Botany The Nature of Life

Transcription

1 Botany The Nature of Life I. Attributes of Living Organisms A. It would seem a simple thing to define life, but it actually isn t. Many of the characteristics of life can be found in nonliving things. 1. It is easier to describe the characteristics of life. B. Composition and Structure 1. The of life. An ascending order of complexity: a. organize to become b.. Tissues are classified as simple or complex. Tissues organize to become organs. 1) Simple plant tissues have only one cell type. 2) Complex plant tissues have 2 or more cell types c. - Roots, stems, leaves, and flowers d. Organism C. changes in size and shape a plant undergoes from origin to adult 1. Growth usually results from the production of new cells. 2. Cell lineages differentiate and become adult tissues. 3. Growth is influenced both by genetics and the environment D. - Organisms produce offspring, which resemble the parents 1. Reproduction can occur sexually or asexually E. 1. Plants respond to wounds, light, temperature, gravity, etc. 2. Plants move, but often so slowly that it is only visible using time lapse photography. a. Cytoplasm streams within the cell (cyclosis) 3. Plants adapt to their environment a. Often, this takes natural selection acting upon generations of plants. 4. Plants release perfume & secrete nectar to entice pollinators F. the tendency of an organism or a cell to regulate its internal conditions, usually by a system of feedback controls, despite outside changing conditions. G. all of the biochemical reactions taking place in an organism. In plants, we will specifically focus on photosynthesis and respiration. 1. using the energy of sunlight to convert carbon dioxide (CO2) and water (H2O) into carbohydrates (C6H12O6) and oxygen (O2) 2. releasing the energy of carbohydrate (C6H12O6) bonds to produce carbon dioxide (CO2) and water (H2O). This energy is caught and used to form ATP (the energy currency of cells). H. Complexity of Organization 1. Living organisms are made up of far more complex molecules than nonliving matter. 2. These complex molecules are called and include

2 a. which are chains of simple sugars b., which include triglycerides and cholesterol c., which in turn are made up of chains of amino acids d. which include DNA and RNA II. Chemical Basis of Life A. The Elements units of 1. Matter occupies space, has mass, and is composed of elements. 2. Matter exists in 4 states: solid, liquid, gas, and plasma B. The : Smallest stable subdivision of an element 1. Atoms have a where you find the and neutrons. a. Each proton has a positive charge. 2. Circling around the nucleus are. a. Each electron has a negative charge. b. The electrons occupy electron (or valence) shells. c. The shells can only hold a specific number of electrons. 3. Atoms and molecules try to be as electrically stable as possible. Two ways they can achieve this stability include a. Remaining electrically neutral (i.e. the number of electrons must equal the number of protrons). Any atom or molecule with a charge is an ion. 1) If an atom or molecule has more electrons than protons, it will become negative. a) This is an anion. Important anions in biology are chlorine (Cl - ) and bicarbonate (HCO3 - ). 2) If an atom or molecule has more protons than electrons, it will become positive. a) This is a cation. Important cations in biology are potassium (K + ), sodium (Na + ), and calcium (Ca ++ ). b. Filling their outermost electron shells (known as ). C. Elements can combine to form molecules through chemical bonds.

3 1. There are 3 types of chemical bonds: a. bonds A bond in which one atom loses an electron to form a positive ion and the other atom gains an electron to form a negative ion. (An example is table salt, Na + Cl - ) b. bonds - a chemical bond that involves sharing a pair of electrons between atoms in a molecule. (An example is the phosphoanhydride bonds in ATP which store potential energy.) c. bonds A hydrogen atom of one molecule is attracted to an electronegative atom (especially a nitrogen, oxygen, or fluorine atom) of another molecule. (An example is the hydrogen bonds holding complementary base pairs together in DNA.) 2. Let us consider the water molecule, a covalently bonded molecule. a. The chemical formula of water H2O. It is made of 2 atoms of hydrogen and 1 atom of oxygen. b. The atomic number of hydrogen is 1. That means that it has 1 proton in its nucleus and 1 electron in its electron shell. 1) To fill that electron shell, it would have to gain an electron. 2) That would make it less stable because it would have a -1 charge. c. The atomic number of oxygen is 8. Oxygen has 8 protons in its nucleus. It has 2 electrons in its innermost electron shell and 6 electrons in the next electron shell. 1) To fill its outermost electron shell, it would have to gain 2 electrons. 2) That would give it a -2 charge, which is less stable. 3. Water molecules are formed by covalent bonds. Two hydrogens and one oxygen share their electrons. a. This allows the atoms to have their outermost shells filled at least part of the time, increasing stability.

4 b. By sharing their electrons, they avoid gaining negative charges. 4. Water is a molecule. a. Oxygen has a +8 charge in its nucleus. The two hydrogen atoms have only a +1 charge in their nuclei. b. Because Oxygen has a greater positive charge, it attracts the electrons more strongly. 1) Think about a big kid on a playground by the swings. The big kid will get to swing more often and longer. a. Thus, oxygen develops a charge (δ - ). b. The hydrogen develops a charge (δ + ). 5. Because it is both partially positive and partially negative, it is attracted to & dissolves anything that has a charge. a. Water is referred to as the. Table Salt Dissolving in Water 6. Water molecules are also attracted to each other, forming hydrogen bonds, resulting in surface tension and capillarity. Hydrogen bonding between water molecules. a. is a property of water (resulting from the attraction water molecules have for each other) that causes its surface to behave like a thin, elastic film. Thus the surface can support light objects. b. - The movement of water along the surface of a solid caused by the attraction of water molecules to the molecules of the solid. This help explains why water moves up xylem in plants.

5 7. As a general rule, wherever a charged particle is or goes, water is bound to follow. D. Acids, Bases, Buffers, and Salts 4. The concentration of ions is commonly expressed in terms of the ph scale. d. The ph scale is measured from 0 to 14. 1) Pure water ph = 7 (neutral) 2) Anything with a ph below 7 is acidic 3) Anything with a ph above 7 is alkaline (basic) e. The ph scale is a negative logarithmic scale with a base number of ten. 1) Thus, a solution with a ph of 2 is 10 times more acidic than a solution with ph of release hydrogen (H + ) ions when dissolved in water 6. - release negatively charged hydroxyl (OH - ) ions when dissolved in water 7. - Substances that enable solutions to resist ph changes when an acid or base is added. d. Buffers are very important in helping organisms maintain a relatively constant ph. 8. Salts usually crystalline solid compounds that formed, or can be regarded to have formed, from an acid and a base by replacement of one or more hydrogen atoms in the acid molecules by positive ions from the base d. e.g. Table salt, Na + Cl - III. Physical Basis of Life A. the ability to do work B. - energy is constant in a closed system; it cannot be increased or diminished, but it can be converted from one form to another 1. Energy has different forms chemical, electrical, heat, and light C. - when energy is converted from one form to another form, the amount of useful energy remaining is always less than before. Entropy (randomness) increases. 1. energy in motion 2. stored energy (like a battery)

6 a. e.g. Cells release the energy stored in the bonds of sugar during respiration D. Energy in the electron 1. Electrons with the least potential energy are located within the single spherical orbital (valence shell) closest to the atom s nucleus. 2. Electrons with the most potential energy are in the outermost orbital. 3. Why neon signs work - Electrons get excited and jump to the next valence shell. As they return to their original valence shell, they release light energy. 4. Plant and animal cells utilize this as they make ATP (the energy currency of the cell) by moving electrons down a transport chain during cellular respiration. 5. Plant cells also utilize this by using light energy to excite photosynthetic pigment electrons of chlorophyll. They harvest energy from these electrons to produce sugars during photosynthesis. a. We will revisit respiration and photosynthesis later in this course. IV. Living organisms are made up of far more complex molecules than nonliving matter A. (macromolecules) are formed when 2 or more small monomers bond together. 1. Bonding between monomers occurs by dehydration synthesis and is controlled by enzymes. a. Dehydration synthesis removal of water in the formation of a bond 1) e.g. Amino acids joining to become a polypeptide (protein). 2) e.g. Monosaccharides joining to form a polysaccharide (starch). 2. Bonds between monomers are broken by hydrolysis a. Hydrolysis occurs when a hydrogen becomes attached to one monomer and a hydroxyl group to the other. 1) e.g. Table salt dissolving in water 2) e.g. ATP ADP + Pi b. Energy is released 3. Polymers include carbohydrates, lipids, proteins, and nucleic acids. B. the most abundant organic compounds in nature. Cellulose is the single most abundant organic compound on earth. 1. Molecules composed of C, H, and O in a ratio of [CH2O]n or 1:2:1 a. e.g. Glucose is C6H12O6. Deoxyribose is C5H10O5. b. Sugars end with the.

7 2. There are 3 basic kinds of carbohydrates: monosaccharides, disaccharides, and polysaccharides. 3. simple sugars with backbones of 3 to 7 carbon atoms a. e.g. Glucose and fructose 4. formed when two monosaccharides bond together by dehydration synthesis. a. e.g. Sucrose (table sugar) = glucose + fructose; maltose (malt sugar - building block of starch) = glucose + glucose; lactose (milk sugar) = glucose + galactose 5. formed when several to many monosaccharides bond together. a. Can be in long branched or unbranched chains or in coils of monosaccharides. 1) coils of glucose molecules. The main carbohydrate reserve of plants. a) In animals & fungi, glycogen is formed instead of starch. 2) unbranched chain of glucose molecules. a) Main structural polymer in plant cell walls b) Up to of plants may be bound up in cellulose c) Animals can t digest cellulose i. This often causes animals to rely upon bacteria to supplement their digestive efforts. C. - fatty or oily substances that are insoluble in water 1. Typically store as carbohydrates

8 a. Important as long term energy reserves and as structural components of cells. e.g. 2. Contain carbon, hydrogen, and oxygen, but have proportionately less oxygen than carbohydrates 3. Fats and oils are produced from one molecule of glycerol & 3 fatty acid molecules. a. Most fatty acids consist of a chain with 16 to 18 carbon atoms. 1) Saturated fats - with hydrogen atoms attached to every available bonding site on carbons of fatty acid, and with no double bonds ( at room temperature) 2) Unsaturated fats - with fewer hydrogen atoms and with at least one double bond between carbon atoms ( at room temperature) 4. lipids consisting of long-chain fatty acids bonded to a long chain alcohol (instead of glycerol) a. Found on the surfaces of leaves and stems; reduces water loss 5. constructed like fats, but one of the fatty acids is usually replaced by a phosphate group a. Important components of plasma membranes & other cellular membranes D. Proteins, polypeptiedes, and amino acids 1. Proteins regulate chemical reactions in cells.

9 2. are long chains of. a. The amino acids are joined by. Hence, proteins are also referred to as polypeptides. b. Each amino acid is composed of: 1) Amino group (-NH2) 2) Carboxyl group (-COOH) 3) R group - can vary from one hydrogen to a complex ring a) R groups are distinctive for each of the 20 amino acids found in living cells. 3. Proteins have complex structures. a. Primary Structure - Sequence of amino acids fastened together by peptide bonds b. Secondary Structure - Formation of an alpha helix or of pleated sheets due to hydrogen bonding between amino acids c. Tertiary Structure - Further coiling or folding maintained by interactions among R groups (3 dimensional shape) d. Quaternary Structure - Association of more than one polypeptide to form a single functional protein 4. Storage Proteins Some plants store proteins in addition to large amounts of carbohydrates a. e.g. Potato tubers & onion bulbs b. Seeds usually contain proportionately larger amounts of proteins. 1) A seed s proteins get used during germination and seedling development. 2) Seeds are important sources of nutrition for humans and animals. 5. mostly large, complex proteins that function as biological under specific conditions. (A special type of RNA can also function as an enzyme.) a. Enzymes do the following: 1) Break bonds and allow new bonds to form, facilitating chemical reactions 2) Speed up reaction times (similar to stirring or heating sugar to get it to dissolve faster in tea.) 3) Lower the energy of activation (the minimal amount of energy needed to cause molecules to react with one another) b. Enzymes temporarily bond with a substrate.

10 1) Substrates fit into the active sites of enzymes. a) The reaction occurs rapidly & products are released c. Enzymes remain unchanged in the reaction & usually go on to catalyze further reactions. d. Enzyme names, e.g., maltase, lactase E. very large, complex polymers that are vital to internal cellular communication and cell functioning. 1. There are two types: a. DNA deoxyribonucleic acid b. RNA ribonucleic acid 2. DNA consists of a double helix of repeating subunits of nucleotides. a. are composed of a nitrogenous base, a fivecarbon sugar and a phosphate. 3. Nucleotides include one of 4 different nitrogenous bases. The bases pair with hydrogen bonds. a. always pairs with. b. always pairs with. 4. DNA forms a double helix.

11 5. DNA contains that code the information that determines the form and structure of an organism. a. DNA can be passed on from generation to generation without change. 6. RNA occurs as a single strand and is involved in protein synthesis. a. The sugar is ribose (as opposed to deoxyribose in DNA) b. The nitrogenous base Uracil replaces the Thymine found in DNA