A Look at a Living Plant Ancestor
http://people.westminstercollege.edu/faculty/tharrison/emigration/cladophora.htm
Cladophora sp.
This alga represents an increase in filament complexity in two ways: the cells are multinucleate;
and the filaments are branched. Examine the living culture and prepare a slide of Cladophora.
Cladophora sp.
Prepare a slide from the living culture of Cladophora sp. Examine under the microscope, first under low
power and then high.
In your notebook, make a drawing of Cladophora under both low and high power.. Label your
drawing with a title, the magnification, and identify where the cell wall can be seen. Look for the
small green structures which are chloroplasts and label them.
What is Algae?
Algae are plantlike protists found in the Kingdom Protista. Protists are eukaryotic, unicellular or
multicellular organisms. Like plants, algae have chloroplasts, and their cells are strengthened by the cell
wall. Algae refer to aquatic organisms that carry on photosynthesis. Algae are part of a fresh water's
phytoplankton (phyton=plant and planktos=wandering), which produce energy that maintains an entire
community of organisms. Not only do algae provide food, but they also play a key role in the stream
ecosystem because they produce oxygen.
It has been customary to classify algae according to their color, which come in a variety of color such as
green Chlorophyta, brown Phaeaphyta, golden brown Chrysphyta, and red Rhodophyta. All algae do
contain at least one type of chlorophyll, but they also contain other types of pigments, which mask the
color of the chlorophyll.
Green algae are the most plantlike of the all the algae. Green algae are believed to be closely related to
the first plants because they have a cell wall that contains cellulose, they possess chlorophyll a and b,
and they store reserve food as starch inside the chloroplast.
Some algae are colonial, which means there is a loose association of independent cells that are
specialized for reproduction. Algae that are multicellular have specialized tissues, but are not considered
to be plants because they are adapted to water environments and have not evolved to protect their
gametes and zygotes from drying out.
Habitats and Distribution of Algae
Green algae like to grow in wet places like lakes, ponds, ditches, and streams. They can also be found on
damp soil and on the shaded sides of damp walls and trees. The chemical nature of water is a major
factor that strongly influences the growth, abundance and distribution of algae. Some algae favor acidic
conditions, some like neutral conditions and a few prefer alkaline conditions.
What is Cladophora?
When examined with the microscope, Cladophora filaments are branched, which are often spaced
distantly and sparingly. Fronds are the whole system of branched filaments and are attached to rocks on
the stream bottom. Fronds of Cladophora are frequently covered with ephiphytic diatoms, in fact, there
can be so many diatoms that it is difficult to observe the Cladophora cells.
When growth conditions are favorable, Cladophora reproduces asexually. The adult alga divides, forming
zoospores or flagellated spores that are smaller than the parent cell. A spore is a haploid body that
develops into a mature adult. When growth conditions are unfavorable, Cladophora reproduces sexually.
Gametes from two different mating gamates come into contact and join to form a zygote. When a
zygospore germinates, it produces four zoospore by meiosis. A heavy wall forms around the zygote and it
becomes a resistant zygospore, which is able to survive until conditions are favorable for germination.
The zoospores are haploid and are released in the spring to grow into adult algal filaments such as those
shown in the above photomicrograph. Isogamy (GK. isos: equal and gamos: marriage, union) is the
conditions where gametes are identical. These gametes are known as isogametes.
1.
Why are algae important members of a community?
2.
Why are green algae considered to be so closely related to the first plants?
3.
What are fronds?
4.
How does Cladophora reproduce when conditions are favorable?
5.
How does Cladophora reproduce when conditions are unfavorable?
Ref: http://people.westminstercollege.edu/faculty/tharrison/emigration/cladophora.htm