Anna Sherman
Bio PLANTS Notes
Plant Diversity I: How Plants Colonized Land (Chapter 29)
I.
Land plants evolved from green algae
a. Plants and algae are BOTH…
i. Multicellular
ii. Eukaryotic
iii. photosynthetic autotrophs.
iv. Have cellulose and chloroplasts
b. CHAROPHYTES share these traits with land plants….
i. Rosette-shaped cellulose-making complexes
1. Protein arrays make cellulose microfibrils of the cell wall
ii. Peroxisome Enzymes
1. Both peroxisomes have enzymes that help minimize the
loss of organic products as a result of photorespiration
iii. Flagellated Sperm
iv. Phragmoplast
1. Phragmoplast (group of microtubules) forms between the
daughter nuclei of a dividing cell and gives rise to a cell
plate and new cell wall.
c. Adaptations for the Move to Land
i. Sporopollenin prevents exposed zygotes from drying out in
charophyte algae.
ii. Accumulation of these drying-out-resistant traits probably gave
rise to the first permanent land plants
iii. Alternation of Generations
1. The multicellular sporophyte
iv. Walled Spores Produced in Sporangia
1. Plant spores are haploid, grow into gametophytes by
mitosis
2. Sporopollenin makes the walls of spores tough and resistant
and enables them to be dispersed thru dry air
3. Sporophyte has organs called sporangia that produce
spores. Diploid cells called sporocytes undergo meiosis and
generate haploid spores. These multi cellular sporangia that
produce spores with sporopollenin walls are key
adaptations.
v. Multicellular Gametangia
1. Gametes are created in gametangia. The female ones are
archegonia, the male one is antheridia. They produce eggs
and sperm, respectively. Each egg is fertilized within the
archegonium where the zygote becomes and embryo.
vi. Apical Meristems
1. Plants can’t move, but their roots can elongate to get
resources. This growth is sustained by the activity of apical
meristems, regions of cell division at the tips of shoots and
roots. Cells produced by meristems differentiate into the
outer epidermis. They also generate leaves.
II.
vii. Cuticle
1. Polyester and wax polymers covering the epidermis
2. Waterproofing
3. Protection from microbial attacks
viii. Mycorrhizae
1. Early plants that lacked true roots and leaves developed
mutualistic relatinships with fungi
2. These fungi’s extensive mycelia allow them to absorb
nutrients well and transfer them to their plant
ix. Secondary Compounds
1. Alkaloids, Terpenes, Tannins, Phenolics and flavonoids.
These are all defense chemicals against herbivores and
parasites that are made on secondary metabolic pathways –
secondary to the ones that make carbs, lipids, and proteins.
d. The Origin and Diversification of Plants
i. Vascular Tissue
1. Cells joined into tubes that transport water and nutrients
throughout the plant body
2. Most plants have complex vascular systems and are
therefore called vascular plants
3. Non-vascular plants are informally called byrophytes
4. Seedless vascular plants (a grade)
a. Lycophytes (club mosses)
b. Pterophytes (ferns)
5. Seed Plants
a. Seed – embryo packaged with a supply of nutrients
inside a protective coat
i. Gymnosperms – Seeds not enclosed in
chambers (conifers)
ii. Angiosperms – all flowering plants. Seeds
develop in ovaries.
Mosses and other nonvascular plants have life cycles dominated by
gametophytes
a. Liverworts, hornworts, and mosses (Hepatophyta, Anthocerophyta,
Bryophyta)
b. Bryophyte Gametophytes
i. Gametophytes are the dominant stage of their life cycles
1. Longer living and larger than sporophytes
ii. Protonema
1. Germinating moss spores produce this mass of green,
branched, one celled filaments.
2. Large surface area encourages absorption ofo nutrients
3. Sprouts buds, which has an apical meristem and generates a
gamete-producing structure: a gametophore.
iii. Tend to be ground-hugging because they cannot support a full
plant
iv. No vascular tissue, so no long distance nutrient transport
v. Rhizoids
1. Anchor gametophytes
2. Long, tubular single cells or filaments of cells
3. They are not roots because they are not composed of tissues
and have no special conduction cells
4. Do not play a primary role in nutrient absorption
vi. Gametangia
1. Mature gametophytes form them
2. They produce gametes and are covered by protective tissue
3. Archegonia
a. Female gametangium
b. Creates and nurtures egg
4. Antheridia
a. Male gametophytes
b. Produce flagellated sperm
vii. Fertilization
1. Sperm swims through water toward eggs
2. Enters archegonium due to chemical attractants
3. Eggs are not released but grow and develop in the
archegonia
4. The sporophyte develops and is dependant on the female
gametophyte (the archegonium)
5. *The requirement of water for fertilization means that
bryophytes tend to be found in moist habitats
viii. Some mosses reproduce asexually with brood bodies, which detach
from parent plant and grow to be genetically identical.
c. Bryophyte Sporophytes
i. Dependant on gametophytes
ii. Tiny – larger sporophytes evolved later with vascular plants
iii. Structure:
1. Foot – absorbs nutrients
2. Seta – conducts materials to the sporangium, elongates to
elevate sporangium
3. Sporangium/Capsule – uses nutrients to produce spores by
meiosis
a. Upper part has a ring of interlocking toothlike
structures – the peristome – which closes in moist
conditions and opens in dry ones, allowing spores to
be released gradually on gusts of wind
4. Hornworts and mosses have stomata, which are also found
in vascular plants.
III.
a. These are pores that support photosynthesis by
allowing the exchange of CO2 and O@ between
outside and inside. They can close to minimize
water loss.
d. The Ecological and Economic Importance of Mosses
i. Can colonize bare, sandy soil because they help retain nitrogen
ii. Can survive loss of body water and rehydrate and thus can live in
very harsh environments
iii. Sphagnum, or peat moss, forms extensive deposits of partially
decayed organic mater called peat.
1. Boggy regions dominated by it are called peatlands
2. Does not decay readily due to phenolic compounds and low
temperature, pH, and oxygen level of peatlands
3. Can preserve corpses for thousands of years
4. Source of fuel
5. Soil conditioner
6. A lot of organic carbon is stored in peat and helps stabilize
atmospheric CO2.
Ferns and other seedless vascular plants were the first plants to grow tall
a. Origins and Traits of Vascular Plants
i. Ferns still have flagellated sperm and must live in moist
environments
ii. First vascular plants
1. had sporophytes that were not dependent on gametophytes
for nutrition
2. They were taller than mosses and branched, which allowed
for complex bodies with multiple sporangia
3. Lacked roots
iii. Living vascular plants
1. Life cycles with dominant sporophytes
2. transport in vascular tissues (xylem and phloem)
3. well developed roots and leaves
a. spore bearing leaves called sporophylls
b. Life Cycles with Dominant Sporophytes
i. Sporophyte/Diploid generation is larger and more complex
ii. Gametophytes become more reduced with the evolution of
vascular plants and then seed plants
c. Transport in Xylem and Phloem
i. Xylem conducts most of the water and minerals
1. Includes tracheids, tube shaped cells that carry water and
minerals up from roots
2. Vascular plants may be referred to as tracheophytes
3. Water conducting cells are lignified, their walls are
strengthened by the phenolic polymer lignin.
ii. Phloem has cells arranged into tubes that distribute sugars, amino
acids, and other organic products
d.
e.
f.
g.
iii. Lignified vascular tissues
1. Permit plants to grow tall
2. Stems are stronger to provide support and enable transport
3. Tall plants can outcompete other plants for light – tallness
is a trait favored by natural selection
Evolution of Roots
i. Roots are organs that absorb water and nutrients from the soil
ii. Anchor vascular plants and allow shoots to grow taller
iii. Evidence points to convergent evolution
Evolution of Leaves
i. Leaves increase the surface area of the plant body
ii. Are the primary photosynthetic organs of vascular plants
iii. Microphylls
1. Only and All lycophytes have these
2. Small, spiny leaves supported by a single strand of vascular
tissue
3. May have originated from sporangia located on the sides of
stems
iv. Megaphylls
1. All other vascular plants have them
2. Highly branched vascular system
3. Large, support greater photosynthetic productivity than
microphylls due to their network of veins
4. May have evolved from branches lying close together on a
stem. One branch may have overtopped and flattened the
rest to make a leaf.
Sporophylls and Spore Variation
i. Sporophylls
1. modified leaves that bear sporangia
2. Vary greatly in structure
3. Fern sporophylls produce clusters of sporangia – sori – on
the undersides of sporophylls
4. Lycophytes and gymnosperms have groups of sporophylls
form cone-like structures called strobili
ii. Seedless vascular plants are homosporous – one type of
sporangium that produces one type of spore which typically
becomes a bisexual gametophyte
iii. Heterosporous species have two types of sporangia and two types
of spores. All seed plants and some seedless vascular plants are
like this.
1. Megasporangia on megasporophylls produce megaspores –
these develop into female gametophytes
2. Microsporangia on microsporophylls produce microspores
– these develop into male gametophytes
Classificatino of Seedless Vascular Plants
i. Two clades of seedless vascular plants
1. Phylum Lycophyta (Lycophytes)
a. Club mosses, spike mosses, quillworts
b. Most ancient group of vascular plants
c. Thrived in Carboniferous period in both small and
large forms
2. Phylum Pterophyta (Pterophytes)
a. Ferns, horntails, whisk ferns
b. Closer related to seed plants than to lycophytes
h. Significance of Seedless Vascular Plants
i. With the evolution of vascular tissue, the rateof photosynthesis on
the Earth accelerated, causing CO2 to be removed from the
atmosphere much faster than before.
ii. This caused global cooling and glacier formation
iii. These plants eventually became peat then coal
1. The plants that at first contributed to global cooling now
contribute to global warming.