Stems

Stem Structure Stems are one of 2 main structures in vascular plants (the other is the root) Stems are made up of nodes and internodes nodes hold leaves and buds which grow into branches internodes are the spaces between the nodes

Functions of Stems Support for leaves, flowers and fruits (allow leaves to reach sunlight) Transport of fluids between the roots and the shoots in the xylem and phloem Storage of nutrients Production of new living tissue. normal life span of plant cells: one - three years meristems generate new living tissue hint: meristems - stem cells - new growth

Stem Tissues There are 3 main tissues: Tissue Function Dermal Tissue -outer surface of the stem, used to waterproof, protect and control gas exchange Ground Tissue -mainly parenchyma cells that perform photosynthesis, functions as storage and support (sometimes called fundamental tissue) Vascular Tissue -provides long distance transport and structural support

Herbaceous Dicot Stems: stems with primary growth (growth that occurs as a result of cell division at the tips of stems and roots) have these characteristics: pith (ground tissue) in the centre vascular bundles form a distinct ring around outside epidermis and cuticle protect the outside of the stem Usually don’t grow very tall because can’t support much weight

Herbaceous Dicot Stem:

Woody Dicot Stems: have secondary growth that causes stems to thicken instead of elongate vascular cambium cells (a type of meristematic cell) divide to produce secondary xylem to the inside and secondary phloem to the outside. As the stem increases in diameter the cortex and epidermis are eventually destroyed and cork cambium develops producing cork cells Secondary xylem eventually stops transporting materials and becomes structural support and this is what we commonly call wood Video

Woody Dicot Stems:

Tree Rings At the end of each growing season, the vascular cambium stops growing, this produces a growth ring. In the spring, lots of xylem is produced. The cells are larger and the wood is less dense. In the fall, fewer and smaller xylem is produced, and the wood is very dense (this is what we see as a ring) tree rings and climate

Monocot Stems: vascular bundles (screaming faces) are scattered throughout rarely produce secondary growth, therefore seldom woody (exceptions: palm trees and bamboo)

YOUR TASK: Share the pictures with your teacher Using the microscope and monocot/dicot slides: take a picture of: monocot cross-section label the ground, vascular and dermal tissue dicot cross-section monocot vascular bundle label the xylem and phloem dicot vascular bundle Share the pictures with your teacher **make sure that your labels follow the rules you learned in your biological drawing activity