Finally Figuring out Photosynthesis


  1. What is photosynthesis?
  2. How to test for photosynthesis
  3. What 4 things are needed for photosynthesis?


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GoStudent Expert Chloe's Guide to Photosynthesis


If you take a science class for long enough, you’ll realise that photosynthesis is the one unavoidable topic no one particularly cares about but everyone has to learn.

Although most of us might dread learning about it, we’re here to show you how fun it can be to experiment with plants.

Photosynthesis experiments at home are one of the best ways to learn about this area of science. Science can be quite abstract if not experienced in practice and it's easy to dismiss things if you can't visualise them. Keep on reading to get some ideas on how you can turn one of the most dreaded science topics into a week of fun!


Firstly, what is photosynthesis?


At first glance, understanding photosynthesis might seem difficult. It’s a long word and a concept which doesn’t make much sense to us, but the explanation can be a lot simpler than we make it out to be.

Simply put, it is the process by which plants make their own energy. All organisms need energy, and whilst animals get that from the food they eat, I doubt you’ve seen many plants hunting for food! Plants don’t get their energy from food like we do, so they’re left to their own devices.

We’re going to go through all the elements needed for photosynthesis, but for now you simply need to know that photosynthesis produces sugar. You’ve probably already made the connection between sugar and energy if you’ve ever had a post-chocolate bar sugar-high!


How to test for photosynthesis


We can prove that photosynthesis happens in plants through a chemical called iodine, which turns from brown to blue black when it encounters starch (starch is the form in which plants store glucose, more on this in a future article).

So here’s what you need to do (with some adult assistance/supervision):

  • Heat a plant leaf in boiling water for 30 seconds
  • Heat it in boiling ethanol for a few minutes 
  • Wash with water
  • Spread onto a white tile
  • Add a few drops of iodine

If photosynthesis took place then the leaf would have starch in it and so the iodine would turn blue black. If no photosynthesis took place the iodine would stay brown.

So now that we’ve covered the basics we can get into greater detail as we try to understand the process using more fun experiments!


What 4 things are needed for photosynthesis?


Let’s list them: water, carbon dioxide, chloroplasts, sunlight

And now you may be starting to lose interest. What are chloroplasts? What’s Carbon dioxide? Why is this important?

Let’s start with chloroplasts

These structures are the reason plants are green. Only the green parts of the plant photosynthesize because they have access to the most sun (more on the sun later). 

Chloroplasts contain a green pigment called chlorophyll which absorbs light from the sun and uses it for photosynthesis. Photosynthesis can’t happen without it, which is part of the reason why we humans can’t photosynthesize!

Testing the importance of chlorophyll at home

First you’ll need to pop into your garden/the local park to find a variegated leaf. These are leaves with more than one colour. From what we know about chlorophyll, you might already realise that the green part of the leaf has chlorophyll whilst the white part doesn’t - you may even predict that the white part won’t be able to photosynthesize.

But can you predict what will happen to the leaf if we put iodine on it?

If you guessed that the iodine touching the white part of the plant will stay brown whilst the iodine touching the green part will turn blue black, you’re correct! This is a fun and easy way to understand why plants are green. If the whole leaf was white, it wouldn’t be able to make any food!

Next let’s talk about sunlight

Photosynthesis actually stems from Greek words “photo” meaning light and “synthesis” meaning to make. Put them together: to make something using light.

Chlorophyll is needed because it’s the pigment which absorbs sunlight, but you can’t have photosynthesis if there’s nothing there to absorb!

Place a plant in a dark cupboard for a few days and see for yourself what happens when you try to test for starch.

Now that we know the importance of sunlight and chlorophyll, let’s talk about the actual chemical process; the reaction between carbon dioxide and water.

Let’s look at water first

You can learn more about photosynthesis very easily with this next easy-peasy experiment.

  • You have probably realised by now that plants start to die when they don’t get water. But what you may not know is that they also struggle to make food when they don’t have enough water.
  • Leave a plant with no water for a few days and watch as the iodine doesn’t turn blue black when you test for starch.

And lastly, we have carbon dioxide

This one might get confusing, especially because you may have to learn what carbon dioxide is. Simply put, it's one of the gases in the air.

This test is slightly more complicated and might involve some online shopping and adult supervision if you’re committed enough to carry it through.

So here’s how to test the importance of carbon dioxide in photosynthesis:

  1. Destarch a plant by putting it in a dark place for a few days.
  2. Place a bowl of sodium hydroxide next to it. This will absorb any carbon dioxide.
  3. Wrap a clear plastic bag around it to make sure that the plant encounters no fresh (carbon dioxide rich) air.
  4. When you try to test for starch, the iodine will remain brown, indicating that the plant didn’t manage to photosynthesize.

So there it is! A simple guide to photosynthesis, and an even simpler guide to how you can learn a bit about it yourself. As with any science topic, it is filled with fun and simple experiments you can do yourself at home. Hands-on learning experiences are usually the most memorable and successful. This is what we try to do at GoStudent! Why not ask a parent to book a trial lesson so you can see for yourself?