Biol3180 - Lecture 23

Front 1

what are the two major groups of vascular plants?

Back 1

vascular cryptograms: those that produce spores

spermatophytes: those that produce seeds (the majority of extant plants are spermatophytes)

Front 2

what is a seed?

Back 2

a highly adapted structure in which the embryo (the young 2N sporophyte) is shed from the parent plant (also 2N), enclosed within a resistant coat, together with a supply of food that aids its establishment (1N in Gymnosperms; 3N or greater in Angiosperms)

Front 3

what are the three extinct phyla of cryptograms, and what characteristics do they share?

Back 3

rhynia, zosterophyllum, and trimerophyton:

- Relatively simple plants18 in to 36 inches tall
- Naked photosynthetic stems
- No roots or true leaves – microphylls (Rhynia, Zosterophyllum) yielding to megaphylls (Trimerophyton)
- Mostly terminal sporangia (Rhynia, Zosterophyllum) but some lateral sporangia (Trimerophyton)
- Homosporous (Rhynia, Zosterophyllum,Trimerophyton)

Front 4

def: homosporous

Back 4

Plants that are homosporous produce spores of the same size and type.

Front 5

what are the primary differences between rhynophytes and zosterophyllophytes?

Back 5

sporangia: terminal in rhynophytes, lateral in zosterophyllophytes

vascular system: endarch in rhynophytes, exarch in zosterophyllophytes

Front 6

what is an endarch?

Back 6

type of vascular tissue with protoxylem centrally, and metaxylem at edges

Front 7

what is an exarch?

Back 7

type of vascular tissue with protoxylem at edges, and metaxylem centrally

Front 8

what are protoxylem?

Back 8

fast developing small/narrow tracheids

Front 9

what are metaxylem?

Back 9

slow developing large tracheids

Front 10

what are the two theories for the origins of the modern plant lifecycle?

Back 10

transformation versus interpolation

Front 11

what is transformation in terms of the evolution of lifecycles?

Back 11

(1) Gametophytes and sporophytes similar- upright and dichotomously branched

(2) With time sporophytes became larger and more complex and gametophytes became simpler

(3) Continued reduction of megaspore and megagametophyte becames retained in sporophyte body -- supported by presence of plants like Horneophyton in fossil record.

Front 12

what is interpolation in terms of the evolution of lifecycles?

Back 12

(1) Earliest land plants have no persistent sporophyte generation; rapid meiosis of sporophyte;

(2) Sporophyte becomes retained in gametophyte.

(3) The sporophyte increased in size becoming larger and more complex and the gametophyte becomes reduced -- some Zosterophyllophytes and liverworts and mosses.

Front 13

what are psilotophyta and their general characteristics?

Back 13

the simplest of extant vascular plants:

1. No roots or leaves

2. Sporophytes is dominant and consist of a simple dichotomously branched photosynthetic stem that commonly approach 30 cm in height; Rhizome (horizontal underground stem).

3. Enations, which are tiny green, flat-tened protuberances without veins, are spirally arranged at intervals along the stems

4. Epidermis with stomata

5. The gametophytes, which arise from the spores, are found beneath the surface of the soil and are colorless

Front 14

definition: microphyllous leaf

Back 14

an appendage supplied by a single, unbranched vein

Front 15

definition: megaphyllous leaf

Back 15

leaves a "leaf gap" when they depart the stele

Front 16

what are lycopsids and their general characteristics?

Back 16

the oldest/most primitive of extant vascular plants:

1. Microphylls, although the leaves may be long, they are still microphylls with a single vascular trace and no leaf gaps

2. Protosteles

3. Both homosporous (Lycopodium) and heterosporous (Selaginella) genera

4. Sporangia are borne in the axils of leaves called sporophylls; some sporophylls may be arranged into a cone-like structure called a strobilus (strobili)

examples: club mosses, quillworts,

Front 17

what is a protostele?

Back 17

early vascularization with a central bundle of xylem in the middle with phloem surrounding

Front 18

what is a siphonostele?

Back 18

more modern vascularization with a central pith with a cylinder surrounding the pith containing the vascular tissue

Front 19

what are some changes in reproductive strategy adopted by early vascular plants?

Back 19

formations of grouped sporangia called a strobilus

change from homospory (ex: psilophytes, sphenophytes, most ferns) to heterospory (micro/megaspores)

Front 20

give an example of an early heterosporous plant

Back 20

selaginella

Front 21

what are sphenophyta, and what are some general characteristics?

Back 21

1. The stems have very well defined nodes and internodes; tiny scalelike leaves (microphylls) in whorls at the nodes

2. The leaves are very reduced to scales, but are megaphylls

3. Photosynthetic stems have sunken stomata

4. Most have siphonostele

Front 22

what is a strobilus?

Back 22

an organ of many plants that contains the reproductive structures. Strobili are ordinarily called cones in many of these groups. Strobili are characterized by a central axis (anatomically a stem) surrounded by spirally arranged or decussate structures that bear sporangia or other reproductive parts.

The nature of the lateral organs varies among different plant lineages, being derived from either leaf or stem

Front 23

what are two major classifications of ferns?

Back 23

spore development: eusporangiate and leptosporangiate

Front 24

what is eusporangiate physiology?

Back 24

Sporangia develop from several epidermal cells

sporangium wall several cells thick

more spores produced

ferns and all other vascular plants

Front 25

what is leptosporangiate physiology?

Back 25

Sporangia develop from a single epidermal cell

Sporangium wall one cell thick

Only exists in some ferns

Produces fewer spores

Front 26

what is the physiology of fern leaves?

Back 26

megaphyllous

tissue differentation:
- palisade mesophyll: closely packed tall cells above that maximize light collection for photosynthesis

- spongy mesophyll: a meshwork of cells with open spaces below for gas exchange

Front 27

what is the general reproductive strategy of ferns?

Back 27

all have archegonia (neck, venter) and antheridia (sterile jacket)

all have sessile egg and flagellate sperm

Front 28

what is an archegonium?

Back 28

a multicellular structure or organ of the gametophyte phase of certain plants producing and containing the ovum or female gamete. The archegonium has a long neck and a swollen base

Front 29

what is an antheridium?

Back 29

the gametophyte phase of lower plants like mosses and ferns, and also in the primitive vascular psilotophytes

Front 30

terrestial leaf structures evolved 20my after aquatic leaves, why?

Back 30

One theory was that exceptionally high atmospheric CO2 levels in the middle Paleozoic delayed the origin of leaves by restricting stomatal development. This would have limited evaporative cooling, leading to lethal overheating of leaves absorbing large quantities of solar energy.

Recent morphometric analysis of 300 plant fossils show a 25-fold enlargement of leaf blades in two phylogenetically independent clades as atmospheric CO2 levels fell during the late Paleozoic.

The first abrupt increase in leaf size was accompanied by an 8-fold rise in stomatal density.

These evolutionary patterns support the relaxation of biophysical constraints on leaf area predicted by theory and point to a significant role for CO2 in plant evolution.