Ask students to get out a blank piece of paper, and imagine the Hudson River. Ask them to draw a map of all the things within that ecosystem, and all the things that contribute to keeping that ecosystem healthy. These maps are to guide the teacher in understanding student preconceptions and will be used again during the lesson. The teacher should move around the room during this time to view the students’ maps, in order to find out what students know and what type of information they are lacking. Most students have little knowledge of what actually lives in the river, although they will likely provide the visible organisms in big categories such as fish and birds.
Lay out a number of items at the front of the room that could be alive or not. You can vary these items depending on their availability; items such as Mexican jumping beans work well to pique a students’ interest. Have students make a list of the things they think are alive, those that aren’t, and those that were ‘once alive’. Then, they should get into groups and debate the placement of the items on their lists, attempting to convince the other students to change their minds. When students have discussed for a few minutes, they should be encouraged to come up with characteristics that can distinguish between something that is ‘alive’ and something that is not.
Bring the class back together and ask for their answers to the alive versus not-alive question, and see if the class can come to a consensus on which items are alive and which are not. This works well if you ask students to vote in groups; it is easier to count their answers to the alive/not alive. It is also interesting to ask the students to arrange the items on a continuum from alive to not alive.
Students should now have a sense of the complexity of life and of defining it! Encourage students to think about how things change when a flower is picked, or an animal hibernates, or a plant becomes dormant. Sometimes it is difficult to decide what is alive and what isn’t. Scientists have come up with a few traits that all living things seem to share: have cells, require the use of energy (metabolize), reproduce, evolve and adapt, respond to stimuli, and maintain homeostasis (maintain stable internal environment). Sometimes educators include growth and development as a characteristic, but this can also be included in evolving and adapting and responding to stimuli. Now that students know what types of things are alive, they should be able to add to their ecosystem diagrams. Review the terms biotic and abiotic.
Formative assessment: Ask students to name three living and three non-living things that are part of the Hudson River ecosystem. Pay attention to whether students are just providing generic terms or whether they can remember to include the smaller organisms (microbes and bacteria, fungi) and whether they can provide any specific species or just general terms.
Draw a cross-section of the Hudson River on the chalkboard. Pass out sticky notes to student pairs. Ask each student group to write down something that might be included in the Hudson River ecosystem on their sticky note, and come up to the board and place it in the appropriate area of the diagram (in the river, the air, the sediment, etc). Once all students have added their ecosystem components, remove the duplicates.
Now, use the “Journey down the Hudson” PowerPoint to give students a visual perspective of the river. While viewing the PowerPoint, you can ask students to answer questions on the "Journey Down the Hudson River Student Questions/Notes" worksheet and/or add to their personal drawings of the Hudson whenever they see something they missed.
At the beginning of the slide show are several slides that discuss the physical characteristics of the river. A good way to illustrate the differences between the upper and lower sections of the Hudson is to do the following activity:
1. Ask for three volunteers to come up to the front of the room. One volunteer will be Mt. Marcy, the start of the Hudson, a second will be in the middle at the Federal Dam at Troy, and the third will be the mouth of the Hudson in NYC.
2. Ask ‘Mt.Marcy’ to hold the string up very high, as this is the highest point in New York State at 5,344 feet and also the start of the headwaters of Lake Tear of the Clouds, the origins of the Hudson River.
3. Then, ask the New York City volunteer how high his/her end of the string should be; this may take the students a few minutes to realize that since New York City is at sea level, the string should be down on the ground.
4. Ask the volunteer at Troy how high his/her string should be, since Troy is almost in the middle of the length of the Hudson. Generally, students think that Troy is about 2500 feet high, and they want the volunteer to hold the string in between the heights of ‘Mt Marcy’ and ‘NYC’. Reveal that the Troy dam is only about 4 feet above sea level. This should help students understand the large physical differences between the upper and lower parts of the river.
5. Then have the rest of the class come up and stand along either side of the string between the Troy dam an NYC. Tell the students that because the Hudson is an estuary, it has special characteristics.
6. Instruct half of the students standing along the string that they are going to represent the Hudson’s tides. They will bend down, touch the ground, and say in a low voice “low tide” and then stand up, raise their arms overhead and say in a high voice “high tide,” and repeat.
7. The other half of the students along the string are going to represent the salty nature of the Hudson. They should make a mixing motion with their hands, as if they were using two hands to hold the spoon while mixing cookie dough. While making the mixing motion, they should repeat “Salt water/ Fresh water.”
8. Then tell both groups of students to “Go.”
9. After they’ve been salty, fresh, and tidal for a while, ask them why they think you instructed them to only stand below the Troy dam. The Hudson is only tidal up to the Troy dam. And in fact, the ‘salt front’ is usually much farther south in the Hudson, by the Tappanzee bridge. Yet in spring when there’s a lot of snow runoff, the salt front can be all the way down to NYC. In late summer, and particularly in drought conditions, the salt front can reach as far north as Newburgh and even Poughkeepsie (about ½-way in between the dam and NYC).
Finally, pass out another round of sticky notes to those students who would like to add items to the drawing on the board, and try to complete the diagram. Suggested inputs and outputs include: oxygen, sunlight, nitrogen, phosphorous, carbon, carbon dioxide, detritus, rain, plants, phyto/zooplankton, fish, birds, crustaceans, etc.
Formative Assessment: Ask students to describe three interactions between living and non-living things in the Hudson River ecosystem. Extra points if they can name ways that living things impact the non-living environment! (Examples: aquatic vegetation increases the level of dissolved oxygen in the water; filter feeders such as the zebra mussel increase the depth that sunlight reaches into the water.)
1. Supplement the ‘Alive versus not Alive’ activity by turning it into a lab experience using one of the ‘Is it Alive?’ labs. These explore the definition of ‘living’ using small objects and organisms (algae, human hair, etc). This online interactive activity from Stanford’s Virtual Urchin lab may be useful for you and your students as they calculate the size of microscopic organisms: http://stanford.io/14h5SWu
2. Ask students to pick another, preferably very local, ecosystem and create a diagram showing all of the inputs and outputs. They should be given time to do some research to complete this task. The “Hudson as an Ecosystem" PowerPoint provides additional information for students.
Students should be able to use their initial ecosystem diagrams that they created and update them with the information they learned during class. These diagrams can be used throughout the unit as they learn more about the types of things that are important within an ecosystem.
“Is it Alive?” lab sheet version 1 was written by Lecia Zulak, science teacher, FDR High School, Hyde Park, NY.
“Is it Alive?” lab sheet version 2 was written by Patricia Tomaseski, science teacher, Millbrook High School, Millbrook, NY.