Plants
Plant Diversity
• About 280,000 species of plants have been
identified
• By total mass, plants are the dominant
organisms on Earth
• Common features include:
– multicellular
– eukaryotic
– cell walls made of cellulose
• Most are autotrophic (photosynthetic); a few
are parasitic
Plant Groups
Classifying Plants
(video clip 5:26)
• Nonvascular – no
system of tubes to
transport nutrients,
water
– Examples = mosses
(bryophytes)
• Vascular – have
tubes inside for
transport
Types of Vascular Plants
• Seedless – have spores;
eg. Ferns
• Gymnosperms – “naked
seed;” cone-bearing
Vascular Plants (cont’d)
• Angiosperms –
“enclosed seed;”
fruit-bearing
– Monocots – one
seed leaf; flower
parts in sets of 3;
parallel veins on
leaves
– Dicots – two seed
leaves; flower parts
in sets of 2, 4, or 5;
netted / branching
veins on leaves
Plant Tissues
Three Types of Plant Tissues
1. Dermal tissue – protective
outer layer; also functions in
gas exchange and
absorbing minerals
–
–
epidermis in nonwoody
plants; coated with a waxy
cuticle to reduce water loss
cork in woody plants;
contains a waterproof
chemical (no cuticle)
Plant Tissues, cont’d
2. Ground tissue – makes up
inside of most plants, esp.
nonwoody plants; provides
structure and support;
other functions depend on
location in plant
–
–
in leaf – photosynthesis
in stem and root – storage
of water, sugar, starch
Plant Tissues, cont’d
3. Vascular tissue – transports substances through
plant
–
–
Xylem – conduct water and minerals from roots, through
stems, to leaves
Phloem – conduct sugar and nutrients from leaves
throughout body
Roots (video clip – 1:43)
• absorb water & minerals
– must get oxygen from soil b/c
roots don’t photosynthesize –
this is why overwatered plants
can “drown” and die
• consist of:
– vascular tissue (xylem,
phloem)
– cortex (surrounding ground
tissue)
– dermal tissue (root hairs, root
cap)
Types of Roots
•
•
•
taproot – large, central
root; eg. carrot
fibrous roots – highly
branched, w/ many roots
all the same size
adventitious roots –
grow from aboveground
stems or leaves to
extract water or oxygen
from air; eg. orchids
Stems
(video clip 3:16)
• support leaves
• contain vascular tissue
• other specialized functions include:
– water storage; eg. cactus
– sugar / starch storage; eg. onion, white potato
Nonwoody/Herbaceous Stems
• xylem and phloem arranged in vascular
bundles, surrounded by ground tissue
– monocots – x & p scattered throughout
– dicots – x & p arranged in ring; ground tissue
outside ring = cortex, inside ring = pith
Woody Stems
• innermost cylinder
(wood) is xylem;
exterior to this is a
cylinder of phloem
covered by cork
(phloem + cork = bark)
– heartwood –
nonfunctioning xylem
in center of mature
woody stems
– sapwood – functioning
xylem around
heartwood
Leaf – Major Structures
(video clip 2:52)
• blade – flat part of leaf
• petiole – stalk
connecting blade to
stem
• cuticle – waxy coating
• veins – contain x & p
Leaf – Major Structures, cont’d
•
mesophyll – ground tissue in
leaves; full of chloroplasts; 2
layers
–
–
•
palisade layer – upper layer of
close, columnar cells
spongy layer – bottom layer or
loose, spherical cells
stomata – in epidermis; opening
surrounded by two guard cells;
connects air spaces in spongy
layer to outside air
Adapted/Modified Leaves
•
•
•
•
•
large, broad – for moist, shady
environments; eg. philodendron
needles – for cold, windy environments;
eg. pine
w/ fleshy petioles - for food and water
storage; eg. celery
spines – for protection; eg. cactus
tendrils – for climbing; eg. peas
Plant Reproduction
• May be asexual
– Pro: faster than sexual reprodn
– Con: offspring genetically identical to parent
• May be sexual
– specifics of process vary between major plant
groups
Plant Life Cycle Terminology
• sporophyte – 2n phase; produces spores in
sporangium via meiosis
• spore – n reproductive cell; develops into
gametophyte
• gametophyte – n phase; produces haploid
gametes via mitosis; eggs produced in
archegonium, sperm produced in antheridium
• gamete – n cells that fuse (fertilization) and give
rise to 2n zygote (which develops into
sporophyte)
Reproduction in Nonvascular Plants
• gametophytes are
dominant
• sporophytes grow
from, and remain
attached to,
gametophytes
• a film of water is
needed for sperm to
swim to nearby
archegonia to fertilize
eggs
• animation
Reproduction in
Seedless
Vascular Plants
• sporophytes
are dominant
• sporophytes
grow from, and
then destroy,
gametophyte
• animation
Reproduction in Seed Plants
• sporophyte dominant
• gametophytes only visible under
microscope
• male gametophyte = pollen grains, which
fertilize the female gametophyte in the
ovule
• zygote then develops into embryo
• embryo and surrounding tissues becomes
the seed
• animation