2.3 Photosynthesis and Respiration Study Guide

2.3 Photosynthesis and Respiration (Bio.2.3)

Explore this Phenomenon

Terrariums, like the one shown above, are closed systems. This means that the container is sealed. Plants can survive for a long time in a terrarium, even though no water or air is added to the system. Plants have been growing in one terrarium since 1960, and water has only been added to the terrarium once (in 1972)!

1. Write an explanation or create a model to show how plants can survive in a closed system.
2. What are three questions we could investigate to figure out how the plants can live for so long without water or air being added to the system.

 Bio.2.3 Photosynthesis and Respiration

Develop and use a model to illustrate the cycling of matter and flow of energy through living things by the processes of photosynthesis and cellular respiration. Emphasize how the products of one reaction are the reactants of the other and how the energy transfers in these reactions. (PS3.D, LS1.C, LS2.B)

Photosynthesis and cellular respiration move matter and energy through living things. As you read this chapter, gather information about how matter and energy move through organisms during photosynthesis and cellular respiration.

Matter Cycles and Energy Flows

Matter cycles, which means that it is used over and over again. Matter can move from one part of an ecosystem to another, and then return back to where it started. In section 1.3, you learned that carbon can move from the atmosphere to plants and then to animals in the biosphere, and back to the atmosphere. The carbon is reused as it cycles through the ecosystem.

Energy does not cycle. It can move from one part of an ecosystem to another, but unlike matter, it doesn’t return to its starting place. Energy is converted from one form to another as it moves through the ecosystem, and at the end, it is not in a form that can be reused. Light energy from the sun is converted by plants into chemical energy, and the chemical energy can be passed to the animals that eat the plants. The chemical energy is converted to heat, sound, and other forms of energy.

Photosynthesis and Cellular Respiration are Opposite Reactions

Photosynthesis and cellular respiration are connected through an important relationship. This relationship enables life to survive as we know it. The products of one process are the reactants of the other. Notice that the equation for cellular respiration is the direct opposite of photosynthesis:

Photosynthesis

Photosynthesis is the process that converts the energy of the sun, or solar energy, into carbohydrates, a type of chemical energy. During photosynthesis, carbon dioxide and water combine with solar energy, yielding glucose (the carbohydrate) and oxygen. The carbon dioxide and water molecules have less energy than the carbohydrate molecules that they are used to make. Where does the extra energy in the carbohydrates come from?

Plants convert light energy from the sun into the chemical energy in carbohydrates. The energy in the carbohydrates can be stored, or the plants can use the energy to perform necessary life functions.

Photosynthesis mostly takes place in the leaves of a plant. The green pigment in leaves, chlorophyll, helps to capture solar energy. The veins within a leaf carry water which originates from the roots, and carbon dioxide enters the leaf from the air through special pores called stomata.

The overall chemical reaction for photosynthesis is six molecules of carbon dioxide (CO2) and 6 molecules of water (H2O), with the addition of solar energy, yields 1 molecule of glucose (C6H12O6) and 6 molecules of oxygen (O 2 ). Using chemical symbols the equation is represented as follows:

Oxygen is a byproduct of the process of photosynthesis and is released to the atmosphere through the stomata. Therefore, plants and other photosynthetic organisms play an important ecological role in converting carbon dioxide into oxygen. Animals need oxygen to carry out the energy-producing reactions of their cells. Without photosynthetic organisms, many other organisms would not have enough oxygen in the atmosphere to survive. Oxygen is also used as a reactant in cellular respiration. Oxygen cycles through both processes of photosynthesis and cellular respiration.

Respiration

 How does the food you eat provide energy? When you need a quick boost of energy, you might reach for an apple or a candy bar. Although foods with sugars can give you a quick boost of energy, they cannot be used for energy directly by your cells. Energy is simply stored in these foods. Through the process of cellular respiration, the energy in food is changed into energy that can be used by the body's cells.

Glucose and oxygen are converted to ATP, which is a molecule that your cells can use for energy. During this process, carbon dioxide and water are formed. Cellular respiration is simply a process that changes one type of chemical energy, the energy stored in sugar, into another type, ATP.

Most often, cellular respiration proceeds by breaking down glucose into carbon dioxide and water. As this breakdown of glucose occurs, energy is released. Glucose has more energy than the carbon dioxide and water molecules that it is broken down to form. What happens to the extra energy?

Energy that is released from glucose is transferred to molecules of ATP. Your cells can use the energy in the ATP molecules to perform work, such as contracting your muscles as you walk down the street, performing active transport, or generating heat to keep you warm.

Notice that the equation for cellular respiration is the direct opposite of photosynthesis. While water was broken down to free hydrogen and oxygen during photosynthesis, in cellular respiration oxygen is combined with hydrogen to form water. While photosynthesis requires carbon dioxide and releases oxygen, cellular respiration requires oxygen and releases carbon dioxide. This cycle of carbon dioxide and oxygen in all the organisms that use photosynthesis and/or cellular respiration worldwide, helps to balance atmospheric oxygen and carbon dioxide.

Plants, animals, fungi, and bacteria all use respiration to get energy from carbohydrates. Plants are able to produce their own carbohydrates; however, animals, fungi, and bacteria all rely on plants to convert energy from the sun into a form of energy they can use. They also rely on plants to produce oxygen.

Putting It Together

Terrariums, like the one shown above, are closed systems. This means that the container is sealed. Plants can survive for a long time in a terrarium, even though no water or air is added to the system. Plants have been growing in one terrarium since 1960, and water has only been added to the terrarium once (in 1972)!

1. Review your original explanation or model that shows how plants can survive in a closed system. After reading this chapter, what revisions should be made to make your explanation or model more complete?

2. What other phenomena could be explained using your understanding of photosynthesis and respiration?