Lesson 1: Introduction

As plants moved from an aquatic environment to land, many adaptations were evolved. Those include a vascular system, roots and seeds among others. The dominant type of plants on the planet are flowering plants known as angiosperms. There are 250 000 known species. Most of our foods come from a few hundred domesticated species.

Angiosperms are divided into two categories based in several structural features. These two groups are called monocots and dicots. These terms derive from the first leaves of the plant embryo which are called cotyledons. The monocots have one leaf while the dicots have two.

A large group of related plants that include orchids, bamboos, palms, lilies, grasses and grains. Monocot characteristics One cotyledon Parallel leaf venation Scattered vascular bundles Flower parts in threes or multiples of threes Fibrous roots

Most dicots are in a related group called the eudicots. Most flowering shrubs and trees, as well as nearly all the fruits and vegetables that we eat are eudicots. Dicot characteristics Two cotyledons Branched leaf venation Ring of vascular bundles Flower parts in fours or fives or multiples of fours or fives A taproot system

A typical plant body contains three basic organs; roots, stems and leaves. Plant organs consist of several types of tissues that together carry out particular functions.

Plants use a root system to Anchor the plant to the soil Absorb and transport water and minerals Store food Some plants have modified roots to grow larger than necessary in order to store carbohydrates.

The shoot system consists of stems, leaves and adaptations for reproduction. The shoot system is used by plants to absorb the sun’s energy and carbon dioxide from the air. A stem has nodes and internodes. A node is the point at which leaves are attached and internodes are the portions of the stem between the nodes.

Plants typically have two kinds of buds. Terminal buds are at the apex of stems, with developing leaves and a compact series of nodes and internodes. Axillary buds are found in the angles formed by the leaf and the stem. In many plants, the terminal bud produces hormones that inhibit growth of the axillary buds in a phenomenon called apical dominance.

Plant root and shoot systems are interdependent. Plant roots depend on shoots for carbohydrates produced via photosynthesis. Plant shoots depend on roots for water and minerals.

Stems may be modified as stolons, for asexual reproduction, tubers, for storage and asexual reproduction, rhizomes, for storage and asexual reproduction, or cactus stems, for water storage and photosynthesis.

Leaves may be modified for climbing, such as a pea plant tendril, or protection, such as a cactus spine.

Each plant organ (root, stem, or leaf) has three types of tissues. • Dermal tissue provides a protective outer covering. • Vascular tissue provides support and long-distance transport. • Ground tissue composes the bulk of the plant body and is involved in: food production, storage, and support.

Dermal tissues form a layer of tightly packed cells called the epidermis, the first line of defense against damage and infection a waxy layer called the cuticle, which reduces water loss. In a leaf, the epidermis is interrupted by tiny pores called stomata, which allow exchange of CO2 and O2 between the surrounding air and the photosynthetic cells inside the leaf Each stoma is flanked by two guard cells that regulate the opening and closing of the stoma.

Vascular tissue is composed of xylem and phloem and arranged in a vascular cylinder in a root or vascular bundles in stems.

Ground tissues lie between dermal and vascular tissue. Eudicot stem ground tissue is divided into pith and cortex. Leaf ground tissue is called mesophyll.