General Biology lab Lab 12 & 13 Parts of Plant

Three Basic Plant Organs: 1.Roots 2.Stems 3.Leaves Root system Stem Leaf Shoot system

The stem – is a part of the plant that holds up other structures such as the leaves and flowers. Function of stem Stems support photosynthetic leaves and reproductive structures. Stems supply water and minerals to shoots via the xylem and photosynthate to roots via the phloem.

Component of dicot stem: –Epidermis –Ground tissue (parenchyma, collenchyma, sclerenchymta, cortex, pith), –Vascular tissue (xylem, phloem). Protoxylem vessels: are the smallest vessels, their typical location is towards the pith. Metaxylem vessels: are the larger vessels, typical location is towards the cortex. The Dicotolydonous Stem (Dicots stems)

Fascicular cambium: –is the area between the primary xylem and phloem. It is the vascular cambium found within the vascular bundle. It cells were derived from procambium and maintain their ability to undergo cell division.

outside to center Epidermis: reduce evaporation, gas exchange Cortex: photosynthesis, collenchyma support Vascular Bundles: conduction Pith Vascular Bundle: Phloem Fibers: support Functional Phloem: conduct CH 2 O away from leaf Vascular Cambium: add 2° Xylem and 2° Phloem Xylem: conduct minerals up from soil outside to center

The Monocot stem Component of monocot stem: –Epidermis –Ground tissue (parenchyma, collenchyma, sclerenchymta) –Vascular tissue (xylem & phloem). Random arrangement of the vascular bundles, and its surrounding by sclerenchyma. These vascular bundles are closed bundles with no are of cambium.

PhloemXylem Ground tissue connecting pith to cortex Pith Cortex 1 mm Epidermis Vascular bundle Cross section of stem with vascular bundles forming a ring (typical of eudicots) (a) Key to labels Dermal Ground Vascular Cross section of stem with scattered vascular bundles (typical of monocots) (b) 1 mm Epidermis Vascular bundles Ground tissue In most monocot stems, the vascular bundles are scattered throughout the ground tissue, rather than forming a ring Stems

The Root

–is the organ of a plant that typically lies below the surface of the soil. The root must fulfill two fundamental roles: –absorption of water and nutrients. –anchorage. Further, in many plants, roots function to store food.

The Dicotolydonous root (Dicots roots) An epidermis –surrounds the entire root. The vascular tissue – is in the very center of the root. The ground tissue – surrounding the vascular cylinder is the cortex. The central region of vascular tissue is termed the vascular cylinder.

Note that the innermost layer of the cortex is stained red. This layer is the endodermis which have casparian strips. –The endodermis was derived from the ground meristems and is properly part of the cortex. Xylem fills the very middle of the vascular cylinder. Outside of this cylinder of xylem and phloem, located immediately below the endodermis, is a region of cells called the pericycle. these cells give rise to lateral roots and also important in secondary growth.

The monocotolydonous roots (monocot roots) The roots monocots are organized into a cortex, with primary xylem and primary phloem alternating around central pith. The endodermal cells have casparian strips. A uniseriate partly sclerified pericycle occurs between the endodermis and the outermost vascular elements.

Origin of branch roots Roots don’t have leave, nodes or axillary buds. In roots, branching occurs from the pericycle. Observe the demonstration series of slides on the side bench of lateral branching in salix (willow)

Epidermis Cortex Endodermis Vascular cylinder Pericycle Core of parenchyma cells Xylem Phloem 100 µm Root with xylem and phloem in the center (typical of eudicots) (a) Root with parenchyma in the center (typical of monocots) (b) 100 µm Endodermis Pericycle Xylem Phloem Key to labels Dermal Ground Vascular Plant Growth - Roots

Dicots Monocots Monocots and dicots differ in the arrangement of vessels in the roots and stems Root Stem