The main food groups

• 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

Classification of plants • Plants can be classified as cultivated and wild plants. • Both cultivated and wild plants are very useful to people, animals and the environment. 1. Cultivated plants: • Cultivated plants are plants grown by people for selling. • They can be grown in the field, vegetable garden, home garden and orchard. Classification of plants 2. Wild plants Wild plants are plants that grow on their own outside the garden, orchard or field. They have many uses such as: • Food for people and animals • Shelter • Source of fuel in form of firewood. • Examples include, grasses, msasa, yellow wood, mahogany, mopane Plant Nutrition • The presence of plant nutrients in the soil make them grow well. • The three major plant nutrients are nitrogen, phosphorus and potassium. Sources of plant nutrients • The source for plant nutrients are grouped into organic and inorganic sources. Organic sources of plant nutrients • These are found in nature. • They are natural materials such, decayed plant and animal matter which include: • Animal manure from cattle, sheep, goats, poultry and pigs. • Green manure • Legume crops like beans, peas and groundnuts. • Humus • These material sources may also be called natural fertilizers. Inorganic sources of plant nutrients • These are sources of plant nutrients made by people in industries. They include: • Compound fertilizers like compound A, B, C and D. • These have two or more nutrients. • Straight fertilizers like ammonium nitrate, single super phosphate and urea. • A straight fertilizer supplies a single or more nutrient to the crop. A straight fertilizer A Compound fertilizer Sources of N,P,K • Ammonium nitrate and Urea- contain nitrogen Double super Phosphate, Single super phosphate-contain phosphorus • Muriate of Potash contains Potassium 2 . Compound fertilisers -have two or three of the three major plant nutrients (N.P.K). N-nitrogen P-phosphorus K-potassium Examples Compound D Wednesday 17 May 2023 Revision exercise (Plant nutrition) 1 .Name the 3 plant nutrients needed by plants. 2. What are the 2 groups of plant nutrients sources? 3. Give 3 examples of organic sources of plant nutrients. 4. What is a straight fertilizer? 5. Compound fertilizer supplies ……………or ………………. Nutrients. Vegetable crops • A vegetable is any part of a plant that is eaten by humans as food part of a meal. • Vegetables are grouped and named according to the part that is eaten. • These are leaf, root, fruit, flower, bulb, tuber and legume vegetables. Leaf vegetables Types of veg Legume etable cropsvegetables Fruit vegetables Root, bulb and tuber Flower vegetables Cabbage Peas Tomato Root: carrots Cauliflower Rape Green beans Pepper Parsnip broccoli Spinach Melons Beetroot Tsunga Cucumber Bulb: onion Lettuce Squash Garlic kale Egg plant Leek chillies Tuber: Irish potato Wednesday 31 May 2023 Vegetable crops 1. What is a vegetable? 2. Which one is not a vegetable from the list below? a. Covo B. cabbage C. wheat D. tomato 3. Choose a vegetable which is not a fruit vegetable. a. tomato B. pepper C. kale D. egg plant 4. From which pair of vegetables do we eat the flower? A. cauliflower and garlic B. broccoli and cauliflower C. broccoli and rape D. cauliflower and pepper 5. Give one example of a vegetable belonging to each of the following groups. a. root b. legume c. bulb 6. Name any 5 groups of vegetable classification according to the parts eaten. Growing leaf vegetables • Although there are many types of vegetables, the leaf, fruit and bulb vegetables are widely grown. • Leaf vegetables form the greater part of vegetable crops. • Leaf vegetables belong to a family called brassica. • Brassicas include cabbages, lettuce, spinach, covo and many others. • Each brassica family has got its own varieties called cultivar. • They usually grow under the same climatic conditions and are affected by the same pests and diseases. • The selection of a variety depends on the following : The intended use of the vegetable, for example, salad, stew or snacks. Days taken to mature. Disease resistant Season of the year Seedbed preparation • Brassica vegetables are usually raised in seedbeds. • The seedbeds are prepared by: • Marking the position of the bed 1 meter in width by any length using a tape measure, hammer and pegs. • Digging a seedbed to a depth of 25 to 30cm using a hoe. • Breaking lumps of soil using a garden rake. Soil requirements • Brassicas need: • Well drained soils. • Fertile soil for good growth • Slightly acidic soils (pH 5.5-6) Climatic requirements • Brassicas need cool to warm temperatures. • Very low temperatures cause cabbages to flower which is called bolting. • Brassicas can be grown throughout the year. Seedbed preparation • Brassica seedlings are usually raised in seedbeds. • A seedbed is prepared by: Marking the position of the bed 1 metre in width by any length using a tape measure, hammer and pegs. Digging a seedbed to depth of 25 to 30 cm using a hoe. Breaking lumps of soil using a garden rake. This is done in order to have a fine tilth and improve soil to seed contact. Making ridges that a 15cm high. Apply 3 to 5kg/m² of well decomposed manure. 60 to 100g/m² of compound fertilizer can be added into the soil. Management of vegetable crops • After transplanting the seedlings, the seedlings need to be looked after. (a)Controlling weeds: all vegetables must be kept weed free. • This is done either by hand pulling weeds or shallow cultivation using a hand fork. (b) Pest control: common pests that affect the brassicas are aphids and diamond black moth larva. • Aphids are small green insects that suck the juice from the leaves leaving them with curls. • They are controlled by spraying malathion using the instructions on the label. (c) Disease control: bacterial diseases are common in brassicas. • Common diseases are black rot and soft rot, especially in cabbages. • These are controlled by: Crop rotation Early planting Planting resistant cultivars (d) Top dressing: brassicas are top dressed using Ammonium Nitrate at a rate of 2.5g per plant. • Top dressing is usually done 3 or 4 weeks after germination. FIELD CROPS • Field crops are crops that are grown on a large piece of land. • Example of field crops:  Maize  Cotton  Groundnuts  Roundnuts  Wheat  Sunflower  Tobacco  Sugar cane  Tea  Coffee  Soya beans  sorghum Classification of field • Field crops can be classified according to use such crops cereal, fibre, sugar and oil. 1. Cereal crops: • A cereal is a grass grown for its edible seeds. • They are also known as grain crops. • The major cereal crops are maize, wheat, rice, barley, sorghum and millet. 2 . fiber crops : • these are crops which are grown for their fiber and are used in making textiles, ropes and rugs. • Important fiber crops are cotton, flax and sisal 3. Oil seed crops: • These crops are grown for the purpose of extracting oil from their seed. • The main oil seed crops are groundnuts, sunflower, soyabean and cotton seed. 4 . Sugar crops : • Sugar crops include sugarcane,

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.

Nutrition Notes Nutrition- study of how your body uses food Process by which body uses nutrients How you look and feel Resist diseases and illness How you perform physically and mentally Nutrients: substances in food your body needs to grow, repair and supply energy to your body cells 6 Classes of Nutrients 1.Carbohydrates: 1 gram= 4 calories 2. Protein: 1 gram- 4 calories 3. Fats: 1 gram= 9 calories 4.Water 5. Vitamins 6. Minerals Calorie: measurement of energy in food Metabolism: Rate at which body burns energy(calories) Hunger: physical drive to eat Appetite: pshycological desire for food What influences your food choices: Foods you like Health Reasons Family and Culture Time & Money Advertising Emotions Friends Social Media: Modeling Nutrients Carbohydrates: your body’s main source of energy sugars/starches in food 45%-65% of diet #1 source of energy Simple: sugars converted to glucose= energy (fruits, dairy, honey, some manufactured foods) Complex: sugars linked together (starches) (grains, bread, pasta, beans, vegetables) Fiber: tough, indigestible carbohydrates Cleans our digestive system Prevents some types of cancer Prevents heart disease (fruits, vegetables, whole grains,nuts) 2. Protein: growth and repair of body tissues Made up of chemicals called “amino acids” Basic building material of all body cells (muscles, bones, skin, internal organs) Secondary source of energy protein(hemoglobin) attaches to oxygen in blood Functions as hormones regulating body functions 10-15% of diet *Body uses 20 Amino Acids found in food ( body produces 11 and 9 must come from diet) Essential amino acids: 9 amino acids body doesn't produce Complete Amino Acids: foods that contain all 9 essential amino acids ( animal products) Incomplete Amino Acids: food products that do not contain all 9 essential amino acids. Fats 15-25% of diet Secondary source of energy Blood clotting Controlling inflammation Maintains healthy skin/hair absorb /transport fat soluble vitamins Regulates body temperature Types of Fat Unsaturated: “good” fat Liquid at room temperature Can help fight heart disease (veg oil, nuts) Saturated: “bad” fat Solid at room temp Clogs arteries Causes strokes, heart attack, diabetes (animal products, meat, dairy) Cholesterol: waxy like fat substance found in meat products HDL: good type of cholesterol Body creates(liver) Creates cell wall, hormones, and vit D LDL: bad cholesterol- found in foods (clogs arteries) 4. Trans Fat: “one of the worst type of fats” Formed by a process called “hydrogenation”: adding Hydrogen molecules to unsaturated fats to make it more solid and resistant to chemical change. Vitamins A vitamin is a chemical compound that is needed in small amounts for the human body to work correctly. Vitamins are classified as either fat soluble (vitamins A, D, E and K) or water soluble (vitamins B and C). This difference between the two groups is very important. It determines how each vitamin acts within the body. The fat soluble vitamins are soluble in lipids (fats). Fat soluble vitamins can be stored in our body Water soluble vitamins must be taken every day Human body produces some amounts of Vitamin D & K

Agriculture Agriculture is the main source of livelihood in every country in the region except Brunei and Singapore. Agricultural employment, however, has been declining. More than two-thirds of the workforces of Cambodia and Laos practice agriculture. As the economies of the ASEAN countries have been restructured toward growth in industry and services, there has been a corresponding decline in the proportion of the gross domestic product (GDP) derived from agriculture, most significantly in Indonesia, Malaysia, and Thailand. Agricultural output in Southeast Asia has increased significantly since 1970. There are wide variations in this growth across the region, with the greatest gains in Malaysia and Thailand and little or no increase in Cambodia, Laos, and Vietnam. Hunger and malnutrition are problems in pockets of even the most developed countries, but they have been especially serious in Cambodia because of crop failures and internal strife. The condition of the rural population everywhere is clearly related to limited access to land, the landless experiencing greater poverty and poorer health. Landlessness is perhaps most serious in the Philippines. The dominant form of agriculture in the region is wet-rice cultivation. Where conditions permit, two crops typically are planted each year. Other food crops such as corn (maize), cassava, and pulses (legumes) frequently are grown in drier areas where there is too little water for a second planting of rice. Rice production requires a reliable water supply. Thailand and the Philippines rely heavily on rain-fed systems, while Indonesia utilizes irrigation to a large extent. Irrigation or some other form of water control is especially critical in the cultivation of the high-yielding varieties (HYVs) of rice that have been introduced since the 1960s. The spread of the so-called Green Revolution—in which HYVs and chemical fertilizers and pesticides are utilized—has brought mixed results. There is little doubt that production has increased because of the higher yields of these hybrid strains and because their more rapid maturation increases the possibility of multiple annual crops. Frequently, however, poorer farmers are not able to take advantage of these strains, because of the high cost of their use. The goal of rice self-sufficiency has been difficult to achieve for most countries. A large variety of cash crops are grown for the local and export markets, both on large commercial estates and by individual growers or smallholders. Tree crops are the most important in terms of value, although the area devoted to them is limited largely to equatorial areas. Rubber and palm oil are significant in Malaysia, Indonesia, and southern Thailand, while coconuts and sugar are important in the Philippines. Other major export crops are cacao, coffee, and spices, while crops grown largely for local and regional consumption include chilies, sweet potatoes, peanuts (groundnuts), and tobacco. The cultivation of opium poppies is important in parts of Myanmar and Thailand. The emphasis on rubber and palm oil production is in response to a considerable (though fluctuating) worldwide demand for these commodities and because of a nearly continuous harvest period that provides year-round employment. Foreign corporations once dominated production, but, as the region’s countries gained independence, much of the production was nationalized. Government ownership continues to predominate, with increasing private ownership. Fishing contributes only a token amount to the GDP of Southeast Asian countries, but it is an important livelihood in certain areas and supplies a significant portion of the local diet. Marine output has gradually expanded with new technologies. The maritime nations of Thailand, Indonesia, Malaysia, and the Philippines all have globally important fishing industries. Shrimp catches are especially in demand in the world economy. Aquaculture has become increasingly important in the region, such species as shrimp, carp, and grouper being raised in excavated ponds.

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

Where Is It? Russia is a very big country. It is the largest country in the world almost twice as big as the United States. Russia is part of both Europe and Asia. Moscow is the capital of Russia. It is a big city in the European part of the country. More than twelve million people live there. The Russian president lives in a famous group of buildings in Moscow. People. Most people in Russia live and work in cities. The main language is Russian. In the country, jobs have to do with the land and the sea. For example, many people fish, mine oil and coal, and cut trees for wood. Sports such as soccer and ice hockey are popular in Russia. Russia is famous for music and a kind of dance show called ballet. Swan Lake is a famous Russian ballet. Land. The land in Russia is mainly low flatlands, high flatlands, and mountains. The deepest lake in the world, Lake Baikal, is in Russia. Russia has frozen flatlands in the north and wide grassy lands in the south. In between are huge forests. Russia is a cold country, and it is home to the coldest village in the world. But many places in Russia also have beautiful summers. History. In the past, czars, or emperors, ruled Russia. During that time, the peasants in Russia were unhappy. They didn't like the way the czars ruled the people. They fought in 1917 to change their country's ways. After the fight, Russia took control of a group of other nearby countries. Together they formed the Union of Soviet Socialist Republics (USSR). The USSR had many problems, so it broke up in 1991. Today, Russia has a president. Celebrations. Many people celebrate Christmas and Easter in Russia. On Easter, they eat cakes and paint hard-boiled eggs. Russian Easter egg Russians also have a holiday to celebrate the end of winter. For this holiday, people eat pancakes with butter. They also have fun with sleigh rides and snowball fights. Food. A popular soup in Russia is famous around the world. People make the soup from beets and other vegetables. Beets are red, so the soup also has a red color. Many Russians like a homemade drink. The drink has a sour flavor. Conclusion Russia is home to both crowded cities and wild forests. Russia has a long, rich history and many interesting things to do. The Russian people value the traditions of their beautiful homeland.

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