Chapter 14 - The Greatest Species on Earth?
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How many species have scientists identified, and how many are estimated to exist?
Scientists have identified more than 1.3 million different species, and possibly more than 100 million different species might exist on Earth today. Scientists estimate that about 80 percent of species currently present on Earth are still unknown.
How many genera of animals have been described compared to the number predicted to exist?
About 92,000 genera have been described of the 110,000 or so predicted to exist.
What defines the geologic eras that subdivide the history of life?
The history of life can be subdivided into geologic eras that are defined by a particular set of fossils.
What is the most appropriate way to classify living organisms according to most biologists?
According to most biologists, the most appropriate way to classify living organisms is by using evolutionary relationships among organisms.
What is the broadest category of biological classification?
The broadest category of biological classification is domain.
What are the three domains of life?
All living things can be sorted into one of three domains, the Bacteria, Archaea, or Eukarya.
How is a species defined when identifying biodiversity?
A species is a group of individuals who can interbreed and are distinct from other species in appearance and/or behavior.
What are the two prokaryotic domains?
The two prokaryotic domains are Archaea and Bacteria. Both Bacteria and Archaea are prokaryotic, which means they are simple single-celled organisms without a nucleus or other membrane-bound organelles.
Which of the three domains are most closely related?
Bacteria share a distant common ancestor with Archaea and Eukarya, and the last two groups are more closely related.
When did life on Earth begin, and what were the first organisms?
Life on Earth began about 3.6 billion years ago with prokaryotes.
What is the endosymbiotic theory?
The idea that eukaryotes evolved from mutually beneficial relationships among cells is known as the endosymbiotic theory. Eukaryotes evolved as a result of symbioses among ancestral eukaryotes and prokaryotes.
According to the endosymbiotic theory, how did the second membrane of chloroplasts and mitochondria come about?
The second membrane resulted from the infolding of the host cell membrane when it engulfed the bacterium.
What evidence supports the hypothesis that mitochondria evolved before chloroplasts?
Mitochondria in plant and animal cells are identical, indicating that they evolved before plants and animals diverged.
How did an extra, third membrane likely evolve in the chloroplasts of some algal phyla?
These chloroplasts likely evolved through a process of secondary endosymbiosis, in which the ancestral cell engulfed but did not consume a eukaryotic green algal cell.
What advantage would an ancient eukaryotic cell gain by providing a safe haven for an oxygen-using bacterium?
An oxygen-sensitive cell that kept an oxygen-consuming prokaryote alive inside of it would be protected from the damaging effects of oxygen, as any nearby oxygen would quickly be used up by the prokaryote.
What are the four major kingdoms within the domain Eukarya?
Protista, Animalia, Fungi, and Plantae.
What are the main characteristics of the kingdom Protista?
The Protista is a hodgepodge of organisms that are typically unicellular eukaryotes. Protists include organisms that are both unicellular and multicellular and that have plant-like, animal-like, or fungus-like lifestyles.
What are the main characteristics of the kingdom Animalia?
Animals are motile, multicellular eukaryotes that rely on other organisms for food.
When did multicellular organisms first appear?
Multicellular organisms did not appear until approximately 600 million years ago.
What was the Cambrian explosion?
The short period of time in which animal groups evolved.
What are the main characteristics of Fungi?
Fungi are immobile, multicellular eukaryotes that rely on other organisms for food and are made up of thin, threadlike hyphae. They are like animals in that they rely on consuming other organisms for energy.
Why does a fungus produce a mushroom outside the food resource used by its hyphae?
To allow dispersal of spores away from the food source that is already in use.
What are the main characteristics of Plantae?
Plants are multicellular, photosynthetic eukaryotes that make their own food.
What reproductive structures are produced by the largest group of plants on Earth today?
The largest group of plants on Earth today produces reproductive structures called flowers.
How is a seed plant embryo similar to an astronaut in space?
The embryo is like an astronaut in that it is protected within a tough outer coating that contains all the resources it requires for at least short-term survival in a harsh environment.
How does a seed plant embryo differ from an astronaut?
It can still exchange materials with the environment, whereas an astronaut cannot get any materials required for life from space.
What is adaptive radiation?
Adaptive radiation occurs when several new species appear quickly after the evolution of a new structure or feature or the death of a competing group.
What is a virus?
A virus consists primarily of a segment of genetic material that cannot reproduce without infecting a living cell. They are nonliving entities made up of genetic material in a transport container and reproduce only by using the replication machinery inside living cells.
What is a phylogeny?
A phylogeny is a diagram that represents a hypothesis of the evolutionary relationship among organisms.
How are phylogenetic trees created and tested?
Phylogenies are created and tested by evaluating the shared traits of different species that indicate they shared a recent ancestor. To test phylogenetic trees, scientists will often examine DNA sequences.
How do scientists infer the ancestral sequence in a phylogenetic tree?
They use base pairs that are common to all groups as a framework and then infer that older species are more likely to possess the ancestral bases than younger species.
How does convergence complicate the creation of phylogenetic trees?
Creating a phylogenetic tree based on examining physical traits is complicated by the fact that convergence may make unrelated species appear similar.
In scientific classification, what is the genus name of a species equivalent to in human naming conventions?
The genus name of a species is somewhat equivalent to a person’s family or last name.
How would a phylogenetic tree change to accommodate a group of protists that share a recent common ancestor with animals?
We’d have to draw an extra branch on the tree that shows a common ancestor between animals and this protistan group. The phylum of Protista would also be broken up, potentially.
Why might biologists classify organisms by similarity in diets rather than evolutionary relationships?
Grouping species by similarity in diets could help biologists understand the common needs for species of interest and perhaps simplify natural resource management.
Why might biologists classify organisms by similarity in habitat needs?
Grouping species by similarity in habitat need can help identify whether species with similar habitat needs may be at risk of extinction due to habitat loss.
What traits cause amateur bird watchers to classify vultures as birds of prey instead of scavengers?
A beak that can tear meat, long wings, large size, and the ability to soar.
What information helps scientists determine the proper placement of animals like vultures among bird groups?
DNA sequence analysis, detailed morphological comparisons, and the fossil record.
What does the root "anima-" mean?
It means breath or soul.
What does the root "botan-" mean?
It means pertaining to plants.
What does the root "eu-" mean?
It means true.
What does the root "in-" mean?
It means without.
What does the root "-karyo-" mean?
It means kernel.
What does the root "myco-" mean?
It means fungal.
What does the root "pro-" mean?
It means before.
What does the root "zoo-" mean?
It means pertaining to animals.
What percentage of all animal species do animals with backbones account for?
Animals with backbones make up only 4% of all animal species.
Where are antibiotics and other drugs derived from in the tree of life?
Antibiotics are prevalent in bacteria and fungi, whereas other drugs are derived from plants.
How can an unknown organism be identified as an animal if it feeds by straining algae out of pond water while anchored to a rock?
Although it is not very motile, it is probably an animal because it is not photosynthetic and consumes other organisms by ingestion, unlike fungi.
How many species are believed to exist today based on "Make the Connection" estimates?
As many as 8.7 million species are believed to exist today.
What specific evidence indicates that all living organisms share a common ancestor?
The commonality of DNA and ribosomes.
What are two ways certain prokaryotes can survive extreme conditions?
Certain prokaryotes can live in environments that appear inhospitable to life, and others can live as spores for millions of years waiting for ideal conditions to reanimate.
What may have caused the diversity of flowering plants through adaptive radiation?
The immense diversity of flowering plants through adaptive radiation was primarily driven by their coevolution with animal pollinators and the evolutionary innovation of specialized reproductive structures, such as flowers and fruits, which enabled them to rapidly exploit a wide variety of ecological niches.
Why are flowering plants arguably the most important group of organisms on land?
They provide the basis for human agriculture.
How does knowledge about phylogenetic relationships help us understand previously unknown species?
It can help us predict their traits.
Are humans uniquely capable of exploiting biodiversity?
No, there are organisms throughout the kingdoms of life that are older, larger, faster, more cooperative, and just as able to exploit biodiversity as humans are.
What remarkable ability do humans have regarding the environment?
Humans have the ability to change behavior to prevent the loss of biodiversity.
Do prokaryotes only exist as single cells?
No, while nearly all are unicellular, some live in colonies.
When did eukaryotes evolve relative to prokaryotes?
Eukaryotes evolved 2 billion years after prokaryotes.
How long have plants been present on land?
Plants have been present on land for approximately 400 million years.
What is the relative chronological order of appearance for the domains and kingdoms on Earth?
Prokaryotes (Archaea and Bacteria) appeared first around 3.6 billion years ago, followed by Eukaryotes 2 billion years later. Multicellular organisms appeared about 600 million years ago, animals rapidly diversified during the Cambrian explosion, and plants appeared on land about 400 million years ago.
What is biodiversity?
Biodiversity is the variety of life in the world or in a particular habitat or ecosystem, encompassing the vast number of different species on Earth.
What are systematics and systematists?
Systematics is the study of the diversification of living forms and their evolutionary relationships over time. Systematists are the scientists who classify organisms based on these relationships.
What are paleontology and paleontologists?
Paleontology is the scientific study of the history of life on Earth based on fossils. Paleontologists are the scientists who study these fossils to understand extinct organisms and their evolution.
In which domains and kingdoms can microbes be found, and why are they important?
Microbes are found in all three domains (Bacteria, Archaea, and Eukarya—specifically within Protista and Fungi). They are ecologically crucial as photosynthetic organisms that produce oxygen and as decomposers that recycle nutrients.
What is the difference between vertebrates and invertebrates?
Vertebrates are animals that possess a backbone or spinal column (accounting for only 4% of animal species), whereas invertebrates are animals that lack a backbone.
What are mycorrhizae?
Mycorrhizae are mutually beneficial symbiotic relationships between the roots of plants and fungi, helping plants absorb water and nutrients from the soil.
What evolutionary advantages did vascular tissue and pollen provide for plants?
Vascular tissue allowed plants to efficiently transport water and nutrients, enabling them to grow larger and survive further inland. Pollen allowed seed plants to reproduce without needing water for sperm to swim to the egg.
How big are viruses, and how do they lead to disease?
Viruses are incredibly small—much smaller than cells. They lead to disease by invading host cells, hijacking the cell's genetic machinery to replicate themselves, and typically destroying the host cell in the process.
In chloroplasts with three membranes, what are the evolutionary origins of each of the three membrane layers?
The original bacterial membrane is surrounded by a secondary membrane from the engulfed cell, and both are surrounded by the vacuole membrane from the ancestral host cell.
It supports the idea that humans are not the most common species on Earth.