Module 4: Section 3 - Classification and Evolution

Question 1

Classification is the act of arranging organisms into groups based on their similarities and differences. This makes it easier for scientists to identify them and to study them. Taxonomy is the study of classification. There are a few different classification systems in use, but they all involve placing organisms into groups in a taxonomic hierarchy. Please explain this hierarchy

Answer 1

1) there are eight levels of groups (called taxonomic groups) used in classification
2) similar organisms are first sorted into one of three very large groups called domains, e.g. animals, plants and fungi are in the Eukarya domain
3) similar organisms are then sorted into slightly smaller groups called kingdoms, e.g. all animals are in the animal kingdom
4) similar organisms from that kingdom are then grouped into phylum then class and so on
5) as you move down the hierarchy, there are more groups at each level but fewer organisms in each group
6) the hierarchy ends with species - the group that contain only one type of organism (e.g. humans, dogs)

Question 2

What’re the eight levels of taxonomic hierarchy?

Answer 2

Domain 
Kingdom 
Phylum 
Class 
Order
Family 
Genus
Species

Question 3

What are the four kingdoms, please give an example of each and list their main features

Answer 3

Kingdom: Prokaryotae, protoctista, fungi, plantae, animalia

Examples: bacteria, algae, moulds, mosses/ferns/flowering plants, insects/fish/reptiles

Features: prokaryotic, unicellular, no nucleus less than 5 nanometres

eukaryotic cells, usually live in water, single-celled or simple multicellular organisms

eukaryotic, chitin cell wall, saprotophic, single-celled or multicellular

eukaryotic, multicellular, cells walls made of cellulose, can photosynthesise, contain chlorophyll, autotrophic (produce own food)

eukaryotic, multicellular, no cell walls, heterotrophic (consume plants and animals)

Question 4

What nomenclature is used for classification, how does it work and why is it useful?

Answer 4

1) the nomenclature used for classification is called the binomial system - all organisms are given one internationally accepted scientific name in Latin that has two parts
2) the first part of the name is the genus name and has a capital letter. The second part is the species name and begins with a lower class letter. Names are always written in italics or they’re underlined if they’re handwritten
3) the binomial system helps to avoid the confusion of using common names. e.g. over 100 different plant species are called raspberries and one species of buttercup has over 90 different common names

Question 5

What is phylogeny?

Answer 5

Phylogeny is the study of evolutionary history of groups of organisms. Phylogeny tells us who’s related to whom and how closely related they are

Question 6

What does a phylogenetic tree show?

Answer 6

All organisms have evolved from shared common ancestors. This can be shown on a phlylogenetic tree.

Question 7

What is known as cladistics?

Answer 7

Classification systems now take into account phylogeny when arranging organisms into groups. Classifying organisms in this way is known as cladistics

Question 8

According to phylogenetics a species is what?

Answer 8

According to phylogenetics, a species is the smallest group that shares a common ancestor - in other words, the end of a branch on a phylogenetic tree

Question 9

Early classification systems only used observable features - what is the issue with this method?

Answer 9

Early classification systems only used observable features - this method has problems; scientists don’t always agree on the relative importance of different features and groups based solely on physical features may not show how related organisms are

Question 10

Classification systems are now based on observable features along with other evidence. What evidence is used?

Answer 10

1) molecular evidence - the similarities in proteins and DNA. More closely related organisms will have more similar molecules
2) embryological evidence - the similarities in the early stages of an organism’s development
3) anatomical evidence - the similarities in structure and function of different body parts
4) behavioural evidence - the similarites in behaviour and social organisation of organisms

Question 11

What does new technologies means for classification?

Answer 11

1) new technologies (e.g. new DNA techniques, better microscopes) can result in new discoveries being made and the relationships between organisms being clarified
2) scientists can share their new discoveries in meetings and scientific journals. How organisms are classified is continually revised to take account of any new findings that scientists discover

Question 12

The five kingdom classification has now been replaced with the three domain system, what is this?

Answer 12

1) in the older system the largest groups were the five kingdoms - all organisms were placed into one of these groups
2) in 1990, the three domain system was proposed. This new system has three domains - large superkingdoms that are above the kingdoms in the taxonomic hierarchy
3) in the three domain system, organisms that were in the kingdom Prokaryotae (which contain unicellular organisms without a nucleus) are separated into two domains - the Archaea and Bacteria
4) organisms with cells that contain a nucleus are placed in the domain Eukarya (this includes four of the five kingdoms)
5) the lower hierarchy stays the same - kingdom, phylum etc…

Question 13

The three domain system was proposed because of new evidence, mainly molecular. For example, the prokaryotae were reclassified into two domains because new evidence showed large differences between the Archaea and Bacteria - what did the new evidence show?

What did this evidence lead to scientists agreeing on?

Answer 13

1) molecular evidence - the enzyme RNA polymerase is different in Bacteria and Archaea. Archaea, but not bacteria have similar histones (proteins that bind to DNA) to Eukarya
2) cell membrane evidence - the bonds of the lipids in the cell membranes of Bacteria and Archaea are different. The development and composition of flagellae are also different

Most scientists now agree that Archaea and Bacteria evolved separately and that Archaea are more closely related to Eukarya than bacteria. The three domain system now reflects how different the Archaea and Bacteria are

Question 14

Variation is the differences that exist between individuals. Every individual organism is unique - even clones show some variation. Where can variation occur?

Answer 14

1) within species - variation within a species is called intraspecific variation. For example, individual European robins weigh between 16 g and 22 g and show some variation in many other characteristics including length, colour etc…
2) between species - the variation between different species is called interspecific variation

Question 15

Continuous variation is when the individuals in a population vary within a range - there are no distinct categories. Please give some examples of continuous variation

Answer 15

mass - e.g. humans can be any mass range

number of leaves - e.g. a tree can have any number of leaves within a range

width - e.g. the width of e-coli bacteria varies within a range

Question 16

Discontinuous variation is when there are two or more distinct categories - each individual falls into only one of these categories, there are no intermediates. Please give some examples of discontinuous variation

Answer 16

blood group - e.g. humans can be blood group A, B, AB or O

colour - e.g. courgettes are either yellow, dark green or light green

pigment production - e.g. some types of bacteria can produce a coloured pigment, some can’t

Question 17

Variation can be caused by genetic factors, environmental factors or a combination of both. What 6 genetic factors cause variation?

Answer 17

1) different species have different genes
2) individuals of the same species have the same genes, but different versions of them (called alleles)
3) the genes and alleles an organism has make up its genotype
4) the differences in genotype result in variation in phenotype - the characteristics displayed by an organism
5) examples of variation caused by only genetic factors include blood group in humans and antibiotic resistance in bacteria
6) you inherit your genes from your parents. This means variation caused by genetic factors is inherited

Question 18

Variation can be caused by genetic factors, environmental factors or a combination of both. What 3 environmental factors cause variation?

Answer 18

1) variation can also be caused by differences in the environment, e.g. climate, food, lifestyle
2) characteristics controlled by environmental factors can change over an organism’s life
3) examples of variation caused only by environmental factors include accents and whether people have pierced ears

Question 19

Variation can be caused by genetic factors, environmental factors or a combination of both. What combination of both environmental and genetic factors cause variation?

Answer 19

Genetic factors determine the characteristics an organism’s born with, but environmental factors can influence how some characters develop. for example:

1) height
2) flagellum - genes determine if a microorganism can grow a flagellum, but some will only start to grow them in certain environments, e.g. if metal ions are present

Question 20

How could you use the mean to look for variation between samples?

Answer 20

1) to investigate variation you usually take samples of a population
2) the mean is an average of the values collected in a sample. It can be used to tell if there is variation between samples, for example:

the mean height of a species of tree in woodland A = 26 m, in woodland B = 32 m. So the mean height varies

3) most samples will include values either side of the mean, so you end up with a bell-shaped graph - this is called a normal distribution. A normal distribution is symmetrical about the mean

Question 21

What does the standard deviation?

What does a large/small standard deviation tell you?

Answer 21

1) the standard deviation tells you how much the values in a single sample vary. It’s a measure if the spread of values about the mean
2) sometimes you’ll see the mean written as, e.g. 9 +_ 3. This means that the mean is 9 and the standard deviation is 3, so most of the values are spread between 6 and 12
3) a large standard deviation means the values in the sample vary a lot. A sample standard deviation tells you that most of the sample data is around the mean value, so varies little

Question 22

What are adaptations and why do they develop?

Answer 22

1) being adapted to an environment means an organism has features that increase its chances of survival and reproduction, and also the changes of its offspring reproducing successfully
2) these features are called adaptations and can be behavioural, physiological and anatomical
3) adaptations develop because of evolution by natural selection
4) in each generation, the best-adapted individuals are more likely to survive and reproduce - passing their adaptations on to their offspring. Individuals that are less well adapted are more likely to die before reproducing

Question 23

Adaptations can be behavioural, physiological and anatomical. Please give two examples of behavioural adaptations

Answer 23

Ways an organism acts that increase its chance of survival. For example:

• possums sometimes ‘play dead’ - if they’re being threatened by a predator they play dead to escape attack. This increases their chance of survival
• scorpions dance before mating - this makes sure they attract a mate of the same species, increasing the likelihood of successful mating

Question 24

Adaptations can be behavioural, physiological and anatomical. Please give two examples of physiological adaptations

Answer 24

Processes inside an organism’s body that increase its chance of survival. For example:

• brown bears hibernate - they lower their rate of metabolism over winter. This conserves energy, so they don’t need to look for food in months when its scarce - increasing its chance of survival
• some bacteria produce antibiotics - these kill other species of bacteria in the area, meaning less competition

Question 25

Adaptations can be behavioural, physiological and anatomical. Please give two examples of anatomical adaptations

Answer 25

Structural features of an organism’s body that increase its chance of survival. For example:

• otters have a streamlined shape - making it easier to glide through the water. Easier to catch prey and escape predators so easier to survive
• whales have a thick layer of blubber to stay cosy. increases chances of survival

Question 26

Organisms from different taxonomic groups may have similar features even though they’re not closely related - why?

Answer 26

this is usually because the organisms have evolved in similar environments and to fill similar ecological niches

Question 27

There are three different groups of mammals. Most mammals are placental mammals, while some are marsupials

Marsupials are found mainly in Aus and the Americas. They diverged from the placental mammals many millions of years ago and have been evolving separately ever since - how have they evolved separately?

Answer 27

Marsupial mammals (e.g. kangaroos):

• have a short gestation period (pregnancy)
• don’t develop a full placenta
• are born early in their development and climb into their mother’s pouch. Here they become attached to a teat and receive milk while they continue to develop

Placental mammals (e.g. humans):

• have a longer gestation period
• develop a placenta during pregnancy, which allows the exchange of nutrients and waste products between the foetus and the mother
• are born more fully developed

Question 28

Marsupial and placental moles look alike but aren’t closely related

1) marsupial moles and placental moles aren’t closely related - they evolved separately on different continents
2) they do share similar anatomical features though. How have they both evolved to live in similar environments? What are their adaptions for this lifestyle?

Answer 28

Both types of mole live in tunnels in the ground. They burrow to reach their food supply. Their adaptions to this lifestyle include:

• small or non-existent eyes because they don’t need to be able to see underground
• no external ears, to keep a streamlined head for burrowing
• scoop-shaped and powerful front paws, which are good for digging
• claws that are specialised for digging
• a tube shaped body and cone shaped head, which makes it easier to push through sand or soil

Question 29

What four observations did Darwin base his theory of evolution by natural selection on?

Answer 29

1) organisms produce more offspring than survive
2) there’s variation in the characteristics of members of the same species
3) some of these characteristics can be passed on from one generation to the next
4) individuals that are best adapted to their environment are more likely to survive

Question 30

Darwin wrote his theory of natural selection to explain his observations - please outline this theory

Answer 30

1) individuals within a population show variation in their phenotypes
2) selection pressures create a struggle for survival
3) individual with better adaptations are more likely to survive and have reproductive success - they reproduce and pass on their advantageous adaptions to their offspring
4) over time, the proportion of the population possessing the advantageous adaptations increases
5) over generations this leads to evolution as the favourable adaptations become more common in the population

Question 31

We now know that genes determine what? What did individuals show variations in and what happens when an organism with advantageous characteristics reproduces?

Answer 31

1) we now know that genes determine many of an organism’s characteristics and that individuals show variations in their phenotypes partly as a result of genetic variation, i.e. the different alleles they have
2) when an organism with advantageous characteristics reproduces, the alleles that determine those characteristics may be passed on to its offspring

Question 32

Alfred Russel Wallace, a scientist working at the same time as Darwin, played an important part in developing the theory of evolution of natural selection - what did he do?

Answer 32

1) he independently came up with the idea of natural selection and wrote to Darwin about it
2) he and Darwin published their papers on evolution together and acknowledged each other’s work - although they didn’t always agree on the mechanisms involved in natural selection
3) Wallace’s observations provided lots of evidence to support the theory of evolution by natural selection. E.g., he realised that warning colours are used by some species (e.g. butterflies) to deter predators from eating them and that this was an example of an advantageous adaptation that had been evolved by natural selection

Question 33

Why is Darwin remembered better than Wallace?

Answer 33

1) unfortunately for Wallace, it wasn’t until Darwin published his book that other scientists began to pay attention to the theory
2) in this book Darwin gave lots of evidence to support his theory and expanded on it. For example, he wrote about all the species that he had observed during his trip to South America and the Galapagos Islands in the 1830s
3) the book is partly why Darwin is usually better remembered than Wallace - even though Wallace helped to come up with the theory

Question 34

What fossil record evidence is there to support evolution? Please use the example of a horse

Answer 34

fossils are the remains of organisms preserved in rocks. By arranging fossils in chronological order, gradual changes in organisms can be observed that provide evidence of evolution

For example - the fossil record of the horse shows a gradual change in characteristics, including increasing size

Question 35

What DNA evidence is there to support evolution?

Answer 35

1) the theory of evolution suggests that all organisms have evolved from shared common ancestors
2) closely related species diverged more recently
3) evolution is caused by gradual changes in the base sequence of an organisms’ DNA
4) organisms that diverged away from each other more recently, should have more similar DNA, as less time passed for changes in the DNA sequence occur. This is exactly what scientists have found

Question 36

What molecular evidence is there to support evolution?

Answer 36

In addition to DNA, the similarities in other molecules provide evidence. Scientists compare the sequence of amino acids in proteins can compare antibodies. Organisms that diverged away from each other more recently have more similar molecules, as less time has passed for changes in proteins and other molecules to occur

Question 37

Pesticides are chemicals that kill pests. Scientists have observed the evolution of pesticide resistance in many species of insect. For example, some populations of mosquito have evolved resistance to the pesticide DDT. Please explain the evolution of pesticide resistance by natural selection?

Answer 37

1) there is variation in a population of insects. Genetic mutations create alleles that make some insects naturally resistant to a pesticide
2) if the population of insects is exposed to that pesticide only the individuals with resistance will survive to reproduce
3) the alleles which cause the pesticide resistance will be passed on to the next generation, and so the population will evolve - more individuals will carry the allele than in the previous generation

Question 38

What three implications does the evolution of pesticide resistance have for humans?

Answer 38

1) crop infestations with pesticide-resistant insects are harder to control - some insects are resistant to lots of different pesticides. Farmers might end up killing beneficial insects
2) if disease-carrying insects become pesticide resistant, the spread of diseases could increase
3) a population of insects could evolve resistance to all pesticides in use. To prevent this new pesticides need to be produced. This takes time and costs money

Question 39

What two implications does the evolution of drug resistance have for humans?

Answer 39

1) infections caused by drug-resistant microorganisms are harder to treat. It can take a while for doctors to figure it out and which drugs will get rid of the infection. By this time, the patient could have died
2) there could come a point where a pathogen has become resistant to all the drugs we currently use against it. To prevent this, new drugs need to be developed. This takes time and costs a lot of money

Question 40

Take a break

Answer 40

Relax

:)