Vital Dust: Life as a Cosmic Imperative

By Christian De Duve | Go to book overview

Chapter 16
The Primitive Phagocyte

THE PICTURE IS CLEAR. When Giardia's lineage branched from what was to become the main eukaryotic trunk, probably more than two billion years ago, almost all the key features of eukaryotic cells, with the exception of endosymbiont- derived organelles, had already emerged. The crucial prokaryote-eukaryote transition occurred some time during the 1.0 to 1.5 billion years following the primeval forking that led to the eukaryotic branch. During that time, a simple prokaryote developed into a primitive phagocyte, a large nucleated cell capable of capturing food and digesting it intracellularly. What pathway did this momentous transformation follow? And, especially, why was this road actually taken in reality?

Extant organisms offer a number of valuable clues to the first question, but we have only educated guesses to help us answer the second. Remember the rule: foresight excluded. There was no goal, no eukaryotic ideal beckoning from the distant future, inviting evolving cells to overcome hurdles and vanquish difficulties. Every step of this extraordinary voyage was taken in its own present context, the consequence of some chance mutation that happened to confer an immediate benefit favoring the survival and proliferation of the affected cell there and then. What hidden selective forces cut open this trail, step by step, over an immensely long period of time, to produce what was probably the most epoch-making innovation in the history of life? This question will be with us as we try to retrace the main steps of the voyage.

From what we have seen of Giardia, there are really two major developments to be accounted for within the context of an enlarging cell: cytomembranes and cytoskeletal elements, with a fenced-off nucleus arising through a special combination of the two. We have no clues to the origin of the cytoskeleton, which may be a true innovation. But we know the origin of eukaryotic cytomembranes. According to all available evidence, they come from the ancestral prokaryotic cell membrane.

-147-

Notes for this page

Add a new note
If you are trying to select text to create highlights or citations, remember that you must now click or tap on the first word, and then click or tap on the last word.
One moment ...
Default project is now your active project.
Project items

Items saved from this book

This book has been saved
Highlights (0)
Some of your highlights are legacy items.

Highlights saved before July 30, 2012 will not be displayed on their respective source pages.

You can easily re-create the highlights by opening the book page or article, selecting the text, and clicking “Highlight.”

Citations (0)
Some of your citations are legacy items.

Any citation created before July 30, 2012 will labeled as a “Cited page.” New citations will be saved as cited passages, pages or articles.

We also added the ability to view new citations from your projects or the book or article where you created them.

Notes (0)
Bookmarks (0)

You have no saved items from this book

Project items include:
  • Saved book/article
  • Highlights
  • Quotes/citations
  • Notes
  • Bookmarks
Notes
Cite this page

Cited page

Style
Citations are available only to our active members.
Buy instant access to cite pages or passages in MLA, APA and Chicago citation styles.

(Einhorn, 1992, p. 25)

(Einhorn 25)

1. Lois J. Einhorn, Abraham Lincoln, the Orator: Penetrating the Lincoln Legend (Westport, CT: Greenwood Press, 1992), 25, http://www.questia.com/read/27419298.

Cited page

Bookmark this page
Vital Dust: Life as a Cosmic Imperative
Table of contents

Table of contents

Settings

Settings

Typeface
Text size Smaller Larger Reset View mode
Search within

Search within this book

Look up

Look up a word

  • Dictionary
  • Thesaurus
Please submit a word or phrase above.
Print this page

Print this page

Why can't I print more than one page at a time?

Help
Full screen
/ 362

matching results for page

    Questia reader help

    How to highlight and cite specific passages

    1. Click or tap the first word you want to select.
    2. Click or tap the last word you want to select, and you’ll see everything in between get selected.
    3. You’ll then get a menu of options like creating a highlight or a citation from that passage of text.

    OK, got it!

    Cited passage

    Style
    Citations are available only to our active members.
    Buy instant access to cite pages or passages in MLA, APA and Chicago citation styles.

    "Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences." (Einhorn, 1992, p. 25).

    "Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences." (Einhorn 25)

    "Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences."1

    1. Lois J. Einhorn, Abraham Lincoln, the Orator: Penetrating the Lincoln Legend (Westport, CT: Greenwood Press, 1992), 25, http://www.questia.com/read/27419298.

    Cited passage

    Thanks for trying Questia!

    Please continue trying out our research tools, but please note, full functionality is available only to our active members.

    Your work will be lost once you leave this Web page.

    Buy instant access to save your work.

    Already a member? Log in now.

    Oops!

    An unknown error has occurred. Please click the button below to reload the page. If the problem persists, please try again in a little while.