Why does photosynthesis not continue during the night like cellular respiration does

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What is Respiration in Plants

All living things use a process called respiration to get energy to stay alive. Cellular respiration in plants is the process used by plants to convert the glucose made during photosynthesis into energy which fuels the plants cellular activities.

On the other hand, photosynthesis is the process where light energy is converted into chemical energy stored in glucose that can later be used in respiration. Photosynthesis occurs on the green parts of the plant that contain chlorophyll.

During respiration, plants consume food to keep plant cells alive while during photosynthesis, plants create their own food.

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pink flower and green leaves in bowls of waterpink flower and green leaves in bowls of water

How Do Plants Breathe Experiment

Prep Time: 5 minutes
Active Time: 10 minutes
Additional Time: 1 hour
Total Time: 1 hour 15 minutes

Here is a popular science experiment to visually see how plants breathe.

In this experiment, we can see how gases produced during photosynthesis and respiration are released into the environment.

Print

Materials

  • water
  • plant (e.g. a flower or a leaf. Pick it from a living plant, not one that has fallen onto the ground)
  • sunlight (optional)

Tools

  • shallow bowl

Instructions

Steps

  1. Submerge the plant into a bowl of water. The flower or leaf may float to the top, but try to make at least part of the plant stay underwater.Leave in water, air bubbles on stemLeave in water, air bubbles on stem
  2. Put the bowl under the sunlight and wait. (You can also leave it in the dark but it may take longer to see results.)Leaf in water, air bubbles on leafLeaf in water, air bubbles on leaf
  3. After an hour, observe the plants surface. There should be some air bubbles formed on the pedals or the leaf.

Explore

  1. Observe different parts of the plant. Do air bubbles form everywhere?
  2. Do air bubbles form if you leave the plant in the dark?

Did you try this project?

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Diagram showing respiration definition Plants, photosynthesis and stomataDiagram showing respiration definition Plants, photosynthesis and stomata

Plant Respiration And Photosynthesis Formula

Respiration:
oxygen + glucose -> carbon dioxide + water + heat energy

Photosynthesis:
carbon dioxide + water+ light energy -> oxygen + glucose

When Does Photosynthesis Occur

So when do plants start photosynthesis?

Well, while plants respire all the time, day and night, photosynthesis only occurs during the day when there is sunlight.

Do Plants Need Oxygen

Depending on theamount of sunlight, plants can give out or take in oxygen and carbon dioxide as follows​1​.

Dark Only respiration takes place. Oxygen is consumed while carbon dioxide is released in plant respiration at night.

Dim sunlight Photosynthesis rate equals respiration rate. A plant consumes all the oxygen photosynthesis generates. It also uses all the carbon dioxide respiration creates. As a result, no gas exchange takes place with the environment.

Bright sunlight Photosynthesis uses carbon dioxide and makes oxygen faster than respiration produces carbon dioxide and consumes oxygen. Extra oxygen is released into the atmosphere.

During daytime, photosynthesis produces oxygen and glucose faster than respiration consumes it. Photosynthesis also uses carbon dioxide faster than respiration produces it. Oxygen surplus is released into the air and unused glucose stored in the plant for later use.

This is why plants are so important to human and other animals survival. Without photosynthesis, we wouldnt have oxygen or food to stay alive.

What Is The Difference Between Cellular Respiration And Breathing

People breathe. Animals breathe. Do plants breathe?

Breathing refers to the act of inhaling air into the lung and then expelling it out of the bodies afterwards. So its a physical process of exchanging gases between the living objects and the environment.

Diagram of human lungs. What is the difference between cellular respiration and breathing?Diagram of human lungs. What is the difference between cellular respiration and breathing?

Plants do not breathe in the strictest sense of the word. Plants respire through plant pores, called stomata.

During respiration and photosynthesis, gases go in and out of the plants through stomatausing diffusion, not breathing.

But in everyday lives, we use those words slightly differently because we are not all biologists or chemists.

Respiration in plants is strikingly similar to why living objects breathe.

Living objects breathe because they need to obtain oxygen to carry out cellular respiration to stay alive, just like plants need to respire to stay alive. Then byproducts such as carbon dioxide and water are released and removed from the living objects through breathing, just like plants do when they respire.

Because of these parallel processes, people sometimes imprecisely call respiration in plants as breathing.

This is why it is not entirely incorrect if youre not using this as an answer in exams, but rather, just use it as an analogy.Plants dont breathe in and out using lungs, but it is an analogy nonetheless.

Oxygen and carbon dioxide pass in and out of the stomata in the plants through diffusion.

When the plant is submerged in the water, bubbles of oxygen or carbon dioxide released are trapped and they stick on the leaves or petals temporarily.

Since these gases are lighter than water, if you shake the plant, the bubbles will quickly rise to the surface and burst. It is similar to you releasing a breath underwater.

Books On Plants, Photosynthesis And Respiration in Trees

  • Botany: Plants, Cells and Photosynthesis book coverBotany: Plants, Cells and Photosynthesis book cover
    Botany: Plants, Cells and Photosynthesis

This is Book 8 in the Super Smart Science book series.

This colorful picture bookis a great introduction to botany. It teaches key vocabulary such as leaf, stem, root, xylem, cellulose, chloroplast, photosynthesis and respiration, and the pronunciation. It is thorough and easy to understand.

Othertopics covered in the series including biology, chemistry, astronomy, anatomy and physiology are also great additions to kids library.

  • Understanding Photosynthesis with Max Axiom, Super Scientist book coverUnderstanding Photosynthesis with Max Axiom, Super Scientist book cover
    Understanding Photosynthesis with Max Axiom, Super Scientist

This book presents a lot of fun facts about plants. For example, did you know that planting one tree produces enough oxygen to support four people for one year?

Scientific concepts such as photosynthesis is well explained by excellent graphics and interesting stories about Max Axiom. Max is a super hero and a super scientist. He really helps make science learning fun.

  • Photosynthesis book coverPhotosynthesis book cover
    Photosynthesis
  • How Plants Work: The Science Behind the Amazing Things Plants Do book coverHow Plants Work: The Science Behind the Amazing Things Plants Do book cover
    How Plants Work: The Science Behind the Amazing Things Plants Do

References

  1. 1.
    Makino A, Mae T. Photosynthesis and Plant Growth at Elevated Levels of CO2. Plant and Cell Physiology. January 1999:999-1006. doi:10.1093/oxfordjournals.pcp.a029493

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