Spring is the perfect time to get outside, breathe the fresh air, and try some fun outdoor science activities that we haven’t been able to do all winter! We’ve got the perfect spring science activity using our Cobalt Chloride test papers to learn about how a leaf functions. Let’s get to it!

Materials

Background

The world of plants is a fascinating thing. We watch them grow and blossom in an array of colors every spring, thrive throughout the summer, change colors and die off in the fall. It might seem simple enough, but plants are living things that are just as intricate as we human beings are. They have their own system that allows them to use energy for growth, breathe and eliminate waste just like us.

Let’s look specifically at a leaf. How does it perform some of these everyday functions?

Leaves contain stomata, or pores, that are used for gas exchange. In most plants, there are more stomata found on the underside, or back side, of the leaves. They are found just beneath the surface of a leaf, and each individual stoma, or pore, contains the chloroplast, a cell wall, a vacuole, and a cell nucleus.

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Stomata are surrounded by guard cells that open and close the pores. Protons are pumped into the guard cells, water then enters them, and as the cells get hard, they push open. When a plant opens its stomata, oxygen and water vapor exit and carbon dioxide enters. The carbon dioxide is used in photosynthesis, and the oxygen is produced by photosynthesis.

Transpiration is the evaporation of water from plants, and it pulls water through a plant. Water enters a plant at its roots through osmosis, and exits through the pores of the leaves into the atmosphere. The amount of water that exits a plant can vary significantly depending upon size, sunlight intensity, temperature, humidity, wind and water supply.

Procedure

In this experiment, we’re going to use cobalt chloride test paper to see if a leaf’s stomata are releasing water vapor, and if there really are more stomata on the underside of the leaf.

Start by getting outside! For this experiment, let’s use a variety of leaves. Try to find leaves from a couple different plants, or leaves in different environments, for example, a leaf from a plant that gets hit with a lot of direct sunlight and a leaf from a plant that is mostly shaded. Another example is a leaf from a plant very close to a water source versus a leaf from a plant that is not.

spring leaf science activity, cobalt chloride test paper, humidity detection, humidity test strips, cobalt chloride test strips, leaf scienceIt’s important that the leaves stay attached to the tree, so they can continue to live and function during this experiment. Thus, you might need to perform the next steps in a few different locations, so taking pictures or writing down notes in your lab notebook at each location could be helpful.

Tape a strip of cobalt chloride test paper to each side of the leaf. Be sure to use clear tape, so you can see the paper change color. Using your timer or stop watch, record the color of the paper or snap a picture every minute.

Cobalt chloride test paper starts out blue and turns pink in the presence of moisture. What do your results show? Is the paper still blue? Is it partially pink? Did the whole strip turn pink? Are you getting different results on the top side and the back side of the leaf? Are you finding different results in different environments?

Try making a table to show your results. For example:

Time

(Minutes)

Paper color

Top of leaf (shade)

Paper color

Back of leaf (shade)

Paper color

Top of leaf (sun)

Paper color

Back of leaf (sun)

1        
2        
3        
4        
5        
6        
7        

Review your findings. Was there more moisture on the back of the leaf, proving there are more stomata there? Did the leaf’s environment impact the amount of water loss? How so? Did the type of leaf impact the amount of water loss?

We’d love to hear your results by region! For example, if you’re in a more humid, tropical climate like Florida, how did your results compare to someone from the desert? Plants must adapt to their climate and environment to survive. Pretty amazing, aren’t they?