Week 7 - Chemistry of life and natural selection

Question 1

List and explain the characteristics of life

Answer 1

1. Structurally complicated
2. Highly organised
3. Capable of extracting, transforming or using energy from their environment
4. Capacity for self-replication and self assembly

Question 2

Explain which elements are important to life and why?

Answer 2

1. Hydrogen, Carbon, Nitrogen & Oxygen.
2. All non-metallic & form bonds to other similar elements by sharing electrons (covalent bonding)
3. Some of smallest atoms. Form very strong bonds. (all except H can form multiple bonds)

Question 3

What are metabolic options for obtaining energy in organisms

Answer 3

1. Phototroph - light as energy source
2. Chemotroph - energy from oxidation of chemical compounds
3. Autotroph - CO2 as sole or principle carbon source
4. Heterotroph - reduced, perform organic molecules as carbon source for growth
5. Lithotroph - reduced inorganic substances as electron source
6. Organotroph - use of reduced organic compounds as electron source

Question 4

Explain why we think life might have started in Earths atmosphere

Answer 4

Miller-Urey experiment - attempt to simulate early Earth.

1. Mix water, water vapour, ammonia & methane.
2. Apply electric sparks to resultant gas.
3. Gas condensed and rained back to initial mixture.

Found amino acids + organic molecules.

Question 5

Explain why we think life might have come from space.

Answer 5

Panspermia - life did not arise on Earth but migrated from another world

Question 6

Explain why we think life might have come from ocean.

Answer 6

Deep sea vents - geothermal energy, extremophiles

Question 7

Explain what is meant by natural selection

Answer 7

1. Individuals in any species can potentially reproduce rapidly
2. Not all individuals survive, not all survivors reproduce
3. Survival and reproduction is determined by competition
4. Variation among individuals: Traits which make superior competitors will be the most successful at survival and reproduction.
5. Winning traits (if genetic) passed on to offspring = more common in future generations
6. Genetic mutation (errors by DNA when cell divides) supply new variation on which natural selection can act

Question 8

Explain why sex ratio is 50:50 for most species

Answer 8

Frequency-dependent selection - average fitness is greater for the minority sex

Question 9

Examples which support natural selection

Answer 9

1. Ancient organism remains
2. Fossil layers
3. Similarities among organisms alive today
4. Similarities in DNA
5. Similarities of embryos

Question 10

Apply idea of natural selection to explain specific examples

Answer 10

Yeast experiment. Gen 1, 2, 3, 4 & 5.

Successive gen was “fitter” than previous.

Fitter only relative to existing population = Gen 2 outperformed Gen 5. Gen 1 outperformed Gen 4.