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11 - Chapter 1 Introduction to Biology B RI AL iology is...

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Chapter 1 Introduction to Biology B iology is the science that studies living things, their structure and function. All living things ( organisms ) are composed of microscopic (too small to be seen by the human eye) units called cells. The cell is the basic unit of function for all living things. How can we tell if something is alive? Living things perform various life functions or processes. Life Functions The following sections introduce the major life functions. Nutrition Nutrition is the process by which an organism takes in food and uses this food for energy, growth, and repair. First the organism takes in food from its environment. This process is called ingestion. These large food molecules are digested, broken down into many small molecules, so that they can enter the cells through a process called absorption. When digested, large food molecule AB is broken down to produce small food molecules A and B (AB A+B). When in the cell, some end products of digestion can be used for energy production. Is a green plant alive? We all know that plants don’t eat food. Plants make their own food by photosynthesis. Plants take in carbon dioxide and water from their environment, producing a sugar called glucose. This glucose serves as food for the plant. Transport Transport is the life function by which materials such as food, water, and oxygen from the environ- ment are distributed to all cells of the organism. The transport system also carries waste products away from the cells. In humans and other animals, the blood circulatory system is responsible for carrying out this life function. In many plants, specialized structures called vascular bundles carry materials throughout the organism. Respiration Respiration provides the organism with the energy needed to carry out all the other life processes. During the process of respiration, oxygen is brought into the organism and is used to chemically release energy that is stored in food. Respiration in animals takes place on two different levels. On the organism level, oxygen is taken in and carbon dioxide is released. We usually refer to this process as breathing. On the cellular level, food and oxygen interact chemically to produce energy and the waste products carbon dioxide and water. This process is generally referred to as cellular respiration. 15 COPYRIGHTED MATERIAL
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Excretion As organisms perform their various life functions, waste products are produced. These waste products are often harmful or poisonous to the organism. Excretion is the removal of cellular waste products such as water, carbon dioxide, and nitrogen waste from an organism. Elimination Not all the food that is eaten by an organism is capable of being digested and can be classified as waste. The removal of undigested food as a semisolid waste material is called elimination.
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