Chapter 17, Problem 1PDT

Summary Introduction

To explain: The advantages for separate organisms to become united into a single organism in the evolution of eukaryotes.

Introduction: Change in the heritable characteristics of the living organisms over time is known as evolution. There are changes in the genome that are transferred over generations. Evolution takes place mainly due to evolutionary forces such as mutation, genetic recombination, and so on. Organisms having a nucleus enclosed within the nuclear membrane are known as eukaryotes.

Explanation of Solution

Archaea, bacteria, and eukaryotes are three large domains of living organisms. Archaea and bacteria, when compared to eukaryotes, are relatively small and simple. Eukaryotes have a nucleus enclosed within a nuclear membrane in a cell. Linear DNA is present inside the nucleus of eukaryotes. The eukaryotic cell is complex as compared to archaea and bacteria. Eukaryotic cells evolved into multicellular organisms, and a new era of life exploded on the Earth. Mitochondria existed as a free-living organism before, and it exists now inside the eukaryotic cell, which acts as a powerhouse of the cell. Mitochondria produce chemical energy required for the cell. Eukaryotes are the descendants of the separate prokaryotic cells according to the evidence. Eukaryotic cells and separate prokaryotic cells joined together in a symbiotic union giving rise to multicellular eukaryotic organisms.

“Internal” symbiosis, where one organism lives permanently inside another organism and eventually becomes united into a single organism is known as endosymbiosis.

Following are the advantages for separate organisms to become united into a single organism in the evolution of eukaryotes:

• Mitochondria produce chemical energy required for the cell.
• Cell provides protection and nutrient-rich environment to the mitochondria.

Therefore, establishing a mutually beneficial symbiotic relationship between the mitochondria and the eukaryotic cell is advantageous for both.

Thus, mitochondria provide chemical energy and receive a secured environment in return, making it beneficial for the mitochondria and the eukaryotic cell to become united into a single organism.

Summary Introduction

To explain: The more recently evolved, examples of intimate symbiosis that function as a single integrated organism.

Introduction: Change in the heritable characteristics of the living organisms over time is known as evolution. There are changes in the genome that are transferred over generations. Evolution takes place mainly due to evolutionary forces such as mutation, genetic recombination, and so on. Organisms having a nucleus enclosed within the nuclear membrane are known as eukaryotes.

Explanation of Solution

When an organism lives inside another organism permanently and they become united into one organism, it is known as intimate symbiosis. When two organisms belonging to different species exist in a relationship where each organism benefits from the other is known as mutualism.

Following are the more recently evolved examples of intimate symbiosis:

• Algae–fungus association:

  Green algae live among the filaments of fungus, and this symbiotic relationship gives rise to a single united organism called lichen. Fungus derives essential nutrients from the algae, and it provides algae an environment to live safely.

• Zooxanthellae and corals:

  Coral tissues provide a safe place for the zooxanthellae to live, and the zooxanthellae also use waste products by the corals to obtain nutrients in order to perform photosynthesis. The sugars produced by the photosynthesis done by zooxanthellae are in turn used by the corals as a source of energy.

• Rhino and tickbird:

  Tickbird feeds on parasites such as ticks that live on the large mammals such as rhino. Tickbirds, therefore, feed on these parasites obtaining a source of food, and rhino, on the other hand, gets rid of the parasites living on them.

• Crocodile and plover bird:

  Plover bird is a small bird, and as crocodile is unable to floss its teeth, plover birds help it get rid of the food stuck between its teeth when the crocodile invites the bird to do so after opening the mouth. The bird flies away after clearing the food. This way the bird gets its daily requirement of food, and the food stuck between the teeth of the crocodile is also removed by the bird.

• Sea anemone and clown fish:

  Clown fish are protected from the stingy tentacles of sea anemone, as they have a slimy mucus covering. Sea anemone provides food to the clown fish, and the clown fish in return cleans the leftovers of small fishes as well as algae from the sea anemone. Clown fish also fans fins of sea anemone, providing them better circulation.

• Ants and non-toxic acacia trees:

  Non-toxic acacia trees provide the plant with a place to live along with food and in return ants act as protectors and protect the plants from herbivores and pathogens.