29: Evolution I

Question 1

State the Oparin-Haldane hypothesis.

Answer 1

Organic molecules are produced in chemical reactions between inorganic molecules using energy from ultraviolet light and lightning.

Question 2

Describe the Miller-Urey experiment.

Answer 2

A mixture of methane, ammonia, hydrogen and water vapour is exposed to electric sparks in an apparatus. This results in the formation of simple organic molecules including amino acids.

Question 3

Describe how a simple cell may have formed from simple organic molecules.

Answer 3

1. Simple organic molecules like amino acids, sugars and nitrogenous bases were formed from inorganic molecules.
2. Simple organic molecules joined to form complex organic molecules like proteins, polysaccharides and nucleic acids.
3. Complex organic molecules were enclosed by a membrane sac, which allowed an internal environment different from the surroundings.
4. Self-replicating and catalytic molecules formed inside the membrane sac and gave rise to a simple cell.

Question 4

Explain the meaning of fossils.

Answer 4

Fossils are the preserved remains or traces of ancient organisms.

Question 5

Name and define two types of fossils.

Answer 5

Body fossils, formed from the remains of ancient organisms; and trace fossils, signs of life left by ancient organisms.

Question 6

Give 4 examples of body fossils and 5 examples of trace fossils.

Answer 6

Body fossils: bones, teeth, wood, shells
Trace fossils: footprints, burrows, nests, eggs, dung

Question 7

Name 3 pieces of information which can be revealed by body fossils and 2 pieces of information which can be revealed by trace fossils.

Answer 7

Body fossils: kinds, sizes, and structures of ancient organisms
Trace fossils: Behaviour of ancient organisms (eg. how they moved, what they ate)

Question 8

Describe how a fish fossil is formed and exposed.

Answer 8

1. Shortly after a fish dies and sinks to the bottom of a lake, the dead fish is covered by sediments. The soft parts of the dead body decompose, leaving behind the hard parts like the skeleton.
2. Over millions of years, new sediments cover the older ones and compress them into layers of sedimentary rocks. Meanwhile, minerals in the water deposit in the skeleton and turn it into a fossil.
3. Earth movement raises the sedimentary ross above water. Further earth movement and weathering expose the fossil.

Question 9

Explain the meaning of a fossil record.

Answer 9

A fossil record is a set of fossils which are arranged in chronological sequence in which they appeared.

Question 10

Explain how the relative age of fossils can be determined from the layers of sedimentary rocks in which they are found.

Answer 10

Sedimentary rocks are formed by the deposition of one layer of sediments over the top of another. Thus, the lowest layer is the oldest rock that contains the oldest fossils, whereas the uppermost layer is the youngest rock that contains the youngest fossils.

Question 11

Name a method which can estimate the absolute age of fossils.

Answer 11

Radioisotope dating

Question 12

Give an example illustrating how the sequence in which the fossils appeared matches the ecological relationships between different groups of organisms.

Answer 12

Fossils of land plants appeared before fossils of land animals. This is consistent with the fact that plants are producers and animals are consumers.

Question 13

List 2 ideas which can be illustrated when comparing modern species with ancient species.

Answer 13

1. Their similarities support the idea that existing life forms arose from pre-existing life forms.
2. Their differences suggest that organisms have changed over time to adapt to the changing environment.

Question 14

Name the gaps in a fossil record.

Answer 14

Missing links

Question 15

List 6 reasons for gaps in the fossil record.

Answer 15

Inability to form fossils:
1. Soft-bodied organisms cannot be fossilised.
2. The remains of organisms have been eaten by other organisms or have decomposed before they can be fossilised.
3. The conditions in which organisms die are not suitable for fossil formation.
Inability to form a complete fossil record:
4. Some fossil are located in inaccessible areas.
5. Most fossils are only body parts and not whole organisms. They may be damaged.
6. The chance of discovering fossils is low.

Question 16

Name two pieces of evidence for evolution in addition to fossil record.

Answer 16

Similarities in anatomical structures and similarities in biomolecules.

Question 17

State the definition of homologous structures and their implication in evolution theory.

Answer 17

Homologous structures are anatomically similar structures which serve similar or different functions in different species. They suggest that the species evolved from a common ancestor.

Question 18

List 4 pieces of evidence in the biomolecules of organisms which suggest that all the species evolved from a common ancestor.

Answer 18

1. DNA containing the same 4 bases is the genetic material in all organisms.
2. The genetic cod is universal in all organisms.
3. Proteins in all organisms are synthesised from the same 20 amino acids.
4. ATP is the energy carrier in all organisms.

Question 19

List and explain one important assumption when comparing the base sequence of DNA for different organisms.

Answer 19

The species with more similarities in their base sequences of DNA have a closer phylogenetic relationship. More similarities in DNA base sequences suggests that there were fewer mutations accumulated in their genome, which implies less time have passed since the two species shared a common ancestor. Thus, the two species have a closer phylogenetic relationship.

Question 20

List and explain one important assumption when comparing the amino acid sequences of proteins for different organisms.

Answer 20

The species with more similarities in their amino acid sequences of an essential protein have a closer phylogenetic relationship. More similarities in the among acid sequence of an essential protein between two species suggest that there were more similarities in the genetic code for the amino acid sequence, implying that fewer mutations accumulated in the base sequence of the coding region of DNA. This then suggests less time have passed since the two species shared a common ancestor, thus the two species have a closer phylogenetic relationship.

Question 21

Name a diagram which can be used to represent phylogenetic relationships between different species.

Answer 21

Evolutionary tree