Honors biology plants
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What is a Plant?
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Multicelled
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Eukaryote
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Autotrophic
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Cell wall
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Where did plants come from?
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Most evidence points to land plants evolving from algae.
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Invading the Land
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Cyanobacteria were probably the first to spread into and up freshwater streams
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Later, green algae and fungi made the journey together
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Every plant is descended from species of green algae
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Adaptations to Land
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Root systems
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Shoot systems
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Vascular tissues
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Waxy cuticle
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Alternation of Generations
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Haploid (1n) generation: Gametophytes
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Diploid (2n) generation: Sporophyte
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Bryophytes
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Small, nonvascular, nonwooody
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Gametophyte dominates life cycle; has leaflike, stemlike, and rootlike parts
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Usually live in wet habitats
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Flagellated sperm require water to reach eggs
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Types of Bryophytes
Mosses (most common)
Liverworts (simplest)
Hornworts
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Pteridophyte
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Like bryophytes
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Live in wet, humid places
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Require water for fertilization
Unlike bryophytes
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Sporophyte is free-living and has vascular tissues
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Traits of
Seed-Bearing Plants
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Pollen grains
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Develop into male gametophytes
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Can be transported without water
Seeds
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Embryo sporophyte inside nutritive tissues and a protective coat
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Can withstand hostile conditions
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Gymnosperms
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Plants with “naked seeds”
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Seeds don’t form inside an ovary
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Four groups
Conifers
Cycads
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Ginkgos
Gnetophytes
Pine Cones
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Woody scales of a “pine cone” are the parts where megaspores formed and developed into
female gametophytes
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Male cones, where microspores and pollen are produced, are not woody
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Angiosperms
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Flowering plants
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Dominant land plants (260,000 species)
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Ovules and (after fertilization) seeds are enclosed in an ovary
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Three main groups: magnoliids, monocots, and eudicots
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Fruit
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Simple fruit: Single fruit from a single ovary (apple, cherry, soybean)
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Aggregate fruit: Single flower with multiple carples (blackberry)
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Multiple fruit: Multiple flowers fuse together to form one fruit (pineapple)
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Monocots & Dicots
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Cotyledons: Embryonic leaves
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Monocots: 1 embryonic leaf
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Dicots: 2 embryonic leaves
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Monocots
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One cotyledon
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Parallel veins in leaves
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Vascular bundles
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Flower parts in 3’s
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Fibrous roots
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Dicots
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2 cotyledons
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Veins usually branched
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Vascular bundles in rings
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Flower parts in 4 or 5’s
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Taproot
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Sexual Life Cycle of Flowering Plants
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Sepal: usually green, look like leaves
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Stamen: Male reproductive organs
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Anther: Tip of stamen were pollen is
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Carpel: Female reproductive organ
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Stigma: Receiving surface for pollen
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Ovary: Base of carpel that stores ovule
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Ovule: Contains developing egg
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Double Fertilization
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Distinctive feature of angiosperms
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Male gametocyte delivers two sperm to an ovule
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One fertilizes egg; other fertilizes a cell that gives rise to endosperm
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Seed Dispersal
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Wind blown
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Animal carried (external)
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Animal carried (internal)
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Seed Development
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Endosperm: Nutrient-rich multicellular mass that nourishes embryo
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Seed coat: Ovule’s coat that has lost water that encloses embryo and endosperm
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Seed dormancy: A period when the embryo stops developing until environmental conditions are
right
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Seed Germination
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Asexual Reproduction
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Vegetative reproduction: Fragmentation of plant parts growing into new plants
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Also known as vegetative propagation
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Bulbs
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Shoots and Roots
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Shoots
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Produce food by photosynthesis
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Carry out reproductive functions
Roots
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Anchor the plant
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Penetrate the soil and absorb water and dissolved minerals
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Store food
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Angiosperm
Body Plan
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Ground tissue system
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Vascular tissue system
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Dermal tissue system
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Complex Tissues
Composed of a mix of cell types
Xylem
Phloem
Epidermis
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Simple Tissues
Made up of only one
type of cell
Parenchyma
Collenchyma
Sclerenchyma
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Parenchyma: A Simple Tissue
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Most of a plant’s soft primary growth
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Pliable, thin walled, many sided cells
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Cells remain alive at maturity and retain capacity to divide
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Mesophyll is a type that contains chloroplasts
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Collenchyma: A Simple Tissue
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Specialized for support for primary tissues
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Makes stems strong but pliable
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Cells are elongated
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Walls thickened with pectin
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Alive at maturity
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Sclerenchyma: A Simple Tissue
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Supports mature plant parts
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Protects many seeds
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Thick, lignified walls
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Dead at maturity
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Two types:
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Fibers: Long, tapered cells
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Sclereids: Stubbier cells
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Meristems
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Regions where cell divisions produce plant growth
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Apical meristems
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Lengthen stems and roots
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Responsible for primary growth
Lateral meristems
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Increase width of stems
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Responsible for secondary growth
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Mesophyll:
Photosynthetic Tissue
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A type of parenchyma tissue
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Cells have chloroplasts
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Two layers in dicots
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Palisade mesophyll
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Spongy mesophyll
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Acquisition of Nutrients
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Plants take in CO2 through the leaves and water and Minerals (inorganic ions) through the roots.
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Nitrogen, phosphorus, and magnesium
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Root Hairs
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Extensions from the root epidermis
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Greatly increase the surface area available for absorption
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Transpiration
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Transpiration: The pulling force from water loss through the leaves
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Root pressure: Water enters the roots through osmosis and pushes the xylem sap up a few
meters.
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Cohesion tension: The sticking together of water molecules to each other and to the cellulose
molecules of the xylem
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Stomata
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The cells around the stomata
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Guard cells can close or open depending on the temperature
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They control the amount of water loss through the leaves and the amount of CO2 entering
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Carnivorous Plants
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Capture animals to supplement their nutrient intake
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Venus flytrap lures insects with sugary bait; closes on victim
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Cobra lily lures insects down a one-way passage
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Epiphyte & Parasites
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Epiphytes: Live on other plants but do not take nutrients from host plant (Spanish moss)
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Parasites: Live on other plants and do take nutrients form host plant (mistletoe)
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Plant Hormones
Auxin
Cytokinins
Gibberellins
Abscisic acid
Ethylene
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Plant Hormones
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Auxins: Stimulate stem elongation, branching, apical dominance
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Gibberellins: Promote seed and bud germination, stem elongation, leaf growth, apical root
growth
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Abscisic acid: Inhibits growth, closes stomata during water loss, helps maintain dormancy
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Tropism
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Tropism: Growth response caused by a stimulus
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Phototropism: Response towards light
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Gravitropism: Response to gravity