Natural history illustration involves painting plants, animals, and other wonders of the natural world. Micro-organisms fall under this umbrella, and although extremely small they are still deserving of our attention (and illustrations). Last week I looked at the Ameoba. This week it's the turn of the Paramecium.
Like the ameoba, the Paramecium is an independent, free-living unicellular organism. Paramecium can be found in abundance in stagnant water where they feed off tiny bits of plant, and bacteria. The largest are only 1/2mm long, so to examine them a microscope is required.
They're part of a phylum called Ciliophora which refers to the cilia, or tiny "hairs", found all over their bodies. Each row of cilia beats in a wave-like metachronal rhythm, and are used to propel the animal through the water. As these rows spiral around the body, the Paramecium tends to spin as it swims.
The cilia protrude from a flexible yet stiff cell membrane, called a pellicle.
At the top of the diagram you can see the contractile vacuole (there's one at either end of the paramecium, who have a consistent body shape). These osmoregulate and make sure there's neither too much nor too little water within the animal's cell membrane. Spreading out from these vacuoles are radiating canals which provide paths to the vacoule.
The paramecium eats through an oral groove, which directs the food into the paramecium's mouth (or cytosome). Food is brought to this area by ciliary action, and once at the mouth it's packaged into food vacuoles where the food is digested as it circulates within the animal's body. To see this process in action, follow the link to Craig Smith's youtube video.
A paramecium body is full of cytoplasm which maintains the organelles of the organism.
The macro or meganucleus programmes and runs the paramecium, controlling digestion, growth, movement, and other cell funtions.
The micronucleus is separate and controls reproduction. Paramecium can reproduce asexually (two or three times a day) by dividing with binary fission. Less usually, they can reproduce sexually through conjugation. This involves fusing material from two micronuclei, which undergo meiosis before three of the four resulting nucleii diintegrate. The remaining nucleus undergoes mitosis. Daughter nuclei join before the cells split apart. The original macronucleus disintegrates, being replaced with a newly formed one. After this, asexual reproduction normally occurs.
Paramecium can defend themselves with the use of trychocysts, similar in function to those found in the jellyfish and sea anenomes. These trychocysts are needle llike projections that can be ejected out from the cell mebrane. Click on the link to see paramecium trychocysts in action.
More on paramecium can be found at 101Science's site where I did some research.
Next week: the Euglena!
Although I love micro-organisms I am certainly no expert, so please get in touch if you spot any errors, I'd be more than happy to fix them.
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Category: Zoology Terms and Anatomy | Comments: 0 | Viewed: 2189