Origin of Land Plants

Question 1

When did land plants first appear?

Answer 1

~0.46 Ga

Question 2

Define the following terms:

1. Bryophytes
2. Pteridophytes
3. Gynosperms

Answer 2

1. Mosses and liverworts
2. Seedless vascular plants
3. Naked seeds

Question 3

What 6 key challenges did plants have to overcome to colonize the land?

Answer 3

1. Support structure
2. Desiccation
3. Access to nutrients
4. Temperature variation (more severe)
5. Damaging UV radiation
6. High oxygen concentration (3.5% in water)

Question 4

What reproductive issue does living on land pose?

Answer 4

No medium on land for sperm to swim, also danger of desiccation of sex cells and propagules

Question 5

What were the 3 advantages of living on land?

Answer 5

1. More photosynthetically active radiation
2. High CO2 concentrations
3. Escaping competition and herbivorous animals

Question 6

How did early land plants deal with the problem of support?

Answer 6

Initially not a problem, spread out flat. Only developed later with increasing competition

Question 7

How did early land plants deal with the problem of desiccation?

Answer 7

Only initially lived in watery environments. However developed rhizoids to anchor plants to the ground and a waxy cuticle to reduce water loss

Question 8

How did early land plants deal with sexual challenges?

Answer 8

1. Initially relied on water for sperm dispersal

2. Later to avoid desiccation, invention of sporopollenin (walled spores)

Question 9

Why are the green algae group charophytes believed to be the likely ancestor of land plants?

Answer 9

• Common photosynthic pigments
• Have hexamic cellulose synthesis
• Phragmoplast formation during cell division
• Have plasmodesmata
• Have peroxisomes to protect from photorespiration
• Sequence ribosomal RNA

Question 10

What 4 things define a land plant?

Answer 10

1. Apical meristems (3 faces)
2. Multicellular gametangia
3. Alternation of generations
4. Sporollenin

Question 11

What are the two generations in the life cycle of a land plant?

Answer 11

1. Sporophyte generation - asexual, diploid

2. Gametophyte generation - sexual, haploid

Question 12

What phase was dominant in early land plants?

Answer 12

Gametophyte

Question 13

In what way are bryophytes different from early land plants?

Answer 13

Sporophyte is dependent on gametophyte throughout its life

Question 14

What makes liverworts unique from all other land plants?

Answer 14

They lack stomata (have pores for similar function but less efficient)

Question 15

What are 2 other features of liverworts?

Answer 15

1. Lack conductive tissue (hence size restraint)

2. Have unicellular rhizoids

Question 16

What is the name of the liverwort:

1. Male reproductive structure
2. Female reproductive structure
3. Female gamete

Answer 16

1. Antheridium (Antheridia - sperm)
2. Archegonium (archegonia - egg)
3. Sessile

Question 17

Describe the reproductive process of Mechantia

Answer 17

1. Fertilised by rain splash mechanism, where rain splash splashes male gametes on to archegonium where sessile is then fertilised.
2. Sporophytes then grow from under the female structure
3. Seta enlarges 20 times its original size and spores are eventually released, with elators aiding their dispersal

Question 18

How are mosses different to liverworts

a) structurally
b) sexually

Answer 18

a) Have stomata and conductive tissue. Also rhizoids are branched, multicellular and with opaque cell walls
b) Gametophytes are leafy and radially arranged

Question 19

In spores, which generation supports the other?

Answer 19

Gametophyte generation supports the sporophyte. Meiosis in sporangia produces spores which are released as the capsule dries

Question 20

Name 3 features of ferns

Answer 20

1. First to develop megaphyll leaves whith a highly branched vascular system
2. Multiple branched vascularised stem
3. Siphonostele - pith with vascular cylinder

Question 21

How is it hypothesized that ferns developed from bryophytes?

Answer 21

That sporophytes began to enlarge and develop autotrophic independence and outlive the gametophyte which is used as a food store. This allowed for increased size and complexity. Several gametophytes may be fertilised but only a few may develop to assure food abundance

Question 22

Where can the spores be found in ferns?

Answer 22

On the underside of the leaf, called sori. Idusium dires up to release them.

Question 23

How are the gametophytes of pteridophytes bisexual?

Answer 23

Can produce both male and female gametophytes at different times, dictated by hormones.

Question 24

Name 3 features of gynosperms

Answer 24

1. Development of SEEDS
2. Well developed vascular system
3. True roots, stems and leaves

Question 25

What conditions in the Permian period contributed to the rise of seeds?

Answer 25

Dry and cold, lack of water for fertilisation

Question 26

What are flying plant gametes called?

Answer 26

Progynosperms

Question 27

Describe heterospory

Answer 27

Two types of gametophytes dispersed instead of spores

1. Microspores (male) produced by microsporangia
2. Megaspores (female) produced by megasporangia

Question 28

Why did microspores become more abundant and develop increasingly for flight?

Answer 28

• Increase chance of reaching a megaspore
• In order to reach mother plant which can assist the sperms journey to the egg and also support the gametophyte and zygote after fertilisation (no need for dependence on water)

Question 29

In what 3 ways did female gametes become spcialised?

Answer 29

1. Size and complexity reduction
2. Dependence on mother plant
3. Enclosing (2n) structure

Question 30

How could the mother plant support the zygote post fertilsation?

Answer 30

• Development of structures before release such as roots and leaves
• When released provide ingrument (2n) for protection
• Provide nucellus (2n deriver from sporangium) for nutrition