Chapter Two: Living Systems Lesson 2.1Organisms Lesson 2.2Living Conditions Lesson 2.3Classification and Dichotomous Keys

How are living things organized? Investigation 2.1 Organisms

2.1 Organisms An organism is an individual, functioning living thing. A tree is an organism and so is yeast.

The Five Characteristics of Living Things Living things respond to their surroundings. Living things grow and develop. Living things are able to reproduce. Living things use energy. Living things have the ability to exchange gasses (oxygen/carbon dioxide).

Is it alive? This is a barnacle. Read about the five characteristics of life on page 31. Then decide whether the barnacle is alive.

It is alive because… 1.Barnacles respond to their environment by closing their shells at low tide, and opening them at high tide. 2.Barnacles grow and develop. They begin life as free- swimming creatures. Once they find a good spot, they “glue” themselves to a rock and form a shell. 3.Barnacles reproduce. After fertilization from a male barnacle, females hold the eggs in their shells until they hatch. 4.By waving their legs, barnacles capture food. They use energy from the food to move their legs, open and close their shells, and carry out all life processes. 5.Barnacles have the ability to exchange gasses through the thin membranes of their skin.

Variables in living systems Living things can respond to changes in their surroundings to maintain a steady internal environment. The process of maintaining a life- supporting system is called homeostasis.

Variables that affect life All sorts of variables affect an organism’s ability to stay alive. These include temperature, food, water, and the level of oxygen. All organisms have built-in processes to help them survive when variables change. Your normal body temperature is 37°C. How does sweating or shivering help you maintain a constant body temperature?

Energy is sometimes defined as the ability to cause change or do work. There are many forms of energy. Any form can be converted into any other form. Organisms and energy