(REP) Photosynthesis and Respiration Lesson

Photosynthesis and Respiration Lesson

Have you ever experienced a tired or sluggish feeling? Maybe you even stated that you wish you had more energy to stay up late or swim an extra lap in the pool. All living things need energy to carry out metabolic activities, or work, necessary for life. We get our energy from eating food and by maintaining a healthy diet.

Our cells require energy work on a very small scale for many reasons, including:

• Growth and Repair,
• Transporting molecules, and
• Reproduction.

The ultimate source of energy for all organisms is the sun. Producers (organisms using photosynthesis) convert sunlight energy into chemical energy (sugars) that is stored in food. Then that food is broken down (in eukaryotes) by the mitochondria to release ATP, an energy storage molecule that is usable by the cell. This process is called cell respiration.  Prokaryotes are able to use energy from food, but they do so in a much simpler set of steps.

 

Take a look at the picture below and trace the movement of energy from the sun into ATP (useable energy).   

                                                                See description of diagram Links to an external site.

 

The most important source of energy is the sun. Most living things directly or indirectly obtain energy from the sun. Plants use sunlight to make their food in a process called photosynthesis. We indirectly obtain that energy from the sun when we eat plants or animals that have eaten plants.

Plants are autotrophs because they can make their own food or glucose. Along with sunlight, carbon dioxide and water are used to make glucose and oxygen. The equation below summarizes the process of photosynthesis.

 

 

During photosynthesis, specialized organelles (chloroplasts) within plant cells capture the energy from sunlight using the pigment chlorophyll and use it make glucose, a simple sugar.

• Glucose is not only found in plant cells but also in our blood.

• Humans obtain glucose by eating foods rich in carbohydrates such as fruits, pasta, bread, and cereal.

• Carbohydrates are an important source of energy to many organisms. Carbohydrates are made up of long chains of sugars that contain the elements carbon, hydrogen, and oxygen.  

To summarize: Chlorophyll absorbs the energy from sunlight and uses it to split water into hydrogen and oxygen. The hydrogen is now available to combine with carbon dioxide to form glucose whereas the oxygen leaves the plant through the stomata.

Plants play an important role in releasing oxygen into the atmosphere.

Oxygen and carbon dioxide are two of the gases in the air we breathe. Plants obtain carbon dioxide from the air too. CO2 enters the small openings on the underside of a plant's leaf called the stomata. Plants produce oxygen as a waste product of photosynthesis, and this is released through stomata.

The roots of a plant absorb water from soil and bring it to other parts of the plant. Xylem is the vascular tissue of a plant that moves water and minerals from the roots to the stem and leaves.

In the end, photosynthesis has converted solar (sun) energy into the chemical energy stored in the bonds holding the glucose molecule together. Later, the plant may break those bonds (using respiration) to release the energy.  In this way, the plant stores energy (photosynthesis) and then later uses it to carry out many of the metabolic and cellular functions within the plant such as growth, reproduction, and building strong cell walls. Some of the glucose molecules are converted into starch, which is stored in the plant's cells for later use, or it can be converted into cellulose.  Plants such as potatoes, rice, bread, and carrots contain starch. When we eat plants, the stored energy made during photosynthesis enters our bodies.

The following video clip explores photosynthesis and looks at the critical role this process plays in providing food and oxygen. An explanation is given of the key steps involved, and the importance of the process to almost all other living organisms is stressed. The video is approximately 14 minutes long. Pause the video when necessary to make notes.

 

The World of Plants - Photosynthesis

 

 

Use the link below to listen to the song I Need a Little Light and learn the fundamental process of photosynthesis.

 

Now listen to the catchy song Photosynthesis performed by the larger-than-life science-rockers, They Might Be Giants from the They Might Be Giants Podcast for Kids. Compare the details of this song with that of Mr. Durand's song above. Do both songs contain similar information, or does one supply more details than the other?

 

 

 

Respiration

How do we use that stored energy, glucose, made during photosynthesis? Just like plants, the cells within animals break down glucose molecules to release the chemical energy stored in them. This process is called cellular respiration and it is responsible for converting food into energy that can be used by the cells in your body.

See description of diagram Links to an external site.

 

Equation for Cell Respiration

 

Cell respiration is a complicated process.   It involves many steps to release the energy from a molecule of glucose.   The breakdown of glucose molecules begins in the cytoplasm. Very little energy is produced in this first stage.

 In the next stage, the broken-down glucose molecules travel to the mitochondria  where they are separated into tinier molecules in a series of reactions. These small molecules combine with oxygen to produce water and  carbon dioxide as waste products. A great amount of energy is released during this stage in the mitochondria. The carbon dioxide diffuses out of the cell and eventually exits the body when you breathe out, or exhale.  

 

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