Chapter 8, Problem 27A

Summary Introduction

To describe:

Two alternative photosynthetic pathways found in plants and how these adaptations help plants.

Introduction:

Photosynthesis is a process in which light energy from the Sun is converted to chemical energy for use by the cell. Autotrophs use the solar energy along with carbon dioxide and water to form glucose and oxygen. The environment in which an organism lives has an impact on the organism’s ability to carry out photosynthesis. Decreased amount of water and carbon dioxide decreases the organism’s ability to convert light energy to chemical energy. Hence, many plants follow alternative pathways to maximize energy conversion.

Answer to Problem 27A

Two alternative photosynthetic pathways found in plants are C₄and CAM pathways. These pathways allow for sufficient CO₂ uptake while minimizing the water loss.

Explanation of Solution

There are alternative photosynthetic pathways found in plants:

1. C₄plants- This pathway helps plants like sugar cane and corn maintain photosynthesis while minimizing water loss. These plants are called C₄ plants because they fix carbon dioxide into four carbon compounds instead of three- carbon compounds during the Calvin cycle. In these plants, the stomata remain closed during hot days while the four- carbon compounds are transferred to special cells where CO₂ enters the Calvin cycle. This allows for sufficient CO₂ uptake while minimizing the water loss.
2. CAM plants- This is called the crassulacean acid metabolism (CAM photosynthesis) used by some plants to maximize photosynthesis when there is scarcity of water. It is found in plants that live in deserts, salt marshes and other places where access to water is limited. CAM plants allow CO₂ to enter leaves only at night when the air is cooler and humid. At night, these plants fix CO₂into organic compounds. During the day, CO₂ is released from the compounds and enters the Calvin cycle. This pathway also allows for sufficient CO₂ uptake while minimizing the water loss.