Parts of a Seed • Mature embryo: was formed by mitosis root tip, shoot tip, cotyledon(s) • Seed coat: formed from maternal flower tissue, encloses embryo and endosperm to protect seed. • Endosperm: surround embryo and provides nourishment • Cotyledon: not true leaves (also called seed leaves) but may be capable of photosynthesis. Two major groups of plants monocots and dicots
Seed Germination • Germination - the sprouting of seeds when conditions are favorable • Seed increases metabolic rate, water absorbed restores turgor pressure • Seed coat fractures and embryo emerges • Many seeds have interesting adaptations. What examples did you read about?
Plant Structure • Shoot tip - location of apical meristem • Root tip- location of apical meristem • Node - point where leave attach • Internode- space between nodes
Plant Meristems • Apical meristems - in herbaceous in woody plants • Responsible for primary growth, growth in length of roots and shoots • Lateral meristems - in woody plants • Responsible for secondary growth increasing the width (girth) of a plant in regions of plant where primary growth has stopped • Contains two layers- the vascular cambium and cork cambium
Primary Growth in Roots • What is happening at each root zone? • As the apical meristem divides, some daughter cells remain part of the meristem. Some daughter cells specialize into other tissues • The location of the cells often determines how they will specialize because plant cells are locked in position by cell walls (cells on the outside become dermal tissue etc.) • Primary growth in roots produces new dermal, ground and vascular tissue.
Primary Growth in Shoots • Apical meristem located at tip of terminal bud • Axillary buds develop from meristem tissue left by apical meristem • Elongation of shoot caused by elongation of cells of slightly older internodes
Secondary growth • Occurs in the lateral meristems of woody plants • The lateral meristem includes two layers of cells that form two columns around the plant. The vascular cambium and the cork cambium
Vascular Cambium • The vascular cambium produces secondary layers of xylem and phloem (recall that primary growth made the primary xylem and phloem) • As the lateral meristem divides, some daughter cells remain part of the meristem. Some daughter cells specialize into secondary xylem and secondary phloem • Xylem cells are made inside the vascular cambium and phloem cells are found outside
Vascular Cambium • The secondary xylem is concentrated in the center of the plant in multiple layer • The old secondary phloem layers are incorporated into the cork cambium as the tree increases in width
Secondary Growth • Cork Cambium - produces cork cells on the outside of the cambium • As these cells mature they produce suberin and water proof layer that protects the plant • Layers of cork are sloughed off as the tree grows in girth