BI302: Plant Biology - Exam 3

protoderm

The outermost primary meristem, which gives rise to the epidermis of roots and shoots.

Procambium

matures to form the vascular tissue

Ground Meristem

matures to form the ground tissue

auxin

growth hormone used for cell elongation associated with gravitropism and phototropism; apical dominance

apical dominance

Concentration of growth at the tip of a plant shoot, where a terminal bud partially inhibits axillary bud growth.

How to get seedless fruit?

remove seed and add auxin

Gibberellins

promote stem and leaf elongation (hormone)

Cytokinins

Plant hormones that stimulate cell division in root and shoot meristems and cytokinesis

apical meristem

Embryonic plant tissue in the tips of roots and in the buds of shoots that supplies cells for the plant to grow in length.

subapical meristem

Region that produces new cells a few micrometers behind an active shoot or apical meristem.

primary tissues are produced by the apical meristem

primary growth and tissue formation that results from apical meristem activity

Secondary growth

Growth produced by lateral meristems, which thickens the roots and shoots of woody plants.

Secondary tissues

derived from lateral meristems called cambia

Vascular cambium

produces secondary xylem and phloem (wood)

Cork cambium

produces bark tissues that replace epidermis in stem and root

Through more 400 million years of history of plant evolution, woody plants only evolved ______ times

4-6

Where is the oldest tissues of a tree found?

At the pith and furthest from the vascular cambium

Wood rays

group of cells that radially across the stem

Uniseriate rays

one line of cells

Multiseriate rays

multiple lines of cells

Cross section

cut in half (through the center of the pith)

Radial section

longitudinal cuts along a stem or root radius (through the center of the pith)

Tangential section

longitudinal cuts that does not go through the center of the pith

Fusiform initials

divides periclinally (and longitudinally) occassionally divide anticlinally (and longitudinally).

Periclinal cell division

produces one secondary cell (xylem or phloem) and one cambial cell

Anticlinal cell division produces

two cambial cells (expands the cambium laterally)

Ray initials divide

periclinally, similar to fusiform inintials (but they are short and cuboidal parenchyma)

Wood cells include:

secondary xylem, rays, fibers, xylem parenchyma, laticifers, resin and gum duct epithelial cells

laticifers

Ducts found mostly in phloem that have latex-secreting cells

Hard wood

tough with many fibers, vessels present, angiosperms

Soft wood

lack of fibers, vessel absent, gymnosperm

Heartwood

dark, heavier, tylosis occurred (in the center)

Sapwood

lighter, contains living cells, circles the heartwood

Early wood

formed in the spring, has thin cell walls to maximize water delivery; big cavity

Late wood

formed in late summer, has thick-walled cells and contributes more to stem support; small cavity

Outer bark

outside cork cambium

Inner bark

from cork cambium to vascular cambium

Anomalous growth

refers to unusual or atypical patterns of growth, often due to genetic mutations, environmental stress, or other factors

Herbaceous Plants

no secondary growth

Compare herbaceous and woody plants

Big Woody Trees: Slow-growing, long-lived, invest heavily in defense and structural integrity, produce fewer but larger seeds with slower dispersal methods.
Small Herbaceous Plants: Fast-growing, short-lived, focus on rapid reproduction with many small seeds, and often use quick and efficient dispersal strategies to colonize environments.
4o mini

Woody plants evolved _______ seed plants

before

Progymnosperm

transitional group of plants that resembled conifers because they produced wood, yet still reproduced like ferns (seedless, gymnosperm like cs of wood + fern-like foliage)

Progymnosperm (including the first true tree) evolved _______

in Middle Devonian (420-350 MYA)

What was happening during the Middle Devonian

Earth experienced significant terrestrial plant diversification (rise of the first true trees); was warm and humid

What is a tree?

has a main trunk (main stem); Not all trees are woody plants

What is wood?

Consists of secondary growth, specifically secondary xylem (ex. carrots are wood but not a tree)

Petrified wood

fossilized wood

megasporangium

A plant structure in which megaspores are formed, such as those of the female cones of pines.

megaspore

A spore from a heterosporous plant species that develops into a female gametophyte.

Explain the origin of the ovule/integument

sterile branches (or structures) fused around fertile ones to form a protective covering that eventually evolved into the integument.

What did these fertile branches contain?

the megasporangium (2n; belonged to sporophyte)

What is the ploidy level of the sterile branches?

2n since they belonged to the sporophyte (became the integument)

Why is the megaspore only one N?

The megasporangium undergoes meiosis to produce the megaspore

The female (mega-) gametophyte is what ploidy level?

N (gametophyte is only haploid)

The embryonic sporophyte is 2n because

it's fertilized and results from the fusion of two haploid gametes

Gymnosperm

"naked seeds"; seeds develop on the surface or tip of an appendage, not encased within it; no fruits

Angiosperm

"clothed seeds"; seeds develop within the fruit; later fruits may open and release seeds but early seed development is completely within the fruit

Are seed plants heterosporous or homosporous?

All seed plants are heterosporous

Are seed plants endosporic or exosporic gametophytes?

endosporic gametophytes; both male and female gametophytes develop inside the spore wall (the gametophytes remain enclosed and protected by the sporangium or seed structures)

Four potential megaspores are produced in the megasporangium through meiosis

only ONE becomes the functional megaspore (other 3 degenerate)

Megasporangium is surrounded by a special covering called

integument

megasporangium (nucellus) + integument =

ovule

micropyle

A pore in the integuments of an ovule

megaspore

A spore from a heterosporous plant species that develops into a female gametophyte.

the functional megaspore develops into

female (mega-) gametophyte inside the ovule; never released into the environment; endosporic but not thick-walled; mature female gametophyte produces egg(s_

Developing male gametophyte and its surrounding microspore wall are released/shed as

pollen grain

transfer of pollen to region near ovules

pollination

Pollination does not equal fertilization

TRUE; not all pollination leads to fertilization since some pollen may fail to germinate

Fertilization and early development of next-generation sporophyte occur within female gametophyte

which is still inside the ovule (integumented megasporangium)

seed

mature ovule + developing embryonic sporophyte

In gymnosperms

pollination involves transfer of pollen grains (male gametophyte) directly to the micropyle of the ovule

How do seeds disperse?

windblown fruits, aherent fruits, fleshy fruits (through wind, animals and water)

Gymnosperms include

Seed ferns, cycads, ginkgos, conifers, gnetophytes

Pteridospermatophyta (Extinct "seed ferns")

seeds + fern-like fronds: somewhat look like cycads or tree ferns. Seed fern is not a tree fern

Key Features of cycads

- commonly shoot unbranched
- large leaves
- dioecious: pollen cone plus various seed cone
- large pith and cortex
- little secondary xylem but a lot of parenchyma (similar to seed ferns)

Ginkgophyta (Ginkgo)

Living fossils; a living species strikingly similar to a species only known from fossils

Key Features of Gingko

- dioecious
- slow growth in early years
- medicinal purposes

Coniferophyta (conifers)

phylum that includes seed plants that form cones; biggest of the gymnosperm; well adapted to cold and dry place

Dioceious

having the male and female reproductive organs in separate individuals.

monoceious

having both the male and female reproductive organs in the same individual

What is in a pollen grain

• Microspores develop into pollen grains, which contain the male gametophytes
• Pollen grains have a generative cell which produces the sperm and a tube cell which produces the pollen tube. If a pollen grain germinates, it gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule

Gnetophyta

- monophyletic
- contains 3 families, each with only one genus
- relationship with angiosperms is not certain

What makes gnetophyta different from the rest of the gymnosperms?

primitive vessels in wood, no archegonia, naked eggs, evidence for "double fertilzation" and origin of endosperm

microspore

A spore from a heterosporous plant species that develops into a male gametophyte.

flowering plants (angiosperms)

largest group of land plants that all have: flowers, carpels, fruits, double fertilization with triploid endosperm, specialized conductive cells

How do angiosperms differ from gymnosperms?

they're seed plants BUT ovules are contained WITHIN a structure (pistil) that will become the fruit

Carpel

evolutionary equivalent of a single megasporophyll

Pistil

one or more folded megasporophylls, evolutionarily (thus, it consists of one or more carpels) Develops into the fruit (multiple carpels make up one pistil)

In angiosperm, the pollen germinates on the

pistil, not directly on the ovule

In angiosperms, male and female gametophytes further reduced (fewer cells)

form seeds in weeks or even days

In angiosperms, two sperm cells produced but BOTH function in fertilization process

this is double fertilization

Where do both sperm cells do in double fertilization?

One fuses with egg (2N zygote); One fuses with two nuclei of central cell of female gametophyte (3N Endosperm)

3N Endsoperm

tissue that nourishes embryo (not mega-gametophyte tissues); endosperm feeds the world

Endosperm is found in (3n)

angiosperm (from double fertilization)

Megagametophyte tissue (n)

Gymnosperm (comes from the megaspore)

Both serve as nutrients for the embryo

but have different origins

Angiosperms have the presence of

the flower

Steps of female gametophyte development

1. diploid megaspore mother cell forms inside ovule's nucellus
2. this undergoes meiosis, producing 4 haploid megaspores

Of the 4 megaspores,

3 degenerate, leaving one functional megaspore

This functional megaspore undergoes how many rounds of mitotic divisions?

3 rounds, resulting in 8-nucleate.