Plant Biology and Photosynthesis Flashcards

Plant Cellular Anatomy and Cell Wall Structure

• Cellular Components and Organelles:

  • Cell: The fundamental structural and functional unit of plant life.

  • Cell Membrane: The selectively permeable phospholipid bilayer surrounding the cytoplasm.

  • Mitochondrion: Organelle responsible for cellular respiration and ATP generation.

  • Vacuole: Membrane-bound organelle involved in storage, waste breakdown, and maintaining turgor pressure.

  • Plasmodesmata: Microscopic channels traversing the cell walls of plant cells, enabling transport and communication between individual cells.

  • Plastid: A class of membrane-bound organelles found in photosynthetic organisms, involved in synthesis and storage of food.

    • Chloroplast: Specialized plastid containing chlorophyll, serving as the site of photosynthesis.

    • Chromoplast: Specialized plastid containing pigments other than chlorophyll (e.g., carotenoids), responsible for yellow, orange, or red colors in plant tissues.

    • Amyloplast: Non-pigmented plastid responsible for the synthesis and storage of starch granules.

  • Nucleus: Membrane-enclosed organelle containing the cell's genetic material (DNA).

• Cell Wall Architecture:

  • Primary Cell Wall: The outer layer deposited during cell growth, composed of cellulose, hemicellulose, and pectin.

  • Secondary Cell Wall: A rigid, thick layer deposited inside the primary cell wall after the cell has stopped growing, often reinforced with specialized polymers.

  • Pit Field: A localized thin area in the primary cell wall through which plasmodesmata typically pass.

  • Pit: A depression or opening in the secondary cell wall where the primary cell wall remains exposed, facilitating fluid movement between adjacent vascular cells.

  • Suberin: A hydrophobic, waxy polymer deposited in cell walls (e.g., endodermis, cork) that acts as a barrier to water and solute movement.

  • Lignin: A complex, rigid organic polymer deposited in the secondary cell walls of vascular and structural cells, providing mechanical support and waterproofing.

Levels of Plant Organization and Tissue Systems

• Hierarchical Levels of Organization:

  • Tissue: A group of structural and functional cells working together to perform a specific activity.

  • Organ: A structure composed of multiple tissues integrated to perform primary functions (e.g., leaf, stem, root).

  • Organ System: A group of organs working together in an organism (e.g., shoot system, root system).

• Primary Tissue Systems and Meristematic Origins:

  • Dermal Tissue System: Outer protective cell layer originating from the protoderm.

  • Vascular Tissue System: Transport tissue network originating from the procambium.

  • Ground Tissue System: Structural, storage, and photosynthetic tissue originating from the ground meristem.

• Cell Types and Tissues:

  • Simple Tissues: Tissues composed of a single cell type.

    • Parenchyma: Unspecialized, thin-walled, living cells involved in photosynthesis, storage, and tissue repair.

    • Collenchyma: Living cells with unevenly thickened primary cell walls that provide flexible structural support in growing shoot regions.

    • Sclerenchyma: Lignified, thick-walled cells that provide rigid structural support, usually dead at functional maturity.

      • Sclereid: Short, irregularly shaped sclerenchyma cell providing hardness (e.g., in seed coats or fruit pulp).

      • Fiber: Long, slender, elongated sclerenchyma cell arranged in strands providing tensile strength.

  • Complex Tissues: Tissues composed of multiple distinct cell types.

    • Xylem: Vascular tissue adapted for conducting water and dissolved minerals upward from roots.

      • Vessel: A continuous conducting tube formed by stacked vessel elements.

      • Vessel Element: Short, wide xylem cell with perforated end plates for efficient water flow.

      • Tracheid: Long, tapered xylem cell with pitted walls for water conduction and mechanical support.

    • Phloem: Vascular tissue adapted for conducting organic nutrients (sugars) throughout the plant body.

      • Sieve Tube: A continuous transport structure formed by stacked sieve tube elements.

      • Sieve Tube Element: Elongated phloem cell lacking a nucleus at maturity, specialized for translocation.

      • Sieve Plate: Porous end wall between adjacent sieve tube elements facilitating solute flow.

      • Companion Cell: Specialized parenchyma cell connected to a sieve tube element via plasmodesmata, maintaining its metabolic functions.

Plant Shoot, Leaf Anatomy, and Structural Modifications

• Shoot and Stem Morphology:

  • Shoot: Aboveground part of the plant comprising stems, leaves, and buds.

  • Bud: An undeveloped embryonic shoot containing meristematic tissue.

    • Lateral/Axillary Bud: Bud located in the axil of a leaf, capable of forming lateral branches or flowers.

    • Terminal Bud: Bud located at the apex of a stem responsible for primary vertical growth.

  • Stem: Structural axis of the plant supporting leaves, flowers, and fruits.

  • Node: The specific point on a stem where leaves or buds originate.

  • Internode: The region of stem located between two successive nodes.

  • Axil: The upper angle formed between a leaf petiole and the supporting stem axis.

• Leaf External Morphology and Arrangements:

  • Leaf Parts:

    • Blade: Expanded, flattened portion of the leaf adapted for light absorption.

    • Petiole: The stalk attaching the leaf blade to the stem node.

  • Leaf Arrangement (Phyllotaxy):

    • Alternate: A single leaf present per node.

    • Opposite: Two leaves present per node, attached directly across from each other.

    • Whorled: Three or more leaves attached at a single node.

  • Leaf Complexity:

    • Simple Leaf: Leaf featuring an undivided single blade.

    • Compound Leaf: Leaf with a blade divided into distinct leaflets.

      • Pinnately Compound: Leaflets attached along both sides of a central axis (rachis).

      • Palmately Compound: Leaflets radiating outward from a single central point at the apex of the petiole.

  • Leaf Venation Patterns:

    • Pinnate: Major veins branching off sequentially from a single central midrib.

    • Palmate: Several major veins radiating outward from a single point at the base of the leaf.

    • Dichotomous: Veins branching repeatedly in equal pairs.

    • Parallel: Major veins running parallel to each other along the length of the leaf (typical of monocots).

• Internal Leaf Anatomy and Adaptations:

  • Anatomical Layers:

    • Epidermis: Outer protective layer of cells covering both upper and lower leaf surfaces.

    • Mesophyll: Internal photosynthetic ground tissue situated between upper and lower epidermal layers.

      • Palisade Mesophyll: Upper layer of columnar, tightly packed photosynthetic cells optimized for light capture.

      • Spongy Mesophyll: Lower layer of loosely packed, irregularly shaped photosynthetic cells with abundant air spaces for gas exchange.

    • Vascular Bundle (= Vein): Conducting strand containing xylem and phloem, bounded by bundle sheath tissue.

  • Stomatal Complex and Xerophytic Modifications:

    • Stomata: Microscopic pores in the epidermis facilitating gas exchange ($\text{CO}_2$ and $\text{O}_2$) and transpiration.

    • Guard Cells: Pair of specialized epidermal cells surrounding each stoma that regulate opening and closing.

    • Sunken Stomate: Stoma recessed into deep epidermal pits, reducing water loss due to wind and heat.

    • Xerophyte: Plant adapted to survive in extremely dry or arid environments.

    • Cuticle: Waxy hydrophobic layer secreted onto the outer surface of the epidermis to restrict evaporation.

    • Trichome: Hair-like outgrowth on the epidermal surface providing defense, shade, or moisture retention.

• Specialized Plant Modifications:

  • Leaf Modifications:

    • Tendril: Slender, coiling leaf modification used by climbing plants for structural attachment.

    • Spine: Hard, sharp modified leaf providing physical defense against herbivores.

  • Stem Modifications:

    • Thorn: Sharp, woody modified stem arising from an axillary bud for defense.

    • Tuber: Swollen, underground modified stem adapted for nutrient storage and vegetative propagation.

Primary and Secondary Growth, Stem, and Wood Anatomy

• Primary Growth and Stem Organization:

  • Primary Growth: Growth originating from apical meristems that increases the length of shoots and roots.

  • SAM (Shoot Apical Meristem): Meristematic tissue at the shoot tip giving rise to primary stem tissues and leaves.

  • RAM (Root Apical Meristem): Meristematic tissue at the root apex giving rise to primary root tissues.

  • Cotyledon: Seed leaf present in the embryonic plant within a seed.

  • Monocot: Angiosperm characterized by a single cotyledon, parallel leaf venation, and scattered vascular bundle distribution in stem cross section.

  • Eudicot: Angiosperm characterized by two cotyledons, reticulate leaf venation, and vascular bundles arranged in a distinct ring in stem cross section.

  • Cortex: Ground tissue located between the dermal layer and vascular tissue in stems and roots.

  • Pith: Central ground tissue located interior to the ring of vascular bundles in eudicot stems.

• Secondary Growth and Wood Structure:

  • Vascular Cambium: Lateral meristem producing secondary xylem (wood) inwardly and secondary phloem outwardly.

  • Wood: Secondary xylem produced by the vascular cambium over growth seasons.

  • Bark: All tissues present external to the vascular cambium.

    • Inner Bark: Functional secondary phloem responsible for sugar transport.

    • Outer Bark: Protective periderm layers composed of dead cork cells.

  • Wood Zonation:

    • Heartwood: Older, non-conducting inner secondary xylem that accumulates resins and tannins, providing structural support.

    • Sapwood: Functional outer secondary xylem actively transporting water and dissolved minerals.

    • Springwood (Earlywood): Secondary xylem produced early in the growing season characterized by large vessel diameters and thin cell walls.

    • Summerwood (Latewood): Secondary xylem produced later in the growing season characterized by smaller vessel diameters and thick cell walls.

  • Periderm: Secondary dermal tissue replacing the primary epidermis during secondary growth.

    • Cork Cambium (Phellogen): Lateral meristem producing cork tissue outwardly and phelloderm inwardly.

    • Phelloderm: Secondary cortex parenchyma tissue produced inwardly by the cork cambium.

    • Cork Tissue (Phellem): Outer protective tissue composed of dead cells impregnated with suberin.

  • Wood Cutting Sectional Planes:

    • Tangential Section: Cut made perpendicular to the vascular rays along a line tangent to the annual growth rings (plainsawn lumber).

    • Radial Section: Cut made parallel to the vascular rays along a line passing through the longitudinal center of the stem (quartersawn lumber).

  • Wood Grain Features:

    • Vessels: Tubular water-conducting structures present in angiosperm secondary xylem.

    • Vascular Rays: Radial bands of parenchyma cells extending horizontally through secondary xylem and phloem, transporting nutrients and water laterally.

    • Annual Rings: Concentric growth layers in secondary xylem resulting from seasonal variations in springwood and summerwood production.

Root Morphology, Internal Anatomy, and Transport Pathways

• Root Morphological Regions:

  • Root Cap: Protective cellular structure covering the root tip that secretes mucilage and senses gravity.

  • Root Hair: Tubular outgrowth of a root epidermal cell located in the region of maturation, greatly expanding surface area for water absorption.

  • Region of Elongation: Area behind the RAM where newly produced cells elongate rapidly, driving the root tip through soil.

  • Region of Maturation: Area behind the region of elongation where primary tissue differentiation completes and root hairs develop.

• Root Internal Anatomy and Transport Routes:

  • Endodermis: Innermost single layer of cortex cells surrounding the vascular cylinder, acting as a selective filter.

  • Casparian Strip: Ring of suberin-impregnated wall material in endodermal cells blocking apoplastic water transport into the vascular cylinder.

  • Pericycle: Layer of meristematic parenchyma cells interior to the endodermis from which lateral roots originate.

  • Cortex: Extensive ground tissue layer between the root epidermis and endodermis serving as a storage site.

  • Apoplast Route: Pathway of water and solute movement through non-living spaces, including cell walls and intercellular spaces, without crossing plasma membranes.

  • Symplast Route: Pathway of water and solute movement through the living cytoplasm of interconnected cells via plasmodesmata.

Plant Transport Dynamics, Water Potential, and Pressure Flow

• Thermodynamic Principles of Transport:

  • Osmosis: Diffusion of water molecules across a selectively permeable membrane from a region of higher water concentration to lower water concentration ($=\text{higher water potential to lower water potential}$).

  • Chemiosmosis: Diffusion of hydrogen ions ($H^+$) across a membrane down their concentration gradient, moving from a higher $H^+$ concentration to a lower $H^+$ concentration.

  • Acidity: Increases proportionally with higher $H^+$ concentration (lower pH).

• Water Potential Parameters:

  • Water Potential ($\Psi$): Physical property predicting the direction in which water will flow, measured in megapascal ($\text{MPa}$).

  • Components of Water Potential:

    • Solute Potential ($\Psi_s$): Component of water potential proportional to the number of dissolved solute molecules (always zero or negative).

    • Pressure Potential ($\Psi_p$): Physical pressure exerted on a solution (can be positive, zero, or negative).

  • Cell Turgor States:

    • Isotonic: Solute concentration outside the cell equals solute concentration inside the cell; no net water movement.

    • Hypertonic: Higher solute concentration outside the cell, causing net water loss from the cell.

    • Hypotonic: Lower solute concentration outside the cell, causing net water influx into the cell.

    • Turgid: Firm, swollen cell state resulting from high internal hydrostatic pressure in a hypotonic environment.

    • Flaccid: Limp cell state resulting from loss of pressure potential in an isotonic environment.

    • Plasmolysis / Plasmolyzed: Structural collapse where the plasma membrane pulls away from the cell wall due to severe water loss in a hypertonic environment.

• Environmental and Cellular Water Dynamics:

  • Water Potential Gradient: Continuous drop in water potential extending from soil through the root, stem, leaf, and into the atmosphere.

  • Atmospheric Water Potential: Strongly influenced by relative humidity; lower relative humidity results in a significantly lower (more negative) atmospheric water potential, driving transpiration.

  • Water Chemical Properties:

    • Partial Charge: Asymmetric charge distribution in water molecules leading to polarity.

    • Cohesion: Hydrogen bonding attraction between identical water molecules, allowing continuous water columns to be pulled up xylem.

• Guard Cell Opening Mechanics:

  • Potassium Ions ($K^+$): Influx of $K^+$ into guard cells lowers their solute potential ($\Psi_s$), driving osmotic water uptake, increasing turgor pressure, and causing guard cells to bow outward to open the stoma.

• Phloem Translocation Mechanics:

  • Sugar Sources: Organs that produce or release sugar (e.g., mature photosynthesizing leaves, storage roots during spring sprout).

  • Sugar Sinks: Organs that consume or store sugar (e.g., growing root tips, developing fruits, expanding buds).

  • Pressure Flow Model: Mechanism of translocation in phloem:

    1. Active loading of sugar into sieve tube elements at the source lowers solute potential.

    2. Water enters sieve tubes from xylem via osmosis, raising pressure potential ($\Psi_p$).

    3. Sugar is actively unloaded into sink tissue, raising solute potential in the sieve tube.

    4. Water leaves sieve tubes via osmosis, lowering pressure potential.

    5. Bulk flow of sap occurs along the pressure gradient from high pressure at source to low pressure at sink.

  • Aphids: Insects used by researchers to analyze phloem sap composition and pressure flow, as their stylets tap directly into individual sieve tube elements.

Biological Molecules, Chemical Bonding, and Protein Structure

• Polymer and Monomer Foundations:

  • Polymer: Large molecule constructed from repeating smaller subunit molecules.

  • Monomer: Individual building-block unit of a polymer.

• HONCP Valence Bonding Capacities:

  • Hydrogen (H): Forms $1$ covalent bond.

  • Oxygen (O): Forms $2$ covalent bonds.

  • Nitrogen (N): Forms $3$ covalent bonds.

  • Carbon (C): Forms $4$ covalent bonds.

  • Phosphorus (P): Forms $5$ covalent bonds.

• Major Biological Macromolecules:

  • Nucleic Acids:

    • Polymers: DNA and RNA.

    • Monomers: Nucleotides.

    • Nucleotide Types: There are $5$ different nucleotides utilized in standard nucleic acids.

    • Single-letter abbreviations: A (Adenine), T (Thymine), C (Cytosine), G (Guanine), U (Uracil).

  • Polysaccharides:

    • Examples: Cellulose, Starch.

    • Monomers: Glucose monomers.

  • Polypeptides:

    • Monomers: Amino acid monomers.

    • Natural Amino Acids: $20$ different amino acids are used in natural polypeptides.

• Amino Acid Structural Components:

  • Central Carbon: Core atom bonded to four distinct functional groups.

  • Amino Group: $-\text{NH}_2$ basic group.

  • Carboxyl Group: $-\text{COOH}$ acidic group.

  • Side Group (R-group): Variable chemical group specifying amino acid identity and chemical behavior.

• Levels of Protein Structure:

  • Primary Protein Structure: Linear sequence of amino acids in a polypeptide chain ordered from the amino terminus ($N$-terminus) to the carboxy terminus ($C$-terminus).

  • Secondary Protein Structure: Local structural folding patterns determined by backbone hydrogen bonds, specifically producing alpha helices ($\alpha$-helices) and beta sheets ($\beta$-sheets).

  • Tertiary Protein Structure: Overall three-dimensional shape of a single polypeptide chain, stabilized by disulfide bridges between cysteines and other non-covalent interactions.

  • Quaternary Protein Structure: Spatial arrangement and assembly of multiple individual polypeptide subunits composing a functional multi-subunit protein.

Cell Membrane Structure, Transport, and Enzyme Dynamics

• Biological Membrane Architecture:

  • Lipid Bilayer: Double-layered sheet forming the foundational structural matrix of biological membranes.

  • Phospholipids: Amphipathic membrane lipids containing:

    • Hydrophilic Head: Polar phosphate group that interacts directly with aqueous environments.

    • Hydrophobic Tail: Nonpolar fatty acid chains oriented interiorly away from water.

  • Membrane Protein Types:

    • Peripheral Proteins: Proteins loosely attached to the exterior or interior surface of the membrane bilayer.

    • Integral Proteins: Transmembrane proteins penetrating deep into or spanning completely across the lipid bilayer.

• Enzyme Kinetics:

  • Enzyme: Functional protein acting as a biological catalyst to accelerate chemical reactions.

  • Activation Energy: Energy barrier required to initiate a chemical reaction; lowered by specific enzyme interactions.

  • Nomenclature: Enzyme names routinely end with the suffix "-ase".

• Key Biological Energy Carriers and Redox Chemistry:

  • ATP (Adenosine Triphosphate):

    • Synthesis equation: $\text{ADP} + \text{P} + \text{energy} \rightarrow \text{ATP}$.

    • Adenosine structure: The "A" in ATP represents adenosine, one of the fundamental monomers making up DNA and RNA.

  • NADPH (Nicotinamide Adenine Dinucleotide Phosphate):

    • Reduction reaction equation: $\text{NADP}^+ + \text{H}^+ + 2\,e^- \rightarrow \text{NADPH}$.

    • Reduction: Chemical process where electric charge is reduced via electron gain (gain of $2\,e^-$).

    • Oxidation: Reverse chemical process where electrons are lost and overall charge increases ($\text{NADPH} \rightarrow \text{NADP}^+ + \text{H}^+ + 2\,e^-$).

Light Physics, Photosynthetic Pigments, and Chloroplast Anatomy

• Physics of Light Energy:

  • Visible Light: Electromagnetic radiation spectrum spanning wavelengths from $400\,nm\text{ to }700\,nm$.

  • Wavelength Relationship: Inverse relationship between light wavelength and light energy: shorter wavelengths deliver higher light energy.

  • Ultraviolet (UV): High-energy electromagnetic radiation with wavelengths shorter than visible light ($< 400\,nm$).

  • Infrared (IR): Lower-energy electromagnetic radiation with wavelengths longer than visible light ($> 700\,nm$).

• Photosynthetic Pigments:

  • Chlorophyll: Primary light-absorbing green pigment in photosynthetic tissues.

  • Carotenoids: Accessory pigments (occurring in many distinct chemical kinds) absorbing blue-green light wavelengths and protecting photosynthetic complexes from excess light damage.

• Chloroplast Internal Ultrastructure:

  • Stroma: Fluid-filled inner matrix surrounding thylakoids where light-independent reactions take place.

  • Thylakoids: Flattened membranous sacs containing photosystems and electron transport chains.

  • Thylakoid Membrane: Lipid bilayer membrane physically separating the outer stroma from the inner thylakoid space (lumen).

  • Granum: Stack of interconnected thylakoid discs (plural: grana).

Photosynthesis Mechanisms: Light-Dependent and Light-Independent Reactions

• Global Reaction Overview:

  • Light-Dependent Reactions:

    • Inputs: Light energy and water ($\text{H}_2\text{O}$).

    • Outputs: Oxygen ($\text{O}_2$), ATP, and NADPH.

  • Light-Independent Reactions (Calvin-Benson Cycle):

    • Inputs: ATP, NADPH, and carbon dioxide ($\text{CO}_2$).

    • Outputs: Sugar (triose phosphates / PGAL).

• Molecular Machinery of Light-Dependent Reactions:

  • Photosystem II (PSII): Protein-pigment complex that absorbs photons and extracts electron pairs from water, generating $\text{O}_2$ as a byproduct.

  • Cytochrome Complex: Electron transport protein complex accepting electrons from PSII and pumping $H^+$ into the thylakoid lumen.

  • Photosystem I (PSI): Protein-pigment complex re-energizing electrons via photon absorption for reduction of $\text{NADP}^+$.

  • NADP+ Reductase: Membrane-associated enzyme catalyzing the reduction reaction: $\text{NADP}^+ + \text{H}^+ + 2\,e^- \rightarrow \text{NADPH}$.

  • ATP Synthase: Transmembrane enzyme utilizing the electrochemical gradient of $H^+$ running down its concentration gradient (chemiosmosis) from the thylakoid lumen back into the stroma to synthesize ATP from ADP and inorganic phosphate.

  • Origin and Fate of Oxygen: Water ($\text{H}_2\text{O}$) split at PSII provides the oxygen gas that plants and animals breathe; oxygen acts as a byproduct of supplying electrons to the photosynthetic transport system.

• Calvin-Benson Cycle Mechanics:

  • RuBP (Ribulose 1,5-bisphosphate): $5\text{-carbon}$ acceptor molecule starting the fixation cycle.

  • CO2: $1\text{-carbon}$ molecule fixed from the atmosphere.

  • PGA (3-Phosphoglycerate): $3\text{-carbon}$ intermediate compound formed following carbon fixation.

  • PGAL (Phosphoglyceraldehyde / G3P): $3\text{-carbon}$ energy-rich sugar molecule produced by reduction using ATP and NADPH.

C3, C4, and CAM Photosynthetic Pathways

• Photorespiration Challenge:

  • Photorespiration: Wasteful metabolic process occurring when Rubisco fixes $\text{O}_2$ instead of $\text{CO}_2$, resulting in energy loss and release of previously fixed carbon.

• Pathway Variations:

  • C3 Photosynthesis: Standard pathway where initial carbon fixation yields a $3\text{-carbon}$ compound (PGA); highly susceptible to photorespiration in warm, dry conditions.

  • C4 Photosynthesis: Spatial separation strategy where initial carbon fixation occurs in mesophyll cells via PEP carboxylase (PEPC) to produce a $4\text{-carbon}$ intermediate (malate), which is transported to bundle sheath cells to release concentrated $\text{CO}_2$ around Rubisco.

  • CAM (Crassulacean Acid Metabolism): Temporal separation strategy where stomata open at night to fix $\text{CO}_2$ into malate via PEPC, storing it until daytime when light reactions provide ATP and NADPH for the Calvin cycle while stomata stay closed.

• Key C4 Intermediate Compounds and Enzymes:

  • PEP (Phosphoenolpyruvate): $3\text{-carbon}$ primary acceptor molecule in C4 and CAM pathways.

  • PEP Carboxylase (PEPC): Enzyme fixing $\text{CO}_2$ onto PEP; shows no affinity for $\text{O}_2$, eliminating photorespiration.

  • Malate: $4\text{-carbon}$ organic acid intermediate transporting fixed carbon.

  • Pyruvate: $3\text{-carbon}$ product regenerated after malate decarboxylation, converted back to PEP using ATP.

Botanical Structural Diagrams and Pathway Schema

• Whole Plant Morphological Diagram:

  • Illustration requirements: Clearly label root system, stem main axis, leaf blades, petioles, lateral/axillary buds, and terminal apical bud.

• Detailed Plant Cell Schema:

  • Illustration requirements: Display primary cell wall, secondary cell wall layers, pit fields, pits, plasmodesmata channels, cell membrane, nucleus, central vacuole, mitochondria, and plastids (chloroplast, chromoplast, amyloplast).

• Leaf Cross-Sectional Anatomy:

  • Illustration requirements: Display upper epidermis with cuticle layer, palisade mesophyll layer, spongy mesophyll layer with intercellular air spaces, lower epidermis with guard cells forming stomatal pores, and vascular bundle (vein) maintaining xylem positioned towards the upper surface and phloem positioned towards the lower surface.

• Comparative Stem Cross Sections:

  • Illustration requirements: Contrast monocot stem cross section (scattered vascular bundles throughout ground tissue with no distinct pith/cortex division) with eudicot stem cross section (vascular bundles arranged in a distinct outer ring separating central pith from outer cortex, with vascular cambium running between xylem and phloem).

• Biological Membrane Structural Model:

  • Illustration requirements: Detail phospholipid bilayer with hydrophilic heads facing aqueous environments and hydrophobic tails facing internally. Show integral membrane proteins spanning the membrane and peripheral proteins on the surfaces. Annotate exact sites where polar water molecules cling to hydrophilic head groups.

• Thylakoid Membrane Light Reaction System:

  • Illustration requirements: Position PSII, cytochrome complex, PSI, $\text{NADP}^+$ reductase, and ATP synthase across the thylakoid membrane. Trace electron pairs originating from water splitting at PSII ($\text{H}_2\text{O} \rightarrow 2\,H^+ + \frac{1}{2}\text{O}_2 + 2\,e^-$), traveling through the electron transport chain, re-energizing at PSI, and ending up reducing $\text{NADP}^+$ to NADPH. Show $H^+$ pumping into the lumen and flowing back out through ATP synthase into the stroma to produce ATP.

• Calvin-Benson Cycle Quantitative Stoichiometry Schema:

  • Illustration requirements:

    • Input stage: $3\text{ RuBP}$ ($5\text{ carbons}$ each = $15\text{ carbons}$ total) combine with $3\text{ CO}_2$ ($1\text{ carbon}$ each = $3\text{ carbons}$ total) to yield $6\text{ PGA}$ molecules ($3\text{ carbons}$ each = $18\text{ carbons}$ total).

    • Reduction stage: $6\text{ PGA}$ are reduced to $6\text{ PGAL}$ ($3\text{ carbons}$ each = $18\text{ carbons}$ total). ATP and NADPH produced during light reactions are consumed during this reduction step.

    • Output stage: Net yield of $1\text{ extra PGAL}$ ($3\text{ carbons}$) exits the cycle to synthesize sugars.

    • Regeneration stage: The remaining $5\text{ PGAL}$ ($15\text{ carbons}$ total) consume additional ATP to regenerate $3\text{ RuBP}$ ($15\text{ carbons}$ total).

• C4 Pathway Two-Cell Spatial Diagram:

  • Illustration requirements: Draw two distinct contiguous cell circles representing a Mesophyll Cell and a Bundle Sheath Cell.

    • In the Mesophyll Cell: $\text{CO}_2$ ($1\text{ carbon}$) combines with PEP ($3\text{ carbons}$) via PEPC to form Malate ($4\text{ carbons}$).

    • Intercellular transport: Malate ($4\text{ carbons}$) moves via arrow from Mesophyll Cell into Bundle Sheath Cell.

    • In the Bundle Sheath Cell: Malate ($4\text{ carbons}$) splits to release $\text{CO}_2$ ($1\text{ carbon}$) directly into the Calvin cycle, producing Pyruvate ($3\text{ carbons}$).

    • Return transport: Pyruvate ($3\text{ carbons}$) moves via arrow from Bundle Sheath Cell back into Mesophyll Cell.

    • Regeneration: Pyruvate ($3\text{ carbons}$) consumes ATP to regenerate PEP ($3\text{ carbons}$). Carbon counts represented by explicit black dots or numbers ($1\text{C}$, $3\text{C}$, $4\text{C}$) at each step.

Here is a guide to labeling and explaining each of the drawing prompts listed in your study material:

1. Plant Body Diagram

• Terms to label: Root system, stem, node, internode, axil, leaf blade, petiole, lateral/axillary bud, terminal bud.

2. Plant Cell Structure

• Terms to label: Primary cell wall, secondary cell wall, pit field, pit, plasmodesmata, cell membrane, nucleus, central vacuole, mitochondrion, plastids (chloroplast, chromoplast, amyloplast), suberin, lignin.

3. Leaf Cross-Section

• Terms to label: Cuticle, upper epidermis, palisade mesophyll, spongy mesophyll (with air spaces), vascular bundle (vein) with xylem towards the upper surface and phloem towards the lower surface, lower epidermis, guard cells, stomatal pore, trichomes.

4. Monocot vs. Eudicot Stem Cross-Section

• Monocot stem: Epidermis, scattered vascular bundles, ground tissue (no distinct pith/cortex division).

• Eudicot stem: Epidermis, cortex, vascular bundles arranged in a ring, central pith, vascular cambium (between xylem and phloem).

5. Biological Membrane Diagram

• Terms to label: Phospholipid bilayer, hydrophilic heads, hydrophobic tails, integral membrane proteins, peripheral proteins.

• Water interaction: Water molecules cling to the polar hydrophilic head groups of the phospholipids on the outer surfaces of the membrane.

6. Thylakoid Membrane & Light-Dependent Reactions

• Components: Photosystem II (PSII), Cytochrome complex, Photosystem I (PSI), $\text{NADP}^+$ reductase, ATP synthase, thylakoid lumen, stroma.

• Mechanism:
  
  

  • Electron origin: Electron pairs originate from splitting water ($\text{H}_2\text{O} \rightarrow 2\,\text{H}^+ + \frac{1}{2}\text{O}_2 + 2\,e^-$) at PSII.

  • Electron pathway: Electrons pass through the cytochrome complex (which pumps $\text{H}^+$ into the thylakoid lumen) to PSI, where they are re-energized by light.

  • Final electron acceptor: Electrons end up reducing $\text{NADP}^+$ to NADPH via $\text{NADP}^+$ reductase ($\text{NADP}^+ + \text{H}^+ + 2\,e^- \rightarrow \text{NADPH}$).

  • ATP production: The accumulation of $\text{H}^+$ in the lumen creates a concentration gradient. As $\text{H}^+$ flows down its gradient back into the stroma through ATP synthase (chemiosmosis), ATP is synthesized from ADP and inorganic phosphate.

7. Calvin-Benson Cycle Stoichiometry

• Fixation: $3\text{ RuBP}$ ($5\text{C}$ each) + $3\text{ CO}_2$ ($1\text{C}$ each) yield $6\text{ PGA}$ ($3\text{C}$ each).

• Reduction: $6\text{ PGA}$ are reduced to $6\text{ PGAL}$ ($3\text{C}$ each). ATP and NADPH produced in the light reactions are used during this reduction step.

• Output: Net yield of $1\text{ extra PGAL}$ ($3\text{C}$) leaves the cycle to synthesize sugars.

• Regeneration: The remaining $5\text{ PGAL}$ ($15\text{C}$ total) consume additional ATP to regenerate $3\text{ RuBP}$ ($15\text{C}$ total).

8. C4 Pathway Spatial Diagram

• Mesophyll Cell: $\text{CO}_2$ ($1\text{C}$) combines with PEP ($3\text{C}$) via PEP carboxylase (PEPC) to form Malate ($4\text{C}$).

• Transport to Bundle Sheath: Malate ($4\text{C}$) moves from the mesophyll cell into the bundle sheath cell.

• Bundle Sheath Cell: Malate ($4\text{C}$) decarboxylates to release $\text{CO}_2$ ($1\text{C}$) directly into the Calvin cycle, producing Pyruvate ($3\text{C}$).

• Return & Regeneration: Pyruvate ($3\text{C}$) travels back to the mesophyll cell, where ATP is used to regenerate PEP ($3\text{C}$).