Plant Parts - Function and Structure

Plants continue to grow as long as they live because they contain tissue called meristem that continually divides and generates new cells

Primary growth – elongation of the plant down into the soil and up into the air.

Secondary growth – increase in girth

Apical meristem found at the tips of the root and in the buds of short is the source of primary growth.

Lateral meristem – provides secondary growth.

Roots

Function
-    absorb nutrients from the soil,
-    anchor the plant
-    store food


Structure

Epidermis – covers the entire surface of the root and is modified for absorption
Root hairs – cytoplasmic projections that increase absorption
Cortex – consists of parenchymal cells that contain many plastids for the storage of starch and other substances
Stele – consists of vascular tissue surrounded by one or more layers of tissue called the pericycle, from which lateral roots arise.
Endodermis – surrounds the vascular cylinder or the stele. Composed of cells wrapped with the Casparian strip, a continuous band of suberin, a waxy material impervious to water and dissolved minerals. Selects what minerals enter the stele and the plant body.

Three zones of cells at different stages of primary growth
Zone of cell division / Apical meristem – meristem cells that are actively dividing
    - responsible for producing new cells that grow down into the soil.
Zone of elongation – Cells elongate and are responsible for pushing the root cap downward deeper into the soil
Zone of differentiation – cells undergo specialization into three primary meristems that give rise to three tissue systems in the plant:
1.    protoderm – becomes the epidermins
2.    ground meristem – becomes the cortex (for storage)
3.    procambium – becomes the primary xylem and phloem

Types of Roots
Taproot – single, large root that give rise to lateral branch roots
- common in dicots
- maybe modified for storage

Fibrous root system – holds the plant firmly in place
- common in monocots like grasses

Stem

Leaf