Plant Structure, Growth and Development

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Plant Structure, Growth, and Development

Introduction to Plants

Kingdom:Plantae

-Cell wall

-Autotroph

-Multicellular

-Lower plants, Gymnosperms, Angiosperms (flowering plants)

--Angiosperms make up ~90% of plants

--Produce seeds within a fruit

--key adaptations: flowers and fruits

Plant Organization:

-organs: roots, stems, leaves

-tissues: dermal, vascular, ground

-cell types: xylem, phloem, parenchyma

Plant Organs:

-shoot system: above ground. Stems and leaves.

-root system: underground (usually). Roots.

Roots:

-anchors plant, absorbs water and minerals, stores sugars and starches

-root hairs – tiny extensions of epidermal cells, increase surface area for water and mineral absorption

-mycorrhizae: fungus + plant root symbiotic relationship

-Fibrous roots: mat of thin roots just below surface. Shallow. Increased surface area. ex: scallion

-taproots: one thick vertical root. Mant lateral (branch) roots. Firmly anchors. Stores food. ex: carrot

-modified roots: prop roots, storage roots, aerial roots, buttress roots

Stems:

-function: display leaves

-termianl bud – growth concentrated at top end of stem

--secretes hormone to prevent growth of axillary buds; growth directed upward, toward light.

-axillary buds – lovated in V between leaf and stem; forms branches (lateral shoots)

--pinching/pruning – removing terminal bud

-modified stems:

--runner or stolin: aspen, strawberries, grass. Grow on surface. For asexual reproduction.

--rhizome: iris, ginger, potato, onion. Grows underground. Store food and DNA for new plant. Tuber = end of rhizome.

--bulb – underground shoot. Onion.

Leaves:

-function: photosynthetic organ

-parts: blade and petiole

modified leaves: tendrils, spines, storage leaves, reproductive leaves, bracts

Plant tissues:

-Dermal Tissue:

--single layer, closely packed cells that cover entire plant.

--protect against water loss and invasion by pathogens (viruses, bacteria)

--cuticle = waxy layer

-Vascular Tissue:

--continuous throughout plant

--transports minerals between roots and shoots – xylem and phloem.

-Ground Tissue:

--anything that isn’t dermal or vascular

--function – storage, photosynthesis, support

--pith: inside vascular tissue

--cortex: outside vascular tissue

Cell Types:

-Xylem = conducts water and minerals up from roots

-dead, tubular, elongated cells

-Phloem = conducts sugar/organic compounds from leaves to other parts of plants

-living cells aid movement of sugar

--2 cell types: sieve tubes, companion cells

Plant Growth:

Types of flowering plants:

-annuals – 1 year life cycle

-biennials – 2 years

-perennials – continuous life cycle for many years

Meristems = perpetually embryonic tissues

-cells divide for plant growth

-apical meristem: growth at tips of roots and buds of shoots; cause primary growth

--primary growth = increase length

-lateral meristem (cambium): growth thickens shoots and roots; secondary growth

Root anatomy:

-zone of maturation – primary growth becomes functionally mature

-zone of elongation – cells elongate, push root tip ahead

-zone of cell division – root apical meristem, new cells produced via mitosis

-root cap – protects meristem as it pushes through soil

Shoot anatomy:

Shoot apical meristem = dome of dividing cells at tip of terminal bud; divide and elongate

Leaf Anatomy:

-epidermis of underside interrupted by stomata (pores), flanked by guard cells (open/close stomata)

-mesophyll: ground tissue between upper/lower epidermis. Palisade mesophyll and spongy mesophyll.

-parenchyma: sites of photosynthesis

Secondary Growth = increases diameter

-involves lateral meristems

-vascular cambium: produces secondary xylem (wood)

-cork cambium: produces tough covering that replaces epidermis

-bark = all tissues outside vascular cambium

remember:

primary growth = up (length)

secondary growth = out (width)