Classification and Evolution

Question 1

What is the taxonomic heirarchy?

Answer 1

• The taxonomic hierarchy – kingdom, phylum (organisms with the same body plan), class, order, family, genus, species – King Philip Came Over From Great Spain
• Domain is the highest taxonomic rank – includes Archaea, Eubacteria and Eukaryotae
• Kingdom includes the Prokaryotae (no nucleus), Fungi, Animalia, Plantae, Protoctista

Question 2

Why is using a taxonomic hierarchy helpful?

Answer 2

convenient / easier to identify living organisms / see relationships between species / the study of living things becomes more manageable

Question 3

What is the binomial system of naming species?

Answer 3

• In this system, the genus name and species name are used – i.e. Homo sapiens
• The genus name always has a capital letter and when printed it is in italics but in handwritten text it is underlined

Question 4

Why is the binomial system of naming species important?

Answer 4

o Translation of languages / dialects will not give different names
o The same species is called one name, not various ones in different parts of the country or even different parts of the world
o Everyone uses the same name – avoiding confusion caused by common names

Question 5

How can organisms be classified?

Answer 5

• In original classification, the used of similarities in observable features were used to divide and classify organisms in different kingdoms
• The five kingdoms were developed based on observable features of their anatomy, but at a microscopic level

Question 6

What are the features of Prokaryotae?

Answer 6

o No nucleus
o Have a loop of DNA – not arranged in linear chromosomes
o Have naked DNA (not associated with histone proteins)
o No membrane-bound organelles
o Smaller ribosomes, compared to other groups
o Cells are smaller than those of eukaryotes
o May be free-living or parasitic

Question 7

What are the features of Fungi?

Answer 7

o Eukaryotic
o Can exist as single-cells (yeasts) / have a mycelium that consists of hyphae
o Walls made of chitin
o Cytoplasm is multinucleate
o Mostly free-living and saprophytic – cause decay of organic matter

Question 8

What are the features of Animalia?

Answer 8

o Eukaryotic
o Multi-cellular
o Heterotrophic – digest large organic molecules to form smaller ones for absorption
o Usually able to move around

Question 9

What are the features of Plantae?

Answer 9

o Eukaryotic
o Multi-cellular
o Cells surrounded by a cellulose cell wall
o Autotrophic – the organisms absorb simple molecules, building them into larger organic molecules
o Contain chlorophyll

Question 10

What are the features of Protoctista?

Answer 10

o Eukaryotic
o Mostly single-celled – algae are multicellular
o Show a wide variety of form – none of the organisms qualify for any of the other kingdoms so are put into this one
o Show various plant-like / animal-like features
o Mostly free-living
o Have autotrophic / heterotrophic nutrition – some photosynthesise / ingest prey / feed using extracellular enzymes / parasites

Question 11

Why have new classification systems arisen?

Answer 11

The more recent use of biological molecules and other genetic evidence has made way for a more detailed classification of organisms, that does not solely rely on the observable features.

Question 12

How do biological molecules help classify organisms?

Answer 12

• Evidence from biological molecules helps determine how closely related one species is to another
• Certain molecules are found in almost all organisms – but may not be identical
o Cytochrome C is a protein used in respiration, so all respiring organisms have this molecule, but it is not identical in all species
o The amino acid chain can vary which lead to the conclusions that the species are closely related (identical sequence – i.e. humans and chimpanzees), not so closely related (some difference – i.e. rhesus monkeys and humans, with one difference) and the more difference (less closely related – i.e. dogfish and humans, with eleven differences)
o DNA is another biological molecule found in all living organism – instructions for protein synthesis – and can help classify organisms, most accurately
o Mutations occur at random in the DNA sequence so the more similar the sequence in a part of DNA is, the more closely related the species are / lots of difference, the species have evolved separately for a long time and can be considered as less closely related

Question 13

Why were the three domains of life established?

Answer 13

• Three domains of life were established when the Prokaryotae kingdom was split into two groups: Bacteria and Archaea because bacteria are very different from Archaea and Eukaryotae
o Bacteria have a different cell membrane structure / flagella / no proteins bound to genetic material / different enzymes (RNA polymerase) for RNA synthesis / different mechanism of DNA replication and RNA synthesis
• Moreover, the Archaea and Eukaryotae domains shared features too
o Similar mechanisms for DNA replication and RNA synthesis / similar enzymes for synthesising RNA / production of some proteins to bind to their DNA
• It was argued that the differences between the Bacteria and Archaea was fundamental and these two were more dissimilar than the Archaea from the Eukaryotae
• This was a result of technological advancement and further evidence, which supported the case

Question 14

What is artificial classification?

Answer 14

Artificial classification is based on only a few characteristics / does not reflect any evolutionary relationships / provides limited information / is stable – i.e. the colour of the flower of a plant.

Question 15

What is natural classification?

Answer 15

• Natural classification uses many characteristics / reflects evolutionary relationships / provides a lot of useful information / may change with advancing knowledge – i.e. hierarchy / relations of dogs
• Natural classification is useful for finding out more about endangered/rare species, without harming any members of the group – the information can be applicable to the closely related species and could make conservation more successful

Question 16

Define phylogeny.

Answer 16

Phylogeny is the study of evolutionary relationships between species – studying how closely related species are.

Question 17

Describe key features of phylogenetic trees and how phylogeny links back to classification.

Answer 17

• The more recent the common ancestor (which do not survive today), the more closely related the species are
• If species all evolved from the same ancestral species, they are monophyletic

Question 18

What is the evidence for the theory of evolution?

Answer 18

• There is lots of evidence for the theory of evolution by natural selection, which was formulated by the contribution of Darwin and Wallace
• Fossil evidence showed that new species that have arisen are often like older ones that were found in the same place – i.e. the modern horse
o Species back then were different to today, old species died out, new species arose
o There is similarity and sequence over time, which suggest that species arose from previous ones
o Molecular evidence provides strong evidence for evolution
o Certain molecules are found throughout the living world shows that if one species gives rise to another, it is likely they have all the same biological molecules from one original ancestor
o Closely related species that have separated recently will have similar/identical biological molecules, compared to species that took different evolutionary paths, whose biological molecules are likely to differ
o Evidence from molecules (i.e. cytochrome c) and other proteins shows this pattern of change
o The sequence of DNA can be compared to identify evolutionary relationships – i.e. 1.2% of the coding sequence is different from chimpanzees from humans
o Mitochondrial DNA (mDNA) is passed on from the mother in the egg and mutates more frequently than nuclear DNA, so there is lots of variation in the sequence but it can help trace back to a single female of whom we all are descendants of

Question 19

Describe the steps of natural selection.

Answer 19

Natural selection came into play when too many offspring were born, there was a competition for food and resources, a selective force, which was easier to get for those who were better adapted than their peers, so could live long enough to reproduce and pass their characteristics on to the next generation and perhaps, over time, several changes will give rise to a new species.

Question 20

What is variation?

Answer 20

Variation is the difference that are present between two individuals.

Question 21

Define interspecific variation.

Answer 21

Interspecific variation is differences between species.

Question 22

Define intraspecific variation.

Answer 22

Intraspecific variation is the variation between members of the same species – i.e. eye/hair/skin colour. The greater the genetic diversity of a species, the greater the intraspecific variation.

Question 23

What is continuous variation?

Answer 23

• Continuous variation is where there are two extremes and a full range of values in between
o Regulated, often, by more than one gene
o Can be influenced by the environment
o Most individuals are close to the mean value
o This type of variation is quantifiable – use a histogram to plot this data
o Includes height in humans / length of leaves on an oak tree / number of flagella on bacterium

Question 24

What is discontinuous variation?

Answer 24

• Discontinuous variation is where there are distinct categories and no intermediate values
o Members of a species will be evenly distributed between the different forms / more of one type than another
o Regulated, usually, by a single gene
o Not influenced by the environment in which the organism lives
o Includes human blood groups / whether bacteria have a flagellum, or not / gender in plants – male/female/hermaphrodite

Question 25

What are the causes of variation?

Answer 25

• Genetic (inherited)
o The combination of alleles inherited is not the same as any other living thing (except twins)
o Possess a unique combination of characteristics
• Environmental
o Many characteristics are affected by the environment
o Overfed pet becomes obese / more exposure to sunlight results in darker skin
• Combined effects
o Environmental and genetic variation are not isolated and many characteristics are caused by both types
o In the past century, humans have grown taller due to a better diet but if your whole family is short, you will not grow to be so tall
o Not all genes are active at once and changes in the environment can affect which genes are active when

Question 26

What are adaptations?

Answer 26

An adaptation is a characteristic that enhances the survival of an organism in their habitat.

Question 27

What is convergent evolution?

Answer 27

• Organisms of different taxonomic groups can show similar anatomical features because if they live in a similar environment, similar adaptations will arise
o The marsupial mole and the placental mole look very similar and have similar characteristics (i.e. small eyes / short fur / short tail / nose with tough skin for protection / large claws on strong front legs / cylindrical body)
o This is known as convergent evolution

Question 28

What types of adaption are there?

Answer 28

There are anatomical (structural features) / physiological (affect the way processes work) / behavioural (modified behaviour for survival) adaptations.

Question 29

What are anatomical adaptations of emperor penguins?

Answer 29

• They have wings that seem to be more like flippers and propel the penguins with a downward force, when underwater
• Have glands under the eyes to remove excess salt – so they can drink seawater and not become ill
• Have a short and stiff tail, so they can balance on it, when leaning backwards – reduces heat loss from the feet
• Have 3 stores of oxygen – in the blood, lungs, myoglobin in muscles
• Have heavy solid, bones with no airspace – act as a diver’s weight belt to keep them underwater
• The colour of the penguin’s body camouflages the animal, when underwater – the black back seems to be part of the water and the white front blends in with the sky
• Have four layers of scale-like feathers to protect them from the icy winds and act as a waterproof layer

Question 30

What are physiological adaptations of emperor penguins?

Answer 30

• Male penguins can survive without food for around 100 days – survive during winter, when there is no available food
• During a dive, the heart rate slows down greatly so oxygen is conserved and the penguins can remain underwater for around 20 minutes
• Non-essential organs shut down, when a penguin is diving
• The blood vessels dilate, when they are too warm, to dissipate heat
Have a heat exchange system that allows 80% of the heat in the breath to be recaptured by the nasal passages

Question 31

What are behavioural adaptations of emperor penguins?

Answer 31

• Reproduce during winter – ensures that offspring is independent in the summer, when more food is available
• Huddle together in winter – prevents heat loss
• No nests are made – the egg is covered by the fold of skin on the parents’ feet to keep the egg warm
• Ruffle their feathers to break the insulating layer of air near the skin, if they feel too warm
Maintain a streamline shape to reduce drag when swimming – head hunched into shoulders and feet held close to the body, against the tail to aid steering

Question 32

What is natural selection?

Answer 32

• An individual with a characteristic that helps it survive in an environment is more likely to live long enough to reproduce
• Evolution works by selecting individuals with particular adaptations to survive and reproduce – these adaptations are then passed on to future generations
Eventually, more individuals within the population hold that adaptive characteristic – the adaptation has been selected

Question 33

Describe the mechanism of natural selection.

Answer 33

1. Mutation creates alternative versions of a gene – alleles.
2. This creates genetic variation between individuals of a species – intraspecific variation.
3. Once variety exists, the environment can now ‘select, so when resources are scarce, the environment will select the characteristics that give the advantage – there is selection pressure
4. Individuals with an advantageous characteristic will survive and reproduce – reproductive success (or failure for disadvantaged offspring)
5. Therefore, they pass their advantageous characteristics to the next generation – inheritance.
6. The next generation will have a higher proportion of individuals with the successful characteristics and over time, the group of organisms becomes well-adapted to its environment – adaptation.
   • Variation (due to environmental factors can’t be passed onto the offspring) must occur before evolution can take place – genetic variation is important for evolution

Question 34

How do insects become resistant to pesticides?

Answer 34

• Some insects are pest, which eat food crops and can damage them but they can also act as vectors that transmit pathogens
• Pesticides are chemicals designed to kill pests – insecticides for insects, which are a great selection pressure
• If the individual insect is susceptible, it will die – if it is resistance, it may survive
• This allows the individual with some resistance to reproduce and pass on the resistant characteristic – then resistance spreads quickly through the whole population (short life)
• Resistance was first seen in 1914 but new classes of insecticides were introduced but cases of resistance arose again within 20 years but can arise in as little as 2 years
• If insects become resistant to insecticides, it can cause the pesticide to accumulate in the food chain/they survive further application of the chemicals
• If the insects are eaten by a predator, it receives a larger dose of the insecticide and this can carry on throughout the food chain – even coming back to humans, who receive massive doses
• The increasing resistance and the accumulation of DDT (insecticide) in the food chain, it has been banned in many area but is still used as a household spray in some countries

Question 35

How does antibiotic resistance occur?

Answer 35

• Using antibiotics is a very strong selection pressure
• When taking antibiotics, most of the bacteria are killed but there may be a few that are resistant to the antibiotic
• These are rarely completely unaffected by the antibiotic, they just are more resistant than most
• When most of the bacteria are killed, the patient will feel better and many people will not finish their course – which allows resistant bacteria to survive and reproduce to make a resistant strain of bacteria
• Overuse and incorrect use of antibiotics has led to strains of bacteria that is resistant to virtually all antibiotics in use
• Some doctors may now prescribe multiple antibiotics, which greatly reduces the chances that the bacteria will survive
• MRSA (methicillin-resistant Staphylococcus aureus)– the ‘superbug’ – is a bacteria that has gained a particularly wide range of antibiotic resistance
• This bacterium has developed resistance to more and more stronger drugs – an example of the ‘evolutionary arms race’
• Medical researchers are struggling to find new and effective drugs, while the bacterial population continue to grow resistant
1. Before selection there is a variety in levels of resistance – this variation is cause by mutations that create genetic variation within the species
2. Directly after selection the least resistant individuals have been killed and the individuals that have some level of resistance remain.
3. The remaining population of resistant individuals reproduces and the next generation causes a much higher proportion of resistant individuals.