Photosynthesis and Cellular Respiration in Plants

Most living things obtain their energy either directly or indirectly from the energy of sunlight captured through photosynthesis.

Photosynthesis in 2 Stages

1. Pigments in the leaves' cells (chlorophyll) capture or absorb the sun's energy, which is used to power the second stage. The leaf cells also need water (absorbed through roots) and carbon dioxide (that enters through small openings on the undersides of leaves called stomata).
2. Inside the chloroplasts, water and carbon dioxide are transformed into glucose and oxygen. Plants use glucose for food and store what they don't need as starch (energy for later use) and cellulose (that makes up the cell walls). Oxygen and water exit the leaf through the stomata.

Stomata

Carbon dioxide enters the plant through small openings on the undersides of the leaves called stomata. Water can also be absorbed in the leaves through osmosis. Oxygen and water exit through the stomata.

Photosynthesis Equation

Water + Carbon Dioxide + Light Energy -> Glucose + Oxygen

6H₂O + 6CO₂ + Light Energy -> C₆H₁₂O₆ + 6O₂

Aerobic Respiration

Glucose + Oxygen -> Carbon Dioxide + Water + Energy

C₆H₁₂O₆ + 6O₂ -> 6CO₂ + 6H₂O + Energy

During photosynthesis, plants capture the energy from sunlight in the chloroplasts and save it in the form of carbohydrates, including sugars and starches. These carbohydrates are broken down in the cell's mitochondria when the cell needs energy during respiration.

Respiration in 2 Stages

1. In the cytoplasm, glucose molecules are broken down into smaller molecules.
2. In the mitochondria (powerhouse), the small molecules are broken down even further. These reactions require oxygen and produce a lot of energy.

Anaerobic Respiration

For some bacteria and yeasts, oxygen is toxic. These organisms use fermentation as a method of obtaining energy that does not require oxygen. However, the energy output is much lower with fermentation than with respiration.

Since fermentation is far less effective than cellular respiration, it is typically seen only in small organisms, such as bacteria, fungi, and yeast, that can survive on this low energy yield.

2 Types of Fermentation

• Type 1: Alcoholic fermentation is the conversion of glucose to alcohol and carbon dioxide without oxygen, to produce energy.
• Type 2: Lactic-acid fermentation is produced by some fungi and bacteria, such as Lactobacillus, where glucose is broken down to lactic acid to produce energy.

Lactic Acid (C₃H₆O₃)

When you run as fast as you can for as long as you can, your muscle cells run out of oxygen, and lactic acid fermentation supplies the cells with energy.

The lactic acid is what makes your muscles ache.