Students usually know that plants need water, light, and air, and sunlight to survive. This activity -- plus its multiple extensions -- helps students expand their knowledge of plants beyond the land and into the deep ocean environment. For example, many students may not be aware that although the plants they're familiar with are multi-celled, many plants are single-celled (e.g., algae). In fact, half the oxygen that we breathe is produced by phytoplankton, single-celled plants that are found throughout the world's oceans; these tiny "critters" travel about 30 - 100 feet per day, the equivalent of a 5-foot tall human walking 2000 miles a day!
As an introduction, discuss as a class the parts of a land-based plant and what "job" these parts have; for example, the leaves are where photosynthesis takes place; the stem or trunk provide vertical support; the roots hold the plant in place and take in nutrients. Such a plant is a multi-cellular organism and each "job" is undertaken by a different type of cell: some cells have chlorophyll and can convert light energy into chemical energy, others hold the plant upright, etc.
In textbooks, the typical representation of a "plant cell" is really a leaf cell because it contains chlorophyll (<<). Interestingly, it is even more like a phytoplankton cell, because it performs the "jobs" of a multicelluar plant within one cell! And although a single-celled plant may seem dull, phytoplankton come in many shapes and (small) sizes, some can swim, some are toxic, etc.
  • Plants need the same resources to live, whether they located on land or in the water
  • Marine phytoplankton are well-adapted to living in the deep ocean environment
  • Like land-based plants, phytoplankton are primary producers, converting carbon dioxide into oxygen
Paper, pencils (preferably colored pencils), "Shallow to deep water environments" diagram (click here for an example; students can also create their own). NOTE: Some "Extension Activities" have materials needs, as well.
  1. Help students construct a "Needs List" of resources that plants need to live (water, air, and sunlight). The teacher may have to guide students to list nutrients. Students will likely list soil and warmth. Discuss where plants might get these necessary "ingredients." (For elementary students, see "Extension Activity #1," below).
  2. If students want to learn more about plants' need for sunlight, try "Extension Activity #2," below.
  3. It is safe to assume that the students' "Needs List" will be based on the land-based plants with which they are most familiar. Repeat the "Needs List," but ask them to do it for plants that live in water. Most students will base their answers on seaweeds or other plants that live in nearshore or freshwater environments. Is the "Needs List" identical to their previous one?
  4. Using a "shallow to deep water environments" diagram, ask students to brainstorm about the types of plants that live in shallow water. For these plants, have the students identify where (a) the soil is, (b) the sun is, (c) the air is, (d) they get water from.
  5. You may want to mention the water lily, which has soil-bound roots and its leaf rests on top of the water. Why is a water lily designed this way? Do all marine plants have roots in the bottom and leaves on top of the water?
  6. Shift your discussion to how plants survive in deeper water. Have students identify how deep ocean plants fulfill their needs. Like land plants, deep ocean plants take in carbon dioxide from the atmosphere and release oxygen; but where does the air come from? (Dissolved in seawater.) Without soil-bound roots, how do they take in phosphates and other nutrients? (Diffusion.) Where is sunlight found in ocean waters? (Upper ocean waters: called the "photic zone.")
  7. If students have difficulty understanding that there is dissolved "air" in water, try "Extension Activity #3," below.
  8. If students aren't convinced that some plants don't need soil, try "Extension Activity #4," below.
  9. Ask the students, "Now that you're familiar with the resources available for deep ocean plants, imagine being a phytoplankton. What type of physical adaptations and/or behaviors would you adpat to survive?"
  10. An important aspect of survival for any species is reproduction. Some plants grow fruit; the fruit is the plant part that holds the seeds. But do all plants grow from seeds? If not, might other plants reproduce? Given that phytoplankton are single-celled organisms, how do they reproduce? (Phytoplankton have the option of reproducing in many different ways. Many species can reproduce both sexually -- e.g., by exchanging genes -- or asexually -- e.g., cell division. Flexibility in reproductive styles allows phytoplankton species to thrive under a variety of circumstances.)
  1. For elementary students, ask them to draw a picture of a plant(s) within an environment. They can choose any environment (farm, garden, forest, field, etc.). In the picture, he or she will have to show where (a) the air is, (b) the water comes from, (c) the sun is, and (d) the soil is.
  2. How do plants get the light they need? Land-based plants bend their stems to get light. To demonstrate this, find a dark corner of the classroom (or create one) and suspend a plant that is NOT considered to be a "hanging plant." Position a strong light source UNDER the hanger. Over time, the plant will grow downward to reach the light source. (Please be careful about leaving the light source on while unattended.). Alternatively, take two identical plants, water them equally and feed them equal amounts of Miracle-Gro (i.e., nutients). Keep one in a well-lit window and the other in a dark cupboard or closet. Compare their growth over time.
  3. Invite discuss about how oceanic plants get oxygen from seawater; begin by asking students to consider how fish breathe: they pass water through their gills and remove the dissolved oxygen. This concept is well demonstrated in the "Observing Dissolved Air in Water" activity.
  4. Plants in the deep ocean do not have roots in soil; but do all plants need soil? Many students will initially think that the answer is "yes." To demonstrate otherwise, place some radish or bean seeds on a damp sponge or paper towel in a plastic zipper bag. Within 48 hours, the seeds will germinate and sprout, proving that not all plants need soil. Are there other plants that don't need soil?
Bigelow Laboratory for Ocean Sciences, Copyright 2000