Key Knowledge 11

Question 1

Speciation

Answer 1

is the process by which populations genetically diverge until they become distinct species.

Question 2

species 

Answer 2

a group of individuals who are able to breed with each other and produce viable and fertile offspring

Question 3

allopatric speciation

Answer 3

the geographic separation of a population from a parent population resulting in the formation of a new species

Question 4

sympatric speciation 

Answer 4

the divergence of a species from an original species without the presence of a geographical barrier

Question 5

 Pre-reproductive isolating mechanisms

Answer 5

Geographical – individuals may not be able to interact with each other due to
separation by barriers (e.g. body of water).
Ecological – individuals may inhabit different ecological niches or habitats so
they do not interact with each other.
Temporal – the time of the day or year when individuals are ready to breed
may differ.
Behavioural – the type of mating behaviours, such as mating call, of individuals
may vary.
Structural – the physical characteristics of individuals may drastically vary,
physically preventing breeding.

Question 6

 Post-reproductive isolating mechanisms

Answer 6

Gamete mortality – the sperm may be unable to penetrate the ovum for
fertilisation.
Zygote mortality – fertilisation may occur and a zygote may be formed,
however, it will not survive.
Hybrid sterility – a viable offspring may be formed and may survive until
adulthood, but will not be fertile

Question 7

 The process of allopatric speciation

Answer 7

1. A geographical barrier separates a population, preventing gene flow.
2. Different selection pressures act upon each population, favouring different phenotypes and allowing for genetic differences to accumulate.
3. Eventually, sufficient genetic differences accumulate so that the two populations can no longer interbreed to produce viable and fertile offspring

Question 8

Students can sometimes struggle to answer short answer questions on allopatric speciation. However, in most of these questions, you simply need to apply the following principles to the scenario provided:

Answer 8

1. Geographical barrier – state that a geographical barrier (e.g. a mountain) has isolated a population (or populations) of the same species from each other, thereby preventing gene flow.
2. Environment – state that the isolated populations are subjected to different selection pressures, allowing for the accumulation of genetic differences.
3. Speciation – explain that once sufficient genetic differences accumulate and the two populations can no longer interbreed to form viable and fertile offspring, a new species has been formed.

Question 9

Galápagos finches

Answer 9

Despite the significant variation in their beak shapes, they are all closely related. They have evolved rapidly by allopatric speciation; a process known as adaptive radiation.

Question 10

Howea palms

Answer 10

This island has become a place of interest in investigating sympatric speciation, with the Howea palms serving as one of the most conclusive examples of sympatric speciation.
While there are many different species of palms that inhabit Lord Howe Island, two species of particular interest include Howea forsteriana and Howea belmoreana. By analysing the distribution of the two species of Howea palms, researchers hypothesised that differences in soil pH were the catalyst for speciation.

Question 11

fossil record 

Answer 11

the information derived from fossils. The fossil record is arranged in chronological order and helps us map the history of life on Earth, placing species in the appropriate geologic time frame

Question 12

Some key moments, include:

Answer 12

• the emergence of prokaryotes (3.8 bya)
• widespread photosynthesis (2.4 bya)
• the first eukaryotes (2 bya)
• the first multicellular organisms (900 mya)
• the Cambrian explosion (535 mya)
• animals on land (530–400 mya)
• mammals (251 mya)
• flowering plants (140 mya)

Question 13

Typically, the process of fossilisation occurs when:

Answer 13

1. Remnants of an organism are rapidly covered by sediment, meaning that the dead organism is not exposed to oxygen, microorganisms, and other disturbances that would increase its rate of decomposition.
2. Over time, sediment layers build upon each other and compact, layer by layer, until pressure cements them together to form sedimentary rock (Figure 2).
3. Within this rock, the fossilised remains can take many forms, including a permineralised (Figure 3), mould, or cast fossil.

Question 14

permineralised fossil

Answer 14

fossil formed when mineral-rich groundwater deposits minerals like silica and calcite into organic material, creating a mineral relic

Question 15

No matter the fossil type, the conditions that increase the likelihood of fossilisation include:

Answer 15

• physical protection from scavengers and decomposers (e.g. fungi, bacteria)
• areas of rapid sediment accumulation
• constant cool temperatures
• low oxygen availability
• low light exposure.

Question 16

The process of a dinosaur becoming fossilised via permineralisation after being covered in sediment

Answer 16

1. The dinosaur dies in a river.
2. The body is covered with sediment. The soft tissues decompose and the hard body structures become fossilised by permineralisation.
3. The sedimentary layers accumulate and the resultant pressure forms sedimentary rock.
4. The earth’s movements raise the layers of the rocks to the surface.
5. The rock erodes, exposing the fossilised body structures.

Question 17

relative dating 

Answer 17

a dating technique used to determine the relative age of a fossil by comparing its position to other fossils or rock in surrounding rock strata (layers)

Question 18

absolute dating 

Answer 18

a dating technique used to determine the absolute age of a fossil by measuring the relative amounts of radioisotopes to their products. Also known as radiometric dating

Question 19

fossil succession 

Answer 19

the principle that fossils of the same age will be in the same layer of sedimentary rock, and fossils found in a higher or lower sedimentary layer will be younger or older, respectively. Also known as faunal succession

Question 20

relative age 

Answer 20

the age of a fossil as determined by relative dating techniques. Describes the age of a fossil compared to other fossils, instead of a fossil’s exact age in years

Question 21

index fossil 

Answer 21

a group of widespread fossils which existed for a short period and have a known age. Can be used as a reference to easily determine the age of unknown fossils

Question 22

For the best index fossils, the species must be:

Answer 22

• physically distinctive
• have had a large population
• have existed in many geographical areas
• only lived within a known short period of time.

Question 23

transitional fossil 

Answer 23

a fossil that shows traits that are common to both its ancestral group and its descendant group. They are particularly important when the descendant species is physically very distinct from the ancestral species, such that the transitional fossil can help demonstrate evolutionary changes between the two

Question 24

absolute age 

Answer 24

an estimate of the age (in years) of a fossil or rock

Question 25

radioactive isotope 

Answer 25

a radioactive atom of a specific element. This atom breaks down into a predictable and stable product. Also known as a radioisotope

Question 26

absolute dating is based on the following three principles:

Answer 26

1. Radioisotopes are unstable elements that will break down over time into a more stable product.
2. While these radioisotopes can break down at any point, on average the rate of breakdown is constant and can be modelled.
3. Half-life describes the amount of time before half of the mass of a radioisotope is broken down into predictable and stable products.

Question 27

The general principles of radiocarbon dating are as follows:

Answer 27

1. All living things contain carbon.
2. When the organism dies, its 14C will begin to decay.
3. At any point, scientists can measure the amount of 14C present in the fossil and determine how long ago it died.