Hi friends, in our previous session we discussed that the green algae which we found spreading all over the lakes and ponds actually have some interesting features which let us relate them to green plants. First in discussion is the green algae Chlamydomonas. which are the simplest unicellular motile green algae. Now guys, the green pond that you see here is green because of the presence of a number of green algae in it.
And friends, one of the most important green algae present in this green pond is Chlamydomonas. Yes guys, Chlamydomonas are mostly found in fresh water like ponds as well as lakes. Also guys, do you know that we can find Chlamydomonas in some unusual habitats too, like in snow and ice. Yes friends, the snow found in the Alps region appears red in colour because of the species of Chlamydomonas which is Chlamydomonas nivellus. The snow becomes red in colour because of the spores that are released by this Chlamydomonas.
Also friends, Chlamydomonas usually delve in waters which are rich in ammonium compounds. Let us now see how does a single chlamydomonas cell look like. So friends, chlamydomonas cell has a pier shaped or a droplet shaped structure.
This pier shaped or droplet shaped structure has a cell wall and this cell wall is made of glycoproteins. Thus, there is no cellulose in the cell wall of chlamydomonas. Also guys, some species have mucilaginous covering around them. Now guys, what is to be noted here is that from the anterior end of the droplet shaped cell comes out two flagella. And now, these two flagella are equal in their length and they are of whiplash type.
Whiplash type flagella means that the flagella are broad at the bottom and they are tapering at their ends. The chlamydomona cell pull itself forward in the watery environment with the help of these two flagella. Also friends, the flagella which you see here from the anterior end are arise from the basal granules.
These basal granules which are found at the anterior end give rise to these two equal size flagella. And they are also known as, the basal granules are also known as Also friends, at the anterior end of this droplet shaped cell is present a protoplasmic papilla known as apical papilla. Now friends, like any other eukaryotic cell, cell. There is a centrally placed nucleus in this cell.
Also there is a cup shaped chloroplast and there are two contractile vacuoles just below the basal granules. Let us now see what are the roles and what are the details of contractile vacuole chloroplast in the chlamydomonas cell. Any guesses what could be the role of contractile vacuole in a chlamydomonas cell well guys we all know that chlamydomonas are found in watery habitat so guys the contractile vacuole of chlamydomonas cell helps it to maintain a balance of water and minerals inside the water and also this contractile vacuole enables the cell to excrete out excess of water which might enter into the cell from the watery habitat.
Yes guys, maintenance of water and minerals is known as osmoregulation. So in other words, we can say that contractile vacuole of chlamydomonas cell enables it in osmoregulation. Are these green algae reminding you of any other protist that you might have learnt? Yes, I know most of their features are resembling Euglena but there is a difference guys.
Euglena is both a plant like as well as an animal like protist but chlamydomonas are solely plant like green algae. algae. Now guys let's move on and talk about the cup shaped chloroplast. The cup shaped Chloroplast in chlamydomonas occupies most of the space in the cell and it is because of this chloroplast that chlamydomonas are able to manufacture their food by the process of photosynthesis inside This big cup shaped chloroplast is found a distinct round protein body which is known as pyranoid. Pyranoid is made of protein but it is the site of synthesis of starch.
Yes, production as well as storage of starch occurs around or inside these pyrenoids. At one end of this cup shaped chloroplast is found a tiny spot like organ which is known as eye spot or stigma. Now friends, eye spot is a photoreceptive organ. So it is pigmented and and it is photoreceptive which means that it can sense the light stimulus.
As soon as it senses the light stimulus, it enables the chlamydomonas to swim towards the light. Now guys, if we see this cell, So this is how this cell looks like. Yes, there is an anterior end, there is a drop shaped and there are two flagellas.
Along with it, there is a big cup shaped chloroplast, a tiny spot. known as eye spot, a single pyrenoid inside the chloroplast and also a single nucleus along with it two contractile vacuoles and two basal granules. So it's a wonderful structure of this unicellular green algae. Apart from all these structures, there are usual organelles like mitochondria, golgi, ER which makes it a perfect eukaryotic plant-like cell. Let's move on and talk about reproduction in chlamydomonas.
Guys, chlamydomonas can reproduce both by asexual method and sexual method. Asexual methods of reproduction can occur by four means which are formation of flagellated zoospores or by formation of thin-walled non-motile aplanospores. Also, it can occur by formation of thick-walled non-motile hypnospores and by Pamela stage formation. Now guys, zoospore formation occurs under favorable conditions and it is also the most common method of asexual reproduction in chlamydomonas. So, when there is a sufficient amount of water and food in the surroundings, chlamydomonas produce motile zoospores by mitotic division.
But, aplanospore formation, hypnospore formation, and pormala stage formation occurs only under unfavorable conditions. Now guys, Hypnospores as I said are thick walled non-motile spores and they are also resting spores. But there is something special about these hypnospores which we will talk. The hypnospores are red in color.
Yes. They have a reddish pigment hematochrome in them. And if you remember I said that Clomidomonas nivellus which lives in ice and snow gives the red colour to the ice and snow. And that red colour is because of the hematochrome which is present in the hypnospores. The Clomidomonas nivellus secretes out the hypnospores which give red colour to the snow.
I mentioned that one of the important method of asexual reproduction in chlamydomonas under unfavorable conditions was parmala stage formation and I'm sure guys you definitely want to know more about this unique stage. So friends during unfavorable conditions like the presence of toxic chemicals or extreme drought condition chlamydomonas forms parmala stage formation stage now what is this stage? What actually happens is that during these unfavourable conditions individual chlamydomonas cell withdraw their flagella.
After withdrawal of flagella the cells start dividing. They divide into 2s, 4s, 8s and so on and the repeated division continue to make some hundreds and thousands of cells and these hundreds and thousands of cells get enclosed in a gelatinous matrix secreting the cell. treated by the parent cell.
This stage which is form guys is known as Pamela stage. All the daughter cells in this gelatinous matrix are non-motile. Once the favorable conditions return, like there is a surplus amount of water in the surroundings, then the gelatinous covering of the parmilla stage dissolves and the cells come out.
These cells develop flagella and now they can grow up to make new individual chlamydomonas cell. Isn't it wonderful guys? The Chlamydomonas green algae is so smart.
It knows how to survive in crisis situations. Next in discussion comes the sexual reproduction in Chlamydomonas which can occur by Isogamy, Anisogamy, Oogamy and Hologamy. Now guys, we are all aware of all these processes.
Yes, in Chlamydomonas, Isogamy means that the gametes which are formed by chlamydomona cells are exactly similar in their shape as well as size. Anisogamy means that the gametes which are formed are unequal. Oogamy means that the gametes which are formed, one of the gamete which is usually female gamete is larger in size and is non-mortile and the male gamete is smaller in size and more time and hologamy means that the vegetative chlamydomona cell directly accesses the act as gamete and during the gametic fusion their wall dissolves.
Now guys after these processes what happens is the fusion of gametes. Yes the gametes fuse together and fertilize to form a diploid zygote. This diploid zygote undergoes the process of meiosis immediately. Yes, the diploid zygote undergoes meiosis to form haploid spores which are flagellated.
These haploid spores known as zoomeospores can further develop into the new haploid individual chlamydomonas cells. So what do you infer from this? Yes, individual chlamydomonas green algae is haploid and the only diploid state is the zygote, which makes the life cycle of chlamydomonas haplontic type of life cycle.
So knowing all about the features as well as the behavior of chlamydomonas, aren't these green algae also very fascinating? And thus, they contribute a lot to the varied world of green algae. On this note, let us conclude this session and discuss another beautiful green algae ballwalks in the upcoming session. But before concluding, it is the right time to summarize whatever we have learned in this session.
session about chlamydomonas. Chlamydomonas is the simplest unicellular motile green alga found mostly in fresh water. Chlamydomonas cells are pear shaped and the anterior pointed end of the cell contains contains two equal size flagella.
The flagella in chlamydomona cell arise from basal granules also known as blepharoplast and they also contain two contractile vacuoles which help to in excretion and osmoregulation. Chlamydomonas cells have a large cup-shaped chloroplast which contains a distinct round protein body called pyranoid. Asexual reproduction in chlamydomonas can occur by four methods which are formation of flagellated zoospores, formation of non-motile thin-walled aplanospores, formation of non-motile called hypnospores and parmala stage formation.
Sexual reproduction in chlamydomonas can occur by isogamy, anisogamy, oogamy and hologamy. The zygote formed in chlamydomonas as a result of fertilization is diploid and undergoes meiosis to produce haploid spores which later form individual chlamydomonas cells which are haploid.