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Topic 9 - Plant Science
A.S. 9.1 Plant Structure & Growth
IB Biology HL
Domain Eukaryota
Domain Bacteria
Domain Archcaea
425 mya
2 bya
488 mya
385 mya
400 mya
5 Main Groups Plants
• 1) Chlorohyta (green algae):chloroplasts-usually,
unicellular, aquatic environments
• LAND PLANTS:
• 2) Bryophytes (mosses): spores, not vascular, no true
roots, need moisture
• 3) Ferns: Roots, leaves, short stems. Spores on
underside of frond.
• 4) Conifers: Roots, stems, leaves, seeds. Narrow
leaves w/waxy cuticle, seeds produced from ovules on
scales of cones
• 5) Angiosperms (flowering plants): Roots stems,
leaves, seeds. Seeds produces in ovary in flower.
3 Groups Land Plants
Plant Group
Major features
Non-vascular land
plants
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~488 mya
Paleozoic
Ordovician
Seedless vascular
plants
~425 mya
Paleozoic
Silurian
Seeded vascular
plants
~385 mya
Paleozoic
Devonian (Gymn)
Less dependent on water-live on land
No conducting tissue (so need moist environ)
Produce spores (not seeds)
Often grouped together as bryophytes
Usually small and grow close to ground
Include mosses, liverworts, and hornworts
• Well-developed vascular tissue
• Produce spores (underside of frond-no seeds)
• Include horsetails, ferns, club mosses, and whisk ferns
(most extant specimens small—some extinct species
very large)
• Most living plant species are in this group
• Seeds contain an embryo, a supply of nutrients, and a
protective outer coat
• Have extensive vascular tissue and include some of the
world’s largest and oldest organisms
seeds
Vasc
non-vasc
Non-Vascular: Bryophytes ~ 450 mya
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•
•
•
•
•
•
•
•
Simple plants, limited size
Hold loose dirt in place
Live in moist areas
Depend on external water
transport for reproduction:
motile male gamete
No vascular tissue = movement
through osmosis/diffusion
No true roots = have rhizoids like root hairs (absorb water,
anchor plant)
No stems
No leaves = similar structures
but only one cell thick.
Produce spores in a capsule at
end of a stalk
moss
liverwort
Filicinophytes
Vascular tissue—spores on underside
of frond
Vascular-Alternating Life Cycle
Filicinophytes, or Ferns
frond
• Have vascular tissue: can be bigger
– Xylem: H2O + minerals
– Phloem: sap (sugar, AAs, hormones...)
• Live in moist areas
• Have roots, stems and leaves
(fronds)
• Motile male gametes: can occupy
terrestrial environments BUT still
needs water for reproduction
• Spores (no seeds) produced in
sporangia, generally on the
underside of the leaf
• Leaves are curled, and then uncurl
as they mature
young frond
rhizome
roots
http://www.biology87.org/apbio/diversity/PlantLabPicts/s
tatio6.jpg
http://www.biology87.org/apbio/diversity/PlantLabPicts/statio4.jpg
Spermatophytes
(seeded vascular plants)
Synapomorphy--seeds
2 Groups Seeded Plants
~144 mya
Mesoozoic
Cretaceous
(Angioperms)
~385 mya
Paleozoic
Devonian
(Gymnosperms)
ORIGIN OF SEEDS (Progymnosperms) – 385 mya
385 mya
Coniferophytes
Conifer
• Contain a well developed vascular
tissue (big plants!), roots, stems
(woody) and leaves
• Produce male (contain pollen) and
female (contain ovules) cones
• Produce seeds which develop on
the scales of the female cones
• Gametes are not motile: does not
depend on water for reproduction
• Tough, needlelike leaves with thick
cuticles and sunken stomata:
adaptations for dry environments
• NO REAL FLOWERS + NO FRUITS
e.g. pines, spruces, firs,
cypress, yews
Sequoias
National Park in California
Angiospermophytes
Flowering Plants
• Flowering plants with roots, stems and leaves
• Occupy all environments
• Gametes are not motile (does not need water for
reproduction)
• Seeds are produced – develop inside the ovaries in the
flower
• Ovary develops into a fruit which aids in seed dispersal
Why are angiosperms so successful?
• Seed protected in fruit
• Fruit skin and flowers can be different colors, have
different scents, and have different nutritional values
• Can attract dispersers (reds and yellows attract birdsothers bear, primates, and so on
• Pollen easily dispersed by wind, birds, insects including
butterflies
Drawing a flower:
• Female Reproductive Organs: stigma + style + ovary = PISTIL
• Male Reproductive Organs: anther + filament = STAMEN
• Petals: attract animals
• Sepals: protection
Monocotiledonous x Dicotiledonous
• Two types of angiospermophytes
• Cotyledon= seed leaf
• Differences in leaves, arrangement of vascular tissue, root system and
stem composition.
Monocotiledonous x Dicotiledonous
Characteristic
Cotyledons
Leaf
Flowers
Roots
Stem
Mono
1
Parallel veins
Floral organs x 3
No main root
Vascular tissues scattered
Di
2
Netlike veins
Floral organs x4 or x5
Main root present
Vascular tissue in ring
Monocotyledenous Plants
Corn and wheat, etc.
Dicotyledenous Plants
Bean, etc.
9.1.1 Draw and label plan diagrams to show the distribution
of tissues in the stem and leaf of a dicotyledonous plant.
9.1.1 Draw and label plan diagrams to show the distribution
of tissues in the stem and leaf of a dicotyledonous plant.
9.1.1 Tissues in stem of dicotyledonous plant
9.1.1 Tissues in leaf of dicotyledonous plant
9.1.1 Tissues in leaf of dicotyledonous plant
9.1.2 Outline three differences between the
structures of dicotyledonous and
monocotyledonous plants.
From BioNinja.com
Upper Epidermis
•Function: Main function is water conservation (secretes cuticle to create a waxy
outer boundary)
•Distribution: On top of leaves where light intensity and heat are greatest
Palisade Mesophyll
•Function: Main photosynthetic tissue (cells contains many chloroplasts)
•Distribution: Upper half of leaf where light intensity is greatest (upper epidermal
cells are transparent)
Spongy Mesophyll
•Function: Main site of gas exchange (made of loosely packed cells with spaces)
•Distribution: Lower half of leaf, near the stomatal pores (where gases and water
are exchanged with the atmosphere)
Vascular Tissue
•Function: Transport of water (xylem) and the products of photosynthesis
(phloem)
•Distribution: Found in middle of leaf (allowing all cells optimal access)
9.1.4 Identify modifications of roots, stems, and leaves for different
functions: bulbs, stem tubers, storage roots, and tendrils.
A storage organ is a part of a plant specifically modified to store energy (e.g.
carbohydrates) or water
They are usually found underground (better protection from herbivores) and may
result from modifications to roots, stems or leaves:
Storage roots: Modified roots that store water or food (e.g. carrots)
Stem tubers: Horizontal underground stems that store carbohydrates (e.g.
potato)
Bulbs: Modified leaf bases (may be found as underground vertical shoots) that
contain layers called scales (e.g. onion)
Some plants (called succulents) have modified leaves or stems (thickened, fleshy
and wax-covered) to enable water storage (e.g. cacti)
Other plants (e.g. vines) have modifications to their leaf or stem to enable
climbing support and attachment - these are called tendrils
9.1.4 Identify modifications of roots, stems, and
leaves for different functions: bulbs, stem tubers,
storage roots, and tendrils.