Students will be able to:
- build a simple representation of a coral polyp, and
- explain why corals are animals, rather than plants.
"Close-up of Coral Polyps" © 2009 Mark Yokohama
By building an edible coral polyp, students will learn the anatomy of coral and be able to explain why corals are animals, rather than plants.
|Science & Engineering Practices||Disciplinary Core Ideas||Crosscutting Concepts|
|Science & Engineering Practices||Constructing explanations.
Use evidence (e.g., measurements, observations, patterns) to construct or support an explanation.
||Disciplinary Core Ideas||4-LS1.A: Structure and Function.
Plants and animals have both internal and external structures that serve various functions in growth, survival, behavior, and reproduction.
Students will be able to:
hard coral: marine animal that produces a hard, calcium carbonate skeleton and grows into coral reefs
coral polyp: a marine animal with a body shaped like a cylinder and tentacles around a central mouth
algae: a general term for microscopic or larger aquatic plant-like organisms. They differ from trees and bushes because they don't have true roots, stems, and leaves.
zooxanthellae: tiny algae that sometimes live inside other organisms such as coral
tentacles: a flexible body part that is used for feeding, grasping, or moving
Teacher Tip: Students are often split in their ideas about this question. Some students might firmly believe a coral is a plant or an animal, and some students might be totally unsure. That's OK! Be sure to have a brief discussion to elicit students' reasoning and explanations about their ideas.
Teacher Tip: In this portion of the lesson, you will be drawing the coral polyp anatomy on the board while your students build their edible polyp. The TEACHER GUIDE shows what to draw on the board while students build their polyp. Before starting the hands-on building, be sure to set expectations so students do not consume any of their building materials. You can reassure students that they will get a chance to consume their coral polyps at the end of the lesson.
NGSS SCIENCE AND ENGINEERING PRACTICES CONNECTION: This portion of the lesson connects to the Practice of Constructing Explanations because students are asked to explain why they think coral is a plant, animal, or something else. Students' explanations should come from the observations they made while building the representation of a coral polyp, and from the plant vs. animal brainstorm in Part 1.
Discuss students' lingering questions about corals and coral polyps.
Corals are animals that belong to the phylum Cnidaria, which contains sea anemones, jellyfish, hydra, and corals. The name "Cnidaria" comes from the Greek word "cnidos" which means stinging nettle. Cnidarians are radially symmetrical (symmetrical around a central axis) with an opening at one end that is surrounded by tentacles. The tentacles have specialized stinging structures called nematocysts that are used for protection and to capture prey. The tentacles bring food into the animal's one opening, which is used both to take in food and to expel waste materials. The coral animal, made up of its tube-shaped body, its tentacles, and its mouth, is called a coral polyp.
There are two main types of corals: hard corals and soft corals. Hard corals are classified within the subclass Hexacorallia because their tentacles are arranged around the mouth in multiples of six (hexa = six). They are called hard corals because they extract calcium and carbon from the ocean water and deposit a hard calcium carbonate skeleton that surrounds the lower portion of the body. Coral polyps fuse their skeletons together and form large coral colonies. These fused polyps are the basis for coral reefs. Coral polyps extend their tentacles from their skeleton to feed and withdraw into the skeleton for protection. Thus, the appearance of a coral colony can look very different depending on whether the polyps are extended or not. When hard coral polyps die, the calcium carbonate skeleton remains intact. You can often find pieces of white coral, the remains of former coral colonies, washed up on tropical beaches.
Soft corals are classified within the subclass Octocorallia because their tentacles are arranged around the mouth in multiples of eight (octo = eight). Soft corals do not produce a hard external calcium carbonate skeleton and therefore do not contribute significantly to the building of reefs.
Hard corals and some soft corals contain zooxanthellae within their tissue. Zooxanthellae are microscopic marine algae, some of which are free living and some of which live inside the fleshy tissue of corals and other marine organisms. Zooxanthellae that live inside corals have a mutually beneficial symbiotic relationship with their host. This means that both the coral and the alga benefit from the relationship. The zooxanthellae photosynthesize from within their coral host and produce sugars that provide nutrition to both the zooxanthellae and the coral. In return, the coral provides protection and assists the growth of the zooxanthellae by passing on some of its waste, which the zooxanthellae use as a nutrient source. Because zooxanthellae need sunlight to perform photosynthesis, they are the reason why corals need sunshine to survive. The colorful zooxanthellae also contribute to the coral animal's bright color.
Adapted from Ayres, R. California Academy of Sciences. Coral Polyp Party. California Academy of Sciences' Educator Resource Materials. (2007).
Alastair Fothergill (Director). (2002). The Blue Planet: Coral Reefs [Documentary]. Britain: BBC Video.
Coral Symbiosis: Coral Polyp and Zooxanthellae. University of California Museum of Paleontology, Taxon Lift. Introduction to Cnidaria. Retrieved April 28, 2008 from http://www.ucmp.berkeley.edu/help/taxaform.html
Castro, P. and Huber, M.E. 2013. Marine Biology, 9th Edition. New York, NY: McGraw-Hill
Image: "Close-up of Coral Polyps" by Mark Yokohama, licensed and modified under CC BY-NC 2.0; originally sourced from https://www.flickr.com/photos/theactionitems/3606129306