Lecture 23 Flashcards
What is the importance of the seed evolving?
-one of the most dramatic innovations in land plant evolution -dramatic advance in evolution, protection of embryos by seeds -seed= container= embryo inside and diploid outside coating and nutrient material
What were the main advancements developed in seed plants?
-wind pollination= no need to swim -secondary growth= girth increase -embryo develops partially on the parent
When did seed plants evolve?
Fossil record extending back to the late Silurian (c. 420 million years)
What are the three divisions of seed plants?
-cycads -conifers -angiosperms (flowering plants)
How do cycads grow?
not much secondary growth, grow in columns
What is special about the ginko?
another group -believed to be extincted= it was in china 17th centuryone tree only= all of them from this one today
How do conifers reproduce?
-in cones segments= seeds large numbers of layer seeds juniper berries= modified cones= falvour of gin
What sort of environment do conifers need?
australia too arid for evergreens usually -not much to eat in conifer forests -has to be humid -they are the world’s greatest carbon sink
What are the four main events in land plant evolution?
- Development of secondary growth - produces woody tissues 2. Produce two types of spores: megaspores (in ovules - female) and microspores (pollen - males) 3. Reproduce by seeds - female gametophyte & embryo enclosed within an ovule, which is nourished and protected on the parent plant 4. Male gametes transported in pollen, by wind in the conifers (pollination).
What is the secondary growth?
• The Vascular Cambium is a meristem that produces additional (secondary) vascular tissue (xylem and phloem). • Secondary growth increases the girth of a stem by adding wood and bark. • Secondary growth is essential for development of shrubs and trees.
What are the growth rings?
one ring= one year as it gets cold and hot= depends on weather, if drought etc
What vessel network do the conifers have?
-tracheid vessels
What are the characteristics of pollen?
• Pollen grains are transported to the ovule (female gamete) prior to sperm cell development. • Pollen are wind-blown to the female ovule. • The sperm cells do not require free water. -sticky ovules= draw in the pollen
What does a seed develop from?
- from fertilized ovules.
What is an ovule?
An ovule is a sporangium surrounded by a protective covering (integument).
What is a sporangium?
an enclosure in which spores are formed - Sporangia can produce spores by mitosis, but in nearly all land plants and many fungi, sporangia are the site of meiosis and produce genetically distinct haploid spores.
How many functional spores does an ovule contain?
-one functional spore, which is retained on the parent plant.
Describe pollination:
Describe fertilization:
How long does it take for a fertlized ovule to develop into a seed?
- 2 years
Describe the life cycle of a pine tree:
Cycads and Gingko - what feature of their reproduction reminds us of the ferns and mosses?
-when the sperm reaches the surface of the egg= grows two flagella and swims last few microns to reach the nucleus
-like ferns in that they swim= but these only swim the last few microns= so need water!!! like mosses!
How are the cycads and ginko reproduced?
-pollinated by insects
In which plants did these develop first:
cuticle
secondary growth
vascular cambium
pollen
xylem
stomata
sporophyte dominance
cuticle= mosses
secondary growth=conifers
vascular cambium=conifers
pollen=conifers
xylem=mosses
stomata=mosses
sporophyte dominance=ferns
What is interesting about Conifers?
- c.600 species of shrubs and trees
- Tallest and longest-lived organisms
- Ecological and biogeographic importance
- Economic value (softwood timber, paper)
Are conifers the oldest plants?
-possibly, Redwoods of california
–look dead, older then the fungi 5000 years old!
What is the history and distribution of the Southern Conifers?
- New Zealand rich in conifers, mainly podocarps and Kauri
- Australia is relatively poor in conifers because of aridity
- Australia does have a range of conifers (e.g., Kauri, Callitris, Huon pine)
• The latest Australian conifer: the Wollemi pine! • The history of Australian conifers can be traced back to
Gondwana, its breakup and resulting climate change. • How is it that we know about Gondwana and its past vegetation
-tasmania= conifers as well, mostly australia= too dry, since small groups= hard to reproduce= wind pollination
wollemi pine= new found, believed to have been extinct, living fossil
What is the story with Huon pine and wollemi pine?
- thought to be extinct because heavily logged
- wollemi discovered recently that it still exists= from dinosaur ages
What is the story of gondwana?
About 300 million years ago, Australia, Antarctic, S. America, Africa and S. India formed the supercontinent GONDWANA
• •
About 150 mya GONDWANA began to fragment. India and S. Africa drifted away. About 50 mya Australia separated from Antarctica - it has drifted north to its present latitude
- Australia was part of Gondwana until about 30mya.
- As Gondwana broke up, the climates and vegetation of the continents changed significantly.
- Some of Australia’s flora is an “ancient” component derived from Gondwana times (e.g., it’s southern conifers including the Wollemi Pine
How did Scott prove that antarctica was part of gondwana?
scott= natural scientists, nobody believed that antarctica was an different than then= found the glosspteris fossil= proved that the gondwana was real
