Plant Organs – Roots & Stems 3 things to know STRUCTURE - anatomy FUNCTION – what is the primary purpose MODIFICATION – other possible functions (aside from the primary purpose)

Roots/Purpose Plant organs that anchor a plant Absorb water, dissolved minerals Contain vascular tissue

Basic types of modified roots Fibrous roots – many small branching roots Tap roots – single, thick structures store food (carrots) Prop roots – support a plant (corn) Aerial roots – allow plants to attach to trees, rocks, etc. (spanish moss) Pneumatophores – ‘breathing’ roots in swamps (mangroves)

Examples

Mangrove swamps

Root structure Layers of the root 1. Root hairs – increase surface area Absorb water, oxygen and dissolved minerals 2. Cortex – transports water and minerals parenchyma cells

Root structure 3. endodermis – layer of cells with waterproof cell walls to form a seal controls the flow of water 4. pericycle – new roots arise as offshoots of older roots

Root growth Roots grow two ways 1. apical meristem -protective root cap 2. vascular cambium New cells increase root diameter

Stems Purpose - Transport food and water & act as support Xylem moves water up from roots Phloem carries food (sugar) as well as hormones and viruses Sink – any portion of the plant that stores food Translocation – movement of sugar in the phloem

Stems – Basic Types Herbaceous (soft) and can photosynthesize (green) Woody – like tree trunks contain vascular and cork cambium

Stems/Function Specialized stems store food Allow plant to survive drought, cold and grow Examples Corms – short, thickened, underground stem surrounded by leaf scales Tuber – swollen, underground stem that has buds Rhizomes – underground stems

Corm

Stem internal structure Vascular tissue arrangement determined by plant type Woody stems Xylem becomes wood Phloem and cork make up bark

Growth of the stem Apical meristems –at the tip Secondary growth – increase in diameter via the vascular cambium or lateral meristem Meristems along the stem give rise to leaves and branches