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inheritance, variation and evolution Flashcards

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1
Q

Define meisosis

A
  • Formation of four non-identical cells from one cell
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2
Q

Define mitosis

A
  • Formation of two identical cells from one cell
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3
Q

Describe sexual reproduction

A
  • Involves the joining of male and female gametes (each containing genetic information from the mother or father)
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4
Q

Where does sexual reproduction occur?

A
  • Sperm and egg cells in animals
  • Pollen and egg cells in flowering plants
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5
Q

Describe what happens during sexual reproduction

A
  • Two sets of chromosomes (father and mother)
  • Each gamete has 23 chromosomes and fuse in fertilisation
  • Mixing of genetic information which leads to variety in the offspring
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6
Q

How are gametes formed?

A
  • By meiosis
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7
Q

Describe asexual reproduction

A
  • Involves one parent and no fusion of gametes
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8
Q

Describe what happens during asexual reproduction

A
  • happens using the process of mitosis
  • no mixing of genetic information
  • leads to clones which are genetically identical to each other and the parent
    e.g. bacteria
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9
Q

Explain how meiosis halves the number of chromosomes in gametes

A
  • the cell makes copies of its chromosomes - double the amount of genetic info
  • the cell divides twice to form four gametes, each with a single set of
    chromosomes
  • all gametes are genetically different from each other
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10
Q

Explain how fertilisation restores the full number of chromosomes

A
  • gametes (23) join at fertilisation to restore the normal number of
    chromosomes (46)
  • the new cell divides by mitosis to produce many copies - number of cells
    increases
  • embryo forms as more cells are produced
  • as the embryo develops cells differentiate
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11
Q

How do cells in reproductive organs divide?

A
  • divide by meiosis to form gametes
  • gametes only have one copy of each chromosome
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12
Q

What are the advantages of sexual reproduction?

A
  • produces variation in the offspring - if the environment changes variation gives a survival advantage by natural selection, variation decreases the chance of the whole species becoming extinct
  • natural selection can be speeded up by humans in selective breeding - organisms with different desirable characteristics can be bred to produce offspring with even more desirable characteristics
    e.g. to increase food production (breeding animals with lots of meat)
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13
Q

What are the advantages of asexual reproduction?

A
  • only one parent needed
  • no need to find a mate so it’s more time and energy efficient
  • faster than sexual reproduction
  • many identical offspring can be produced when conditions are favourable
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14
Q

Explain how malarial parasites reproduce sexually and asexually

A
  • causes malaria (spread by mosquitoes and transferred to humans through a bite)
  • reproduce sexually in the mosquito
  • reproduce asexually in the human host (in the liver and blood cells).
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15
Q

Explain how fungi reproduce sexually and asexually

A
  • many species can undergo both types of reproduction, releasing
    spores which land and become new fungi
  • spores produced asexually are genetically identical.
  • spores are produced sexually when the conditions change, in order to
    increase variation and avoid extinction.
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16
Q

Explain how plants reproduce sexually and asexually

A
  • many reproduce sexually using pollen (pollination) which must reach the egg cells in the female parts of another flower - forms seeds.
  • strawberry plants reproduce asexually, as they produce runners - new
    identical plants grow off the runner.
  • daffodils reproduce asexually - grow from bulbs and new bulbs can grow
    from the main one, producing a new identical plant.
  • advantageous in plants - can reproduce even if the
    flowers have been destroyed by frost or other animals
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17
Q

Describe the structure of DNA

A
  • the genetic material in the nucleus of a cell is composed of a chemical
    called DNA
  • DNA is a polymer made up of two strands forming a double helix
  • the DNA is contained in structures called chromosomes.
  • between the two strands are the four nitrogenous bases lined up in single rows - they come together to form a series of complementary pairs
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18
Q

Define a gene

A
  • small section of DNA on a chromosome
  • each gene codes for a particular sequence of amino acids to make a specific protein
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19
Q

Define a genome

A
  • all the genes coding for all of the proteins within an organism.
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20
Q

Discuss the importance of understanding the human genome

A
  • the whole human genome has now been studied
  • has improved our understanding of the genes linked to different types of disease and the treatment of inherited disorders
  • helped in tracing human migration patterns from the past
  • understanding the human genome will have great importance for medicine in the future.
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21
Q

What is DNA?

A
  • stands for deoxyribonucleic acid
  • a polymer made from four different nucleotides
  • contains instructions for the body
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22
Q

What are chromosomes?

A
  • structures made up of long molecules of DNA found in the nucleus of a cell
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23
Q

What are nucleotides made up of?

A
  • consists of a common sugar phosphate group with one of the four different bases attached to the sugar
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24
Q

Name the four types of organic bases

A
  • A, C, G, T
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25
Q

What codes for a particular amino acid?

A
  • sequence of three bases is the code for a particular amino acid.
  • amino acids are joined together to make a protein
  • it is the different types and order of amino acids that determine which type of protein it is
  • therefore the order of bases controls the order in which amino acids are assembled to produce a particular protein
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26
Q

What do long strands of DNA consist of?

A
  • alternating sugar and phosphate sections
  • attached to each sugar is one of the four bases
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27
Q

What is a DNA polymer made up of?

A
  • repeating nucleotide units
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28
Q

What are the complementary base pairngs?

A
  • A and T
  • C and G
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29
Q

Define protein synthesis

A
  • the process of producing a protein from DNA
  • if a gene is coded to make a protein, it has been expressed
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30
Q

Explain how protein synthesis works

A
  1. DNA contains the genetic code for making a protein, but it cannot move out of the nucleus as it is too big.
  2. The two strands pull apart from each other, and mRNA nucleotides (messenger RNA: a different type of nucleotide) match to their complementary base on the strand.
  3. The mRNA nucleotides themselves are then joined together, creating a new strand called the mRNA strand. This is a template of the original DNA.
  4. The mRNA then moves out of the nucleus to the cytoplasm and onto structures called ribosomes.
  5. At the ribosomes, the bases on the mRNA are read in threes to code for an amino acid (the first three bases code for one amino acid, the second three bases code for another etc).
  6. The corresponding amino acids are brought to the ribosomes by carrier molecules.
  7. These amino acids connect together to form a protein.
  8. When the chain is complete the protein folds to form a unique 3D structure.
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31
Q

What can proteins be?

A
  • enzymes
  • hormones
  • structural proteins
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32
Q

Define an enzyme

A
  • biological catalysts that speed up the rate of reaction
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33
Q

Define a hormone

A
  • chemical messengers that send signals around the body
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34
Q

Define a structural protein

A
  • strong proteins in order to form structures such as collagen
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35
Q

What do mutations do?

A
  • change the sequences of bases in DNA
  • can be either: insertion, deletion, or substitution
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36
Q

What happens when a base is inserted into he code?

A
  • as they are read in threes, this changes the way it is read.
  • it may change all the amino acids coded for after this insertion.
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37
Q

What happens when a base is deleted from the code?

A
  • like insertions they change the way it is read.
  • it may change all the amino acids coded for after this deletion
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38
Q

What happens when a base is substituted?

A
  • this will only change one amino acid in the sequence or it may not
    change the amino acid (as the new sequence can sometimes still code
    for the same amino acid)
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39
Q

How does a change in the type/sequence of amino acids affect DNA?

A
  • affects the way it folds and therefore the structure
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40
Q

What effect does mutation have?

A
  • most mutations do not alter the protein or only do so slightly
  • however, some have a serious effect and can change the shape
  • the substrate will not fit into the active site so it cannot act as a protein
  • a structural protein may lose its shape
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41
Q

Where else can there be mutations?

A
  • in the non-coding parts of DNA that control whether the genes are expressed
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42
Q

What do the non-coding parts of DNA do?

A
  • not all parts of DNA code for proteins.
  • non-coding parts of DNA can switch genes on and off
  • so variations in these areas of DNA
    may affect how genes are expressed
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43
Q

How does variation between two organisms arise?

A
  • the coding DNA that determines the proteins and their activity
  • the non-coding DNA that determines which genes are expressed
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44
Q

Define a gamete

A
  • an organism’s reproductive cell (egg in female and sperm in males), which has half the number of chromosomes (23).
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45
Q

Define a chromosome

A
  • a structure found in the nucleus which is made up of a long strand of
    DNA
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46
Q

Define a gene (characteristics)

A
  • a short section of DNA that codes for a protein, and therefore contribute to a characteristic.
  • some characteristics are controlled by a single gene, such as fur colour in mice and red-green colour blindness in humans.
  • however, most characteristics are the result of many different genes interacting.
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47
Q

Define alleles

A
  • the different forms of the gene - humans have two alleles for each gene
    as they inherit one from each parent.
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48
Q

Define dominant allele

A
  • only one (out of the two alleles) is needed for it to be expressed and for the corresponding phenotype to be observed.
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49
Q

Define recessive allele

A
  • two copies are needed for it to be expressed and for the corresponding
    the phenotype to be observed.
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50
Q

Define homozygous

A
  • hen both inherited alleles are the same (i.e. two dominant alleles or
    two recessive alleles).
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51
Q

Define heterozygous

A
  • when one of the inherited alleles is dominant and the other is recessive.
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52
Q

Define genotype

A
  • the combination of alleles an individual has, e.g. Aa
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53
Q

Define phenotype

A
  • the physical characteristics that are observed in the individual, e.g. eye
    colour
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54
Q

What do family trees show?

A
  • show the inheritance of different phenotypes over generations in the same family
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55
Q

How do you find the probability of the offspring of two parents having certain genotypes and phenotypes?

A
  • using a punnet square diagram
    ____I__B___I__b__I
    _B__I__BB_I__Bb_I
    _b__I__Bb_I_bb__I
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56
Q

How do you represent dominant and recessive characteristics in a punnet square?

A
  • uppercase for dominant
  • lowercase for recessive
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57
Q

How do you get a genetic disorder?

A
  • by inheriting certain alleles
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58
Q

What is polydactyly?

A
  • having extra fingers or toes
  • caused by dominant allel
59
Q

What is cystic fibrosis

A
  • disorder of the cell membranes, resulting in thick mucus in the airways and pancreas
  • caused by recessive allele
  • both parents need to either be carriers or one must have CF themselves and the other is a carrier
60
Q

What is embryonic screening?

A
  • allows scientists to observe whether the child will have a genetic condition or not
61
Q

How does embryonic screening work?

A
  • if the embryo is developed in the lab, cells can be taken from it and analysed
  • DNA from embryos in the womb can also be extracted
62
Q

What are the arguments for embryonic screening?

A
  • reduces number of people suffering (ethical)
  • treating disorders is very expensive (economic)
  • many regulations in place to stop it getting out of hand (social)
63
Q

What are the arguments against embryonic screening?

A
  • could encourage people to pick characteristics - creating designer babies (ethical).
  • expensive to carry out screening (economic)
  • may promote prejudice as it suggests that those with genetic disorders will not live a full life or are unwanted (social).
  • decisions about terminating a pregnancy have to be made (social).
  • procedure can lead to a miscarriage (social)
64
Q

How many chromosomes do human body cells have?

A
  • 23 pairs
65
Q

What do chromosomes control?

A
  • 22 pairs control characteristics only, but one pair carries the genes that determine sex
66
Q

What are the two possible chromosomes in the 23rd pair?

A
  • X and Y
  • Y much smaller than X
67
Q

What are the sex chromosomes in females?

A
  • XX
68
Q

What are the sex chromosomes in males?

A
  • XY
69
Q

How can punnett squares link to sex inheritance?

A
  • can be used to show sex inheritance
  • 50% chance of child being male, and 50% chance of child being female
    ____I__X___I__X___I
    _X__I__XX_I__XX__I
    _Y__I__XY_I__XY__I
70
Q

What does the phenotype an organism has depend on?

A
  • Genotype
  • Environment
71
Q

Define variation

A
  • Differences in the characteristics of individuals in a population is called
    variation
72
Q

How does variation occur?

A

Variation may be due to differences in:
* the genes they have inherited (genetic causes)
* the conditions in which they have developed (environmental causes)
* a combination of genes and the environment.

73
Q

Define genotype

A
  • The genes it inherited
74
Q

How does variation occur through genetic causes?

A
  • Genes are passed on from the parent in sex cells.
  • The combining of genes from the mother and father creates genetic
    variation.
  • Only identical twins have the same genotype.
  • There is lots of genetic variation in a population.
75
Q

Define environment

A
  • The place it lives in
76
Q

How does variation occur through environmental causes?

A
  • The conditions the organism grows and develops in also affects its
    appearance.
  • Examples include scars in animals, or smaller and yellow leaves in plants.
77
Q

How does variation occur through a combination of genetics and the environment?

A
  • Sometimes characteristics can result from a combination of genetics and the environment, such as weight.
  • Weight depends on the food you eat but also how quickly your body
    breaks it down and how much it stores as fat depends on your genes.
78
Q

How is genetic variation introduced?

A
  • Genetic variation is introduced by mutations in the sequence of DNA.
  • Mutations occur continuously
79
Q

How does genetic variation as a result of mutations affect the phenotype of an organism?

A
  • Most have no effect on phenotype.
  • Some will influence phenotype but it is unlikely that it will lead to a new
    phenotype.
  • somtehing about environment, check spec
  • If the mutation does determine the phenotype and it is advantageous, natural
    selection will mean it becomes the common phenotype relatively quickly.
80
Q

Define evolution

A
  • Evolution is a change in the inherited characteristics of a population over time through a process of natural selection which may result in the formation of a new species.
81
Q

Describe the Theory of Evolution

A
  • Theory of Evolution: All species have evolved from simple life forms that first developed more than three billion years ago.
82
Q

Why does evolution occur?

A
  • Evolution occurs because of natural selection.
83
Q

Explain how natural selection works

A
  • Mutations occur which provide variation between organisms.
  • If a mutation provides a survival advantage the organism is more likely to survive to breeding age.
  • The mutation will then be passed onto offspring.
  • Over many generations, the frequency of the mutation will increase within the population.
84
Q

Define speciation

A
  • If two populations of one species become so different in phenotype
    that they can no longer interbreed to produce fertile offspring they have
    formed two new species.
85
Q

Define selective breeding

A
  • Selective breeding is when humans choose which organisms to breed in order to produce offspring with a certain desirable characteristic (e.g animals with more meat, plants with disease resistance or big flowers)
  • Selective breeding (artificial selection) is the process by which humans breed plants and animals for particular genetic characteristics.
  • Humans have been doing this for thousands of years since they first bred food crops from wild plants and domesticated animals.
  • This has been happening for many years since animals were domesticated and plants were grown for food.
86
Q

How does selective breeding work?

A
  • Parents with desired characteristics are chosen.
  • They are bred together.
  • From the offspring those with desired characteristics are bred together.
  • The process is repeated many times until all the offspring have the desired
    characteristic
87
Q

Why do we use selective breeding?

A
  • The characteristic can be chosen for usefulness or appearance:
  • Disease resistance in food crops.
  • Animals which produce more meat or milk.
  • Domestic dogs with a gentle nature.
  • Large or unusual flowers.
88
Q

What are the problems of selective breeding?

A
  • The problem is that it can lead to inbreeding.
89
Q

Explain why inbreeding can be a problem

A
  • Breeding those with similar desirable characteristics means it is likely you are breeding closely related individuals.
  • This results in the reduction of the gene pool, as the number of different alleles reduce (as they mostly have the same alleles).
  • This means if the environment changes or there is a new disease, the species could become extinct as they all have the same genetic make-up (so the chance of a few organisms having a survival advantage and not dying is reduced).
  • Another problem is that the small gene pool leads to a greater chance of genetic defects being present in offspring, as recessive characteristics are more likely to present.
90
Q

Define genetic engineering

A
  • Modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic.
91
Q

What have plant cells been engineered for?

A
  • Plant cells have been engineered for disease resistance or to have larger fruits
92
Q

What have bacterial cells been engineered for?

A
  • Bacterial cells have been engineered to produce substances useful to humans, such as human insulin to treat diabetes
93
Q

Explain the process of genetic engineering

A
  1. Genes from chromosomes are ‘cut out’ using restriction enzymes leaving ‘sticky ends’ (short sections of exposed, unpaired bases)
  2. A virus or bacterial plasmid is cut using the same restriction enzyme to also create sticky ends. This also contains an antibiotic marker gene.
  3. The loop and gene sticky ends are then joined together by DNA ligase enzymes
  4. The combined loop is placed in a vector, such as a bacterial cell, and then allowed to multiply as it will now contain the modified gene.
  5. As the bacteria grows we can see which ones are resistant to antibiotics. The colonies that are will be the bacteria that are also producing the modified gene, as they were inserted together.
    In plants the vector is put into meristematic cells (unspecialised cells) which can then produce identical copies of the modified plant.
94
Q

Describe genetic engineering in crops

A
  • Genetically modified crops are engineered to be resistant to insects and to herbicides.
  • This will result in increased yields as less crops will die.
95
Q

Describe genetic engineering in medicine

A
  • Genetic modification in medicine include gene therapy
  • It may be possible to use genetic engineering to cure inherited disorders.
96
Q

What is gene therapy?

A
  • Using genetic engineering to cure inherited disorders
  • Involves transferring normal genes (not faulty) into patients so the correct proteins are produced
97
Q

What are the benefits of genetic engineering?

A
  • It can be very useful in medicine to mass produce certain hormones in
    microorganisms (bacteria and fungi)
  • In agriculture it can be used to improve yields by improving growth rate & introducing modifications that allow the crops to grow in different conditions, e.g. hotter or drier climates
  • Introducing modifications that allow plants to make their own pesticide or
    herbicide
  • Crops with extra vitamins can be produced in areas where they are difficult to obtain.
  • Greater yields can help solve world hunger, which is becoming an increasingly bigger issue due to population growth.
98
Q

What are the risks of genetic engineering?

A
  • GM crops might have an effect on wild flowers and therefore insects.
  • GM crops are infertile and these genes could spread into wild plants, leading to infertility in other species, which affects the entire environment.
  • Growing with herbicides and pesticides can kill insects and other
    plants, which would reduce biodiversity
  • People are worried that we do not completely understand the effects of GM crops on human health.
  • Genetic engineering in agriculture could lead to genetic engineering in humans. This may result in people using the technology to have designer babies.
  • They pose a selection pressure, which could lead to increased resistance in other species, creating super weeds and pests.
99
Q

Define cloning

A
  • Cloning is creating genetically identical copies of an organism.
100
Q

What are the methods of plant cloning?

A
  • Tissue culture:
  • Cuttings: an older, easier method to produce clones
101
Q

Why do we clone plants?

A
  • It is important to preserve rare plant species or commercially in plant nurseries
102
Q

Explain how tissue culture is used to clone plants

A
  • Plant cells are taken
  • They are placed in a growth medium with nutrients and hormones
  • They grow into new plants, and are clones as they are genetically identical to the parent
103
Q

Explain how cuttings is used to clone plants

A
  • Cuttings, such as a section of the stem, are taken from a plant with a
    desirable feature
  • They are planted and produce clones as they are genetically identical to the
    parent
104
Q

What are the methods of animal cloning?

A
  • Embryo transplants
  • Adult cell cloning
105
Q

Explain how embryo transplants is used to clone animals

A
  • Sperm cells and egg cells from parents with desirable features are obtained.
  • In the lab, they are fertilised to form an embryo.
  • The embryo divides many times and is then inserted into a host mother.
  • The offspring which is eventually born is genetically identical (with the
    desirable feature) as they have genetic information from the same mother
    and father
106
Q

Explain how adult cell cloning used to clone animals

A
  • The nucleus is removed from an unfertilised egg cell.
  • The nucleus from an adult body cell, such as a skin cell, is removed and inserted into the (denucleated) egg cell.
  • An electric shock stimulates the egg cell to divide to form an embryo.
  • These embryo cells contain the same genetic information as the adult
    skin cell.
  • When the embryo has developed into a ball of cells, it is inserted into
    the womb of an adult female to continue its development.
  • The offspring born is a clone of the adult body cell
107
Q

What are the benefits of cloning?

A
  • Produces lots of offspring with a specific desirable feature.
  • The study of clones could help research into embryo development.
  • Can help extremely endangered species, or even bring back species that have become extinct.
108
Q

What are the risks of cloning?

A
  • The gene pool is reduced through producing clones, meaning it is less
    likely that the population will survive if a disease arises with low diversity in the population.
  • Clones have a low survival rate, and tend to have some genetic problems.
  • It may lead to human cloning.
109
Q

Who is Charles Darwin and what did he do?

A
  • Charles Darwin was a scientist and naturalist
  • He put forward the theory of evolution
  • This was supported by experimentation and his knowledge of geology and fossils that he discovered on a round the world expedition
  • Published ‘On the Origin of Species’ in 1859
110
Q

Explain the Theory of Evolution

A
  • Variation exists within species as a result of mutations in DNA
  • Organisms with characteristics most suited to the environment are more likely to survive to reproductive age and breed successfully – called survival of the fittest.
  • The beneficial characteristics are then passed on to the next generation
  • Over many generations the frequency of alleles for this advantageous characteristic increase within the population
111
Q

Why was there controversy surrounding Charles Darwin’s theory of evolution?

A
  1. It contradicted the idea that God was the creator of all species on Earth.
  2. There was not enough evidence at the time as few studies had been done on how organisms change over time.
  3. The mechanism of inheritance and variation were not known at the time.
112
Q

Explain the ideas Jean-Baptiste Lamarck had about evolution

A
  • Changes that occurred during the lifetime of an organism were passed onto offspring
  • If an individual continually repeated an action, the characteristic that allowed it to do this would develop further
  • For example, if a giraffe stretched to reach leaves on a tree high up, its neck would become longer allowing it to do this more easily. This characteristic would then be passed on to its offspring.
113
Q

How was Larmarck’s theory proven wrong?

A
  • Lamarck’s theory was proven wrong when it was understood that changes caused by the environment were not passed on in the sex cells.
114
Q

How was Darwin’s theory supported?

A
  • Darwin’s theory was supported by genetics as it provided a mechanism for beneficial characteristics caused by mutations to be passed on.
  • Fossil evidence showed how developments in organisms arose slowly.
115
Q

What is speciation?

A
  • Speciation is the process of a new species developing through the selection of different alleles.
  • This increases the genetic variation until the new population cannot breed with those in the old population to produce fertile offspring.
116
Q

What did Alfred Russel Wallace develop?

A
  • Alfred Russel Wallace developed the theory of speciation, and therefore evolution by natural selection.
117
Q

How did Alfred Russel Wallace develop the theory of speciation?

A
  • On his travels, he had the idea that the individuals who did not have characteristics to help them survive a change in the environment would die out.
  • He published joint studies with Darwin.
  • The publication of ‘On the Origin of Species’ meant Darwin received the credit for the theory
  • He continued to work across the world to collect evidence – one of his most
    important works was on warning colouration in animals
  • Much more evidence over time has resulted in our current understanding.
118
Q

Explain the process of speciation

A
  1. Variation exists within a population as a result of genetic mutations.
  2. Alleles which provide a survival advantage are selected for through natural selection.
  3. Populations of a species can become isolated, for example through physical barriers such as a rock fall preventing them from breeding together.
  4. Different alleles may be advantageous in the new environment, leading to them being selected for.
  5. Over time the selection of different alleles will increase the genetic variation between the two populations.
  6. When they are no longer able to breed together to produce fertile offspring, a new species has formed.
119
Q

Explain Gregor Mendel’s work with pea plants

A
  • Gregor Mendel trained in mathematics and natural history in Vienna
  • Worked in the monastery gardens and observed the characteristics passed on to the next generations in plants
  • He carried out breeding experiments on pea plants.
  • He used smooth peas, wrinkled peas, green peas and yellow peas and observed the offspring to see which characteristics they had inherited
120
Q

What conclusions did Gregor Mendel come too

A
  • Through keeping a record of everything he did and eventually publishing his work in 1866, he came to the conclusions that:
  • Offspring have some characteristics that their parents have because they inherit ‘hereditary units’ from each.
  • One unit is received from each parent.
  • Units can be dominant or recessive, and cannot be mixed together.
121
Q

Why was Mendel’s work not recognised till after his death?

A
  • Mendel was not recognised till after his death as genes and chromosomes were not yet discovered, so people could not understand.
122
Q

How have our current understanding of genetics developed over time?

A
  • In the late 19th century behaviour of chromosomes during cell division were observed
  • In the 20th century, it was observed that chromosomes and Mendel’s ‘units’ (now called genes) were located on chromosomes.
  • In the mid-20th century, the structure of DNA was determined and the mechanism of gene function worked out, which meant we were able to understand how genes work
123
Q

What did the scientific work by many scientists lead to?

A
  • This scientific work by many scientists led to the gene theory being
    developed.
124
Q

Why is the theory of evolution by natural selection is now widely accepted?

A
  • Evidence for evolution is seen in:
    1. Fossils: the remains of organisms from many years ago, which are found in rocks
    2. Antibiotic resistance in bacteria: the selection pressure of antibiotics leads to advantageous mutations being selected for in bacteria populations so they are no longer killed when exposed to antibiotics.
125
Q

What are fossils?

A
  • Fossils are the remains of organisms from millions of years ago, which are found in rocks.
126
Q

How are fossils formed?

A
  1. Parts of organisms that have not decayed because oxygen or moisture were not present, meaning that the microbes that cause decay cannot survive.
  2. Parts of the organism such as teeth, shells and bones are replaced by minerals as they decay, forming a rock structure of the original part.
  3. Preserved traces such as footprints, burrows and rootlet traces (the plants roots) remain due to the ground hardening around them and forming a cast
127
Q

What can we use fossils for?

A
  • Fossils are used to show how the anatomy of organisms has changed over time.
  • They can be used to compare how closely related two organisms are, through looking at the number of similarities they have.
  • This information is used to create evolutionary trees.
128
Q

Why can’t fossils be used to tell us how life started on Earth?

A
  • Most early life forms are soft-bodied and therefore decay completely, so there are few fossils of them.
  • Any traces left have been destroyed by geological activity.
129
Q

Define extinction

A
  • When an entire species has died out
130
Q

What are the factors which can contribute to extinction?

A
  1. Changes in environment which the species cannot adapt fast enough to.
  2. New predators may have evolved or migrated to the area.
  3. A new disease arises and there are no resistant alleles to it.
  4. They have to compete with a species which has advantageous mutations for the same food source.
  5. A catastrophic event can wipe out a species.
  6. Destruction of habitat
131
Q

When are bacteria labelled resistant?

A
  • Bacteria are labelled resistant when they are not killed by antibiotics which previously were used as cures against them
132
Q

How does the population of antibiotic resistant bacteria increase?

A
  • Bacteria reproduce at a fast rate.
  • Mutations during reproduction can result in new genes, such as the gene for antibiotic resistance. This the creation of a new strain.
  • Exposure to antibiotics creates a selection pressure, as those with antibiotic resistant genes survive and those without die.
  • As a result those with antibiotic resistance can reproduce and pass on the advantageous gene to their offspring.
  • This population of antibiotic resistant bacteria increases.
133
Q

Why do bacterial diseases spread rapidly?

A
  • Bacterial diseases spreads rapidly because people are not immune to these new resistant bacteria and there is no treatment for it.
134
Q

What is an example of an antibiotic resistant bacteria?

A
  • An example is MRSA.
  • Called a ‘superbug’ as it is resistant to many different types of antibiotics
  • Common in hospitals: spreads when doctors and nurses move to different patients
135
Q

How can we slow the development of resistance in bacteria?

A
  1. Antibiotics should not be given for viral or non-serious infections
  2. Specific antibiotics should be given for specific bacteria
  3. Patients should complete their course of antibiotics – if they do not some bacteria may survive and mutate to become antibiotic resistant.
  4. Antibiotics should be used less in agriculture – farmers currently use them to prevent their livestock dying from disease, but this overuse leads to antibiotic resistant bacteria which are then transferred to humans when they consume the meat
136
Q

How can we slow the transmission of bacteria?

A
  1. Maintain high standards of hygiene in hospitals
  2. Medical staff and visitors should wash hands regularly
  3. Medical staff should wear disposable clothing or clothing that is regularly sterilised
137
Q

Why is it difficult to keep up with the development of resistant strains?

A
  • As the development of antibiotics is expensive and slow, it is difficult to keep up with the development of resistant strains.
138
Q

Define classification

A
  • Classification involves putting organisms into groups depending on their structure and characteristics.
139
Q

Who put forward the Linnaean system and what did it do?

A
  • Carl Linnaeus put the Linnaean system forward in the 1700s
  • Traditionally living things have been classified into groups depending on their structure and characteristics
  • Linnaeus classified living things into kingdom, phylum, class, order, family, genus and species.
140
Q

How are organisms named?

A
  • Binomal system
141
Q

What does the binomial system do?

A
  • The binomial system gives each organism a name which is used worldwide (overcomes language barriers).
  • The first part is their genus and the second part is their species.
    e.g. the ladybug, which has the name Harmonia (genus) axyridis (species).
142
Q

How did the three domain system come about?

A
  • Developments in science such as the improvement of the microscope and increased knowledge of biochemistry (for example, RNA sequence analysis) found that some species were more distantly related than first thought
  • So Carl Woese added three large groups called domains above kingdoms
  • As evidence of internal structures became more developed due to
    improvements in microscopes, and the understanding of biochemical processes progressed, new models of classification were proposed.
  • Due to evidence available from chemical analysis there is now a ‘threedomain system’ developed by Carl Woese. In this system organisms are
    divided into:
143
Q

What were the three domains that Carl Woese added above kingdoms?

A
  • Archaea: primitive bacteria which live in extreme environments such as hot springs
  • Bacteria: true bacteria (despite having similar features to archaea)
  • Eukaryota: organisms who have a nucleus enclosed in membranes,
    includes the kingdoms protists, fungi, plants and animals
144
Q

What are evolutionary trees and how do we complete them?

A
  • Evolutionary trees are used to show how closely related organisms are.
  • To complete this they use classification data and fossils for extinct species.

ZZ Biology P2 (3 decks)

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