Chapter 23 Roots, Stems, and Leaves

The main organs of plants are roots, stems, and leaves. All plant organs are made of several types of tissue. a. Dermal – outer covering of plant i. Made of epidermal cells and a thick waxy covering called cuticle ii. Considered the “skin” of the plant

b. Vascular – transport system that moves water and nutrients throughout the plant i. Considered the “bloodstream” of the plant 1. Xylem – made of tracheids and vessel elements - moves water - tracheids are pierced with openings called pits that allow water to move from tracheid to tracheid

2. Phloem – made of connected sieve tube cells and companion cells moves sugars and foods

C. Ground - tissue that lies between dermal tissue and vascular tissue i. Considered “everything else”

Meristems – clusters of tissue that continue growing throughout the plant’s life a. Meristems are the only plant tissue that produces cells by mitosis b. Apical meristem – located at the tip of each growing shoot and root

Roots a. 2 types of roots i. Taproot – one large central root - mostly in dicot plants - Ex. carrot

- mostly in monocot plants - Ex: grasses ii. Fibrous - many thin, shallow roots - mostly in monocot plants - Ex: grasses

Root functions Absorb water and dissolved nutrients Anchor plants in ground Hold plants upright against wind and rain

Root structures i. Root hairs – help increase surface area to absorb more water ii. Root cap – protects apical meristem near root tip

Stems Functions of stems i. Produce leaves, branches, and flowers ii. Hold leaves up to sunlight iii. Transports substances between roots and leaves

Primary growth i. Produced by cell divisions in apical meristem of all seed plants

Secondary growth Occurs in 2 types of tissue Vascular cambium – produces vascular tissue (xylem and phloem) and stem thickness Cork cambium – produces outer covering of stems (bark)

Leaves a. Flat structure of leaf is optimized for absorbing light and carrying out photosynthesis

Leaf Tissues i. Mesophyll – ground tissue that makes up most of the leaf 1. Palisade mesophyll a. Located just under epidermis b. Absorbs light for photosynthesis

2. spongy mesophyll a. Contains airspaces that connect with stomata and guard cells in epidermis b. Stoma (stomata) - openings in leaf that allow gas exchange - regulates/prevents water loss for plant

c. Guard cells - epidermal cells found on undersides of leaves - control opening and closing of stomata due to water pressure