Chapter 23

Roots, Stems, and Leaves

I. The main organs of plants are roots, stems, and leaves.

II. All plant organs are made of several types of tissue.

a. Dermal – outer covering of planti. Made of epidermal cells and a thick

waxy covering called cuticleii. Considered the “skin” of the plant

• b. Vascular – transport system that moves water and nutrients throughout the plant

i. Considered the “bloodstream” of the plant1. 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 tissuei. Considered “everything else”

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

IV. Rootsa. 2 types of roots

i. Taproot – one large central root- mostly in dicot

plants- Ex. carrot

ii. Fibrous - many thin, shallow roots- mostly in

monocot plants- Ex: grasses

b. Root functionsi. Absorb water and dissolved nutrientsii. Anchor plants in groundiii. Hold plants upright against wind and

rain

c. Root structuresi. Root hairs – help increase surface area to

absorb more waterii. Root cap – protects apical meristem near

root tip

V. Stemsa. Functions of stems

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

and leaves

b. Primary growthi. Produced by cell divisions in apical meristem of all seed plants

c. Secondary growthi. Occurs in 2 types of tissue

1. Vascular cambium – produces vascular tissue (xylem and phloem) and stem thickness

2. Cork cambium – produces outer covering of stems (bark)

VI. Leavesa. Flat structure of leaf is optimized for absorbing light and carrying out photosynthesis

b. Leaf Tissuesi. Mesophyll – ground tissue that makes up most of the leaf

1. Palisade mesophylla. Located just under epidermisb. Absorbs light for

photosynthesis

2. spongy mesophylla. 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