Lecture 2: Origin of land plants: hidden world of bryophytes

Question 1

Bryophytes basics

Answer 1

• most basal form of land plants
• share common ancestor of ancestral green algae
• first land plants. although first land plants there are some still present today b’cos so basal and adapted.

Question 2

Reproductive strategy of bryophytes

Answer 2

homosporous reproductive strategy. With the Gametophyte the dominant phase of the life cycle

Question 3

Steps for reproduction of bryophyte

Answer 3

1) Gametophyte produces both egg and sperm
2) sperm swims over to egg
3) Forms a sporophyte
4) Meiosis occurs resulting in haploid cells again
5) cycle repeats

Question 4

What is necessary for reproduction and WHY

Answer 4

WATER for sperm to move to egg

Question 5

During reproduction the ________ is dependent on the _______ for nutrition. Sporophyte is ____ lived and the Gametophyte is the _____ stage.

Answer 5

sporophyte
Gametophyte
short
dominant

Question 6

Characteristics of living Bryophytes: heterosporous or homosporous?

Answer 6

homosporous - producing asexual spores of old one type

Question 7

Characteristics of living Bryophytes: sex organs have

Answer 7

a sterile jacket. Egg cells enclosed in a single flask-shaped archegonium

Question 8

Archegonia?

Answer 8

multicellular structure or organ of the gametophyte phase of certain plants, producing and containing the ovum or female gamete

Question 9

antheridia?

Answer 9

Male sex gametes

Question 10

zooidogamous?

Answer 10

type of plant reproduction in which male gametes (antherozoids) swim in a film of water to the female gametes (archegonium)

Question 11

Characteristics of living Bryophytes: their sperm!

Answer 11

• Spermatozoids zooidogamous with two whiplash flagella (sperm have two flagella, required for swimming to egg)

Question 12

Characteristics of living Bryophytes: type of embryogeny

Answer 12

Embryogeny exoscopic (way the organism grows)

Question 13

isospore?

Answer 13

asexual spore = spore which does not arise through sexual reproduction.

Question 14

Characteristics of living Bryophytes: what does the sporophyte produce

Answer 14

numerous isospores (same size) enclosed in a protective sporopoellenin wall

Question 15

gemma (plural gemme)?

Answer 15

a single cell, or a mass of cells, or a modified bud of tissue, that detaches from the parent and develops into a new individual

Question 16

Characteristics of living Bryophytes: capable of vegetative propagation?

Answer 16

Some are of the gametophyte by fragmentations or specialised gamma (sexual and non-sexual reproduction)

Question 17

Growth form of Bryophytes

Answer 17

• Generally v small (soft as no lignin present)
• Gametophyte either
  - thallus flattened with some internal gametophyte differentiation
  - main axis with leafy appendages
• The thallus bears rhizoids - but no roots
• some have primitive water conducting cells - but these are NOT lignified

Question 18

rhizoid

Answer 18

root like filaments

Question 19

how are the spores dispersed?

Answer 19

widely dispersed by wind and they have colonised most of the planet

Question 20

are they able to survive in cold and dry environments?

Answer 20

yes as have the ability to lose most of their body water without dying, then rehydrate and reactivate their cells when moisture again becomes available

Question 21

dependant on what for reproduction?

Answer 21

free water - movement of sperm

Question 22

what sort of plant are they?

Answer 22

Colonisers of bare rock and soil surfaces (primary colonisers - e.g. Sertsey)

Question 23

What allows them to survive in desert, high altitudes (mountainous regions) and high latitudes (polar regions)

Answer 23

Phenolic compounds in cell walls protects against UV radiations

Question 24

They are epiphytes what does this mean?

Answer 24

grows harmlessly upon another plant. Doesn’t necessarily negatively affect host, grow or physical support

Question 25

why are sphagnum bogs useful?

Answer 25

removes CO2 form atmosphere, holds lots of water

Question 26

liverworts definition:

Answer 26

a small flowerless green plant with leaf-like stems or lobed leaves, occurring in moist habitats. They lack true roots and reproduce by means of spores released from capsules.

Question 27

protonema:

Answer 27

thread like chain of cells that form the earliest stages of a bryophyte life cycle. First growth from the spore and develops into Gametophyte (•The protonemal phase of the gametophyte is usually ill defined).

Question 28

thallus:

Answer 28

a plant body that is not differentiated into stem and leaves and lacks true roots and a vascular system. Thalli are typical of algae, fungi, lichens, and some liverworts.

Question 29

Gametophyte thallus of liverwort:

Answer 29

may be thalloid or leafy but the mature thallus usually shows dorsiventrality

Question 30

dorsiventrality:

Answer 30

extension along an axis joining the dorsal and ventral surfaces

Question 31

Leaf shapes on liverworts

Answer 31

Leafs may be simple more-or-less circular plates of cells or lobed (twice or several times)

Question 32

In leafy liverworts the stem is..

Answer 32

inclined or lying flat down with dorsiventral symmetry

Question 33

characteristic feature of liverwort gametophyte:

Answer 33

is the presence of oil bodies in the cytoplasm

Question 34

how are leave usually arrange din liverworts?

Answer 34

in 3 ranks, but only those on the dorsal side are full developed

Question 35

dorsal side means

Answer 35

surface of an organ or part facing away from the axis

Question 36

antheridores and archegoniophores:

Answer 36

Some species have complex antheridia/archegonia where male and female gametes are produced on upright umbrella-shaped structures termed antheridiophores and archegoniophores respectively. They develop from one half of a dichotomy (division into two parts).

Question 37

``` EVOLUTIONARY HISTORY OF THE BRYOPHYTES: Mid Ordovician (475 Ma) ```

Answer 37

The first land plants evolves from an aquatic green algal ancestor. Fossil evidence is in the form of dispersed spores identical (in terms of morphology and ultrastructure) to those of extant bryophytes. The three major groups of bryophytes (liverworts, mosses, hornworts) diverge early. The plants are v. small with the gametophyte dominant and homosporous reproduction when the subsidiary sporophyte appears. The vegetation is widespread but confined to damp environments.

Question 38

``` EVOLUTIONARY HISTORY OF THE BRYOPHYTES: Early Silurian (435 Ma) ```

Answer 38

Tracheophytes (vascular plants) evolve. They outcompete the bryophytes and rapidly diversify. Bryophytes persist but as an inconspicuous element of the vegetation confined to harsh and unstable damp environments that the tracheophytes cannot inhabit.

Question 39

``` EVOLUTIONARY HISTORY OF THE BRYOPHYTES: Mid Devonian (380 Ma) ```

Answer 39

The first trees evolve and forests form. Bryophytes rediversify as they discover a new niche they can exploit: as epiphytes on trees.

Question 40

Commercial use of bryophytes:

Answer 40

- seed fuel - fuel - absorbant bandages