Where Does the Eelgrass Go?

Build a model of matter moving through a shoreline community.

Investigate the Shore

Read the passage. Use its evidence to answer the questions. In a matter model, an arrow points from the source of matter to where that matter goes.

The Wrack Pile at Shellstep Shore

At Shellstep Shore, waves leave piles of dead eelgrass beside rocky tide pools. These piles are called wrack. A science club studies the wrack without collecting live animals. Nearby, living eelgrass grows rooted in wet sand under shallow seawater. Unlike seaweed, eelgrass is a flowering plant.

The club's field guide explains that eelgrass takes in water and carbon dioxide dissolved in seawater. Carbon dioxide can move between air and seawater. Water and carbon dioxide provide most of the matter used to build new eelgrass. Roots also take in small amounts of dissolved minerals from wet sand. Sunlight supplies energy for growth, but sunlight is not matter.

During several visits, students watch shore hoppers nibble dead eelgrass. These small animals shelter inside the damp piles. Sandpipers search the piles and swallow shore hoppers. Some matter from an animal's food becomes part of its growing body. Some leaves its body as waste. Animals also release carbon dioxide into their surroundings.

The students find fungal threads on dead eelgrass. A scientist's close-up observations show bacteria breaking down shore-hopper waste. Fungi and bacteria are decomposers. They can break down dead plants, dead animals, and animal waste. Some matter becomes part of the decomposers' bodies. As decomposers work, they also release carbon dioxide and dissolved minerals into their surroundings. Tides move water and dissolved materials between the wrack, tide pools, and eelgrass beds.

To observe changes over time, the club puts 20 grams of air-dried dead eelgrass in a mesh pouch. The pouch stays at one marked, damp location for four weeks. Its mesh keeps shore hoppers out but allows seawater, microbes, dissolved materials, and tiny plant fragments through. Students record fungal threads growing on the eelgrass. After four weeks, they air-dry the remaining eelgrass pieces using the same drying method. The pieces have a mass of 12 grams. The students measured the dry eelgrass pieces, not everything that passed through the pouch or grew inside it.

For their final model, students prepare labels for living eelgrass, dead eelgrass, shore hoppers, sandpipers, decomposers, and the nonliving surroundings. They must decide which arrows to draw, how to label them, and whether their model leaves any matter pathways out.

A model shows dead eelgrass → shore hopper. What should this arrow mean?

A. The hopper gives matter to the dead eelgrass.
B. The hopper takes in matter by eating dead eelgrass.
C. The dead eelgrass becomes a whole shore hopper.
D. The dead eelgrass gets energy from the hopper.

Select the TWO arrows that show matter entering an animal's body through feeding.

Seawater → living eelgrassDead eelgrass → shore hopperShore-hopper waste → bacteriaShore hopper → sandpiperLiving eelgrass → dead eelgrass

A new eelgrass leaf grows. Which pair supplies most of the matter used to build it?

A. Sunlight and dissolved minerals
B. Wet sand and sunlight
C. Animal waste and grains of sand
D. Water and dissolved carbon dioxide

Sort each arrow by what it transfers.

Sun → living eelgrass: sunlight for growthWet sand → eelgrass roots: dissolved mineralsShore hopper → sandpiper: foodAir → seawater: carbon dioxide

Transfers matter	Transfers energy from sunlight

Test the Pathways

Use the feeding observations and pouch investigation to judge each idea.

A sandpiper does not eat eelgrass. How could matter that was once in eelgrass become part of the bird's body?

A. A hopper eats eelgrass, and the bird eats the hopper.
B. Eelgrass releases sunlight, and the bird absorbs it.
C. A bird stands on eelgrass, and matter enters its feet.
D. Eelgrass breaks into sand, and the bird becomes heavier.

A student draws arrows into decomposers only from dead plants. Which change would make the model more complete?

A. Remove dead plants and show living plants instead.
B. Replace dead plants with sunlight entering decomposers.
C. Add arrows from dead animals and animal waste.
D. Reverse the arrow so decomposers make whole dead plants.

Select the TWO observations that support including pathways into decomposers from both dead plant material and animal waste.

Sandpipers swallowed shore hoppers.Fungal threads grew on dead eelgrass.Shore hoppers sheltered inside damp wrack.Bacteria broke down shore-hopper waste.Living eelgrass stayed rooted in wet sand.

Suppose decomposers become much less active while other conditions stay the same. Which change would the model predict?

A. Less dead material builds up, and minerals return faster.
B. More dead material builds up, and minerals return more slowly.
C. More dead material builds up, and minerals return faster.
D. Less dead material builds up, and minerals return more slowly.

The dry eelgrass pieces in the pouch decreased from 20 grams to 12 grams. Which conclusion is supported?

A. The 8 grams became part of shore hoppers in the pouch.
B. The 8 grams stopped existing as the eelgrass decayed.
C. The 8 grams became new eelgrass growing inside the pouch.
D. The 8 grams could be in materials the students did not weigh.

Complete the Matter Model

Think about more than a single feeding chain. Include matter moving into living things and back into the nonliving surroundings.

10.

A model ends with dead eelgrass → decomposers. Which added arrow would show matter returning to the nonliving environment?

A. Decomposers → sunlight, labeled 'make light'
B. Decomposers → sandpipers, labeled 'make whole birds'
C. Decomposers → seawater, labeled 'release dissolved minerals'
D. Seawater → decomposers, labeled 'take in water'

11.

A model sends all matter eaten by a shore hopper straight to a sandpiper. Which revision best represents another path described in the passage?

A. Add a branch from the hopper through waste to decomposers.
B. Add a branch from the hopper through sunlight to eelgrass.
C. Add a branch from the hopper directly to grains of sand.
D. Add a branch from the hopper through roots into sandpipers.

12.

Draw a matter model using these six labels: living eelgrass; dead eelgrass; shore hoppers; sandpipers; decomposers; seawater and wet sand.
Draw arrowheads to show where matter goes. Label arrows with a process or material. Include feeding, two different sources of matter entering decomposers, and a path from decomposers back to living eelgrass through the nonliving environment.

13.

Could some matter from the old wrack become part of a new eelgrass leaf? State a claim and explain a possible route. Use at least two details from the passage as evidence, including the roles of decomposers and the nonliving environment.