Photosynthesis Lesson : Definition, Process, and Diagrams

Lesson Overview

• What Is Photosynthesis?
• What Does Photosynthesis Produce?
• Factor Affecting Photosynthesis
• What Is the Process of Photosynthesis?
• Stages of Photosynthesis
• Photosynthesis Assessment

Photosynthesis process fuels plant growth and development. It is vital for Earth's ecosystems, playing a critical role in regulating the planet's climate. Understanding photosynthesis is key to comprehending plant biology and its significance for life on Earth.

What Is Photosynthesis?

Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water. Oxygen is released as a byproduct. 

Essentially, light energy is converted into chemical energy in the form of sugars (glucose). For instance, a sunflower uses photosynthesis to create the energy it needs to grow tall and produce its seeds. This process occurs in organelles called chloroplasts, which contain the green pigment chlorophyll. 

Fig.1 Depicting photosynthesis in a sunflower, showing inputs of sunlight, carbon dioxide, and minerals, and outputs of oxygen and sugar.

What Does Photosynthesis Produce?

Photosynthesis primarily produces two essential substances: glucose and oxygen.  

• Glucose: This is a type of sugar that serves as the primary source of energy for plants. It's the fuel that powers their growth, development, and all metabolic processes. Plants use glucose in several ways: 
  
  • Immediate Energy: Glucose can be used directly for cellular respiration, the process that converts the chemical energy in glucose into a usable form of energy for the plant (ATP). 
    
  • Storage: Glucose can be converted into starch for long-term energy storage. Starch is stored in various plant parts, such as roots, stems, and leaves. Think of potatoes, which are storage organs packed with starch. 
    
  • Structural Material: Glucose can be used to build cellulose, a major component of plant cell walls. Cellulose provides structural support to the plant, making it rigid and strong. 
    
• Oxygen: This gas is a byproduct of photosynthesis. It's released into the atmosphere and is essential for the respiration of most living organisms, including animals, fungi, and many bacteria. We breathe this oxygen, and it's vital for our survival.
  
  

Factor Affecting Photosynthesis

Several factors influence the rate of photosynthesis. Understanding these factors is crucial for optimizing plant growth.  

• Light Intensity: As light intensity increases, the rate of photosynthesis generally increases up to a certain point. Beyond this point, excessive light can damage the photosynthetic machinery, leading to a decrease in the rate. Think of it like a car engine – it performs best within a certain RPM range; pushing it too hard can cause damage. 
  
• Carbon Dioxide Concentration: Similar to light intensity, increasing carbon dioxide concentration generally increases the rate of photosynthesis up to a certain point. However, very high concentrations can be detrimental. 
  
• Temperature: Photosynthesis is an enzyme-driven process, and enzymes are sensitive to temperature. There's an optimal temperature range for photosynthesis. Below this range, the rate slows down, and above it, the enzymes can become denatured, also slowing down the process. 
  
• Water Availability: Water is a crucial reactant in photosynthesis. A lack of water can cause plants to close their stomata (small pores on leaves), reducing carbon dioxide uptake and thus slowing down photosynthesis. Water stress also affects other processes important for photosynthesis. 
  
• Chlorophyll Content: Chlorophyll is the pigment that absorbs light energy. A higher chlorophyll content generally leads to a higher rate of photosynthesis. This is why healthy, green plants are typically more efficient at photosynthesis.
  
  

What Is the Process of Photosynthesis?

The process of photosynthesis, by which plants convert light energy into chemical energy in the form of sugars, occurs within specialized organelles called chloroplasts, primarily in the leaves. Chloroplasts contain the green pigment chlorophyll, essential for absorbing light energy. 

Fig. 2 Highlighting the two main stages: the light-dependent reactions and the Calvin cycle.

Stages of Photosynthesis

Photosynthesis can be broadly divided into two main stages: the light-dependent reactions and the light-independent reactions (Calvin cycle).

1. Light-Dependent Reactions:

• Location: Thylakoid membranes within the chloroplasts.  
• Process: Light energy is absorbed by chlorophyll and other pigments. This energy is used to split water molecules into oxygen, protons (H+), and electrons. The electrons are passed along an electron transport chain, releasing energy that is used to create ATP (adenosine triphosphate), an energy-carrying molecule, and NADPH (nicotinamide adenine dinucleotide phosphate), an electron carrier. Oxygen is released as a byproduct.  

2. Light-Independent Reactions (Calvin Cycle):

• Location: Stroma, the fluid-filled space within the chloroplast.  
• Process: ATP and NADPH from the light-dependent reactions provide the energy and electrons needed to convert carbon dioxide into glucose. This is a cyclical process involving a series of enzyme-catalyzed reactions. The initial carbon dioxide molecule is fixed into an organic molecule, and through a series of steps, it is eventually regenerated to continue the cycle. 
  
  

Photosynthesis Assessment

1. Fill in the Blanks

1. Photosynthesis is the process by which plants convert ________ energy into ________ energy.  
2. The green pigment that absorbs light energy in plants is called ________.  
3. ________ is the primary source of energy for plants.  
4. Besides glucose, ________ is another crucial product of photosynthesis that is vital for most living organisms.
5. Small pores on the leaves of plants through which gases enter and exit are called ________.  

2. Short Answer Questions

1. Briefly describe the two main stages of photosynthesis.
2. Explain why photosynthesis is important for life on Earth.
3. List three factors that can affect the rate of photosynthesis.
4. How do plants store the glucose produced during photosynthesis?
5. What is the role of chlorophyll in photosynthesis?

Answer:

Fill in the Blanks

1. light, chemical
2. chlorophyll
3. glucose
4. oxygen
5. stomata

Take This Quiz :

Photosynthesis In Green Plants Quiz