Plant Nutrition, Transport, and Reproduction

TL;DR

Plants make glucose through photosynthesis, then transport water and nutrients through specialized vessels. They reproduce sexually via flowers or asexually through vegetative methods. Understanding these three systems explains how plants survive, grow, and create new generations.

1. The Mental Model

Think of a plant as a self-sustaining factory with three departments. The nutrition department (leaves) manufactures food from sunlight. The transport department (stems and roots) moves materials around like a highway system. The reproduction department (flowers or runners) ensures the next generation. That's the whole idea.

2. The Core Material

Photosynthesis: The Food Factory

Photosynthesis happens in chloroplasts, mainly in leaf cells. The equation you need to memorize is:

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (in the presence of light and chlorophyll)

This process has two stages. The light-dependent reactions occur in the thylakoids, where chlorophyll captures light energy to split water molecules, releasing oxygen as a waste product. The energy gets stored in molecules called ATP and NADPH.

The light-independent reactions (Calvin cycle) happen in the stroma. Here, CO₂ from the air gets "fixed" into glucose using the ATP and NADPH from stage one. This is why plants need both light and carbon dioxide.

Limiting factors control photosynthesis rate. If light intensity is low, adding more CO₂ won't help much. If temperature drops too low, enzymes work slowly even with plenty of light. You'll see this in graphs where one factor plateaus while others increase.

Plants also need mineral ions from soil. Nitrates make amino acids for proteins. Phosphates help with DNA and energy transfer. Potassium assists with enzyme function and water regulation. Without these, you get deficiency symptoms like yellow leaves or poor growth.

Transport Systems: Moving Materials Around

Plants have two transport tissues working like separate road networks. Xylem carries water and minerals upward from roots to leaves. Phloem moves dissolved sugars from leaves to everywhere else.

Xylem vessels are dead, hollow tubes made of lignin - a strong, waterproof material. Water moves up through transpiration, which is basically evaporation from leaf surfaces. As water evaporates from stomata (tiny pores), it pulls more water up through the xylem like sucking through a straw. This creates transpiration pull.

Stomata control