B13-Variation + Evolution

Question 1

Genetic variation

Answer 1

Caused by differences in genotype

Question 2

Genotype

Answer 2

All the genes and alleles an organism has

Question 3

Phenotypes

Answer 3

The characteristics organisms display

Question 4

Variation

Answer 4

Difference between organisms of the same species

Question 5

What affects an organism’s phenotype

Answer 5

Genotype
Interactions with its environment

Question 6

How can organisms’ interactions with their environment influence phenotype

Answer 6

A plant grown on a nice sunny windowsill could grow luscious and green.
The same plant grown in darkness would grow tall and spindly and its leaves would turn yellow

Question 7

Mutation

Answer 7

A rare, random change in an organism’s DNA that can be inherited. Mutations occur continuously and mean the gene is altered. Which produces a genetic variant(different form of the gene).
As the gene codes for the sequence of amino acids that make up a protein, gene mutations sometimes lead to changes in the protein that it codes for.

Question 8

Impact of genetic variants on protein genes code for

Answer 8

Most genetic variants have very little or no effect on the protein the gene codes for. Some will change it to such a small extent that its function is unaffected. This means most mutations have no effect on an organism’s phenotype.

Question 9

Examples of variants with a small influence on the organism’s phenotype

Answer 9

Some characteristics e.g. eye colour, are controlled by more than one gene. A mutation in one of the genes may change the eye colour a bit, but the difference might not be huge.

Question 10

Examples of variants with a dramatic effect so they determine phenotype

Answer 10

The genetic disorder, cystic fibrosis, is caused by a mutation that has a huge effect on phenotype. The gene codes for a protein that controls the movement of salt and water into and out of cells, however the protein produced by the mutated gene doesn’t work properly. This leads to excess mucus production in the lungs and digestive system, making it difficult to breathe and digest food.

Question 11

Positive benefits of mutations

Answer 11

If the environment changes, and the new phenotype makes an individual more suited to the new environment, it can become common throughout the species quickly by natural selection.

Question 12

Theory of evolution

Answer 12

All of today’s species have evolved from simple life forms that first started to develop over three billion years ago.

Question 13

Charles Darwin theory of evolution by natural selection

Answer 13

1) Darwin knew organisms in a species show wide variation in their characteristics(phenotypic variation). He also knew that organisms have to compete for limited resources in an ecosystem.
2) He concluded the organisms with the most suitable characteristics for the environment would be successful competitors and would be more likely to survive. This idea is called the ‘survival of the fittest.’
3) The successful organisms that survive are more likely to reproduce and pass on the genes for the characteristics that made them successful to their offspring.
4) The organisms that are less well adapted would be less likely to survive and reproduce, so are less likely to pass on their genes to the next generation.

Question 14

Disadvantages of Darwin’s evolution theory

Answer 14

Because the relevant scientific knowledge wasn’t available at the time, he couldn’t give a good explanation for why new characteristics appeared or exactly how individual organisms passed on beneficial adaptations to their offspring

Question 15

Supporting evidence for Darwin’s theory of evolution by natural selection

Answer 15

The discovery of genetics provided an explanation that organisms could pass on beneficial characteristics via their genes and it’s genetic variants that give rise to phenotypes suited to the environment.
Looking at fossils of different ages(the fossil record) showed how changes in organisms developed slowly over time and the discovery of how bacteria can evolve to become resistant to antibiotics further supports evolution by natural selection.

Question 16

Speciation

Answer 16

When the phenotype of organisms changes so much over a long period of time because of natural selection, that a completely new species is formed. It occurs when populations of the same species change enough to hecome reproductively isolated.

Question 17

Reproductively isolated species

Answer 17

Can’t interbreed to produce fertile offspring

Question 18

Extinct

Answer 18

Species that don’t exist any more

Question 19

Why species become extinct

Answer 19

1) The environment changes too quickly(e.g. destruction of habitat)
2) A new predator kills them all.
3) A new disease kills them all.
4) They can’t compete with another species for food.
5) A catastrophic event(e.g. a volcanic eruption) occurs that kills them all

Question 20

Selective breeding

Answer 20

When humans artificially select the plants or animals that are going to breed so the genes for particular characteristics remain in the population. Organisms are selectively bred to develop useful features.

Question 21

Examples of organisms that are selectively bred

Answer 21

Animals that produce more meat or milk
Crops with disease resistance
Dogs with a good, gentle temperament.
Decorative plants with big or unusual flowers

Question 22

Process of selective breeding

Answer 22

1) From your existing stock, select the ones which have the characteristics you’re after.
2) Breed them with each other.
3) Select the best of the offspring, and breed them together.
4) Continue this process over several generations, and the desirable trait gets stronger and stronger. Eventually, all the offspring will have the characteristic.

Question 23

Disadvantages of selective breeding

Answer 23

1) Reduces gene pool(number of different alleles in a population) because the farmer keeps inbreeding(breeding from the best, closely related animals/plants).
2) Inbreeding can cause health problems, because there’s more chance of the organisms inheriting harmful genetic defects when the gene pool is limited.
4) Problems if a new disease appears, because there’s not much variation in the population so if one of them is killed by a new disease, the others are also likely to succumb to it.

Question 24

Examples of animals vulnerable to selective breeding

Answer 24

Some dog breeds are particularly susceptible to certain defects because of inbreeding e.g. pugs often have breathing problems.

Question 25

Genetic engineering

Answer 25

Transfer of a gene responsible for a desirable characteristic from one organism’s genome into another organism, so it also has the desired characteristic

Question 26

Stages of genetic engineering

Answer 26

1) A useful gene is isolated(cut) from one organism’s genome using enzymes and is inserted into a vector.
2) The vector is usually a virus or a bacterial plasmid(a fancy piece of circular DNA found in bacterial cells), depending on the type of organism the gene is being transferred to.
3) When the vector’s introduced to the target organism, the useful gene is inserted into its cells.
4) The transfer of the gene is carried out when the organism receiving the gene is at an early stage of development(e.g. egg or embryo). This means the organism develops with the characteristics coded for by the gene.

Question 27

Uses of genetic engineering

Answer 27

1) Bacteria has been genetically modified to produce human insulin that can be used to treat diabetes.
2) Genetically modified crops have had their genes modified e.g. to improve the size and quality of their fruit, or make them resistant to disease, insects and herbicides(chemicals used to kill weeds).
3) Sheep have been genetically engineered to produce substances like drugs, in their milk that can be used to treat human diseases.

Question 28

Disadvantages of genetic engineering

Answer 28

We can’t be sure what effects GM crops will have on populations of wild flowers and insects.
Some people are concerned that we don’t know what effects they may have on human health.
Some worry it may lead to people wanting to manipulate the genes of humans to produce designer babies.

Question 29

Disadvantages of genetically modified crops

Answer 29

Not everyone is convinced GM crops are safe and people are concerned we might not fully understand the effects of eating them on human health.
Growing GM crops will affect the number of wild flowers living in and around crops - reducing farmland biodiversity.
Transplanted genes might get out into the natural environment

Question 30

Advantages of genetically modified crops

Answer 30

1) The characteristics chosen for GM crops can increase the yield, making more food.
2) Can be engineered to contain the missing nutrients in people’s diets in developing nations.
3) GM crops are already being grown in some places, often without any problems.

Question 31

Fossils

Answer 31

Remains of organisms from many thousands of years ago, found in rocks to provide evidence organisms lived ages ago.

Question 32

How fossils formed

Answer 32

1) From gradual replacement by minerals
2) From casts and imprssions
3) From preservation in places where no decay occurs.

Question 33

Fossils forming(gradual replacement by minerals)

Answer 33

1) Things like teeth, shells and bones can last a long time when buried.
2) These are replaced by minerals eventually as they decay, forming a rock-like substance shaped like the original hard part.
3) The surrounding sediments also turn to rock, but the fossil stays distinct inside the rock and eventually someone digs it up.

Question 34

How do fossils form(from casts and impressions)

Answer 34

1) Fossils are sometimes formed when an organism is buried in a soft material like clay. The clay later hardens around it and the organism decays, leaving a cast of itself. An animal’s burrow or a plant’s roots(rootlet traces) can be preserved as casts.
2) Things like footprints are pressed into these materials when soft, leaving an impression when it hardens.

Question 35

How do fossils form(from preservation in places where no decay happens)

Answer 35

1) In amber(a clear yellow stone made from fossilised resin) and tar pits, there’s no oxygen or moisture so decay microbes can’t survive.
2) In glaciers, it’s too cold for the decay microbes to work.
3) Peat bogs are too acidic for decay microbes.

Question 36

Why can’t hypotheses suggesting how life first came into being be supported or disproved?

Answer 36

There’s a lack of good, valid evidence:
1) Many early forms of life were soft-bodied, and soft tissue tends to decay away completely - so the fossil record is incomplete.
2) Fossils that did form millions of years ago may have been destroyed by geological activity.

Question 37

How bacteria evolves and become antibiotic-resistant

Answer 37

1) Like all organisms, bacteria sometimes develop random mutations(changes in their DNA). This can lead to changes in the bacteria’s characteristics e.g. being less affected by a particular antibiotic. This can lead to antibiotic-resistant strains forming as the gene for antibiotic resistance becomes more common in the population.
2) Because bacteria are so rapid at reproducing, they can evolve quite quickly, live for longer and reproduces many more times. This increases the population size of the antibiotic-resistant strain.

Question 38

Disadvantages of antibiotic resistant strains

Answer 38

A problem for people who become infected with these bacteria, because they aren’t immune to the new strain and there is no effective treatment, so the infection easily spreads between people. Superbugs that are resistant to most known antibiotics are becoming more common.

Question 39

Examples of common superbugs

Answer 39

MRSA is a relatively common superbug, often affecting people in hospitals and it can be fatal if it enters their bloodstream

Question 40

Causes of antibiptic resistance

Answer 40

The overuse of antibiotics - the more often they’re used, the bigger the problem of antibiotic resistance becomes, so it’s important doctors only prescribe antibiotics when they really need to, because antibiotics create a situation where naturally resistantbacteria have an advantage and increase in numbers.
In farming, antibiotics can be given to animals to prevent them being ill and make them grow faster, leading to the development of antibiotic-resistant bacteria in the animals which can then spread to humans e.g. during meat preparation and consumption.

Question 41

How to deal with antibiotic resistance

Answer 41

1)Take the full course of antibiotics, ensures all the bacteria are destroyed, meaning there are none left to mutate and develop into antibiotic-resistant strains.
2) Other drug companies have tried to work on developing new antibiotics that are effective against the resistant strains, but the rate of development is slow and this is a costly process.

Question 42

Linnean system

Answer 42

In the 1700s by Carl Linnaeus, which groups living things according to their characteristics and the structures that make them up. Living things are first divided into kingdoms(e.g. The plant kingdom) but these are divided into smaller and smaller groups

Question 43

Small groups in Linnaean system

Answer 43

1) Phylum
2) Class
3) Order
4) Family
5) Genus
6) Species

Question 44

Three-domain system

Answer 44

In 1990 Carl Woese proposed this system, finding out species thought to be closely related in traditional classification systems aren’t as closely related as first thought. In this system, organisms are first of all splits into three large groups called domains, which are subdivided into smaller groups(kingdom, phylum, class, order, family, genus, species)

Question 45

Three domain system(domains)

Answer 45

1) Archaea- Organisms in this domain are primitive bacteria, found in extreme places like hot springs and salt lakes.
2) Bacteria - This domain contains true bacteria like E.Coli and Staphylococcus, which look similar to Archaea, but have lots of biochemical differences between them.
3) Eukaryota - Includes broad range of organisms including fungi, plants, animals and protists

Question 46

Who developed the binomial naming system?

Answer 46

Carl Linnaeus

Question 47

Classification

Answer 47

Older classification systems grouped organisms depending on their characteristics and structures

Question 48

What do modern classification systems group living organisms based on?

Answer 48

DNA analysis

Question 49

How does the binomial system work?

Answer 49

1) Every organism is given its own two-part Latin name.
2) The first part refers to the genus the organism belongs to, giving information on tne organism’s ancestry.
3) The second part refers to the species

Question 50

What do modern classification systems group extinct species based on?

Answer 50

Information from the fossil record

Question 51

Impact of herbicides like glyphosate

Answer 51

Glyphosate kills weeds among crops, meaning less competition for light, stopping the growth of crops