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Biology IGCSE > Chapter #17 - Variation And Selection > Flashcards

Chapter #17 - Variation And Selection Flashcards

1
Q

Variation

A

differences between individuals of the same species.

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2
Q

Discontinuous Variation

A

variation with distinct categories of phenotypes (no intermediaries).

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3
Q

What is an example of discontinuous variation?

A

Human blood groups are an example of discontinuous variation. Only four blood groups are possible - A, B, AB or O. You cannot have a blood group in between these four groups.

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4
Q

How is discontinuous variation graphed?

A

We present this type of data using a bar chart.
Bars do not touch, because categories are distinct and not related.

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5
Q

Continuous Variation

A

a continuous range of phenotypes between 2 extremes.

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6
Q

What are examples of continuous variation?

A
  • weight
  • height
  • arm span
  • etc.
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7
Q

How is continuous data graphed?

A
  • Line graphs – bell shaped curve
  • Or histogram (frequency diagram). The x axis goes up steadily. The bars touch each other because it is continuous
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8
Q

What are the causes of variation?

A
  • genetic - different genes
  • enviornment
  • It can also be caused by a mixture of these 2 (weight, height)
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9
Q

Mutation

A

a random change in a gene (change in the base sequence of DNA) which can produce new alleles.

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10
Q

What are the causes of genetic variation?

A
  • mutation
  • meiosis
  • random mating and random fertilization
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11
Q

What are some factors that make mutation more likely?

A
  • ionising radiation (X-rays, gamma radiation, beta radiation, alpha radiation) = can damage bases in DNA
  • mutagens - chemicals that cause radiation like heavy metals = interfere with the way DNA is copied.
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12
Q

How can meiosis cause genetic variation?

A

during meiosis pairs of homologous chromosomes exchange genes. This causes genetic variation.

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13
Q

How can random mating and random fertilization cause genetic variation?

A

The random combination of genes through reproduction (it is “random” which sperm makes it to the egg and which egg is developed that month)leads to many possible combinations of DNA.

The chance of 2 offspring having identical DNA is so small it is considered practically impossible.

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14
Q

Adaptive feature

A

An inherited feature that helps an organism survive and reproduce in its environment.

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15
Q

Do all organisms have adaptive features?

A

Yes, some are obvious – eg. All fish have gills to allow them to get oxygen under water.

Some may be less:2 species may have different enzymes intheirdigestive systems, adapted to suit their different diets.

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16
Q

Why are all individules not the same within a population?

A

Because of variation

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17
Q

How does being well-adapted to its environment benefit an organism?

A

An organism that is well adapted to its environment is more likely to survive and reproduce.

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18
Q

How do alleles with better adaptive features affect an individual’s survival and reproduction?

A
  • Individuals whose alleles give them slightly better adaptive features are more likely to survive than others in the population.
  • Therefore they are more likely to reproduce, and pass on those alleles.
  • Over time, more and more of the population may end up having thosealleles.
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19
Q

Natural selection

A

a process by which individuals with advantageous features are more likely to survive, reproduce and pass on their alleles to the next generation.

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20
Q

What are the steps of natural selection?

A
  • Variation
  • Overproduction
  • Best-adapted individuals more likely to survive and reproduce
  • Alleles that give useful adaptations more likely to be passed on
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21
Q

Describe each step of natural selection in greater detail.

A
  1. Variation - There is variation within a population of organisms. Some variation is genetic. Some variation affects the adaptive features of an organism.
  2. Overproduction - Within a wild population, many more offspring are produced than will survive and reach adulthood.
  3. Best-adapted individuals more likely to survive and reproduce - In wild populations, organisms “struggle to survive” for various reasons – eg.competition for food/resources, predation.
    Those with advantageous adaptive features are more likely to survive.
  4. Alleles that give useful adaptations more likely to be passed on - The animals that survive are the ones that reproduce. Therefore their adaptive features are “selected for” and will appear in the future generations.
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22
Q

What can natural selection sometimes cause in a population?

A

sometimes natural selection causes a change in a population.

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23
Q

Why can natural selection sometimes cause changes in the population?

A
  • Random mutation causes a new allele to arise, by chance.
    If this new allele gives the organism a better adaptive feature, it will be selected for.
  • The environment could change, so that the features that were once helpful for survival are no longer useful.
    e.g. climate change
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24
Q

Xerophytes

A

plants with adaptive features that help them to survive in an environment where water is scarce.

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25
Q

How do plants lose water?

A

Plants lose water as water vapour through stomata.

26
Q

What happens when the stomata are closed

A

When the stomata are closed, transpiration slows or practically stops.

27
Q

Why is it a problem if the stomata are closed?

A

If the stomata are closed, CO2 cannot diffuse into the leaf, and the plant cannot photosynthesize.

28
Q

When do stomata typically close?

A

Stomata close when it is hot or dry, as well as during the night when photosynthesis cannot take place anyway.

29
Q

What happens to the guard cells when a plant is short of water?

A

When a plant is short of water, the guard cells become flaccid, closing the stomata

30
Q

What happens to the guard cells when a plant has plenty of water?

A

When a plant has plenty of water, the guard cells become turgid. The thick inner cell wall prevents stretching, so as the guard cells swell, they curve away from each other, opening the stomata.

31
Q

What are some of the adaptive features of xerophytes?

A
  • closing stomata
  • waxy cuticle
  • Hairy leaves
  • sunken stomata on underside of leaves
  • reducing SA of the leaves
  • deep or spreading roots
32
Q

How does having waxy cuticles help xerophytes survivr?

A
  • makes the leaf water proof
  • prevents water loss
33
Q

How does having hairy leaves help xerophytes survive?

A
  • It layer of moist air near the leaf.
  • This reduces the diffusion gradient, so that lesswater vapor diffuses out of the leaf.
34
Q

How does having sunken stomato on the underside of leaves help xerophytes survive?

A
  • In most leaves there are more stomata on underside than upper. The lower surface is usually cooler than the upper one, so less water evaporates.
  • When water vapour diffuses out, it is collected in the pits, reducing the diffusion gradient = less water diffuses out.
35
Q

How does reducing the SA opf leaves help xerophytes survive?

A
  • Smaller the SA = less water vapour will diffuse.
  • Instead of using their leaves for photosynthesis, they havechloroplastsin the outer cells of their thick stem.
  • Cells deep inside stem = adapted to store water.
36
Q

How does having deep or spreading roots help xerophytes survive?

A
  • Desert plants may seek water from very deep down in the soil or across a wide area.
  • So, they usually have either deep or roots that spread a long way sideways
  • Some have both types
37
Q

Hydrophytes

A

plants that have adaptive features that help it survive in water.

38
Q

What are the adaptive features of hydrophytes?

A
  • Roots float freely
  • Stems and leaf stalks have hollow spaces
  • stomata on leaf upper surface as well as lower
  • No need to close stomata
39
Q

How does having stems and leaf stalks with hollow spaces help hydrophytes survive?

A
  • The stems and leaf stalks are filled with air
  • This helps them float on the surface
  • And absorb light easier for photosynthesis
40
Q

Why do hydrophytes have on the leaf’s upper surface more than the lower one?

A
  • because upper = in contact with the air (CO2 for photosynthesis).
  • No need for stomata to beunderneath in order to conserve water – the plant does not need to conserve water.
41
Q

Why do hydrphytes not need to close stomata?

A

it has more water that it can possibly need

42
Q

What is a specific type of hydrphyte?

A

A cabomba - adapted to live completely under water.

43
Q

What are the adaptive features of a cambomba and why does it have these>

A
  • Thin featheryleaves, that spread out easily in the water to get plenty of sunlight and help theplant float.
  • Thin leaves = allow strong water currents to pass by without damaging the leaves.
  • Some have roots attached to the soil, but they do not need to go deep.
44
Q

What can happen over a long period of time in terms of mutations?

A

Over a long period of time, many mutations can occur.

45
Q

What happens to the DNA base sequence over time due to mutations?

A

The DNA base sequence can become more and more different from the ancestor’s DNA.

46
Q

What occurs when the DNA becomes so different that the new population can no longer breed with the original population?

A

When the DNA becomes so different, the new population cannot breed with the one it originated from, leading to the formation of a new species.

47
Q

How can biologists classify organisms (in steps) ?

A
  1. Base sequence of one species is determined (DNA extraction).
  2. The same is done for another species.
  3. The two base sequences are compared.
    * If identical = same species.
    * If only a few differences = these 2 species only stopped reproducing with each other recently = more closely related to one another.
    * If a lot of differences = a lot of mutations, indicating a long time period = more distantly related.
48
Q

Adaptation

A

the process, resulting from natural selection, by which populations become more suited to their environment over many generations.

49
Q

Drug

A

any substance taken into the body that modifies or affects chemical reactions in the body.

50
Q

What is an example of a medicinal drug?

A

antibiotics

51
Q

Antibiotic

A

A substance which is taken into the body that kills bacteria, but does not affect human cells or viruses

52
Q

Why are antibiotics important?

A

Antibiotics are important because they help to cure bacterial infections that could be very serious or even fatal.

53
Q

What has happened to many populations of bacteria over the last few decades?

A

Over the last few decades, many populations of bacteria have become resistant to antibiotics.

54
Q

Describe the process by which bacteria become resistant to bacteria

A
  1. In a population of bactera, not aeveryone is alike. By chance, one may have an allele that makes it resistant to antibiotic.
  2. Antibiotic is added, which kills the bacteria which are not resistant
  3. The resistant one multiplies and forms a population of resistant bacteria just like itself
55
Q

What is an example of an atibiotic we should know about?

A

Penicillin

56
Q

How does penecillin work?

A

Penicillin stops bacteria from forming cell walls, so they burst open.

57
Q

Describe how bacteria becomes resistant to penecillin.

A
  1. It is likely at least 1 or 2 individuals withan allele that makes themresistant to penicillin.
  2. Those individuals have a large selective advantage.
  3. They will reproduce, where other individuals cannot.
  4. Their descendants may form a population of resistant bacteria
58
Q

Selective breeding

A

choosing particular organisms with desired characteristics to breed together, and continuing this over many generations. Also known as artificial selection.

59
Q

Describe how selective brfeeding is implimented in terms of cows.

A
60
Q

Complete the following table:

A
61
Q
A

Biology IGCSE (20 decks)

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