Major stages in the evolution of living things Flashcards
what are four of the MAIN key dates
Formation of the Earth - 4.56 Billion years ago
Earliest unicellular life (prokaryote) - 3.8 - 4 Billion years ago
Oxygen from autotrophic prokaryotes (photosynthesis) - 2 Billion years ago
Eukaryotic cells - approx 1.5 Billion years ago
The current scientific thinking is that the major stages in the evolution of life are Earth are:
organic molecules
membranes
prokaryotic heterotrophic cells
prokaryotic autotropic cells
eukaryotic cells
colonial organisms
multicellular organisms
functions of membranes
They perform the function of containing and protecting the organic molecules within.
Controls the movement of materials between the internal and external environments. One quarter of the energy used by cells is designated to this function.
Separates the internal and external environment. This makes it possible for different substances to be present and enables life processes to occur.
Macromolecules (large molecules) would have difficulty reproducing unless they were surrounded by membranes that prevent the loss of materials to the surroundings. This protection is another advantage of membranes.
When did a membrane-bound unit become a cell?
Around 3.8 billion years ago.
This simple unit developed the ability to survive and reproduce independently–the first cell.
what what the first cell to form
the prokaryotic cell
how are prokaryotes different from other cells?
they have no internal membrane-bound organelles.
are prokaryotes autotrophic or heterotrophic?
both
how abundant are prokaryotic cells
they are still the most abundant form of life on the Earth
were the earliest prokaryotic cells autotrophic or heterotrophic?
heterotrophic
heterotrophic prokaryotes would probably have utilised nutrients such as?
carbohydrates
amino acids
other organic compounds in their environment
why would some heterotrophic prokaryotes have disappeared?
Gradually, as the nutrients were depleted, the competition between the organisms would have increased.
Those organisms that were inefficient at obtaining nutrients would have disappeared and only those that were able to most efficiently obtain nutrients would survive.
It follows then that natural selection would have favoured any changes or mutations in an organism that enhanced its ability to gain nutrition.
For example, organisms capable of biochemical reactions to synthesise materials required to sustain living process would be advantaged.
how would some heterotrophic prokaryotes have survived as nutrients were depleted
already efficient at obtaining nutrients
organisms with advantageous gene or mutation that was beneficial
some organisms may have developed alternate methods of obtaining nutrition such as parasitism, predation, or saprophytism
which was most important for scientists, autotrophic or heterotrophic prokaryotes
autotrophic prokaryotes
what did the existence of autotrophic prokaryotes mean about the conditions on early earth
the presence of free oxygen in the atmosphere (oxic environment)
the start of the ozone layer which reduced the amount of ultraviolet radiation hitting the Earth’s surface
changed the earths atmosphere
how did autotrophic organisms mean oxygen levels increased
because during photosynthesis they would have released oxygen as a waste product
the introduction of oxygen into the atmosphere meant what could no occur
respiration, a more efficient way of gaining energy
why is the ozone layer so important
absorbs most of the Sun’s ultraviolet radiation, preventing it from reaching the Earth’s surface
Ultraviolet radiation is harmful to life
Without the ozone layer, life could only exist underwater
This is thought to be the reason why both plants and animals were thought to move onto land (terrestrial environments) around the same time, approximately 350 million years ago
how is it is thought that eucaryotic cells evolved?
from large procaryotic cells that ingested other free-floating procaryotes
they formed a symbiotic relationship with the cells they engulfed
