Introduction to the Euglena

It is found in fresh water (often in puddles or ponds) and differs from ameoba and paramecium in being able to photosynthesize, and so produce its own source of food.  The euglena appears green due to the chloroplasts in its cytoplasm, sites where photosynthesis occurs.  In reality, these can often appear clearer and larger than in my diagram, like green rods.

The euglena can also surround and take on food through phagocytosis (see my blog on ameoba) so is not entirely autotrophic (producing its own food).

Movement in Euglena

Euglena moves by thrashing its whip-like tail or flagellum.  In fact, it has two flagella, one far smaller (not shown).  These produce a spiral, helicoidal motion which casues the euglena to spin along as it moves forward.  To see euglena moving, and how bright green they are, have a look at Craig Smith’s euglena video.

The eye of the Euglena

The stigma is a visibly red eye-spot, its colour coming from caratenoid pigmentation.  This little spot will cover up a photo-receptive area (the paraflagellar body) at the base of the flagella periodically, causing the euglena to change position until the photoreceptor is exposed again.  This cunning process means the euglena can sense where light is, and move towards it.  Obviously, in an organism that requires sunlight to photosynthesize and thus feed itself, moving towards light is paramount.

As with amoeba and paramecium, the unicellular euglena needs to regulate water levels within its body.  It uses a contractile vacuole for this, which expells excess water and thus ensures osmoregulation.  As with paramecium, there are radiating canals, functioning like drainage paths, leading to the vacuole.  Without a contractile vacuole; euglena, ameoba, and paramecium would absorb too much water through osmosis and would explode.

Euglena store carbohydrates in their bodies in the form of paramylon or paramylum granules, similar to starch.  These reserves vary in size and act as food reserves.

Their nucleus controls all the life functions; feeding, growth, regulation, digestion and (within the nucleolus inside the nucleus) reproduction.  Euglena can only reproduce asexualy, through binary fission,  The nucleus divides mitotically and then the cytoplasm will split longditudinally.

I’m no expert on micro-organisms, and in fact when I was at University they were all still bundled together into the now obsolete phylum of “protozoa”.  Please do let me know if there are any mistakes that need fixing, and I’d be delighted to fix them.

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Introduction to the Paramecium

Like the amoeba, 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.  They are used to propel the animal through water.  As these rows of hairs spiral around the body, the Paramecium spins as it swims.

The cilia protrude from a flexible yet stiff cell membrane, called a pellicle.

Anatomy of the Paramecium

At the top of the diagram you can see the contractile vacuole.   There’s one at either end of the paramecium; unlike amoeba, paramecium have a consistent body shape.  These vacuoles make sure there’s not too much nor too little water inside the animal’s cell membrane.  Spreading out from these vacuoles are radiating canals which provide paths to the vacoule.

A paramecium body is full of cytoplasm which maintains organelles.

Paramecium feeding

Paramecium eat through an oral groove, which directs food into the paramecium’s mouth (or cytosome).  Food is brought to this area by ciliary action; once at the mouth it’s packaged into food vacuoles.  Here, the food is digested as it circulates in the animal’s body.  See this process in action below.

Nucleus of the Paramecium

The macronucleus programs and runs the paramecium; it controls digestion, growth, movement, and other cell functions.

The micronucleus is separate and controls reproduction.  Paramecium can reproduce asexually ( up to two or three times a day) by dividing with binary fission.  Less usually, they reproduce sexually through conjugation. This involves fusing material from two micronuclei, which undergo meiosis before three of the four resulting nucleii disintegrate.  The remaining nucleus undergoes mitosis. Daughter nuclei join before the cells split apart. The original macronucleus disintegrates, and is replaced with a newly formed one. After this, asexual reproduction normally occurs.

Paramecium can defend themselves!

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.  Below are some trychocsyts in action:

More 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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Amoeba: an introduction

Amoeba are free-living aquatic creatures, and can be seen in any drop of standing fresh water, if you put it under a compound microscope.  They also occur in salt-water, and as parasites within other animals (such as humans).  The largest is a little under 1mm in size. They change shape by oozing outwards into pseudopods, and use these to engulf food.  So these pseudopods surround foodwith a water droplet, then take it into their bodies to digest. These packets of food are called food vacuoles. The engulfing process is known as phagocytosis. For a video showing this process please click on the link: Ameoba eats two paramecium.

Anatomy of the Amoeba

Amoeba aren’t blue.  (Interestingly, another micro-organism called Stentor certainly IS blue).  I used the colour to show the amoeba’s features.

Although they always change shape, amoeba seem to have a  definite end, which is known as its uroid.

Their contractile vacuole is used to regulate the amount of water in their body, and is near the uroid.

The nucleus is where information and genetic material is stored; it controls reproduction, eating, and growth.

Pseudopodium are organelles which “walk”.  They extend from the body, then cytoplasm flows into them, and the amoeba is propelled forward.

The amoeba body is full of cytoplasm.  This is clear plasmagel (seen toward the edges of the pseudopods, just below the cell membrane); or it is granulated endoplasm (further inside the body).

Amoeba breathe by diffusing oxygen through their cell membranes.  They reproduce asexually by dividing their cytoplasm and nucleus through mitotic division, in a process called binary fission.  This produces two identical daughters.

Although I love micro-organisms I am no expert, so get in touch if you spot errors, I’ll be more than happy to fix them.  Next week: the Paramecium! And for the third micro-organism, I’ll be looking at the euglena.

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