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IGCSEs > Biology πŸƒ | Variation & Selection | 18 > Flashcards

Biology πŸƒ | Variation & Selection | 18 Flashcards

1
Q

Define variation

A

Differences between
individuals of the same species

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2
Q

Define phenotypic variation

A

The difference in features between individuals of the same species

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3
Q

What is continuous variation?

A

When there are very many small degrees of difference for a particular characteristic between individuals and they are arranged in order and can usually be measured on a scale

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4
Q

What is discontinuous variation?

A

When there are distinct differences for a characteristic

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5
Q

Discontinous variation is caused by __

A

genes only

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6
Q

Continuous variation is caused by __

A

both genes and environment

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7
Q

What are examples of discontinuous variation?

A

ABO blood groups, seed shape in peas and seed colour in peas

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8
Q

What is a mutation?

A

A random genetic change

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9
Q

What are the two ways phenotypic variation is caused?

A

By genetics or the environment

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10
Q

What is gene mutation?

A

A random change in the base sequence of DNA

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11
Q

Why do most mutations not have an effect on the phenotype?

A

The protein that a mutated gene
produces may work just as well as the protein from the non-mutated gene

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12
Q

How are new alleles formed?

A

By mutations that affect the phenotype

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13
Q

What can increase rate of mutation?

A
  • Ionising radiation: gamma rays, x rays, UV rays
  • Chemicals such as tar in tobacco
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14
Q

What are the different sources of genetic variation in offspring?

A

Mutation, meiosis, random mating and random fertilisation

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15
Q

Define adaptive feature

A

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

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16
Q

Define fitness

A

The probability of an organism surviving and reproducing in the environment in which it is found

17
Q

What are hydrophytes?

A

Plants adapted to live in extremely wet conditions

18
Q

What are some adaptations of hydrophytes?

A
  • Large air spaces in their leaves
  • Small roots
  • Stomata usually open all the time and mainly found on the upper epidermis of the leaf
19
Q

Why do hydrophytes have large air spaces?

A

To keep them close to the surface of the water where there is more light for photosynthesis

20
Q

Why do hydrophytes have small roots?

A

So they can also extract nutrients from the surrounding water through their tissues

21
Q

Why is the stomata of hydrophytes on the upper epidermis and always open?

A

So they can exchange gases much more easily with the air

(proximity)

22
Q

What are xerophytes?

A

Plants adapted to live in extremely dry conditions

23
Q

What are some adaptations of xerophytes?

A
  • Thick waxy cuticle
  • Sunken stomata
  • Leaf rolled with stomata inside and an inner surface covered in hairs
  • Small leaves
  • Extensive shallow roots
  • Thickened leaves or stems
24
Q

Why do xerophytes have a thich waxy cuticle?

A

The cuticle cuts down water loss in two ways: it acts as a barrier to evaporation and also the shiny surface reflects heat and so lowers temperature

25
Q

Why do xerophytes have a sunken stomata?

A

Stomata may be sunk in pits in the epidermis; moist air trapped here lengthens the diffusion pathway and reduces evaporation rate

26
Q

Why do xerophytes have a leaf rolled with stomata inside and an inner surface covered in hairs?

A

Traps moist air and prevents air movement across stomata which reduces transpiration

27
Q

Why do xerophytes have small leaves?

A

Many xerophytic plants have small, needle-shaped leaves which reduce the surface area and therefore the evaporating surface

28
Q

Why do xerophytes have extensive shallow roots?

A

They allow for the quick absorption of large quantities of water when it rains

29
Q

Why do xerophytes have thickened leaves or stems?

A

They contain cells which store water

30
Q

Define natural selection

A

The process through which species adapt to their environments over many generations

31
Q

How does natural selection work?

A
  1. Individuals in a species show a range of random variation
  2. When organisms reproduce, they produce more offspring than the environment is able to support
  3. This leads to competition for food and other resources
  4. Individuals with characteristics most suited to the environment have a higher chance of survival and more chances to reproduce
  5. Therefore the alleles resulting in these characteristics are passed to their offspring at a higher rate than those with characteristics less suited to survival
  6. This means that in the next generation, there will be a greater number of individuals with the better-adapted variations in characteristics
32
Q

Define adaptation

A

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

33
Q

Define selective breeding

A

To select individuals with desirable characteristics and breed them together over many generations

34
Q

How is selective breeding carried out?

A
  1. Selection by humans of individuals with desirable features
  2. Crossing these individuals to produce the next generation
  3. Selection of offspring showing the desirable features
35
Q

How can antibiotic resistant bacteria form?

A
  1. When the population is treated with an antibiotic, the resistant bacteria do not die
  2. This means they can continue to reproduce with less competition from non-resistant bacteria, which are now dead
  3. Therefore the genes for antibiotic resistance are passed on with a much greater frequency to the next generation
  4. Over time the whole population of bacteria becomes antibiotic-resistant because the bacteria are best suited to their environment
36
Q

For what characteristics do we selectively breed plants?

A
  • Disease resistance in food crops
  • Increased crop yield
  • Hardiness to weather conditions (e.g. drought tolerance)
  • Better tasting fruits
  • Large or unusual flowers
37
Q

For what characteristics do we selectively breed animals?

A
  • Cows, goats and sheep that produce lots of milk or meat
  • Chickens that lay large eggs
  • Domestic dogs that have a gentle nature
  • Sheep with good quality wool
  • Horses with fine features and a very fast pace
38
Q

What is the result of natural VS artificial selection?

A
  • Natural: Populations with features suited for survival
  • Artificial: Populations with features suited for humans
39
Q

Which is faster: natural or artificial selection

A

Natural selection takes a long while. Artificial selction takes little time.

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