1. Photosynthesis & Respiration
Biology 9(B)

2. Photosynthesis & Respiration
Learning Objectives
Understand photosynthesis
Understand respiration
Relate photosynthesis and respiration
After this lesson, you will know what occurs during photosynthesis and respiration. You will also be able to describe the interconnectedness between the two in terms of both matter and energy.

3. Energy & Matter All living things use energy
Autotrophs can capture energy from the environment
Heterotrophs must consume other organisms
Matter cycles through ecosystems
Constantly recycled and reused
Energy flows through ecosystems
In from the sun
Transferred between organisms
Out as heat
All living things must use energy to perform required functions, such as growing and reproducing. Autotrophs such as plants can capture the energy the need from their environment. Heterotrophs such as humans must consume other organisms for energy.
Matter cycles through ecosystems. This means that matter is constantly recycled and reused. For example, the oxygen atoms you are breathing have been breathed by countless other people and animals before you. These molecules might have come from water molecules or other compounds.
Energy flows through ecosystems. The majority comes from the sun. It is then transferred between organisms through a food chain, and then leaves the ecosystem as heat. Without input from the sun and other sources, the flow of energy would stop.

4. Photosynthesis Stores Energy
Photosynthesis process by which some autotrophs capture energy from the environment
carbon dioxide
solar energy
water
sugars
oxygen
Photosynthesis is the process by which some autotrophs capture energy from the environment. This process creates sugars, which can be used for energy later. Therefore, photosynthesis allows these autotrophs to store energy for later use.
In this process, carbon dioxide, solar energy, and water are used within cells to create sugars and oxygen. In plants, this sugar is in the form of glucose.
Stores Energy

5. Photosynthesis Can be expressed chemically
6CO H2O + energy  C6H12O O2
Photosynthesis can be written as a chemical equation. Since carbon dioxide, water, and energy are used, these are the reactants. They react to make glucose and oxygen, the products.
Reactants
Products

6. Respiration Releases Energy
Cellular Respiration process by which organisms convert sugars into usable energy and waste products
sugars
oxygen
carbon dioxide
energy
water
Cellular respiration is the process by which living things use energy from sugars. This process releases energy for immediate use in the form of ATP. Once used by the cell, this energy is released as heat.
In this process, sugars and oxygen are used within cells to create carbon dioxide, energy, and water. Carbon dioxide and water are the waste products. The energy is used to power cellular activities, such as growth and transport of molecules.
Releases Energy

7. Respiration Can be expressed chemically
C6H12O O2  6CO H2O + energy
Respiration can be written using chemical notation. Since glucose and oxygen are used, these are the reactants. They react inside cells to make carbon dioxide, water, and energy.
Reactants
Products

8. Photosynthesis & Respiration
Autotrophs
Captures energy
Uses carbon dioxide, water, and solar energy
Creates sugar and oxygen
Respiration
Autotrophs & heterotrophs
Releases energy
Uses sugar and oxygen
Creates carbon dioxide and water, converts energy
Photosynthesis and cellular respiration are related, but they have many differences. Photosynthesis can only be performed by autotrophs, such as plants. Respiration is done by all living things, both autotrophs and heterotrophs. Remember that heterotrophs must obtain stored energy such as sugars by consuming other organisms.
Photosynthesis converts solar energy into sugars. Respiration converts this energy into ATP. As the ATP is used to do work, some of the energy is released as heat.
Photosynthesis uses carbon dioxide, water, and energy while respiration uses sugar and oxygen.
Photosynthesis creates sugar and oxygen while respiration creates carbon dioxide and water and converts energy.
You may notice that the reactants of photosynthesis are the same as the products of respiration. Similarly, the products of respiration are the reactants of photosynthesis. Remember that matter flows through an ecosystem. Here, carbon, hydrogen, and oxygen atoms are being recycled as energy flows through and powers the process.

9. Photosynthesis & Respiration
We can draw this relationship as a cycle. Photosynthesis begins with carbon dioxide and water. It is powered by energy from the sun. It produces sugar and oxygen.
Respiration starts with sugar and oxygen. It releases energy and forms carbon dioxide and water as byproducts.
Keep in mind that these molecules could be used as something else in the ecosystem, but they could re-enter this cycle.

10. Photosynthesis & Respiration
6CO H2O + energy  C6H12O O2
Respiration
C6H12O O2  6CO H2O + energy
Remember that both photosynthesis and respiration can be written chemically. Here, you can see that the reactants of one process are the products of the other.
Reactants
Products

11. Photosynthesis & Respiration
Learning Objectives
Understand photosynthesis
Understand respiration
Relate photosynthesis and respiration
You should now understand and be able to describe both photosynthesis and respiration. You should also be able to describe the interconnectedness between the two in terms of both matter and energy.