Plant Physiology Cheat Sheet

The core ideas of Plant Physiology distilled into a single, scannable reference — perfect for review or quick lookup.

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Quick Reference

Photosynthesis

The process by which plants convert light energy into chemical energy (glucose), using carbon dioxide and water, while releasing oxygen as a byproduct. It occurs in two stages: the light-dependent reactions in the thylakoid membranes and the Calvin cycle in the stroma of chloroplasts.

Transpiration

The loss of water vapor from plant surfaces, primarily through stomata on leaves. Transpiration creates a negative pressure (tension) that drives the ascent of water through xylem vessels from roots to shoots, as described by the cohesion-tension theory.

Phytohormones

Naturally occurring chemical signaling molecules in plants that regulate growth, development, and responses to environmental stimuli. The five classical groups are auxins, gibberellins, cytokinins, abscisic acid, and ethylene, though additional hormones like brassinosteroids, jasmonates, and salicylic acid are also recognized.

Stomatal Regulation

The opening and closing of stomatal pores on leaf surfaces, controlled by the turgor pressure of paired guard cells. Stomata balance the competing demands of CO2 uptake for photosynthesis and water conservation, responding to light, humidity, CO2 concentration, and the hormone abscisic acid.

Calvin Cycle

The series of light-independent biochemical reactions occurring in the chloroplast stroma that fix atmospheric CO2 into organic molecules. The enzyme RuBisCO catalyzes the initial carbon fixation step, and the cycle uses ATP and NADPH from the light reactions to produce glyceraldehyde-3-phosphate (G3P).

Cellular Respiration in Plants

The metabolic process by which plants break down glucose and other organic molecules to produce ATP for cellular work. Like animals, plants carry out glycolysis, the citric acid cycle, and oxidative phosphorylation in mitochondria, consuming oxygen and releasing CO2.

Photoperiodism

The physiological response of plants to the relative lengths of day and night, which regulates developmental transitions such as flowering, dormancy, and tuber formation. Plants are classified as short-day, long-day, or day-neutral based on their flowering response to photoperiod.

Mineral Nutrition

The study of how plants acquire, transport, and utilize essential mineral elements from the soil. Plants require macronutrients (nitrogen, phosphorus, potassium, calcium, magnesium, sulfur) and micronutrients (iron, manganese, zinc, copper, boron, molybdenum, chlorine, nickel) for normal growth and metabolism.

Tropisms

Directional growth responses of plants toward or away from environmental stimuli such as light (phototropism), gravity (gravitropism), touch (thigmotropism), and water (hydrotropism). These responses are mediated by asymmetric distribution of the hormone auxin.

Water Potential

A measure of the free energy of water in a system, expressed in units of pressure (megapascals). Water potential determines the direction of water movement in plants, always flowing from regions of higher water potential to lower water potential. It is influenced by solute concentration (osmotic potential) and physical pressure (pressure potential).

Key Terms at a Glance

Photosynthesis:The biochemical process by which plants, algae, and some bacteria convert light energy, carbon dioxide, and water into glucose and oxygen.

Transpiration:The evaporative loss of water from aerial plant parts, primarily through stomata on leaf surfaces.

Chloroplast:A double-membrane organelle in plant cells containing chlorophyll where photosynthesis occurs. It has internal thylakoid membranes and a fluid-filled stroma.

Auxin:A class of plant growth hormones, primarily indole-3-acetic acid (IAA), that regulate cell elongation, apical dominance, tropisms, and root development.

Phloem:Vascular tissue composed of sieve tube elements and companion cells that transports dissolved sugars and organic compounds from source to sink tissues.

Xylem:Vascular tissue composed of tracheids and vessel elements that transports water and dissolved minerals upward from roots to leaves.

Stomata:Microscopic pores on the surface of leaves and stems, bounded by guard cells, that regulate gas exchange (CO2 in, O2 and H2O out).

Water Potential:A quantitative measure of the tendency of water to move from one area to another, determined by solute concentration and physical pressure, expressed in megapascals (MPa).

Calvin Cycle:The light-independent reactions of photosynthesis in the chloroplast stroma where CO2 is fixed by RuBisCO and reduced to glyceraldehyde-3-phosphate (G3P) using ATP and NADPH.

RuBisCO:Ribulose-1,5-bisphosphate carboxylase/oxygenase, the enzyme that catalyzes the first step of carbon fixation in the Calvin cycle and also initiates photorespiration.

Abscisic Acid:A plant hormone involved in stress responses, promoting stomatal closure during drought and maintaining seed dormancy until conditions favor germination.

Ethylene:A gaseous plant hormone that regulates fruit ripening, flower and leaf senescence, abscission, and the stress response known as the triple response.

Gibberellin:A class of plant hormones that promote stem elongation, seed germination, and flowering by stimulating cell division and elongation.

Cytokinin:A plant hormone class that promotes cell division, delays leaf senescence, and stimulates shoot development, often working antagonistically with auxin.

Photoperiodism:The response of plants to the relative lengths of light and dark periods, which controls physiological processes such as flowering, dormancy, and tuber formation.

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