Plant Structure and Function Explorer

Leaves are the primary site of photosynthesis. Chloroplasts in palisade mesophyll cells capture light energy to convert carbon dioxide and water into glucose and oxygen.

• Chlorophyll absorbs mainly red and blue light, reflecting green (why leaves look green).
• Stomata open during the day to let CO2 in and O2 out. Guard cells control pore size.
• C3 plants (most plants) fix CO2 directly via the Calvin cycle using RuBisCO.
• C4 plants (corn, sugarcane) pre-fix CO2 in mesophyll cells to minimize photorespiration.

The overall reaction is: 6CO2 + 6H2O + light energy forms C6H12O6 + 6O2.

Vascular plants have two transport systems running through roots, stem, and leaves.

• Xylem is made of dead, hollow cells (tracheids and vessel elements) that form continuous tubes. Water moves upward by cohesion-tension: evaporation from stomata creates a pull that extends to root hairs.
• Phloem consists of living sieve-tube cells connected by sieve plates. Sucrose and amino acids move from sources (leaves, storage roots) to sinks (growing tips, fruits, roots) by pressure flow.
• The Casparian strip in root endodermis forces water and minerals through cell membranes (not between cells), allowing selective uptake.

Flowering plants reproduce sexually through pollination and fertilization, and some also reproduce asexually through runners, bulbs, or rhizomes.

• Pollination transfers pollen from the anther to the stigma of the same or another flower. Agents include bees, butterflies, wind, birds, and water.
• Double fertilization is unique to angiosperms: one sperm fertilizes the egg (forming the embryo), and a second sperm fertilizes two polar nuclei (forming triploid endosperm).
• Seed dispersal strategies include fleshy fruits eaten by animals, winged fruits carried by wind, hooked fruits attached to fur, and explosive pods that launch seeds.

After fertilization, the ovary wall becomes the fruit and the ovules become seeds.

Plants have specialized cell types organized into three tissue systems: dermal, ground, and vascular.

• Parenchyma cells have thin walls and carry out photosynthesis, storage, and basic metabolism. They make up the bulk of leaves and fruit flesh.
• Collenchyma cells have unevenly thickened walls providing flexible support for growing organs (like the strings in celery).
• Sclerenchyma cells have rigid, lignin-thickened walls. They are dead at maturity and provide structural support (wood fibers, nut shells).
• Guard cells are kidney-shaped cells flanking each stoma. They swell with water to open the pore and shrink to close it.