Liverworts and Hornworts

Question 1

Hornworts and some liverworts are thalloid

What does this mean

Answer 1

Undifferentiated bodies, lacking roots, steam and leaves

Gametophytes May appear to have leaves and stems but have no vascular tissue.

Question 2

What are rhizoids for

Answer 2

Anchoring -> absorption through the thallus

Question 3

Through fall and stem flow

Answer 3

Through fall- rain water falling into leaves and then ground

Stem flow-rain water flowing down trunk

Nutrients more commonly found in an ionic form were found to move very rapidly from the forest canopy to the available nutrient pool in through fall and stem flow

Question 4

Pores on some bryophyte gametophytes have what purpose

Answer 4

Increase CO2 diffusion
Reduce H2O loss

Analogous to the stomata of vascular plants

Cells at the bottom of the barrel-like pore can remain turgid when in a moist environment. When dry, these cells can collapse and narrow the opening of the pore.

Question 5

Cells of bryophytes are interconnected with……

Answer 5

Plasmodesmata

Desmotubules (derived from ER) similar to vascular plants and some Charophyceae green algae

Question 6

How do bryophytes reproduce asexually

Answer 6

Gemmae
Fragmentation

Question 7

Bryophyte sperm and zoospores

Answer 7

Flagella only produced by sperm therefore absence of flagellated zoospores

Loss of centrioles in bryophytes (organelle redouble for development of flagella) resulted in loss of an ability to produce zoospores.

Question 8

Sexual reproduction in bryophytes and parts

Answer 8

Via archegonia and antheridia

Archegonia:
-Venter encloses a single egg cell
-neck canal cells disintegrate when egg is mature -> fluid filled tube for sperm access.
-chemical attraction of sperm cells.
-Mateotrophy: sugars, amino acids produced to zygote by maternal gametophyte tissue (transfer cells)

Antheridia:
-single/-cell sterile jacket layer
-each spermatogenous cell produces a single bi-flagellated so Soren cell-> H2O

Question 9

Placenta of bryophytes

Answer 9

Placenta: gametophyte-sporophyte junction

Transfer cells form a highly branched network to increase surface area for nutrient transfer

Extensive wall in growth develop in transfer cells

Question 10

Elaters

Answer 10

In some liverworts, the spores are actively discharged by elaters, but without the explosive force.

Elaters twist or untwist, depending on whether the surrounding air is drying out or becoming moister

Spore capsules held under umbrella like structure -> mass of spores intermixed with long, straight-> mature capsules split open-> elaters dry out, twist and entangle. As elaters may suddenly become free, movement throws spores into the air.

Question 11

Sex determination of bryophytes

Answer 11

The sex of unisexual gametophytes is determined by the segregation of sec chromosomes at meiosis.
-All sporophytes are FM heterozygotes: each meiotic tetras contains two F-bearing spores that develop into females and 2 M-bearing spores that develop into male gametophytes

-Females typically outcompete males probably because femLes expend fewer resources than males in the production of gametes

Question 12

Earliest fossils of liverworts

Answer 12

Devonian (360mya)

Question 13

Order Jungermanniales (the leafy liverworts) characteristics

Answer 13

-Gametophytes are very small
-Two later rows of leaves and a row of leaves on the ventral side of the stem (amphigastria)
-Leaves are only 1 cell layer thick
-Many disk shaped plastics
-Rhizoids unicellular for anchoring, and passive condition of water and nutrients as well as penetration by endophytic fungi.

Question 14

Some Jungermanniales have a symbiotic relationship with….

Answer 14

Cyanobacteria (Nostoc) for N fixation

Question 15

Thalloid liverworts shape

Answer 15

No stem or leaves; instead their main body is flat, like a green pancake

The tissue in the thallous can be well differentiated (Marchantiales) or poorly differentiated (Metzgeriales)

Question 16

Order Metzgeriales

Answer 16

Relatively undifferentiated thalli, one to several cell layers thick

Question 17

Order Marchantiales

Answer 17

-Thalli are composed of multiple layers
-unicellular rhizoids located on the ventral side of the gametophyte
-some have scales with rhizoids (scales are multicellular and pigmented)

Question 18

Liverwort habitat

Answer 18

Found in most terrestrial ecosystems except extremely dry ones or those exposed to high levels of direct solar radiation

Most common in tropical and moist areas

Question 19

What are liverworts greatest economic importance

Answer 19

Indirect reduction of erosion along stream banks, their collection and retention of water in tropical forests. May contribute to soil crusts.

Can be used as bio indicators for metal and pollution levels in air and water

Question 20

Ancient economic importance of liverworts

Answer 20

Believes to be able to cure liver diseases because it looks like a liver

Question 21

Liverworts
Hornwort

Scientific names

Answer 21

Hepatophyta
Anthocerophyta

Question 22

Hepatophyta, Anthocerophyta and Bryophyta all belong to what collective group

Answer 22

Bryophytes

Question 23

Oldest hornworts are from when

Answer 23

Oldest fossils are spores from late Cretaceous (100mya)

Analysis suggests that the group originated early in the history of plants: before the Devonian (400mya)

Question 24

Habitat of hornworts

Answer 24

Common and widespread group of plants which may be found in tropical forests, along streams and distributed in fields around the world

Question 25

What is the least diverse lineage of bryophytes

Answer 25

Hornworts (300 species)

Question 26

Superficially hornworts resemble thalloid liverworts except….

Answer 26

Most species have cells with single, large chloroplast and large Pyrenoids (independent origin from those of green algae)

Question 27

Hornwort Pyrenoid

Answer 27

Rubisco concentrated inside Pyrenoid which has the presence of Grana: stacked arrangements of thylakoids involved in light capturing

Question 28

Carbon Concentrating Mechanism (CCM)

Answer 28

Cyanobacteria, some algae, and hornworts have a CCM.

Sucks in CO2 into Pyrenoid to concentrate into photosynthetic use. Enhances photosynthetic rate.

Question 29

How did hornworts get their name

Answer 29

Tall narrow sporophyte which are embedded in the top of the plant

Question 30

Many cells of the epidermis of hornworts secrete ______ to conserve water

Answer 30

Mucilage

Question 31

Every Hornwort species is capable of forming _______ with ________

Answer 31

Symbiosis with nitrogen fixing Cyanobacteria and mycorrhizal fungi

Mucilage clefts on the ventral thallus through which Nostoc enters the plant and becomes established as an internal colonial endosymbiont

Question 32

Hornwort lifecycle

Answer 32

Spore (n)-germinating spore-gametophyte (n)-antheridium and archegonium-sporophyte (2n)

Zygote retains without the archegonium. The resultant embryo develops into the sporophyte which spores are produced via meiosis

Question 33

Hornwort sporophyte parts

Answer 33

-Foot penetrates gametophyte and forms placenta
-meristem develops at base of sporophyte

Sporophyte remains attached to its parent gametophyte throughout its life

Sporophyte continues to grow throughout its life; this happens as a group of cells at the base of the horn divide repeatedly (UNIQUE MERISTEM)

Question 34

In hornworts, an assimilative (photosynthetic) layer underlies the ________ and the sporogenous tissue is situated between this layer and the ______

Answer 34

Epidermis
Columnella

Question 35

Why do stomata remain open in hornworts

Answer 35

Do not have an opening and closing mechanism, but this helps with Spore dispersal

Question 36

What is in the center of a hornwort sporophyte?

What is in the rest of the cross section?

Answer 36

Hydroids
Leptoids (sugar transport)
Spores in retreads

Cutinized epidermis
Cortex cells for photosynthesis

Question 37

What shape do hornwort sporophytes become

Answer 37

Elongate and split into 2 halves lengthwise, releasing spores as they mature=spore liberation over an extended period of time.

Question 38

Along with spores of Horowitz are cells called _______, which change the shape as they dry out and thereby assist in scattering the spores

Answer 38

Pseudoelaters

Question 39

How are hornworts similar to vascular plants

Answer 39

Photosynethic sporophyte (less parasitic)

Indeterminate growth

Intermediate reproductive capacity

Characteristics of vascular plants