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Plant-Science-Lessons

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).

plants-in-fieldScientists 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?

little-cactus-05really-good-saguaroNot 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.)

2. Do all plants have flowers?

ferns-0347Although flowering plants are widespread and abundant, not all plants have flowers. Ferns, mosses, liverworts and horsetails all produce new plants via spores.

3. Are all plants green?

red-japanese-mapleII0147 pitcher-plant-11Although 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.

Dodder_(Cuscuta)_fruitThe 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?

mushrooms-211Fungi 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.

cattails-36

cattail-nc

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.

Plant_cell_structureSecondly, 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

  • are multicellular
  • 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. Let us know what you think in the comments.

A. Is this a plant?

is it a plant

B. Is this a plant, yes or no?

is it a plant quiz

 

C. Are these plants?

is this a plant

D. Are the things growing on the rock below considered to be plants?

is-this-a-plant-d

How did you do? Did you learn anything new about plants?

leaf-border

To see our complete plant science lessons, either visit the plant science category (newest posts to oldest posts) or the plant science section of our experiment archive page (links to posts in order).

For more information about plants and seeds, try our Seed of the Week archive or the mystery seed tag and Seed of the Week category.

3

After 257 Mystery Seed of the Week posts, it seemed like it was time for a change. But what to do next?

The answer was inspired by a book, Seed to Seed: The Secret Life of Plants by Nicholas Harberd.

Seed to Seed is the journal of plant geneticist Nicholas Harberd from the year 2004. In it, he records his personal observations and discoveries. Because of his prominence in the field, in many ways it is also the story of the uncovering of the genetic control of plant growth.

Right in the first entry in the book, Harberd reveals that over the last few decades plant scientists have decided on a unifying method to help move the field of plant genetics forward more quickly. Instead of trying to examine a little of the genetics and development of many, many different plants, perhaps it would be more enlightening for everyone to study one plant thoroughly and assume that the other plants probably had the same or similar properties.

The plant they chose to investigate was thale-cress, Arabidopsis thaliana.

Arabis_thaliana_illustration(Public domain illustration of Arabidopsis thaliana by Johann Georg Sturm from Wikimedia)

Why did they select this small weedy plant? Arabidopsis thaliana is the lab rat of the plant world. It is small and it self-pollinates, so it can be grown easily in the lab. It completes its life cycle quickly, producing flowers within approximately three weeks and seeds in about six weeks. In addition, thale-cress has a small genome that has been completely sequenced, so geneticists can build on what is already known.

Where does this unifying idea take us?

Rather than moving randomly from plant species to plant species as we have been doing with Seed of the Week up to now, let's change gears.  Following in Nicholas Harberd's footsteps, let's learn more about plant science by delving deeply into the secrets of a single type of plant over the next few months. Who knows what we might find out!

What do you think of this plan? Would you like to join in the journey? What questions about plants would you like to answer?

4

If you have been following Growing With Science, you know that we have been closely observing the insects on a small planting of zinnias for the last few weeks (posts about zinnia insects 1, 2, and 3).

mix-of-zinnias-87

The variety of zinnias we have been observing are Profusion® Fire, which are hybrids between regular zinnias (Zinnia elegans), and the Mexican or narrowleaf zinnias (Zinnia angustifolia).

While initially observing the insects on the plants, we also noticed something about the plants themselves, specifically the flowers. Do you notice anything about the flowers in the photograph above?

As it turns out, the flowers change as they become older.

tightly-closed-zinnia-bud-63The zinnia flower head starts out as a tightly closed bud.

young-red-zinnia-flower-19

When the flower head first opens, it is deep, bright orange, almost scarlet.

medium-orange-zinnia-22

As the flower head matures, it becomes a medium orange. Do you see any other changes?

old-yellowed-zinnia-11

The oldest flower heads have faded to almost yellow. They look a bit worse for wear.

There have been some changes to the flowers within the flower head as well, but we need to learn some vocabulary before we can investigate it.

Flower Parts

 

Mature_flower_diagram.svg

(“Mature flower diagram” by Mariana Ruiz LadyofHats. Public Domain image at Wikimedia Commons.)

You may have seen a diagram like this one describing the various parts of a hypothetical flower. Basically, the ovary, style and stigma form the female part of the flower that receives the pollen. The stamens, made up of filaments and anthers, are the male parts of the flower that produce pollen.

Very few flowers actually conform to this simple diagram, and the zinnias are certainly much more complex. Rather than a single flower, what we see is actually a cluster of minute flowers called disk and ray florets.

 

young-floret-parts

You may have to scroll back up to the bigger photographs above to see the parts clearly, but in the young flower head the ray florets around the outside are flowering, which is evident by the yellow stigmas. Only a few disk florets in the center have begun to open.

 

medium-floret-parts

In the middle-aged flower head, most of the ray florets have finished flowering and many of the disk florets around the outside have begun to flower.

older-floret-parts

In the older flower heads, the outer florets have finished flowering and are developing the all-important seeds. Only the disk florets at the very center are still flowering.

Flower Part Dissection Activity for Children

Note: check whether the children have severe pollen allergies before starting this activity.

Gather:

  • Living flowers of different types (see flower notes)
  • Safety scissors and other dissecting equipment (age appropriate)
  • Diagrams/illustrations of flower part with labels
  • Dissecting microscope (optional)
  • Paper (optional)
  • Pens or markers (optional)
  • Tape (optional)

Flower notes:  Tiger lilies or other lilies are excellent examples of simple flowers as seen in the diagram. Daisies and sunflowers are good examples of the complex flowers. Working with a large group? You might want to ask your local grocery store or florist if they would be willing to donate flowers that have passed their freshness date. Keep the flowers alive in a vase of water.

Have the children observe the different types of flowers closely. Provide diagrams or illustrations naming the flower parts. Once everyone has had a chance to observe the flowers, allow the children to dissect the flowers to examine the parts more fully. Very young children can simply pull them apart. Older children might use safety scissors. Still older children can use dissecting pins and a dissecting microscope, if available.

Remove the petals or pull off the ray florets. Can you find the stigma? What about the stamens? Is the stamen releasing pollen? What color is the pollen? What is inside a disk floret?

Older children might want to spread the parts onto a piece of paper or card stock and tape them down. Label the parts.

Extension:  If the flower parts aren't damaged too badly, allow the children resemble the parts to make their own mix of "Franken-flowers."

Resources:
The Clover & the Bee; A Book of Pollination by Anne Ophelia Dowden

This image does not do this beautiful book justice. It includes many highly-detailed, scientifically-accurate diagrams of different types of flowers with their parts labelled. It also discusses pollinators and how they use differently-shaped flowers in different ways. Super scientific reference for educators and older children.

Age Range: 10 and up
Hardcover: 90 pages
Publisher: HarperCollins; 1st edition (May 1, 1990)
ISBN-10: 0690046774
ISBN-13: 978-0690046779

This is an older book by the same author which covers similar material.

Publisher: Ty Crowell Co (June 1963)
Language: English
ISBN-10: 0690506562
ISBN-13: 978-0690506563

 

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