what makes protozoa move?

Since protozoa have no brain, nervous system, muscles etc, but are only single-celled how do scientists explain their movement and why and how they choose to go one direction or another? I find that to be a difficult question.

cilia: small rythmically beating microtubule “hairs” on the cells surface move in waves and propel protozoans such as paramecium throug the water. (cilia are also present in your lungs, and move dirt and other debreis upwards , our of the bronchi)

Flagella: a larger, microtubule structure shaped like a whip that beats regularly, somewhat like a fishes tail (human sperm cells have flagelae).

Pseudopods: Amoeba use their cytoskeleton (i think) to distort the cells shape into little blobs that look like limbs. by moving these blobs, they can move themselves and engulf food.

but what makes that stuff move when they have no nervous system to coordinate it?

protozoa gas…



That’s a damn good question, ben123. I looked it up and found something similiar to T’s post, though its movement was not explained.

My guess is that due to the simplicity of the organism and its nervous system (or lack thereof), it doesn’t respond to an enviroment in the sense that it can anticipate or react to anything, such as organisms with nervous systems and sensory organs. I think the metabolic processes within the organism do not direct it, via the nervous system and memory reflex, in such a way as to align it with its enviroment in an ‘action+assessment=reaction’ process. I think the thing just simply moves in one direction until it impacts with a food source which it then consumes, maybe. As for how it moves, well, I guess at an elementary level all that is happening is a series of chemicle reactions that propel it by electrical impulses. Similiar to muscle fibers flexing and contracting, though the movement isn’t created through any specific anatomical function, such as the cilia, which we would have to assume is the function of the cilia, such as T mentioned.

I don’t know about that. That would suggest that there is indeed a nervous system that coordinates the appendages. I dunno.

I have heard that some microbes respond to magnetic forces and temperatures. Perhaps the same thing happens with protozoan.

Damn that’s a good question. Abgrund knows about this kind of shit, I’m sure. Speak up, dude, if your out there.

Meanwhile let’s run a google.

Bonus points for the first one to find an explaination.

Interesting topic!

How is this movement coordinated? Well, it isn’t.


Plants have no nervous system and no muscles. Yet they grow towards the light. How? Throughout the plant’s stem there is an even concentration of a substance (a plant hormone) that induces growth. This substance is sensitive to light, in the sense that light causes the molecule to change. Basically, the hormone is destroyed by the light. Given the fact that the light intensity is much higher at sunside than at shadowside, the rate of destruction of the hormone is much higher at sunside. In effect, hormone concentrations at shadowside are higher and that side of the stem grows faster. This causes the stem to bend towards the light. It’s basic photchemistry, really.

This example is relevant because it shows that organisms need not have muscles and/or neurons in order to show directed movement.

In the case of single-cellular organisms, not every question has been answered (far from it). Yet the general idea seems to be that the organism responds to the presence of certain external fields, such as gradients in the concentration of foodstuffs or gases, temperature, pressure or even magnetism (the pigeon is capable of detecting the Earth’s magnetic field), each external field leading to the asymmetrical distrubution of certain substances, which in turn causes processes to occur locally in the cell.

(Sidenote #1: I’d like to point out that the directional movement of a single-cellular organism is rather trivial, as in aquatic media even the smallest disturbance of its surroundings will be much more powerful than any movement of the organism itself.)

(Sidenote #2: The question posed by ben123 is not unlike the question how a single-celled zygote (a fertilized human egg) develops systematically into a multicellular organism. Again, the method seems to hinge on concentration differences in various substances within the cell.)

So much for general principles regarding the perceived “coordination” of the movement. In more detail, the actual mechanism of how cilia and flagelles move is well understood. Click here for an oustanding animated explanation of the mechanism (this is really good stuff, by all means take a moment to see this!). In the case of an amoeba (which doesn’t have cilia or flagelles), in layman’s terms, a scaffolding is present inside the amoeba. This scaffolding is erected at one end of the organism and taken down at another end (much like laying rails in front of a moving locomotive and removing it again once it has passed). the scaffolding is made of actin and myosin fibres. If you’ve done some biology, then those names should ring a bell. See this page for some wonderful images. And for (just some) of the scientific nitty gritty about the shape of amoeba and the effect of myosin and actin on it, click here.

thanks for the responses. I guess I understand it better now and I understand how a plant appears to be almost coordinated in its movements because of the hormones but protozoa move very rapidly especially paramecia whereas plants move very slowly. Could hormones react to environmental stimuli fast enough to account for rapid changes in direction? I suppose its possible because maybe the individual plant cells respond to light just as quickly though I’ve never seen the process at a microscopic level. I like the idea of responding to magnetism too and stuff but it’s hard to be completely satisfied by this. Also does the nucleus in any way act as a very rudimentary brain? i guess this question always bothered me because with multi-celled animals they always taught us that the brain sends an electrical signal to the muscle which contracts and voila there is movement but when you take away neurons and these critters are smaller than a single neuron it’s hard for me to explain the movement though yes plants move without a nervous system but the movement seems different. Because what keeps cilia moving back and forth when there are no electrical impulses being sent since there are no neurons to conduct them? In other words overall direction of movement can be explained by sensitivity to various stimuli but I guess I’m looking for how the organism internally coordiantes these processes. Plant movement is powered by uneven growth rate which takes awhile while animal movement is powered by electricity which is fast I guess is what I’m saying but there doesn’t appear to be a nervous system. I liked the website on the flagellum movement but I’m not sure if it answers my question or not. I guess the ATP is the power source as I imagine it is in all cellular processes but it’s not very clear in my mind how the whole thing works but it’s a difficult question. The gradient answer almost suggests the protozoa is powered by changes in the environment shifting its molecules unevenly rather than its internal processes being self powered or internally coordinated in a certain way and these things do at least appear to be more than say leaves blowing in the wind where the movement is totally caused by the environment.