Genes Evo & Dev L3

Question 1

Describe theories of how Life began on Earth?

Earth vs. Geothermal vents

Answer 1

• Earth -> 4 billion yrs -> Heredian -> “Darwin’s warm muddy pond theory”
• ->Repeated destruction -> Brings water.
• ->Strong sun -> high UV radiation at surface of water. -> no life above.
• Deep Sea -> 3.8 billion years
• ->Proton gradients surrounding alkaline hydrothermal vents Eg. “Lost City” in mid-Atlantic -> possibly supplied energy to fuel first replication.

Question 2

Evidence supporting theory life started with Hydrothermal vents?

Answer 2

- Harbour geological manifestations of both kinds of energy used by life -> chemically reactive compounds & natural proton gradients.
- Remain active for up to 100,000 yrs -> provide constant source of energy over long geological timescales.
- Proton gradients at Lost City -> same magnitude & orientation as those in modern auto-trophic cells.

Question 3

First replicating molecules?

Answer 3

RNA

Question 4

How did proteins & DNA evolve from RNA in the RNA world hypothesis?

Answer 4

 Basis for both reproduction & biochemical interaction -> acting as enzymes.
–> Possible combination of Amino acids -> found on comets -> by RNA -> creates proteins. Re-placed RNA enzymes -> wide range of biological functions eg. structural, enzymes, etc. ad-vantageous.
–> DNA evolved & replaced RNA.
- Double helix -> more stable for storage of info & identification of errors
- More resistant to effects of sunlight & cell membrane additional protection.
- Faster chemical reactions & DNA replication using protein enzymes.
 - Formed LUCA

Question 5

What is thought to have existed first, life or cells? Support your answer & mention two examples of where this may be found.

Answer 5

•Likely that cells existed before life itself.
–> RNA extremely reactive / unstable -> needs protection/barrier.
–>In order for chemical reactions to occur & creation of energy -> life; tiny molecules have to react/combine. -> Miniscule therefore requiring contained environment for reaction to occur as molecules otherwise may not have met.

- Tiny pores in rocks around hydrothermal vents
- Also hypothesised -> lipid protobionts reproduced & metabolised.

Question 6

What conditions were required on earth for LUCA/life?

Answer 6

Requires cool temperatures, gravity, water & protection from radiation

Question 7

Outline evolution of first prokaryotes

Answer 7

• -> Cyanobacteria -> produced O2
• -> Methanogeneic bacteria consumed this O2 for hundreds of millions of years.
• -> Methanogens extinct -> possibly changes in trace metals in sea.

Question 8

Describe how eukaryogenesis may have occurred.

Answer 8

Evolution of eukaryotes -> 2 billion years ago.
 Eukaryotes can be single-celled ; but to be multicellular -> must be eukaryote.
 Likely caused by heterotrophic eubacterium being engulfed by archaebacterium.
 This eventually became mitochondria.
 Mitochondria enable large complex life due to energy they provide.
 Bacterium engulfed by eukaryotic plant ancestor.

Question 9

Examples of Ediacaran biota

Answer 9

• Spriggina -> Annelid worm/arthropod? – 3cm long
   - Dikinsonia -> Up to 1m in length
   - Rangeomorphs -> Fractally branched, fern-like. -> Dark depths of ocean. -> Ecology suggests they were animals.
   - Erniettmorphs -> modular or quilted.

Question 10

Evidence of the Cambrian explosion?

Answer 10

The Cambrian Explosion -> 515-540 million years ago -> Burgess Shale.
 Most types of common animal today appeared over 20-30 million years. Eg. Arthropods, chordates, worms.
Soft bodies preserved in Burgess Shale (Canada), China, Greenland & Russia
 Some can’t be categorised into modern taxonomy Eg. Opabinia -> 7cm long.

Question 11

How/why did the Cambrian explosion occur?

Answer 11

• Physiological change -> dissolved O2 levels enabled active lifestyle
• Geographical change -> Formation of new seas -> new niches
• Geochemical change -> Changing Sea levels led to abundance of trace metals -> used to make exoskeletons.
• Biological change -> Incr. zooplankton enabled enabled evolution of new predators -> further incr. selection pressures.
• Other geological & biological factors -> Eruptions caused by comet impacts weakened species
   Dinosaurs & large reptiles died
   Ecological niches of extinct species (pterosaurs, mesosaurs) -> left space for evolution of birds & mammals.
  (–NB. -> Mammals present for majority of Jurrasic era.)
  -> Recovery of ecosystem from mass extinction -> 20 million years.

Question 12

How were eukaryotes able to evolve as a result of Cambrian explosion?

Answer 12

• Other geological & biological factors -> Eruptions caused by comet impacts weakened species
   Dinosaurs & large reptiles died
   Ecological niches of extinct species (pterosaurs, mesosaurs) -> left space for evolution of birds & mammals.
  (–NB. -> Mammals present for majority of Jurrasic era.)
  -> Recovery of ecosystem from mass extinction -> 20 million years.

Question 13

Describe the Permian mass extinction, what caused it & the resulting factors.

Answer 13

• End of Permian -> mass extinction. (250 million years ago)

• 95% sea-life extinct -> All trilobites & placoderms (armoured fish) , 99% plankton genera.
• 70% all families of land animal extinct
• Multiple factors Eg. Volcanism, tectonic plates, asteroids may have caused rapid widespread climate change.
• Diapsids (early dinosaurs) & cartilaginous fishes populations able to grow.
• Theraspids (our ancestors) just survived.

Question 14

Outline evolution of the eye

Answer 14

• Evolution of the eye: (50-100 times)
1. Light-sensitive cells/photoreceptors/pigment built onto membrane -> single celled organisms.
 Enabled them to swim toward light.
2. Cup-shaped hollows
 Enabled to sense direction of light.
3. Pinhole iris
 Incr. resolution -> sharper image.
 Narrows to become sharper -> this decreases available light & decr. sensitivity.
4. Protective crystalline covering over iris.
 Focus & control of light entering eye.
 Lens to focus light.

Question 15

Why was evolution of the lens successful?

Answer 15

Protein opsins -> molecular basis for all sight
First functioned as clocks more than light sensors -> combined with melatonin which dies upon contact with light -> enabling detection of daybreak by absence of melatonin.
 Continually generate melatonin for next day of use but chromophores could just change shape continuously.

Question 16

Conclusions on study on pupil shape & foraging?

Answer 16

• Strong correlation between pupil shape & foraging technique.
   Herbivores – horizontal
   Active predators – circular & sub-circular
   Ambush predators – vertical
• Relationship between pupil shape and period of activity during daylight.
• Foraging mode has higher significant impact on pupil shape than time of activity.
• No relationship between circular shape & activity period.

Question 17

Pupil shape related to foraging styles?

Answer 17

Herbivores – horizontal
 Active predators – circular & sub-circular
 Ambush predators – vertical

Question 18

How are vertical slit pupils ideal for survival of predators?

Answer 18

 In low light helps determine distance to prey.

 This advantage diminishes as height from ground incr.

Question 19

How are horizontal slit pupils ideal for survival of prey?

Answer 19

Better scope of surroundings for detection of predators & escape routes.