Topic 4: Evolution

Question 1

What came first, the chicken or the egg?

Answer 1

The egg, dummy. If you really want an explanation come see me after class.

Question 2

What were likely the first cells on Earth?

Answer 2

Prokaryotes living in the ocean that did not require oxygen, as the atmosphere likely contained no oxygen, but rather large amounts of carbon dioxide and nitrogen

Question 3

What likely resulted in an increase in oxygen in the atmosphere?

Answer 3

After the first prokaryotes, photosynthetic prokaryotes became prominent and produced oxygen, releasing it into the atmosphere, making it possible for some cells to use oxygen as part of their metabolism and thus becoming more complex

Question 4

What type of cell likely came first? Provide evidence

Answer 4

Prokaryotic cells are fundamentally simpler in their metabolism and structure than eukaryotic cells. They likely came first, as eukaryotic cells would not have been able to survive the early hostile conditions
Stromatolites are some of the oldest fossils, made up of bacteria (prokaryotes) and sediment which formed rocks

Question 5

What is the proposed theory on how the first eukaryotic cells were formed?

Answer 5

It is proposed that the first eukaryotic cells were formed when larger prokaryotic cells engulfed some smaller ones in a process similar to phagocytosis
In some cases, the smaller cell was able to respire aerobically or could photosynthesise, allowing the newly formed ‘super cell’ to carry out more functions than either cell could do on their own

Question 6

What do the terms symbiosis and endosymbiosis refer to?

Answer 6

The term symbiosis is used to describe the situation in which two organisms help one another and both benefit.
In the case of endosymbiosis one cell lives in another and both benefit

Question 7

It is thought that what organelles are descendants of ancient bacterial cells, and what evidence supports this?

Answer 7

Mitochondria and chloroplasts.
They have their own circular and unbound DNA with no introns, similar to prokaryotic DNA.
They have their own ribosomes that are similar in size and rRNA sequence to bacterial ribosomes.
They are able to self-replicate independently of the cells, similar to binary fission of prokaryotes.
They have two membranes, the outer is similar to the host cell’s outer membrane and was likely formed in the same way vesicles are formed during endocytosis, and the inner is similar to the outer membrane of bacteria.

Question 8

Evidence suggests that organic molecules were first formed when?

Answer 8

When the Earth’s condition was still hostile.
Some of these organic molecules were fatty acids that likely formed simple membranes in the form of primitive vesicles

Question 9

What molecules did the first cells likely use to store and transmit genetic information?

Answer 9

RNA, as it is a simpler molecule than DNA, so it is likely that it was formed first
It has also been discovered that some RNA can catalyse chemical reactions under certain circumstances, these are known as ribozymes

Question 10

What evidence suggests that all cells descend from an original ancestor (LUCA)?

Answer 10

All cells have:
A cell membrane
Nucleic acids (DNA and RNA)
Proteins - made of the same 20 amino acids and are synthesised in the same way
Water - made up of 50-80% water

Question 11

Define a population and community

Answer 11

A group of organisms of the same species living in the same area at the same time
A community consists of several populations

Question 12

What does the biological species concept define a species as?

Answer 12

A group of sexually reproducing organisms which can actually or potentially interbreed to produce fertile offspring

Question 13

What is a hybrid?

Answer 13

An offspring formed by animals of different species

Question 14

What are other criteria used to define a species?

Answer 14

Morphological similarity - similarities in shape and anatomy.
Biochemical similarity - similarities in the chemical composition of cells and tissues, including metabolic processes.
Common gene pool - similarities in genetic composition (nucleotide sequences) of the genome.

Question 15

What is the most accurate method of classifying species?

Answer 15

Comparing DNA and amino acid sequences

Question 16

What are the pre-zygotic barriers that isolate species?

Answer 16

Temporal isolation - Species may produce gametes at different times (time of day/season).
Behavioural isolation - Species may have different mating recognition behaviours that do not interest each other.
Mechanical isolation - Species may have anatomical differences in their genitals, so the transfer of gametes from male to female cannot take place.
Gamete isolation - Species may have sperm and ovum that have incompatible cell membrane receptors and so cannot form a zygote.
Ecological/habitat isolation - When species occupy different habitats.

Question 17

What are the post-zygotic barriers that isolate species?

Answer 17

Hybrid inviability - Offspring fail to reach maturity by dying before or just after birth.
Hybrid sterility - Hybrid offspring remain healthy and viable but are sterile

Question 18

What is reproductive isolation?

Answer 18

A mechanism that prevents gene flow between populations OF DIFFERENT SPECIES
Includes pre-zygotic and post-zygotic barriers

Question 19

What is a mutation? How can they occur?

Answer 19

A permanent change in the sequence of a DNA molecule and is the ultimate source of genetic variation in a species.
They can occur spontaneously or be induced

Question 20

What is an example of a spontaneous mutation, and what can induce mutations?

Answer 20

Copying errors when DNA is replicated.
Environmental factors such as high energy radiation (X-ray, UV), mutagenic chemicals, and viruses can induce mutations

Question 21

What happens when mutations occur in germ cells?

Answer 21

They can be passed on to the next generations, accumulating
This results in genetic variation in organisms

Question 22

What is the only source of genetic variation in asexually (Involves mitosis) reproducing organisms?

Answer 22

Mutation

Question 23

Where can genetic variation arise from in sexually reproducing organisms?

Answer 23

Mutations, crossing over and independent assortment in meiosis, and the random fertilisation of gametes

Question 24

What suggests that two species evolved recently?

Answer 24

There would not be enough time for new mutations to take place, so their DNA should be very similar

Question 25

What suggests that two species have been separated for a long time?

Answer 25

They will likely have more differences in their DNA as more mutations would have occured

Question 26

The fact that all cells use the same DNA system indicates that they have a common ancestry. What term refers to the comparison of DNA between species?

Answer 26

Comparative genomics

Question 27

Why are the amino acid sequences of proteins of different species analysed?

Answer 27

We can determine how closely related the species are. Species that are more closely related will have more similarities between the amino acid sequence of their proteins due to the accumulation of fewer mutations

Question 28

What is DNA-DNA hybridisation?

Answer 28

A method to gain evidence for comparative genomics Involves DNA from two species being hybridised (combined) to examine how closely they complement each other

Question 29

Explain the steps of DNA-DNA hybridisation (please)

Answer 29

Samples of DNA from different species are heated to separate the strands. The DNA strands are then mixed and cooled, allowing them to join in a complementary fashion and form hybrid DNA. The DNA is then reheated to see how readily the strands separate - poorly matched strands separate more easily (less energy) than well matched ones

Question 30

What is an advantage and disadvantage of DNA-DNA hybridisation?

Answer 30

Advantage: cheap and relatively simple Disadvantage: less precise than DNA sequencing

Question 31

How is DNA sequencing involved in comparative genomics?

Answer 31

DNA sequencing techniques are used to determine the base sequence of DNA from two different species, which can then be compared directly Closely related species will have more similar DNA sequences (less mutations)

Question 32

What is an advantage and disadvantage of DNA sequencing? (Comparative genomics)

Answer 32

Advantage: is a very precise method of comparison Disadvantage: time-consuming and expensive

Question 33

How and why are rRNA genes sequenced and analysed?

Answer 33

Similar method to DNA sequencing. These genes evolve very slowly, and so can be used to determine relationships between organisms separated long ago Also helps with determining relationships of prokaryotes

Question 34

What is a gene pool?

Answer 34

Refers to all the alleles of all the genes in the individuals of a population at any time

Question 35

What does the size of a gene pool indicate?

Answer 35

The level of genetic diversity in the population

Question 36

When does evolution occur? What can it be brought about by?

Answer 36

Occurs when there is a change in the frequency of alleles in the gene pool. Can be brought about by natural selection, sexual reproduction, and genetic drift These can change the gene pool, changing the frequency of genes.

Question 36

What is natural selection?

Answer 36

A process in which individuals in a population who are better suited to the environment tend to survive and reproduce, passing on their genes to future generations

Question 36

How can natural selection lead to evolution?

Answer 36

Causes only favourable genes to be expressed, leading to a change in the frequency of alleles, leading to evolution

Question 37

What is gene flow?

Answer 37

The movement of alleles between populations of the same species Changes allele frequencies, and if a new allele is introduced to a population, gene pool increases

Question 38

Compare the effects of increased and decreased gene flow

Answer 38

Increased gene flow between populations limits differences in their gene pools Decreased gene flow between populations leads to genetic isolation, where they can become distinctly different

Question 39

What is genetic drift?

Answer 39

The change in allele frequencies of a population and occurs by chance alone (NOT natural selection) Especially apparent in smaller populations Two main types: bottleneck and founder effects

Question 40

What is the bottleneck effect?

Answer 40

Type of genetic drift Caused by a catastrophe that kills majority of a population, often natural disaster Causes random genes to be extinguished, decreasing gene pool and changes allele frequencies and hence decreasing genetic diversity

Question 41

What is the founder effect?

Answer 41

Type of genetic drift that involves small groups of organisms separating from a larger population and founding small, new populations By chance, the allele frequencies in the colony will differ to those in the original population, and will likely have a smaller gene pool

Question 42

Why are species/populations with reduced genetic diversity at greater risk of extinction?

Answer 42

A small gene pool, and hence reduced genetic diversity, is more susceptible to a change in environmental conditions as few individuals would be able to withstand them, and are therefore more likely to become extinct

Question 43

What is speciation?

Answer 43

The process where to or more species evolve from one Occurs when gene flow has stopped between populations, causing genetic differences to accumulate until they are too genetically different to successfully reproduce (reproductively isolated)

Question 44

Describe allopatric speciation

Answer 44

Population is separated by a geographical barrier, resulting in no gene flow If environmental conditions are different, each population is affected by different selective pressures, and any mutations that occur are not shared, leading to them becoming genetically different, forming new species that cannot successfully interbreed

Question 45

What is convergent evolution?

Answer 45

When species are subject to similar selection pressures, causing them to evolve similar features (analogous) even though they are unrelated

Question 46

When does divergent evolution occur?

Answer 46

As species with a common ancestor accumulate are separated by a geographical barrier and accumulate genetic differences in their genomes, forming new species Leads to the development of homologous structures - similar (but different) features as they diverged from a common ancestor

Question 47

What is adaptive radiation?

Answer 47

A special case of divergent evolution in which there is a sudden (only over a few thousand years) emergence of new species from a common ancestor They occupy different ecological niches, experiencing different selective pressures

Question 48

What is succession?

Answer 48

The progression in an area over time from pioneer species to a climax community Can be categorised as primary or secondary

Question 49

Describe primary succession

Answer 49

New land is exposed via a volcano eruption, glacier/sea retreating, etc. Pioneer species such as lichen and moss begin to grow on the rock, breaking it up with their roots and dying and decomposing, forming soil and altering the environment. Once it is suitable for them, intermediate species will also begin to grow, further altering the environment and attracting smaller species, forming a secondary community. Eventually, the environment will be suitable for large species such as trees to begin growing, which will outcompete pioneer species and form a climax community.

Question 50

Describe secondary succession

Answer 50

An event, such as fire or flood, destroys an existing community, but leaves the soil intact. This allows for pioneer species, such as lichen and moss, to begin growing almost immediately, altering the environment so that it becomes more suitable for other organisms again. Intermediate species will begin growing after, further altering the environment and attracting small animals, forming a secondary community. Eventually, larger plants such as trees will grow and will slowly outcompete some pioneer species, forming a climax community. Occurs much faster than primary succession as it begins in a nutrient rich environment Seeds of plants may be from original community, or may be new seeds brought by the wind or animals, which can take advantage of the empty land and grow in this area, changing the mix of species.

Question 51

How can human activities lead to climate change? (example/s)

Answer 51

Burning fuels releases carbon dioxide into the atmosphere, which increases the Earth's atmospheric temperature due to the greenhouse effect. This will cause ice to melt, raising sea levels which affects weather patterns, shorelines, etc., leading to climate change

Question 52

How can human activities change the environment? (example/s)

Answer 52

Acid rain caused by fuel burning increases water acidity, killing organisms Deforestation and habitat destruction disrupt natural communities

Question 53

State the three ways to look at why biodiversity is important.

Answer 53

Human-centred All life is interconnected Moral obligation

Question 54

Describe the human-centred view on why biodiversity is important

Answer 54

We need resources from living things such as foods, medicines, and plant materials

Question 55

Describe the "interconnected" view on why biodiversity is important

Answer 55

It is thought that all life is interconnected, including humans, and that environments are self-regulatory, but altering biodiversity can have severe impacts. The Gaia theory stats all living things work together to maintain the planet

Question 56

Describe our moral obligation in regards to maintaining biodiversity

Answer 56

All life should be respected, and humans should not be allowed to decide life or death for other species; we all have equal right to live (We should also save animals bcs they're pretty)