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Membrane Infolding Hypothesis Statement

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Term
biologists hypothesize that the earliest eukaryotes were probably ______.
Definition
single celled organisms with a nucleus and endomembrane system, mitochondria, and a cytoskeleton, but no cell wall
Term
all eukaryotes alive today have 3 things
Definition
1. a nucleus and endomembrane system
2. mitochondria or genes that are normally found in mitochondria
3. a cytoskeleton
Term
the leading hypothesis to explain the origin of the nuclear envelope is based on ____
Definition
infoldings of the plasma membrane
Term
two lines of evidence support the infolding hypothesis
Definition
1. infolding of the plasma membrane occur in some bacteria living today
2. the nuclear envelope and ER of today's eukaryotes are continuous
Term
the endosymbiosis theory proposes that ____
Definition
mitochondria originated when a bacterial cell took up residence inside a eukaryote about 2 billion years ago
Term
mitochondria are organelles that generate ___ using ___ as an electron donor and ___ as the ultimate electron acceptor
Definition
Term
___ is said to occur when individuals of two different species live in physical contact
Definition
Term
endosymbiosis occurs when ____
Definition
an organism of one species lives inside an organism of another species
Term
in its current form, the endosymbiosis theory proposes that mitochondria evolved through a series of steps, beginning with ___
Definition
a eukaryotic cell that was capable only of anaerobic fermentation - meaning it could not use oxygen as an electron acceptor in cellular respiration
Term
3 major evolutionary developments of eukaryotes
Definition
1. nuclear envelope
2. endosymbiosis theory
3. multicellularity
Term
___: two organisms living together, one inside the other
Definition
Term
___: allows organisms to get bigger and diversify
Definition
Term
4 branches in the diversification of terrestrial plants
Definition
1. bryophytes
2. ferns, mosses
3. gymnosperms
4. angiosperms
Term
___: multiple, variable forms
Definition
Term
current estimates are that there are ___ different eukaryotic species identified with ____ still unknown
Definition
1.8 million; another 10 million or more
Term
99.9% of life forms are ___; most species ____
Definition
are now extinct; failed at attempts to survive
Term
___: the death of all members of a species
Definition
Term
what 3 features allowed eukaryotes to diversify?
Definition
1. development of the nuclear envelope
2. endosymbiosis of mitochondria
3. multicellularity
Term
___ happens within the nuclear envelope
Definition
Term
eukaryotes are ____ with ____
Definition
living organisms; defining features
Term
first eukaryotes were ____
Definition
Term
___ allowed for greater diversification
Definition
Term
history of eukaryotic diversity; about ___ years ago; ____ organs
Definition
500 million; multicellular
Term
advantages of eukaryotes for living in water
Definition
1. buoyancy (effects of gravity and weight are not a problem)
2. water is abundant
3. reproduction via mobile sperm and eggs work
Term
disadvantages of living in water
Definition
1. light doesn't penetrate water well, so organisms that need light must stay near the surface.
2. nutrients and gasses are in relatively low abundance in water
3. lots of predators and competition around
Term
eukaryotes began moving on land around ____ years ago
Definition
Term
plants made the jump onto land ___
Definition
Term
the first plants to make landfall were believed to be ___, and from this ___
Definition
green algae; 4 lineages arose from this group
Term
___ were the first eukaryotes to make landfall
Definition
Term
why didn't animals move onto land first?
Definition
plants were autotrophic/phototrophic and could make their own food
Term
green plants acquired ___ around 700 million years ago
Definition
Term
____: a heritable trait (ability or structure) that enhances the fitness of an individual to survive in a particular environment
Definition
Term
Definition
Term
in an adaptation, the trait is ___, is does not ____
Definition
already present; develop as a response to the environment
Term
the first plants to make landfall already had chloroplasts which allowed them to ____
Definition
capture light + CO2 and make sugars
Term
the first plants to make landfall already had ___ lineages
Definition
Term
4 challenges that were overcome as plants moved onto land
Definition
1. avoid, minimize water loss
2. modify reproductive strategies
3. fight gravity
4. circulate materieals
Term
first plants to make landfall were the ___
Definition
Term
the bryophytes were able to make it to ___ but _____
Definition
the water's edge; not much farther
Term
a ___ helped these first plants minimize water loss
Definition
Term
____ helped plants to allow gases to enter and exit from the cuticle
Definition
thousands of tiny little holes
Term
the reproductive strategy of plants is termed _____
Definition
alternation of generations
Term
explain alternation of generations
Definition
a sporophyte (2N) releases spores (1N) which become gametophytes which release gametes (1N sperm and eggs) which combine to form a zygote (2N) which turns into a sporophyte
Term
___ were modified when plants moved on land; how?
Definition
spores; spores were encapsulated
Term
when plants made landfall; ____ were created on the gamtophytes
Definition
specific reproductive organs
Term
mature plant body is named after ____
Definition
Term
3 ways in which the bryophytes modified reproductive strategies
Definition
1) encapsulated spores to prevent water loss
2) build gametangia - protect gametes
3) retained eggs, sporophyte growth off of existing gametophyte
Term
3 big challenges for movement of plants onto land
Definition
1) any group that could stiffen up and provide support to grow larger
2) move water from one location (soil) to another (leaves)
3) modify reproductive strategy so not dependent on water
Term
Definition
acheive all 3 of the previous statements
Term
___ appeared on land around 400 mya and dominated the landscape for around 100 million years
Definition
Term
ferns are made up of what 3 different plant lineages
Definition
1. ferns
2. club mosses
3. horsetails
Term
2 Adaptations that helped ferns survive on land
Definition
1) fighting gravity and circulating materials
2) lignin and cellulose deposited into cell walls
Term
ferns had ___ made from ___
Definition
vascular tissue; tracheids
Term
tracheids are ___ and have ___
Definition
Term
in ferns, the vascular tissue is only present in the ____
Definition
Term
ferns could ____ but still had ___
Definition
stiffen up and move water from one location to another; swimming sperm
Term
ferns could do what two things?
Definition
1. stiffen up (provide support to grow larger)
2. move water from one location (soil) to another (leaves)
Term
ferns did not have ___; still had ___
Definition
a modified reproductive system; swimming sperm
Term
ferns were limited to ___ environments
Definition
Term
the next group of terrestrial plants to make landfall was the ___; around ____
Definition
Term
what two advantages did gymnosperms have over club mosses and ferns
Definition
Term
the gymnosperm pollen had a minimal ____; shifts emphasis to ___;
Definition
gametophyte stage; sporophyte generation
Term
at this moment in time; only ___ had vascular tissue
Definition
Term
gymnosperm seeds had a ___; and the seeds were ____
Definition
seed coat; pumped with nutrients to increase survival if fertilized
Term
the ___ protected the seed and kept it from dehydration
Definition
Term
gymnosperms also thickened up the ___, which caused ____, and helped to minimize ____
Definition
cuticle; waxy needles; water loss
Term
Definition
Term
in order to fight gravity, gymnosperms had ____
Definition
Term
the vessel elements of gymnosperms are ___ and have ___ as well as ____
Definition
short and wide; perforations; pits
Term
gymnosperms have thickened ____
Definition
Term
gymnosperms include ___, ___, ___
Definition
Term
which lineage of terrestrial plants dominate the landscape right now?
Definition
angiosperms (in the sporophyte stage)
Term
angiosperms are ___ plants
Definition
Term
angiosperms have greatly modified ____
Definition
Term
the flower is a reproductive organ with ___ and ___
Definition
Term
angiosperms have a way to further protect the egg with the ___
Definition
Term
some angiosperms have a ___ and ____ ____
Definition
Term
angiosperms still used ___ and still have ___ generation
Definition
pollen; sporophyte dominant generation
Term
the angiosperms had ___ male and female gametophyte
Definition
Term
in angiosperms, the egg is protected by ___, which is a ___
Definition
Term
angiosperms developed ___, which are part of the ___; in order to provide sperm
Definition
Term
___ can attract animals in order to use them to transport pollen
Definition
Term
Plant Groups Vascular Tissue Seeds
Definition
1. bryophytes no no
2. ferns yes no
3. gymnosperms yes yes
4. angiosperms yes yes
Term
around 500mya, the first plants made landfall, these were ___, they were ___ and had ___; they also had a primary ___
Definition
green algae; photosynthetic; chloroplast; cuticle
Term
after green algae, the next group to make landfall around 475 mya were the ____, they had ___, ___, and a ___
Definition
bryophytes; respiratory parts; chloroplast; cuticle
Term
around 400mya, the next group of plants to make landfall were the ___; they had ___ in the form of ___; ___ and ___ helped them overcome gravity; and the plants became more ____
Definition
ferns; vascular tissue; tracheids; lignin; cellulose; sporophyte dominant
Term
around 300 mya the ___ made landfall; they had ___ and improved ___ (___), along with ___ for reproduction
Definition
gymnosperms; seeds; vascular tissue (vessel elements), pollen
Term
around 150mya, the ___ made landfall; they had ___, and they protected the egg in the ___, all of this helped to increase ____
Definition
angiosperms; flowers; ovule; increase dispersion
Term
three examples on how to classify an organism
Definition
dna (genome), how it survives in its environment, how it reproduces
Term
___: used to describe/identify the origin and evolutionary changes
Definition
Term
____ and ___ have taken understanding to a new level
Definition
DNA and molecular technology
Term
fossil record is very limited prior to ___
Definition
Term
rapid diversification around ___ during the ___
Definition
Term
during this rapid diversification era; ___ was first observed in the fossil record
Definition
Term
by about ___; the first animals appeared in the fossil record
Definition
Term
early acquatic animals had what 3 traits
Definition
1. multicellularity
2. acquire food by ingestion (most)
3. extracellular matrix
Term
___: process of bringing food and nutrients into the body for absorption
Definition
Term
___: organisms that rely on other organisms for food
Definition
Term
___: helps to keep cells together
Definition
Term
what is the plant equivalent structure to the animals extracellular matrix?
Definition
Term
early aquatic animals were limited to ___ life; there were no ____ on land yet; ___ were present (pre-dates plants)
Definition
oceanic life; plants or other animals; tissues
Term
Definition
connective, epithelial, muscle, nervous
Term
___ and ___ tissue are related and are found in most animals
Definition
Term
both plants and animals have evolved ___ and ___, but only animals have ___ and ___ tissue
Definition
connective and epithelial tissues; muscle and nervous
Term
what was the advantage of multicellularity?
Definition
cells could now specialize and could now grow bigger to diversify
Term
are all eukaryotes multicellular?
Definition
Term
are all eukaryotes multicellular?

Posted by endosymbiotichypothesis.

Similarities Between Bacteria and Semiautonomous Organelles

Since the symbiotic hypothesis states that mitochondria and chloroplasts arose from bacteria entering a eukaryotic cell to form a symbiotic relationship, similarities between bacteria and these semiautonomous organelles show strong evidence that this hypothesis is correct.

Mitochondria share very similar characteristics with purple-aerobic bacteria. They both use oxygen in the production of ATP, and they both do this by using the Kreb’s Cycle and oxidative phosphorylation. (mitochondria on the left and purple aerobic bacteria on the right)

Chloroplasts are very similar to photosynthetic bacteria in that they both have very similar chlorophyll that harness light energy to convert into chemical energy. (Chloroplast on the left and photosynthetic bacteria on the right)

Although there are many similarities between mitochondria and purple aerobic bacteria and chloroplasts and photosynthetic bacteria, they appear to be slight and to have arisen via evolution.

Size of mitochondria and chloroplasts in comparison to bacteria is another simple observation that supports the endosymbiotic hypothesis. Mitochondria, chloroplasts, and prokaryotes (bacteria) range from about one to ten microns in size. (1 micron=1X10-6 Meters) This seems very basic, but if there was a large difference in sizes between these three components, the hypothesis would appear to be false.

  • DNA, RNA, Ribosomes and Protein Synthesis

The first piece of evidence that needed to be found to support the endosymbiotic hypothesis was whether or not mitochondria and chloroplasts have their own DNA and if this DNA is similar to bacterial DNA. This was later proven to be true for DNA, RNA, ribosomes, chlorophyll (for chloroplasts), and protein synthesis. This provided the first substantial evidence for the endosymbiotic hypothesis. It was also determined that mitochondria and chloroplasts divide independently of the cell they live in.

Mitochondria having their own DNA and dividing independently of the cell is what ultimately results in only mitochondrial DNA being inherited by one’s mother since only an egg cell has DNA while a sperm cell does not. (This relationship also further proves that the discovered characteristics of mitochondria are true.)

This level of independence among semiautonomous organelles shows that they are not very related to the nucleus or other organelles of a eukaryotic cell. Since they are not related, it appears to be even more probable that mitochondria and chloroplasts were originally bacteria that entered the eukaryotic cell via endocytosis to form a symbiotic relationship.

Evolutionary Drive

Scientists (particularly Lynn Margulis) then began to think that if mitochondria and chloroplasts were truly bacteria that were taken into eukaryotic cells via endocytosis, then there must be a historical drive to promote this symbiotic relationship. About 3.8 billion years ago, there were only anaerobic bacteria in existence because Earth’s atmosphere did not contain any oxygen. The first photosynthetic bacteria arose around 3.2 billion years ago and began producing large quantities of oxygen as a byproduct of photosynthesis. Oxygen is very toxic to cells, and as a result, these anaerobic, photosynthetic bacteria became less effective at surviving in their environment. At this point, some of the anaerobic bacteria evolved into aerobic bacteria. Aerobic bacteria are much better suited to this oxygen containing environment and they even use oxygen in the process of making ATP (a molecule that stores a great amount of easily accessible energy). One important factor that both of these bacteria lacked was the ability to ingest large quantities of nutrients from the surrounding environment via phagocytosis. About 1.5 billion years ago, the first nucleated cell (the eukaryote) was arose through evolution, and this cell had the groundbreaking ability to take in large quantities of nutrients via phagocytosis. The fact that bacteria, which are very similar to mitochondria and chloroplasts, existed before the eukaryotic cell shows evidence that it was bacteria that was integrated into a eukaryotic cell rather than eukaryotes being entirely separate in evolutionary history. This timeline also gives evidence as to why a symbiotic relationship would be beneficial.

The photosynthetic and aerobic bacteria were naturally driven to enter into this relationship because the eukaryotic cell supplies both protection and nutrients, and the bacteria supply ways for eukaryotes to harness more energy than they previously could using only glycolysis.

This (above) is the second stage of the glycolysis process (the only stage that actually produces the ATP), and as you can see it only produces a total of 4 ATP (2 net ATP). When this process is combined with the Krebs cycle and oxidative phosphorylation (which requires mitochondria), the net amount of ATP produced is 36-38 molecules.

By eukaryotic cells engulfing photosynthetic bacteria, they could then create  glucose molecules that could then be used to go through the catabolic processes in the mitochondria, and hence, the eukaryotic cell harnesses even more energy than it would on its own. Having so much energy to drive cellular processes makes this new eukaryotic cell more fit for survival.

Double Phospholipid Bilayer

A fairly simple piece of evidence for the endosymbiotic hypothesis is the fact that both mitochondria and chloroplasts have double phospholipid bilayers. This appears to have arisen by mitochondria and chloroplasts entering eukaryotic cells via endocytosis. Both purple, aerobic bacteria (similar to mitochondria) and photosynthetic bacteria (similar to chloroplasts) only have one phospholipid bilayer, but when they enter another cell via endocytosis, they are bound by a vesicle which forms the second layer of their double phospholipid bilayer.

This video shows the process of endocytosis of aerobic bacteria and photosynthetic bacteria very well.

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