Chapter 21, Problem 7A

Summary Introduction

Introduction :

Plants are vital to our survival. The oxygen we breathe, the food we eat, and many of the things that make our lives comfortable, such as clothing, furniture, and our homes, come from or are parts of plants. Many of the differences between plants and charophytes have to do with the adaptations of the plants to life on soil. Plants living on land face four big challenges: having food, keeping standing, preserving fertility and reproducing.

Answer to Problem 7A

Correct answer :

The correct answer is option (C) obtaining enough water

Explanation of Solution

Explanation/justification for the correct answer :

Option (D) obtaining enough water. Materials provided by a land-growing photosynthetic organism are found in two somewhat different environments: air and soil. Light and carbon dioxide are predominantly present above ground, while water and mineral nutrients are present mostly in soil. Thus, it was a major obstacle for plants to live on land. So, the correct answer is option (D).

Explanation for incorrect answer :

Option (A) obtaining enough light. Light is mostly available above the ground. Thus, it was not a major obstacle for plants to live on land. So, this is an incorrect answer.

Option (B) obtaining enough soil. Beneath the earth, the roots of a plant accumulate water and important soil minerals. Thus, it was not a major obstacle for plants to live on land. So, this is an incorrect answer.

Option (C) obtaining enough oxygen. Shoots bear leaves above ground. The leaves make food from carbon dioxide using sunlight as an energy source. There are areas of certain plants above the ground that helps the plant body to hold water. The cuticle often reduces the carbon dioxide and oxygen flow between the ambient air and the interior of the photosynthesizing plants. Thus, it was not a major obstacle for plants to live on land. So, this is an incorrect answer.