hook students into the question, they are introduced to “glue monsters” (sometimes known as “scooting glue”) and the class discusses whether the “monsters” are alive or not. Next, students are given cards with the names of various objects and asked to sort them into categories: alive, once was alive, never alive, and not sure. Finally, students create a list defining the characteristics of life – a set of characteristics that all living things share. The list is initially developed in pairs, then in larger groups of 4, and ultimately as a whole class. The final list is turned into a poster that can be referenced and modified throughout the remainder of the unit as students learn more about what it takes to be alive.

Physiology Box

Physiology is the study of living things – their structure, organization, and biochemistry. This unit gives students an opportunity to discover the fundamental characteristics of living things and explore some basic cell biology. Students begin with several activities culminating in the creation of a list of characteristics that all living things have in common – the characteristics of life list. From here, students learn to test for signs of life by growing microbes on agar plates, conducting biochemical tests, visualizing cells, and experimenting with photosynthesis and respiration. Finally, students learn about the organization plants and animals through dissection and the raising of plants and fish in the classroom. Throughout the unit, students return to the characteristics of life list, refining and revising their list as they learn new concepts. A planning guide for a voyage with the Marine Science Institute is included as a way for students to learn about the many forms of life in the San Francisco Bay.