Evidence for evolution 1

Bio3B

Palaeontology

• This involves the collection of evidence of past life or fossils

The fossil record shows:• similarities between prehistoric organisms and organisms

living today eg mammoths & elephants• changes in some species such as horses, whales, pigs• some organisms have changed little throughout their history.

This may be due to little change in the selection pressures

These organisms are called living fossils eg coelacanth, crocodile, cockroach

Some problems with using fossils includeincomplete records eg human recordsproblems with dating eg changing CO2 levels affect carbon dating

Fossils

• Fossils are preserved remains of dead organisms. This includes body parts eg shells, bones, teeth, mummified bodies, pollen and evidence of their presence eg footprints, burrows, copraliths (fossilised faeces)

• They provide evidence for evolution because they show sequences of changes in a species eg horse, whale and the presence of species that no longer exist eg dinosaurs

Fossil formation

Fossils are formed when organisms die and are preserved rather than being eaten or decaying.

Fossils that are preserved include shells, bones, skulls, teeth, mummified bodies, pollen, footprints, burrows, copraliths (fossilised faeces)

Conditions that favour fossilisation• rapid burial eg by silt, sand, ash, mud, ice, etc

so that the organism is not eaten or decayed• exclusion of oxygen eg by burial so that decay is

slowed• wet, acidic, oxygen depleted soils eg peat bogs

so that decay is slowed (bones are dissolved, but soft tissue mummifies)

• dry alkaline conditions eg sand, ash so that hard tissues eg bone and teeth are preserved

• The reasons that so few fossils are found are: most dead organisms are eaten or decay, or are destroyed by volcanoes, erosion, etc

Fossilisation

What sorts of fossils (if any) are most likely to be formed by these events?

1. a dead tree in a tropical rainforest2. a dead elephant washed into an African river 3. a dead snail on the bottom of a lake4. an animal fallen into a peat bog5. a mammoth trapped in a glacier6. a herd of buffalo walking over volcanic ash 7. a forest covered by volcanic lava 8. an insect trapped in pine resin, which is then

covered by a mud slide

Fossilisation

What sorts of fossils (if any) are most likely to be formed by these events?

1. a dead tree in a tropical rainforest none - decompose2. a dead elephant washed into an African river skull,

bones, teeth, tusks3. a dead snail on the bottom of a lake shell4. an animal fallen into a peat bog mummified body with no

bones, skull or teeth as these dissolve5. a mammoth trapped in a glacier whole preserved animal6. a herd of buffalo walking over volcanic ash footprints7. a forest covered by volcanic lava none – destroyed by

the heat8. an insect trapped in pine resin, which is then covered by

a mud slide whole insect preserved in amber

Short answer Q34a & b 2006Scientists have recently discovered that people who spend more time in 'deep

sleep' at night have a different allele of the gene for the production of the enzyme adenosine deaminase. They have called this allele the 'slumber gene'. Adenosine builds up in the brain during the day as a product of the breakdown of ATP, ADP and other molecules involved in providing energy for cellular processes. During deep sleep, adenosine in the brain is broken down by adenosine deaminase. The enzyme produced by the slumber gene is less efficient than the normal enzyme and occurs in about 10% of the general population.

(a) Provide an hypothesis to explain the variation in deep sleep amongst individuals that incorporates the function of adenosine deaminase.

(b) (i) Give two characteristics of all enzymes

(ii) In the case of the 'slumber gene', what is meant by the efficiency of enzyme action?

Short answer Q34a & b 2006

(a) Provide an hypothesis to explain the variation in deep sleep amongst individuals that incorporates the function of adenosine deaminase.

Decreasing or low levels of adenosine deaminase (2 marks) increases time spent in deep sleep (2 marks)

Varying efficiencies in versions of adenosine deaminase (2 marks) lead to variations in the amount of time in deep sleep (2marks)

Increasing adenosine (2) results in increased deep sleep (2marks) b) (i) Give two characteristics of all enzymesAny two of:• Most are proteins • Denatured by high temperature/have an optimum temperature

• Substrate specific/active site/substrate specific/catalyses specific reaction• pH sensitive/ have an optimum pH • reusable• function at low concentration • reduces activation energy• biological catalyst/catalyst/accelerate reactions

(ii) In the case of the 'slumber gene', what is meant by the efficiency of enzyme action?

The rate at which adenosine is broken down/reaction occurs more slowlyHow easily the enzyme-substrate complex forms/level of activation energy required

Short answer Q34c 2006Scientists have recently discovered that people who

spend more time in 'deep sleep' at night have a different allele of the gene for the production of the enzyme adenosine deaminase. They have called this allele the 'slumber gene'. Adenosine builds up in the brain during the day as a product of the breakdown of ATP, ADP and other molecules involved in providing energy for cellular processes. During deep sleep, adenosine in the brain is broken down by adenosine deaminase. The enzyme produced by the slumber gene is less efficient than the normal enzyme and occurs in about 10% of the general population.

c) This part of the question refers to the axes below

i) From the information provided on the efficiency of the two enzymes, sketch the relationship between adenosine concentration and time for each enzyme. Include a key (legend).

(ii) Name one assumption that must be made for the comparison to be valid.

Short answer Q34c 2006Scientists have recently discovered that people who spend

more time in 'deep sleep' at night have a different allele of the gene for the production of the enzyme adenosine deaminase. They have called this allele the 'slumber gene'. Adenosine builds up in the brain during the day as a product of the breakdown of ATP, ADP and other molecules involved in providing energy for cellular processes. During deep sleep, adenosine in the brain is broken down by adenosine deaminase. The enzyme produced by the slumber gene is less efficient than the normal enzyme and occurs in about 10% of the general population.

c) This part of the question refers to the axes below

(ii) Name one assumption that must be made for the comparison to be valid. Any one of the following for 2 marks:• same temperature • same pH• same starting concentration • same enzyme concentration• same substrate concentration

i) From the information provided on the efficiency of the two enzymes, sketch the relationship between adenosine concentration and time for each enzyme. Include a key (legend). Curves labelled (legend)Curves correct with slumber gene above normal enzyme (no marks if any of the following: lineshave different start points/lines increase across the whole graph (increase followed by decline is acceptable)/lines cross over

slumber

normal

Short answer Q34d 2006 (replaced)

(d) (i) explain how different people can have different versions of a gene.

(ii) How could the enzymes produced by two different alleles of the

same gene be different in efficiency?

(iii) Compare and contrast the 2 theories of how enzymes are thought to work

Short answer Q34d 2006 (replaced)(d) (i) explain how different people can have different versions of a gene.• Mutation – new forms appearSexual reproduction shuffles genes variation eg • Crossing over• Independent assortment• Random recombination / fertilization

(d) How could the enzymes produced by two different alleles of the same gene be different in efficiency? Any two of:• change of protein shape/different amino acid sequence leads to• change of active site leads to • different optimal pH

(ii) Compare and contrast the 2 theories of how enzymes are thought to workhow are they similar Enzymes are catalysts – they speed up reactions / enzymes are specific to a particular substrate /

substrates attach to active site / substrate fits into the active site / a substrate-enzyme complex is formed / substrates are turned into products / enzymes are not used up in the reaction

How they are differentLock and key model - Substrate fits into active site perfectly – like a key into a lock / Enzymes are specific

because their active sites are exactly the right shape for only 1 particular substrateInduced fit - Substrate does not fit into active site perfectly – the enzyme changes shape to fit the substrate

/ This strain as the enzyme changes shape helps reduce the energy needed for the reaction to occur

Short answer Q34e 2006

e) Adenosine deaminase removes a breakdown product of ATP.

(i) Name two specific cellular processes requiring ATP.

(ii) Predict, with an explanation, how deep sleep time might be affected the night after a person has studied 12 hours for an examination

Short answer Q34e 2006e) Adenosine deaminase removes a breakdown product of ATP.

(i) Name two specific cellular processes requiring ATP.

Any two of:

• muscle action • anabolism • protein synthesis

• active transport • growth/repair

• cell division/mitosis/meiosis • DNA replication • photosynthesis

• cell movement • endocytosis/exocytosis/phagocytosis/pinocytosis

• transmitting nerve impulses • bioluminescence

(ii) Predict, with an explanation, how deep sleep time might be affected the night after a person has studied 12 hours for an examination

Any two of:

• need for more deep sleep (to get rid of adenosine)

and maximum one mark for either of:

• high activity level/concentration

leads to

• high adenosine