As we embark on a grand adventure into plant science, let’s start by thinking about what we mean by the term “plant” (links go to prior posts here at Growing With Science or to Wikimedia, as indicated).
Scientists currently group living organisms into three domains: the Bacteria, the Archaea and the Eukarya. Within the Eukarya are four divisions known as kingdoms. They are the Protista, Fungi, Animalia and Plantae.
So, basically we are asking what criteria scientists use to classify a given kind of living thing as belonging to the Kingdom Plantae.
Activity: Brainstorm about Plants (Prior Knowledge)
When you think of plants, what features or traits come to mind? Leaves? Flowers? Things that are green? Things that don’t move around? On a board or sheet of paper, brainstorm all the qualities of plants you know.
Now let’s take a look at what features that separate plants from other kinds of living things.
1. Do plants all have leaves?
Not all plants have leaves. Some types of plants, like these cacti, don’t have obvious leaves (although the spines are actually modified leaves). Parasitic plants also lack obvious leaves (see dodder below.)
Although most plants are green because of chemicals called chlorophyll, there are also plants that are red like the Japanese maple tree in the photograph above or these pitcher plants.The red pigments in the leaves are called carotenoids. Carotenoids also give fall leaves their color when the predominant cholorophyll pigments are lost.
Plants may also be golden yellow, or have white and green patterns.
4. Do plants make their own food?
One important aspect of plants is that they can make their own food via a process known as photosynthesis.
This is not an exclusive characteristic, however. There are some other organisms – particularly protists- that can also do this, and a few parasitic plants obtain their food entirely from other plants without making any themselves.
The yellow strands in the photograph are from a parasitic plant named dodder (public domain image retrieved from Wikimedia). The green leaves are from the host plant.
Along with making their own food, plants also store the excess food as starch.
5. Can plants move?
Seeds can move, passively for the most part (which we will learn about in an upcoming post), but once the plant has set down roots it is no longer capable of movement. Plants lack the ability to move about via contracting fibers like animals can.
6. So, if something can’t move, is it a plant?
Fungi were once lumped with plants because they can’t move on their own either. Now scientists consider fungi to belong their own kingdom because they have many important differences from plants.
7. Do plants live in the water?
With a few exceptions, plants live on land. That means they have special structures to keep from drying out that organisms living in the water wouldn’t need. For example, seeds have a tough outer seed coat to protect them from the relatively harsh environment of dry land.
Some plants like cattails and water lilies appear to live in water, but most of their structures are actually above the water.
What about organisms that live underwater, like kelp? Although kelp may look like a plant, it is actually a form of algae. According to current classification schemes, algae are not plants.
7. What differences are there inside plants? What about the cells?
If you could look at plant cells under the microscope, you could find two other features of plants. One is that plants are multicellular, which means they have many cells, not just one. That is a feature of the Domain Eukarya.
Secondly, plants have a cell wall around the outside of the cell, which is made up of cellulose (public domain image from Wikimedia).
Finally, with more advanced study, scientists have determined that plants have what is called an alternation of generations during the life cycle. We’ll learn more about that later.
In summary, plants
have cells surrounded with cell walls made of cellulose
live mostly on the land
make their own food via photosynthesis
store their excess food as starch
lack the ability to move
have alternation of generations during their life cycle
Activity 2. Which Are Plants Quiz
Now that you are an expert on the characteristics of plants, pick out the organisms below that are plants.
A. Is this a plant?
B. Is this a plant, yes or no?
C. Are these plants?
D. Are the things growing on the rock below considered to be plants?
Don’t you love going to the grocery store this time of year, with all the pretty pumpkins and fresh apples? Wouldn’t it be fun to use some pumpkins and apples for science activities?
Pumpkins and apples. Get some different sizes, kinds and colors, if possible.
Bathroom/kitchen scale (depending on activities you choose)
Container, such as a large plastic bin, to hold water
Age-appropriate cutting implement
Trays for holding fruit parts
Activity 1. Exploration/Botany Vocabulary
Have your children look at the pumpkins and apples. How are they different, how are they the same?
Both pumpkins and apples are fruit. They both have seeds inside. Both have stems, can you find the stem? What is the stem for? Apples have a skin, does a pumpkin? (Yes, it does). You can ask older children what they think the fleshy meat (the part we eat) is for. Do both pumpkins and apples have a flower or blossom end?
Activity 2. Sorting
Have the children sort the pumpkins from the apples. They can also sort the sizes, from smallest to biggest, or by color. (Sorting is such an important scientific skill, one that tends to get forgotten.)
Activity 3. Weight Estimation
Have the children estimate how much they think each pumpkin/apple weighs. Ask them how they would weigh a big pumpkin.
Help them weigh the pumpkins and apples.
Activity 4. Pumpkin/Apple Floating
Will a pumpkin float? Will an apple float? Does how big it is determine whether it floats or not?
Fill up a large container with enough water to float the biggest pumpkin without slopping over. See if the different fruit will float or not. Have the children bob for apples, if appropriate. Have the children draw what happened.
Activity 5. Seed Estimation
Have the children estimate how many seeds they think are inside each pumpkin or apple before you cut the fruit open. Write down the estimations and compare with the results when you open them in the next activity.
Activity 6. Pumpkin/Apple Exploration
Begin to cut into the pumpkins by cutting around the stem, like you were going to make a jack-o’-lantern. Allow the children who want to explore to get their hands inside. Let them feel the seeds.
Cut the apples and allow the children to search for seeds. Have them count the apple seeds. See if slices will float differently than whole fruit.
Activity 7. Let It Rot!
Rotting or decay is a mysterious and fascinating process for children. In our modern ultra-clean world of antibiotics and hand sanitizers, we forget what an important process it is. If at all possible, find a quiet corner in the yard and let the pumpkin or apple rot. Check the progress daily. Admire the molds that develop. Discuss the odors. If rotting isn’t progressing, add a bit of water.
Activity 8. Grow or Eat the Pumpkins Seeds
You might want to save some of the pumpkin seeds to grow. If so, wash them and let them dry. Don’t heat them/cook them if you want to plant the seeds. Check one of the websites below for more information on growing pumpkin seeds.
Activity 9. Eating
You can oven-dry some of the pumpkin seeds for eating.
Celebrate Fall by making some of your favorite recipes. Here’s one of ours:
Pumpkin Pie in a Glass Smoothie
Add to blender:
1 to 1 1/2 cups canned or pureed cooked pumpkin
2 cups milk, soymilk or ricemilk
1/3 cup sweetener such as maple syrup
1 cup tofu
1 tsp cinnamon
1/4 tsp cloves