4.5 & 4.6 & 4.7 | Species and taxonomy, Biodiversity within a community, Investigating diversity

What is the definition of a species?

A group of organisms that can interbreed to produce fertile offspring.

Suggest two reasons why two different species are unable to produce fertile offspring.

1. They have different chromosome numbers.
2. This leads to offspring with an odd chromosome number, preventing homologous pairs from forming and meiosis from occurring, so gametes cannot be produced.

Why is courtship behaviour a necessary precursor to successful mating? (Give 4 reasons)

1. Allows recognition of the same species to ensure fertile offspring can be produced.
2. Stimulates and synchronises the release of gametes.
3. Establishes a pair bond to raise young together.

4. Indicates sexual maturity and fertility.

Describe a phylogenetic classification system.

A system that arranges species into groups (taxa) based on their evolutionary origins and relationships, using a hierarchical structure where smaller groups are placed within larger groups without overlap.

List the eight taxonomic groups in order, from the broadest to the most specific.

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

How is each species universally identified?

By a binomial name, which consists of its genus and species name (e.g., Homo sapiens).

What is a key advantage of the binomial naming system?

It is universal, preventing confusion that arises from the use of multiple common names for the same organism.

Why might an offspring from two different species (like a mule) be infertile?

Because it has an odd number of chromosomes, which prevents the formation of homologous pairs and the successful completion of meiosis to produce viable gametes.

On a phylogenetic tree, what does a branch point represent?

A common ancestor.

On a phylogenetic tree, what does a branch represent?

An evolutionary path.

How can you tell which two species on a phylogenetic tree are the most closely related?

They share the most recent common ancestor (e.g., the branch point where their two lines meet is closest to the present).

Describe two technological advances that have helped clarify evolutionary relationships.

1. Advances in genome sequencing.
2. Advances in immunology.

How does genome sequencing help determine how closely related two species are?

It allows scientists to compare DNA base sequences. More differences in the sequences mean the species are more distantly related, as more mutations have built up over time since they shared a common ancestor.

How does immunology help determine how closely related two species are?

It allows comparison of protein tertiary structure. If a protein from one species binds strongly to an antibody made against the same protein from another species, it indicates a similar structure and amino acid sequence, meaning they are more closely related as less time has passed for mutations to build up. 

What is the underlying principle that allows both DNA and protein comparisons to reveal evolutionary relationships?

Mutations build up over time. Closely related species have had less time for mutations to accumulate in their DNA and the proteins they code for.

If two species have very few differences in their DNA base sequences for a particular gene, what can you infer about their relationship?

They are very closely related and shared a common ancestor relatively recently.

What is biodiversity?

The variety of living organisms, which can refer to species, genetic, and ecosystem diversity. It can relate to a range of habitats, from a small local area to the entire Earth.

What is a community?

All the populations of different species that live in a particular area.

What is species richness?

A measure of the number of different species in a community.

What does an index of diversity describe?

It describes the relationship between the number of species in a community (species richness) and the number of individuals in each species (the population size).

Why is an index of diversity more useful than just measuring species richness?

Because it also takes into account the number of individuals in each species, which means it accounts for whether some species are present in very small or very high numbers.

What is the formula for calculating the index of diversity (d)?

d = N(N-1) / Σn(n-1)
Where:
N = the total number of organisms of all species
n = the total number of organisms of each species
Σ = the sum of

What are the steps involved in calculating an index of diversity?

1. Calculate the total number of organisms (N).
2. Multiply N by (N - 1).
3. For each species, multiply its number of organisms (n) by (n - 1).
4. Add up all the values from step 3 to get Σn(n - 1).
5. Divide the answer from step 2 by the answer from step 4.

How do you interpret a high index of diversity value?

A high value indicates that many different species are present and that the species are evenly represented, with no single species dominating.

How do you interpret a low index of diversity value?

A low value indicates that the habitat is dominated by one or just a few species.

In a woodland, Community A has 5 species of tree with roughly equal numbers of each. Community B has 5 species, but one species makes up 95% of the trees. Which community has a higher index of diversity?

Community A. Although they have the same species richness, Community A has a higher index of diversity because the species are more evenly represented.

How does the removal of woodland and hedgerows reduce biodiversity?

It reduces the variety of plant species, which leads to fewer habitats and niches, and less variety of food sources for other organisms.

How does monoculture reduce biodiversity?

Growing only one type of crop reduces the variety of plant species, leading to fewer habitats, niches, and food sources.

How does the use of pesticides reduce biodiversity?

Pesticides kill pests, which then reduces the population of the predators that feed on those pests.

Why is there a conflict between conservation efforts and farming?

Conservation increases biodiversity but can reduce crop yields and farmer profits, for example, by reducing land for crops, increasing competition, or increasing pest populations.

How is the conflict between farming and conservation often managed?

Financial incentives or grants are offered to farmers to offset the loss of income from implementing conservation methods.

What are four ways to increase biodiversity in agricultural areas?

1. Reintroducing field margins and hedgerows.
2. Reducing the use of pesticides.
3. Growing different crops in the same area (intercropping).
4. Using crop rotation with nitrogen-fixing crops instead of fertilisers.

What are four ways to measure genetic diversity within or between species?

1. Comparing the frequency of measurable or observable characteristics.
2. Comparing the base sequence of DNA.
3. Comparing the base sequence of mRNA.
4. Comparing the amino acid sequence of a specific protein.

How can comparing DNA, mRNA, or amino acid sequences indicate how closely related two organisms are?

More differences in the sequences mean the organisms are more distantly related and shared a common ancestor longer ago. This is because mutations build up over time, leading to more changes to their amino acid sequences. 

How do mutations affect the relationship between DNA and protein sequences?

More mutations in the DNA base sequence cause more changes in the amino acid sequence of the protein it codes for.

How were early estimates of genetic diversity made, and what were two limitations of this method?

They were made by inferring DNA differences from observable characteristics.
Limitations:

1. Many characteristics are coded for by more than one gene, making them difficult to interpret.

2. Many characteristics are influenced by the environment, so differences might not be due to genes.

How has the method of investigating genetic diversity changed over time?

It has shifted from inferring diversity from observable characteristics to the direct investigation of DNA sequences, due to advances in gene technologies.

According to the diagram, what is the flow of genetic information from DNA to a characteristic?

DNA base sequence (gene) is transcribed into mRNA base sequence, which is translated into a protein's amino acid sequence, which then determines an organism's characteristics.

How should you collect data to avoid bias when investigating variation?

By taking random samples, for example by using a grid and a random number generator to select coordinates.

Why is it important to use the same measurement method and a large sample size?

Using the same method ensures consistency. A large sample size makes the data more representative of the entire population.

What is a running mean and how is it used in sampling?

A running mean is a mean that is recalculated as each new data point is added. You continue sampling until this mean becomes fairly constant.

What ethical consideration must be followed during sampling?

The organism must not be harmed and must be released unchanged.

What two statistical values should you calculate to process data on variation?

The mean (average) and the standard deviation.

What does the standard deviation tell you about a set of data?

It shows the spread of values around the mean. A higher standard deviation means there is greater variation within the sample.

If the standard deviations of two data sets overlap, what does this suggest about the difference between them?

It suggests that the difference between the two sets of data may be due to chance and is not statistically significant.

What is the purpose of using a named statistical test on the data?

To analyse whether there is a significant difference between the populations being studied.

A student is measuring the height of dandelions in two fields. They calculate the mean and standard deviation for each field. The standard deviations overlap. What conclusion can they draw?

They cannot conclude there is a real difference in dandelion height between the fields, as the difference may be due to chance.

Describe a step-by-step method for obtaining a random sample of plants in a field.

1. Place a grid over a map of the field.
2. Use a random number generator to obtain coordinates.
3. Locate the coordinates in the field and sample the plant found there.