Plant Form and Function: Structure, Tissues, and Growth in Plants

Plant Form and Function

Introduction

Plants exhibit a complex organization of tissues and structures that enable them to grow, reproduce, and respond to their environment. Understanding plant form and function is fundamental in general biology, as it provides insight into how plants sustain life on Earth.

Plant Tissues

Overview of Plant Tissues

Plant tissues are groups of cells that work together to perform specific functions. There are three main types of plant tissues:

• Dermal tissue: Covers and protects the plant's surface.

• Ground tissue: Makes up most of the plant body and is involved in photosynthesis, storage, and support.

• Vascular tissue: Transports water, nutrients, and sugars throughout the plant.

Example: In a leaf, the dermal tissue forms the outer layer, ground tissue fills the interior, and vascular tissue forms veins.

Plant Gross Anatomy

Shoot and Root Systems

Plants are organized into two main systems: the shoot system and the root system, each specialized for distinct functions.

• Shoot System: Aboveground parts, including stems, leaves, and flowers. Specialized for harvesting light and carbon dioxide ($CO_2$).

• Root System: Belowground parts, primarily roots. Absorbs water and key nutrients such as nitrogen (N), phosphorus (P), and potassium (K).

Example: The shoot system of a tomato plant includes its stems and leaves, while the root system anchors the plant and absorbs nutrients.

The Shoot System

Components of the Shoot System

The shoot system consists of several specialized structures:

• Stem: Vertical, aboveground structure that supports leaves and flowers.

• Leaves: Main site of photosynthesis.

• Nodes: Points where leaves attach to the stem.

• Internodes: Segments between nodes.

• Axillary Buds: Sites of new growth along the stem.

• Apical Buds: Sites of new growth at the tip of the stem or branches.

Example: In many plants, pruning the apical bud encourages growth from axillary buds, resulting in bushier plants.

Plant Growth

Primary Growth

Primary growth increases the length of shoots and roots, allowing plants to grow taller and roots to extend deeper into the soil.

• Meristems: Regions of undifferentiated cells that retain the ability to divide and specialize.

• Apical Meristems: Located at the tips of roots and shoots; responsible for primary growth.

Example: Grass continues to grow after mowing due to active meristems near the base of the leaves.

Secondary Growth

Secondary growth increases the width (girth) of stems and roots, primarily in woody plants.

• Cambium: Lateral meristem tissue responsible for secondary growth.

• Cork Cambium: Produces cork, which forms part of the bark.

• Vascular Cambium: Produces secondary xylem (wood) and secondary phloem.

Example: Trees grow wider each year due to the activity of the vascular cambium, forming annual growth rings.

Secondary Growth in Trees

Process and Structure

Secondary growth in trees involves the division of vascular cambium cells, resulting in the production of new xylem and phloem cells. More xylem cells are produced compared to phloem cells, contributing to the thickening of the trunk.

• Vascular Cambium: Divides to produce new xylem (toward the inside) and phloem (toward the outside).

• Annual Rings: Formed by the periodic activity of the vascular cambium, visible in cross-sections of tree trunks.

Example: Counting the annual rings in a tree trunk can estimate the tree's age.

Meristem Type	Location	Function
Apical Meristem	Tips of roots and shoots	Primary growth (length)
Vascular Cambium	Between xylem and phloem	Secondary growth (width)
Cork Cambium	Outer stem/root	Produces cork (bark)

Additional info: Secondary growth is characteristic of most dicotyledonous plants and gymnosperms, but not monocots.