Plant Form and Physiology
The Plant Body
Plant Tissues and Organ Systems
Plants are made up of meristematic and permanent tissues and are supported by shoot and root organ systems.
A stem connects the roots to the leaves, provides support, stores food, and holds the leaves, flowers, and buds.
The stem's anatomy consists of three tissue systems that work together to support, protect, and aid in nourishing the plant.
Growth in Stems
Plants undergo primary growth to increase length and secondary growth to increase thickness.
Stem modifications, either aboveground, underground, or aerial, enable plants to survive in particular habitats and environments.
Types of Root Systems
The root tip has three main zones: a zone of cell division, a zone of elongation, and a zone of maturation.
Plants have a wide variety of roots for functions as diverse as structural support, food storage, and parasitism.
Leaf Structure and Arrangment
Most leaves have similar essential structures, but differ in venation patterns and leaf arrangement (or phyllotaxy).
Leaves may be categorized as simple or compound, depending on how their blade (or lamina) is divided.
Leaf Structure, Function, and Adaptation
Leaves have many structures that prevent water loss, transport compounds, aid in gas exchange, and protect the plant as a whole.
Plant meristematic tissues are cells that divide in order to give rise to various organs of the plant and keep the plant growing.
Genetic control of flowers
A variety of genes control flower development, which involves sexual maturation and growth of reproductive organs as shown by the ABC model.
Transport of Water and Solutes in Plants
Water and Solute Potential
Water potential is the measure of potential energy in water and drives the movement of water through plants.
Pressure, Gravity, and Matric Potential
Water potential is affected by factors such as pressure, gravity, and matric potentials.
Movement of Water and Minerals in the Xylem
Transpiration aids in the movement of water and minerals in the xylem, but it must be controlled in order to prevent water loss.
Transportation of Photosynthates in the Phloem
Translocation moves photosynthates via the phloem from sources to sinks.
Plant Sensory Systems and Responses
Plant Responses to Light
Plants respond to light stimuli by growing, differentiating, tracking the time of day and seasons, and moving toward or away from the light.
The Phytochrome System and Red Light Response
Plants use a phytochrome system to sense the level, intensity, duration, and color of environmental light to adjust their physiology.
Blue Light Response
The protein-based receptors, phototropins and cryptochromes, sense blue light to alter plant physiology accordingly.
Plant Responses to Gravity
Plant shoots grow away from gravity, toward sunlight, while plant roots grow into the soil in the direction of gravity.
Auxins, Cytokinins, and Gibberellins
All physiological aspects of plants are affected by plant hormones (chemical messengers), including auxins, cytokinins, and gibberellins.
Abscisic Acid, Ethylene, and Nontraditional Hormones
All physiological aspects of plants are affected by plant hormones, including abscisic acid, ethylene, and nontraditional hormones.
Plant Responses to Wind and Touch
Plants respond to wind and touch by changing their direction of growth, movement, and shape.
Plant Defense Mechanisms
Defense responses against herbivores
Plants defend against herbivores with mechanical wounding, barriers, secondary metabolites, and attraction of parasitoids.
Defense responses against pathogens
Plants defend against pathogens with barriers, secondary metabolites, and antimicrobial compounds.