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Topic 7
Plants
I. Structure of the leaf and
adaptations for
photosynthesis
 A.
Algae - large percentage of the
world’s photosynthesis is carried on by
algae in the oceans
 B. Vascular Plants - most of the
photosynthesis occurs in the leaves
– 1. Large surface permits maximum
amount of light absorbed
– 2. Parts of the leaf
Leaf diagram
a.
epidermis - outer layers - protect/prevent
water loss
b. cuticle - waxy coating - prevent water loss
c. stomates - openings for gas exchange
d. guard cells - control the opening and
closing of stomates
e. palisade layer - long cells that contain
many chloroplasts
f. spongy layer - many air spaces with some
chloroplasts
g.
chloroplasts - found in the guard cells,
palisade layer, and spongy layer for
photosynthesis
h. veins - contains xylem (water flow) and
phloem (transport food)

C. adaptations for circulation in plants and
algae
– 1. Roots - specialized structures that hold the
plant in the ground, absorb water and other
nutrients, and conduct materials up through the
plant
 a.
root hairs - increase surface area to absorb water
 b. xylem - carries water
 c. phloem - carries food
– 2. Stems - contain xylem and phloem for
transport - support the leaves
– 3. Transport in the xylem
a.
transpiration pull - as water evaporates
from leaves it pulls more water up through the
plant
b. capillary action - water traveling upward
against gravity in tiny spaces
c. root pressure - pressure built up from
osmosis and active transport
 D.
adaptations for respiration
– 1.
a.
stomates - allow gas exchange
b. lenticels - openings on stems that allow for
gas exchange
c. roots - moist membranes of roots allow
gases to cross the cell membrane
 E.
adaptations for excretion
– 1. Excess carbon dioxide and oxygen
passes out through the stomates,
lenticels and roots
– 2. Excess water is released through
transpiration in the leaves
– 3. Toxic wastes are sealed off and stored
– 4. Nitrogeneous wastes are used again
II. Chemical regulation
in plants
A. Hormones - chemical substance released
 B. chemical control in plants

– 1. Plant hormones - auxins - used in growing
– 2. Tropisms - growth response – due to auxins
 a.
phototropism - bending of stem toward light - dark
side of stem grows more
 b. geotropism - growth towards gravity - roots
 c. hydrotropism - growth towards water
 d. thigmotropism – reacts to touch such as ivy
– 3. cytokinins – stimulate cytokinesis and
cell division
Promote
growth and cell division
Delay senescence (aging) by inhibiting
protein breakdown
Produced in the roots and travel upward
– 4. giberellins – promote stem and leaf
elongation
Work
with auxins to promote cell growth
Induce bolting (rapid growth of a floral stalk)
– 5. absciscic acid – ABA – inhibits growth
Enables
plants to withstand drought
Closes stomates during times of water stress
Promotes seed dormancy
– 6. ethylene – a gas
Promotes
ripening
Facilitates apoptosis (cell death)
Promotes leaf abscission (leaf dies and falls
from the plant)
III. Classification of
Plants
 A.
Bryophytes
– 1. primitive plants that lack vascular tissue
– 2. must live in moist environments because they
have no roots or xylem and must absorb water
by diffusion
– 3. tiny because they lack the lignin-fortified
tissue necessary to support tall plants on land
– 4. example - mosses
 B.
Tracheophytes
– 1. have transport vessels, xylem, and
phloem
– 2. include ancient seedless plants, like
ferns, that reproduce by spores
– 3. include modern plants that reproduce
by seeds
– 4. those with seeds are further divided
into gymnosperms and angiosperms
 C.
gymnosperms
– 1. cone-bearing plants
– 2. have various modifications to help
them survive under dry conditions –
needle-shaped leaves – thick, waxy
cuticle
– 3. examples – cedars, sequoias,
redwoods, pines
 D.
angiosperms
– 1. flowering plants
– 2. also called anthophyta
– 3. most diverse and plentiful of all the
plants
– 4. Divided into monocotyledons
(monocots) and dicotyledons (dicots)
– 5. examples – roses, daises, fruits, nuts,
grains, grasses
 E.







Monocots vs. Dicots
Characteristic
Cotyledons
Vascular bundles
Leaf venation
Floral parts
Roots
Examples
Monocot
1
scattered
parallel
in 3’s
fibrous
wheat, corn
Dicot
2
in a ring
netlike
in 4’s or 5’s
taproots
daisies,
carrots
IV. Strategies that Enabled
Plants to move to land





A. cell walls made of cellulose that lend support to
the plant cell
B. roots and root hairs absorb water and nutrients
from the soil
C. stomates open to exchange photosynthetic
gases and close to limit water loss
D. cutin – waxy coating on leaves – prevents water
loss from the leaves
E. gametangia – protective jacket of cells formed
around gametes and zygotes to prevent them from
drying out



F. Sporopollenin – a tough polymer – found in the
walls of spores and pollen – resistant to all kinds of
environmental damage – protects plants in a harsh
terrestrial environment
G. seeds and pollen have a protective coat that
prevents desiccation – also used for dispersing
offspring
H. reduction of the primitive gametophyte (n)
generation
V. How plants grow
 A.
Plants grow in two ways:
– 1. primary growth – vertical growth
a.
Elongation of the plant down into the soil
and up into the air
b. Apical meristem – dividing cell tissue found
at the buds and tips of roots
c. Three zones of growth in the roots
– 1. apical meristem – zone of cell division –
responsible for making new cells
– 2. zone of elongation
– 3. zone of differentiation – epidermis, ground
tissue, and xylem/phloem
– 2. Secondary growth – lateral growth –
increase in width
meristem – in herbaceous or
nonwoody plants, there is only primary growth
for one season
Woody plants – rings – show each year of
growth
Lateral
VI. Roots
 A.
Structure
– 1. epidermis – covers the entire surface of the root –
increases absorption – root hairs extend out to increase
area
– 2. cortex – consists of parenchyma cells that contain
plastids for the storage of starch and other organic
substances
– 3. stele – vascular cylinder consists of xylem and phloem –
surrounded by the pericycle
– 4. endoderm – surrounds the vascular cylinder – wrapped
with the Casparian strip which is a waxy band – selects
what minerals enter
Cross section of roots –
monocots and dicots
 B.
Types of roots
– 1. taproot – single, large root that gives
rise to lateral branch roots
Taproot
– 2. adventitious roots – roots that arise
above ground
aerial roots – stick up out of the water –
mangrove tree
b. prop roots – grow above ground - corn
a.
Aerial Roots
Prop Roots
fibrous roots – lots of branching
roots off of the stem
 3.
Fibrous Roots
VII. Stems
VIII. Types of Plant
Tissue
dermal tissue – outer protective
covering of plants – usually a single
layer of epidermal cells
 A.
– 1. may have cuticle
– 2. may have trichomes – which are
spikelike projections
– 3. usually don’t have chloroplasts
vascular tissue – transports water
and nutrients
 B.
– 1. xylem – contains tracheids and vessel
elements
– 2. phloem – contains sieve tube elements
and companion cells
 C.
Ground tissue
– 1. parenchyma cells – traditional plant cell
– 2. collenchyma cells – unevenly
thickened cell wall – ex. Strings of celery
– 3. sclerenchyma cells – thick primary and
secondary cell walls – fortified with lignin
for support
IX. Plant Reproduction
Asexual reproduction – clone
themselves or go through vegetative
propagation – examples: grafting,
cuttings, bulbs, and runners
 A.
 B.
Sexual Reproduction in Flowering
Plants
– 1. petals – brightly colored, modified
leaves – attract animals
– 2. sepals – outermost circle of leaves –
green – enclose bud before it opens
– 3. pistils or carpels – female part of the
flower
– 4. ovary – part of pistil – ova are
produced
– 5. ovule – structure inside the ovary
where the ova (egg) is produced
– 6. style – long, thin portion of the pistil
– 7. stigma – sticky top of the style where
pollen lands
– 8. stamen – male part of the flower
– 9. anther – part of the stamen – where
pollen (sperm) is made
– 10. filament – part of the stamen –
supports the anther
 C.
Pollination and fertilization
– 1. pollination – one pollen grain
containing three monoploid nuclei lands
on the sticky stigma of the flower
– 2. the pollen grain absorbs moisture and
germinates or sprouts producing a pollen
tube that travels down the style into the
ovary
– 3. the two sperm nuclei travel down the
pollen tube into the ovary
– 4. inside the ovary, the two sperm nuclei
enter the ovule through the micropyle
– 5. one sperm fertilizes the egg and
becomes the embryo (2n) and the other
sperm fertilizes the two polar bodies and
becomes the triploid (3n) endosperm
which becomes the food for the growing
embryo
– 6. this process is called double
fertilization because two fertilizations
occur
– 7. After fertilization, the ovule becomes
the seed and the ripened ovary becomes
the fruit
– 8. in monocots, food reserves remain in
the endosperm
– 9. in dicots, food reserves of the
endosperm are transported to the
cotyledons
 D.
Seed
– 1. consists of a protective seed coat, an
embryo, and the cotyledon or endosperm
– 2. embryo
hypocotyl – becomes the lower part of the
stem and roots
b. epicotyl – becomes the upper part of the
stem
c. radicle – embryonic root – first organ to
emerge from the germinating seed
a.
 E.
Alternation of generations
– 1. monoploid (n) and diploid (2n)
generations alternate with each other
during the sexual life cycle of plants
– 2. the gametophytes (n) produces
gametes that fuse during fertilization to
make 2n zygotes
– 3. each zygote develops into a
sporophyte (2n) that makes spores (n)