Chapter 6 Lesson 3 "Water Balance and Wastes"

Materials:

• Water Balance Review Sheet.

Objective:

• Students will explain how animals maintain water balance in the sea, in freshwater, and on land.
• Students will explain how animals excrete wastes.

Alaska Content Standards:

• SCI A-10 Students will understand that living things are made up mostly of cells and that all life processes occur in Cells (Cells)
• SCI A-12 Students will distinguish the patterns of similarity and differences in the living world in order to understand the diversity of life and understand the theories that describe the importance of diversity for species and ecosystems.
• SCI A-14 Students will understand the interdependence between living things and their environments; that living environments consists of individuals, populations, and communities; and that a small change in a portion of an environment may affect the entire environment (Interdependence);
• SCI A-15 Students will use science to understand and describe the local environment.
• SCI B-1 Students will use the processes of science: observing, classifying, measuring interpreting data, inferring, communicating, controlling variables, developing models and theories, hypothesizing, predicting, and experimenting;

Anticipatory Set: Show pictures of the a person stranded on a deserted island. Ask, if this person is stranded here what is his biggest danger? Lead students to dieting of thirst. If humans will die of thirst because they can't drink water then how do fish and other animals survive in the ocean. Review osmosis with the students and explain how it would lead to the dehydration of the man on the island using these pictures. pic 1, pic 2, pic 3. Define osmosis:

Teacher Input: Most sea organisms survive because the water concentration in their bodies is the same as in the sea water. Show the students invertebrates such as a starfish, a crab, and a clam. Some vertebrates such as Sharks (the shark is not a real picture), rays, and skates have the same water concentration as well.

Other organisms must figure out a way to take in water because their body will lose water to the ocean. See picture on P128. Describe how bony fish lose water through their skin so they take in water and salt from the ocean and then excrete the salt with their gills. The sea turtle has glands of excretion near its eyes. These glands secrete salty "tears" that get rid of excess salt.

Teacher Modeling: If these are the problems of saltwater organisms what are the problems of freshwater organisms? Remind the students of the protists. Protists have a special structure in their cells to force out excess water. Do you remember what it is? (contractile vacuole) In a larger organism this would not solve the problem because the water is still in the body and you would blow up like a balloon. How does your body get rid of excess water? (don't wait for answer)

Start by explaining what simple organisms do. Show this picture of the Flatworm. Most animals have special organs to get rid of excess water. In this flatworm it is the flame cell. Here is an actual picture of a flame cell with a microscope. Gets its name from the cilia looking like flickering flames.

Freshwater bony fish have the opposite problem as saltwater bony fish. Show this picture of a freshwater bony fish. What organ in the vertebrate has developed to get rid of excess water? (kidney) A fish must then absorb salt from the water.

How do land animals maintain their water balance? Show the different things land animals have to hold in moister.

snails, insects, birds, mammals, reptiles

Check for Understanding:

Ask this question again, How do land animals maintain their water balance? Show the students a picture of the Kangaroo Rat and tell them that this animal has never been found to drink water. A lot of research has been done on the Kangaroo Rat and it doesn't drink water and survives just fine. How? (the kangaroo rat gets all the water it needs from the food it eats. seeds and plants contain water)

Guided Practice: What organ maintains water balance in land animals? (kidney) Low concentrations of water in the body and urine is very concentrated. High concentrations of water in the body the urine is not concentrated.

Ammonia, a highly toxic substance, forms in the body as a result of breakdown of proteins. In aquatic animals, ammonia diffuses across the gills or entire body surface into the surrounding war. Land animals convert ammonia into urea or uric acid, chemicals that are mush less toxic than ammonia then excrete it in the urine.

Closure: Give the students two rectangles and ask them which direction water would move from A to B or from B to A.

Independent Practice: Read Section 6-3, Complete the review worksheet. They are welcome to take the quiz the first time but they will have another chance tomorrow.

Duration:

30 minutes + 10-15 for Independent Practice (Could be longer if taken for homework).