Plant Structure, Growth, and DevelopmentChapter 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