Jaime Crosby, CHS Plant Organs: Roots and Stems Roots: arise from the seed first in the embryo stage and grow downward into the soil Function: to absorb water and minerals from soil and distribute it to the rest of the plant for nourishment; anchor

2 Main types of roots: Fibrous root Close to surface, spread to absorb water quickly Grasses and trees

Tap root One deep, growing root that goes deep into the soil to absorb water from deeper Carrot Trees have a combo of both

A third, less common type is called adventitious roots—develop along stems or leaves and go directly into the ground Plants may have Up to 15 million Roots to total 644 Km 400 miles!

Root Hairs Cover roots to increase surface area and thus absorption Up to 14 billion per plant, live 2 days to 3 weeks and then are replaced

4 Zones or Regions of roots Root cap: thimble shaped mass of cells at the tip that lubricate and prevent damage as root grows Region of cell division: Makes root cap. Contains Apical meristem and thus is where mitosis and growth occur. Also contains procambium, which makes epidermis, xylem and phloem

Region of elongation Cells made in the zone of division elongate and become rectangular Vacuoles develop

Region of maturation Cells develop into various tissues like root hairs, cuticle (waxy coating) Cortex for food storage Endodermis (inner boundary in which xylem and phloem are located) Xylem: carries water up from roots Phloem: carries food down from leaves

Casperian strips: fuses endodermis to waterproof central cylinder Pericycle: where lateral roots form

Woody plants also contain cork cambium which produces bark

Specialized roots Mycorrhizae: mutualism between roots and a fungus which absorbs phosphorous for the plant Root nodules: on the roots of legumes (peas on beans), contain nodules which “fix” nitrogen from ammonia into N 2 for the plant

Relevance of Roots Prevent soil erosion Beets, radishes, carrots, Yams, sweet potatoes, Spices (licorice, root beer) Read chapter 7, answer questions On page 122: #2, 6, 7, 8

Plant organs: Stems Function of stems To hold up leaves to sunlight To conduct substances between roots and leaves

Four tissues in stems Parenchyma (Pith) Vascular tissue: xylem and phloem in veins Cambium: “makes new cells”: vascular and cork Cork: Bark

Parenchyma or Pith Located throughout the stem, used for storage

Vascular tissue Continuous tubes from roots through stems to leaves Monocots (monkey faces) vs. Dicots scatteredin a ring

Woody Dicots Xylem forms tree rings Size of rings indicates weather conditions Old xylem near center of tree: heartwood New xylem: currently transports water, called sapwood Phloem: always only one, Just inside bark, carries sugars

Cork Cambium Produces cork tissue, the outer bark of trees Outermost layer is dead

Modified Stems: store food during dormancy to be used in emergencies Rhizomes: Thick, creeping stems just below the surface. Examples: Ferns, Iris Tubers: Swollen, underground stems filled with starch Eyes are lateral buds that grow new stems Example: potato

Bulbs: Small, underground stems surrounded by thick leaves which store food Example: tulip Corms: Like bulbs, with thinner leaves and food stored in the stem itself Example: Crocus

Specific parts of stems Node: Where each leaf attaches Internode: In between nodes Apical Meristem Axillary Buds: bud where leaf attaches Roots and Shoots

Properties of water that help it be drawn up a stem Cohesion Capillarity Osmosis