Biology Sample

Unit I

Biological Systems, Evolution and Biodiversity

Chapter 1

Introduction to Concepts of Biology 1.1

INTRODUCTION

Welcome to biology, the scientific study of life. We are living in a golden age of biology and you are becoming involved with biology during its most exciting era. The largest and best-equipped community of scientists in history is beginning to solve biological puzzles that once seemed unsolvable. We are moving ever closer to understanding how a single microscopic cell develops into a complex plant or animal; how plants convert solar energy to the chemical energy of food; how the human mind works; how various forms of life network in biological communities such as forests and coral reefs; and how the great diversity of life on Earth evolved from the first microbes. The more we learn about life, the more fascinating it becomes, as progress on one question leads to even more questions that will captivate curious minds for decades to come. More than anything else, biology is a quest, an ongoing inquiry about the nature of life. Modern biology is as important as it is inspiring, with exciting breakthroughs changing our very culture. Genetics and cell biology are revolutionizing medicine and agriculture. Molecular biology is providing new tools for investigating ancestry and solving crimes. Ecology is helping us evaluate environmental issues, such as the causes and consequences of global warming. Neuroscience and evolutionary biology are reshaping psychology and sociology. These are just a few examples of how biology is woven into the fabric of society as never before. It is no wonder that biology is part of our daily lives. The phenomenon we call life defies a simple, one-sentence definition. Yet almost any child perceives that a dog or a bug or a plant, is alive, while a rock is not. We recognize life by what living things do. Figure 1.1 highlights some of the properties and processes we associate with life. As we set off to explore life, it helps to have a panoramic view of the vast field of study before us. This opening chapter introduces the wide scope of biology, highlights the diversity of life, describes themes, such as evolution, that unify all of biology, and examines methods of inquiry that biologists use to explore life.

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Biology Exploring life has never been more exhilarating. In this chapter, we begin our exploration of biology, the scientific study of life, by introducing some common themes in biology, which will help guide our study of life, its evolution, and all its diversity.

(a) Order. This close-up of a sunflower illustrates the highly ordered structure that characterizes life.

(d) Regulation. The regulation of blood flow through the blood vessels of this jackrabbit’s ears helps maintain a constant body temperature by adjusting heat exchange with the surrounding air.

(b) Evolutionary adaptation. The appearance of this pygmy seahorse camouflages the animal in its environment. Such adaptations evolve over many generations by the reproductive success of those individuals with heritable traits that are best suited to their environments.

(c) Response to the environment. This Venus’ flytrap closed its trap rapidly in response to the environmental stimulus of a damselfly landing on the open trap.

(e) Energy processing. This hummingbird obtains fuel in the form of nectar from flowers. The hummingbird will use the chemical energy stored in its food to power flight and other work.

(f) Growth and development. Inherited information carried by genes controls the pattern of growth and development of organisms, such as this Nile crocodile.

(g) Reproduction. Organisms (living things) reproduce their own kind. Here an emperor penguin protects its baby.

Figure 1.1 Some properties of life. 2

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Introduction to Concepts of Biology

1.2

THEMES IN THE STUDY OF BIOLOGY

1.2.1 Hierarchy of Biological Organization The study of life extends from the microscopic scale of cells and molecules to the global scale of the biosphere. Figure 1.2 takes you on a tour of these levels of biological organization, starting at the highest level. The biosphere, which consist of all the environments on Earth that support life—most regions of land, bodies of water, and the lower atmosphere. Ecosystems consist of all the organisms living in a particular area, as well as all the nonliving, physical and chemical components of the environment with which the organisms interact, such as air, soil, water, and sunlight. The entire array of organisms inhabiting a particular ecosystem is called a community. The community in the coastal ecosystem shown in Figure 1.2 includes the pelicans and the fish they eat, as well as seagulls; raccoons that eat pelican eggs; a huge diversity of insects, mollusks, and worms; many different kinds of plants and fungi; and enormous numbers of microscopic organisms, such as protists, algae, and bacteria. Each of these unique forms of life is called a species. A population consists of all the individuals of a species living in a specified area, such as all the brown pelicans in the coastal community. Below the population level in the hierarchy is the organism, an individual living thing.

Figure 1.2 Life’s hierarchy of organization. 3

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Biology Within a complex organism such as a pelican, life’s hierarchy continues to unfold. An organ system, such as a circulatory system, digestive system, or nervous system (shown in Figure 1.2) consists of several organs that work together in performing specific functions. For instance, the main organs of the nervous system, are the brain, the spinal cord, and the nerves that transmit messages between the spinal cord and other parts of the body. A bird’s nervous system controls its ability to fly. As we continue down through the hierarchy, each organ is made up of several different tissues, each with a specific function and made up of a group of similar cell. The nervous tissue in a pelican’s brain has millions of nerve cells organized in a communication network of spectacular complexity. A cell is separated from its environment by a boundary called a membrane. In the nerve cell shown in Figure 1.2, you can see several organelles, such as the nucleus. An organelle is a membrane-bound structure that performs a specific function in a cell. Finally, we reach the level of molecules in the hierarchy. A molecule is a cluster of atoms held together by chemical bonds, for example DNA (deoxyribonucleic acid). DNA molecules provide the blueprint for constructing the organism’s other molecules and transmit this information from parents to offspring. In the computer graphic of a small section of DNA at the bottom of Figure 1.2, each of the spheres represents an atom, the smallest particle of ordinary matter. Now work your way in the opposite direction in Figure 1.2, building life’s hierarchy from molecules to the biosphere. It takes many molecules to build organelles and make a cell, many cells to make a tissue, several kinds of tissues to make an organ, and so on. At each new level, notice that there are novel properties that emerge, properties that were not part of the components of the preceding level. For example, life emerges at the level of the cell—a test tube full of organelles is not alive. Such properties illustrate an important theme of biology, called emergent properties. The familiar saying that “the whole is greater than the sum of its parts” captures this idea. The emergent properties of the whole result from the specific arrangement and interactions of the component parts.

Feedback Regulation in Biological Systems A kind of supply-and-demand economy applies to some of the dynamics of biological systems. For example, when your muscle cells require more energy during exercise, they increase their consumption of the sugar molecules that provide fuel. In contrast, when you rest, a different set of chemical reactions converts surplus sugar to substances that store the fuel. In feedback regulation, the output, or product, of a process regulates that very process. In life, the most common form of regulation is negative feedback, in which accumulation of an end product of a process slows that process (Figure 1.3). Though less common than negative feedback, there are also many biological processes regulated by positive feedback, in which an end product speeds up its production. The clotting of your blood in response to injury is an example (Figure 1.4).

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Introduction to Concepts of Biology

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Figure 1.3 Negative feedback. This

three-step chemical pathway converts substance A to substance D. A specific enzyme catalyzes each chemical reaction. Accumulation of the final product (D) inhibits the first enzyme in the sequence, thus slowing down production of more D.

Figure 1.4 Positive feedback. In positive

feedback, a product stimulates an enzyme in the reaction sequence, increasing the rate of production of the product. Positive feedback is less common than negative feedback in living systems.

Feedback is a regulatory motif common to life at all levels, from the molecular level to the biosphere. Such regulation is an example of the integration that makes living systems much greater than the sum of their parts.

As a follow up to this overview of life’s structural hierarchy, we will take a closer look in just two biological levels near opposite ends of the size scale, ecosystems cells. Check Your Progress 1.2

1. Which of the following levels of biological organization includes all others in the list: cell, molecule, organ, tissue?

1.3 1.3.1

A CLOSER LOOK AT ECOSYSTEMS Life Does Not Exist in a Vacuum

Organisms interact with both the living and nonliving components of their environment. Figure 1.5 is a simplified diagram of these interactions. Plants and other photosynthetic organisms are the producers that provide the food for a typical ecosystem. Consumers are organisms, such as animals that feed on producers and other consumers. A tree, for example absorbs water (H2O) and minerals from the soil, and its leaves

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Biology

Figure 1.5 The cycling of nutrients and flow of energy in an ecosystem.

take in carbon dioxide (CO2) from the air. In photosynthesis, a tree’s leaves use energy from sunlight to convert CO2 and H2O to sugar and oxygen (O2). The tree releases O2 to the air, and its roots help form soil by breaking up rocks. Thus, both organism and environment are affected by the interactions between them. The consumers of the ecosystem eat plants and other animals. The giraffe in Figure 1.5 eats leaves; the leopard eats meat. All animals take in oxygen from the air and release carbon dioxide. Their wastes return other chemicals to the environment. Another vital part of the ecosystem includes the bacteria, fungi, and small animals in the soil that decompose wastes and the remains of dead organisms. These decomposers act as recyclers, changing complex matter into simpler mineral nutrients that plants can use.

System Dynamics System dynamics denotes those intrinsic functions through which a system becomes self-regulating, self-sustaining and capable of recovery from external forces. For example ecosystem dynamics (Module 1.3.2).

1.3.2

Ecosystem Dynamics

The dynamics of ecosystems include two major processes—the recycling of chemical nutrients and the flow of energy. These processes are illustrated in Figure 1.5. The most basic chemicals necessary for life—carbon dioxide, oxygen, water, and various minerals—flow from the air and soil to plants, to animals and decomposers, and back to the air and soil. As shown by the blue arrow in the Figure 1.5, chemical nutrients cycle within an ecosystem. By contrast, an ecosystem gains and loses energy constantly. Energy flows into the ecosystem when plants and other photo synthesizers absorb light energy from the sun (yellow arrow) and convert it to the chemical energy of sugars and other complex molecules. Chemical energy (green arrow) is then passed through a series of consumers and, eventually, decomposers, powering each organism in turn. In the process of these energy conversions between and within organisms, some energy is converted to heat, 6

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Introduction to Concepts of Biology which is then lost from the system (red arrows). In contrast to chemical nutrients, which recycle within an ecosystem, energy flows through an ecosystem, entering as light and exiting as heat. Check Your Progress 1.3

1. Explain how the photosynthesis of plants functions in both the cycling of chemical nutrients and the flow of energy in an ecosystem.

1.4 1.4.1

A CLOSER LOOK AT CELL Cells Are the Structural and Functional Units of Life

The cell has a special place in the hierarchy of biological organization. It is the level at which the properties of life emerge—the lowest level of structure that can perform all activities required for life. A cell can regulate its internal environment, take in and use energy, respond to its environment, and develop and maintain its complex organization. The ability of cells to give rise to new cells is the basis for all reproduction and for the growth and repair of multicellular organisms. Your every movement and thought are based on the activities of muscle cells and nerve cells. Even a global process such as the cycling of carbon is the result of cellular activities, including the photosynthesis of plant cells and the cellular respiration of nearly all cells, a process that breaks down sugar for energy and releases carbon dioxide. Cells illustrate another theme of biology: the correlation of structure and function. Experience shows you that form generally fits function. A screwdriver tightens or loosens screws, a hammer pounds nails. Because of their form, these tools can’t do each other’s jobs. Applied to biology, this theme of form fitting function is a guide to the structure of life at all its organizational levels. As you can see in Figure 1.2, the long extension of the nerve cell enables it to transmit impulses throughout the body. Often, analyzing a biological structure gives us clues about what it does and how it works. The properties of life emerge from the ordered interactions of the structures of a cell. Such a combination of components forms a more complex organization called a system. Cells are examples of biological systems, as are organisms and ecosystems. Systems and their emergent properties are not unique to life. Consider a box of bicycle parts. When all of the individual parts are properly assembled, the result is a mechanical system you can use for exercise or transportation.

Systems Biology The ultimate goal of systems biology is to model the dynamic behavior of whole biological systems. Accurate models will enable biologists to predict how a change in one or more variables will impact other components and the whole system. How, for example, will a slight increase in a muscle cell’s calcium concentration affect the activities of the dozens of proteins that regulate muscle contraction? Systems biology is relevant to the study of life at all levels. The basics of the systems strategy are straightforward enough. First, it is necessary to inventory as many parts as possible, such as all the known genes and proteins in a cell 7

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