Paper 2: Topic 6 Inheritance, variation & evolution - Development of understanding of genetics & evolution

Question 1

What evidence did Charles Darwin use propose his theory of ‘survival of the fittest’?

Answer 1

1. Fossils
2. Geology
3. Animal behaviour
4. Observational studies of some species
5. Discussion with other Scientists

Question 2

State Charles Darwin’s 3 key observations

Answer 2

1. Individual organisms within a particular species show a wide range of variation for a characteristic
2. Individuals with characteristics most suited to the environment are more likely to survive to breed successfully
3. The characteristics that have enabled these individuals to survive are then passed on to the next generation

Question 3

Explain Charles Darwin’s concept of ‘survival of the fittest’ Hint: 7 key steps

Answer 3

1. Variation within a population exists
2. Some individuals are more suited to their environment (due to the characteristics they possess)
3. The individuals who are more suited to the environment are more successful
4. These individuals are more likely to survive and breed
5. These individuals will pass on the alleles for the beneficial characteristics to the their offspring
6. Over a LONG period of time and MANY generations the beneficial alleles will become more common in the population
7. Over time the characteristics of the population change – this means it has evolved

Question 4

Give 3 reasons why Charles Darwin’s theory was not fully accepted at the time

Answer 4

1. The theory challenged the idea that God made all the animals and plants that live on Earth
2. There was insufficient evidence at the time the theory was published to convince many scientists
3. The mechanism of inheritance and variation was not known until 50 years after the theory was published

Question 5

Name a Scientist, other than Charles Darwin, who put forward an alternative hypothesis for evolution

Answer 5

Jean-Baptiste Lamark

Question 6

Describe Lamarck’s hypothesis for evolution

Answer 6

• He proposed that changes that occur in an organism during its lifetime can be inherited
• He suggested in an organism used a characteristic a lot then it would become more developed in its life time
• He suggested offspring would then inherit these acquired characteristics from their parents

Remember: We now know that in the vast majority of cases this type of inheritance cannot occur

Question 7

Give an example of Lamarck’s theory of acquired characteristics

Answer 7

Example 1

• A giraffe stretches their neck to reach the leaves on a higher tree
• The neck would get longer during the giraffe’s lifetime
• The giraffe’s offspring would then inherit the longer neck

Example 2

• A rabbit uses its legs a lot to run away from predators
• The rabbit’s legs would get longer during its lifetime
• The rabbit’s offspring would then inherit the longer legs

Question 8

Explain why Lamarck’s hypothesis was rejected

Answer 8

• Experiments did not support his proposal
• E.g. colouring the fur of a rabbit does not result in the rabbit having babies with a different colour fur

Question 9

Explain why over time Darwin’s hypothesis was accepted

Answer 9

• The study of genetics supported his hypothesis
• Other evidence was also found in fossils
• Recent discoveries of the evolution of antibiotic resistance in bacteria by natural selection have also provided more proof

Question 10

Explain when a hypothesis becomes a theory

Answer 10

When there have been sufficient investigations and experiments into the hypothesis that have generated data & evidence to support the hypothesis

Question 11

Describe the work of Alfred Russel Wallace

Answer 11

• Alfred Russel Wallace independently proposed the theory of evolution by natural selection
• He published joint writings with Darwin in 1858 which prompted Darwin to publish On the Origin of Species (1859) the following year
• Wallace worked worldwide gathering evidence for evolutionary theory
• He is best known for his work on warning colouration in animals and his theory of speciation
• Alfred Wallace did much pioneering work on speciation but more evidence over time has led to our current understanding of the theory of speciation

Question 12

Give an example of the work carried out by Alfred Russell Wallace

Answer 12

• He studied warning colours in butterflies that were used to deter predators from eating them
• He proposed that the warning colours were a beneficial characteristic that had evolved by natural selection

Question 13

According to the theory of evolution where did all life originate from?

Answer 13

Simple life forms that first developed more than 3 billion years ago

Question 14

Define the term ‘species’

Answer 14

• A group of similar organisms that can interbreed to produce fertile offspring
• They share a common ancestor and have similar characteristics

Question 15

Define the term ‘speciation’

Answer 15

When a single population of one species evolves so that different phenotypes can no longer interbreed with each other to form fertile offspring In summary – it is the development of a new species

Question 16

Describe what may cause speciation may occur

Answer 16

A population becomes separated due to a geographical barrier e.g. ocean, mountain range

Question 17

Explain the process of speciation (i.e. how speciation occurs)

Answer 17

1. A population of one species shows variation between individuals
2. The population becomes separated by a geographical barrier e.g. mountain range
3. The 2 different groups experience different environmental conditions in their respective habitats e.g. one side of the mountain range has a warmer climate than the other side
4. In each group there is variation in the characteristics beneficial characteristics to the their offspring
5. Over a LONG period of time and MANY generations the beneficial alleles will become more common in the population
6. Over time the variants in the two groups change so that they can no longer breed with each other to form fertile offspring
7. The groups are now defined as two separate species

Question 18

Who was the pioneer scientist of the theory of speciation?

Answer 18

Alfred Russell Wallace

Question 19

Define the term ‘extinction’

Answer 19

Extinctions occur when there are no remaining individuals of a species still alive

Question 20

Give 5 reasons why extinction may occur

Answer 20

1. Significant environmental change e.g. destruction of their habitat
2. A new disease
3. A new predator e.g. humans hunting and killing them
4. Individuals fail to compete against successfully against a new species for food
5. A catastrophic event e.g. volcanic eruption

Question 21

Name the Scientist who made major discoveries in genetics

Answer 21

Gregor Mendel

Question 22

Describe the work of Gregor Mendel

Answer 22

In the mid-19th Century Gregor Mendel carried out breeding experiments on plants.

Question 23

State Mendel’s main observation from his studies on plants

Answer 23

The inheritance of each characteristic is determined by ‘units’ that are passed on to descendants unchanged

Question 24

State Mendel’s 3 main conclusions that he drew from his studies on plants

Answer 24

1. Characteristics in plants are determined by hereditary units
2. Hereditary units are passed on unchanged from parents to offspring (one hereditary unit is passed from each parent)
3. Hereditary units are either dominant or recessive – if both types of units are present the dominant unit will be expressed

Question 25

Give 3 reasons why it took time for people to accept and understand Mendel’s work

Answer 25

1. Mendel’s work was new and innovative – there was no similar work being undertaken and Scientists did not know about DNA or genes
2. His work was only appreciated after his death
3. It was only with the observations of many Scientists who used Mendel’s work as a starting point that we began to understand about genes

Question 26

Give 3 key dates in the history of the understanding of genes and DNA

Answer 26

• Late 1800s = scientists could observe and study the behaviour of chromosomes during cell division
• Early 20th Century = The concept (idea) of units of hereditary being located on chromosomes was suggested. This led to the idea that the ‘units’, now called genes, were located on chromosomes.
• 1953 = Structure of DNA was determined and the mechanism for gene action was worked out This scientific work by many scientists led to the gene theory being developed

Question 27

State the 2 main sources of evidence for the theory of natural selection

Answer 27

1. Fossils
2. Antibiotic resistance in bacteria

Question 28

Define the term ‘fossil’

Answer 28

The preserved remains of organisms that live many thousands of years ago found in sedimentary rock

Question 29

State the 3 ways in which fossils can form

Answer 29

1. Gradual replacement by minerals
2. From casts and impressions
3. From preservation in areas where no decay occurs

Question 30

Explain how gradual replacement by minerals forms a fossil

Answer 30

1. Hard materials such as booth, shells, teeth etc do not decay easily even when they are buried
2. These substances are slowly replaced by minerals
3. The layers of minerals builds up over the original part
4. The surrounding sediments are compressed to form sedimentary rock
5. The fossil remains as a distinct shape within the sedimentary rock

Question 31

Explain how fossils form from casts and impressions

Answer 31

• An organism is buried in soft material e.g. clay
• The clay hardens around the organism
• The organism decays inside the hardened clay
• This forms a cast around the organism
• Casts can also form around animal’s burrows or plant’s roots
• Footprints can also be pressed into clay and leave an impression when the clay hardens

Question 32

Explain how preservation can occur in areas where no decay occurs

Answer 32

1. Amber and tar pits have no oxygen or moisture so no decay occurs in these areas
2. Glaciers are too cold for decay to occur
3. Peat bogs are too acidic for decay to occur

Question 33

Explain why Scientists can’t be sure how life began

Answer 33

• The fossil record is incomplete
• It is not possible to regenerate the conditions that existed when life began so no experiments can be carried out
• This means there is a lack of valid and reliable evidence

Question 34

Why is the fossil record incomplete

Answer 34

• Some organisms are soft-bodied and fully decay leaving no fossil
• Not all fossils have been found yet
• Some organisms die in areas where fossils do not form e.g. centre of a forest
• Some fossils have been destroyed e.g. geological activity