Energy Transformation: Photosynthesis vs. Cellular Respiration

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  • 0:03 Energy in Living Things
  • 1:11 Energy Changes in…
  • 2:44 Energy Change:…
  • 3:48 Comparisons
  • 5:09 Lesson Summary
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Lesson Transcript
Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

In this lesson, explore how energy is converted between different forms during two biological processes: photosynthesis and cellular respiration. Learn how energy from the sun is harvested by plants and ultimately gives us the energy we need.

Energy in Living Things

Right now, even though you may just be sitting down and reading this lesson, your body is using energy. You need energy just to think, breathe and pump blood through your body. So where do we get this energy? You might be thinking food or drinks, which is true. But ultimately, your food comes from plants. Even if you eat a diet rich in meat and dairy, those animals originally got their energy from plants, which was transferred to you when you ate them. But where do plants get their energy to begin with?

Plants are autotrophs, or organisms that make their own food through a process called photosynthesis. Plants use photosynthesis to convert light energy from the sun to a more usable form during a process called energy transformation. Humans use energy transformations as well. The body takes the energy stored in food and converts it to a form that the body can use. This process is called cellular respiration. Learn about how each process happens, and then compare and contrast photosynthesis and cellular respiration.

Energy Changes in Photosynthesis

Photosynthesis is the process plants use to convert energy from the sun into usable energy for their cells. Plants use the light energy of the sun, carbon dioxide, and water to make glucose (a sugar), and oxygen. The energy of the sun is captured and stored in the bonds between atoms in glucose molecules.

The tiny compartments where photosynthesis occurs are called chloroplasts, using a pigment called chlorophyll, which makes the plants green. The first energy transformation occurs when light energy from the sun is converted to chemical energy in the form of adenosine triphosphate (or ATP) and another molecule called nicotinamide adenine dinucleotide phosphate (or NADPH). ATP and NADPH provide the energy needed for the next energy transformation.

The plant cells then use the ATP and NADPH to assemble molecules of carbon dioxide and other carbon chains into glucose molecules. The glucose molecules can then be linked together to form cellulose, which plants can use to grow new leaves and stems.

The reactions in photosynthesis are referred to as anabolic reactions, or chemical reactions that are used to store energy or create molecules. These types of reactions usually require an initial input of energy - in the case of photosynthesis, light energy from the sun - to produce larger molecules like glucose.

Energy Change: Cellular Respiration

Cellular respiration is a different type of reaction, called a catabolic reaction, where complex molecules are broken down to release energy. In cellular respiration, glucose and oxygen are used to make ATP, and carbon dioxide is released as a waste product. Some cells perform cellular respiration along their main barrier, the plasma membrane, and others do it in a small compartment similar to the chloroplast, called the mitochondria.

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