AP Biology Unit 6 Part 2
Plant Diversity, Form & Function
What is a Plant?
• Eukaryotic– All plant phyla including algae
• Multicellular– Non-vascular & vascular plants
• Cell walls made of Cellulose– Non-vascular & vascular plants
• Photoautotrophic– Non-vascular & vascular plants
Plant Phyla
NONVASCULAR EXTANT SPECIESBryophyta (Mosses) 10,000Hepatophyta (Liverworts) 6,500Anthocerotophyta (Hornworts) 100
VASCULAR SEEDLESSPsilophyta (Wiskferns) 10 – 13Lycophyta (Club Mosses) 1,000Sphenophyta (Horsetails) 15Pterophyta (Ferns) 12,000
VASCULAR SEED PLANTSConiferophyta (Conifers) 550Cycadophyta (Cycads) 100Ginkgophyta (Ginkgo) 1Gnetophyta (Gnetae) 70Anthophyta (Flowering Plants) 235,000
The Transition to Terrestrial Life• The first plants were algae and these still thrive in
a range of aquatic habitats today
• Aquatic environment is predictable (stable). Why venture onto land? Selection pressure may have been competition!
• Selective pressures on pioneer land plants – Desiccation - the plants would dry out – Water for reproduction - even if there was sufficient
water for survival they would need free water for fusion of gametes
– Support - buoyancy supports the body. These plants would now be splattered on the mud
– Water for spore dispersal - to colonize new terrestrial habitats spores would have to be released in air not water
2 Trends in Life Cycles
• Trend 1: Alternation of Generations– Life cycle unique to plants– Sporophyte = plant body form that produces
haploid spores by meiosis.– Spores divide by mitosis to form gametophyte.– Gametophyte = plant body form that produces
sperm & egg cells. – Sperm & egg cells unite to restore the diploid
sporophyte.
Plant Phyla
• Non-Vascular Plants - Bryophytes– No conducting (vascular)tissues• Must live near water or in High humidity• Cannot support large, tall structures
– Sperm rely on water to reach egg cell– No true roots, stems or leaves– Gametophyte dominant (seen year-round)– Sporophyte ephemeral (seen periodically)
Summary of Bryophytes1. Bryophytes
– Did not evolve into the vascular plants – but they probably were the earliest land plants, evolved
from green algal ancestors. – well-adapted to moist habitats.
2. Similarities to vascular plants– multicellular sex organs, (gametes enclosed by a sterile
jacket of cells)– Have supporting tissues (parenchyma)– retain the zygote within the female sex organ for
development – have cutin (a cuticle) on the plant and spores
3. Differences from vascular plants – no lignin (usually)– small, low-lying, (generally)– Depend on free standing water for reproduction– no true roots, only filamentous rhizoids– dominant generation is the gametophyte; sporophyte is
parasitic on the gametophyte.
2 Trends in Life Cycles
• Trend 2: Development of Seeds– Seeds surround the developing embryo and
provide nourishment during development.
– Seedless plants’ embryos are completely dependent on the gametophyte for support & protection during development.
Seedless Vascular Plants
• Development of Vascular Tissue– Provide a nutrient transport system• Xylem & Phloem Cells
– Allow for taller & more advanced structures
• No seeds, so water still imperative for keeping embryo from drying out.
• Sperm still rely on water for transport.
Seed Plants
• Seeds are found with one of two reproductive structures:– Cones: Seeds attached to surface of cone– Fruits: Seeds enclosed inside a fruit
Gymnosperms
• Produce cones• Gametophyte is retained in the
sporophyll• Sperm travels by wind, water, etc.
(POLLEN)• Animals can eat exposed seeds!
Angiosperms
• Produce Fruits– Means of dispersing seeds by animals!– Animals eat the aromatic & nutritious fruits and
excrete/pick out the hard seeds.– Seeds are dispersed far distances… evolutionary
advantage and one reason why Angiosperms are the most dominant on the planet!
Angiosperms
• Produce Flowers– Means of attracting pollinators!– Animals receive nutritious nectar when visiting
flowers, but pick up pollen on their skin/fur. – Pollen is transferred almost assuredly to similar
plant… cross pollination. Evolutionary advantage due to hybridization, increased variation.
– Second reason why Angiosperms are so successful.
Angiosperms
Angiosperms
Plant Morphology
• 3 main organs– Roots Stems Leaves
• 4 Tissue types in each organ– Dermal– Vascular– Ground– Meristem (roots & stems
only)
Dermal Tissue
• 1-2 layers of epidermal cells • Waxy cuticle forms waterproof covering– Thickness varies by species
• Functions in water balance & protection
Vascular Tissue
• Form a transport network through plant body• Xylem & Phloem cells in various arrangements– Plant organ - Plant species/phyla
• Collectively called a Stele
Xylem
• Tracheids (narrow)– Support
• Vessel Elements (wide)– Water & minerals– Perforated– Unidirectional flow– TACT
TACT
• Transpiration: Evaporation from leaves driven by the sun.
• Adhesion: Hydrogen bonding!• Cohesion: Hydrogen bonding!• Tension: Water droplets in leaf tissues pull
water from area of high concentration to low concentration (roots to leaves).
Phloem
• Transport of organic nutrients (Translocation)– Sucrose – Hormones– Amino Acids
• Multidirectional– Pressure Flow Hypothesis
• Sieve Tube Elements• Companion Cells
Pressure (Mass) Flow Hypothesis
• Sugar actively transported from SOURCE to phloem .
• Water from Xylem enters phloem by osmosis.
• Pressure builds, so solutions move to lower pressure areas
• Sugars are actively transported to the SINK.
Ground Tissue
• All the cells between dermal tissue and vascular tissue-Photosynthesis - Storage - Support
• Parenchyma: The “average cells” with chloroplasts.• Collenchyma: Have very thick cell walls. Give plants
extra support.• Sclerenchyma: have thick cell walls and sclerids. Give
extra support.
Sclerenchyma
Meristem Tissue
• Tissue specializing in division• Apical Meristems (primary growth)– Shoot growth: Upwards (usually)– Root growth: Downwards (usually)
• Lateral Meristems (secondary growth)– Increases width– Not all plants have lateral meristems• Herbaceous Vs. Wood plants
Primary Growth
• Definition: Elongation of the primary plant body (root & shoot)
• Purpose: Lengthen the roots & stems.– Roots can reach water & minerals more effectively– Leaves can attain sunlight more effectively.
Primary Growth• Apical meristems
elongate the shoot upwards
• Actively dividing regions• Axillary meristems
elongate branches
Primary Growth
• Apical meristems elongate the roots down into the soil.
Primary Growth
• Lateral roots grow outwards from the pericycle.
• Increased anchorage & absorption.
Secondary Growth
Secondary Growth
Secondary Growth
Secondary Growth
Secondary Growth
Roots
• Function: Anchorage & water/mineral absorption.
• Nutrients needed by plants1. Nitrogen 2. Phosphorous3. Potassium 4. Magnesium5. Calcium
Root Structure
Root Growth
Stems
• Function in nutrient transport, leaf production & facilitating the acquisition of sunlight for leaves.
• Nodes: Point of leaf attachment• Internodes: Area in between two nodes
Stems
Stems
• Monocots– Vascular tissue spread
throughout stem
• Eudicots• Vascular tissue in a ring
towards outer edge
Leaves
• Function: Photosynthesis, water conservation
• Parts– Blade: The scientific
name for a leaf– Petiole: Attaches a
leaf to a stem
Leaves
• Simple Leaf– Blade not divided into
more than one piece
• Compound Leaf– Blade divided into more
than one piece.
Leaves
• Outer covering called a cuticle• Outer tissue layer: Epidermis (Dermal
tissue)• Middle tissue layers: Palisade mesophyll
cells are very close together. Spongy mesophyll cells are spread out. (Both cell types make up Ground tissue)
Leaves
• Transport tissue: Xylem & Phloem (Vascular tissue)
• Stomata: Openings in the leaf surface that let materials in and out.
• Guard Cells: Cells outside stomata that can open and close (like doors).
Leaves
Plant Response
• Hormones: Chemical signals produced in response to a stimuli. Transported to area in which response is needed
• Tropisms: Any growth response that results in curvatures of whole plant organs toward or away from stimuli.
• Positive = towards Negative = away
Plant Response
• Phototropism
• Gravitropism
• Thigmotropism
• Light
• Gravity
• Touch
Plant Response
Plant Nutrition
Plant Nutrition
Plant Nutrition
• Nitrogen is a major nutritional requirement
Plant Nutrition
• Adaptations for Nutrient Acquisition
– Bacterial Symbiotes– Fungal Symbiotes– Epiphyte Plant Species– Parasitic Plant Species– Carnivorous Plant Species
