Chloroplasts and Evolution
Chloroplasts are just one type of plastid - a category of closely-related organelles found in photosynthetic eukaryotes. Chloroplasts are specialized to perform photosynthesis, while other types of plastids perform other functions, such as starch or oil storage, pigment production and storage, gravity sensing, and production of secondary metabolites (Solymosi, 2012).
The activities on the previous page are intended to demonstrate that the cells of land plants tend to have relatively large numbers of similar-looking chloroplasts, while algal cells tend to contain relatively few chloroplasts, with much more variety in shape across species. And while we didn't provide any information about chloroplast size, it is also true that algal chloroplasts are relatively large compared with plant chloroplasts. They are also less specialized than plant chloroplasts, in some cases taking on the metabolic functions that are performed by different plastids in plant cells. In other words, algal chloroplasts are multi-taskers (Solymosi, 2012)!
A recent paper by Dalhousie researchers Jan de Vries and John Archibald (2018) summarizes the evidence supporting the hypothesis that land plants evolved from the streptophyte lineage of algae. They assert that land plants evolved just once, and are most closely related to the Zygnematophyceae, a group of unicellular and filamentous freshwater algae.
Click on the thumbnail to view a larger version of the summary figure from de Vries and Archibald (2018), and compare it to the figure from Chapter 29 of your textbook (Reece et al., 2018) reproduced below. The de Vries and Archibald (2018) figure provides more detailed information about the evolutionary relationships among members of the group identified as 'Viridiplantae' in your textbook.
Study the de Vries and Archibald (2018) figure and answer the last question in the lab assignment.
References
de Vries J and Archibald JM. 2018. Plant evolution: landmarks on the path to terrestrial life. New Phytologist 217: 1428-1434.
Reece JB, Urry LA, Cain ML, Wasserman SA, Minorsky PV, Jackson RB, Rawle F, Durnford D, Moyes C, Scott K, Walde S. 2018. Campbell Biology. Second Canadian Edition. Hoboken, NJ: Pearson Education Inc.
Solymosi K. 2012. Plastid Structure, Diversification and Interconversions I. Algae. Current Chemical Biology 6: 167-186.