Plant Transport and Conduction

Water and Mineral Transport in Plants

• Xylem transports water and dissolved minerals from roots to shoots via the process of transpiration.

• Stomata are pores on the leaf surface controlled by guard cells; they regulate gas exchange and water loss.

• Properties of Water: Cohesion (water molecules stick together), adhesion (stick to cell walls), and high surface tension facilitate upward movement in xylem.

• Transpiration: The evaporation of water from plant leaves creates a negative pressure that pulls water upward through the plant.

• Plant tissues involved: Xylem vessels (water/minerals), phloem (sugars/hormones/proteins).

Translocation of Sugars and Other Substances

• Phloem transports sugars (mainly sucrose), hormones, and proteins throughout the plant.

• Translocation is the movement of these substances from sources (e.g., leaves) to sinks (e.g., roots, fruits).

• Pressure Flow Model: Sugars are actively loaded into phloem, increasing osmotic pressure and causing water to flow in, pushing sap toward sinks.

Osmosis, Water Potential, and Transport Mechanisms

• Osmosis: Movement of water across a semipermeable membrane from high to low water potential.

• Water Potential (Ψ): Determines the direction of water movement; includes solute potential and pressure potential.

• Active Transport: Requires energy (ATP) to move substances against their concentration gradient.

• Passive Transport: Movement of substances down their concentration gradient without energy input.

Photosynthesis and Cellular Respiration

Chloroplast Structure and Photosynthesis Overview

• Chloroplasts contain thylakoids (site of light reactions) and stroma (site of Calvin Cycle).

• Stomata allow CO2 to enter for photosynthesis and O2 to exit.

• Overall Equation for Photosynthesis:

• Cellular Respiration Equation (reverse):

• Leaves are green due to chlorophyll reflecting green wavelengths; red and blue light power photosynthesis.

• Chlorophyll a & b are main pigments; carotenoids are accessory pigments that protect against excess light.

Photosystems and Electron Transport Chain (ETC)

• Photosystem II (P680): Splits water, releases O2, and passes electrons to ETC.

• Photosystem I (P700): Produces NADPH.

• ETC Components: Plastoquinone (PQ), cytochrome b6/f, plastocyanin (PC), ferredoxin (Fd), ferredoxin-NADP+ reductase (FAD), ATP synthase.

• ATP is produced as electrons move from PSII to PSI, driving H+ into thylakoid space and powering ATP synthase.

• Active and passive transport are involved in moving ions and molecules during the ETC.

Stages of Photosynthesis

1. Light Reactions: Convert light energy to chemical energy (ATP, NADPH); occur in thylakoid membranes.

2. Calvin Cycle (C3 Pathway): Uses ATP and NADPH to fix CO2 into sugars; occurs in stroma.

• O2 production: Produced from splitting H2O in PSII.

• 3 CO2 molecules are needed to produce one G3P (glyceraldehyde-3-phosphate), which can be converted to glucose.

• Uses of glucose: Energy (respiration), storage (starch), building cellulose, making other organic molecules.

Calvin Cycle Details

• RuBP (ribulose bisphosphate): 5-carbon molecule that accepts CO2.

• Rubisco: Enzyme that catalyzes CO2 fixation; can also bind O2 (photorespiration).

• Three phases: Carbon fixation, G3P generation, RuBP regeneration.

• Rubisco is a "two-timing" enzyme because it can fix both CO2 and O2.

Alternative Pathways: C4 and CAM

• C4 Plants: Spatial separation of steps; CO2 fixed in mesophyll cells, then transported to bundle sheath cells.

• CAM Plants: Temporal separation; CO2 fixed at night, used during the day.

• Enzyme: PEP carboxylase converts CO2 to 4-carbon malate.

• Photorespiration: Occurs when Rubisco binds O2 instead of CO2, reducing efficiency.

• Plants combat global warming by absorbing CO2 during photosynthesis.

Basic Cellular Respiration

• Autotrophs: Organisms that produce their own food (e.g., plants).

• Heterotrophs: Organisms that consume other organisms for energy.

• Chemical cycling: Photosynthesis and respiration are complementary processes.

• Cellular respiration occurs in mitochondria; plants use some O2 they produce for their own respiration.

• ATP produced in chloroplasts is used for the Calvin Cycle; ATP for other cellular work is made in mitochondria.

Plant Signaling, Movement, and Growth: Hormones and Nutrients

Plant Nutrients and Mycorrhizae

• Major inorganic nutrients: Nitrogen, phosphorus, potassium, calcium, magnesium, sulfur.

• Uptake: Roots absorb nutrients from soil; mycorrhizae (fungal symbionts) enhance nutrient absorption.

• Nitrogen fixation: Some plants partner with bacteria (in root nodules) or are carnivorous to obtain nitrogen in poor soils.

Plant Hormones

• Hormones: Chemical messengers that regulate growth and development.

• Five major groups: Auxins, gibberellins, cytokinins, ethylene, abscisic acid.

• Functions: Control cell elongation, division, fruit ripening, seed dormancy, and stress responses.

Tropisms and Nastic Movements

• Tropisms: Directional growth responses to stimuli.

• Types: Phototropism (light), gravitropism (gravity), thigmotropism (touch), hydrotropism (water).

• Nastic movements: Non-directional responses (e.g., leaf folding in Mimosa).

Meiosis and Basic Plant Life Cycles

Phases of Meiosis

• Meiosis I: Prophase I (crossing over), Metaphase I, Anaphase I, Telophase I.

• Meiosis II: Prophase II, Metaphase II, Anaphase II, Telophase II.

• Crossing over: Exchange of genetic material between homologous chromosomes during Prophase I; increases genetic diversity.

• Independent assortment: Random distribution of chromosomes during Metaphase I.

• Non-disjunction: Failure of chromosomes to separate; can lead to polyploidy in plants.

Haploid vs. Diploid and Plant Life Cycles

• Haploid (n): One set of chromosomes (gametophyte).

• Diploid (2n): Two sets of chromosomes (sporophyte).

• Alternation of generations: Plants alternate between haploid gametophyte and diploid sporophyte stages.

• Meiosis in plants: Produces spores, which grow into gametophytes that produce gametes by mitosis.

• Sexual vs. asexual reproduction: Sexual involves meiosis and fertilization; asexual involves mitosis only.

Comparison Table: Mitosis vs. Meiosis

Basics of Genetics and DNA

Genetics Fundamentals

• Genotype: Genetic makeup of an organism.

• Phenotype: Observable traits.

• Dominant allele: Expressed when present; recessive allele: masked by dominant.

• Punnett square: Tool to predict offspring genotypes and phenotypes from parental crosses.

• Father of genetics: Gregor Mendel; worked with pea plants (Pisum sativum).

• Key terms: Genes, alleles, locus (loci), homozygous, heterozygous, homologous chromosomes, F1/F2 generations.

• Incomplete dominance: Heterozygote shows intermediate phenotype.

• Codominance: Both alleles are fully expressed.

• Transposable elements: DNA sequences that can move within the genome; discovered by Barbara McClintock.

DNA and RNA Structure and Function

• DNA: Deoxyribonucleic acid; double helix of nucleotides (deoxyribose, phosphate, nitrogenous base).

• RNA: Ribonucleic acid; single-stranded, contains ribose and uracil instead of thymine.

• Nucleotides: Composed of a sugar, phosphate, and nitrogenous base (A, T, C, G for DNA; A, U, C, G for RNA).

• Base-pairing rules: DNA: A-T, C-G; RNA: A-U, C-G.

• DNA replication: Occurs during S phase; enzymes include helicase (unwinds), DNA polymerase (synthesizes), ligase (joins fragments), primase (lays primer).

• Leading vs. lagging strand: Leading is synthesized continuously; lagging in Okazaki fragments.

Gene Expression and Mutations

• Central Dogma: DNA → mRNA (transcription) → protein (translation).

• Transcription: DNA is copied into mRNA.

• Translation: mRNA is decoded by ribosomes and tRNA to build a polypeptide.

• Mutations: Changes in DNA sequence; types include substitution, deletion, insertion.

• Effects: Not all mutations are harmful; some are neutral or beneficial.

Biotechnology Techniques

• PCR (Polymerase Chain Reaction): Amplifies DNA; steps include denaturation, annealing, extension; requires template DNA, primers, nucleotides, DNA polymerase.

• Gel electrophoresis: Separates DNA fragments by size; DNA is negatively charged and moves toward positive electrode.

• Transcriptomics: Study of RNA transcripts; used to understand gene expression and develop plant-based medicines.

Plant Propagation, Biotechnology, and GMOs

Plant Propagation and Cloning

• Asexual reproduction: Plants reproduce via runners, tubers, cuttings, etc.

• Cloning: Humans propagate plants by cuttings, tissue culture, grafting.

Recombinant DNA Technology and GMOs

• Recombinant DNA technology: Combining DNA from different sources to create new genetic combinations.

• GMOs: Organisms with artificially introduced genes; transgenic organisms have genes from other species.

• Major U.S. GMO crops: Corn, soybeans, cotton.

• Golden rice: Produced by inserting genes for beta-carotene synthesis; addresses vitamin A deficiency.

• Plasmids: Small circular DNA in bacteria; used as vectors in genetic engineering.

• Methods: Electroporation, particle bombardment, viral vectors, bacterial transformation.

• Benefits of GMOs: Increased yield, pest resistance, nutritional enhancement.

• Negatives: Environmental concerns, gene flow to wild species, ethical debates.