Chapter 40, Problem 40.1CR

Summary Introduction

To explain: The challenges for a spherical shape pose of a large animal in carrying out exchange with the environment.

Introduction:

The fundamental aspects of an animal is to interact with its environment are size and shape. These aspects are referred as the elements of body plan or design. This does not imply a process of conscious invention. A pattern of development programmed by the genome results in the body plan of an animal and is also the product of millions of years of evolution.

Explanation of Solution

Animals must exchange gases, nutrients, and waste products with the environment. This requirement imposes an additional limitation on body plans. A single-celled animal can perform its exchange activities easily as it is composed of sufficient membrane surface area compared to large animal. The rate of exchange is proportional to the membrane surface area involved in exchange, whereas the amount of material that must be exchanged is proportional to the body volume. The spherical-shaped large animal has the minimum surface area per unit volume, the ratio of surface area to body volume decreases, as body size increases. Hence larger animals with a spherical shape would face many challenges in carrying out exchange with the environment due to their body plan.

Conclusion

As evolution results in many changes in the elements like shape and size of animals, some evolutionary changes cause difficulties in their survival. The exchange of materials with the environment takes place across the membrane surface area of the animal. As there is no sufficient membrane surface area for spherical-shaped large animals, they face many complications in their exchange of material with the environment.