Lecture 19:Plant Structure and Function

Plant structure can be divided into two systems: roots and shoots

The Root System

• Parts under ground

• Used for anchorage

• Used for absorption of water and nutrients

Tap root

Fibrous root

Roots are often covered with root hairs which increase the surface area for

absorptionEpidermal cell

Root hair

Modified roots

The Shoot System

• Stems, leaves, buds

• Nodes are places on the stem where leaves are attached and buds form.

Figure 35.5 Simple versus compound leaves

Figure 35.19 Leaf anatomy

Figure 35.6 Modified leaves: Tendrils, pea plant (top left); spines, cacti (top right); succulent (bottom left); brightly-colored leaves, poinsettia (bottom right)

Figure 35.4 Modified shoots: Stolons, strawberry (top left); rhizomes, iris (top right); tubers, potato (bottom left); bulb, onion (bottom right)

Plant structures are composed of 3 types of tissues

• ground tissue -- bulk of plant body

• vascular tissue -- distribution of water and solutes

• dermal tissue -- covering, protection of plant surface.

Vascular tissue: xylem and phloem

Plant growth occurs at localized regions called meristems

• Meristem cells are undifferentiated and can divide through mitosis

• Continued divisions of meristem cells keeps a plant growing throughout it's life = indeterminate growth.

• apical meristems -- results in increase in length of stems and roots

• lateral meristems -- growth produces thickening of stems and roots

Growth at apical meristems = primary growth• As a stem or root grows,

primary meristems develop behind the growing tip

• These differentiate into the three tissue systems:

• Dermal tissue comes from:

• protoderm --> epidermis (waxy covering in shoots)

• Vascular tissue comes from:

• procambium --> vascular cambium--> primary xylem and phloem

• Ground tissue comes from:

• ground meristem -> ground tissues--> cork cambium

Figure 35.17 The terminal bud and primary growth of a shoot

Growth at lateral meristems: Secondary growth

• In woody plants vascular cambium forms a ring

• each growing season a new layer of xylem is produced which pushes the cambium and all outer tissues further out.

• Old phloem cells are crushed and only a thin strip of newly- formed phloem remains alive.

Figure 35.22 Anatomy of a three-year-old stem

Figure 35.23 Anatomy of a tree trunk

• As the stem expands, it ruptures the epidermis

• Bark is composed of phloem and ground issue cells called cork cells

Tree Girdling

If you hammer a nail into a tree 10 feet above the ground, and wait 20 years, where will the nail be?

10 feet

?

Angiosperms are often divided into the monocots and dicots

Monocots

Dicots