General Botany Laboratory Notes
General Botany Laboratory Notes
Chemistry Basics
Basic Chemical Principles
Matter
Definition: Anything that occupies space and has mass.
Atom
Definition: The smallest portion of an element that can enter into a chemical reaction.
Element
Definition: The most basic of substances; there are approximately 92 naturally occurring elements. Matter is comprised of one or more elements.
Ion
Definition: Charged atom.
Types:
Cation: Positively charged ion.
Anion: Negatively charged ion.
Monatomic Ions: Contain only one atom.
Polyatomic Ion
Definition: Naturally occurring ions containing two or more atoms (common in specific forms in nature).
Importance: Many serve as nutrient sources for plants and are absorbed from the soil.
Compound
Definition: Two or more elements combined with ionic or covalent bonds; a pure substance with invariant composition that can be decomposed into elements or other compounds via chemical change.
Molecule
Definition: The smallest portion of a compound; it consists of two or more atoms bonded together, either of the same or different elements.
Ionic Bond
Definition: A bond where electrons are transferred from one atom to another, forming ions that are held together by the attraction of opposite charges. The electron donor becomes positively charged while the acceptor becomes negatively charged.
Covalent Bond
Definition: A bond formed by the sharing of one or more pairs of electrons between two atoms.
Types:
Polar Covalent Bond: Electrons are not shared equally due to differing electronegativities between the atoms.
Coordinate Covalent Bond: One atom contributes both shared electrons.
Example: In CO, two covalent bonds are standard, while one bond is coordinate where oxygen donates both electrons.
Cohesion
Definition: The attraction of like substances to one another.
Example: Hydrogen bonding between water molecules.
Adhesion
Definition: The attraction of unlike substances to one another.
Example: Hydrogen bonding between water and cellulose molecules.
Water Structure and Chemistry
Water (HOH, H$_2$O)
Constitutes over 50% of all living matter; accounts for over 90% of the weight in most plant tissues.
Characteristics: Universal solvent, dissolves many substances.
Chemical property: Hydrogen bonding, vital for unique chemical and physical properties of water.
Polarity and Hydrogen Bonding
Polar Molecule: Water has a partially positive end (hydrogens) and a partially negative end (oxygen).
Importance of polarity:
Key reason for the formation of hydrogen bonds among water molecules.
Composition: Contains two hydrogen atoms and one oxygen atom; both elements can engage in hydrogen bonding.
Electronegativity
Definition: The tendency of an atom to attract electrons in a bond.
Factors Affecting Electronegativity:
Positive charge in nucleus.
Distance of valence electrons from nucleus.
Amount of electron shielding.
Comparison: Hydrogen has low electron affinity, while oxygen and nitrogen have high electronegativities.
Structure of Water
Water is dipolar: Hydrogen has partial positive charges; oxygen has a partial negative charge.
Bond angle: Hydrogens form an angle of 104.5° with oxygen.
Non-bonding pairs of electrons create a tetrahedral arrangement around the oxygen.
Hydrogen bonding results in water's liquid state at room temperature and a lower density of ice.
Solubility in Water
Polar Solutes: Dissolvable in water due to favorable interactions replacing water-water interactions with water-solute interactions (electrostatic, hydrogen bonds).
Examples: CH$3$OH, NH$4^+$, Ca$^{2+}$, H$2$PO$4^-$, H$_3$O$^+$.
Nonpolar Molecules: Poorly soluble in water (e.g., CO$2$, CH$4$, C$2$H$6$, benzene).
Reason for poor solubility: Minimize unfavorable water-water interactions by clustering together.
Noncovalent Interactions:
Hydrogen Bonding: Electrostatic attraction.
Ionic Interactions: Electrostatic interactions between charged groups.
Hydrophobic Interactions: Nonpolar group attractive interactions.
Van der Waals Forces: Attractive forces between closely positioned molecules.
Importance of Hydrogen Bonds
Hydrogen bonds are longer (0.26–0.31nm) than covalent bonds.
Required for stability and integrity of biological macromolecules.
Carbon Chemistry
Basic Carbon Chemistry
Carbon: Vital for life, making up the structure of most biomolecules in living organisms.
Valence: Carbon has a valence of +4 due to four unpaired outer electrons, requiring four covalent bonds for stability.
Additional Characteristics:
Capable of forming double and triple bonds and various structures (chains, branches, rings).
Functional Groups
Definition: Chemically active portions that greatly influence the properties of biomolecules containing carbon.
Elements included: O (Oxygen), N (Nitrogen), P (Phosphorous), S (Sulfur).
Functional groups enhance polarity and solubility of molecules in water.
Cell Chemical Composition
Types of cellular chemicals:
Water.
Inorganic chemicals (ions, elements, compounds).
Organic molecules (biomolecules).
Four Major Classes of Biomolecules:
A. Carbohydrates: Sugars.
B. Lipids: Fats, oils, waxes.
C. Proteins: Polymers of amino acids.
D. Nucleic Acids: Polymers of nucleotides (DNA and RNA).
Organic vs. Inorganic Compounds
Organic Molecule: Contains carbon and other elemental species. Examples: CH$4$, C$2$H$5$OH, C$6$H${12}$O$6$, CH$_3$OH.
Inorganic Compound: Lacks carbon. Examples: H$2$PO$4^-$, HPO$4^{2-}$, CaCl$2$, HCl, HF, HNO$3$, H$2$SO$4$, H$2$O, O$_2$.
Carbohydrates
Monosaccharides: Simple sugars, usually with 3 to 7 carbons (e.g., glucose, fructose).
Disaccharides: Two monosaccharides covalently bonded.
Examples:
Sucrose: Most commonly transported sugar in plants; consists of one molecule of alpha D glucose and beta D fructose.
Maltose: Principal product of starch degradation; consists of two alpha D glucose units.
Polysaccharides: Three or more monosaccharides linked together.
Examples:
Starch: Consists of amylose (unbranched) and amylopectin (branched), significant energy storage in plants.
Cellulose: Polymer of beta–1,4–glucose, major component of cell walls.
Hemicellulose: Heterogeneous polymers, significant in cell wall composition.
Pectins: Gelatinous polymers, structural component of cell walls.
Fructans: Polymers of fructose with sucrose, storage polysaccharides in grasses.
Lipids
Definition: Nonpolar (hydrophobic) molecules, used mainly for energy storage and as membrane components.
Classes of Lipids:
Fats, waxes, oils, steroids.
Importance of structure: Determined by alkyl lengths, double bonds, and functional groups.
Phospholipids: Amphipathic molecules essential for lipid bilayer formation in membranes.
Specific Lipids in Plants:
Cutin: Component of epidermal cell walls.
Suberin: Found in cork cells, provides similar function as cutin.
Proteins
Definition: Polypeptides made of amino acids linked by peptide bonds, formed from condensation reactions between amino and carboxyl terminals.
Composition: Composed of 20 naturally occurring amino acids.
Synthesis: Via translation from mRNA using ribosomes; tRNA transports amino acids.
Nucleic Acids
DNA (Deoxyribonucleic Acid): Encodes genes in nucleotide sequences.
Structure: Double-stranded, twisted arrangement; forms a double helix with complementary base pairing (A-T and C-G bonds).
RNA (Ribonucleic Acid): Generally single-stranded, replaces thymine with uracil.
Functions: DNA contains genes; RNA translates genetic information into proteins via transcription and translation.
External Plant Anatomy
Vascular Plant Structures: Stems produce lateral organs from nodes via the apical meristem in repeating arrangements known as phytomeres (leaf, node, internode, axillary bud).
Phyllotaxy
Arrangement of leaves and axillary buds.
Types of leaves:
Simple Leaf: Single unit blade; may be unlobed, palmately, or pinnately lobed.
Compound Leaf: Blade dissected into leaflets; may be palmately or pinnately compound, and can be further categorized.
Important Plant Terms
Abaxial: Lower leaf surface.
Adaxial: Upper leaf surface.
Node: Stem portion where lateral structures are produced.
Internode: Stem portion between nodes.
Petiole: Leaf stalk; absent in sessile leaves.
Petiole/petiolule: Structures supporting leaflets or leaf stalks.
Tendril/Thorn: Modified stems/leaves aiding climbing or defense.
Vines: Plant structures adapted for climbing, utilizing various methods (twining, tendrils, etc.) to reach sunlight.
Genetics and Polyploidy
Essential Terms
Gene: Basic unit of heredity; a sequence of DNA that encodes a polypeptide.
Chromosome: Structure carrying genes, made of DNA and histones.
Allele: Different forms of the same gene.
Phenotype: Visible or measurable expression of a genotype, influenced by the environment.
Genotype: Complete genetic makeup of an organism.
Homozygous: Identical alleles for a gene.
Heterozygous: Different alleles for a gene.
Genetic Concepts
Polyploidy: Variation from the duplication or addition of chromosome sets; important for plant evolution (e.g., 35-70% of land plants).
Types of Polyploidy:
Euploidy: True polyploidy with whole-genome alterations.
Aneuploidy: Variations where the number of chromosomes is altered without duplication of whole sets.
Forms of Polyploids
Autopolyploids: Genome doubling within a single species.
Allopolyploids: Polyploids with genomes from different species after hybridization.
Intermediate Types: Mixoploid chimeras formed through somatic mutations during mitosis.
Endopolyploidy or somatic polyploidy
A condition where certain tissues or cells within an organism undergo polyploidy while others remain diploid, often seen in plants for growth and development.
Generative polyploidy
Uses unreduced gametes to increase genetic diversity and contribute to the formation of new species through hybridization.
Two principal categories of euploids:
autopolyploidy or autoploidy: is an in-house doubling of the number of chromosomes (Fig)
allopolyploidy or alloploidy: a polyploid that possesses genomes from two or more species
homologous- when two genomes are extremely similar and can often undergo hybridization, resulting in fertile offspring that can reproduce successfully.
General Chemistry
Introduction to Cellular Respiration
Cellular respiration is a vital biological process that converts high-energy carbon compounds into usable energy, primarily in the form of ATP. This section serves as a foundation for understanding the fundamental concepts related to this process, linking it to previous discussions on carbohydrates and photosynthesis.
Overview of Cellular Respiration
Macromolecules Discussed
This section transitions from carbohydrates to lipids, emphasizing their roles in cellular respiration.
Notes on carbohydrates are available on page six, highlighting important diagrams and key information on monosaccharides, disaccharides, and polysaccharides.
Objective
To establish a foundational understanding of cellular respiration, which will be revisited in upper-division courses such as cell biology and physiology.
Key Points about Cellular Respiration
Energy Source
The energy for cellular respiration originates from sunlight, captured in the form of high-energy carbon compounds during photosynthesis (e.g., sucrose, glucose).Oxidation of Compounds
These energy-rich compounds undergo oxidation, releasing energy that is ultimately converted into ATP.Diversity of Substrates
While carbohydrates are predominantly oxidized, lipids and proteins can also serve as energy sources after conversion to simpler forms (e.g., acetyl-CoA).Aerobic and Anaerobic Respiration
This discussion focuses primarily on aerobic respiration, emphasizing the use of oxygen as the terminal electron acceptor in the process.
General Equation for Cellular Respiration
The overall reaction of cellular respiration can be represented as:
Stages of Cellular Respiration
Glycolysis
Occurs in the cytosol, breaking down glucose or fructose bisphosphate into two molecules of pyruvate, yielding a net gain of 2 ATP and 2 NADH.
Oxidative Pentose Phosphate Cycle
This alternative pathway contributes to 10-25% of sugar oxidation, occurring in the cytosol or chloroplast, producing NADPH and ribulose-5-phosphate.
Krebs Cycle (Citric Acid Cycle)
Following glycolysis, pyruvate enters the mitochondria, undergoing oxidative decarboxylation to form acetyl-CoA and subsequently entering the Krebs cycle, producing ATP, CO₂, NADH, and FADH₂.
Oxidative Electron Transport Chain
Involves the transfer of electrons through protein complexes in the mitochondria, generating a hydrogen ion gradient used for ATP synthesis via oxidative phosphorylation.
Glycolysis: Detailed Steps
Process: Glycolysis initiates with the phosphorylation of fructose bisphosphate (a six-carbon sugar), resulting in the production of two three-carbon sugars (3-PGA and DHAP).
Output: Produces four ATP but nets two or three ATP due to phosphorylation requirements.
Fate of Pyruvate: In aerobic conditions, pyruvate enters the mitochondria for further oxidation; in anaerobic conditions, it can be converted to lactate or ethanol.
Oxidative Pentose Phosphate Pathway
Function: Converts glucose-6-phosphate to form NADPH and ribulose-5-phosphate, integrating with glycolysis and contributing to various biosynthetic pathways.
Utility of Products: NADPH generated here is crucial for biosynthesis, particularly during periods of darkness when photosynthesis does not occur.
Krebs Cycle Overview
Begins with the conversion of pyruvate to acetyl-CoA, leading into the Krebs cycle.
Key Outputs of the Krebs cycle for each acetyl-CoA:
2 CO₂ molecules
1 ATP (or equivalent GTP)
3 NADH
1 FADH₂
The cycle regenerates oxaloacetate, illustrating its continuous nature.
Structural Features and Functions of Lipids
Lipids include fats, oils, and waxes, displaying great diversity in chemical structures and functions. The commonality among lipids is their hydrophobic or non-polar nature.
Functions of Lipids:
Energy Storage
Lipids are more efficient for energy storage than carbohydrates due to their higher energy density.
Structural
Form critical components of cellular membranes.
Biosynthetic Precursors
Serve as building blocks for hormones and signaling molecules.
Lipid Structure: Triacylglycerides and Phospholipids
Triacylglycerides: Comprised of glycerol and three fatty acid side chains, formed through condensation reactions, leading to the creation of ester bonds.
Phospholipids: Have a similar structure but consist of two fatty acids and a phosphate group attached to glycerol, allowing them to form bilateral membranes due to their amphipathic nature.
External Plant Anatomy
The upcoming lab involves the external anatomy of plants, divided into two components:
Definitions and Concepts
Focused on the external anatomy of the sporophyte plant body.Practical Application
An outdoor activity where students observe actual plants and assess characteristics like phyllotaxy, leaf complexity, and armed appendages.In this study guide, we will walk through the practical component using slides of real plant examples instead of conducting live observations in the field.
Focus: Tracheophytes and Seed Plants
Target Group:
We will concentrate on tracheophytes (vascular plants), particularly seed plants (gymnosperms and angiosperms).Sporophyte Phase:
Discussion will primarily address the sporophyte phase of these plants, while root anatomy will not be extensively covered at this time, as the root apical meristem does not produce lateral organs. Instead, we will focus on external shoot anatomy, which includes leaves and stems that generate lateral organs.
Key Terminology and Concepts in External Plant Anatomy
Important terms related to plant anatomy are outlined in the notes, found primarily on page 11. Key concepts include:
Phyllotaxy: Arrangement of leaves and axillary buds on a stem.
Node: Point on the stem where leaves and buds are attached.
Internode: Segment of stem between nodes.
Lamina: Flat part of a leaf.
Axillary Bud: Bud located in the axil of a leaf that can develop into a new shoot.
Overview of Vines
Vines utilize specialized structures for climbing, which can be classified into several mechanisms:
Twining: Stems coil around substrates for support (e.g., kudzu, morning glories).
Tendrils: Modified stems or leaves that wrap around objects (e.g., Virginia creeper).
Adventitious Roots: Roots that arise from stems and assist in climbing (e.g., English ivy).
Clamoring: Stems that lean against surfaces for support without holdfasts (e.g., trumpet vine).
Types of Phyllotaxy
Alternate: One leaf and one axillary bud per node.
Opposite: Two leaves and two axillary buds per node.
Verticillate (Whorled): Three or more leaves per node.
Leaf Anatomy
Leaves can be classified as:
Simple: Single unit blade; may have various margins (entire, toothed, lobed).
Compound: Divided into leaflets, including:
Pinnate: Leaflets arranged along a central rachis (mid vein).
Palmatifid: Leaflets arise from a common point on the leaf stalk.
Decompound: More than one level of compound leaf structure.
Armed Appendages
Prickles, Spines, and Thorns:
These structures provide defense mechanisms against herbivores:
Prickles: Sharp outgrowths from the epidermis or underlying cell layers (e.g., rose bushes).
Spines: Modified leaves providing defense (e.g., holly plants).
Thorns: Modified stems that deter large herbivores (e.g., honey locust trees).
Conclusions
This section introduces key concepts and terminology concerning plant structure, focusing on vascular plants. Practical applications will include studying real examples through slides, enhancing our understanding of these concepts in various plant taxa.
Understanding these structures and their functions provides foundational insight into plant biology and ecological interactions, including the mechanisms of herbivory defense and resource allocation.
Mitosis
The upcoming lab will cover the process of mitosis, a crucial aspect of the eukaryotic cell cycle. This session is structured to ensure a clear understanding of the mitotic process using diagrams and schematics.
Structure of the Lab
Conceptual Understanding
This lab will break down the steps of mitosis from the ground up and provide a thorough explanation of the process.
Comparative Analysis
Mitosis will be discussed alongside meiosis in the following lab.
Key Concepts
Cell Theory
Cells arise from preexisting cells. Mitosis and meiosis are the processes through which new cells are produced in eukaryotes.
Importance of Mitosis
Growth and repair of damaged or wounded tissues in plants.
Asexual (clonal) reproduction in some plant species.
Mitosis is an equational division process, resulting in daughter cells that are genetically identical to the parent cell.
Cellular Information
Representative Cell
The cell used will have a simple chromosome number (four chromosomes) for ease of understanding.
Genomic Formula
N: Number of chromosomes.
x: Number of homologous chromosomes per set.
Nuclear Composition
Focused on nuclear DNA, excluding plastid or mitochondrial DNA.
Stages of Mitosis
Interphase: The longest phase where the cell prepares for division.
G1 Phase: Cell prepares for DNA replication, increasing metabolic activity, enzyme function, and gene expression.
S Phase: DNA replication occurs, resulting in sister chromatids.
G2 Phase: Further preparation for mitosis, including the formation of the pre-prophase band in plants.
Prophase: Chromosomes condense, and the nuclear membrane begins to dissolve.
Metaphase: Chromosomes align in the center of the cell along the metaphase plate. Kinetochore microtubules form connections to chromatids.
Anaphase: Sister chromatids separate and are pulled toward opposing poles of the cell.
Telophase: Two nuclei form as the chromosomes de-condense. The nuclear membrane reappears.
Cytokinesis: The cytoplasm divides, resulting in two separate daughter cells.
Cytokinesis in Plants
Cytokinesis in plant cells involves building a cell plate that will develop into the new cell wall between the daughter cells. The fragment zone plays a critical role in guiding this phase by helping position the nucleus properly for division.
Observational Studies
Allium Root Tip: The lab will examine the stages of mitosis in the cells of an Allium root tip where preserved cells demonstrate the different phases of mitosis:
Interphase: Mostly visible with no condensed chromosomes.
Prophase: Visible condensed chromosomes.
Metaphase: Chromatids aligned at the metaphase plate.
Anaphase: Sister chromatids moving towards poles.
Telophase: Cells with two nuclei starting to reform their membranes.
Conclusion
This lab aims to provide a comprehensive understanding of the mitotic process, solidifying the connection between cellular structure and function while distinguishing it from meiosis in preparations for subsequent studies of cell division and genetic variation. The series of drawings and diagrams will facilitate visualization of these concepts, aiding in retention and understanding of the subsequent lab activities on meiosis and cell cycling.
Meiosis
In this lab, we will focus on meiosis, a fundamental process in the eukaryotic cell cycle. This session is designed to guide you through the stages of meiosis, demonstrating its significance compared to mitosis, especially in the context of sexual reproduction.
Structure of the Lab
Conceptual Foundation
The lab will provide a detailed understanding of meiosis, similar to the previous discussions on mitosis.
Comparative Analysis
We will revisit the process of mitosis in the next lab to highlight the differences and similarities between the two cell division processes.
Key Concepts
Importance of Meiosis
Meiosis is essential for sexual reproduction, producing gametes (sperm and eggs in animals and spores in plants).
Most cell division in plants is accomplished via mitosis, but meiosis specifically enables genetic diversity through the production of sex cells.
Advantages of Asexual vs. Sexual Reproduction
Asexual reproduction produces genetically identical offspring rapidly, while sexual reproduction promotes genetic variation, which is crucial for adaptation and survival in changing environments.
In sexual reproduction, genetic diversity helps plants adapt to environmental stressors and selection pressures.
Meiosis Overview
Definition
Meiosis is a reductive division process, resulting in cells with half the number of chromosomes as the parent cell.
Chromosome Number Reduction
The original cell undergoes two rounds of division—meiosis I (reductive division) and meiosis II (equational division)—resulting in four haploid cells from one diploid precursor.
The genomic formula for meiosis includes the number of chromosomes (N) and the number of homologous pairs (X).
Stages of Meiosis
Interphase
The cell prepares for division by engaging in metabolic activity and replicating its DNA, producing sister chromatids.
Meiosis I (Reduction Division)
Prophase I: Chromosomes condense, and homologous chromosomes pair via synapsis, including crossing over and forming structures called chiasmata.
Metaphase I: Homologous chromosomes align at the metaphase plate in a random orientation, demonstrating independent assortment.
Anaphase I: Homologous chromosomes are separated, with each chromosome set moving to opposite poles (disjunction).
Telophase I: Two new nuclei form, cytokinesis can vary (full separation or remaining as a syncytium).
Meiosis II (Equational Division)
Prophase II: Chromosomes re-condense, and nuclear membranes break down again.
Metaphase II: Sister chromatids align on the metaphase plate (similar to mitosis).
Anaphase II: Sister chromatids are pulled apart toward opposite poles.
Telophase II: Nuclear membranes reform around each set of chromosomes, leading to the final separation into four haploid cells.
Key Outcomes of Meiosis
Four Haploid Spores: At the end of meiosis, each spore can develop into a gametophyte that produces gametes for sexual reproduction (sperm and eggs in animals, spores in plants).
Genetic Variation: Due to processes like crossing over and independent assortment, meiosis contributes to genetic diversity among offspring.
Conclusion
This lab aims to provide a comprehensive understanding of meiosis, establishing a clear distinction from mitosis and emphasizing its role in sexual reproduction and genetic diversity. The diagrams and interactive elements will help facilitate visualization of the meiotic process, aiding retention for upcoming examinations. Each step prepares for further in-depth discussion on plant reproductive strategies and genetic inheritance.