To Leaf or Not to Leaf
Grade Level: 2nd - 8th; Type: Life Science
To determine whether lettuce that is harvested gradually yields more produce than lettuce that is harvested all at once.
Does harvesting single leaves of lettuce increase the amount of lettuce you can harvest from one plant?
Plants are amazing organisms. Unlike animals, they can make their own food using their leaves. Plants use carbon dioxide, water, and sunlight to create food through photosynthesis. If a plant has all of its leaves removed, it cannot create its own food.
But what if a plant loses one or more of its leaves while some remain? Does this enough the plant to grow more leaves to replace the ones it lost, or does the plant’s growth slow down a little because it does not have as much food available? In this experiment, you will selectively prune lettuce leaves to see if this pruning changes the total amount of lettuce produced by a plant.
- 6 lettuce plants of the same type of lettuce
- Two garden beds
- Watering can
- Kitchen scale
- Notebook and pen
- Grow lettuce plants in two garden beds with similar light and soil conditions. If you wish, the lettuce can be in a single garden bed. Give each lettuce plant the same amount of care. Grow at least three lettuce plants in each plot.
- Designate one garden bed for the lettuce that will be pruned.
- Over the lettuce’s growing season, take several leaves of lettuce from each plant in the bed that is pruned. Before you eat the lettuce, weigh the leaves and note the weight in your notebook. Weigh the leaves you harvest every week before you eat them.
- When the mature lettuce is ready to harvest, remove it from the ground. Take off any roots and soil. Wash the lettuce.
- Weigh the mature plants and note the weights in your book. Also note whether the lettuce was from the plot that was pruned or the plot that was left alone.
- Take the average of the weights of each plant in the two different beds.
For example, if the three lettuce plants in the bed that was not disturbed weigh
½ lb, ¾ lb, and 1 lb each, the average weight of the lettuce in that bed is ¾ lb.
- Compare the average of the bed that was not disturbed with the average of the bed that was pruned. Which one is larger? Is it much larger?
- Now add in the weight of the leaves that were harvested from the bed that was pruned. .If you harvested a total of 1 lb of leaves from the three plants throughout the season, add another 1/3 of a pound to the average weight of the lettuce in that bed. Now which average is larger?
- Based on these weight averages, do the pruned plants yield a higher biomass of leaves? Does pruning help plants create more leaves?
Terms/Concepts: Learn about pruning and its impact on a plant; Learn about growing lettuce; Learn about plants that regenerate leaves when leaves are removed
http://www.naturallifemagazine.com/9704/lettuce.htm (Natural Life Magazine
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