Stems and Plant Growth Basics. Shoots vs. Roots Stems are part of the shoot system (stems, leaves,...
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Transcript of Stems and Plant Growth Basics. Shoots vs. Roots Stems are part of the shoot system (stems, leaves,...
Stems and Plant Growth Basics
Shoots vs. Roots
• Stems are part of the shoot system (stems, leaves, flowers)
• The shoot system depends on the roots for water and minerals, and to store excess sugar created by photosynthesis
Anatomy of a Stem
• Node: area where leaf branches off from stem• Internode: area in between nodes• Apical meristem: terminal bud where upward
growth in concentrated• Axillary bud: site of new branches• Petiole: area connected leaf to stem
Anatomy of a Stem
• Leaf scar: area where leaf has fallen from stem
• Terminal bud scar: remnant of previous year’s terminal bud; marks one year of growth
Terminal vs. Axillary Buds
• The growth of young shoots is concentrated at the terminal bud, where cells are dividing rapidly
• The terminal bud is dominant over the axillary buds in young plants, keeping them dormant
• We can prune/pinch plants to influence shape– Trimming terminal bud increases width– Trimming axillary buds increases height
Inside a Stem
• Young stems are made of xylem, phloem, a pith, vascular cambium, and epidermis– Xylem: transports water from roots to leaves– Phloem: transports sugar from leaves to roots– Pith: center of stem; functions in storage– Vascular cambium: layer of cells that makes new
xylem and phloem– Epidermis: protective coating
Inside a Stem• Dicots have a large central pith, with vascular
bundles around the edges (a vascular cylinder)• Monocots have vascular bundles randomly
dispersed throughout the pith
Why do plants grow forever?
• Plants can grow throughout their lives because of meristems
• Meristems are bundles of stem cells that make new cells throughout a plant’s life– Apical meristems: responsible for primary plant
growth (increase in height)– Lateral meristems: responsible for secondary
plant growth (increase in diameter)
Primary Plant Growth
• Apical meristems are located at the tips of roots and stems
• Apical meristems give rise to the epidermis, vascular tissue (transport), and ground tissue (storage)
Secondary Plant Growth
• Secondary growth increases plant diameter• Lateral meristems cause secondary growth– Vascular cambium– Cork cambium
Vascular Cambium
• The vascular cambium is located between layers of xylem and phloem
• The vascular cambium makes secondary xylem and phloem (wood and bark)
Cork Cambium
• The cork cambium makes cork, a tough outer coating that replaces the epidermis on stems and roots
• This is what we think of as ‘bark’, but technically bark includes secondary phloem, the cork cambium, and cork