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All living organisms share several key characteristics or functions: order, sensitivity or response to the environment, reproduction, adaptation, growth and development, homeostasis, energy processing, and evolution. When viewed together, these characteristics serve to define life. Different sources may use slightly different terms to describe these characteristics, but the basic ideas are always present.
Organisms are highly organized, coordinated structures that consist of one or more cells. Even very simple, single-celled organisms are remarkably complex: inside each cell, atoms make up molecules; these in turn make up cell organelles and other cellular inclusions. In multicellular organisms, such as the toad seen in Figure 1, similar cells form tissues. Tissues, in turn, collaborate to create organs (body structures with a distinct function). Organs work together to form organ systems.
In this class, we will be focusing on how cells function, so we will be concentrating on biological molecules, how they make up cells, and how those cells function.
SENSITIVITY OR RESPONSE TO STIMULI
Organisms respond to diverse stimuli. For example, plants can bend toward a source of light, climb on fences and walls, or respond to touch (Figure 2). Even tiny bacteria can move toward or away from chemicals (a process called chemotaxis) or light (phototaxis).
Single-celled organisms reproduce by first duplicating their DNA, and then dividing it equally as the cell prepares to divide to form two new cells. Multicellular organisms often produce specialized reproductive germline (reproductive) cells that will form new individuals. When reproduction occurs, DNA is passed from the organism to that organism’s offspring. DNA contains the instructions to produce all the physical traits for the organism. This means that because parents and offspring share DNA ensures that the offspring will belong to the same species and will have similar characteristics, such as size and shape.
GROWTH AND DEVELOPMENT
All living things increase in size and/or change over their lifespan. For example, a human grows from a baby into an adult and goes through developmental processes such as puberty. Organisms grow and develop following specific instructions coded for by their genes (DNA). These genes provide instructions that will direct cellular growth and development, ensuring that a species’ young will grow up to exhibit many of the same characteristics as its parents, like the kittens seen in Figure 3.
HOMEOSTASIS AND REGULATION
In order to function properly, cells need to have appropriate conditions such as proper temperature, pH, and appropriate concentration of diverse chemicals. These conditions may, however, change from one moment to the next. Organisms are able to maintain internal conditions within a narrow range almost constantly, despite environmental changes, through homeostasis (literally, “steady state”)—the ability of an organism to maintain constant internal conditions. For example, an organism needs to regulate body temperature through a process known as thermoregulation. Organisms that live in cold climates, such as the polar bear (Figure 4), have body structures that help them withstand low temperatures and conserve body heat. Structures that aid in this type of insulation include fur, feathers, blubber, and fat. In hot climates, organisms have methods (such as perspiration in humans or panting in dogs) that help them to shed excess body heat.
All organisms use a source of energy for their metabolic activities. Some organisms capture energy from the sun and convert it into chemical energy in food (such as grass and bacteria that can perform photosynthesis); others use chemical energy in molecules they take in as food (such as the condor seen in Figure 5).
- Living Terrarium Student sheet
- Sorting sheets
- Living, nonliving, and once living sorting sheets
- Items for the sorting activity. There are many possibilities for items to sort. Try and have at least 5 — 6 items for each category. Examples of living items are: a mealworm, a plant with roots, soil with microorganisms, and pond water with microorganisms and/or insect larvae.
- 1 tsp. of cornmeal in a Ziploc bag marked ‘unknown 1’, one per group
- 1 tsp. of fast acting yeast in a Ziploc bag marked ‘unknown 2’, one per group
- 2 tsps. of sugar per group
Pre-lab discussion: Show students a rock, a stick, and a mealworm. Ask the students which one is living, nonliving, and once alive. Ask students what it means to be alive. Have them come up with the five characteristics and write them on the board. Show the students the bags of yeast and cornmeal and have them predict if one, either, or both are alive. Have students make a prediction and discuss a way to experiment on their prediction.
I. Sorting Living, Once Living or Nonliving Objects
- Take turns handing each student an item on the table. Have them decide if they should place the item on the living, once living or nonliving paper. Be sure and remind them we are making a hypothesis and that we might need to change their placements after we think some more.
- After all the items are placed go through the following checklist and be sure that each item was placed in the correct group. Correct any wrong placements. Remember:Is it living, once living or nonliving? It is important to realize that there is controversy over where to put such items as an apple or seed. Let the kids decide where it should go and realize there is no absolute correct answer on this.
II. Which One is Alive?
- Have the students look at the two bags on the table and describe the powder that is inside each. (The powders are #1 corn meal and #2 yeast but don’t tell them.) Ask the students if they think the powders are alive.
- Add a teaspoon of sugar to each bag. Tell them that if the powder is alive, it needs to eat.
- Add 2 tablespoons of warm to slightly hot water to the two bags. Tell them that if they are alive, they will need to have water.
- Close up the bag and make sure there is some air left in the bag because if they are alive, they need to breathe.
- Close the bag and observe the solutions for 5 minutes.
- While they are waiting, discuss their observations and decide if they think either powder is alive. How will they know? Notice that bag #2 begins to have bubbles given off. The yeast is eating the sugar and giving off carbon dioxide as a waste product.
- After the 5 minutes tell them what the two solutions are and which one is alive. Explain how each one fits into its own living vs. nonliving category. Yeast is alive but it was dormant until sugar and water were added. Cornmeal is not alive but was once part of a living corn plant.
III. Living and Nonliving Interactions in an Ecosystem
- Look at the terrarium with a plant, frog, cricket, water, dirt, rocks etc. Discuss how the objects interact with each other. Things to discuss: Animals give off carbon dioxide which plants need; plants give off oxygen which animals need. Dirt, rocks and other structures provide food and shelter for the living organisms. Who eats who or what in this aquarium? Do we need nonliving items? Do nonliving items need us???
- Make some predictions. If water dried up in the aquarium what would happen to the frog and plant?How does this terrarium compare to a forest?
- For everything in the aquarium, decide if it is living, nonliving, or was once living.
Rio Tinto Hands-on Science Curriculum Team
- Ms. Rae Louie — Administrator, Principal Beacon Heights Elementary
- Emily Mortensen — Grant writer, teacher outreach, 2nd grade teacher at Beacon Heights Elementary
- Ruth Li — Curriculum design, K-6 Science Educator at Indian Hills Elementary
- Deirdre Straight — Curriculum development, K-6 Science Educator at Beacon Heights Elementary
- Tim Rausch — Website development, Library Media at Beacon Heights Elementary