Chapters 31 & 32: Plant Structure & Reproduction
1. Flowering Plant Structure
2. Plant Reproduction & Development
1. Flowering Plant Structure
“Roots & Shoots” 2 basic parts of flowering plants: shoot system • stems • leaves • flowers, fruits
root system • taproot (dicots) • roots
1 Plant Tissue Types 1) Dermal tissue • outer, protective covering of the plant
Dicot stem Monocot stem Vascular Vascular 2) Vascular bundle bundle Cortex tissue • transport of fluids & Pith
Epidermis Epidermis structural support
Xylem Vascular Phloem cylinder
Key 3) Ground Epidermis Dermal tissue Ground tissue tissue Cortex Vascular tissue • everything Dicot root else!
PHLOEM XYLEM Vascular Tissue High sugar concentration 1 High water pressure sugar 2 Phloem water • transports products of photosynthesis Source cell (sugars) throughout plant from sugar sources to sugar sinks • driven by osmosis, SUGAR Sink SINK increased pressure due cell to more sugar solutes near source 3 sugar
4 Xylem water • transports water & Low sugar concentration Low water pressure minerals “upward” Low water pressure (towards shoots, leaves)
How is water moved “upward”?
Xylem sap Water lost by Mesophyll cells
Air space within leaf transpiration Stoma from leaves Outside air “pulls” water Transpiration Adhesion Cell upward wall Water through xylem molecule to replace what was lost.
Xylem Cohesion, Cohesion and cells by hydrogen Flow of waterFlow of adhesion in the xylem bonding Depends on:
Root hair • cohesion due
Soil particle to H-bonding
Water • adhesion to Water uptake from soil xylem cells
2 Leaf Structure epidermis
palisade mesophyll sheath xylem
spongy mesophyll phloem
guard cells stomata
Epidermis • outer cell layer on both sides of leaf • secrete waxy cuticle to waterproof the leaf Mesophyll (ground tissue of leaf) • loosely packed photosynthetic cells • palisade or spongy arrangement Vascular Bundles • phloem & xylem • surrounding sheath Stomata (singular = “stoma”) • openings for gas exchange, transpiration • regulated by guard cells
Root Function Roots supply the plant with: CO2 • anchorage in the soil • water • mineral nutrients
• oxygen (O2)
• for respiration since O2 plants make ATP just as Minerals we do
• over-watering can H2O suffocate a plant!
3 Importance of Nitrogen Fixation Plants require the element nitrogen in the form of + - ammonium (NH4 ) or nitrate (NO3 ) ions, however they CAN’T “fix” atmospheric nitrogen (N2) into these forms.
ATMOSPHERE
N2
Amino ammonium & nitrate acids, etc.
N2 Nitrogen-fixing ions taken up by roots bacteria NH + H+ 4 Soil + NO – NH3 NH4 3 (nitrate) (ammonium) Nitrifying bacteria Ammonifying bacteria Organic material Root Soil bacteria and some fungi CAN fix nitrogen, thus plants depend on these microbes for useable nitrogen.
Monocots vs Dicots Flowering plants are of 2 basic types:
Seed Leaves Leaf veins Stems Flowers Roots MONOCOTS
One Vascular bundles Floral parts Fibrous cotyledon Main veins usually parallel in complex usually in root system arrangement multiples of three
DICOTS
Vascular bundles Floral parts arranged in ring usually in Two multiples of Taproot cotyledons Main veins usually branched four or five usually present
Monocot vs Dicot Features Cotyledons (embryonic “seed leaves”) • nourish the seedling: monocots have 1, dicots have 2 Roots • dicots have a central taproot, monocots do not Stems • dicots have a vascular structure organized into rings Leaves • monocots have narrow, smooth leaves w/parallel veins • dicots have broader leaves w/branched vein patterns Flowers • monocots – layered flower parts come in groups of 3 • dicots – layered flower parts come in groups of 4 or 5
4 2. Plant Reproduction & Development
Basic Modes of Reproduction Plants reproduce in 2 basic ways:
Asexually: • piece of parent plant gives rise to new plant • involves mitotic cell division only • offspring are genetically identical to parent
Sexually: • fusion of haploid gametes generates offspring • offspring are genetically unique
Life Cycle of Plants (sexual)
• fertilization produces a zygote that develops into a diploid sporophyte
• haploid spores produced by meiosis in flowers grow into multicellular haploid gametophytes, some cells of which are gametes
5 The Plant Sexual Life Cycle The sexual life cycle of plants is unique, occurring by “Alternation of Generations”:
The sporophyte stage (diploid) • the plant is made of diploid cells • produces haploid spores by meiosis in the reproductive structures (e.g., flowers)
The gametophyte stage (haploid)
• grows from haploid spore (via mitosis) • produces gametes (sperm and/or egg) • fertilization then produces a new diploid sporophyte!
Life Cycle in different Plant Phyla
• gametophyte is more s prominent in p or more primitive op hy plant species g te am (2 et n) op • in more hy te advanced (n plant species, ) the sporophyte is much more prominant
The Structure of Flowers
reproductive organ of angiosperms
6 …more on Flower Structure Flowers have 4 main parts: Sepals • outermost structure (encloses flower bud) Petals • usually colored, inside sepals
Stamen (anther & filament) • male reproductive structure • anthers produce male gametophytes (pollen grains)
Carpel (stigma, style & ovary) • female reproductive structure • produces female gametophytes (embryo sacs)
Fertilization in Angiosperms
• pollen grains adhere to the stigma (pollination)
• tube cell in pollen elongates down style to penetrate ovule in ovary
• 2 sperm are released to fertilize the egg & fuse with a special diploid cell in ovule
Seed Production endosperm = nutrients for plant embryo
• zygote develops into embryo, triploid cell forms endosperm • seed coat derived fr. ovule wall encloses embryo, endosperm • fruit develops from ovary wall to aid seed dispersal
7 Seed Dispersal Seeds can be dispersed via fruits by:
Water • floating on water (e.g., coconuts)
Air • lightweight seeds can be transported by the wind (e.g., dandelion, maple)
Animal • edible fruits entice animals to eat them • “hitchhiker” fruits stick to animals
Plant Growth Plant growth occurs in 2 basic ways:
Terminal bud Primary growth • growth in length of roots & shoots • due to special “stem cell” tissue called Axillary buds apical meristem
Secondary growth • growth in width due
Arrows = to lateral meristem direction of growth • occurs in “woody” Root tips perennial plants
o Apical Leaves Primary (1 ) Growth meristem
Vascular cylinder Cortex Root hair Epidermis
Zone of maturation 1o Root Growth
Zone of elongation Axillary bud ×
meristems LM 103
1 o 2 Zone of 1 Shoot cell division Apical Growth meristem region
Key Root Dermal tissue system cap Ground tissue system Vascular tissue system
8 Secondary (2o) Growth Due to lateral meristem tissue which consists of: Vascular Cambium (new phloem & xylem) Cork Cambium (cork replaces the epidermis during 2o growth)
Year 1 Year 1 Year 2 Early Spring Late Summer Late Summer Key Dermal tissue system Ground tissue system Vascular tissue system Shed epidermis
wth wth wth Gro Gro Gro
Primary xylem Epidermis Secondary Cork Vascular xylem Cortex Cork Secondary xylem cambium (wood) cambium Bark (2 years’ growth) Primary phloem Secondary phloem
Secondary Growth in Woody Plants Vascular cambium produces new phloem & xylem ea yr: • spring & summer growth look diff., producing an annual ring Sapwood
Rings
Wood rays Heartwood
Sapwood
Vascular cambium
Secondary phloem Heartwood Bark Cork cambium Cork Heartwood Sapwood • old, dead xylem from • new, functioning xylem previous years from most recent 2o growth
Key Terms for Chapters 31 & 32
• mesophyll, stomata, phloem, xylem • asexual vs sexual, “alternation of generations” • sporophyte, gametophyte • sepal, petal • stamen – anther & filament (pollen, tube cell) • carpel – stigma, style, ovary (ovule, embryo sac) • monocot, dicot
Relevant Review Questions: Ch. 31 – 2-4, 6-11 Ch. 32 – 1, 3
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