Topic 6 - Inheritance, Variation and Evolution Flashcards
1
Q
What is DNA
A
-The chemical that all of the genetic material in a cell is made up from.
-It contains coded information
2
Q
What determines what inherited characteristics you have
A
DNA
3
Q
Where is DNA found
A
In animal and plant cells in long structures called chromosomes
4
Q
What is the structure of DNA like
A
It is polymer and is made up of two strands coiled together in the shape of a double helix.
5
Q
What is a gene
A
Small section of DNA found on a chromosome
6
Q
What do genes do
A
-Each gene codes for a particular sequence of amino acids which are put together to make a specific protein
-Tells cells in what order to put the amino acids together
7
Q
What does DNA determine
A
-What proteins a cell produces (e.g. haemoglobin or keratin)
-In turns determines what type of cell it is (e.g. red blood cell or skin cell)
8
Q
What is a genome
A
The entire set of genetic material in an organism
9
Q
Why is understanding the human genome so important for medicine and science
A
-Allows scientists to identify genes in the genome that link to diseases
-Scientists may be able to develop effective treatments for inherited genes if they knew what genes caused
-Can use genomes to trace the migration of populations of people around the world. Differences in genomes can determine when new populations split off in a different direction and what route they took
10
Q
What are DNA strands made up of
A
Repeating units called nucelotides
11
Q
What does a nucleotide consist of
A
A sugar, a phosphate group and one base
12
Q
What do the sugars and phosphate groups in the nucleotides do
A
Form a backbone to the to the DNA
They alternate
13
Q
What do bases do in nucleotide
A
One of four bases - A, T, G or C join to each sugar
14
Q
What bases always pair with each other (complementary pairing)
A
-T and A
-C and G
15
Q
What decides the order of amino acids in a protein
A
The order of bases in a gene
16
Q
How many bases code for one amino acid
A
Three bases
17
Q
What do amino acids do do after being coded for
A
The amino acids are joined together to make various proteins all depending on the order of the gene’s bases
18
Q
What do some non-coding parts of DNA do
A
Switch genes on and off, so they control whether or not a gene is expressed (used to make a protein)
19
Q
Where are proteins made?
A
In cell cytoplasm on ribosomes
20
Q
Why can’t cells get codes straight from the DNA to the ribosomes
A
DNA is found in the cell nucleus and can’t move out of it because it’s really big
21
Q
How does protein synthesise
A
mRNA is made by copying the code from DNA. The mRNA acts as a messenger between the DNA and the ribosome it carries the code between the two. Once the template is at the cytoplasm the protein will be synthesised, and depending on the template used a different protein will be made. The correct amino acids are brought to the ribosomes in the correct cells order by carrier molecules
22
Q
How do carrier molecules work?
A
One side binds to a corresponding amino acids and the other is shaped to fit a specific mRNA. There’s a specific carrier molecule for each protein. The carrier molecule binds to the mRNA. Enzymes link the amino acids together and the carrier is released
23
Q
Give some examples of proteins and their functions
A
- Enzymes - act as a biological catalyst to speed up chemical reactions in the body
- Hormones - used to carry messages around the body (e.g. insulin is released into the blood by the pancreas to regulate the blood sugar level.
- Structural proteins - are physically strong like collagen is a structural protein that strengthens connective tissues (like ligaments and cartilage)
24
Q
What are mutations?
A
A random change in an organisms DNA
25
When do mutations occur and what can increase the chance
-They occur continuously and can be spontaneous (e.g. when a chromosome isn’t replicated correctly)
-Exposure to certain substances or some types of radiation can increase the chance
26
What do mutations do
-They change the sequence of DNA bases in a gene, which produces a genetic variant. This can lead to changes in the protein that the gene codes for
-Most have little or no effect on the protein or some will change it to such a small extent that the function or appearance isn’t affected
27
What will happen if a mutation seriously affects a protein
It may code for an altered protein with a change of shape so it may not perform its function well (e.g. in enzymes if the active site is changed the substrate won’t fit into it - denaturing)
28
What happens if there is a mutation in non-coding DNA
It can alter how genes are expressed
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What is an insertion mutation
Where a new base is inserted into the DNA base sequence where it shouldn’t be
30
What effects can insertion mutation have
It can change the amino acids that the three bases code for and can change more then one amino acid as they have a knock-on effect on the bases further on in the sequence
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What are deletion mutations and what effect will this have
-When a random base is deleted from the DNA base sequence
-The base sequence will be “read” differently so may code for different amino acids and could have a knock-on effect further down the sequcne
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What are substitution mutations
-When a random base in the DNA base sequence is changed to a different base
33
What is sexual reproduction
Where genetic information from two organisms is combined to produce offspring which are genetically different to either parent
34
In humans how many chromosomes does each gamete contain
23 - half the chromosomes in a normal cell
35
What happens during fertilisation
The egg and sperm cell fuse together to form a cell with the full number of chromosomes
36
How can flowers reproduce sexually
They have egg cells that fuse with pollen
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How does asexual reproduction happen
There’s only one parent and it happens by mitosis - an ordinary cell making a new cell by dividing it in two. The new cell has exactly the same genetic information as the parent cell making it a clone.
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What reproduces asexually
Bacteria, some plants and animals
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How does sexual reproduction produce variation in offspring
Due to two parents the offspring contain a mixture of their parents genes and this mixture produces variation
40
How do gametes only have half the original number of chromosomes
Because cells divide by meiosis
41
Outline the process of meiosis
-Cell duplicates it’s genetic information forming two armed chromosomes - one arm of each is an exact copy of the other arm. After replicationthe chromosomes arrange into pairs
-In the first division in meiosis the chromosome pairs line up in the centre of the cell
-The pairs are then pulled apart so each new cell has only one copy of each chromosome
-In the second division the chromosomes line up again in the centre of the cell and the arms of the chromosomes are pulled apart.
42
What are the products of meiosis
-4 gametes each with only a single set of chromosomes in it. Each of the gametes is genetically different from the others because the chromosomes all get shuffled during meiosis and each gamete only gets half of them, at random.
43
What happens to the cell produced by gamete fusion
-The cell by mitosis to make a copy of itself.
-This repeats many times to produce lots of new cells in an embryo.
-As the embryo develops the cells start to differentiate into the different types of specialised cell that make up a whole organism
44
Why does variation caused by sexual reproduction give species a survival advantage
-It increases the chance of a species surviving a change in the environment. The variation may allow some offspring being able to survive in the new environment
45
What is natural selection and why is it an advantage for sexual reproduction
Individuals with better adapted characteristics for the environment have more chance of survival so they are more likely to breed successfully and pass the characteristics on.
46
What is selective breeding?
Individuals with a desirable characteristic are bred to produce offspring that have the desirable characteristic too. We can use selective breeding to speed up natural selection.
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What are the advantages of asexual reproduction
-There only needs to be one parent so it uses less energy than sexual reproduction as organisms don’t have to find a mage
-Faster than sexual reproduction
-Many identical offspring can be produced in favourable conditions
48
How does a malaria parasite reproduce
-The parasite is spread when a mosquito bites a human and it is transferred
-It reproduces sexually in the mosquito and asexually when in the human host.
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How do fungi reproduce
-Both sexually and asexually when spores are release which become new fungi when landing in a suitable place
-Asexually produced spores are genetically identical to the parent fungus
-Sexually produced spores introduce variation and are often produced in response to a change in the environment
50
How do strawberries reproduces by both asexual and sexual reproduction
The plants produce ‘runners’ which are stems that grow horizontally on the surface of soil away from a plant and at various points an identical strawberry plant forms
51
How do plants from bulbs reproduce both sexually and asexually
New bulbs can form from the main bulb and divide off of the plant. Each new bulb can grow into a new identical plant
52
What chromosomes determine gender
-Out of the 23 pairs, the 23rd pair are labelled either XY or XX and are the two chromosomes that determine sex
-Females have two X chromosomes
-Males have an X and a Y chromosome
53
What is the probability of each sperm cell getting an X and Y chromosome
50% each as when the sperm is made the X and Y chromosome are drawn apart in the first division in meiosis
54
What sex chromosomes do egg cells have
Original cell has two chromosomes but after meiosis the eggs have one X-chromosome
55
What is the name for different versions of the same gene
Alleles
56
What is homozygous
If an organism has two alleles for a particular gene that are the same
57
What is heterozygous
If two alleles for a particular gene are different
58
What is a genotype
The combination of alleles you have
59
What is a phenotype
The characteristic you get from the alleles you have
60
Outline cystic fibrosis in a genetic cross diagram
-The allele which caused some it is a recessive allele ‘f’ carried by 1/25 people
-People with only one copy of the allele won’t have the disorder but will be ‘carriers’
-For a child to have the disorder both parents must be a carrier or have it themselves
-There’s a 1/4 chance of a child having the disorder if both parents are carriers
61
What is cystic fibrosis
Genetic disorder of the cell membrane which results in the body producing a lot of thick sticky mucus in the air passages and in the pancreas
62
What is polydactyly
A genetic disorder where a baby’s born with extra fingers or toes. It doesn’t usually cause any other problems so isn’t life-threatening
63
Outline polydactyly in a genetic diagram
-The disorder is caused by a dominant allele ‘D’, so can be inherited if just one parent carries the allele
-The parent that has the defective allele will have the condition too all the allele is dominant
-There’s a 50% chance of a child having the disorder if one parent has one D allele
64
What is embryonic screening
Before an embryo is implanted during IVF it can have a cell removed and analyse its genes, which can detect many genetic disorders. It’s also possible to get DNA from an embryo in the womb and test that for disorders.
65
Why is embryonic screening controversial
-For embryos produced by IVF after screening embryos with ‘bad’ alleles would be destroyed
-For embryos in the womb - screening could lead to the decision to terminate the pregnancy
66
What are the arguments against embryonic screening
-It implies people with genetic problems are ‘undesirable’ which could increase prejudice
-There may come a point where everyone wants to screen their embryos so they can pick the most ‘desirable’ one (e.g. blue eyed, blonde haired, intelligent boy)
-Screening is expensive
67
What are the arguments for embryonic screening
-It will help to stop people suffering
-Treating disorders costs the government a lot of money
-There are laws to stop it going too far, at the moment parents cannot even select the sex of their baby (unless it’s for health reasons)
68
How have organisms traditionally been classified
According to a system first proposed in the 1700s by Carl Linnaeus, which groups living things according to their characteristics and the structures that make them up
69
In the Linnaeus system how are things divided up
-First divided into kingdoms (e.g. the plant kingdom)
-The Kingdoms are then subdivided into smaller and smaller groups - phylum, class, order, family, genus, species
70
After the Linnaeus System why did people put forward new models for classification
Because information of the biochemical process inside organisms developed and microscopes improved allowing us to find out more about the internal structures of the organisms
71
What model for classification did Carl Woese propose in 1900
The three-domain system which used evidence gathered from new chemical analysis techniques such as RNA sequence analysis he found in some cases species thought to be closely related in traditional classification systems are not as closely related as thought
72
In the three-domain systems what are the three large groups organisms are first split into
1. Archaea - Organisms in this domain were first thought to be primitive bacteria but they’re actually a different type of prokaryotic cell. They were first found in extreme places such as hot springs and salt lake.
2. Bacteria - This domain contains true bacteria like E. Coli and Staphylococcus and although they often look similar to archaea there are lots of biochemical differences between them
3. Eukaryota - This domain includes a broad range of organisms, including fungi, plants, animals and protists
73
After the three large groups of the three-domain system what are organisms then subdivided into
Smaller groups - Kingdom, phylum, class, order, family, genus, species.
74
What is the binomial system
The system where every organism is given its own two-part Latin.
75
How does the binomial system naming work?
-The first part refers to the genus of the organisms
-The second part refers to the species
-E,g, homo sapiens (homo = genus) (sapiens = species)
76
Why is the binomial system used worldwide
As scientists in different countries who speak different languages all refer to a particular species by the same name avoiding potential confusion
77
What do evolutionary trees show
-How scientists think different species are related
-They show common ancestors and relationships between species and the more recent the common ancestor the more closely related the two species - the more characteristics they’re likely to share
78
How do scientists work out evolutionary relationships for evolutionary trees
-Analyse lots of different types of data
-For living organisms they use the current classification data (e.g. DNA analysis and structural similarities)
-For extinct species they use information from the fossil record
79
What did Darwin conclude about evolution
-The organisms with the most suitable characteristics for the environment would be more successful competitors and would be more likely to survive
-The successful organisms are more likely to reproduce and pass on the genes for the characteristics that made them successful to their offspring
-Organisms that are less adapted would be less likely to survive and reproduce, so they are less likely to pass on their genes to the next generation
-Over time beneficial characteristics become more common in the population and the species changes - it evolves
80
What was the basis for Darwin’s theory on evolution
He knew that organisms in a species show wide variation in their characteristics (phenotype variation). He also knew that organisms have to compete for limited resources in an ecosystem.
81
Why has new scientific information helped develop Darwin’s ideas
His theory wasn’t perfect as the scientific knowledge wasn’t available at the time so he couldn’t give a good explanation why new characteristics appeared or exactly how individual organisms passed on beneficial adaptations to their offspring
82
What scientific knowledge do we have now that helps develop Darwin’s theory
We know that phenotype is controlled by genes and new phenotypic variations arise because of genetic variants produced by mutations and beneficial variations are passed onto future generations in the genes that parents contribute to their offspring
83
What is speciation
Over a long period of time, the phenotype of organisms can change so much because of natural selection that a completely new species is formed.
84
When does speciation happens and what does this cause
When populations of the same species change enough to become reproductively isolated - so they can’t interbreed to produce fertile offspring
85
What are the five reasons for extinction
1. The environment changes too quickly (e.g. destruction of habitat)
2. A new predator kills them all (e.g. humans hunting them)
3. A new disease kills them all
4. They can’t compete with another new species for food
5. A catastrophic event happens that kills them all (e.g. a volcanic eruption or a collision with an asteroid)
86
Why was Darwin’s theory of natural selection controversial
-It went against common religious belief of how life on earth developed as it was a plausible reason for the existence of life without a ‘creator’
-Darwin couldn’t explain why the new useful characteristics appeared or how they were passed on from individual organisms to their offspring as genes or mutations were discovered 50 years later
-There wasn’t enough evidence to convince many scientists, because not many other studies had been done into how organisms change over time.
87
What was Lamarck theory about evolution
-He argued that changes an organism acquires during its lifetime will be passed on to its offspring. (e.g. if a characteristic was used a lot by an organism it would become more developed during their lifetime and the offspring would inherit the acquired characteristic)
88
Give an example of Lamarck’s theory
-If a rabbit used its legs to run a lot (from predators) then it’s legs would get longer so the offspring of that rabbit would be born with longer legs
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Why might scientists developed different hypothesise for the same thing
They have different beliefs or have been influenced by different people or just think differently
90
How was Lamarck’s theory proved wrong
-Lamarck’s hypothesis wasn’t supported by experiments so was rejected (e.g. if you dye a hamsters fur pink the offspring will be born with the normal fur colour so the new characteristic wasn’t passed)
91
How was Darwin’s theory proven correct
-The discovery of genetics supported his idea as it provided an explanation of how organisms born with beneficial characteristics can pass them on
-Fossils of different ages allowed us to see how changes in organisms developed slowly over time.
-Discovery of how bacteria are able to evolve to become resistant to antibiotics also further supports evolution by natural selection
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What is a species
A group of similar organisms that can reproduce to give fertile offspring
93
What is isolation of species and why can it happen
-Where populations of species are separated
-This can happen due to a physical barrier (e.g. floods and earthquakes can cause barriers that geographically isolate some individuals from the main population). Conditions on each side of the barrier will be slightly different (e.g. different climates) Because the environment is different on each side, different characteristics will become more common in each population due to natural selection operating differently in the populations.
-Eventually individuals from the different populations will have changed so much they won’t be able to breed with one another to produce fertile offspring. The two groups will have become separate species.
94
When species are isolated why would their genetics cause speciation
1. Each population shows genetic variation because they have a wide range of alleles
2. In each population, individuals with characteristics that make them better adapted to their environment have a better chance of survival and so are more likely to breed successfully.
3. So the alleles that control the beneficial characteristics are more likely to be passed on the next generation.
95
Who is Alfred Russel Wallace
A scientist working at the same time as Darwin who was one of the early scientists working on the idea of speciation working on the idea of speciation. His observations greatly contributed to how we understand speciation today, however ideas have developed along with modern scientific knowledge
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What did Wallace do for the theory of natural selection
-Independently came up with the idea and published h work on the subject with Darwin in 1858 prompting Darwin to publish ‘On the Origin of Species’ in 1859
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How did Wallace find evidence for natural selection
-Through observations he made as he travelled the world
-For example he realised that warning colours are used by some species (e.g. butterflies) to deter predators from eating them and that this was an example of beneficial characteristics they had evolved by natural selection
98
Who was Gregor Mendel and did find
-An Austrian monk who trained in maths and natural history at the University of Vienna.
-He noted how characteristic in plants were passed on from one generation to the next. His results were published in 1866 and eventually became the foundation of modern genetics
99
What did Mendel show in his pea plants
The height characteristics were determined by separately inherited “hereditary units” passed on from each parent. The ratio of tall and dwarf plants in the offspring showed the unit for tall plants was dominant over the unit for dwarf plants
100
What were Mendel’s three conclusion
-Characteristics in plants are determined by hereditary units
-Hereditary units are passed on to offspring unchanged from both parents, one unit from each parents
-Hereditary units can be dominant or recessive - if an individual has both the dominant and the recessive unit for a characteristic the dominant characteristics will be expressed
101
What was the initial problem with Mendel’s work
-Scientists at the time didn’t have the background knowledge to properly understand his finding as they had no idea about genes, DNA and chromosomes.
-It wasn’t until after his death people realised how significant his work was
102
How have Mendel’s findings contributed to the understanding we have of genes
-In the late 1800s scientists became familiar with chromosomes. They were able to observe how they behaved during cell division.
-In the early 20th century scientists realised that there were striking similarities in the way chromosomes and Mendel’s units acted. It was proposed units were found in the chromosomes. These units are now “genes”.
-In 1953 the structure of DNA was determined so scientists could find exactly how genes work
103
What is variation
Differences within a species
104
Outline genetic variation
-All plants and animals have characteristics that are in ways similar to their parents
-An organisms characteristics are determined by the genes inherited from their parents.
-These genes are passed on in sex cells, from which the offspring develop
-Most animals get some genes from the mother and some from the father
-Combining of genes from two parents causes genetic variation
-Some characteristics are determined only by genes. In animals these include eye colour, blood colour and inherited disorders
105
Outline environmental variation
-The environment including the conditions that organisms live and grow in, also causes differences between members of the same species this is called environmental variation
-For example a plant grown in plenty of sunlight would be luscious and green, but the same plant grown in darkness would grow tall and spindly and have yellow leaves
- This covers a wide range of differences
106
What are most characteristics due to
-They’re determined by a mixture of genetic and environmental factors
-For example the maximum height a plant or animal can grow is determined by genes, but whether it actually grows that tall depends on environment (e.g. how much food)
107
How do mutations affect variation
-Mutations are changes to the sequence of bases in DNA. Most have no affect on the protein the gene codes for so most have no effect on the organisms phenotype. Some have a small influence on phenotype and so only alter characteristics slightly however mutations can result in a new phenotype being seen in a species
-If the environment changes and the new phenotype makes an individual more suited to the new environment it can become more common throughout the species due to natural selection
108
What is selective breeding
-When humans artificially select the plants or animals that are going to breed so that the genes for particular characteristics remain in the population. Organisms are selectively bred to develop features that are useful or attractive
109
Give examples of features organisms are commonly selectively breeded for
-Animals that produce more milk or meat
-Crops with disease resistance
-Dogs with a good, gentle temperament
-Decorative plants with big or unusual
110
Outline the basic process involved in selective breeding
-From your existing stock select the ones which the characteristics you’re after
-Breed them with each other
-Select the best of the offspring and breed them together
-Continue this process over several generations, and the desirable trait gets stronger and stronger. Eventually, all the offspring will have the characteristic
-People have been doing it for thousands of years and it’s how we ended up with edible crops from wild plants and how we got domesticated animals like cows and dogs
111
How is selective breeding used to improve yields
-In agriculture it is used to improve improve meats (and other) yields by breeding things with the best characteristics. After doing this for several generations the farmer would get cows with a very high meat yield
112
What is inbreeding and why is it a problem with selective breeding
-It reduces the gene pool as the number of different alleles in a population. This is because the farmer keeps breeding from the “best” animals or plants which are all closely related
-This can cause health problems because there’s more chance of organisms inheriting harmful genetic defect when the gene pool is limited. Some dog breeds are particularly susceptible to defects because of inbreeding (e.g. pugs often have breathing problems)
-There can be a problem if a new disease appears as there not much variation in the population. All the stock are closely related to each other, so if one of them is going to be killed by a new disease, the others are also likely to succumb to it.
113
What is genetic engineering
Transferring a gene responsible for a desirable characteristic from one organisms genome into another organism, so that it also has the desired characteristic.
114
How is genetic engineering carried out
-A useful gene is isolated from an organisms genome using enzyme & is inserted into a vector
-The vector is usually a virus or bacterial plasmid depending on the type of organism that the gene is being transferred to
-When the vector is introduced to the target organism, the useful gene is inserted into its cells
- Sometimes the transfer of the gene is carried out when the organism receiving the gene is at an early stage of development. This means that the organisms develops with the characteristic coded for by the gene
115
What can genetic engineering be used for
-Bacteria = genetically modified to produce human insulin that can be used to treat diabetes
-GM crops have genes modified (e.g. to improve size/quality of fruit or disease, insect and herbicides resistance)
-Sheep have been genetically engineered to produce substances like drugs in their milk that can be used to treat human diseases
-Scientists are researching genetic modification treatments for inherited diseases caused by faulty genes (e.g. inserting working genes into people with the disease)
116
Why is genetic engineering controversial
-There are worried about the long-term effects of genetic engineering- they changing an organism’s genes might accidentally create unplanned problems, which could get passed on to future generations
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Disadvantages of genetically modified crops
-May affect number of wild flowers that live around crops reducing biodiversity
-May not be safe and people think we don’t fully understand the effect of eating them on human health (allergies)
-The transplanted genes may get out into the natural environment. For example the herbicide resistance may be picked up by weeds
118
Advantages of genetically modified crops
-Increases yield
-GM crops could be engineered to contain the nutrients that are missing in LICS for example, golden rice is a GM rice crop that contains beta-carotene (lack of this = blindness)
-GM crops are already being grown in some places, often without any problems
119
How are plants cloned by tissue culture
-A few plants cells are put in a growth medium with hormones, and they grow into more plants (clones of the parent plant). These plants can be made very quickly, in very little space, and be grown all year. Tissue culture is used by scientists to preserve rare plants that are hard to reproduce naturally and by plant nurseries to produce lots of stock quickly
120
How are plants cloned from cuttings
-Plant cuttings to produce identical copies of the parent plant
-They can be produced quickly and cheaply. (Older and simpler method)
121
How are animal clones made using embryo transplants
-Sperm cells taken from animal and egg from another. Sperm used to artificially fertilise the egg cell. The embryo that develops in then split many times before cells become specialised
-These cloned embryos can then be implanted into lots of other cows where they grow into baby calves
-Hundreds of ideal offspring can be produced every year from the best bull and cow
122
How is adult stem cell cloning used to make a clone
-Taking an unfertilised egg cell and removing its nucleus. The nucleus is removed from an adult body cell and inserted into the ‘empty’ egg cell.
-The egg cell is stimulated by an electrical shock making it divide just like a normal embryo
-When the embryo is a ball of cells, it’s implanted into the womb of an adult female. It grows into genetically identical of the original adult body cell as it has the same genetic information
123
What are problems are surrounding cloning
-Reduced gene pool and if a new disease appears they could all be wiped out as there may not be an allele that resists it
-Cloned animals might not be as healthy as normal ones
-People worry humans may be cloned in the future with could lead to severe disabilitee
124
What are the advantages of cloning
-The study of animal clones could lead to greater understating of the development of the embryo and of ageing and age-related disorders
-Could be used to help preserve endangered species
125
What are fossils
The remains of organisms from many thousands of years ago, which are found in rocks.
126
How are fossils formed from gradual replacement by minerals
-Things like teeth, shells, bones etc. which don’t decay easily, can last a long time when buried
-They’re eventually replaced by minerals as they decay forming a rock-like substance shaped like the original hard part
-The surroundings sediments also turn to rock, but the fossil stays distinct inside the rock and eventually someone digs it up.
127
How are fossils formed from casts and impressions
-When an organism is buried in a soft material like clay. The clay layer hardens around it and the organism decays, leaving a cast of itself. An animals burrow or a plants roots can be preserved as casts
-Things like footprints can also be pressed into these materials when soft, leaving an impression when it hardens
128
How are fossils formed from preservation in places where no decay happens
-In amber and tar pits there’s no oxygen or moisture so decay microbes can’t survive
-In glaciers it’s too cold for the microbes to work
-Peat bogs are too acidic for decay microbes
129
What hypothesis are there for how life began
-In a primordial swamp
-Simple organic moleucles brought to earth by comets
130
Why can hypotheses about how life began not be disprove
-Many early forms of life were soft bodied and soft tissue tends to decay away completely so the fossil record is incomplete
-Fossils that did form millions of years ago may have been destroyed by geological activity (e.g. the movement of tectonic plates may have crushed fossils already formed in the rock)
131
How do anti-antibiotic resistant bacteria strains form
-Bacteria can develop random mutations which can lead to changes in bacterial characteristics (being less affected by a particular antibiotic). This can lead to strains forming as the gene for antibiotic resistance become more common in the population
-Bacteria are rapid at reproducing they can evolve quickly
132
Why is antibiotic resistance helpful for bacteria
-It’s better shoe to survive in a host who’s being treated to get rid of the infection, so it lives for longer and reproduces many more times, increasing the population of the strain
133
Why is antibiotic resistant strains of bacteria a problem
-People who become infected with the bacteria aren’t immune so there is no effective treatment. This means the infection easily spreads between people. Sometimes drug companies can come up with a new antibiotic that’s effective
-Superbugs that are resistant to most known antibiotics are becoming more common (e.g. MRSA which often affects people in hospitals and can be fatal of it enters the bloodstream)
134
Why is antibiotic resistance becoming more common
-Overuse and inappropriate use of antibiotics (e.g. doctors prescribing them for non-serious conditions or infections caused by viruses)
-The more often antibiotics are use the bigger the problem of antibiotic resistance becomes as a situation where naturally resistant bacteria have an advantage can increase in numbers
-Taking a full course of antibiotics ensures all bacteria are destroyed which means there are none left to mutate and develop into resistant strains
135
How are antibiotic resistant strains forming in farming
-Antibiotics given to animals for prevention and to grow faster. Leafing to development of antibiotic resistant bacteria in the animals which can spread to humans. (e.g. during meat preparation and consumption) Increasing concern about the overuse of antibiotics in agriculture has led to some counties restricting their use.
136
What has an increase in antibiotic resistant strain of bacteria led to in drug companies
Encouraged them to work on developing new antibiotics that are effective against the resistant strains. However the rate of development is slow so we’re unlikely to keep up with demand for new drugs as strains develop and spread, it’s also costly.
