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    Puzzling Phenomenon or Anchoring Event |  Essential Question |  Gapless Explanation |  Alternative Conceptions

    Puzzling Phenomenon or Anchoring Event

    Two minute video showing life cycle and feeding habits of Leafy Sea Dragon.

    Video

    Also available in streaming versions on YouTube and on Vimeo.


    Essential Question

    • Where Do Organisms Live?

    • What Happens to Organisms in Changing Environments? 

    Related/sub-questions: 

    • How Does Living in a Group Help Some Animals Survive?

    • Why Do Offspring Look Similar to Their Parents?

    • How Are Traits Affected by Both Inheritance and the Environment?

    • Why Do Some Members of a Species Survive and Not Others?


    Gapless Explanation

    Big Ideas:

    • Organisms have different inherited traits.
    • The environment can affect the traits that an organism develops.

    Gapless Explanation of Leafy Sea Dragon (Adult Level):

    The video of the Leafy Sea Dragon shows various stages of the life of the organism.  This organism was chosen because its strange appearance is often appealing to children.  Their appearance is a great example of how they have adapted over generations to resemble the plants in which they live.  The advantage is that they are harder for predators to find.

    Leafy sea dragons are exquisitely camouflaged fish. Belonging to the same family as seahorses and pipefish (Syngnathidae), they resemble these with their elongated snout and bony-plated body. Sea dragons are seen either solitarily or in pairs, they are slow-moving and rely on their elegant camouflage to provide protection from predators. In common with seahorses, it is the male sea dragon that carries the developing eggs.

    Much of the video shows various stages in their life.  An early close-up shows the eggs on the body of one of the organisms.  Soon after, we see very young ones swimming in a tank.  Towards the end of the video there are a few shots of the Leafy Sea Dragon feeding – they go by fast.  The Dragon makes a quick sucking motion that pulls the food (often small fish) into their mouths.

    During Spring or early Summer, the male and female Sea dragons move to shallower water and pair up. The female Sea dragon produces up to 300 bright orange - red eggs in her lower abdominal cavity while the male prepares to receive the eggs.

    The lower part of the male Sea dragon's tail swells and becomes wrinkled. He then develops about 120 egg cups or small pits on the tail.

    The eggs are then transferred to the male and fertilized. The male incubates the eggs for about 4 - 6 weeks. The eggs often become coated in algae and scientists believe this helps to hide the them from predators.

    When the babies hatch, they are exact miniature replicas of their parents and they emerge wriggling and squirming from the egg tail first. The young Sea dragons hatch intermittently over several days to help with dispersal and to ensure there is sufficient food available for all.

    At birth, the young Sea dragons are about 20 millimeters long and they are a different color (silver and black) to the adults. Young Sea dragons are independent as soon as they leave their father's tail.

    For the first 2 - 3 days, the young silver and black Sea dragons are sustained by their yolk sac and after this, they hunt small zooplankton such as copepods and rotifers until they are large enough to hunt juvenile mysids. The first few weeks of life are the most perilous for the young sea dragons as they are prey for larger fish. This is when they begin change color.

    Sea dragons grow to about 20 centimeters in their first year and have reached their mature size after 2 years. During each breeding season, a male Sea dragon is capable of hatching more than one batch of eggs. It is not known how long Sea dragons live for in the wild but in captivity they live for about 5 - 7 years.

    Gapless Explanation of Leafy Sea Dragons (Elementary Level):

    Leafy Sea Dragons are fish.  They move very slowly and heavily rely on camouflage for their survival. Their bodies seem to smoothly glide through aquatic plants like kelp and seaweed.

    These fishes use their dorsal and pectoral fins to steer and move.

    Leafy sea dragons use their small mouth and long snout to suck up their prey. Leafy Sea dragons mostly feed on small shrimps, zooplanktons, larval fish, and some other small crustaceans like amphipods.

    Leafy sea dragons have developed some special characteristics that enable them to defend themselves against their predators as well as adapt well to their surroundings. Here are a few of their adaptive features.

    • Leafy sea dragons have protrusions all over their body which they use for camouflage. The small fins of these fishes are nearly transparent and when the leafy sea dragons sway them from side to side to move around, their fins give them the appearance of a floating seaweed.
    • They also have numerous sharp spines along the sides of their bodies which they use to defend themselves against attacking predators.
    • The eyes of leafy sea dragons are capable of moving independently; this gives them the ability to look at two completely different directions at the same time.

    Standards

    The performance expectations in third grade help students formulate answers to questions such as: “How do organisms vary in their traits? What happens to organisms when their environment changes?”

    Students are expected to develop an understanding of the similarities and differences of organisms’ life cycles. An understanding that organisms have different inherited traits, and that the environment can also affect the traits that an organism develops, is acquired by students at this level. In addition, students are able to construct an explanation using evidence for how the variations in characteristics among individuals of the same species may provide advantages in surviving, finding mates, and reproducing. Third graders are expected to develop an understanding of the idea that when the environment changes some organisms survive and reproduce, some move to new locations, some move into the transformed environment, and some die.

    3-LS1-1 From Molecules to Organisms: Structures and Processes
    Students who demonstrate understanding can develop models to describe that organisms have unique and diverse life cycles but all have in common birth, growth, reproduction, and death.
    Clarification Statement: Changes organisms go through during their life form a pattern.
    Assessment Boundary: Assessment of plant life cycles is limited to those of flowering plants. Assessment does not include details of human reproduction.

    3-LS3-1 Heredity: Inheritance and Variation of Traits
    Students who demonstrate understanding can analyze and interpret data to provide evidence that plants and animals have traits inherited from parents and that variation of these traits exists in a group of similar organisms.
    Clarification Statement: Patterns are the similarities and differences in traits shared between offspring and their parents, or among siblings. Emphasis is on organisms other than humans.
    Assessment Boundary: Assessment does not include genetic mechanisms of inheritance and prediction of traits. Assessment is limited to non-human examples.

    3-LS3-2 Heredity: Inheritance and Variation of Traits
    Students who demonstrate understanding can use evidence to support the explanation that traits can be influenced by the environment.
    Clarification Statement: Examples of the environment affecting a trait could include normally tall plants grown with insufficient water are stunted; and, a pet dog that is given too much food and little exercise may become overweight. 

    An expanded discussion of the learning goals is available on the web at: http://bit.ly/LS3-Structures-of-Life


    Alternative Conceptions

    Elementary and middle school students typically use criteria such as “movement”, “breath”, “reproduction”, and “death” to decide whether things are alive. Thus, some believe fire, clouds, and sun are alive, but others think plants, and certain animals are non-living. Upper elementary school students may not believe food is a scarce resource in an ecosystems, thinking that organisms can change their food at will according to the availability of particular sources. Students of all ages think that some populations of organisms are numerous in order to fulfill a demand for food by another population.

    See http://bit.ly/LS3-AlternativeConceptions for a more detailed analysis of Children’s Ideas about Life, Life Cycles and Shape and Structure of Organisms.