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PLANTS
Chapters 23-26
Evolution of PlantsAll Plants…• multicellular, eukaryotic, autotrophic
Angiosperms
Monocots vs. Dicots• named for the numberof cotyledons present on the embryo of the plant
+ monocots- orchids, corn, lilies, grasses
+ dicots- roses, beans, sunflowers, oaks
Alternation of GenerationsSporophyte (diploid)• produces haploid spores via meiosis
Gametophyte (haploid)• produce haploidgametes via mitosis
Fertilization• joins two gametes toform a zygote
Plant MorphologyMorphology (body form)
- shoot system + stems, leaves, flowers- root system + taproot, lateral roots
• vascular tissues + transport materials between roots and shoots
- xylem/phloem
Plant Anatomy Anatomy (internal structure)• division of labor + cells differ in structure and function
- parenchyma, collenchyma, sclerenchyma (below)
ParenchymaSt: “typical” plant cellsFu: perform most metabolic functions
CollenchymaSt: thick wallsFu: provide support but allow growthin young parts of plants
SclerenchymaSt: hardened secondary walls (LIGNIN)Fu: specialized for support; dead
Plant cell types• Xylem • Phloem
WATER-CONDUCTING CELLS OF THE XYLEM
Vessel Tracheids
Tracheids and vessels
Vesselelement
Tracheids
SUGAR-CONDUCTING CELLS OF THE PHLOEM
Companion cell
Sieve-tubemember
Sieve-tube members:longitudinal view
Sieveplate
Nucleus
CytoplasmCompanioncell
Water- and Food-conducting CellsXylem (water)
• dead at functional maturityPhloem (food)• alive at functional maturity• sieve-tube cells- arranged end to end with sieve plates &Companion cells
Plant TissuesThree Tissue Systems• dermal tissue + epidermis (skin)
- single layer of cells that covers entire body- waxy cuticle/root hairs
• vascular tissue + xylem and phloem
- transport and support• ground tissue + mostly parenchyma
- filler tissue- photosynthesis, storage, support
Plant GrowthMeristems• embryonic tissues located at regions of growth
- apical meristems (primary growth- length) + located at tips of roots and shoots- lateral meristems (secondary growth- girth)
Roots• A root
– Anchors the plant– Absorbs minerals and water– Stores organic nutrients– Taproots: vertical– Lateral roots: horizontal branches– Fibrous root system in monocots (e.g. grass)
Figure 35.3
Modified Roots• Many plants have modified roots
(a) Prop roots (b) Storage roots(c) “Strangling” aerial
roots
(d) Buttress roots (e) Pneumatophores
(a) Prop roots (b) Storage roots
Modified Stems
Rhizomes(d)
Tubers (c)Bulbs
Stolons
(a)
Storage leaves
Stem
Root Node
Rhizome
Root
Buds• An axillary bud
– Forms a lateral shoot• A terminal bud
– Causes elongation of a young shoot
Gardening tip:Removing the terminal bud stimulates growth of axillary buds (e.g. makes plants bushier)
The leafIs the main photosynthetic organ of most vascular plants
Modified Leaves
Tendrils
Spines
Storage leaves
Bracts
Reproductive leaves. The leaves of some succulents produce adventitious plantlets, which fall off the leaf and take root in the soil.
Leaf AnatomyEpidermal Tissue• upper/lower epidermis• guard cells (stomata)
Ground Tissue• mesophyll +palisade/spongy parenchyma
Vascular Tissue• veins + xylem and phloem
The Vascular Cambium and Secondary Vascular Tissue
• The vascular cambium– Is a cylinder of meristematic cells one cell thick– Develops from parenchyma cells
Secondary Growth
• As a tree or woody shrub ages– The older layers of secondary xylem, the
heartwood, no longer transport water and minerals
• The outer layers, known as sapwood– Still transport materials through the xylem
PLANT REPRODUCTION
Plant ReproductionSporophyte (diploid)• produces haploid spores via meiosis
Gametophyte (haploid)• produce haploidgametes via mitosis
Fertilization• joins two gametes toform a zygote
Double FertilizationDouble Fertilization• pollen grain lands on stigma + pollen tube grows toward ovule + 2 sperm discharged down the tube
- egg and one of the sperm produce zygote
- 2 polar nuclei and sperm cell produce endosperm
+ ovule becomes the seed coat + ovary becomes the fruit
Seed Structure and Development
Asexual Reproduction in Plants: Vegetative Propagation
• Budding and Grafting: smaller stems from one plant are attached to another plant• Taking cuttings: pieces
of one plant are used to grow another• Stems can be modified:• Runners: horizontal
stems aboveground• Rhizome: horizontal
stems belowground• Tuber: swollen
underground stem
Plant nutrition
Plant NutritionWhat does a plant need to survive?
Soil Bacteria and Nitrogen Availability• Nitrogen-fixing bacteria convert atmospheric N2
– plants absorb ammonium (NH4+), nitrate (NO3
-)
Atmosphere
N2
Soil
N2 N2
Nitrogen-fixingbacteria
Organicmaterial (humus)
NH3
(ammonia)
NH4+
(ammonium)
H+
(From soil)
NO3–
(nitrate)Nitrifyingbacteria
Denitrifyingbacteria
Root
NH4+
Soil
Atmosphere
Nitrate and nitrogenous
organiccompoundsexported in
xylem toshoot system
Ammonifyingbacteria
Nutritional AdaptationsSymbiotic Relationships• Mycorrhizae + symbiotic associations of fungi and roots
- mutualistic relationship: fungus receives food from plant and plant receives increased surface area for root absorption
Unusual nutritional adaptations
Plant Transport
MineralsH2O CO2
O2
CO2 O2
H2O Sugar
Light
• A variety of physical processes– Are involved in the different types of transport
Sugars are produced byphotosynthesis in the leaves.
5
Sugars are transported viaphloem to other parts of the plant.6
Through stomata, leaves take in CO2 and expel O2.
4
Transpiration, the loss of waterfrom leaves, pulls xylem sap upward.
3
Water and minerals aretransported upward in the xylem.
2
Roots absorb waterand mineralsfrom the soil.
1 Roots exchange gases with the soil, taking in O2 and discharging CO2 in cellular respiration
7
• Water and minerals ascend from roots to shoots through the xylem
• Plants lose an enormous amount of water through transpiration, the loss of water vapor from leaves
• The transpired water must be replaced by water transported up from the roots
Control of Transpiration • Water enters guard cells and causes cells to swell, opening
stomata.• Water leaves guard cell and they shrink, closing stomata
TranslocationIs the transport of organic nutrients in the plant
Phloem sapIs an aqueous solution that is mostly sucroseTravels from a sugar source to a sugar sink
Translocation through Phloem
A sugar sourceIs a plant organ that is a net producer of sugar, such as mature leaves
A sugar sinkIs an organ that is a net consumer or storer of sugar, such as a tuber or bulb
Sugar Source & Sink
HOW DO PLANTS RESPOND TO THE ENVIRONMENT?
Write down as many ways you can think of in your lab notebook.
Tropisms
• Growth toward or away from a stimulus
• Gravitropism (Gravity)• Phototropism (Light)• Thigmotropism (Touch)
Plant hormones help coordinate growth, development, and responses to stimuli
• Hormones– Are chemical signals that coordinate the different parts of
an organism
Photoperiod, the relative lengths of night and day+ Is the environmental stimulus plants use most often to detect the time of year and when to flower