Environmental Problems, Their Causes, and Sustainability 1

(a) Eukaryotic CellNucleus(informationstorage)Energyconversion(b) Prokaryotic CellDNA(information storage, no nucleus)ProteinconstructionPackagingCell membrane(transport of rawmaterials andfinished products)Protein constructionand energy conversionoccur without specializedinternal structuresCell membrane(transport ofraw materialsand finishedproducts)Figure 4-3 (a) Generalized structure of a eukaryotic cell. The parts and internal structure of cells in varioustypes of organisms such as plants and animals differ somewhat from this generalized model. (b) Generalizedstructure of a prokaryotic cell. Note that prokaryotic cells lack a distinct nucleus.)Known species1,412,000Other animals281,000Insects751,000Fungi69,000Prokaryotes4,800Protists57,700Plants248,400Figure 4-4 Natural capital:breakdown of the earth’s1.4 million known species.Biologists estimate that weshare the planet with 3.6 millionto 100 million species, with abest estimate of 10–14 millionspecies.white oak trees in a forest, and people in a country. Inmost natural populations, individuals vary slightly intheir genetic makeup, which is why they do not alllook or act alike. This is called a population’s geneticdiversity (Figure 4-6).The place or environment where a population (oran individual organism) normally lives is its habitat. Itmay be as large as an ocean or as small as the intestineof a termite.The area over which we can find a species is calledits distribution or range. Many species, such as sometropical plants, have a small range and may be foundon a single hillside. Other species such the grizzly bearhave large ranges.58 CHAPTER 4 Ecosystems: What Are They and How Do They Work?