Plant Structures

1. Plant Structures Chapter 31

2. Life Span • Annuals – herbaceous (nonwoody) plants that live 1 year only • Biennials – take 2 years for life cycle • Perennials – can be herbaceous or woody but live longer than 2 years • Deciduous – shed leaves before winter • Evergreen – some leaves are always present

3. Plant Tissues • Three main tissue systems each of which extends throughout the plant and consists of 2 or more kinds of cells • Ground tissue – photosynthesis, storage and support • Vascular tissue – conduction of water, dissolved nutrients and sugars • Dermal tissue – covering for plant body • Tissue systems are further arranged into organs: roots, stems, leaves, flowers

4. Ground Tissue • Three cell types distinguished by their cell wall structures • Parenchyma – living, thin primary cell walls; storage, secretion, photosynthesis • Collenchyma – living, unevenly thickened primary cell walls; elastic support • Sclerenchyma – often dead at maturity, thick secondary cell walls; support and strength

6. Vascular Tissue • Two complex tissues: xylem and phloem • Xylem – conducts water and dissolved nutrients • Tracheids – conduct water; provide support • Vessel elements – wider than tracheid; conduct water; provide support • Phloem – conducts food and provides support • Sieve tube elements – conduct dissolved sugar • Companion cells – helps move sugar in and out of phloem

8. Dermal Tissue • Herbaceous plants – a single layer called the epidermis • Woody plants – continuous growth of new tissues, covered by a layer of periderm (bark) • Epidermal cells - protection • Guard cells – open and close stomata • Trichome – hairy outgrowths; protection • Cork cells – reduces water loss; protection from invading organisms

10. Plant Meristems • Specific areas of the plant’s body where growth occurs • Cells in these areas divide by mitosis and do not differentiate • Plants can grow throughout their life span • Two kinds of growth: • Primary – increase in stem and root length • Secondary – increase in girth

11. Apical meristems • Primary growth occurs here • Tips of roots and shoots

12. Lateral Meristems • Secondary growth occurs here – only in woody plants • Vascular cambium – between the wood and bark – adds cells to wood and inner bark • Cork cambium – located in the outer bark and produce cork cells and parenchyma cells