Monday, April 30, 2018

Making Connections. Investigating Invertebrates - Sponges and Jellyfish

From 1990-1996 I worked on with the "100 Schools Project." It was California's implementation of the National Science Foundations grant to integrate science content in a new breed of courses. Monte Vista High School was a leader in curriculum development. I was the editor and primary author of a four textbook series. Titled "Making Connections...", it was published from 1996-2001 by the Grossmont Union High School District. The series is now out of print. 

More often than not over the coming months, I'll be reviving this labor of love. I hope you enjoy learning about science in the way I think makes the most sense. Minor editing has been done to the original text. Additions are in highlighted in this color. My titles for the section of the chapter are this color. Most of the diagrams were retrieved in full color from the Internet since the original books were two-colors only. Content in this series is from Volume 4: Making Connections - Integrating the Science of Energy.
Invertebrate organisms have something supporting their bodies besides bones or bony material. They range in complexity from simple multicellular organisms, like sponges, to animals with complex structures and functions, the crustaceans and arthropods.
Many scientists accept a classification system with five kingdoms.
          Kingdom Monera consists of bacteria and blue-green algae (also known as photosynthetic bacteria).
          Kingdom Protista includes algae and single-celled organisms (protozoa).
          Kingdom Fungi includes only the fungi.
          Kingdom Plantae consists of multicellular land and water plants.
          Kingdom Animalia is made up of all animals, both with and without vertebrae. Every living thing is classified in one of these kingdoms.

The purplish rectangles were added to highlight the content of this blog. The two colors in this volume are black and brownish-yellow. 
Week #1
It's Simple
The least complex invertebrate phylum is Porifera. Phylum Porifera includes the sponges. Sponges are multicellular animals. They have specialized cells. Sponges also have cells which remain unspecialized throughout the life of the animal.
The basic body plan of a sponge is very simple. It consists of a series of holes known as incurrent pores. Water enters the body of the sponge through these pores. Everything the sponge eats and breathes must be in the water that enters through the incurrent pores. The only way out of a sponge is through larger openings known as excurrent pores. Some of the specialized cells in the sponge make up the edges of the openings, others are involved in moving water through the sponge. Other specialized cells, known as spicules, make up the supporting "skeleton" of a sponge.
There are no cells used to move the sponge. Sponges do not move from the spot where they first attach. Animals living attached to a single location are called sessile, or non-moving
A Sponge. A typical sponge has all the parts labeled in this diagram. Note the lack of structures used for movement.

The non-specialized cells in the sponge are of extreme importance to the life of the animal. These amebocytes, as the cells are known, function in reproduction, repair of damaged parts, general growth, and in the protection of freshwater sponges from drying out. The amebocytes have the ability to "become" any type of cell needed by the sponge.
Amebocytes are of interest to scientists as well. If humans had "amebocyte-like" cells, people with heart or kidney problems might be able to grow new organs to replace the diseased or damaged ones. If a finger or arm was cut off in an accident, a new one might be grown from these unspecialized cells. Scientists want to find out why amebocytes do not become specialized until they are needed. Humans begin life as a single unspecialized cell. If some way could be discovered to keep some cells from specializing, a simple sponge might lead to a major breakthrough in human medicine some day.
You might use a sponge while showering. Because the spicules are made of hard material--spongin or a calcium/silicate product, they remove dead skin cells as you rub the sponge on your body. However, you will regret using the same sponge on your brand new Corvette. The spicules will scratch the expensive candy-apple red paint!
This Jelly Ain't For Sandwiches

Phylum Cnidaria (formally classified as Coelenterata) contains animals with two distinct cell layers. An ectoderm which makes up the outer covering of the animal and an endoderm which covers the inside. Between the two layers is a jelly-like material, mesoglea, which separates them. Examples of animals in this phylum include sea anemones, coral, and jellyfish. Jellyfish have a very thick layer mesoglea ("jelly"). That layer gives those animals their name.
The Two Cell Layers of Cnidarians. The endoderm contains cells used in the digestive process. Ectoderm cells include the stinging cells with their trigger hairs. A nerve network is embedded in the "jelly-like" mesoglea. Without the primitive nervous system, medusas would not be able to coordinate its swimming motion.
All cnidarians have tentacles which they use to bring captured food into their mouths. They capture food through the use of stinging cells in the ectoderm. The stinging cells act like tiny hypodermic needles. They inject a sharp point into the victim. Paralyzing poison is pumped into the hole. When the victim stops struggling, it is pulled through the mouth into the body cavity, the coelom, where it is digested.
The coelom is a bag-like body cavity with a single opening. Lining the inside of the coelom is the endoderm. The endoderm contains digestive cells which secrete enzymes to digest food. Undigested waste pieces exit the coelom through the same opening in which the food entered.
Cnidarians come in two styles. Some live their lives attached to one spot.   All sessile cnidarians are known as polyps. The polyp form of cnidarians includes sea anemones and corals. Other cnidarians are not permanently attached to a surface. These animals have the ability to swim through the water. Free-swimming cnidarians are called medusas. Medusas, like jellyfish, swim by pumping water out of the folds of their bodies—medusas are jet-propelled.

Polyp and Medusa. The two basic body plans of Cnidarians are shown here. Polyps are sessile. The medusa is free-swimming.   
Next Making Connections: Investigating Invertebrates. Worms: Flat, Round, and Segmented

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