1. Chapter 6, lesson 3 Water balance and waste

2.  Your body works to keep a normal balance of water. When you sweat a lot  drink more to replace lost water. When you drink too much  get rid of extra water in form of urine.  Animals have ways to maintain, or keep, water balance.

3. Water balance in the sea:  Seawater = salt and water  Fluids of animals contain water and salt. More salt = lower water concentration. –Recall water will move from an area of high concentration to an area of low concentration = osmosis.

4. Sea animals  Sea invertebrates avoid absorbing or losing too much water The water concentration in their fluids equals the water concentration in seawater. Water doesn’t move between them and the ocean.  Also occurs in cartilaginous fish.

5. Bony fish: in salt water  Body fluids have a higher water concentration (less salt) than seawater. Water moves from their body into the sea (because of concentration gradient)

6.  They must drink seawater to replace lost water (by osmosis). This brings in extra salt – not needed They excrete the extra salt through their gills. –Excrete = get rid of wastes or substances that are not needed.

7.  Sea turtles cry salty tears to get rid of excess salt.

8. Water balance in freshwater:  Animals living in freshwater have too much water coming into their bodies. Concentration of water is higher outside than the concentration inside. Osmosis causes water to flow in.  Special organs help remove excess (too much) water.

9. Freshwater organisms  Flatworms  system of tubes all through their body that are connected to flame cells. Cells collect and remove extra water. Cilia on flame cells push water along the tubes Water leaves through pores in body wall.

10. Bony fish: in freshwater  Water enters gills all the time To get rid of extra water, the fish use their kidneys to excrete urine. –Kidneys: organs of excretion in vertebrates  Filter wastes and extra water from blood. –Excretion: get rid of wastes –Urine also gets rid of salts (some salt is needed) Replace salt by absorbing salt with gills.

12. Water balance on land:  Biggest problem with water balance on land  drying out. Animals have ways of limiting water loss. –Snails: withdraw into shell when its hot. –Insects: waxy layer covering exoskeleton. –Reptiles, birds, mammals: watertight skin.

13.  Animals are not completely watertight. All must respire  lose water when oxygen and carbon dioxide are exchanged. Lose water in urine, feces, and sweat.

14.  Maintain water balance by drinking water to replace lost water. Eating leaves, fruits, and roots when open water is scarce. –Kangaroo rat never drinks water – gets all its water from seeds and plant matter.

15.  Kidneys: main organ of water balance. Too much water in body? –Kidneys excrete urine with a high water concentration. Not enough water in body? –Kidneys excrete urine with a low water concentration. –Keeps more water in body.

16. Excreting wastes:  Producing urine does more than maintain water balance. Removes dangerous wastes from the body. –Ammonia: formed when proteins break down in the cells.  This is poisonous to the cell so the body must get rid of it.

17. Excretion  Water animals: ammonia moves into the water and doesn’t build up in animal.  Land animals: change ammonia into less poisonous chemicals. Chemicals excreted in urine.