chapter 10 p2

Question 1

Recent changes to classification systems:

Answer 1

• Originally classification systems were based on observable features.
• Through the study of genetics and other biological molecules, scientists are now able to study the evolutionary relationships between organisms.
• These links can then be used to classify organisms.
• When organisms evolve, their internal and external features change, as does their DNA.
• This is because their DNA determines the proteins that are made, which in turn determines the organism’s characteristics.
  In order for their characteristics to have changed, their DNA must also have changed.
• By comparing the similarities in the DNA and proteins of different species, scientists can discover the evolutionary relationships between them.

Question 2

An example of a protein that has changed in structure

Answer 2

is haemoglobin.
Haemoglobin has four polypeptide chains, each made up of a fixed number of amino acids.
The haemoglobin of humans differs from chimpanzees in only one amino acid, from gorillas in three amino acids and from gibbons in eight amino acids.
As the structure of haemoglobin is remarkably similar, it indicates a common ancestry between the various primate groups.

Question 3

The current classification system used by scientists is known as the “Three Domain System’,

Answer 3

• The current classification system used by scientists is known as the “Three Domain System’, and was proposed by Carl Woese, an American microbiologist in 1977, reusing the word ‘Kingdom’.
• In 1990 it was renamed ‘Domain’.
• Domains are a further level of classification at the top of the hierarchy.
• Woese’s system groups organisms using differences in the sequences of nucleotides in the cells’ ribosomal RNA (rRNA), as well as the cells’ membrane lipid structure and their sensitivity to antibiotics.
• Observation of these differences was made possible through advances in scientific techniques.
• Under the Three Domain System, organisms are classified into three domains and six kingdoms.
• The three domains are Archaea, Bacteria, and Eukarya.
• The organisms in the different domains contain a unique form of rRNA and different ribosomes:

Question 4

The organisms in the different domains contain a unique form of rRNA and different ribosomes:

Answer 4

Eukarya
Archaea
Bacteria

Question 5

Eukarya -

Answer 5

have 80s ribosomes
RNA polymerase (responsible for most mRNA transcription) contains 12 proteins

Question 6

Archaea

Answer 6

have 70s ribosomes
RNA polymerase of different organisms contains between eight and 10 proteins and is very similar to eukaryotic ribosome.

Question 7

Bacteria

Answer 7

have 70s ribosomes
RNA polymerase contains five proteins

Question 8

3 domain, 6 kingdom classification

Answer 8

Question 9

Woese’s system

Answer 9

• the Prokaryotae kingdom becomes divided into two kingdoms - Archaebacteria and Eubacteria.
• The six kingdoms are therefore: Archaebacteria, Eubacteria, Protoctista, Fungi, Plantae and Animalia.
• Although both Archaebacteria and Eubacteria are single-celled prokaryotes, Eubacteria are classified in their own kingdom because their chemical makeup is different from Archaebacteria.
• For example, they contain peptidoglycan (a polymer of sugars and amino acids) in their cell wall whereas Archaebacteria do not.

Question 10

Archaebacteria:

Answer 10

Archaebacteria, also known as ancient bacteria, can live in extreme environments.
These include hot thermal vents, anaerobic conditions, and highly acidic environments.
For example, methanogens live in anaerobic environments such as sewage treatment plants and make methane.

Question 11

Eubacteria:

Answer 11

Eubacteria, also known as true bacteria, are found in all environments and are the ones you will be most familiar with.
Most bacteria are of the Eubacteria kingdom.
Some scientists still use the traditional five kingdom system, but since Archaebacteria have been found to be different chemically from Eubacteria, most scientists now use the three domain, six kingdom system.

Question 12

Answer 12

Question 13

the current classification system is based on

Answer 13

both shared physical characteristics between organisms and on evolutionary relationships.
To discover the links between organisms and common ancestors, scientists study the organisms’ DNA, proteins, and the fossil record.

Question 14

Phylogeny:

Answer 14

• the name given to the evolutionary relationships between organisms.
• The study of the evolutionary history of groups of organisms is known as phylogenetics.
• It reveals which group a particular organism is related to, and how closely related these organisms are.
• Classification can occur without any knowledge of phylogeny, as occurred in the past.
• However, it is the objective of many scientists to develop a classification system that also correctly takes into account the phylogeny of an organism.

Question 15

Phylogenetic trees:

Answer 15

• A phylogenetic tree (or evolutionary tree) is a diagram used to represent the evolutionary relationships between organisms.
• They are branched diagrams, which show that different species have evolved from a common ancestor.
• The diagram is similar in structure to that of a branching tree - the earliest species is found at the base of the tree and the most recent species are found at the tips of the branches.
• Phylogenetic trees are produced by looking at similarities and differences in species’ physical characteristics and genetic makeup.
• Much of the evidence has been gained from fossils.

Question 16

How do you interpret phylogenetic trees:

Answer 16

The tips of the phylogenetic tree represent groups of descendent organisms (often species).
The nodes on the tree [the points where the new lines branch off) represent the common ancestors of those descendants.
Two descendants that split from the same node are called sister groups.
The closer the branches of the tree are, the closer the evolutionary relationship.

Question 17

How do you interpret phylogenetic trees example

Answer 17

Study Figure 2. Begin by looking at the base of the tree.
The organism at this point is the common ancestor of all the organisms on the tree.
The letters A-F represent six different species that have evolved from this ancestor. Then look at the top of the tree.
You will see that species A and B are sister groups as these share a common ancestor.
Species E and Fare also sister groups that share their own common ancestor, which itself shared a common ancestor with species D further back in time.
Further back in time again, C shared a common ancestor with D, E and F.

Question 18

Advantages of phylogenetic classification:

Answer 18

• Phylogeny can be done without reference to Linnaean classification.
• Classification uses knowledge of phylogeny in order to confirm the classification groups are correct or causes them to be changed.
• For example, a dolphin has many of the same characteristics as a fish, so in theory a dolphin could be classified as a fish.
• However, knowledge of the phylogeny of dolphins confirms its classification as a mammal.

Question 19

Other advantages:

Answer 19

• Phylogeny produces a continuous tree whereas classification requires discrete taxonomical groups.
  Scientists are not forced to put organisms into a specific group that they do not quite fit.
• The hierarchal nature of Linnaean classification can be misleading as it implies different groups within the same rank are equivalent.
  For example, the cats (Felidae) and the orchids (Orchidaceae) are both families.
  However, the two groups are not comparable - one has a longer history than the other (cats have existed for around 30 million years, but orchids have been in existence for over 100 million years).
  The two families also have different levels of diversity (with approximately 35 cat species and 20000 orchid species) and different degrees of biological differentiation (many orchids of different genera are able to hybridise, but cats cannot).

Question 20

Evolution

Answer 20

• the theory that describes the way in which organisms evolve, or change, over many many years as a result of natural selection.
• Darwin realised that organisms best suited to their environment are more likely to survive and reproduce, passing on their characteristics to their offspring.
• Gradually, a species changes over time to have a more advantageous phenotype for the environment in which it lives.
• We now know that the advantageous characteristics are passed on from one generation to the next by genes in DNA molecules.

Question 21

Developing the theory of evolution: p1
Background Beliefs

Answer 21

When Charles Darwin was born in 1809, most people in Europe believed, in a literal sense, in the Christian Bible.
They believed God directly created all life on Earth, including human beings.
The Bible doesn’t state how far in the past this occurred - in Darwin’s day the common belief was that this creation had occurred only a few thousand years before.
In 1831 aboard the HMS Beagle, Darwin read ‘Principles of Geology.
This book was written by his friend Charles Lyell, a Scottish geologist.
He suggested that fossils were actually evidence of animals that had lived millions of years ago.

Question 22

Developing the theory of evolution:
p2 Geological Influences

Answer 22

We now have scientific evidence that supports this.
In it Lyell also popularised the principle of uniformitarianism (the concept itself was originally proposed by another Scottish geologist, James Hutton).
This is the idea that in the past, the Earth was shaped by forces that you can still see in action today, such as sedimentation in rivers, wind erosion, and deposition of ash and lava from volcanic eruptions.
In emphasising these natural processes, he challenged the claims of earlier geologists who had tried to explain geological formations as a result of biblical events such as floods.
This concept prompted Darwin to think of evolution as a slow process, one in which small changes gradually accumulate over very long periods of time

Question 23

Developing the theory of evolution: p3 Observations in the Galapagos

Answer 23

Darwin carried out some of his most famous observations on finches in the Galapagos Islands. He noticed that different islands had different finches. The birds were similar in many ways and thus must be closely related, but their beaks and claws were different shapes and sizes.
Through these observations Darwin realised that the design of the finches’ beaks was linked to the foods available on each island.
He concluded that a bird born with a beak more suited to the food available would survive longer than a bird whose beak was less suited.
Therefore, it would have more offspring, passing on its characteristic beak. Over time the finch population on that island would all share this characteristic.

Question 24

Developing the theory of evolution: p4 Development and Peer Review

Answer 24

• Throughout his trip Darwin sent specimens of organisms back to the UK for other scientists to preserve and classify.
• This enabled scientists not only to see specimens first hand but also enabled them to spot characteristics and links between organisms that Darwin had not.
• For example, Darwin did not notice that the tortoises (which the Galapagos islands are named alter) present on different islands were different subspecies.
• Before this was pointed out to him he had simply stacked their shells randomly in the hold.
• Upon his return to England, Darwin spent many years developing ideas.
• He also carried out experimental breeding of pigeons to gain direct evidence that his ideas might work.
• At the same time as Darwin was developing his ideas, another scientist, Alfred Wallace, was working on his own theory of evolution in Borneo.
• In 1858 he sent his ideas to Darwin for peer review before its publication.
• As Wallace’s ideas were so similar to Darwin’s, they proposed the theory of evolution through a joint presentation of two scientific papers to the Linnean Society of London on 1st July 1858.

Question 25

Developing the theory of evolution: p5 Publication and Controversy

Answer 25

• A year later in 1859, Darwin published ‘On the Origin of Species’.
• It was in this book that he named the theory that he and Wallace had presented independently as the theory of evolution by natural selection
• The book was extremely controversial at the time.
• The theory of evolution conflicted with the religious view that God had created all of the animals and plants on Earth in their current form, and only about six thousand years ago.
• A further implication of Darwin’s theory is that humans are simply a type of animal evolved from apes, which conflicted with the widely held Christian belief that God created ‘man’ in his own image.
• Darwin’s theory split the scientific community before his idea became generally agreed.
• Darwin’s theory of evolution is now widely accepted, however, even today, debate with religious groups continues.