Photosynthesis, Chloroplasts, and Plant Structures: Key Concepts for Biology

Light-dependent Reactions

Capture light energy to make ATP and reduce NADP+.

Light-independent Reactions

Use ATP & NADPH for carbon fixation.

General Photosynthesis Equation

6CO2 + 12H2O → C2H12O6 + 6H2O + 6O2

Chloroplast Structure

Site of photosynthesis; contains thylakoids (light-dependent) and stroma (Calvin cycle).

Electromagnetic Spectrum

Visible light = photosynthetically active radiation; shorter wavelength = higher energy; longer wavelength = lower energy.

Photoelectric Effect

Excitation of electrons when photons hit pigments; too much or too little energy prevents reaction.

Absorbance Spectrum

Chlorophyll absorbs violet/blue (450-500 nm) and red/orange (600-680 nm).

Structure of Chlorophyll

Porphyrin ring absorbs light; Mg²I stabilizes; hydrocarbon tail anchors to thylakoid proteins.

Antenna Complex

Collects photons.

Reaction Center

Transfers energy to ETC; water is electron donor.

Electron Transport Chain

Transfers electrons, pumps HI into thylakoid space, forming ATP and NADPH.

Chemiosmotic ATP Production

Proton gradient drives ATP synthase to form ATP (chemiosmosis).

Noncyclic Photophosphorylation

Produces ATP + NADPH.

Cyclic Photophosphorylation

Produces ATP only.

Calvin Cycle

Three stages—carbon fixation, G3P production, RuBP regeneration; requires ATP & NADPH.

Chloroplast vs Mitochondria

Chloroplast: H2O + light → NADPH; Mitochondria: NADH → O2.

Photorespiration

Rubisco binds OI instead of COI → breakdown of RuBP, wasteful.

CI vs CI vs CAM Plants

CI: normal Calvin cycle; inefficient in heat/drought. CI: spatial separation of fixation; less water loss. CAM: temporal separation; open stomata at night.

Haplodiplontic Life Cycle

Alternation between multicellular diploid (sporophyte) and haploid (gametophyte) stages.

Types of Seed-Bearing Plants

Gymnosperms: naked seeds, cones (pines, firs). Angiosperms: flowering plants, fruit covers seed.

Plant Tissues

Dermal: protection. Ground: storage, photosynthesis, secretion. Vascular: water & nutrient transport.

Meristems

Plant 'stem cells.' Apical: tip growth (primary). Lateral: thickening (secondary).

Dermal Tissues

Cutin layer and waxy cuticle prevent water loss; thick in cacti.

Guard Cells

Control stomatal opening via turgor pressure.

Trichomes

Hair-like outgrowths that protect, reflect radiation, sometimes secrete substances.

Root Hairs

Epidermal extensions increasing absorption surface area.

Ground Tissue Types

Parenchyma: storage/photosynthesis. Collenchyma: flexible support. Sclerenchyma: rigid, lignified support.

Xylem

Water/mineral transport upward; dead at maturity; includes tracheids & vessels.

Phloem

Transports sugars both directions; living cells (sieve tubes, companion cells).

Vascular Bundle Arrangement

Eudicots: ring arrangement. Monocots: scattered bundles.

Water Potential

Ψw = Ψp + Ψs; water moves from high → low potential; pressure & solute components determine direction.

Phloem Transport

Pressure-flow mechanism: sugar loading → water inflow → movement toward sink.

Root Structure

Includes primary/lateral/adventitious roots; root hairs for absorption.

Casparian Strip

Blocks movement between root cortex cells; forces water through membranes.

Ion Transport in Roots

Active transport of cations helps water uptake.

Root Specializations

Support: prop, buttress, aerial. Storage: carrots, beets. Respiration: pneumatophores.

Rhizobium

Nitrogen-fixing bacteria in root nodules of legumes.

Mycorrhizae

Symbiosis between roots and fungi; increases nutrient absorption.

Shoot System

Includes stems and leaves; supports transport & photosynthesis.

Stem Internal Structure

Eudicots: vascular ring. Monocots: scattered bundles.

Secondary Growth

Only in eudicots; increases girth via lateral meristems.

Leaf Structure

Cuticle, epidermis, mesophyll (palisade & spongy), stomata.

Leaf Modifications

Floral (poinsettia), spines (cacti), shade leaves, insectivorous leaves.

C3 Plants

Plants that use the Calvin cycle for carbon fixation, typically found in temperate climates.

• have no special features to combat photorespiration.

C4 Plants 

Plants that utilize a modified process of photosynthesis to minimize photorespiration, often found in hot, dry environments.

• They efficiently fix carbon dioxide using a four-carbon compound, performing these steps in different cell types

CAM Plants 

Minimize photorespiration and save water by separating these steps in time, between night and day.