The Fossil Record, Handout
Cells:
Basic features of all cells:
Cells are bound by a plasma membrane and have a cytosol with subcellular
components. They contain chromosomes and ribosomes.
Difference between prokaryotic and eukaryotic cells:
In eukaryotic cells the DNA is in the nucleus (in prokaryotes the DNA is circular and free
in the cytoplasm), and eukaryotes have membrane-bound organelles.
Animal and plant cells are both eukaryotic cells, but there are differences. Plant cells
also have: Chloroplast (photosynthetic organelle), cell walls (surrounds plasma
membrane, for stability and protection) and vacuoles (turgor, growth, storage and
breakdown of waste products). Vacuoles take up water easily, which leads to cell
,expansion. Microfibrils in the cell wall prevent the cell from getting thicker, so growth
happens perpendicular to the orientation of the microfibrils, growth by cell elongation.
Plant cells also have plasmodesmata:
Water and small solutes pass
freely from cell to cell through the
Symplastic route.
Symplast → Continuum of
cytosol connected by
plasmodesmata.
Apoplast → Continuum of cell
walls and extracellular spaces.
Horizontal gene transfer: There are several mechanisms for transferring genes from
one genome to another horizontally across the evolutionary tree. Some argue this was
so common in early life, that it should be represented as a network of branches, rather
than dichotomously.
One of the ways for horizontal gene transfer is Endosymbiosis (fusion of organisms).
The endosymbiosis theory describes how one organism is engulfed by another. Over
time, they form a close relationship that can be advantageous for both partners. The
larger host cell provides protection and essential nutrients, and the internalized
microbe contributes its specialized functions, becoming an organelle within the host
cell. Endosymbiosis happened in a serial order; first the mitochondria was created,
then the plastids (all eukaryotic cells have mitochondria; not all have plastids).
Primary endosymbiosis refers to the initial engulfment of a free-living bacteria by a host
cell, creating a new organelle.
Secondary endosymbiosis involves a eukaryotic cell engulfing another eukaryotic cell
already undergoing primary symbiosis. This leads to a more complex cellular
arrangement. Different groups of algae have acquired plastids through secondary
endosymbiosis.
Evidence that supports the endosymbiosis theory is:
- Structural similarities; organelles in eukaryotic cells share characteristics with free-
living bacteria, such as double membranes and replication by splitting; like bacteria.
Mitochondria and chloroplasts also have independent, circular DNA that is more similar
to bacterial DNA than that of the host. Analysis of genetic sequences also shows that
mitochondria and chloroplasts are more closely related to specific groups of bacteria
than to eukaryotic cells.
p. 284-302 Mitosis
,Mitosis: One diploid (2N) cell becomes two diploid (2N) cells. Mitosis produces cells for
growth and enables multicellular plant (gametophyte or sporophyte) to arise from a
single cell. Gametes in the plant gametophyte are created by mitosis.
Meiosis: One diploid (2N) becomes 4 haploid (1N) cells. Meiosis reduces the number of
chromosomes by half and introduces genetic variability among spores. Spores in the
plant sporophyte are created by meiosis.
p. 304-318 Sexual Life Cycles and Meiosis
, ALGAE:
Green algae are thought to be the direct
ancestors of plants. Starting from
charophytes, plants could acquire traits that
would help them adapt to life on land.
Red and green algae went through primary
endosymbiosis; brown algae also went
through secondary endosymbiosis.
Algae don’t have differentiation of
tissues yet, so they do not have roots, a stem or leaves. We speak of a holdfast, a stipe
and a blade. They are made of thallus, undifferentiated tissue. The gametophyte in algae
is dominant.
Brown Algae:
Brown algae are mostly a marine group and dominate the rocky shore in cooler regions
of the world. Kelp forests exist out of brown algae. There are about 1500 species, e.g.
Laminaria. The pigment fucoxanthin gives them their characteristic colour. They have
an alternation of heteromorphic
generations. Brown algae contain a lot
of algin, an important polysaccharide
from the cell walls.
Lifecycle of Laminaria.
Cells:
Basic features of all cells:
Cells are bound by a plasma membrane and have a cytosol with subcellular
components. They contain chromosomes and ribosomes.
Difference between prokaryotic and eukaryotic cells:
In eukaryotic cells the DNA is in the nucleus (in prokaryotes the DNA is circular and free
in the cytoplasm), and eukaryotes have membrane-bound organelles.
Animal and plant cells are both eukaryotic cells, but there are differences. Plant cells
also have: Chloroplast (photosynthetic organelle), cell walls (surrounds plasma
membrane, for stability and protection) and vacuoles (turgor, growth, storage and
breakdown of waste products). Vacuoles take up water easily, which leads to cell
,expansion. Microfibrils in the cell wall prevent the cell from getting thicker, so growth
happens perpendicular to the orientation of the microfibrils, growth by cell elongation.
Plant cells also have plasmodesmata:
Water and small solutes pass
freely from cell to cell through the
Symplastic route.
Symplast → Continuum of
cytosol connected by
plasmodesmata.
Apoplast → Continuum of cell
walls and extracellular spaces.
Horizontal gene transfer: There are several mechanisms for transferring genes from
one genome to another horizontally across the evolutionary tree. Some argue this was
so common in early life, that it should be represented as a network of branches, rather
than dichotomously.
One of the ways for horizontal gene transfer is Endosymbiosis (fusion of organisms).
The endosymbiosis theory describes how one organism is engulfed by another. Over
time, they form a close relationship that can be advantageous for both partners. The
larger host cell provides protection and essential nutrients, and the internalized
microbe contributes its specialized functions, becoming an organelle within the host
cell. Endosymbiosis happened in a serial order; first the mitochondria was created,
then the plastids (all eukaryotic cells have mitochondria; not all have plastids).
Primary endosymbiosis refers to the initial engulfment of a free-living bacteria by a host
cell, creating a new organelle.
Secondary endosymbiosis involves a eukaryotic cell engulfing another eukaryotic cell
already undergoing primary symbiosis. This leads to a more complex cellular
arrangement. Different groups of algae have acquired plastids through secondary
endosymbiosis.
Evidence that supports the endosymbiosis theory is:
- Structural similarities; organelles in eukaryotic cells share characteristics with free-
living bacteria, such as double membranes and replication by splitting; like bacteria.
Mitochondria and chloroplasts also have independent, circular DNA that is more similar
to bacterial DNA than that of the host. Analysis of genetic sequences also shows that
mitochondria and chloroplasts are more closely related to specific groups of bacteria
than to eukaryotic cells.
p. 284-302 Mitosis
,Mitosis: One diploid (2N) cell becomes two diploid (2N) cells. Mitosis produces cells for
growth and enables multicellular plant (gametophyte or sporophyte) to arise from a
single cell. Gametes in the plant gametophyte are created by mitosis.
Meiosis: One diploid (2N) becomes 4 haploid (1N) cells. Meiosis reduces the number of
chromosomes by half and introduces genetic variability among spores. Spores in the
plant sporophyte are created by meiosis.
p. 304-318 Sexual Life Cycles and Meiosis
, ALGAE:
Green algae are thought to be the direct
ancestors of plants. Starting from
charophytes, plants could acquire traits that
would help them adapt to life on land.
Red and green algae went through primary
endosymbiosis; brown algae also went
through secondary endosymbiosis.
Algae don’t have differentiation of
tissues yet, so they do not have roots, a stem or leaves. We speak of a holdfast, a stipe
and a blade. They are made of thallus, undifferentiated tissue. The gametophyte in algae
is dominant.
Brown Algae:
Brown algae are mostly a marine group and dominate the rocky shore in cooler regions
of the world. Kelp forests exist out of brown algae. There are about 1500 species, e.g.
Laminaria. The pigment fucoxanthin gives them their characteristic colour. They have
an alternation of heteromorphic
generations. Brown algae contain a lot
of algin, an important polysaccharide
from the cell walls.
Lifecycle of Laminaria.
