Chapter 35
Cells make up tissues and tissues make up organs. Plants have 3 main organs: Roots Stems Leaves
Used to anchor vascular plants Absorbs minerals and water Stores organic nutrients The main vertical root is the taproot, which has branches called lateral roots Root tips do most absorption Tiny root hairs increase the surface area of the root
Stems have nodes (where leaves attach) and internodes (in between leaves) Shoots form from axillary buds that grow from where leaves attach to stems Modified stems include: rhizomes (ginger or garlic), tubers (potatoes), bulbs (onions)
Leaves are where sunlight is absorbed by chlorophyll for photosynthesis Consist of a blade and a stalk (petiole) Veins are the vascular tissue (xylem and phloem) Modified leaves include tendrils, spines, bracts (poinsettia), and cacti storage leaves.
Stomata are openings in leaves for gas exchange Guard cells control whether stomata are open or closed Mesophyll is the tissue where photosynthesis occurs Xylem and phloem are in the mesophyll, and are enclosed by bundle sheath cells
Dermal: outer protective covering; includes cuticle, a waxy coating that prevents water loss Vascular: xylem and phloem Ground: used for storage, called pith or cortex
Parenchyma Cells: “typical plant cells” Collenchyma Cells: support young parts of plant shoots Sclerenchyma Cells: Mature cells, functionally dead, used for support
Meristems generate cells for new organs Plants grow throughout their lives, but do die: Annuals: complete their life cycles in a year or less; grains, beans, wildflowers Biennials: live 2 years; beets, carrots Perennials: live many years: trees, shrubs, grasses
Roots and shoots grow from the tips (apical meristems) The root tip is covered by the root cap (protection) Zone of cell division: where mitosis occurs Zone of elongation: root cells elongate Zone of maturation: cells differentiate and become mature
Tissues called vascular cambium and cork cambium produces secondary xylem and phloem which turns into wood Rings of trees build up as trees age. The center is called heartwood; outer layers are called sapwood. Bark is used for protection and has phloem in it