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Summary Plant Biology
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A summary of the lessons of the minor Molecular Plant Biology
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Summary Course 9 Plant Biology term I
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Expert questions for Plant Biology
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Plant Origins13,8 billion years ago there was a big bang, this was an expansion of the universe and it
looked like an explosion. This made for a very unstable environment, there was a lot of
bombardment, radiation and after a while the universe started to cool. This allowed the
formation of particles, which we now know as atoms. These atoms were gasses which
formed a rotating disk of gas.
5 billion years ago there was the solar nebula, this caused the earth to form. The earth back
then had a high temperature, a high CO2 level and no ozone layer. This caused there to be
no life. Slowly the ocean started to form because the content of vulcano’s was vaporised and
later “rained” down back to the planet.
Then 3,8 billion years ago the earth has cooled down so rock and continental plates began
to form, during all this activity there was an increase in oxygen.
3,5 billion years ago the Archean era took place, which formed the 1st bacteria : This first
bacteria is called a stromatolites. We know this because there were fossils found : which
we now know as cyanobacteria. They had a primitive form of photosynthesis meaning they
were prokaryotes (= Pro (before the nucleus was formed) karyotes).
- Single cell organisms
- No internal membrane-bound compartment : no organelles yet
- Protection against UV radiations : living in the ocean, mucilaginous sheath,
biochemical DNA repair system.
They need this protection because there was no ozone layer, the sun was directly on earth.
These prokaryotes increased the O2 levels in the ocean.
They have asexual reproduction, which means that one cell will give
another identical cell, with binary fission. You call it budding when the
cell reproduces.
How do you go from prokaryotic cells to eukaryotic cells?
The bacteria engulfed another bacteria, an a-proteobacterium, and this
bacteria became an organelle in the original bacteria, the
mitochondrium. This caused the production of internal membranes,
which formed a nucleus.
,The bacteria that now had energy started to engulfed a cyanobacterium, this bacteria formed
the chloroplast because it has a primitive form of photosynthetic, so a photosynthetic cell
ontstaat.
The picture represents the endosymbiosis. Sometimes a bacteria would only do the first
endosymbiotic event, which formes a heterotrophic eukaryote, or is also known as the
animal cell. When the bacteria also did the second endosymbiotic event it would become
photosynthetic and by that also autotrophic, which means they are able to make their own
food.
Little by little there was more oxygen being produced from the photosynthetic cells which
gave the bacteria a change to develop themselves in multicellular organisms.
Photosynthetic eukaryotic organism
Three clades of protists
→ glaucophytes, very simple organism
→ red algae, a bit more complex, had their own pigments and it is one group by itself
→ green algae
, The thallus in red algae contains the
gametes, which is proof of the start
of sexual reproduction. The rhizoid
made the algae’s “roots”.
In the algae the chloroplasts are not
completely developed. But they are
the basis for what we now know as
the chloroplasts in plants.
Eukaryotic protists
The life cycle of green algae : Chlamydomonas
→ Axexual and sexual reproduction
In the centre you have the mature cell,
and what happens when the algae
reproduces, it goes to two mitosis, so
it will form 2 identical cells and when
the spores are mature they will be
released and they are ready to be
adults. They are haploid.
What can happen is that the
environment causes stress, those
mature cells will then differentiate in
a +cell and a -cell, they will fuse because of their differences, and that makes a zygote. The
zygote has a hard envelope to protect till the stress is gone, and then it will go through
meiosis. This will form 4 haploid spores which will grow to a mature cell again.
When do the green algae enter the sexual reproduction?
- When they experience stress from i.e. environmental factors.
Know all the life cycles!!
The evolution is still going on, the oxygen is rising in the ocean. This makes for larger
organisms to grow. So let’s look at 570 million years ago.
, There were drastic changes :
- Rising oxygen levels
- Formation of an ozone layer
This made the evolution rate go wild, there was
more diversity than ever before.
= Cambrian Explosion
During the Cambian explosion the plants that were only existing in the ocean were about to
move to the land.
What does a plant need to go to land?
- The plants needed new features to survive desiccation (uitdroging) like stomata
(huidmondjes), cell walls (the cell becoming more complex), cuticle, rhizoids (kind of
root) and sporoporellin (protection for spores).
The colonization of the land was a new challenge for the plants, 450 million years ago.
The first plants to colonize the land were Bryophytes like mosses and Lichen which is the
symbiosis between fungi and algae.
→ a composite organism that arises from algae or cyanobacteria living among filaments of
multiple fungi species in a mutualistic relationship.
Colonization of the land was done by non-vascular plants.
Some non-vascular plants are bryophytes like mosses.
- Large gametophyte (large “starting part”)
- Haploïd
- Hydroids : (primitive vascular cells) but they did not yet
need it
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