Biology: Microbes – Protoctista



The last micro-organism we need to cover for their IGCSE Biology is the Protoctista.  This is basically the ‘rubbish bin kingdom’.  Every organism which is living and eukaryotic but is not an animal, plant, fungi or bacteria belongs to this kingdom.  Protoctista are more complicated than bacteria, containing a cell nucleus, but less complex than fungi, plants and animals.  They are generally single-celled and feed on bacteria, dead matter and even other protoctists.  Most live in wet areas such as ponds, rivers and oceans.

They can be divided into two main groups – protozoa and algae.

  • Protozoa (Animal like Protoctista)


These usually have a means of movement in the form of Cilia (Microscopic hair), flagellum (whip like tail) or pseudopods (false feet).  Protozoa move around looking for food.  An example is an Amoeba.

Some protozoa are parasitic.  A parasite is an organism which feeds off another living organism.  Parasites can also be pathogenic.  Pathogens cause disease in the animal, plant or fungi it feeds off.  An example of a pathogenic protoctist is Plasmodium, responsible for Malaria.

  • Algae (Plant like Protoctista)

Algae is a protoctist which makes its own food via photosynthesis.  It is very similar to plants in that they contain chlorophyl, the agent required to change sunlight and carbon dioxide into energy and oxygen.   Algae is a vital component of the earth’s ecosystem on which almost all of life in the ocean depends.  Lichen is a hybrid formed by the symbiotic relationship between an algae and a fungi.  We had already learnt about Lichens during our pond study during which we had carried out a longitudinal study of the Ash Tree.  I had managed to take some cracking photos of a Lichen growing on our Ash tree:

A different part of the branch

And a close up

Another example of an Algae protoctist is Chlorella.

  • Slime Molds (Fungi like Protoctista)

Plasmodial slime mold are made from just one large single cell which can be up to several feet long.  They may have many nuclei.

Each child chose one of the examples to create, thereby consolidating the structural information they had learnt.  T, as always, made one in Mine Craft and although I distinctly remember taking photos I have either deleted them by accident or they didn’t come out properly.  C chose to make her Paramecium from string and household objects:

DSC_0395c's protista

whilst L decided to draw her Euglena using a computer drawing program:

DSC_0398l's protista

As part of their writing I had them write a report for a microbiology magazine whose target audience was scientifically minded upper elementary children.  I kept reiterating the need for clarity over longevity throughout their report and asked them to keep it to only one page.  This exercise was to encourage my highly verbal child to choose the most important points and write concisely.

We also collected some pond water which we left for a couple of days to grow some Protoctista.  After preparing some slides, we used our TV screen microscope to look for any variety which could be seen:

Ribbet collageprotists1

We didn’t get any clear enough to photograph but we had a look back at this post from our pond study:

This was of a wiggly microscopic worm.  They were see through with a bare eye, but you could sort of 'see' them through the movement of the water.

Next week I will be giving each child an organism from those they need to know and I will be asking them to write a persuasive letter to the reigning microbe prime minister (currently the Slime Mold) to convince him that they should be his predecessor.

After they have done this, they will each begin an electoral campaign to convince Gary, Granny and myself to vote them in as the next Microbe Prime Minister.

These two exercises will complete our microbe learning.  Each week we will be tackling an IGCSE question related to the microbe section of the IGCSE syllabus.  We will also begin our next chosen topic on the syllabus, which will be Inheritance and Genetics.


    1. Yes, it is L. The funny thing is she leaves tufts of hair at the back which are not quite long enough to fit into the bunches – it doesn’t bother her though!

      1. I think I’ve cracked it – I can tell the twins apart! That will be a useful skill if I ever happen to meet you all 😉

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