Primary Growth and Secondary Growth The Growth of Plants Primary Growth and Secondary Growth
Primary Growth Secondary Growth
Primary Growth Plants grow continuously because they have meristem cells Undifferentiated cells that retain the ability to undergo Mitosis and hence produce new cells
Apical Meristem
Primary Growth due to Apical Meristems Plants have 2 apical meristems: at the tips of the root & at the tips of the buds What is the purpose of Primary Growth? A process called Primary Growth produces the new cells that allow a plant to grow in length!
Meristem cells Meristem cells make 3 types of tissues: Vascular Tissue Provides support Transports water, nutrients (Xylem) Transports photosynthetic products (Phloem) Ground Tissue Bulk of plants body Responsible for photosynthesis Epidermal Tissue The “skin”, covering entire plant protection
Dermal, Ground & Vascular Tissue
Secondary Growth Increases the width Purpose: Increase of vascular tissue Structural support Secondary Growth produces wood
Secondary Growth Has a ring of meristem cells: Vascular cambium Produces Xylem & Phloem tubules New cells that develop on the outside of the vascular cambium turn into Phloem New cells that develop on the inside of the cambium vascular turn into Xylem
Secondary Growth
The Structure of a Tree Trunk
3 main parts … Heartwood Sapwood Bark Dead Provides structural support Xylem tissue Bark Inner bark: Phloem Outer bark:
The Structure of a Tree Trunk Rays radiate laterally across the Xylem… Rays move water & nutrients laterally across the stem
Let’s draw the structures of a tree trunk … Heartwood Vascular cambium Bark Xylem Phloem Rays
Growth Rings … Natural Phenomenon: The vascular cambium stops the growth during a portion of the year No growth = dormancy occurs during the winter in cold climates Growth begins again during the spring season
Growth Rings .. 1 growth ring = 1 year Wider rings, good rainy years Smaller, darker band Larger, lighter band Wider rings, good rainy years Narrow rings, cold, dry years