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5 Natural selection and evolution Flashcards

1
Q

What does evolution mean?

A

It is a change in form of organisms over the course of time. Process by which species develop from earlier forms during the history of the Earth.

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2
Q

Is evolution a new idea?

A

No.

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3
Q

What was missing within the studies of evolution?

A

What was missing was an understanding of the mechanism by which evolution could have occurred.

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4
Q

Who proposed the mechanism for evolution that is now widely accepted today?

A

The English biologist, Charles Darwin.

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5
Q

What did he call this mechanism?

A

Natural selection.

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6
Q

What is natural selection?

A

Process where certain individuals
in a population survive because they are better adapted to their environment. They are more likely to pass on their genes to their offspring. The mechanism of evolution.

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7
Q

What did Charles Darwin do at the age of 22?

A

At the age of 22, Charles Darwin became the unpaid biologist aboard the survey ship HMS Beagle, which left England for a five-year voyage in 1831.

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8
Q

What did Darwin do during the voyage?

A

During the voyage, Darwin collected hundreds of specimens and made many observations about the variety of organisms and the ways in which they were adapted to their environments.

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9
Q

How did Darwin notice that life forms were continually changing - evolving?

A

Lyell was using the evidence of rock
layers to suggest that the surface of the Earth was constantly changing. The
layers of sediments in rocks represented different time periods. Darwin noticed that the fossils found in successive layers of rocks often changed slightly through the layers.

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10
Q

How did he arrive at his theory of natural selection?

A

From observations made during his voyage on HMS beagle and from deductions made from those observations.

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11
Q

What were Darwin’s observations?

A
  • Organisms generally produce more offspring than are needed to replace
    them – a single female salmon can release 5 million eggs per year; a giant
    puffball fungus produces 40 million spores.
  • Despite this over-reproduction, stable, established populations of organisms
    generally remain the same size – the seas are not overflowing with salmon,
    and we are not surrounded by lots of giant puffball fungi!
  • Members of the same species are not identical – they show variation.
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12
Q

What were two important deductions that he made from these observations?

A
  • From the first two observations he deduced that there is a ‘struggle for
    existence’. Many offspring are produced, yet the population stays the same size. There must be competition for resources and many individuals must die.
  • From the third observation he deduced that, if some offspring survive
    whilst others die, those organisms best suited to their environment would
    survive to reproduce. Those less suited will die. This gave rise to the phrase
    ‘survival of the fittest’.
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13
Q

What does ‘survival of the fittest’ mean?

A

The continued existence of organisms which are best adapted to their environment, with the extinction of others, as a concept in the Darwinian theory of evolution.

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14
Q

What is a key phrase that should be noticed from the second deduction?

A

The best-suited organisms survive to reproduce.

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15
Q

What does this phrase mean?

A

This means that those characteristics that give the organism a better chance of surviving will be passed on to the next generation.

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16
Q

What behaviour will be repeated in each generation?

A

Fewer of the individuals that are less suited to the environment survive to
reproduce. The next generation will have more of the type that is better
adapted and fewer of the less well adapted type.

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17
Q

What happened when Darwin published a book?

A

This book changed forever the way in which biologists think about how
species originate.

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18
Q

What did Darwin go on to suggest in this book?

A

Darwin went on to suggest that humans could have evolved from ape-like ancestors.

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19
Q

What does the theory of natural selection propose, in short?

A

The theory of natural selection proposes that some factor in the environment ‘selects’ which forms of a species will survive to reproduce.

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20
Q

What happens to forms that are not well-adapted?

A

Forms that are not well adapted will not survive.

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21
Q

What is a summary of how we think natural selection works?

A
  1. There is variation within the species.
  2. Changing conditions in the environment (called a selection pressure) favours one particular form of the species (which has a selective advantage).
  3. The frequency of the favoured form increases (it is selected for) under these
    conditions (survival of the fittest).
  4. The frequency of the less well adapted form decreases under these
    conditions (it is selected against).
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22
Q

What are characteristics of gene mutations?

A
  • Harmful.
  • Neutral.
  • Beneficial.
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23
Q

What happens if some gene mutations are harmful?

A

They are harmful, and the cells that carry them will not usually survive.

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24
Q

What happens if some gene mutations are neutral?

A

Some mutations are ‘neutral’ and if they arise in the gametes, may be passed on without affecting the survival of the offspring.

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25
Q

What happens if some gene mutations are beneficial?

A

Beneficial mutations are the ‘raw material’ that are ultimately the source of new inherited variation.

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26
Q

What are some examples of how natural selection might have worked?

A
  • The hoverfly.
  • The polar bear.
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27
Q

What is an image that shows a hoverfly and a wasp next to each other?

A
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28
Q

What is a brief description of wasps?

A

Wasps can defend themselves against predators using a sting. They also have a body with yellow and black stripes.

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29
Q

What are these stripes known as?

A

Warning colouration.

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30
Q

What does this ‘warning colouration’ do in terms of protection?

A

Predators such as birds soon learn that these colours mean that wasps have the sting, and they avoid attacking them.

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31
Q

What is a brief description of hoverflies?

A

Hoverflies do not have a sting. However, they have an appearance that is very like a wasp, with similar yellow and black stripes – they are ‘mimics’ of wasps.

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32
Q

How do predators treat hoverflies?

A

Predators treat hoverflies as if they do have a sting.

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33
Q

What is an advantage to the hoverfly?

A

Mimicking the wasp is an advantage to the hoverfly.

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34
Q

How could they have evolved this appearance?

A

We can explain how it could have happened by natural selection.

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35
Q

What was the selection pressure?

A

The selection pressure was predation by birds and other animals.

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36
Q

What would have been present in the ancestors of modern-day hoverflies?

A

Among the ancestors of present-day hoverflies there would have been variation in colours.

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37
Q

How did some hoverflies gain genes that produce stripes on their bodies?

A

This was as a result of mutations.

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38
Q

Which advantage did the stripes give to these hoverflies?

A

These insects were less likely to be eaten by predators than hoverflies without the stripes – they had a selective advantage.

39
Q

What is a selective advantage?

A

Any characteristic or trait that gives an organism or a genotype greater chances of surviving and reproducing than the available alternatives

40
Q

What happens because the hoverflies with stripes were more likely to survive being eaten?

A

They were more likely to reproduce, and would pass on the genes for stripes to their offspring.

41
Q

How did this process continue?

A

This process continued over many generations.

42
Q

What happened as a result of this process continuing over many generations?

A

Gradually more mutations and selection for ‘better’ stripes took place, until the hoverflies evolved the excellent warning colouration that they have today.

43
Q

What is important to note about the stripes and their appearance?

A

Note that perfect stripes didn’t have to appear straight away. Even a slight stripy appearance could give a small selective advantage over hoverflies without stripes. This would be enough to result in an increase in stripy hoverflies in the next generation.

44
Q

What is a brief description of a polar bear?

A

The polar bear lives in the Arctic, inhabiting landmasses and sea ice covering the waters within the Arctic Circle. It is a large predatory carnivore, mainly hunting seals.

45
Q

How does the polar bear hunt?

A

One way the bear hunts is to wait near holes in the ice where seals come up to breathe. It also silently approaches and attacks seals that are resting on the ice.

46
Q

What are some of the adaptations that polar bears have?

A
  • A thick layer of white fur, which reduces heat loss and acts as camouflage in the snow.
  • Wide, large paws. These help with walking in the snow, and are used for
    swimming.
  • Strong, muscular legs – a bear can swim continuously in the cold Arctic
    waters for days.
  • Nostrils that close when the bear is swimming under water.
  • Alarge body mass. Polar bears are the largest bears on Earth. An adult male
    averages 350 to 550 kilograms, and the record is over 1000 kilograms. This
    large size results in the animal having a small surface area to volume ratio,
    which reduces heat loss
  • A 10 centimetre thick layer of insulating fat under the skin.
  • A well developed sense of smell – used to detect the bear’s prey.
  • Bumps on the pads of the paws to provide grip on the ice.
  • Short, powerful claws, which also provide grip, and are needed for holding the heavy prey.
47
Q

What is the polar bear believed to have evolved from?

A

The polar bear is thought to have evolved from a smaller species, the brown bear, about 150,000 years ago.

48
Q

How did it evolve its adaptations for life in the Arctic?

A

Let’s consider just one of the adaptations, the thick white fur.

49
Q

What are the two main selection pressures in favour of thick white fur?

A
  • Insulation to reduce heat loss.
  • Camouflage.
50
Q

Why would a polar bear need insulation to reduce heat loss?

A

The polar bear often has to survive
temperatures of –30°C, and temperatures in the Arctic can fall as low as –70°C.

51
Q

Why would a polar bear need to camouflage?

A

White fur camouflages the animal against the snow so that it can approach its prey unseen and then attack it.

52
Q

What would there be among the brown bears that were the ancestors of polar bears?

A

There would have been variations in fur length and colour.

53
Q

What happened when some of these bears came to live in colder, more northerly habitats?

A

Those individuals with longer and
paler fur would have had a selective advantage over others with shorter, darker fur.

54
Q

What genes increased this advantage?

A

Any gene mutations that produced long, pale fur.

55
Q

What did bears with these genes get an advantage over?

A

Bears with these genes were less likely to die from the cold, or from lack of
food.

56
Q

As a result, which bears were more likely to reproduce and pass on their genes?

A

Well-adapted bears.

57
Q

What produced the adaptation that we see in the polar bear today?

A

Over many thousands of years more mutations and selection
for long, white fur produced the adaptation we see in the polar bear today.

58
Q

Can this process be generalised to all the adaptations of a polar bear?

A

The same process of natural selection is thought to have happened to bring about the other adaptations shown by the polar bear.

59
Q

What is a negative about natural selection?

A

Most animals and plants reproduce slowly, so it takes a long time for natural selection to have an observable effect.

60
Q

How can we overcome this disadvantage?

A

We can study organisms that reproduce quickly.

61
Q

What are some examples of organisms that reproduce quickly?

A
  • Bacteria.
  • Insects.
62
Q

What are antibiotics?

A

Antibiotics are chemicals that kill or reduce the growth of microorganisms.

63
Q

What is an image that shows the effectiveness of antibiotics?

A
64
Q

When are antibiotics used?

A

They are used in medicine mainly to treat bacterial infections, although a few antibiotics are effective against fungal pathogens.

65
Q

What are antibiotics not effective against?

A

Antibiotics do not work on viruses, so they are no use in treating any disease caused by a virus.

66
Q

What are natural antibiotics produced by?

A

Natural antibiotics are produced by bacteria and fungi.

67
Q

What do natural antibiotics do?

A

They give a microorganism an advantage over other microorganisms when competing for nutrients and other resources, since the antibiotic kills the competing organisms.

68
Q

What did Alexander Fleming do?

A

Alexander Fleming discovered the first antibiotic in 1929.

69
Q

What was it made of?

A

It is made by the mould Penicillium, and is called penicillin.

70
Q

What is penicillin?

A

It is an antibiotic obtained from the mould Penicillium.

71
Q

How does penicillin work?

A

Penicillin kills bacteria, and was
first used to treat bacterial infections in the 1940s.

72
Q

What has happened in terms of the use of antibiotics over the last 20 years?

A

The use of antibiotics has increased dramatically, particularly over the last 20 years.

73
Q

With this drastic increase, when do we expect to be prescribed antibiotics?

A

We now almost expect to be given an
antibiotic for even the most minor of ailments.

74
Q

What can be a disadvantage of being prescribed antibiotics for nearly everything?

A

This can be dangerous, as it
leads to the development of bacterial resistance to antibiotics, so that the
antibiotics are no longer effective in preventing bacterial infection

75
Q

How does resistance start?

A

Resistance starts when a random mutation gives a bacterium resistance to a particular antibiotic.

76
Q

What happens in a situation where the antibiotic is widely used?

A

In a situation where the antibiotic is widely used, the new resistant bacterium has an advantage over non-resistant bacteria of the same type.

77
Q

Why does the new resistance bacterium have an advantage?

A

The resistant strain of bacterium will survive and multiply in greater
numbers than the non-resistant types.

78
Q

What is a characteristic of bacteria reproduction?

A

Bacteria reproduce very quickly – the
generation time of a bacterium (the time it takes to divide into two daughter cells) can be as short as 20 minutes.

79
Q

What does this short generation time of a bacterium mean?

A

This means that there could be 72 generations in a single day, producing a population of millions of resistant bacteria.

80
Q

What happens to the resistant bacteria in terms of the antibiotic?

A

Resistant bacteria will not be killed by the antibiotic, meaning the antibiotic is
no longer effective in controlling the disease.

81
Q

Is bacterial resistance to antibiotic still a problem today?

A

Bacterial resistance to antibiotics was first noticed in hospitals in the 1950s,
and has grown to be a major problem today.

82
Q

Why is it such a problem?

A

The resistant bacteria have a
selective advantage over non-resistant bacteria – they are ‘fitter’.

83
Q

What is the result of this bacteria evolving?

A

In effect, the bacteria have evolved as a result of natural selection.

84
Q

What have doctors then done in terms of prescriptions concerning antibiotics?

A

Doctors are now more reluctant to prescribe antibiotics.

85
Q

How does prescribing them less help?

A

They know that by using them less, the bacteria with resistance have less of an advantage and will not become as widespread.

86
Q

Is it only pathogenic bacteria that can develop resistances against something?

A

No.

87
Q

What else can develop a resistance against something?

A

Insect pests can develop resistance to insecticides.

88
Q

What did the resistant insects develop?

A

The resistant insects had
developed a gene mutation that stopped them being killed by the insecticide.

89
Q

What was the problem with the new resistant insects?

A

The resistant insects had a selective
advantage over the non-resistant ones.

90
Q

What was the main aim of the resistant insects?

A

They survived to breed, so that with
each generation the numbers of resistant insects in the population increased.

91
Q

Is this a widespread problem?

A

Yes.

92
Q

What is an example of how this is a widespread problem?

A

There are now hundreds of examples of insect pests that have developed resistance to different insecticides.

93
Q
A
94
Q
A

Biology (22 decks)

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