David Beeson, April 2022
A bit of a specialist topic, I agree, but stay with me and perhaps I will change your mind about algae … they can be quite interesting. And, as for a microscope, well, mine cost only £105 and it is first-year university standard, but cheap as an unwanted present bought from eBay. Go on, have a look!
The diversity of life is not straightforward. It would be great if everything followed the rules, yet evolution sometimes twitches off the straight and narrow. And, that makes things interesting. Sure, we have animals – things that move and eat other organisms. Then we have plants – green, photosynthetic … mostly. Fungi are hyphoid, non-green and eat other organisms, be they dead or alive. Bacteria lack a nucleus and are microscopic. Then there are all the leftovers that fail to fit neatly into that package. The famous amoeba, that is unicellular and crawls over the bed of aquatic systems is probably best characterised as an animal-like protist, but what about Eugena which can be green in the light, and photosynthesise, yet loses it green and eats other organisms in the dark? Imagine a pet green houseplant that turns carnivore overnight and eats you up! A triffid?
Some biologists place eugenoids within the Kingdom Protista, others are content to label them a plant.
So, let me take you down to the pond and search out Eugena and Chara.
A glass jar is dipped into the murkiest green-brown sludge of fresh water and is carried back to the kitchen table, to meet your new microscope. A single drop of water is added to your slide and a coverslip added, attempting to exclude air bubbles. Set up your x10 or x4 objective lens and focus (remembering to adjust the condenser and iris diaphragm for the best image). Students never did, but you should now use the mechanical stage to tour your specimen to find the best spot to further study. Now, if not on x10 objective, move there. Wonders of biology will be displayed before you. Perfectly complete organisms greet you whose way of life is a stark contrast to your own.
It takes a while for the organisms to show themselves. Be patient. Filamentous (string-like) algae often show first – strands of quite distinct cells, with cellulose cell walls and clear nuclei and within them a single nucleolus (where the cell is making ribosomes, the protein-manufacturing machines). The green chloroplasts will also be seen, and their design will vary with the species. Along the chloroplast will be granules where carbohydrate is stored – one product of photosynthesis. (Chains of glucose molecules are stitched together, often to form starch grains. But other, similar chemicals are possible.)
If you feel you’d like to be unkind to the algae you could irrigate the slide with a sugar or salt solution. To do this add a drop of solution just outside the coverslip and draw the chemical under the slip with absorbent paper from the opposite side. The osmotically strong solution will suck water out of the cells and their contents will shrink – clearly showing the cytoplasm that forms much of the contents. If you feel guilty, irrigate again with pond water and all will be repaired.
By now you’ll have spotted the unicellular algae actively moving or flowing across the slide. If lucky there could also be colonial algae like Volvox.
A x40 objective is now needed plus a touch to the fine focus knob. You may also my need to adjust the condenser and iris.
The diatoms are characteristic with silica encrusting their cellulose cell walls. The design of the silica is beautiful and seeing it in detail will test your skills with the microscope. Other single-celled algae should also be there and euglenoids – single-celled motile algae with one or more whip-like flagellum.
You will have come across a flagellum before: the tail on human sperm. Internally they are a bit like muscle, with protein fibres (microtubules) that can be moved with the consumption of energy. And you should be able to see this flagellum moving the creature. With luck it is possible to find different types of euglenoids with up to four flagella.
As euglenoids are mobile they can be difficult to ‘pin down’. But, by adding teased out strands of cottonwool to the slide before adding the drop of pondwater, you can slow them down.
Clearly, euglenoids have a flexible cell wall plus a single chloroplast that can be ‘killed off’ by the antibiotic streptomycin, and the bleached individuals survive perfectly well by acting as animals and eating small organisms by engulfing them (phagocytosis). Eugena really is a mixture of plant and animal characteristics.
For the biologists … neither sexual reproduction nor meiosis has been observed … possibly they evolved before such things became common.
The green alga Chara is found in my pond, but is uncommon although spread across the globe. I used it with students to study both nuclei and the movement of cytoplasm (cyclosis) around cell interiors – for it is in constant motion here. Also, the cells are huge, and others have been able to suck out the nucleus and study its impact on the cell. A task beyond my pay grade!
Chara looks like a true aquatic plant, and may be related to ancestral plants. It has root-like anchors (rhizoids) but they contain no transport tissues.
Wikipedia says: Chara is found in freshwater, particularly in limestone areas throughout the northern temperate zone, where they grow submerged, attached to the muddy bottom. They prefer less oxygenated and hard water and are not found in waters where mosquito larvae are present. They are covered with calcium carbonate deposits and are commonly known as stoneworts. Cyanobacteria have been found growing as epiphytes on the surfaces of Chara, where they may be involved in fixing nitrogen, which is important to plant nutrition.
Chara emits a strong musky odour when crushed.
Nitella and Chara are similar.
You will find videos on these organisms on the Internet.