What is Life?
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| Plant Cell Model |
Introduction
Even though it is pretty easy to determine what is living and what is not, it is important for students to learn what the criteria for life is:- All living things have DNA.
- All living things have a method by which they take energy from their environment and convert it into energy to support their life.
- All living things can sense changes in their surrounds and respond to them.
- All living things reproduce.
DNA and Life: All living things have DNA.
DNA is a molecule. A really big molecule...millions of atoms linked together. It stores an incredible amount of information.
The Structure of DNA
The important things you want your students to learn about the structure of DNA is that it is a double helix formed from the backbone composed of two long strands of atoms linked together. These strands have units, called nucleotides (adenine, thymine, cytosine and guanine) attached to them. These four nucleotide types form together in a specific way...adenine only links with thymine and cytosine only links to guanine. So, if you know one part of a pair of nucleotides, you also can determine the other part of the pair.
Building a Model of DNA
You can discuss all of this as your students make a model of DNA.
What You Will Need:
What You Will Need:
Four pipe cleaners, any color
50 pony beads (or you can use pieces of colored straws): 17 in one color (color 1), 17 in another color (color 2), four in four other colors (colors 3, 4, 5 and 6)
Cut two pipe cleaners into 6-inch lengths. Alternate stringing color 1 and color 2 beads on each pipe cleaner until you have 17 beads on each. Fold back the excess length of pipe cleaner to hold the beads in place. These will be the strands of your DNA.
Cut the remaining pieces of pipe cleaner into eight 2 1/2-inch strips. String four pieces with pairs of color 3 and color 4. String the remaining four pieces of pipe cleaner with pairs of color 5 and 6. These will form your base pairs. These represent the four nucleotides adenine, cytosine, guanine and thymine. Adenine always pairs with thymine and cytosine always pairs with guanine. Have your students pick what colors represent the different nucleotides and then make a color key.
Twist your base pair pieces around the strands of your DNA to attach so that there are two strand beads between each set of base pairs. Position each base pair horizontally and evenly around your strands. Make sure to attach these identically on both sides so that your color 1 and color 2 beads match up. Hot glue your pieces in place if desired.
Twist your strands to form your DNA into a double helix. Now you have a model of a DNA sequence.
You could also make an edible model using colored mini-marshmallows, Twizzlers and toothpicks.
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| Strawberry DNA Extraction |
As a follow-up to the DNA model, it might be nice to actually extract some DNA from something around your house such as strawberries.
Energy and Life: All living things have a method by which they take energy from their environment and convert it into energy to support their life.
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| Finding Food in Plants |
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| A Simple Biosphere |
Unlike animals, plants can stay alive and grow in an enclosed environment, which can be demonstrated by making a simple biosphere in a two-liter bottle. The plants use the energy of sunlight through the process of photosynthesis to produce its own food
Sensing and Responding to Change: All living things can sense changes in their surrounds and respond to them.
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| Sensing and Responding to Change |
You can demonstrate to your students that living things sense and respond to change by noting how earthworms respond to light and water added to their environment.
Plants also respond to their environment. An example of this is called phototropism, which can be seen best by watching how a sunflower turns throughout the day to follow the sun as it travels across the sky.
Reproduction and Life: All living things reproduce.
In ancient times when they saw fruit flies form on a piece of fruit that was sealed away, they believed that it was "spontaneous generation" or that the flies formed out of the fruit. This can be easily shown as a false notion by peeling a banana and putting it in a jar. Once you see fruit flies gathering, stretch a nylon stocking over the mouth of the jar. Even though the jar is sealed, within a couple of weeks the fly eggs that were laid on the fruit will hatch.
Another fact to go over with your students is the fact that animals that have more predators or lead a more dangerous life will generally give birth to more young than an animal that is at the top of the food chain.
The Cell -Life's Smallest Unit
There are a lot of things that students can learn about cells:
- Cells are very small.
- It does not necessarily take lots of cells to make a living organism.
- Cells can reproduce.
- You can learn about the various parts of the cell. The nucleus is where you find the DNA of the organism.
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Through the years we have made many models of animal cells. We have made them out of cakes, jello and pizza. (Other examples of creative edible cell models can be found at Debbie's Homeschool Corner.)You can make them out of just about anything. Even if they make a model, however, I always get them to make a notebook page as well.
Sources and Resources:
- Exploring Creation with General Science, Jay Wile, Chapter 9
- Exploring Creation with Human Anatomy and Physiology, Jeannie Fulbright and Brooke Ryan, Chapters 1, 14
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