Introductory plant biology stern 12th edition

Silent spring. Boston: Houghton Mifflin Co. Harvey-Gibson, R. Outlines of the history of botany. Manchester, NH: Ayer Co. Pubs, Inc. Jacobs, P. Guide to information sources in the botanical sciences. Johnson, T. CRC ethnobotany desk reference. McCarthy, S. Ethnobotany and medicinal plants. Minnus, P. Pollan, M. The botany of desire. Sumner, J. American household botany: A history of useful plants, — Portland, OR: Timber Press. Food plants of the world: An illustrated guide.

Lavender is used in soaps, in shampoos, and as an aromatic plant because of its soothing fragrance. These include growth, reproduction, response to stimuli, metabolism, movement, complexity of organization, and adaptation to the environment.

Then it examines the chemical and physical bases of life. A brief look at the elements and their atoms is followed by a discussion of compounds, molecules, valence, bonds, ions, acids, bases, and salts. Forms of energy and the chemical components of cells are examined next. The chapter concludes with an introduction to macromolecules: carbohydrates, lipids, proteins, and nucleic acids. Learn the attributes of living organisms. Define matter; describe its basic state. Understand the nature of compounds and describe acids, bases, and salts.

The solid pellet darts randomly about the surface, looking like a highly energetic bug waterskiing, as the warmer water rapidly converts it to a gas. Does all that motion make the dry ice alive? Hardly; yet one of the attributes of living things is the capacity to move. But if living things move, what about plants? Again the answer is no, but these questions do serve to point out some of the difficulties encountered in defining life. In fact, some argue that there is no such thing as life—only living organisms—and that life is a concept based on the collective attributes of living organisms.

All living cells contain genetic material that controls their development and activities. In the cells of many organisms, this genetic material, known as DNA an abbreviation for deoxyribonucleic acid , is housed in a somewhat spherical structure called the nucleus, which is suspended in the cytoplasm. In bacteria, however, the DNA is distributed directly in the cytoplasm. The cells of plants, algae, fungi, and many simpler organisms have a cell wall outside of the membrane that bounds the cytoplasm.

The cell wall provides support and rigidity. Cells are discussed in more detail in Chapter 3. Know the various forms of energy.

Learn the elements found in cells. Understand the nature of carbohydrates, lipids, and proteins. Most growth results from the production of new cells and includes variations in form—some the result of inheritance, some the result of response to the environment.

If you plant two varieties of tulips near each other and grow them under identical conditions, they are likely to differ in size, color, and other characteristics due to differences in genetic makeup. On the other hand, if you plant bulbs of the same variety next to each other, they may also look different from each other, especially if you treat them differently.

That is, they are exposed to different environments. If you water one just enough to allow it to grow, while you water the other one freely and work fertilizers and conditioners into the soil around it, you might expect the second one to grow larger and produce more flowers than the first. Various aspects of growth are discussed in Chapter Reproduction Dinosaurs were abundant million years ago, but none exist today.

Hundreds of mammals, birds, reptiles, plants, and other organisms are now listed as endangered or threatened species, and many of them will become extinct within the next decade or two. All of these once-living or currently threatened organisms have one feature in common: it became impossible or it has become difficult for them to reproduce. Reproduction is such an obvious feature of living organisms that we take it for granted—until it no longer takes place.

Also, offspring tend to resemble their parents more than they do other individuals of the same kind. The laws governing these aspects of inheritance are discussed in Chapter You might argue, however, that when you stuck a pin into your house plant, nothing happened, even though you were fairly certain the plant was alive. You might not have been aware that the house plant did indeed respond, but in a manner very different from that of a human.

Plant responses to stimuli are generally of a different nature than those of animals. Some studies have shown that callose may form within as little as 5 seconds after wounding. Also, an unorganized tissue called callus, which forms much more slowly, may be produced at the site of the wound. Responses of plants to injury and to other stimuli, such as light, temperature, and gravity, are discussed in Chapters 9 through Metabolism Metabolism is the collective product of all the biochemical reactions taking place within an organism.

All living organisms undergo metabolic activities, which include the production of new cytoplasm, the repair of damage, and normal cell maintenance. The most important activities include respiration, an energy-releasing process that takes place in all living things; photosynthesis, an energy-harnessing process in green cells that is, in turn, associated with energy storage; digestion, the conversion of large or insoluble food molecules to smaller soluble ones; and assimilation, the conversion of raw materials into cytoplasm and other cell substances.

These topics are discussed in Chapters 9 through This does not mean, however, that plants do not exhibit movement, a universal characteristic of living things. The leaves of sensitive plants Mimosa pudica fold within seconds after being disturbed or subjected to sudden environmental changes, and the tiny underwater traps of bladderworts Utricularia snap shut in less than one-hundredth of a second.

But most plant movements, when compared with those of animals, are slow and imperceptible and are mostly related to growth phenomena.

They become obvious only when demonstrated experimentally or when shown by time-lapse photography. Movement is not confined to the organism as a whole but occurs at the cellular level. For example, the cytoplasm of living cells constantly flows like a river within cells; this streaming motion is called cyclosis, or cytoplasmic streaming.

Cyclosis usually appears to run clockwise or counterclockwise within the boundaries of each cell, but movement is not limited to a circular pattern. Complexity of Organization The cells of living organisms are composed of large numbers of molecules the smallest unit of an element or compound retaining its own identity. Even the most complex nonliving object has only a tiny fraction of the types of molecules of the simplest living organism.

Typically there are more than 1 trillion molecules in a single cell. The molecules are not simply mixed, like the ingredients of a cake or the concrete in a sidewalk, but are organized into compartments, membranes, and other structures within cells. Furthermore, the arrangements of these molecules in living organisms are highly structured and complex.

Bacteria, for example, are considered to have the simplest cells known, yet each cell contains a minimum of different kinds of protein as well as hundreds of other substances, with each component playing an important role in the function of the cell. When flowering plants and other larger living objects are examined, the complexity of organization is overwhelming, and the number of molecule types can run into the millions.

Adaptation to the Environment If you move a rock from a cold mountain to a warm desert, the structure of that rock will not change in response to its new environment.

Living organisms, however, do respond to the air, light, water, and soil of their environment, as will be explained in later chapters. They are also, after countless generations of natural selection as discussed in Chapter 15 , genetically adapted to their environment in many subtle ways. Some weeds e. It occupies space. It has mass, which we commonly associate with weight.

It is composed of elements. There are 93 elements that occur naturally on our planet. At least 19 more elements have been produced artificially. Only a few of the natural elements e. Each element has a designated symbol, often derived from its Latin name. The symbol for copper, for example, is Cu from the Latin cuprum ; and for sodium, Na from the Latin natrium.

The symbols for carbon, hydrogen, and oxygen are C, H, and O, respectively. The smallest stable subdivision of an element that can exist is called an atom. Atoms are so minute that until the midls, individual atoms were not directly visible to us with even the most powerful electron microscopes. We have known for over years, however, that atoms consist of several kinds of subatomic particles.

Each atom has a tiny nucleus consisting of protons, which are particles with positive electrical charges, and other particles called neutrons, which have no electrical charges. Both protons and neutrons have a small amount of mass. Objects that hit each other are not actually contacting solid surfaces.

Instead, negative charges on the objects repel each other. Without these charges, the objects would pass through each other. Atoms are extremely long-lived. It is estimated that they survive for about years. Accordingly, the atoms in every living thing were once found in stars. Each tree you see outside your window probably contains a billion atoms, many of which may well have been in the bodies of your ancestors. Each atom of an element has a specific number of protons in its nucleus, ranging from one in hydrogen, the lightest element, to 92 in uranium, the heaviest natural element.

This number is referred to as the atomic number. The atomic number is often shown as a subscript to the left of the chemical symbol. For example, nitrogen, which has seven protons in its nucleus, has its atomic number of seven shown as 7N.

The combined number of protons and neutrons in a single atom is referred to as its atomic mass Table 2. The atomic mass number is commonly shown as a superscript to the left of the chemical symbol. For example, the atomic mass of nitrogen, which has seven protons and seven neutrons in its nucleus, is shown as 14N, and when both the atomic number and the atomic mass are shown, the chemical symbol appears as N. Electron masses are about 1, times lighter than those of both protons and neutrons and are so minute that they are generally disregarded.

Since opposite electric charges attract each other, the positive electric charges of protons attract the negative electric charges of electrons and determine the paths of the electrons whirling around the nucleus. The region occupied by electrons around the nucleus is called an orbital. The nucleus in the center consists of eight electrically neutral neutrons and eight positively charged protons.

Eight negatively charged electrons whirl around the nucleus. In a real atom the electrons would not be spaced or confined as shown in this simple diagram. The nucleus is one-millionth of one-billionth the diameter of the atom. Electrons actually occupy all space in an orbital simultaneously, so they do not circle around the nucleus like planets.

In addition, according to the quantum leap theory of physics, an electron can move instantaneously from one orbital to another without visiting the space between them! Electrons may be located in one or more energy levels of an atom, and their distance from the nucleus depends on their energy level.

Each energy level is usually referred to as an electron shell. The outermost electron shell determines how or if an atom reacts with another atom. Only two electrons can occupy the first and lowest energy level associated with the innermost orbital; this orbital is more or less spherical and is so close to the nucleus that it is often not shown on diagrams of atoms.

One to several additional orbitals, which are mostly spindle shaped like the tips of cotton swabs , generally occupy much more space. Up to eight electrons can be held by the second energy level, and although the third and fourth energy levels can hold more than eight electrons each, they can become unstable if more than eight electrons are present. If an electron in one orbital is provided with more energy, it can jump to an orbital farther away from the nucleus. Conversely, if an electron releases energy, it drops to an energy level closer to the nucleus.

The electrons of each orbital tend to repel those of other orbitals, so that the axes of all the orbitals of an atom are oriented as far apart from each other as possible; the outer parts of the orbitals, however, actually overlap more than shown in diagrams of them. Orbitals usually have diameters thousands of times more extensive than that of an atomic nucleus Fig. The number of neutrons in the atoms of an element can vary slightly, so the element may occur in forms having different weights but with all forms behaving alike chemically.

Such variations of an element are called isotopes. The element oxygen Fig. The nucleus of one of these isotopes contains eight protons and eight neutrons; the nucleus of another isotope holds eight protons A.

Additional orbitals are dumbbell-shaped, trons. If the number of neutrons in an isotope of with axes that are perpendicular to one another. Such an isotope is said to be radioactive. As mentioned in Figure 2. When two or more elements are united in a definite ratio by chemical bonds, the substance is called a compound. Table salt sodium chloride, NaCl , for example, is a compound consisting of sodium and chlorine atoms combined in a ratio.

The molecules of the gases oxygen and hydrogen, for example, exist in nature as combinations of two atoms of oxygen O2 or two atoms of hydrogen H2 , respectively.

Water molecules H2O consist of two atoms of hydrogen and one atom of oxygen Fig. Molecules are in constant motion, with an increase or decrease in temperature speeding up or slowing down the motion. The more molecular movement there is, the greater the chances are that some molecules will collide with each other.

Also, the chances of random collisions increase in proportion to the density of the molecules i. Random collisions between molecules capable of sharing electrons are the basis for all chemical reactions. The reactions often result in new molecules being formed. Each chemical reaction in a cell usually takes place in a watery fluid and is controlled by a specific enzyme. Enzymes are organic catalysts a catalyst speeds up a chemical reaction without being used up in the reaction; enzymes are discussed on page The electrons of the three atoms are shared and form an electron cloud around the core, giving the molecule an asymmetrical shape.

Although the electron and proton charges balance each other, the asymmetrical shape and unequal sharing of the electrons in the bond between oxygen and hydrogen cause one side of the water molecule to have a slight positive charge and the other a slight negative charge. Such molecules are said to be polar. Since negative charges attract positive charges, polarity affects the way in which molecules become aligned toward each other; polarity also causes molecules other than water to be water soluble.

A water molecule is 0. Each sphere represents the electron cloud of the outer orbital. The polarity of water molecules causes them to be attracted to one another in a cohesive network.

The cohesion of water molecules is partly responsible for their capacity to be pulled in a continuous column through fine capillary tubes such as those of living wood. Water molecules form a cohesive network as their slightly positive hydrogen atoms are attracted to the slightly negative oxygen atoms of other water molecules Fig.

The cohesion between water molecules is partly responsible for their movement through fine capillary tubes, such as those present in the wood and other parts of plants. The attraction between the hydrogen atoms of water and other, negatively charged, molecules, such as those of fibers, also causes adhesion attraction of charged molecules to each other and is the basis for water wetting substances.

When there is no attraction between water and other substances e. Valence The combining capacity of an atom or ion based on electron number is called valence. In order for the atoms of these two elements to combine, there must be a balance between electrons lost or gained i.

The compound formed by the union of calcium and chlorine is called calcium chloride. Bonds and Ions Bonds are forces that form molecules by attracting and holding atoms together. Bonds can form in several different ways. If the number of electrons in the outermost energy level is less than eight, the atom may lose, gain, or share electrons, resulting in an outermost energy level that contains the maximum number of electrons. Three types of chemical bonds are of particular significance for living organisms: 1.

Covalent bonds form when two atoms complete their outermost energy level by sharing a pair of electrons in the outermost orbital; they hold two or more atomic nuclei together and travel between them, keeping them at a stable distance from each other.

For example, the single orbital of a hydrogen atom, which has just one electron, is usually filled by attracting an electron from another hydrogen atom. As a result, two hydrogen atoms share their single electrons, making a combined orbital with two electrons. The combined orbital, with its two hydrogen atoms, forms a molecule of hydrogen gas. The covalent bond is shown as a single line, so that hydrogen gas H2 is depicted as H—H.

Except for hydrogen and helium, which have only one orbital, elements can have up to four more orbitals in each energy level. Carbon atoms, for example, have six electrons—two in the innermost orbital and one in each of the four outer orbitals of the second shell; by covalent bonding, carbon can share four electrons. When four hydrogen atoms bond to one carbon atom, a molecule of methane gas CH4 is formed.

To illustrate the bonds, the structural formula for CH4 is shown as follows: H H C 19 of a water molecule are formed when electrons are closer to one atom than to another and therefore are shared unequally. Because the electrons are shared unequally, parts of the molecule are not electrically neutral and are slightly charged. Covalent bonds are the strongest of the three types of bonds discussed here and are the principal force binding together atoms that make up some important biological molecules discussed later in this chapter Fig.

Ionic bonds. In nature, some electrons in the outermost orbital are not really shared but instead are completely removed from one atom and transferred to another, particularly between elements that can strongly attract or easily give up an electron.

Molecules that lose or gain electrons become positively or negatively charged particles called ions. Ionic bonds form whenever one or more electrons are donated to another atom and result whenever two oppositely charged ions come in contact.

Ions are shown with their charges as superscripts. The sodium becomes a positively charged ion when it loses one of its electrons, which is gained by an atom of chlorine.

This extra electron makes the chlorine ion negatively charged, and the sodium ion and chlorine ion become bonded together by the force of the opposite charge Fig.

Such ions can form ionic bonds with two single negatively charged ions such as those of chlorine Cl— , forming magnesium chloride MgCl2. Many biologically important molecules exist as ions in living matter.

Hydrogen bonds form as a result of attraction between positively charged hydrogen atoms in polar molecules and negatively charged atoms in other polar molecules. Hydrogen bonds are very important in nature H H When one pair of electrons is shared, the bond is said to be single. When two pairs of electrons are shared, the bond is referred to as double, and triple bonds are formed when three pairs of electrons are shared. Double bonds are shown in structural formulas with double lines e.

In covalent bonds involving molecules such as those of hydrogen H2 , where electrons are shared equally, the bonds are said to be nonpolar. However, polar covalent bonds e. In a covalent bond, electrons are shared as outer shells of atoms overlap.

In this instance, two pairs of electrons are shared between the two atoms, and the shared electrons are counted as belonging to each atom. The sodium becomes positively charged when it loses one of its electrons, which is gained by an atom of chlorine.

The gained electron makes the chlorine ion negatively charged, and the two ions become bonded together by the attraction of opposite charges. Hydrogen bonds help cellular processes by maintaining the shapes of proteins such as enzymes, which make different compounds fit together precisely to complete a chemical reaction. Acids, Bases, and Salts Water molecules are held together by weak hydrogen bonds.

Some acids, such as the acetic acid of vinegar, release relatively few hydrogen ions and are said to be weak. Strong acids such as sulfuric acid dissociate almost completely into hydrogen and sulfate ions. Bases also referred to as alkaline compounds usually feel slippery or soapy. They are defined as compounds that release negatively charged hydroxyl ions OH — when dissolved in water.

The acidity or alkalinity of the soil or water in which a plant occurs affects how it lives and grows or even if it can exist in a particular environment. Vinegar, for example, has a pH of 3, tomato juice has a pH of 4. Precipitation with a pH of less than 4. Acid rain discussed in Chapter 25 is associated with industrial emissions, and appears to be causing damage to vegetation, soil organisms, and buildings in some parts of the world, including North America. The remaining ions bond together, forming a salt.

Energy exists in several forms and is required for growth, reproduction, movement, cell or tissue repair, and other activities of whole organisms, cells, or molecules. On earth, the sun is the ultimate source of life energy. Thermodynamics is the study of energy and its conversions from one form to another. Scientists apply two laws of thermodynamics to energy. The first law of thermodynamics states that energy is constant—it cannot be gained or lost— but it can be converted from one form to another.

Among its forms are chemical, electrical, heat, and light energy. For example, heat will always flow from a hot iron high energy to cold clothing low energy , but never from 1.

Furthermore, energy will be released during the conversion. The total amount of energy in the universe, however, remains constant. Such energyyielding reactions are vital to the normal functions of cells and provide the energy needed for other cell reactions that require energy. Both types of reactions are discussed in Chapter Forms of energy include kinetic motion and potential energy.

Some chemical reactions release energy, and others require an input of energy Fig. Although all electrons have the same weight and electrical charge, their amount of potential energy varies. Some of the numerous energy exchanges and carriers that occur in living cells are discussed in later chapters.

These simple forms may be converted to very large, complex molecules through the metabolism of the cells. The myriad of chemical reactions of living organisms is based on organic compounds.

Most other molecules that contain no carbon atoms are called inorganic. Today, many organic compounds can be produced artificially in the laboratory, and scientists sometimes hesitate to classify as either organic or inorganic some of the 4 million carbon-containing compounds thus far identified.

Most scientists, nevertheless, agree that inorganic compounds usually do not contain carbon. Dehydration synthesis reactions are controlled by enzymes see page The living substance of cells consists of cytoplasm and the structures within it. The numerous internal structures, which vary considerably in size, are discussed in Chapter 3. When a plant first absorbs these elements from the soil Monomers and Polymers Figure 2.

An individual with a snowboard resting on top of the hill has potential energy capacity to do work owing to its position. The potential energy is converted to kinetic energy when the snowboard goes down the hill. Figure 2. The closer electrons are to the nucleus, the less energy they possess and vice versa. The energy levels are referred to as electron shells. An electron at a second energy level. An electron can absorb energy from sunlight or some other source and be boosted to a higher energy level.

The absorbed energy can be released, with the electron dropping back to its original level see Fig. Hydrolysis, which is essentially the opposite of dehydration synthesis, occurs when a hydrogen from water becomes attached to one monomer and a hydroxyl group to the other. Energy is released when a bond is broken by hydrolysis. This energy may be stored temporarily or used in the manufacture or renewal of cell components.

Four of the most important classes of polymers found in cells are carbohydrates, lipids, proteins, and nucleic acids. Carbohydrates Carbohydrates are the most abundant organic compounds in nature. The number of CH2O units in a carbohydrate can vary from as few as three to as many as several thousand. There are three basic kinds of carbohydrates: 1.

Monosaccharides are simple sugars with backbones consisting of three to seven carbon atoms. Among the most common monosaccharides are glucose C6H12O6 and fructose, which is an isomer of glucose. Isomers are molecules with identical numbers and kinds of atoms, but with different structures and shapes. Glucose, which is produced by photosynthesis in green plant cells, is a primary source of energy in the cells of all living organisms Fig. Disaccharides are formed when two monosaccharides become bonded together by dehydration synthesis.

The common table sugar sucrose C12H22O11 is a disaccharide formed from a molecule of glucose and a molecule of fructose; a molecule of water is removed during synthesis. The removal of a molecule of water during the formation of a larger molecule from smaller molecules is referred to as a condensation reaction. Sucrose is the form in which sugar is usually transported throughout plants and is also the form of sugar stored in the roots of sugar beets and the culms stems of sugar cane. Polysaccharides are formed when several to many monosaccharides bond together.

Polysaccharide polymers sometimes consist of thousands of simple sugars attached to one another in long, branched or unbranched chains or in coils. For example, starches, which are the main carbohydrate reserve of plants, are polysaccharides that usually consist of several hundred to several thousand coiled glucose units. When many glucose molecules bond together to become a starch molecule, each glucose gives up a molecule of water.

The formula for starch is C6H10O5 n , the n representing many units. In order for a starch molecule to become available as an energy source in cells, it has to be hydrolyzed; that is, it has to be broken up into individual glucose molecules through the restoration of a water molecule for each unit. Throughout the world, starches are major sources of carbohydrates for human consumption—the principal starch crops being potatoes, wheat, rice, and corn in temperate areas, and cassava and taro in tropical areas.

Cellulose, the chief structural polymer in plant cell walls, is a polysaccharide consisting of 3, to 10, unbranched chains of glucose molecules. Although cellulose is very widespread in nature, its glucose units are bonded together differently from those of starch, and most animals digest it much less readily than they do starch.

Organisms that do digest cellulose, such as the protozoans living in termite guts, caterpillars, and some fungi, produce special enzymes capable of facilitating the breakdown of bonds between the carbons and the glucose units of the cellulose; the organisms then can digest the released glucose. Lipids Lipids are fatty or oily substances that are mostly insoluble in water because they have no polarized components.

They typically store about twice as much energy as similar amounts of carbohydrate and play an important role in the longer term energy reserves and structural components of cells.

The numbers of atoms and locations of bonds are easy to see in the upper linear diagrams, but when these molecules are in solution, they are in the form of rings, as shown in the lower diagrams.

Unless indicated otherwise, each junction in a ring contains a carbon atom. Examples of lipids include fats, which are solid at room temperature Fig. An oil molecule is produced when a unit of glycerol—a three-carbon compound that has three hydroxyl —OH groups—combines with three fatty acids. A fatty acid has a carboxyl —COOH group at one end and typically has an even number of carbon atoms to which hydrogen atoms can become attached.

Most fatty acid molecules consist of a chain with 16 to 18 carbon atoms. If hydrogen atoms are attached to every available bonding site of these fatty acid carbon atoms, as in most animal fats such as butter and those found in meats, the fat is said to be saturated.

If there is at least one double bond between two carbons and, consequently, there are fewer hydrogen atoms attached, the fat is said to be unsaturated. If there are three or more double bonds between the carbons of a fatty acid, as in some vegetable oils such as those of canola, olive, or safflower, the fat is said to be polyunsaturated.

Unsaturated vegetable oils can become saturated by bubbling hydrogen gas through them, as is done in the manufacture of margarine. Human diets high in saturated fats often ultimately lead to clogging of arteries and other heart diseases, while diets low in saturated fats promote better health. Waxes are lipids consisting of very long-chain fatty acids bonded to a very long-chain alcohol other than glycerol.

Waxes, which are solid at room temperature, are found on the surfaces of plant leaves and stems. They are usually embedded in a matrix of cutin or suberin, which are also lipid polymers that are insoluble in water.

The combinations of wax and cutin or wax and suberin function in waterproofing, reduction of water loss, and protection against microorganisms and small insects. Phospholipids are constructed like fats, but one of the three fatty acids is usually replaced by a phosphate group; this can cause the molecule to become a polarized ion.

When phospholipids are placed in water, they form a double-layered sheet resembling a membrane. Indeed, phospholipids are important components of all membranes found in living organisms. Proteins, Polypeptides, and Amino Acids The cells of living organisms contain from several hundred to many thousands of different kinds of proteins, which are second only to cellulose in making up the dry weight of plant cells.

Each kind of organism has a unique combination of proteins that gives it distinctive characteristics. A typical fatty acid is 4 nanometers long. The hundreds of kinds of daisies are distinguished from each other and from grasses by their particular combinations of proteins.

Proteins consist of carbon, hydrogen, oxygen, and nitrogen atoms, and sometimes also sulfur atoms. Proteins regulate chemical reactions in cells, and comprise the bulk of protoplasm apart from water. Protein molecules are usually very large and consist of one or more polypeptide chains with, in some instances, simple sugars or other smaller molecules attached.

Polypeptides are chains of amino acids. There are 20 different kinds of amino acids, and from 50 to 50, or more of them are present in various combinations in each protein molecule. Each amino acid has two special groups of atoms plus an R group. One functional amino acid group is called the amino group —NH2 ; the other, which is acidic, is called the carboxyl group —COOH. The structure of an R group can vary from a single hydrogen atom to a complex ring.

Some R groups are polar, while others are not, and each is distinctive for one of the 20 amino acids. Amino acids are linked together by peptide bonds, which are covalent bonds formed between the carboxyl carbon of one amino acid and the nitrogen of the amino group of another in a dehydration reaction. Plants can synthesize amino acids they need from raw materials in their cells, but animals have to supplement from plant sources some amino acids they need, since they can manufacture only a few amino acids themselves.

A linear sequence of amino acids fastened together by peptide bonds forms the primary structure of a protein. As hydrogen bonds form between oxygen atoms of carboxyl groups and hydrogen atoms of amino groups in different molecules, the polypeptide chain can coil to form a staircase-like spiral, called an alpha helix.

The helix is one type of secondary structure that may form. Other secondary structures include polypeptide chains that double back to form hydrogen bonds between two lengths in what is referred to as a beta sheet, or pleated sheet.

Tertiary structure develops as the polypeptide further coils and folds. The tertiary structure is maintained by interactions and bonds among R groups. If a protein is composed of more than one kind of polypeptide, a fourth, or quaternary structure, forms when the polypeptides associate Fig. The three-dimensional structure of a protein may be somewhat flexible in solution, but anything that disturbs the normal pattern of bonds between parts of the protein molecule can denature the protein.

Denaturing may be reversible, but if it is brought about by high temperatures or harsh chemicals, it may kill the cell of which the protein is a part. Storage Proteins Some plant food-storage organs, such as potato tubers and onion bulbs, store small amounts of proteins in addition to large amounts of carbohydrates. Seeds, in particular, however, usually contain proportionately larger amounts of proteins in addition to their complement of carbohydrates and are very important sources of nutrition for humans and animals.

One example of an important protein source in human and animal diets is wheat gluten to which, incidentally, some humans become allergic. The gluten consists of a complex of more than a dozen different proteins. Some seed proteins, such as those of jequirity beans Abrus precatorius—used in India to induce abortions and as a contraceptive , are highly poisonous. The primary structure consists of a chain of amino acids bonded together. Stern — Chapter… 44 Stomata are part of this tissue.

Venus flytrap B. Irish white potato C. In turn, adventitious roots harvest minerals from the resulting accumulation of nutrient-rich material. Stern — Chapter… 23 Which of the following is NOT a typical characteristic of a shade leaf as opposed to a leaf of the same plant that is fully exposed to the sun? Venus flytraps Stern — Chapter… 27 Modified leaves are used by insectivorous plants to trap insects. One such plant that has movable modified leaves is A. Venus flytrap.

Stern — Chapter… 28 In the abscission zone of the leaf, which of the following is closest to the stem? Stern — Chapter… 30 Which of the following may cause pectins in the middle lamella of cells of the separation layer to break down in the fall? Manila hemp, a relative of the banana, B. TRUE Stern — Chapter… 48 If you were looking for bundle sheath cells in a leaf, you would usually find them forming a layer next to the upper epidermis. FALSE Stern — Chapter… 51 All the leaves of insectivorous plants function, when they are healthy, in actively trapping insects and other small organisms.

TRUE Stern — Chapter… 53 Anthocyanins are the principal pigments responsible for yellow and orange colors in fall leaves. Stern — Chapter… 2 Osmosis is a special kind of diffusion in which water molecules A. Stern — Chapter… 16 The pressure required to prevent osmosis from taking place is referred to as: A. Brownian motion D. Stern — Chapter… 17 Which of the following plays a role in plasmolysis?

Imbibition B. Turgor pressure C. Plasmolysis D. Active transport E. Stern — Chapter… 3 In which of the following are guard cells that form stomata not directly involved?

Stern — Chapter… 5 The cohesion of water molecules and their adhesion to the walls of narrow tubes that results in water rising in the tubes is called A. Stern — Chapter… 10 Changes in solute ion concentrations that are involved in the opening and closing of stomata pertain primarily to which of the following?

Nehemiah Grew. New terms are defined as they are introduced, and those that are boldfaced are included, with their pronunciation, in a glossary. A list of the scientific names of all organisms mentioned throughout the text is given in Appendix 1. Appendix 2 deals with biological controls and companion planting. Appendix 3 includes wild edible plants, poisonous plants, medicinal plants, hallucinogenic plants, spices, tropical fruits, and natural dye plants.

Appendix 4 gives horticultural information on house plants, along with brief discussions on how to cultivate vegetables. Nutritional values of the vegetables are included. Appendix 5 covers metric equivalents and conversion tables. Do you like this book? Please share with your friends, let's read it!! Search Ebook here:.