On each slide you must have:
1. A photo of the organism
2. Their size range in µm or mm (micro or millimeters)
You can make a scale bar so you don't need a bullet point.
3. How they get their energy
4. Where they are in the food web (may want a summary slide for this?)
5. How they defend themselves from being eaten.
6. How all plankton stay in upper levels of the water column and why it is important for most plankton to stay in the photic zones of the water column.
Figure 1. The regions of the continental shelf and the various pelagic zones.
Google Slide guidelines
Here is a link for tips to making and designing an effective powerpoint: http://desktoppub.about.com/od/microsoft/bb/powerpointrules.htm
Some things I consistently see are that we use too many words pictures or figures on one slide. Remember less is more. I don't necessarily agree with just one photo per slide but use your best judgement.
How many bullet points should I use? http://www.ellenfinkelstein.com/pptblog/how-many-bullets-should-i-put-on-a-slide/
Using a photo to inspire your thoughts and what you would like to say on each slide helps the audience because they can focus on you speaking rather than reading hundreds of words on your slide. Use as few words as you can but use the words wisely.
Have fun making your presentations. It's a chance to be artistic and engage your audience.