Problem 1 - Biology Today and Tomorrow with Physiology

Question

In a land plant, most of the carbon dioxide used in photosynthesis comes from _______ a. glucose b. the atmosphere c. water d. soil

Step-by-Step Solution

Answer

Most carbon dioxide used in photosynthesis comes from the atmosphere.

Step 1: Understanding Photosynthesis Inputs

Photosynthesis is a process used by plants to convert light energy into chemical energy stored in glucose. The inputs for this process are water ( H2O ), carbon dioxide ( CO2 ), and sunlight. This understanding is crucial because it helps identify the source of carbon dioxide.

Step 2: Identifying Sources of Carbon Dioxide

Carbon dioxide ( CO2 ) can come from various sources: the atmosphere, soil, or water. In terrestrial (land) plants, CO2 is primarily absorbed from the air through small openings called stomata on the leaves.

Step 3: Evaluating Answer Options

Let's go through each option: a. Glucose - Produced from photosynthesis, not a source of CO2 . b. Atmosphere - Yes, this is where land plants absorb CO2 from. c. Water - Water provides hydrogen and oxygen but not CO2 . d. Soil - Provides nutrients to plants but not CO2 . Through this evaluation, b (atmosphere) is the only viable source for most of the carbon dioxide used in photosynthesis in land plants.

Key Concepts

Carbon Dioxide Absorption

In the process of photosynthesis, plants absorb carbon dioxide from their surroundings to produce glucose and release oxygen. This crucial function takes place mostly in the leaves where the plant collects carbon dioxide from the atmosphere. The absorbed (
) carbon dioxide serves as a carbon source, which is needed to synthesize glucose, a simple sugar that serves as the plant's energy source.

Plants have a special pigment called chlorophyll that captures sunlight, providing the energy necessary for photosynthesis. During this process, the absorbed carbon dioxide combines with water (
) ( H_2O ) through a series of chemical reactions to form glucose (
) ( C_6H_{12}O_6 ), while oxygen (
) ( O_2 ) is released as a by-product. Understanding carbon dioxide absorption is essential to grasp how plants contribute to the balance of gases in our environment.

Stomata Function

Stomata are small openings found primarily on the surfaces of plant leaves. They function as gateways, allowing gas exchange between the plant's internal tissues and the environment. These tiny pores play an essential role in regulating carbon dioxide uptake, as well as releasing oxygen produced during photosynthesis.

• When stomata open, carbon dioxide from the atmosphere enters the leaf.
• Inside the leaf, carbon dioxide is used in photosynthesis to produce glucose.
• Simultaneously, water vapor and oxygen exit through the stomata.

The opening and closing of stomata are controlled by specialized cells known as guard cells. These cells react to environmental signals such as light, humidity, and carbon dioxide concentration to adjust stomatal openings. This regulation helps prevent water loss, while still allowing for the essential gas exchange needed for photosynthesis.

Atmosphere as CO2 Source

The atmosphere serves as the primary source of carbon dioxide for land plants, which is crucial for photosynthesis. Carbon dioxide makes up a small percentage of the atmospheric gases, a mere 0.04% (
) , yet it is vitally important for plant life.

Plants play a significant role in the carbon cycle by absorbing carbon dioxide and releasing oxygen, maintaining the balance necessary for sustaining life on Earth.

• Plants absorb carbon dioxide from the air through stomata in their leaves.
• Carbon dioxide is then fixed in the Calvin cycle, part of the photosynthetic process.
• This uptake is essential in reducing atmospheric carbon levels and curbing climate change impacts.

Understanding the role of the atmosphere as a CO2 source highlights the importance of protecting our environment and ensuring plants continue to mitigate excess carbon emissions effectively.