water vapor coming together to form drops

can be replaced quickly or reused

Good for the environement, society and the economy

a chemical that causes pollution

Biological magnification

when a toxins concentration increases up the food chain

Earths natural sunscreen but harmful to breathe

Pollutants combine with water vapor forming nitric acids

is the total of all organism variation in the biosphere.

large #'s of species are in immediate danger of extinction

the physical features of a place

Humans in the Biosphere Vocab Quiz

Create a multiple choice test (10 questions with answers) from the following text: The Environment The environment is the combination of forces and conditions that surround and influence living and non-living things. Human beings’ environment includes such factors as temperature, food supply and other people that surround them. A plant’s environment may be made up of soil, sunlight, and animals that will eat the plant. A rock’s environment may be made up of seaweed, water and fish. Non-living environmental factors, such as temperature and sunlight, make up the abiotic (non-living) environment. Living organisms such as seaweed and food, make up the biotic environment. Both the abiotic and biotic environments interact to make up the total environment of living and non-living things. Ecology Ecology studies the relationships between living things and their environment. No living thing, plant or animal, lives alone. Every living thing depends in some way upon certain other living and non-living things to survive. The study of ecology increases our understanding of the world and all its creatures. This is crucial because humanity’s survival and well-being depend on relationships that exist on a world-wide basis: changes in distant parts of the world affect us and our environment. One concern of ecologists is the rate at which we are using up natural resources such as coal, gas, and oil. Along with scientists, they are searching for ways to use sunlight and atomic energy for fuel and power as alternative energy sources. Ecology also studies how many living organisms there are on Earth and how they are distributed. It also considers non-living physical factors of the environment, for example the presence of water, as these can influence where organisms decide to live. It is also important to know which organisms share the same environment, as they may need each other to survive. This kind of information helps ecologists to conserve our natural world, protecting the habitat of animals that are in danger of extinction, or trying to reduce pollution and global warming. Ecosystems Ecosystems are biological communities of all living things like plants, animals and organisms in a specific area that interact with each other and with the non-living forms present in their environment. They are the foundations of the biosphere and determine the health of the entire planet’s system. A biosphere is a global ecosystem, containing many different kinds of ecosystems.

Figure 18-11 represents the amount of energy stored as organic material in each trophic level in an ecosystem. The pyramid shape of the diagram indicates the low percentage of energy transfer from one level to the next. On average, 10 percent of the total energy consumed in one trophic level is incor- porated into the organisms in the next. Why is the percentage of energy transfer so low? One reason is that some of the organisms in a trophic level escape being eaten. They eventually die and become food for decomposers, but the energy contained in their bodies does not pass to a higher trophic level. Even when an organism is eaten, some of the molecules in its body will be in a form that the consumer cannot break down and use. For example, a cougar cannot extract energy from the antlers, hooves, and hair of a deer. Also, the energy used by prey for cellu- lar respiration cannot be used by predators to synthesize new bio- mass. Finally, no transformation or transfer of energy is 100 percent efficient. Every time energy is transformed, such as during the reactions of metabolism, some energy is lost as heat. Limitations of Trophic Levels The low rate of energy transfer between trophic levels explains why ecosystems rarely contain more than a few trophic levels. Because only about 10 percent of the energy available at one trophic level is transferred to the next trophic level, there is not enough energy in the top trophic level to support more levels. Organisms at the lowest trophic level are usually much more abundant than organisms at the highest level. In Africa, for exam- ple, you will see about 1,000 zebras, gazelles, and other herbivores for every lion or leopard you see, and there are far more grasses and shrubs than there are herbivores. Higher trophic levels con- tain less energy, so, they can support fewer individuals.A population is a group of organisms that belong to the same species and live in a particular place at the same time. All of the bass living in a pond during a certain period of time make up a pop- ulation because they are isolated in the pond and do not interact with bass living in other ponds. The boundaries of a population may be imposed by a feature of the environment, such as a lake shore, or they can be arbitrarily chosen to simplify a study of the population. The humans shown in Figure 19-1 are part of the pop- ulation of a city. The properties of populations differ from those of individuals. An individual may be born, it may reproduce, or it may die. A population study focuses on a population as a whole—how many individuals are born, how many die, and so on. Population Size A population’s size is the number of individuals that the population contains. Size is a fundamental and important population property but can be difficult to measure directly. If a population is small and composed of immobile organisms, such as plants, its size can be determined simply by counting individuals. Often, though, individ- uals are too abundant, too widespread, or too mobile to be counted easily, and scientists must estimate the number of individuals in the population. Suppose that a scientist wants to know how many oak trees live in a 10 km2 patch of forest. Instead of searching the entire patch of forest and counting all the oak trees, the scientist could count the trees in a smaller section of the forest, such as a 1 km2 area. The scientist could then use this value to estimate the population of the larger area. SECTION 1 OBJECTIVES ● Describe the main properties that scientists measure when they study populations. ● Compare the three general patterns of population dispersion. ● Identify the measurements used to describe changing populations. ● Compare the three general types of survivorship curves. VOCABULARY population population density dispersion birth rate death rate life expectancy age structure survivorship curve FIGURE 19-1 A population can be widely distributed, as Earth’s human population is, or confined to a small area, as species of fish in a lake are. Copyright © by Holt, Rinehart and Winston. All rights reserved. 382 CHAPTER 19 If the small patch contains 25 oaks, an area 10 times larger would likely contain 10 times as many oak trees. A similar kind of sampling technique might be used to estimate the size of the pop- ulation shown in Figure 19-2. To use this kind of estimate, the sci- entist must assume that the distribution of individuals in the entire population is the same as that in the sampled group. Estimates of population size are based on many such assumptions, so all esti- mates have the potential for error. Population Density Population density measures how crowded a population is. This measurement is always expressed as the number of individuals per unit of area or volume. For example, the population density of humans in the United States is about 30 people per square kilome- ter. Table 19-1 shows the population sizes and densities of humans in several countries in 2003. These estimates are calculated for the total land area. Some areas of a country may be sparsely popu- lated, while other areas are very densely populated. Dispersion A third population property is dispersion (di-SPUHR-zhuhn). Dispersion is the spatial distribution of individuals within the popu- lation. In a clumped distribution, individuals are clustered together. In a uniform distribution, individuals are separated by a fairly con- sistent distance. In a random distribution, each individual’s location is independent of the locations of other individuals in the popula- tion. Figure 19-3 illustrates the three possible patterns of dispersion. Clumped distributions often occur when resources such as food or living space are clumped. Clumped distributions may also occur because of a species’ social behavior, such as when animals gather into herds or flocks. Uniform distributions may result from social behavior in which individuals within the same habitat stay as far away from each other as possible. For example, a bird may locate its nest so as to maximize the distance from the nests of other birds. These migrating wildebeests in East Africa are too numerous and mobile to be counted. Scientists must use sampling methods at several locations to monitor changes in the population size of the animals. FIGURE 19-2 TABLE 19-1 Population Size and Density of Some Countries Population size Population density Country (in millions) (in individuals/km2) China 1,289 135 India 1,069 325 United States 292 30 Russia 146 8 Japan 128 337 Mexico 105 54 Kenya 32 54 Australia 20 3 dispersion from the Latin dis-, meaning “out,” and spargere, meaning “to scatter” Word Roots and Origins Copyright © by Holt, Rinehart and Winston. All rights reserved. POPULATIONS 383 The social interactions of birds called gannets, which are shown in Figure 19-3b, result in a uniform distribution. Each gannet chooses a small nesting area on the coast and defends it from other gannets. In this way, each gannet tries to maximize its distance from all of its neighbors, which causes a uniform distribution of individuals. Few populations are truly randomly dispersed. Rather, they show degrees of clumping or uniformity. The dispersion pattern of a population sometimes depends on the scale at which the popu- lation is observed. The gannets shown in Figure 19-3b are uni- formly distributed on a scale of a few meters. However, if the entire island on which the gannets live is observed, the distribution appears clumped because the birds live only near the shore. POPULATION DYNAMICS All populations are dynamic—they change in size and composition over time. To understand these changes, scientists must know more than the population’s size, density, and dispersion. One important measure is the birth rate, the number of births occur- ring in a period of time. In the United States, for example, there are about 4 million births per year. A second important measure is the death rate, or mortality rate, which is the number of deaths in a

In a single domesticated grain seed, one might see the bud of great civilizations. The birth of agriculture was a turning point in humans' social development, as stable food supplies enabled people to transcend the constraints of food gained by hunting and gathering. After that, people were able to settle down and experience population booms. As one of the major areas around the globe where agriculture originated, China has contributed to the world's domesticated rice, millet, buckwheat and soybeans. Archaeological studies have unveiled that the planting of rice originated around 10,000 years ago in the lower reaches of the Yangtze River, leading to the eventual replacement there of hunting and gathering practices dating back 5,000 to 6,000 years. "It marked the formation of a rice-based agricultural society in the area," said Zhao Zhijun, an archaeologist at the Chinese Academy of Social Sciences. Archaeological studies of the origins of rice-based agriculture are an important part of a national project tracing the origins of Chinese civilization itself. President Xi Jinping has greatly valued the project. At a group study session of the Political Bureau of the Communist Party of China Central Committee on May 27, 2022, Xi, who is also general secretary of the CPC Central Committee, emphasized the significance of the project and the role that archaeological studies play in better understanding Chinese civilization. The project to trace the origins of Chinese civilization, in addition to finding signs of human activity more than 1 million years ago, has also proved that China's history includes 10,000 years of culture and more than 5,000 years of civilization. The project has provided clear knowledge of the origins and formation of Chinese civilization, the history of its development, the process of the formation and development of its pluralistic and integrated pattern, and the characteristics of the civilization and why it was formed in such a way, he added. This was not the first time that Xi emphasized the importance of the origin-tracing project. Since the 18th National Congress of the CPC in 2012, Xi has toured more than 100 historical and cultural locations and issued many instructions related to archaeology and the origin-tracing project. During the 23rd group study session of the Political Bureau of the CPC Central Committee in 2020, Xi called for giving more attention to archaeological research and letting historical facts speak for themselves. "This will provide strong support for our efforts to carry forward the best of traditional Chinese culture and increase our cultural confidence," said Xi. The origin-tracing project has been carried out since 2002. Its ongoing fifth phase, which started in 2020, involves the participation of more than 500 researchers from 29 institutes across the country. It primarily centers on several ancient capital sites, including the Liangzhu site in Hangzhou, Zhejiang province, the Taosi site in Xiangfen county, Shanxi province, the Shimao site in Shenmu, Shaanxi province, and the Erlitou site in Luoyang, Henan province, from 3,500 to 5,500 years ago, as well as other settlements mainly along the basins of the Yellow, Yangtze and Liaohe rivers. The project has also expanded to a wider geographic and chronological framework to decode how Chinese civilization emerged and how its diverse elements formed a unity. Excavation of the Liangzhu site, which is over 5,000 years old and is one of the major sites covered in the origin-tracing project, has yielded an inner city covering 3 million square meters and an outer city of 6.3 million sq m, making it the world's largest capital at the time. It also had a giant water control system, which contributed to the formation of a rice-based agricultural society. By calculating the earthwork volume, archaeologists found that building the entire ancient city, the water control system and Mojiaoshan — a 10-meter-tall man-made terrace in the center of the city — required 10,000 people working daily for seven-and-a-half years. The discoveries show that Liangzhu had a kingship able to organize people for large-scale public construction, and its social differentiation, emergence of the city concept and existence of a kingship prove that it became a civilized society, said Wang Wei, a veteran archaeologist at the Chinese Academy of Social Sciences. Significant topic Wang said that tracing the origins of a civilization is a significant topic in the research of human history. Over the years, the Chinese project has provided China's answer to how to define civilizations. In 2022, Xi commended the efforts and stressed that the project has made creative contributions to the research on tracing the origins of the world's civilizations. Wang said: "International academia has proposed three indispensable elements for a civilized society based on features of Mesopotamian and Egyptian civilizations: written characters, metallurgy and the city concept. But we can find that some of the three elements were absent in many ancient civilizations. For example, the Mayan civilization had no metallurgy, while the Incan civilization didn't have written characters." Western scholars believe that Chinese civilization began with the Yinxu Ruins in Anyang, Henan province, a capital of the late Shang Dynasty (c.16th century-11th century BC), based on the discovery of inscribed oracle bones from that time. However, Chinese archaeologists don't agree. With continued archaeological research, international academia now believes that places around the world can propose criteria for civilization based on their own ancient social development. China's archaeological studies have shaped the nation's criteria in defining a civilization: the development of productivity, an increase in population, the appearance of cities, social differentiation and the emergence of kingship and state. "These criteria are suitable for identifying other civilizations as well," said Wang. "Civilizations have in common the appearance of kingship and state. They are only different in the ways of imposing kingship and the forms of state." In China, kingship and state "were shown by exquisite jade and bronze ritual artifacts, grand palaces and magnificent mausoleums imitating aboveground palaces", he added. "In Mesopotamia and ancient Egypt, they were demonstrated through superb stone temples, pyramids and large-scale tombs." Multidisciplinary subject President Xi said in 2020 that archaeologists should work closely with researchers from other fields to make an interpretive analysis of material remains. Zhang Chi, a professor of archaeology at Peking University, said that since material remains are often the research focus of archaeological studies, these should not only be observed with the eyes, but also studied using scientific and technological tools. Therefore, from the perspective of research methods, archaeology is by nature a multidisciplinary subject, Zhang added.

Life Processes Identify and define the seven life processes (MRS GREN). Classification Group living organisms based on observed similarities and differences. Classify vertebrates into taxonomic groups based on visible physical characteristics. Construct a dichotomous key to classify vertebrates. Cells Compare the structure of generalised plant and animal cells, and selected microbes (e.g. bacteria, fungi and Amoeba) Distinguish among cell wall, cell membrane, nucleus, cytoplasm, temporary and permanent vacuoles, mitochondrion, chloroplast, endoplasmic reticulum and ribosomes. Relate the structure of organelles to their functions; Identify specialised cells such as blood cells, ciliated epithelial cells, nerve cells, root hair cells, sperm cells and egg cells. Explain the importance of cell specialisation in multicellular organisms; include hierarchy of cells, tissues, organs; organ systems and then organism Diffusion, Osmosis, Active transport and Osmoregulation Explain the processes of diffusion, osmosis and active transport. Identify everyday instances of these processes occurring. Discuss the importance of diffusion, osmosis and active transport in living systems. Nutrition in Plants Describe the process of photosynthesis in green plants; test for end products, starch or reducing sugar (glucose). Relate the structure of the leaf of a flowering plant to its function in photosynthesis; draw and label the external features and the internal structure (cross section) of a leaf as seen in cross section under the light microscope. Nutrition in Humans Discuss the importance of a balanced diet in humans. State components of a balanced diet (carbohydrates, fats, proteins, vitamins and minerals, water and roughage and their roles) along with the results of their deficiency or surplus. Suggest dietary recommendations for treating and preventing named deficiency and physiological diseases (such as those outlined in the manual and your notes). Perform tests to distinguish among food substances - Test for proteins (Biuret), fats (grease spot), starch (iodine), reducing sugars (Benedict’s solution). The Digestive System in Humans Relate the structures of the human alimentary canal to their functions; Draw and label simple diagrams of the alimentary canal and internal structure of a tooth required. Describe mastication and the role of teeth in the mechanical breakdown of food to be included. (Compare types of teeth in humans and compare types of teeth in herbivores and carnivores.) Explain the role and importance of enzymes role of digestive enzymes in the mouth, stomach and pancreatic enzymes in the small intestine. Discuss properties of enzymes. Deduce from tables and graphs the effects of temperature and pH on enzyme activity. Experimental Skills Follow all drawing rules as outlined in the drawing skills checklist posted in the classroom (including calculation of magnification).

LESSON 2 Early Theories on the Origin of Life • Identify the different theories on the origin of life. • Describe each theory and determine their differences What are the characteristics of living things? Before learning about the history of Earth based on geological evidence, early scientists explored the possibilities of how the first life-form existed. There are several theories about the origin of life. Theory of Catastrophism The theory of catastrophism supported by French scientists Georges Cuvier (1769-1832) and Alcide Dessalines d'Orbigny (1802-1857), is said to be a modification of the creation story of the Bible. It states that there have been several living creations from God, each encountered a catastrophe that completely destroyed them. Each new creation consisted of new life-forms, which happen to be different from the previous ones. Theory of Abiogenesis The theory of abiogenesis, or the spontaneous generation theory, states that living things were naturally created from nonliving things such as simple organic compounds. The theory supposes that abiogenesis occurred between 3.8 and 4 Gya. The experiment performed by Stanley Miller in 1953 gave way to many speculations and studies on how life on Earth really began. His research involved a simulation of the possible environment on Earth in the past. He demonstrated how an electric spark (which is a simulation for lightning) when passed through simple organic gases (similar to the early Earth atmosphere), resulted in the formation of amino acids, which are now known as the building blocks of proteins and the components of living tissues. Theory of Biogenesis The theory of biogenesis presented a strong argument against abiogenesis. This theory states that living things come from living things. Experiments of Francesco Redi and Louis Pasteur disproved the thought of spontaneous generation during their time (figure 5-1). Louis Pasteur argued that life comes from preexisting life and not from nonliving material. However, it should be noted that the "abiogenesis" or "spontaneous generation" that he opposed referred to any modern, existing, fully-formed organisms, not the original generation of life. Louis Pasteur's law of biogenesis contradicted the common belief during his time that cattle dung gives rise to flies, or old clothes with rotten food gives rise to mice. The idea of spontaneous generation was popular until near the seventeenth century. Even famous scientists of that period, such as Descartes, Galileo, and Jan Baptista van Helmont, believed in this theory. CIENCE PIONEER Francesco Redi (1626-1697). Francesco Redi is a physician, a naturalist, and a poet. His works challenged the popular theory of spontaneous generation. He disproved the idea that living things may arise from nonliving things. He also worked on toxicology using viper's venom. He discovered and worked on some parasites that caused disease in humans. SCIENCE CAREER Evolutionary Biologist An evolutionary biologist studies the descent of species and the origin of new species of living things. Working as evolutionary biologist means studying and researching species diversity, their interaction with the environment, their adaptation to change, their ancestors, and their possible origins. This career is important in the field of science because it seeks an answer to the questions about how life began on Earth.

Lipids are large, nonpolar organic molecules. They do not dissolve in water. Lipids include triglycerides (trie-GLIS-uhr-IEDZ), phospho- lipids, steroids, waxes, and pigments. Lipid molecules have a higher ratio of carbon and hydrogen atoms to oxygen atoms than carbohydrates have. Because lipid molecules have larger numbers of carbon-hydrogen bonds per gram than other organic com- pounds do, they store more energy per gram. Fatty Acids Fatty acids are unbranched carbon chains that make up most lipids. Figure 3-10 shows that a fatty acid contains a long carbon chain (from 12 to 28 carbons) with a carboxyl group, —COOH, attached at one end. The two ends of the fatty-acid molecule have different properties. The carboxyl end is polar and is thus hydrophilic or attracted to water molecules. In contrast, the hydro- carbon end of the fatty-acid molecule is nonpolar. This end tends not to interact with water molecules and is said to be hydrophobic (HIE-droh-FOH-bik), or “water fearing.” In saturated fatty acids, such as palmitic acid, which is shown in Figure 3-10, each carbon atom is covalently bonded to four atoms. The carbon atoms are in effect full, or saturated. In contrast, linoleic acid, also shown in Figure 3-10, has carbon atoms that are not bonded to the maximum number of atoms to which they can bond. Instead, they have formed double bonds within the carbon chain. This type of fatty acid is said to be unsaturated. Triglycerides Three classes of lipids important to living things contain fatty acids: triglycerides (fats), phospholipids, and waxes. A triglyceride is composed of three molecules of fatty acid joined to one molecule of the alcohol glycerol. Saturated triglycerides are composed of saturated fatty acids. They typically have high melting points and tend to be hard at room temperature. Common dietary saturated triglycerides include butter and fats in red meat. In contrast, unsaturated triglycerides are composed of unsaturated fatty acids and are usually soft or liquid at room temperature. Unsaturated triglycerides are found primarily in plant seeds where they serve as an energy and carbon source for germinating plants. Phospholipids Phospholipids have two, rather than three, fatty acids attached to a molecule of glycerol. They have a phosphate group attached to the third carbon of the glycerol. As shown in Figure 3-11, the cell membrane is made of two layers of phospholipids, called the lipid bilayer. The inability of lipids to dissolve in water allows the mem- brane to form a barrier between the inside and outside of the cell. Hydrophilic “head” Phospholipids Hydrophobic “tail” Phospholipids Water Water The lipid bilayer of a cell membrane is a double row of phospholipids.The “tails” face each other.The “head” of a phospholipid, which contains a phosphate group, is polar and hydrophilic.The two tails are two fatty acids and are nonpolar and hydrophobic. FIGURE 3-11 H C H C O OH H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H C H H H H C H H C H H C H H C H H C H C O OH H C H H C H H C H C H C H C H H C H H C H C H H C H H C H C H H H H C H Fatty acids have a polar carboxyl head, highlighted in purple, and a nonpolar hydrocarbon tail, highlighted in green. FIGURE 3-10 Palmitic acid Linoleic acid mb06se_bchs02.qxd 5/18/07 10:49 AM Page 59 60 CHAPTER 3 1. Compare the structure of monosaccharides, dis- accharides, and polysaccharides. 2. How are proteins constructed from amino acids? 3. How do amino acids differ from one another? 4. Describe a model of enzyme action. 5. Why do phospholipids orient in a bilayer when in a watery environment, such as a cell? 6. Describe how the three major types of lipids differ in structure from one another. 7. What are the functions of the two types of nucleic acids? CRITICAL THINKING 8. Applying Information Before a long race, run- ners often “carbo load.” This means that they eat substantial quantities of carbohydrates. How might this help their performance? 9. Recognizing Relationships High temperatures can weaken bonds within a protein molecule. How might this explain the effects of using a hot curling iron or rollers in one’s hair? 10. Applying Information You want to eat more unsaturated than saturated fats. Name examples of foods you would eat more of and less of. SECTION 2 REVIEW Waxes A wax is a type of structural lipid consisting of a long fatty-acid chain joined to a long alcohol chain. Waxes are waterproof, and in plants, form a protective coating on the outer surfaces. Waxes also form protective layers in animals. For example, earwax helps pre- vent microorganisms from entering the ear canal. Steroids Unlike most other lipids, which are composed of fatty acids, steroid molecules are composed of four fused carbon rings with various functional groups attached to them. Many animal hor- mones, such as the male hormone testosterone, are steroid com- pounds. One of the most familiar steroids in humans is cholesterol. Cholesterol is needed by the body for nerve and other cells to func- tion normally. It is also a component of the cell membrane. NUCLEIC ACIDS Nucleic acids are very large and complex organic molecules that store and transfer important information in the cell. There are two major types of nucleic acids: deoxyribonucleic acid and ribonucleic acid. Deoxyribonucleic acid, or DNA, contains information that deter- mines the characteristics of an organism and directs its cell activi- ties. Ribonucleic (RIE-boh-noo-KLEE-ik) acid, or RNA, stores and transfers information from DNA that is essential for the manufactur- ing of proteins. Some RNA molecules can also act as enzymes. Both DNA and RNA are polymers, composed of thousands of linked monomers called nucleotides (NOO-klee-uh-TIEDS). As shown in Figure 3- 12, each nucleotide is made of three main components: a phosphate group, a five-carbon sugar, and a ring-shaped nitrogenous base.

LESSON 3 Characteristics of Living Things Learning Objectives • Describe each characteristic of life • Relate each characteristic of life with how first forms of life evolved What sets living things apart from nonliving things? Organisms are equipped with different characteristics that allow them to grow, adapt, survive, and perpetuate. These include the ability to metabolize, respond to stimuli, interact, and reproduce, among others What are the characteristics of life? Try to look at your surroundings and identify the living things that you see. You have probably identified a lot. Many scientists believe that there are more than 10 million kinds of living things that exist on Earth today. But the question is, how can something be considered living? There are certain characteristics that all living things exhibit: the characteristics of life. Living things are made up of cells. They metabolize, grow and develop, respond to stimulus, adapt to their environment, and reproduce. Living Things Are Made up of Cells All living things are made up of cells. Cells are the basic building blocks of all living things. Each cell contains materials that carry out basic life processes such as respiration. In the 1600s, an argument against the theory of spontaneous generation was made. Italian physician and biologist Francesco Redi disproved the theory that all living things come from nonliving things. Cells have different properties and characteristics. The cell theory describes the properties of all cells. There are three tenets of the cell theory: 1. The cell is the basic unit of life. 2. All living things are composed of one or more cells. 3. All cells arise from preexisting cells. The discovery of the cell is largely attributed to Robert Hooke. Upon examining a piece of cork using a microscope that he built, Hooke observed tiny compartments that he called "cells" (from the Latin word cella, meaning "little room"). Matthias Schleiden suggested that all structural parts of plants are made up of cells. In 1839, Theodore Schwann stated that along with plants, all animals were composed of cells. From these conclusions about plants and animals, advancement on the study of animal parts and functions began. In 1855, Rudolf Virchow included the idea that all cells came from preexisting cells. Some living things are made up of only single cells. Single-celled or unicellular organisms include bacteria, some protists, and some fungi. Even though composed of single cells, these organisms carry out all the functions necessary for life. Most living things such as animals and plants, are multicellular organisms. They are composed of many cells, which are grouped together and perform specific tasks in the body. In different organisms, cells also vary in sizes, shapes, parts, and functions. There are two kinds of organisms according to their cell structure, the prokaryotes and eukaryotes (figure 5-3). Prokaryotes are single-celled organisms that lack a membrane-bound nucleus, mitochondria, and all other organelles. Its name comes from the Greek words pro, which means "before," and karyon, which means "nut or kernel." Eukaryotes are organisms with cells that contain membrane-bound nucleus and other membrane-bound organelles. The nucleus of a eukaryotic cell contains the genetic material (DNA), enclosed by a nuclear envelope. Other membrane-bound organelles are mitochondria, Golgi apparatus, and chloroplast found in photosynthetic organisms such as algae and plants. There are also unicellular eukaryotes known as protozoa. All other eukaryotes are multicellular organisms, such as plants, animals, and fungi. Living Things Metabolize Essential chemical reactions in life can be best described as building up (anabolism) and breaking down (catabolism) processes. In anabolism, the substances needed by organisms to grow, store energy, and repair tissues are synthesized. In contrast in catabolism, some complex substances are broken down, releasing the energy stored in their molecules. This happens in food digestion. This chemical building up and breaking down processes are collectively called metabolism. Metabolism, from the Greek word metabole meaning "change," is the sum total of all the life-sustaining chemical reactions in living things. It allows living things to grow, maintain their structures and functions, and respond to stimuli. Living Things Grow and Develop Growth and development are not new concepts to many. In all living things, growth involves the increase in one's size or height. However, growth is not just an increase in physical structure. It also involves complex changes in an organism. Growth and development occur rapidly from younger stages of life to maturity. In humans, animals, and plants, distinct changes brought by growth and development can be dearly identified. Microorganisms such as bacteria also undergo growth and development until they reach their maximum size and maturity. A life span is the average length of time a aving thing can live. Living things have different life spans. Humans have average life spectancy of 60 to 70 years, while some plants, such as the narra trees, can live for more than 100. Living Things Respond to Stimuli All living things respond to stimuli the environment. This responsiveness Increases survivability. Stimulus (plural: uli) is any signal or change in he environment of an organism that produces a response or reaction from that organism. Responses to stimuli depend on an organism's need. Responding to stimuli also maintains homeostasis in living things. Homeostasis is the internal balance of a body system. This balance is needed for the proper function and regulation of the living thing's body. For example, when a person is in a warmer environment, the body sweats, keeping the body maintain a temperature suited for the normal function of the body. Living Things Interact No living thing can live alone. Interaction among organisms is simultaneously happening on Earth. From the smallest microorganisms to the biggest organism, and from the North Pole to the South Pole of Earth, all are connected in one living system. An ecosystem is formed when a community of organisms interacts with another community and with their environment. Many processes and interactions, such as in a feeding relationship, life cycle, and the exchange of gases between plants and animals, occur in the ecosystem. These are some of the important processes needed to maintain life on Earth. Living Things Reproduce The ability of living things to produce offspring of their kind is called reproduction. Reproduction is not an individual organism's need, rather, it is for the species' perpetuation. In some cases, animals become extinct because of their inability to reproduce their kind. Higher forms of plants and animals reproduce through sexual reproduction. Sexual reproduction involves the union of sex cells or gametes-the egg cell from a female organism and the sperm cell from a male organism. This union gives rise to a new individual with characteristics or traits from both parents. Other simple organisms, such as bacteria and plants, can reproduce asexually. These organisms give rise to a new individual from their body. A bacterial cell divided in two through asexual reproduction gives rise to new bacteria, as shown in figure 5-5. A yeast can form buds that later on become separate individual. Plants grow new plants using their stem, leaf, and roots. Both sexual and asexual reproductions have important functions. In both cases, the genetic material (DNA) is passed on from one generation to the next, ensuring the survival of the species on Earth. 1. Bacteria copy their DNA by starting at any point on the circular chromosomes. 2. The two copies of DNA attach to the inside wall of the bacterial cell. 3. The cell starts to divide, forming a new membrane and cell wall. 4. The bacterial cell splits into two separate cells, each with their own DNA. Living Things Adapt and Evolve All living things can adapt to their environment. This adaptation is necessary for rvival. Adaptation depends on the need of an individual. A polar bear, for example, would not be able to survive in an extremely cold environment without its capacity adapt. Adaptation is any response or reaction toward a stimulus that helps in the survival of an organism. A seed-eating bird will eventually eat a worm when there are seeds to be found. This change in food choice is therefore its adapting mechanism. Prolonged adaptation to certain environments may lead to the gradual evolution of the succeeding generations. Evolution is the gradual change in organisms over a long period in response to changing environment. Living Things Are Organized Life on Earth exhibits organization. The atom is the smallest unit of matter, lowed by molecules, which are combinations of atoms. When these molecules are grouped together, they form a cell. The cell is the basic unit of life. In multicellular organisms, such as plants and animals, cells are grouped as tissues to perform specific Functions. Different tissues can be grouped further and form organs. Organs in animals include the heart, brain, and lungs, among others. The organs form organ systems that makes the function of the body more complex and efficient. Organ systems form the whole organism. All living things exhibit organization, whether they are unicellular or multicellular organisms..

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