Around Saint Patrick's Day the color green seems to be everywhere—from hats to shamrocks. For this Saint Paddy's Day, you could show off your own green creation…by cloning a plant! Many sci–fi tales of cloned organisms have been based on the actual scientific method for cloning animals or plants. In the real world the cloning of plants is often used in modern agriculture. How do you clone a plant? In this activity you will get to find out by making your own cabbage clones!
Unlike most animals, plants commonly use two different ways to reproduce, depending on conditions. These two different types of reproduction are sexual reproduction and asexual reproduction. Many plants we're familiar with, such as flowering plants, undergo sexual reproduction by making seeds, where each seed contains an embryo that will grow into a mature plant under the right conditions. Sexual reproduction requires both male and female parts of a plant, which mix to form the embryo, bringing different sets of genes from both parent plants.
Asexual reproduction in plants is when new plants are made without male and female parts mixing, and it can be done without making seeds. The new progeny plant is a genetic clone of the parent plant. Although asexual reproduction usually produces plants with relatively less diversity compared with those created via sexual reproduction, asexual reproduction can be quite useful. Cloning plants is very common in agriculture because a plant can often be made relatively quickly this way, and it allows a farmer to grow more reliable produce, harvesting essentially the same plant from one year to the next.
• Three paper towels
• Three small, sealable plastic bags
• Scissors (optional)
• Fresh head of cabbage. Napa cabbage is recommended, because it is longer than the more common round cabbage, is less dense, easier to pick apart and has a longer stem.
• Cutting board
• Camera (optional)
• Permanent marker
• Fold a paper towel in half and then fold it in half again so that it can fit into a sealable plastic bag. Slip the folded paper towel into the bag so that the last fold you made is at the bottom of the bag. (If the folded paper towel is too long to fit into the bag, trim it to fit using scissors.)
• Add water to the bag so that the paper towel is damp, but do not add so much water that it is dripping wet. Pour out any extra water.
• Repeat these steps with the other paper towels and sealable plastic bags so that you have prepared three sealable plastic bags with damp paper towels inside.
• Remove the leaves from your cabbage. Beginning with the outer leaves, gently pull all of the leaves of the cabbage off of the stem. Do not worry if you don't get the entire leaf removed—it is better to leave some of the leaf attached than to risk damaging the stem.
• You should have an adult's help to use the knife when cutting the stem in the Procedure.
• Place the cabbage stem on a cutting board and, with an adult's help, use a knife to carefully slice the stem crosswise into three pieces. Try to make each piece about the same length. You should have a top, middle and bottom piece, where the bottom piece would be closest to where the roots were (they should already have been removed) and the top piece would be at the top of the plant. How are the pieces different from each other? How are they similar? What color(s) are they?
• If you have a camera handy, you can take pictures of the stem pieces.
• Put one stem piece into each bag you have prepared. Put each piece in the middle of the folded layers of the paper towel (with two layers above the piece and two below it). Blow a tiny bit of air into each bag before sealing it.
• Once sealed, use the permanent marker to label each bag (as "top," "middle" or "bottom") based on which piece is inside.
• Place the three bags near a window at room temperature.
• The next day open the bags and observe the cabbage stem pieces. Do the pieces seem to have changed? Do some look like they're becoming clones? How can you tell?
• Reseal each bag, again blowing a tiny bit of air into each one before doing so. Place the bags back near the window.
• Continue observing the cabbage stem pieces each day like this until you have observed them for at least a week. How do the pieces change over time? Do some pieces sprout green leaves or develop small green spots? Do some seem to rot—turning brown, slimy and smelly?
• Did one piece (top, middle or bottom) become the best clone? How can you tell? Did a certain piece not clone at all? If some pieces became better clones than others, why do you think this is?
• Extra: You can try to continue growing the clones you started in this activity. To do this, remove the clones from the bags after they've been growing for about 10 to 12 days, have an adult help you carefully use a knife to cut off and discard any rotting pieces, and put the clones onto damp potting soil in a pot or other container. Keep the soil damp and observe how the clones grow and change over time. Do the leaves grow? Do they sprout roots? Do they turn into plants like the original cabbage you used or are they different somehow?
• Extra: You can try cloning other crops as well, such as celery stem parts, tubers of potatoes, slices of carrot, lettuce stems, separated garlic cloves, etcetera. Do clones come from the same part of the plant? Do other crops need different conditions to be cloned? Are some crops cloned much more easily than others?
• Extra: Try comparing the time it takes to produce a mature cabbage by cloning to growing it from a seed. How much faster is cloning a vegetable than growing it from seed? What is the yield from each method?
Observations and results
Did the top stem piece grow green leaves and overall make a much better clone than the middle or bottom pieces? Did the middle piece grow at least a few small green spots, whereas the bottom had fewer green spots—if any?
When you cut the stem into three pieces, you probably saw that all three pieces had had some leaves growing from them, which you could see by the leaf stubs left from when you removed the leaves. The piece that should have had the most leaves was the top piece, the only piece that had leaves on its top side. This is relevant because plants have a type of tissue called the meristem, which is where plants can sprout and is thereby important for asexual reproduction. Meristem tissue is usually in the plant’s root tips (which had been removed from the cabbage) and the stem's tip, where it grows the stem, new leaves and buds. You should have seen that after only a day the top piece looked greener than it had after you removed its leaves—and it became greener each day, growing several leaves mostly from the top of the piece. By the time the week was over, the middle piece should have sprouted a few small green spots where the leaves meet the stem. The bottom piece may have sprouted a few green spots as well, but it probably had rotted much more than the other pieces.
Because you did not need the cabbage leaves for this activity, you could use them to make a cabbage soup or coleslaw. You can also continue trying to grow your clones on soil or compost them.
More to explore
Plant Reproduction–They'll Make More, from Biology4Kids.com
Plant Reproduction: Asexual Reproduction, from Encyclopedia Britannica
Meristem, from Kids.Net.Au
Attack of the Killer Cabbage Clones, from Science Buddies