Plant Structure, Growth, and Development Chapter 35

Remember levels of organization… Organism  Organ Systems  Organs  Tissues  Cells

Monocots vs. Dicots Before we start, we will be looking at 2 different groups of angiosperms: Monocots Dicots

Plant Parts (organs/organ systems) There are 3 main parts to plants: Roots Stems Leaves

Root System Vascular tissue in the center, surrounded by the endodermis Cortex surrounds vascular cylinder (starch storage) Outer covering is epidermis

Root Structure and Function Roots aide in anchoring the plant in place Most water absorption takes place towards tips of roots Root tips have highest number of root hairs Root hairs increase surface area for water absorption

Types of Roots Taproot – One large central root with branches Fibrous – Mat of thin roots Adventitious – Above ground roots

Stems A stem is defined as an alternating system of nodes and internodes Nodes – The points at which leaves are attached Internodes – The stem segments between nodes Between leaves and the stem, there is an axillary bud Axillary Bud – A structure that has the potential to form a vegetative branch The tip of every stem has a terminal bud Terminal Bud – Embryonic tissue at the tip of the stem made of developing leaves, nodes, and internodes

Leaves Leaves are the main photosynthetic organs of plants Leaves consist of a flattened blade and a stalk Petiole – joins the leaf to the node

Leaf Structure Epidermis is composed of tightly interlocked cells covered by a waxy cuticle Stomata – Pores in epidermis flanked by guard cells that control gas exchange Mesophyll – The are ground tissue between upper and lower epidermis Mainly composed of photosynthetic perenchyma Vascular tissue is arranged similarly to stem Branches off vascular bundles are known as veins

Plant Tissues Plant organs are composed of 3 types of tissues: Dermal Vascular Ground

Dermal Tissue AKA – Epidermis Single layer of tightly packed cells Roles of the Dermal Tissue: Protection Water retention (Cuticle) Water absorption (Root hairs)

Vascular Tissue Two types of vascular tissue: Xylem – Conveys water and dissolved minerals upwards, from roots to shoots Phloem – Transports food made in leaves to the roots and other non-photosynthetic parts

Vascular Tissue: Xylem Tracheids and vessel elements are the water conducting elements of xylem They are elongated cells that are dead at functional maturity When they die, the cell walls thicken leaving tubes for water to flow through There are pits in the cell wall that aid in the transport of water (More to come on transport in plants in the next few days)

Vascular Tissue: Phloem Phloem is formed by chains of cells called sieve-tube members They are alive when functioning Vital in the transport of sugars and other organic compounds

Vascular Tissue: Ground Tissue Divided into 2 types: Pith – Ground tissue internal to the vascular tissue Cortex – Ground tissue external to the vascular tissue

Types of Cells Parenchyma – typical plant cells ‘Non-Specialized’ cells Photosynthesis and various other processes occur in these cells Collenchyma – Cells that aide in the support of young plant shoots Have thickened cell walls, but no secondary walls (they do not inhibit growth) Sclerenchyma – Support cell shoots also Have thickened secondary walls, prevent growth once formed and hardened Ex – Hemp fibers, and nut shells are composed of these cells

Plant Growth Apical Meristems – Embryonic tissues at the tips of roots and buds of shoot that produce lateral growth Primary Growth – Elongation of plant (roots grow down, shoots grow up) In roots, there is a root cap which protects the meristems Lateral Meristems – Cylinders of dividing cells along the length of roots and shoots Secondary Growth – Progressive thickening of the roots and shoots