Animals are multicellular organisms with eukaryotic cellular organization. A representative animal cell has a cell membrane, cell nucleus and mitochondria, but no cell wall or chloroplasts. A neuron illustrates how this common plan can acquire a specialized shape and signaling function. See OpenStax Biology 2e, 4.3: animal cell organization.
Reclinomonas americana is a microbial eukaryote whose mitochondrial genome retains an unusually rich set of bacterial features. The 1997 sequence report provides a concrete observation under evidence for bacterial ancestry of organelles.
Algae is a broad name for several photosynthetic eukaryotic groups, rather than one exclusive clade. The older name blue-green algae for cyanobacteria is misleading in a comparison of cellular organization: cyanobacteria are bacteria, with neither chloroplasts nor a cell nucleus.
Plants are eukaryotes. A typical photosynthetic leaf cell has a cell nucleus, mitochondria, chloroplasts, and a cell wall outside its cell membrane. A root cell need not have chloroplasts; the plant's parts specialize for different functions. Plants perform cellular respiration as well as photosynthesis. See OpenStax Biology 2e, 4.3: plant cell organization.
A fungus is a eukaryote that obtains nutrients by absorption rather than photosynthesis. Fungi include unicellular yeasts and multicellular forms. Their cell walls differ from bacterial peptidoglycan walls; having a cell wall does not make a fungus a plant. See OpenStax Biology 2e, 24.1: fungal nutrition and organization.
Endotext Insulin Biosynthesis, Secretion, Structure, and Structure-Activity Relationships by 
Codex 0 2026-10-13
Codex 0 2026-10-13Online text: www.endotext.org/wp-content/uploads/pdfs/insulin-biosynthesis-secretion-structure-and-structure-activity.pdf
Cited passages: Weiss, Steiner and Philipson, Introduction; Insulin Biogenesis and Mechanism of Release; Biochemistry and Electrophysiology of Insulin Secretion, PDF pp. 1, 4–8, 10–11.
Online text: www.ncbi.nlm.nih.gov/books/NBK279127/
Cited passages: Glucagon Physiology, Glucagon Receptor Signalling and Glucagon Stimulates Lipolysis and Ketogenesis: controversy over direct human adipose effects; Glucagon Physiology, Glucagon Receptor Signalling; Glucagon Increases Hepatic Glucose Production; Glucagon Physiology, Structure and Synthesis of Glucagon; Regulation of Glucagon Secretion, Figure 2; Glucagon Physiology, The Role of Glucagon in Diabetes.
Endosymbiotic theory explains the bacterial origins of mitochondria and plastids through enduring internal associations and subsequent integration. Survival inside a biological cell is only part of the problem: exchange through membrane transport, inherited division, gene expression and delivery of required proteins must work together. The elegance is evolutionary reuse of an existing cellular capability, followed by changes that make the partners operate as one system. [ref]
Origin and Evolution of Plastids and Photosynthesis in Eukaryotes by Geoffrey I. McFadden. Abstract and “How to tame your symbiont”: metabolic, genetic and division integration
The historical On the origin of mitosing cells by Lynn Sagan (1967, abstract and Introduction, pp. 225–226) synthesized a symbiotic account of eukaryotic origins and proposed tests using molecular evidence. Its Introduction explicitly acknowledged earlier proposals. It also hypothesized origins for other structures; the modern evidence for mitochondria and plastids should be assessed separately from the rest of that historical scheme.
An endosymbiont is the internal partner in an endosymbiosis. Calling an organism an endosymbiont does not by itself classify it as an organelle or imply an irreversible evolutionary transition.
There are unlisted articles, also show them or only show them.