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3.2.2 Types of volcano
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Industry and Environmental Analysis: Business Opportunities Identification 3.1 Principles, Tools, and Techniques a. competition b. customers c. suppliers d. competitors e. substitutes 3.2 Types of Industries a. agribusiness b. manufacturing c. retail and services d. international trade (exports and imports) 3.3 identification of Business Opportunities
• There are two groups of animals which are important in agriculture. • The groups are domestic and wild animals. 1. Domestic animals • These are animals which are trained to live with people in their homes. • Some examples includes : Uses of domestic animals • Source of food, for example milk, eggs and meat. • For cultural purposes, for example paying lobola. • Some are used for transport and labour. • Domestic animals can also be a source of income. 2 . Wild animals • These are animals which are found in game reserves and in the forests • They are also called game animals. • Examples of wild animals are: Uses of wild animals • Some of the wild animals give us meat, hides and ivory. • Wild animals attract visitors from other countries, so the country gets money. Wednesday 06 September 2023 Exercise: Domestic animals 1. What is a domestic animal? [2] 2. What is a wild animal? [2] 3. Name any 4 domestic animals that you know. [4] 4. State any 2 uses of domestic animals. [2] 5. Name any 3 wild animals that you know. [3] 6. Give 2 uses of wild ani mals. [2] 7. Wild animals can also be called animals. [1] • Animals, like human beings need good food to help them to grow and reproduce. • The main sources of food for animals include stock feeds, pastures, veld grass, crop remains and cereal grains. • These foods contain the most needed essential nutrients. Nutrient Function carbohydrates Gives energy Fats Give energy and warmth Proteins Helps in growth and repair of body parts Minerals Help in the formation of bones and teeth Vitamins Help develop good sight, improve fertility and help animals fight diseases Water Transports food in the body, cools the body and remove waste from the body. • Livestock are domesticated animals that are kept for food, use or for sale. • Small livestock has many uses. • They are a good source of food. • They also give us manure to use in gardens. • We get clothes and medicine as well from small livestock • Examples of small livestock are rabbits, sheep, goats and all form of poultry Poultry • All animals that are kept by farmers which have wings and feathers and lay eggs are called poultry. • They are a good source of white meat, eggs and manure. • They are also a source of income when we well them and their products. • Poultry includes chicken, guinea fowl, ducks, turkey, pigeons and quail birds. Rabbits • Rabbits have 3 known uses which are: They are kept for meat Kept for pelts. (pelt is animal skin used to make blankets, hats and jackets) They are used at agricultural shows • Rabbits are cheap to buy, easy to keep and feed. • They take about 4 months to mature. • Rabbits are fed using green vegetables and rabbit pellets. Wednesday 20 September 2023 Small livestock 1. Give 3 examples of small livestock. [3] 2. State 3 things that are provided by small livestock. [3] 3. What are the 2 uses of rabbits? [2] 4. Pelts are used to make _________________ [1] 5. State any 4 examples poultry. [4] 6. Rabbits take ___________ months to mature. [1] 7. What is poultry? • Apiculture is the keeping of bees in order for them to produce honey for sale. • Apiculture is very important because: (i) Provides honey - a valuable nutritional food (ii) Provides bees wax - which has many uses in industry Uses of wax For making candles Polish furniture Make crayons Prevent tools from rusting (iii) Honey bees are excellent pollinating agents, thus increasing agricultural yields. BEE COLONY Inhabitants of the bee colony and their roles • A honey bee colony typically consists of three kinds of adult bees: workers, drones and the queen 1. Workers • Workers are the smallest and constitute the majority of bees occupying the colony. • They do not lay eggs. • Workers have specialized structures, such as brood food glands, scent glands, wax glands, and pollen baskets. • these allow them to perform all the labors of the hive. Roles of the worker bees they forage for nectar, pollen, water, and plant sap. They clean and polish the cells. feed the brood. care for the queen. remove debris. handle incoming nectar. build beeswax combs. guard the entrance. 2. Drones • Drones (male bees) are the largest bees in the colony. • They are generally present only during late spring and summer. • The drone’s head is much larger than that of either the queen or worker. • Drones have no stinger, pollen baskets, or wax glands. • Their main function is to mate with the queen. 3 . Queen • Each colony has only one queen. • The queen is the largest of the bees in a bee colony. • The Queen Bee plays a vital role in the hive because she is the only female with fully developed ovaries. • She produces both fertilized and unfertilized eggs. • Queens lay the greatest number of eggs in the spring and early summer. • The queen also produce chemical scents that help regulate the unity of the colony. 1. What is apiculture? [2] 2. Give 3 reasons why apiculture is important in Zimbabwe. [3] 3. Name the 3 inhabitants of the bee colony. [3] 4. Briefly explain the roles of each inhabitant named in number 3. • Apart from using hand tools, farmers also use some farm implements and machinery to carry out their field work. • Machines help farmers do their work more easily and quickly. • The most common implements used by farmers to grow, harvest and transport their produces are: mouldboard plough Cultivator Scotch cart Harrow Planter Maize sheller combine harvesters Boom sprayers Disc harrow Spike toothed harrow KNAPSACK SPRAYER • Farming is a business. • Communal farmers grow crops and keep animal mainly for their own use. • If there is any extra they sell to get money. • Commercial farmers grow crops and keep animals for sale. • Crops and animals produced are called farm produce. • There are places were farmers have to sell their produce. • Farmers can take their produce to local markets. • A market is a place where buying and selling occurs. • Some of the local markets includes: A shopping centre A school A nearest bus stop A local village A school Local Grain Marketing Board depot (GMB) Types of farm produce Beef Fruits Mutton Eggs Vegetables Pork Milk Chicken Cereals/grains beans
Make a test, with answers best on the following: Conduct an investigation to provide evidence that living things are made of cells; either one cell or many different numbers and types of cells. Supporting Content LS1.A: Structure and Function • All living things are made up of cells, which is the smallest unit that can be said to be alive. An organism may consist of one single cell (unicellular) or many different numbers and types of cells (multicellular). (MS-LS-1.1) Further Explanation: Emphasis is on developing evidence that living things are made of cells, distinguishing between living and non-living things, and understanding that living things may be made of one cell or many and varied cells. In multicellular organisms, the body is a system of multiple interacting subsystems. These subsystems are groups of cells that work together to form tissues and organs that are specialized for particular body functions. (MS-LS-1.3) Further Explanation: Emphasis is on the conceptual understanding that cells form tissues and tissues form organs specialized for particular body functions. Examples could include the interaction of subsystems within a system and the normal functioning of those systems. Organisms reproduce, either sexually or asexually, and transfer their genetic information to their offspring. (MS-LS-1.4) • Living things share certain characteristics. (These include response to environment, reproduction, energy use, growth and development, life cycles, made of cells, etc.) (MS-LS1.4) Further Explanation: Examples should include both biotic and abiotic items, and should be defended using accepted characteristics of life. Plants, algae (including phytoplankton), and many microorganisms use the energy from light to make sugars (food) from carbon dioxide from the atmosphere and water through the process of photosynthesis, which also releases oxygen. These sugars can be used immediately or stored for growth or later use. (MS-LS-1.5) Further Explanation: Emphasis is on tracing movement of matter and flow of energy. Supporting Content LS1.C: Organization for Matter and Energy Flow in Organisms • Within individual organisms, food moves through a series of chemical reactions (cellular respiration) in which it is broken down and rearranged to form new molecules, to support growth, or to release energy. (MS-LS-1.6) Further Explanation: Emphasis is on describing that molecules are broken apart and put back together and that in this process, energy is released and on understanding that the elements in the products are the same as the elements in the reactants. Organisms, and populations of organisms, are dependent on their environmental interactions both with other living things and with nonliving factors. (MS-LS-2.1) • In any ecosystem, organisms and populations with similar requirements for food, water, oxygen, or other resources may compete with each other for limited resources, access to which consequently constrains their growth and reproduction. (MS-LS-2.1) • Growth of organisms and population increases are limited by access to resources. (MS-LS-2.1) Further Explanation: Emphasis is on cause and effect relationships between resources and growth of individual organisms and the numbers of organisms in ecosystems during periods of abundant and scarce resources. Similarly, predatory interactions may reduce the number of organisms or eliminate whole populations of organisms. Mutually beneficial interactions, in contrast, may become so interdependent that each organism requires the other for survival. Although the species involved in these competitive, predatory, and mutually beneficial interactions vary across ecosystems, the patterns of interactions of organisms with their environments, both living and nonliving, are shared. (MS-LS-2.2) Further Explanation: Emphasis is on predicting consistent patterns of interactions in different ecosystems in terms of the relationships among and between organisms and abiotic components of ecosystems. Examples of types of interactions could include competitive, predatory, and mutually beneficial. Food webs are models that demonstrate how matter and energy is transferred between producers, consumers, and decomposers as the three groups interact within an ecosystem. Transfers of matter into and out of the physical environment occur at every level. Decomposers recycle nutrients from dead plant or animal matter back to the soil in terrestrial environments or to the water in aquatic environments. The atoms that make up the organisms in an ecosystem are cycled repeatedly between the living and nonliving parts of the ecosystem. (MS-LS-2.3) Further Explanation: Emphasis is on describing the conservation of matter and flow of energy into and out of various ecosystems, and on defining the boundaries of the system. Ecosystems are dynamic in nature; their characteristics can vary over time. Disruptions to any physical or biological component of an ecosystem can lead to shifts in all its populations. (MSLS-2.5) Further Explanation: Emphasis is on recognizing patterns in data and making warranted inferences about changes in populations, and on evaluating empirical evidence supporting arguments about changes to ecosystems. Biodiversity describes the variety of species found in Earth’s terrestrial and oceanic ecosystems. The completeness or integrity of an ecosystem’s biodiversity is often used as a measure of its health. (MS-LS-2.6) Supporting Content LS4.D: Biodiversity • Changes in biodiversity can influence humans’ resources, such as food, energy, and medicines, as well as ecosystem services that humans rely on—for example, water purification and recycling. (MS-LS-2.6) Supporting Content ETS1.B: Developing Possible Solutions • There are systematic processes for evaluating solutions with respect to how well they meet the criteria and constraints of a problem. (MS-LS-2.6) Further Explanation: Examples of ecosystem services could include water purification, nutrient recycling, and prevention of soil erosion. Examples of design solution constraints could include scientific, economic, and social considerations. Genes are located in the chromosomes of cells, with each chromosome pair containing two variants of each of many distinct genes. Each distinct gene chiefly controls the production of specific proteins, which in turn affects the traits of the individual. Structural changes to genes (mutations) can result in changes to proteins, which can affect the structures and functions of the organism and thereby change traits. (MS-LS-3.1) Supporting Content LS3.B: Variation of Traits • In addition to variations that arise from sexual reproduction, genetic information can be altered because of mutations. Though rare, mutations may result in significant changes to the structure and function of proteins. Changes can be beneficial, harmful, or neutral to the organism. (MS-LS-3.1) Further Explanation: Emphasis is on conceptual understanding that changes in genetic material may result in making different proteins. Organisms reproduce, either sexually or asexually, and transfer their genetic information to their offspring. (MS-LS-3.2) Supporting Content LS3.A: Inheritance of Traits • Variations of inherited traits between parent and offspring arise from genetic differences that result from the subset of chromosomes (and therefore genes) inherited. (MS-LS-3.2) Supporting Content LS3.B: Variation of Traits • In sexually reproducing organisms, each parent contributes half of the genes acquired (at random) by the offspring. Individuals have two of each chromosome and hence two alleles of each gene, one acquired from each parent. These versions may be identical or may differ from each other. (MS-LS-3.2) Further Explanation: Emphasis is on using models such as simple Punnett squares and pedigrees, diagrams, and simulations to describe the cause and effect relationship of gene transmission from parent(s) to offspring and resulting genetic variation. The collection of fossils and their placement in chronological order is known as the fossil record and documents the change of many life forms throughout the history of the Earth. Anatomical similarities and differences between various organisms living today and between living and once living organisms in the fossil record enable the classification of living things. (MS-LS-4.1, MS-LS-4.2) Further Explanation: Emphasis is on finding patterns of changes in the level of complexity of anatomical structures in organisms and the chronological order of fossil appearance in the rock layers. The collection of fossils and their placement in chronological order is known as the fossil record and documents the change of many life forms throughout the history of the Earth. Anatomical similarities and differences between various organisms living today and between living and once living organisms in the fossil record enable the classification of living things. (MS-LS-4.1, MS-LS-4.2) Further Explanation: Emphasis is on explanations of the relationships among organisms in terms of similarity or differences of the gross appearance of anatomical structures. Scientific genus and species level names indicate a degree of relationship. (MS-LS-4.3) Further Explanation: Emphasis is on inferring general patterns of relatedness among structures of different organisms by comparing diagrams, pictures, specimens, or fossils. Natural selection leads to the predominance of certain traits in a population, and the suppression of others. (MS-LS-4.4) Further Explanation: Emphasis is on using concepts of natural selection, including overproduction of offspring, passage of time, variation in a population, selection of favorable traits, and heritability of traits. In artificial selection, humans have the capacity to influence certain characteristics of organisms by selective breeding. One can choose desired parental traits determined by genes, which are then passed to offspring. (MS-LS-4.5) Further Explanation: Emphasis is on identifying and communicating information from reliable sources about the influence of humans on genetic outcomes in artificial selection (such as genetic modification, animal husbandry, gene therapy), and on the influence these technologies have on society as well as the technologies leading to these scientific discoveries. Adaptation by natural selection acting over generations is one important process by which species change over time in response to changes in environmental conditions. Traits that support successful survival and reproduction in the new environment become more common; those that do not become less common. Thus, the distribution of traits in a population changes. (MS-LS-4.6) Further Explanation: Emphasis is on using mathematical models, probability statements, and proportional reasoning to support explanations of trends in changes to populations over time. Examples could include Peppered Moth population changes before and after the industrial revolution.
create 15 multiple choice question about this topic.Remember working principle of frequency filter circuits 5.1.1 Describe operation and function of filters 5.1.2 Describe applications of filter in electronic equipment 5.1.3 Name types of filter circuit a. Passive filter b. Active filter 5.1.4 Identify difference between passive filter and active filter 5.2 Understand operation and application of passive filters 5.2.1 Explain operation of passive filter 5.2.2 Explain with diagram the types of passive filter a. Low-pass filter b. High-pass filter c. Band-pass filter 5.2.3 Explain applications of each passive filter 5.2.4 Explain operation for each passive filter 5.2.5 Explain voltage gain and maximum voltage gain (Avmax) for passive filter 5.2.6 Explain following terms : a. voltage gain in decibel, Av (dB) b. cut-off frequency, fc c. frequency pass-band d. frequency bandwidth (BW)
Computer Science 2.3 types of programming language
In many cases, cells must move materials from an area of lower concentration to an area of higher concentration, or “up” their concentration gradient. Such movement of materials is known as active transport. Unlike passive transport, active transport requires a cell to expend energy. CELL MEMBRANE PUMPS Ion channels and carrier proteins not only assist in passive trans- port but also help with some types of active transport. The car- rier proteins that serve in active transport are often called cell membrane “pumps” because they move substances from lower to higher concentrations. Carrier proteins involved in facilitated diffusion and those involved in active transport are very similar. In both, the molecule first binds to a specific kind of carrier protein on one side of the cell membrane. Once it is bound to the molecule, the protein changes shape, shielding the molecule from the hydrophobic interior of the phospholipid bilayer. The protein then transports the molecule through the membrane and releases it on the other side. However, cell membrane pumps require energy. Most often the energy needed for active transport is supplied directly or indirectly by ATP. Sodium-Potassium Pump One example of active transport in animal cells involves a carrier protein known as the sodium-potassium pump. As its name sug- gests, this protein transports Na ions and K ions up their con- centration gradients. To function normally, some animal cells must have a higher concentration of Na ions outside the cell and a higher concentration of K ions inside the cell. The sodium- potassium pump maintains these concentration differences. Follow the steps in Figure 5-6 on the next page to see how the sodium-potassium pump operates. First, three Na ions bind to the carrier protein on the cytosol side of the membrane, as shown in step . At the same time, the carrier protein removes a phosphate group from a molecule of ATP. As you can see in step , the phos- phate group from the ATP molecule binds to the carrier protein. Step shows how the removal of the phosphate group from ATP supplies the energy needed to change the shape of the carrier pro- tein. With its new shape, the protein carries the three Na ions through the membrane and then forces the Na ions outside the cell where the Na concentration must remain high. 3 2 1 SECTION 2 OBJECTIVES ● Distinguish between passive transport and active transport. ● Explain how the sodium-potassium pump operates. ● Compare endocytosis and exocytosis. VOCABULARY active transport sodium-potassium pump endocytosis vesicle pinocytosis phagocytosis phagocyte exocytosis www.scilinks.org Topic: Active Transport Keyword: HM60018 mb06se_homs02.qxd 5/18/07 11:02 AM Page 103 104 CHAPTER 5 K+ K+ K+ K+ K+ K+ INSIDE OF CELL OUTSIDE OF CELL Carrier protein Cell membrane P P P P Na+ Na+ Na+ ATP ADP Na+ Na+ Na+ Na+ Na+ Na+ 1 2 3 4 5 6 At this point, the carrier protein has the shape it needs to bind two K ions outside the cell, as step shows. When the K ions bind, the phosphate group is released, as indicated in step , and the carrier protein restores its original shape. As shown in step this time, the change in shape causes the carrier protein to release the two K ions inside the cell. At this point the carrier protein is ready to begin the process again. Thus, a complete cycle of the sodium-potassium pump transports three Na ions out of the cell and two K ions into the cell. At top speed, the sodium-potassium pump can transport about 450 Na ions and 300 K ions per second. The exchange of three Na ions for two K ions creates an electrical gradient across the cell membrane. That is, the outside of the membrane becomes positively charged relative to the inside of the membrane, which becomes relatively negative. In this way, the two sides of the cell membrane are like the positive and nega- tive terminals of a battery. This difference in charge is important for the conduction of electrical impulses along nerve cells. The sodium-potassium pump is only one example of a cell membrane pump. Other pumps work in similar ways to transport important metabolic materials across cell membranes.
2 Types of Adjective (1.3 Choose the correct types of Adjective with the sentence given.
CARBOHYDRATES Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen in a ratio of about one carbon atom to two hydrogen atoms to one oxygen atom. The number of carbon atoms in a carbohydrate varies. Some carbohydrates serve as a source of energy. Other carbohydrates are used as structural materials. Carbohydrates can exist as monosaccharides, disaccharides, or polysaccharides. Monosaccharides A monomer of a carbohydrate is called a monosaccharide (MAHN-oh-SAK-uh-RIED). A monosaccharide—or simple sugar— contains carbon, hydrogen, and oxygen in a ratio of 1:2:1. The gen- eral formula for a monosaccharide is written as (CH2O)n, where n is any whole number from 3 to 8. For example, a six-carbon mono- saccharide, (CH2O)6, would have the formula C6H12O6. The most common monosaccharides are glucose, fructose, and galactose, as shown in Figure 3-6. Glucose is a main source of energy for cells. Fructose is found in fruits and is the sweetest of the monosaccharides. Galactose is found in milk. Notice in Figure 3-6 that glucose, fructose, and galactose have the same molecular formula, C6H12O6, but differing structures. The different structures determine the slightly different properties of the three compounds. Compounds like these sugars, with a single chemical formula but different structural forms, are called isomers (IE-soh-muhrz). SECTION 2 OBJECTIVES ● Distinguish between monosaccharides, disaccharides, and polysaccharides. ● Explain the relationship between amino acids and protein structure. ● Describe the induced fit model of enzyme action. ● Compare the structure and function of each of the different types of lipids. ● Compare the nucleic acids DNA and RNA. VOCABULARY carbohydrate monosaccharide disaccharide polysaccharide protein amino acid peptide bond polypeptide enzyme substrate active site lipid fatty acid phospholipid wax steroid nucleic acid deoxyribonucleic acid (DNA) ribonucleic acid (RNA) nucleotide C HO H C H OH C OH H C CH2OH H C H OH O Glucose C OH C O H OH C OH H CH2OH C H CH2OH Fructose C H HO C OH H C OH H C CH2OH H C H OH O Galactose Glucose, fructose, and galactose have the same chemical formula, but their structural differences result in different properties among the three compounds. FIGURE 3-6 Copyright © by Holt, Rinehart and Winston. All rights reserved. 56 CHAPTER 3 Disaccharides and Polysaccharides In living things, two monosaccharides can combine in a condensa- tion reaction to form a double sugar, or disaccharide (die-SAK-e-RIED). For example in Figure 3-4, the monosaccharides fructose and glu- cose can combine to form the disaccharide sucrose. A polysaccharide is a complex molecule composed of three or more monosaccharides. Animals store glucose in the form of the polysaccharide glycogen. Glycogen consists of hundreds of glucose molecules strung together in a highly branched chain. Much of the glucose that comes from food is ultimately stored in your liver and muscles as glycogen and is ready to be used for quick energy. Plants store glucose molecules in the form of the polysaccha- ride starch. Starch molecules have two basic forms—highly branched chains that are similar to glycogen and long, coiled, unbranched chains. Plants also make a large polysaccharide called cellulose. Cellulose, which gives strength and rigidity to plant cells, makes up about 50 percent of wood. In a single cellu- lose molecule, thousands of glucose monomers are linked in long, straight chains. These chains tend to form hydrogen bonds with each other. The resulting structure is strong and can be broken down by hydrolysis only under certain conditions. PROTEINS Proteins are organic compounds composed mainly of carbon, hydrogen, oxygen, and nitrogen. Like most of the other biological macromolecules, proteins are formed from the linkage of monomers called amino acids. Hair and horns, as shown in Figure 3-7a, are made mostly of proteins, as are skin, muscles and many biological catalysts (enzymes). Amino Acids There are 20 different amino acids, and all share a basic structure. As Figure 3-7b shows, each amino acid contains a central carbon atom covalently bonded to four other atoms or functional groups. A single hydrogen atom, highlighted in blue in the illustration, bonds at one site. A carboxyl group, —COOH, highlighted in green, bonds at a second site. An amino group, —NH2, highlighted in yel- low, bonds at a third site. A side chain called the R group, high- lighted in red, bonds at the fourth site. The main difference among the different amino acids is in their R groups. The R group can be complex or it can be simple, such as the CH3 group shown in the amino acid alanine in Figure 3-7b. The differences among the amino acid R groups gives different proteins very different shapes. The different shapes allow pro- teins to carry out many different activities in living things. Amino acids are commonly shown in a simplified way such as balls, as shown in Figure 3-7c. (a) Many structures, such as hair and horns are made of proteins. (b) Proteins are made up of amino acids. Amino acids differ only in the type of R group (shown in red) they carry. Polar R groups can dissolve in water, but nonpolar R groups cannot. (c) Amino acids have complex structures, so, in this and other textbooks, they are often simplified into balls. FIGURE 3-7 (b) Alanine (an amino acid) (c) Simplified version of amino acid CH3 H N OH C C H O H (a) Copyright © by Holt, Rinehart and Winston. All rights reserved. BIOCHEMISTRY 57 H H N C C OH H O H CH3 H2O Glycine Alanine H N OH C C H O H H H N C C H O H CH3 N OH C C H O H (a) (b) (a) The peptide bond (shaded blue) that binds amino acids together to form a polypeptide results from a condensation reaction that produces water. (b) Poly- peptides are commonly shown as a string of balls in this textbook and elsewhere. Each ball represents an amino acid. FIGURE 3-8 Substrate Products Enzyme 1 2 3 In the induced fit model of enzyme action, the enzyme can attach only to a substrate (reactant) with a specific shape. The enzyme then changes and reduces the activation energy of the reaction so reactants can become products. The enzyme is unchanged and is available to be used again. 3 2 1 FIGURE 3-9 Dipeptides and Polypeptides Figure 3-8a shows how two amino acids bond to form a dipeptide (die-PEP-TIED). In this condensation reaction, the two amino acids form a covalent bond, called a peptide bond (shaded in blue in Figure 3-8a) and release a water molecule. Amino acids often form very long chains called polypeptides (PAHL-i-PEP-TIEDZ). Proteins are composed of one or more polypep- tides. Some proteins are very large molecules, containing hun- dreds of amino acids. Often, these long proteins are bent and folded upon themselves as a result of interactions—such as hydrogen bonding—between individual amino acids. Protein shape can also be influenced by conditions such as temperature and the type of solvent in which a protein is dissolved. For exam- ple, cooking an egg changes the shape of proteins in the egg white. The firm, opaque result is very different from the initial clear, runny material. Enzymes Enzymes—RNA or protein molecules that act as biological catalysts—are essential for the functioning of any cell. Many enzymes are proteins. Figure 3-9 shows an induced fit model of enzyme action. Enzyme reactions depend on a physical fit between the enzyme molecule and its specific substrate, the reactant being catalyzed. Notice that the enzyme has folds, or an active site, with a shape that allows the substrate to fit into the active site. An enzyme acts only on a specific substrate because only that substrate fits into its active site. The linkage of the enzyme and substrate causes a slight change in the enzyme’s shape. The change in the enzyme’s shape weakens some chemical bonds in the substrate, which is one way that enzymes reduce activation energy, the energy needed to start the reaction. After the reaction, the enzyme releases the products. Like any catalyst, the enzyme itself is unchanged, so it can be used many times. An enzyme may not work if its environment is changed. For example, change in temperature or pH can cause a change in the shape of the enzyme or the substrate. If such a change happens, the reaction that the enzyme would have catalyzed cannot occur.