Which of the following statements about melanin is most accurate?

The more brown-black melanin an individual has, the darker their skin.

Everyone has the same type of melanin, but the amount varies from person to person.

The more brown-black melanin an individual has in their skin cells, the more likely they are to get mutations in their DNA.

Having melanin is one of the distinguishing features of humans compared to other animals.

Which of the following statements are true concerning how light interacts with the pigments in a red tomato?

The pigments absorb blue light.

The pigments likely protect the cells in the tomato from DNA damage.

The pigments reflect green light.

In which of the following areas of the globe would you expect to find relatively high amounts of UV radiation?

Areas at a latitude near the equator.

Areas near large bodies of water.

Areas at longitudes in the western hemisphere.

Areas with a large amount of persistent cloud cover.

Which of the following statements apply to the variation in human skin color?

The variation in human skin color correlates with in the intensity of sunlight around the world.

Human skin color variation is primarily determined by the type and amount of food that they eat.

The variation in human skin color cannot be quantified (or measured).

Human skin and the skin our closest living primate relative exhibit a similar range in color variation.

Darker skin is more prevalent in high-UV areas. Dr. Jabionski proposed a hypothesis to explain the selective pressure for darker skin in these environments. On what evidence did she base this hypothesis?

The larger amount of brown-black melanin in darkly pigmented skin protects circulating folate from being destroyed by UV radiation.

In general, people of African descent have less folate, a nutrient important for human reproduction, circulating in their blood

The melanin in darkly pigmented skin protects DNA from UV radiation, which can cause skin cancer.

People of African descent have a very similar version of the MC1R gene, indicating what the selective pressure was for darker skin.

Human populations in low-UV environments tend to have lighter skin tones. One explanation is that the selective pressure for dark skin decreases as UV intensity decreases. At the same time, there is selection for lighter skin to absorb more UV radiation, which is needed for vitamin D production. What evidence supports the vitamin D hypothesis for the evolution of lighter skin tones?

Some indigenous peoples living at high latitudes have darker skin, but they tend to eat foods rich in vitamin D

People with lighter skin cannot synthesize enough vitamin D in high-UV environments, such as equatorial Africa

In general, people with lighter skin tend to be at higher risk of vitamin D deficiency.

Red hair and light skin are typical of people of northern European descent.

Based on the risk factors discussed in the film, which of the following groups should consider taking vitamin D supplements to avoid rickets?

Children born to parents with dark skin living far from the equator.

Adults with dark skin who liver close to the equator.

Adults with light skin who live far from the equator.

Children born to parents with light skin living close to the equator.

In what way does natural selection depend on the specific environment in which an organism lives?

When the environment changes, traits that were beneficial to an organism may become harmful and vice versa.

When an organism enters a new environment, it evolves all of the traits it needs to survive there.

Natural selection produces traits that are always either helpful or harmful regardless of the environment.

Natural selection is random, and the direction of the selective pressure cannot be predicted base on the environment.

The Biology of Skin Color

Cells of different organisms and even cells within the same organism are very diverse in terms of shape, size, and internal organization. One theme that occurs again and again throughout biology is that form follows function. In other words, a cell’s function influences its physical features. Cell Shape The diversity in cell shapes reflects the different functions of cells. Compare the cell shapes shown in Figure 4-4. The long extensions that reach out in various directions from the nerve cell shown in Figure 4-4a allow the cell to send and receive nerve impulses. The flat, platelike shape of skin cells in Figure 4-4b suits their function of covering and protecting the surface of the body. As shown below, a cell’s shape can be simple or complex depending on the function of the cell. Each cell has a shape that has evolved to allow the cell to perform its function effectively. SECTION 2 OBJECTIVES ● Explain the relationship between cell shape and cell function. ● Identify the factor that limits cell size. ● Describe the three basic parts of a cell. ● Compare prokaryotic cells and eukaryotic cells. ● Analyze the relationship among cells, tissues, organs, organ systems, and organisms. VOCABULARY plasma membrane cytoplasm cytosol nucleus prokaryote eukaryote organelle tissue organ organ system Cells have various shapes. (a) Nerve cells have long extensions. (b) Skin cells are flat and platelike. (c) Egg cells are spherical. (d) Some bacteria are rod shaped. (e) Some plant cells are rectangular. FIGURE 4-4 (a) Nerve cell (b) Skin cells (c) Egg cell (d) Bacterial cells (e) Plant cells Copyright © by Holt, Rinehart and Winston. All rights reserved. 1. All cubes have volume and surface area. The total surface area is equal to the sum of the areas of each of the six sides (area = length X width). 2. If you split the first cube into eight smaller cubes, you get 48 sides. The volume remains constant, but the total surface area doubles. 3. If you split each of the eight cubes into eight smaller cubes, you have 64 cubes that together contain the same volume as the first cube. The total surface area, however, has doubled again. CELL STRUCTURE AND FUNCTION 73 Cell Size Cells differ not only in their shape but also in their size. A few types of cells are large enough to be seen by the unaided human eye. For example, the nerve cells that extend from a giraffe’s spinal cord to its foot can be 2 m (about 6 1/2 ft) long. A human egg cell is about the size of the period at the end of this sentence. Most cells, how- ever, are only 10 to 50 μm in diameter, or about 1/500 the size of the period at the end of this sentence. The size of a cell is limited by the relationship of the cell’s outer surface area to its volume, or its surface area–to-volume ratio. As a cell grows, its volume increases much faster than its surface area does, as shown in Figure 4-5. This trend is important because the materials needed by a cell (such as nutrients and oxygen) and the wastes produced by a cell (such as carbon dioxide) must pass into and out of the cell through its surface. If a cell were to become very large, the volume would increase much more than the surface area. Therefore, the surface area would not allow materials to enter or leave the cell quickly enough to meet the cell’s needs. As a result, most cells are microscopic in size. Comparing Surface Cells Materials microscope, prepared slides of plant (dicot) stem and ani- mal (human) skin, pencil, paper Procedure Examine slides by using medium magnification (100). Observe and draw the sur- face cells of the plant stem and the animal skin. Analysis How do the surface cells of each organism differ from the cells beneath the surface cells? What is the function of the surface cells? Explain how surface cells are suited to their function based on their shape. Quick Lab Small cells can exchange substances more readily than large cells because small objects have a higher surface area–to-volume ratio. FIGURE 4-5 mb06se_csfs02.qxd 5/18/07 10:54 AM Page 73 74 CHAPTER 4 BASIC PARTS OF A CELL Despite the diversity among cells, three basic features are common to all cell types. All cells have an outer boundary, an interior sub- stance, and a control region. Plasma Membrane The cell’s outer boundary, called the plasma membrane (or the cell membrane), covers a cell’s surface and acts as a barrier between the inside and the outside of a cell. All materials enter or exit through the plasma membrane. The surface of a plasma mem- brane is shown in Figure 4-6a. Cytoplasm The region of the cell that is within the plasma membrane and that includes the fluid, the cytoskeleton, and all of the organelles except the nucleus is called the cytoplasm. The part of the cytoplasm that includes molecules and small particles, such as ribosomes, but not membrane-bound organelles is the cytosol. About 20 percent of the cytosol is made up of protein. Control Center Cells carry coded information in the form of DNA for regulating their functions and reproducing themselves. The DNA in some types of cells floats freely inside the cell. Other cells have a mem- brane-bound organelle that contains a cell’s DNA. This membrane- bound structure is called the nucleus. Most of the functions of a eukaryotic cell are controlled by the cell’s nucleus. The nucleus is often the most prominent structure within a eukaryotic cell. It maintains its shape with the help of a protein skeleton called the nuclear matrix. The nucleus of a typical animal cell is shown in

The role of the skin in thermoregulation

THE BIOLOGY OF AGING PART 1

The Biology of Extinction

Module 3.3b - Gender and Sexual Orientation: The Biology and Psychology of Sex

Owls, such as the young snowy owls on the previous page, have for centuries been symbols of both wisdom and mystery. To many cultures their piercing eyes have conveyed a look of intelligence. Their silent flight through darkened landscapes in search of prey has projected an air of power or wonder. For this chapter and this book, owls are an engaging example of a living organism from the world of biology—the study of life. BIOLOGY AND YOU Living in a small town, in the country, or at the edge of the suburbs, one may be lucky enough to hear an owl's hooting. This experience can lead to questions about where the bird lives, what it hunts, and how it finds its prey on dark, moonless nights. Biology, or the study of life, offers an organized and scientific framework for posing and answering such questions about the natural world. Biologists study questions about how living things work, how they interact with the environment, and how they change over time. Biologists study many different kinds of living things ranging from tiny organisms, such as bacteria, to very large organisms, such as elephants. Each day, biologists investigate subjects that affect you and the way you live. For example, biologists determine which foods are healthy. As shown in Figure 1-1, everyone is affected by this impor- tant topic. Biologists also study how much a person should exer- cise and how one can avoid getting sick. Biologists also study what your air, land, and food supply will be like in the near future. SECTION 1 OBJECTIVES ● Relate the relevance of biology to a person’s daily life. ● Describe the importance of biology in human society. ● List the characteristics of living things. ● Summarize the hierarchy of organization within complex multicellular organisms. ● Distinguish between homeostasis and metabolism and between growth, development, and reproduction. VOCABULARY biology organization cell unicellular multicellular organ tissue organelle biological molecule homeostasis metabolism cell division development reproduction gene Copyright © by Holt, Rinehart and Winston. All rights reserved. Biology, the study of life, directly applies to your health, life, and future in ways as simple as daily food choices. FIGURE 1-1 6 CHAPTER 1 Biology and Society By studying biology you can make informed decisions on issues that impact you and our society. Every day newspapers, television, and the Internet contain issues that relate to biology. For example, you may read that your local water or air supply is polluted. How will that pollution affect your health and the health of other living things? You may hear about new technologies or tools that biolo- gists have invented. How will we control how those technologies and tools are used? Biologists actively work to solve these and other real-world issues and problems, including improving our food supply, curing diseases and preserving our environment.

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