Next Tuesday. Bring Blue Scan sheet Bring #2 pencils Bring erasers if you want to change your mind. Plant Development and Anatomy. Fig. 40.2. Plant Development. Seed: baby plant (embryo) in box (seed coat) with its lunch (endosperm) Some babies finish lunch early
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Next Tuesday • Bring Blue Scan sheet • Bring #2 pencils • Bring erasers if you want to change your mind
Fig. 40.2 Plant Development • Seed: baby plant (embryo) in box (seed coat) with its lunch (endosperm) • Some babies finish lunch early • All that’s left in box (seed coat) is baby (embryo)! • Example, bean seed.
Plant Development • Embryo parts: • Cotyledons: seed leaves. Bean is dicot (2 cotyledons). These contain stored food. • Epicotyl: Located above cotyledons. Will develop into shoot system (stem and leaves) of plant • Radicle: Will develop into root system of plant • Hypocotyl: Below cotyledons. Stem that connects cotyledons to radicle.
Plant Development • Epicotyl and radicle each have apical meristem • Meristem: tissue (collection of cells) capable of rapid cell division • Epicotyl: shoot apical meristem (SAM) • Radicle: root apical meristem (RAM).
Plant Development • Bean seed germination • Hypocotyl pulls cotyledons/epicotyl from soil • Root and shoot systems start to grow. Fig. 40-15a
Plant Development • Primary growth occurs due to activity of meristems (SAM and RAM) • These produce specialized dividing cells called primary meristems • Primary meristems develop into primary tissues.
Plant Cells • Focus on cell walls: form plant skeleton (supports body) • Primary wall: cellulose, penetrated by plasmodesmata • Middle lamella: “cement” between adjacent walls.
Plant Cells primary • Secondary cell wall: laid down inside primary wall • Thick, contains lignin (strong, rot resistant) • Note: In our lab slides, secondary wall will stain __RED_____ whereas primary wall will stain __GREEN______. secondary
Plant Cells • Secondary cell wall: laid down inside primary wall • Thick, contains lignin (strong, rot resistant) • Opening in secondary wall called pit • Note pits still have primary wall present (pit membrane: pit not a completely open space between cells).
Tissues and cell types • Tissue: Group of cells organized as a functional unit • Tissues made of cell types • Simple tissues contain 1 cell type • Complex tissues contain >1 cell type.
Tissues and cell types • 3 main types of tissues: • 1) ground (yellow) • 2) dermal (white) • 3) vascular (purple).
Ground Tissues: Parenchyma • Usually rounded cells, primary wall • May have chloroplasts, large storage vacuoles • May be used as “packing tissue” to fill space. Purple structures are chloroplasts single cell
Ground Tissues: Collenchyma • Contains collenchyma cells • Elongate cell, thick primary walls, especially thick at corners, alive at maturity • Used as strengthening tissue in young plant parts.
Ground Tissues: Sclerenchyma • Simple tissue: contains 1 cell type • But two types of cells possible: • 1) fiber: elongate, thick secondary wall, often dead at maturity • Strengthening cell/tissue.
Ground Tissues: Sclerenchyma 1 cell • Simple tissue: contains 1 cell type • But two types of cells possible: • 2) sclereid: Not elongated (mostly branched or rounded), thick secondary wall, often dead at maturity • Used to strengthen tissues, protect areas (hard endocarp of drupe is sclereids).
Dermal Tissues • Epidermis: Surface covering of all plant body • Typical epidermal cells: flattened, no chloroplasts, primary wall, thick outer walls • In shoot/stem, outer walls have cuticle (waxy layer) on outside. Thick cuticle (orange layer)
Epidermis • Special cell types: guard cell • In pairs on stems/leaves • Have chloroplasts, primary wall, open and close pore of stoma (plural: stomata) • Control water loss, CO2 uptake.
Epidermis • Special cell types: guard cell • In pairs on stems/leaves • Have chloroplasts, primary wall, open and close pore of stoma (plural: stomata) • Control water loss, CO2 uptake.
Epidermis • Special cell types: trichome cells • On stems/leaves • Have primary wall, elongate.
Epidermis • Special cell types: trichome cells • Function to slow water loss • Function to reflect light to keep leaf cool
Epidermis stinging nettle trichome • Special cell types: trichome cells • Function: defense against herbivores. sticky trichomes
Epidermis • Special cell types: root hairs • On roots • No chloroplasts, little/no cuticle, hair is extension of epidermal cell wall • Increases root surface to take up water/minerals • Ephemeral, hair withers after few days.
Vascular Tissues • Complex tissues (<1 cell type) • Phloem (conducts sugars) • Xylem (conducts water and minerals).
Vascular Tissues • Phloem (conducts sugars) • 4 cell types possible: • 1) Sieve tube elements: conducting cells • Elongate, primary wall, no nucleus • Ends connect by sieve plate (large plasmodesmata). sieve plates face view sieve plates side view
Vascular Tissues • 2) Companion cell: smaller cells with nuclei, direct action of sieve tube element.
Vascular Tissues • Xylem (conducts water and minerals) • 4 cell types possible: • 1) vessel element: elongate, wide, thick secondary wall, holes (perforations) at ends of cell, dead at maturity • Functions as sections of “pipe” to form vessel, which conducts water and minerals • Found almost exclusively in flowering plant xylem.
Vascular Tissues • Xylem (conducts water and minerals) • 4 cell types possible: • 2) tracheid: elongate, wide, thick secondary wall, many pits in wall • Functions to conduct water and minerals also. These must pass through pits to reach next cell (pits have primary wall in center and are not open holes) • Found in xylem of both flowering plants and gymnosperms.
Vascular Tissues • Xylem (conducts water and minerals) • 4 cell types possible: • 3) fibers: covered earlier. Note they have secondary wall and are usually dead at maturity • 4) parenchyma: covered earlier. Note they have primary walls and are alive.
Plant Organs • 2) Special stem modifications • Storage (tuber). Also asexual reproduction • Explore world (runner). Also asexual reproduction.
Plant Organs • 2) Special stem modifications • Underground stems (bulb, rhizome). Bulb (A) and corm (B)
Plant Organs • 3) leaf • major site of photosynthesis • stalk is petiole, flattened part is blade • axillary bud: small meristem (contains a SAM) at base of leaf: can grow to make branch.
Plant Organs • 3) leaf • note stipules: pairs of appendages at base of petiole of some leaves.
Plant Organs • 3) leaf • Venation: netted for dicots, parallel for monocots.
