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Philosophy of the Biology Section

Philosophy of the Biology SectionThe MCAT Prep Course Biology Section is designed to help you understand major concepts in biology and to use this knowledge to solve problems. Each chapter contains MCAT-style questions with answers and full explanations.The MCAT questions are written to test your knowledge of basic concepts in biology and problem solving abilities; they do not stress rote memorization of facts.

Most questions are based on short (approximately 250 word) passages. Four to eight questions will be asked for each passage. These questions may require you to interpret data from graphs, tables or figures. There are 10 to 11 problem sets of this type on the exam, as well as 15 questions that are independent of any passages and of each other.
Topics and concepts in biology are very extensive. The MCAT does not test your comprehension of all areas of basic biology, but instead focuses on vertebrates and microbes, with an emphasis on life processes. Biology Section of MCAT consists of 5 sub-sections, they are:

Molecular Bilology

Molecular biology, as the term is often used today, refers specifically to the study of the molecules involved in the transmission and usage of information, that is, molecular genetics. Modern molecular biology is a relatively new field, and its importance cannot be understated. Understanding the structure and function of DNA, how it enables information to be passed on from parent to offspring, and how it controls the cellular activities of an organism have ushered in the most exciting period in the history of biology. This knowledge has made possible potential advances in medicine and technology that are only now being realized. This section will explore the structure and function of DNA and RNA, their roles in protein synthesis, and the central position these molecules occupy in directing cellular activities.
The molecular biology portion of the MCAT, while including this information, has a broader scope, and thus uses the term in a wider sense. Also included in this section are topics that might traditionally be considered the province of biochemistry. These topics include the structure and function of enzymes and the various processes by which cells transform and utilize energy. This field is sometimes referred to as bioenergetics, or the study of cellular metabolism. All living things need energy in order to survive. Animals employ a complex series of interconnected chemical reactions in order to extract usable energy from the food they eat, and the pathways involved have been elucidated rather thoroughly.
What all of these topics have in common explains their inclusion in this “molecular biology” section. Whether we are discussing genetics, metabolism, or related topics, this section is looking at the processes of life viewed from the perspective of the molecules involved. It was recognized by early biochemists that the chemicals they extracted from living things were similar in all organisms, and could be grouped into four major categories. Initially referred to as “organic” molecules because they were associated with life, we now recognize that the proteins, nucleic acids, lipids, and carbohydrates we will explore in Chapter 2 comprise a small portion of all the carbon-based molecules that exist. However, they are all vital to the survival of every organism. In this section, we will thus also survey the structures and functions of the major biomolecules, and examine their roles in essential life processes. Although this survey of biological molecules is placed in the Chemistry portion of the MCAT, it is necessary to include it here as a foundation for understanding their behaviors and properties in a biological context.


This section covers the following topics:
  1. Biological Molecules
  2. Enzymes and Energy
  3. Cellular Metabolism
  4. DNA Structure and Function
  5. Transcription and Translation


Organisms are classified according to the structure and function of their cells and how those cells may be arranged into tissues, organs and systems. Most scientists use the following classification scheme, known as the Five-Kingdom system: 
  1. Monera (bacteria)- prokaryotes (cells have no nucleus), single-celled;
  2. Protists- eukaryotes (cells have a nucleus), usually single-celled;
  3. Fungi- eukaryotes, mostly multicellular, heterotrophs (feed off of other organisms), digest food outside the cell;
  4. Plantae- eukaryotes, mostly multicellular, autotrophs (rely on photosynthesis for food production);
  5. Animalia- eukaryotes, multicellular, heterotrophs, ingest food. 
Not included in this system are the viruses. Although they are not considered to be alive, viruses have much in common with living cells and depend on them to exist.
The next three sections of this book will explore the structure and function of different cells in detail. This section focuses on microscopic organisms (viruses, bacteria and fungi), often the cause of devastating diseases.
Humans and microbes have evolved together and now coexist in a variety of ways. This coexistence is known as symbiosis and can be classified based on the exact nature of the relationship: 
  1. Mutualism: the relationship is beneficial to both species
  2. Commensualism: one species benefits but the other is unharmed
  3. Parasitism: one species benefits and the other is harmed  
Not all relationships are easy to classify into one particular category. In addition, changes in the environment will often alter the relationship. However, these labels help us to think about the nature and consequences of species interactions.
The transmission of microorganisms to humans (infection), and hence the mode of transmission of diseases, is classified into the following categories:
  • Direct Contact: Sexually transmitted diseases, such as gonorrhea and syphilis, can only be transmitted through direct contact.
  • Indirect Contact: Many microorganisms can be deposited on surfaces, including food, which can then be touched or consumed by other individuals. Two examples are typhoid and athlete’s foot.
  • Inhalation of airborne organisms: Some organisms are spread through the air by coughing and sneezing, or can be inhaled from other sources and infect an individual via the respiratory tract. One example of this is the hanta virus.
  • Transmission by biological vectors: Some microorganisms can be carried by other organisms and, when a human is bitten, the microorganism will be transmitted to the individual. Lyme disease and rocky mountain spotted fever are bacterial diseases spread by ticks, and malaria is a parasite carried by mosquitoes.
This section covers the following topics:
  • Viruses
  • Bacteria
  • Fungi

Eukaryotic Cell Biology

Our discussion of cell biology must begin with two principles stated in The Cell Theory: 
  1. The cell is the basic unit of life.
  2. New cells can only arise from preexisting cells. 
In this section, we will explore the structure and function of eukaryotic cells, specifically animal cells, and how they reproduce. In many instances, cells will develop over time to change their structure and function. This will be addressed in Section IV.
It is important to understand that cells come in many different shapes and sizes.
For example, sperm cells are basically DNA with a tail, muscle cells are filled with mitochondria (to supply energy for movement) and neurons have enormously long axons. The typical animal cell is 10-30 micrometers in diameter, whereas an egg cell is 100 micrometers, and the yolk of a chicken egg (which is one single cell!) is 3 cm. Although all these cells have different shapes, sizes and functions, they all have the same basic structure. In addition, with the exception of sperm and eggs, all cells reproduce in the same manner, via replication of the DNA and cytoplasmic division to produce two equal cells.
The next few chapters will discuss the structure and function of organelles and the cell membrane, and examine the process of mitosis.


This section covers the following topics:

  • Cellular Organelles
  • Plasma Membrane and Transport
  • Mitosis


Vertebrate Anatomy and Physiology

Anatomy and physiology are disciplines usually studied together that deal with the structure and function of multicellular organisms. Anatomy is the science that deals with biological structures (sometimes called morphology, literally, “the study of form”). How are the parts of an organism arranged, and what are their designs? Physiology is the science that explores the functioning of these biological structures. What does each part of an organism do, and how is it accomplished?
Central to the study of anatomy and physiology is a hierarchical way of looking at biological entities. The cell is the fundamental unit of life, even though it has many component parts, so it would not be improper to talk about the anatomy and physiology of the cell itself. Traditionally, however, these terms are more commonly reserved for the study of multicellular organisms, namely animals. We will direct our study at the anatomy and physiology of vertebrate animals (animals with “backbones”) because these are the organisms emphasized on the MCAT. Since humans are vertebrates, it is convenient and reasonable to use human anatomy and physiology as an example of vertebrate systems in general. Remember, however, that you may be asked questions about other vertebrates (including other mammals, birds, reptiles, and fish), and, to the extent it is relevant, any major differences that exist between these and human systems will be emphasized.
Returning to the theme of hierarchy, the structure and function of a multicellular animal may be approached on many levels, from the simplest to the most complex. As noted before, the cell is the fundamental living unit, and the general functioning of the cell itself is the subject of previous chapters. In an animal, cells undergo differentiation and become specialized -- all of the cells in an animal’s body are not the same, and the first chapter in this section deals with the major types of cells that exist in vertebrate bodies. Groups of specialized cells working together towards a common function are referred to as tissues, also discussed in Chapter 13. A structure performing a specific function that is made up of more than one tissue type is referred to as an organ, and groups of organs functioning in concert are said to be organ systems. The remaining chapters in this section deal with the various organ systems in the vertebrate body. These are grouped together due to similarities in structure, function, or both. Ultimately, all of the organ systems functioning together will create and sustain the organism itself, which is the highest level of hierarchy with which we need be concerned here. All of an animal’s systems must function harmoniously in order for homeostasis to be maintained. Homeostasis is the maintenance of the relative constancy of the internal environment of an organism (i.e., temperature, pH, water balance, etc.), and must be preserved if the organism is to remain healthy. A disruption in homeostasis may lead to disease and ultimately death.
This section covers the following topics.
  1. Specialized Eukaryotic Cells and Tissues
  2. The Nervous and Endocrine Systems
  3. The Cardiovascular And Lymphatic Systems And The Immune Response
  4. The Digestive, Respiratory, and Urinary Systems
  5. The Integumentary, Skeletal and Muscular Systems
  6. Reproductive Systems, Gametogenesis, and Early Development

Genetics and Evolution

The topics of genetics and evolution are intimately linked together. Not only do they complement each other, but they are central to our current understanding of all aspects of biology. These two topics unite and unify the various fields of biology, including molecular biology, microbiology, and anatomy and physiology. Therefore, the study of genetics and evolution is an absolute necessity for all students of biology.
In addition, the field of genetics is rapidly advancing. This has important consequences in many areas, not the least of which is medicine. Genetics has aided our understanding of cancer, inherited diseases, reproduction, infectious diseases, and much more. In the future, we will rely heavily on genetics to help us diagnose and treat a host of medical conditions.
This introductory chapter will familiarize you with the concepts that form the foundations of biology. These key ideas are implicit in every topic of biology, and we recommend that you keep them in the back of your mind at all times.


This section covers the following topics.
  • Genetics
  • Evolution

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