3.4 Genetic Information, variation and relationship between organisms Flashcards
what is the difference between the dna in prokaryotes and eukaryotes?
prokaryotes e.g bacteria
- the dna molecules are shorter
- the dna molecule form a circle and are not associated with protein molecules, prokaryotic cells therefore do not have chromosomes
eukaryotes
- dna molecules are longer
- form a line (are linear)
- occur in association with proteins called histones to form structures called chromosomes
what type of dna does the mitochondria and chloroplasts of eukaryotic cell contain?
they contain dna which, like the dna of prokaryotes, is short, circular and not associated with protein
what is a gene?
a gene is a base sequence of dna that codes for either a polypeptide or functional RNA
what is a locus?
the fixed position of a gene on a chromosome/dna molecule
why have scientists come to the conclusion that there must be a minimum of three bases that codes for an amino acis?
- only 20 different amino acids regularly occur in proteins
- each amino acid must have its own code of bases on the dna
- only four different bases (A,T,C,G)
- if each base coded for a different amino acid, only four different amino acids could be coded for
- using a pair of bases, 16 (42) different codes are possible, which is still inadequate
- three bases produce 64 (43) different codes, more than enough to satisfy the requirements of 20 amino acids
as the code has three bases for each amino acid, each one is called a triplet. as there are 64 possible triplets and only 20 amino acids, it follows that some amino acids are coded for by one triplet.
what is this called?
degenerate code
what is meant by a degenerate code?
this is where an amino acid can be coded for by more than one base triplet
what is the advantage of having degenerate codes?
an advantage of having degenerate codes is that when a mutation occurs in a triplet code, it could still end up coding for the same amino acid
what is meant by when it is said that dna is non overlapping?
-this means that in the genetic code, each base triplet is reqad in sequence, seperated from the triplet before and after it
what is meant by when it is said that the genetic code is universal?
-the same specific base triplets code for the same amino acid in all living things
what is the name given to bases in dna which do not code for polypeptides?
introns (in the way)
what is the name given to the sections of dna that code for polypeptides?
exons (extra special)
what is the name of the proteins that dna are wound around and what do they do for dna?
- the dna molecule is wound around proteins called histones
- histones proteins help to support the dna
what is a chromosome?
a thread like structure made of protein and DNA by which hereditary information is physically passed from one generation to the next
what is a chromatid?
one of the two strands of a chromosome that are joined together by single centromere prior to cell division
what is chromatin?
the material that makes up chromosomes
-it consisits of dna and the protein histone
how is chromsome formed?
- you have a dna molecule
- the dna molecule is combined with histones
- the dna-histone complex is coiled
- coils fold to form loops
- the loops coil and pack together to form the chromosome
what are homologous chromosomes?
- a pair of chromosomes, one maternal and one paternal, that have the same gene loci and therefore determine the same features
what is a allele?
different versions of the same gene
homologous chromosomes carry the same genes but they are not genetically identical. explain why
homologous chromosomes carry different alleles
what is the diploid nummber in humans?
46
(46 chromosomes and 23 pairs of chromsomes)
what is a cell’s genome?
the complete set of genes in the cell
what is a cell’s proteome?
this is the full range of proteins that the cell is able to produce.
what does RNA stand for and what is it?
RNA stands for ribonucleic acid
-it is a polymer made up of repeating mononucleotide sub units.
what is a single strand of RNA made up off?
- the pentose sugar
- one of the organic bases (A,U,C,G)
- a phospate group
what are the two types of RNA?
- messenger RNA (mRNA)
- transfer RNA (tRNA)
state:
- what mRNA is
- which process its made in
- what it does
- what it is complementary to
- mRNA is single polynucleotide strand which has three adjacent basesd which are called condons
- mRNA is made during transcription
- mRNA carries the genetic code from the DNA to the robosomes,w where it is used to make a protein during translation
- mRNA is complementary to the DNA triplet code
state:
- what tRNA is
- which process it is involved in
- what it does
- tRNA is a single polynucleotife strand that’s folded into a clover shape and every tRNA molecule has a specific sequence of three bases at one end called an anticodon and an amino acid binding site at the other end
- tRNA is involved in translation
- it carries the correct amino acids that are used to make proteins to the ribosomes
what bonds hold the shape of the tRNA molecule together?
-hydrogen bonds
compare the size, the chain, sugar, bases, stability of DNA, mRNA and tRNA
DNA
size-largest molecule of the three
shape- double polynucleotide chain
sugar- pentose sugar (deoxyribose)
bases- A,T,C,G
stability- chemically very stable
mRNA
size- smaller than DNA but larger than tRNA
shape- single polynucleotide chain
sugar- pentose sugar (ribose sugar)
bases- A,U,C,G
stability- less stable than dna and tRNA, as its broken down in the cell in just a few days
tRNA
size- smallest molecule of the three
shape- smallest shape molecule of the three
sugar- pentose sugar (ribose sugar)
bases- A,U,C,G
stability- chemically more stable than mRNA but less stable than dna
in eukaryotic cells, where does transcription take place?
in the nucleus
in prokaryotic cells, where does transcription takes place? why is this
transcription takes place in the cytoplasm because prokaryotes dont have a nucleus
describe what happens in transcription
- )the enzyme helicase acts on a specific region of the dna molecule to break the hydrogen bons between the bases, causing the two strands to seperate and expose the nucleotide bases in that region
- ) the enzyme RNA polymerase moves alon one of the two DNA strands, know as the template strands, causing nucleotides on this strand to join with the individual complementary nucleotides from the pool which is present in the nucleus
- ) in this way an exposed guanin base on the dna in linked to the cytosine base of a free nucleotide. similarly, cytosine links to guanine and thymine joins to adenine. the exception is adenine which links to uracil rather than thymine.
- ) the enzyme helicase acts on a specific region of the DNA molecule to break the hydrogen bonds between the bases, causing the two strands to seperate and expose the nucleotide bases in that region.
what is the difference in the result of transcription in eukaryotes and prokaryotes
prokaryotes
-transcription results directly in the production of mRNA from DNA
eukaryotes
-transcription results in the production of pre-mRNa; this then splice to form mRNA
what is splicing?
- much of the eukaryotic DNA does not actually code for proteins introns (in the way) so these sections of bases are removed (spliced) before translation occurs
- the remaining exons (extra special) can then be combined in a variety of ways forming lots of different proteins.
describe the process of the translation
- ) the mRNA attached itself to a ribosome and transfer RNA moleculec carru amino acids to it. ATP provides the energy needed for the bond between the amino acid and the tRNA molecule to form.
- ) A tRNA molecule (carrying an amino acid), with an anticodon that’s complementary to the first codon on the mRNA, attaches itself to the mRNA by specific base pairing
- ) a secind tRNA molecule attaches itseld to the next codon on the mRNA in the same way
- ) the two amino acids attached to the tRNA molecule are joined by a peptide bond. The first tRNA molecules moves away, leaving its amino acid behind.
- ) A third tRNA molecule binds to the next codon the mRNA. Its amino acid binds to the first two and the second tRNA molecule moves away.
- ) the process continues, producing a chain of linked amino acids (a polypeptide chain) until there’s a stop signal on the mRNA molecule
- ) the polypeptide chain moves away from the ribosome and translation is complete.
look at this graph:
to investigate how two new drufgs affect nucleic acids and their role in protein synthesis, bacteria were grown under normal conditions for a few generations, the moved to medium containing drugs.
after a short period of time, the concentration of protein and complete strands of mRNA in the bacteria were anlysed. the results are showin the bar graph
-deduce information from the graph about the drugs
Drug 1
both mRNA and protein concentration were lower in the presence of this drug compare to the no-drug contol.
this suggest that drug 1 affects the production of full lenght mRNA, so theres no mRNA for protein synthesis during translation.
this suggests that this drug could be something like a enzyme which digests strands of mRNA so they can be used in translation to make proteins
Drug 2
-as you can see from the no-drug control mRNA production in the presence of this drug was unaffected but less protein was produced - 3mg cm-3 compared to 8mg cm-3
this suggests that drug 2 ineterfered with translation as mRNA was produced, but less protein was translated from it
this suggests that drug 2 could be something like a competitive inhibitior that works by binding to the ribsosome, blocking tRNAS from binding to it and so preventing translation.
what is a mutation?
a change in the base sequence of dna/chromosomes
when do mutations usually occur? why is this?
they can arise during dna replication as bases are exposed after the dna unzips so they are vulnerable
what is the difference between substitution and deletion
substitution is the swapping/replacing of one base for another
deletion is when a base is removed and not replaced
why can some substitution mutations be harmless?
- the degenerate nature of the genetic code means that some amino acids are coded for by more than one DNA triplet.
- This is means that not all substitution mutations wil result in a change to the amino acid sequence of the protein as some substitutions will code for the same amino acid.
why will deletion mutations always lead to a change in the amino acid sequence?
-the deletion of a base will change the number of the bases present which will cause a shift in all the base triplets after it
a mutation can lead to the production of a non-functional enzyme explain how (6 marks)
- a mutation is the change in the base sequence of DNA
- when a mutation happens it causes a change in the amino acid sequence
- this is means that there is a change in the primary structure of the enzyme which affects the secondary structure of the enzyme (folding and twisted of the sequence of the amino acid) which in turn changes the tertiary structure of the enzyme (3d shape of enzyme)
- this means that there is also a change in the hydrogen, ionic and disulphide bonds of the enzyme.
- because the 3d shape is different the enzyme’s active site will therefore be different
- so the substrate can not bind to the active site to form an enzyme substrate complex to produce a product.
what are mutagenic agents? give examples
mutagenic agents increase the rate of mutations e.g
- ultraviolet radiation
- ionising radiation
- chemicals
- viruses
during which part of the cell cycle are gene mutations likely to occur? why?
- interphase,
- because dna replication is taking place.
what does meiosis produce?
meiosis usually produces 4 daughter cells, each with half the number of chromosomes as the parent cell, all genetically different from each other.
what is a gamete?
a reproductive cell
give 2 examples of gametes in humans and in plants
human gametes
- sperm
- egg
plant gametes
- pollen
- ovules
what is a zygote?
a cell produced from the fertilisation of gametes (sperm and egg cell)
what is the difference between meiosis and mitosis?
mitosis produces two daughter cells with the same number of chromosomes as the parent cell and as each other
meiosis produces daughter cells, each with half the number of chromosomes as the parent cell
why meiosis important?
in sexual reproduction of humans, if the two gametes had a full set of chromosomes (46 each) and fused together then the zygote would have 92 chromosomes. This doubling of the number of chromsomes would continue at each generation.
so in order to maintain a constant number of chromosomes in the adults of a species, the number of chromosomes must be halved at some stage in the life cycle
what is the haploid number of chromosomes in a human?
23
what is the diploid number of chromsomes in a human?
46
how many chromosomes does a human gamete have and what name is given to this number?
23 chromosomes (haploid)
describe the process of meiosis
- ) before meisois starts, the DNA unravels and replicates so there are two copies of each chromosome, called chromatids. (2 x 2n)
- ) The dna condenses to form double-armed chromosomes, each made from two sister chromatids. The sister chromatids are joined in the middle by a centromere.
(2 x 2n)
3.) Meiosis I (first divisiom)- the chromosomes arrange themselves into homologous pairs.
(2 x 2n)
4.) these homologous pairs are then seperated halving the chromosome number
(2 x n)
- ) Meiosis II (second division) - the pairs of sister chromatids that make up each chromosome are seperated (the centromere is divided)
- ) Four haploud cell (the gametes) that are genetically different from each other are produced.
(n)
how can you recognise where meiosis occurs in the life cycle of an unfamiliar organism?
- when 2n becomes n (showing that the chromosome number has been halved)
- when gametes are made
what is are chiasmata?
a poiny at which paired chromosomes remain in contact during the first metaphase of meiosis,
and at which crossing over and exchange of genetic material occur between the strands
explain what independant segregation is
- each homologous pair of chromosomes in your cell is made up of one chromosome from your mum (maternal) and one chromosome from your dad (paternal)
- when the homologous pairs are seperated in meiosis I, it’s completely random which chromosome from each pair ends up in which daughter cell.
- so the four daughter cells produced by meiosis have completely different combinations of the maternal and paternal chromosomes
- this is called independant segregation of chromosomes
explain what happens in crossing over and when it happens
- crossing over happens in Meiosis I (seperation of the homologous pairs of chromosomes)
- the homologous pairs of chromosomes come together and pair up
- the chromatids twist around each other and bits of chromatids swap over
- the chromosomes still contain the same gene but now have a different combination of alleles.
what is the formula for working out number of possible chromosome combinations when you know how many pair of homologous chromosomes the organism has
2n (2^n)
where n is the number of homologous pairs of chromosomes
human beings have a diploid number 46
what is the possible number of different chromosome combinations in each gamete?
-find the amount of homologous pair of chromosomes humans have
46/2= 23
-then the number of chromosome combination
2^23= 8388609
what is the formula for finding the number of possible chromosome combinations in zygote after fertilisation
(2^n)^2
where n is the number of homologous pair of chromosomes
human beings have a diploid number of 46
what is the number of possible zygotes that can be produced by random mating?
-find the number of homologous pair of chromosomes
46/2= 23
-then work out the number of zygotes
(2^23)^2= 7.04 x 10^13
a horse has a diploid number of 64 while a donkey has 62
how many chromosome combinations would be possible in the offspring?
- find the haploid number of each animal
horse: 64/2=32
donkey: 62/2= 31 - find the number of chromosome combinations in the gamete of the animals
horse: 2^32= 4.29 x 10^9
donkey: 2^31= 2.14 x 10^9 - multiply to find the combination in the zygote (this would be your (2^n)^2 step but you have organisms with different amounts of chromosome combinations in the gametes instead of the same, so you’re sqauring the number)
4. 29 x 10^9 x 2.14 x 10^9= 9.22 x 10^18
state in two ways in which meiosis leads to an increase in genetic variation
- independant segregation of homologous chromosome
- recombination by crossing over
a mule is a cross between a donkey (62 chromosomes) and a horse (63 chromosomes). Mules therefore have 63 chromosomes.
From your knowledge of meiosis, suggest why mules are sterile (not being able to produce children)
- gametes are produced by meiosis
- in meisosis homologous chromosomes pair up.
- with 63 chromosomes precise pairings are impossible
- this prevents meiosis and hence gamete production
- making them sterile
what is non disjunction and why does it happen?
- non disjunction refers to an error in cell division
- this happens because the homologous chromosomes do not seperate from each other during the cell division
what happens in non-disjunction happens in meiosis I?
- both of the chromosomes of a homologous pair migrate to the same pole, leaving one daughter cell without a chromosome
- the cell goes through meiosis II normally producing 4 gametes with unusual numbers of chromosomes
- two gametes have on complete set of chromosomes plus 1
2 + 1
-the other two lack a chromosome and have
n- 1
what happens if non-disjunction happens in meiosis II?
- if non disjunction occurs in meiosis II both sister chromatids of chromosome migrate to the same pole of the cell
- only one chromsome seperated abnormally but these result in two abnormal cells
- two of the gametes are normal having a haploid number of chromosomes
- the other two are abnormal; 1 has extra chromosome (n + 1)
the other has too few (n - 1)
how does down’s syndrome occur
down’s syndrome is caused by a person having an extra copy of chromosome 21
- non-disjunction means that chromsome 21 fails to seperate properly during meiosis, so one cell gets an extra copy of chromosome 21 and another gets none
- when the gamete with the extra copy fuses to another gamete at fertilisation, the resulting zygote will have 3 copies of chromosome 21 which results in down syndrome
how does Turner syndrom occur?
- this occurs when a normal haploid gamete fuses with a gamete having n - 1 chromosome creating a monosomic zygote (2n - 1)
- in monosomy one chromosome is missing, so the cell only has one copy of a particular chromsome
- in turner syndrome, the female will only have one copy of the X chromosome.
what is meant by genetic diversity?
the total number of different alleles in a population
what decreases genetic diversity?
genetic bottlenecks- an event that causes a big reduction in a population
this reduces the number of different alleles in the gene pool and so reduces genetic diversity
Selection Pressure
determines which traits are successful
e.g climate, food sources, habitat etc which cause some individuals to have an advantage over others
give an example of a genetic bottleneck?
The Founder Effect
- a few individuals from a population start a new colony
- only a small fraction of the range of allele from the original population contribute to this gene pool so genetic diverisity is reduced
- these few individuals then start reproducing the new population has limited genetic diversity
- an allele that might have been rare in the original population may become more common in the new colony e.g an allele for genetic disease, there is more inbreeding within the colony so the incidence of this genetic disease would be increased aka the Amish Community.
what is meant by evolution?
this is the gradual change in species over time, evolution has lead to the huge diversity of living organisms found on earth
Natural Selection
- Within any population of a species there will be a gene pool containing a wide varities of alleles
- randomly occuring mutations sometimes result in a new allele being formed which in most cases can be harmful so the mutated allele quickly dies out
- however some mutations can produce alleles that are beneficial to an organism giving it an advantage over other individuals in the population
- the organism is better adapted and therefore more likely to survive in their competition with others, by more likely obtaining resources, growing more rapidly and living longer
- as a result they have a better chance of breeding successfully and producing more offspring
- only those that reproduce successfully will passs on their alleles to the next generation
- so a greater proportion of the next generation inherits the beneficial allele
- they in turn are more likely to survive, reproduce and pass on their genes
- so the frequency of the beneficial allele increases from generation to generation
- over generations this leads to evolution as the advantageous alleles become more common in population.
Directional Selection (a type of natural selection)
- this is where selection may favour individuals that vary in one direction from the mean of the populaition
- if the environmental conditions change, the phenotypes that are best suited to the new conditions are most likely to survive
- some individuals which fall to either the left or right of the mean, will possess a phenotype more suited to the new conditions
- these individuals are more likely to survive and breed
- they will therefore contribute more offspring (and the alleles they possess) to the next generation than the the other individuals
- over time the mean will then move in the direction of these individuals
Stablising Selection (A type of natural selection)
where individuals with alleles for characterisitics towards the middle of the range are more likely to survive and reproduce
- occurs when the environment isn’t changing and it reduces the range of possible characteristic
- tends to eliminate the phenotypes at the extremes
- these individuals are more likely to survive and breed
- they will therefore contribute more offspring (and the alleles they possess) to the next generation than the the other individuals
what are the three types of adaptations?
Behavioural- how an organism acts
Physiological- the processes inside an organism
Anatomical- structural features of an organism
what is meant by taxonomy?
the sicience of classification
what is the general name given to the eight groups used to classify organisms?
-taxa
each group is called a taxon
how are the groups arranged?
the groups are arranged in a hierarchy with the largest groups at the top and the smallest groups at the bottom
what are three recognised domains?
Bacteria, Archea, Eukarya
what are the eight groups (taxa), used to classify organisms, called?
- Domain (delicious)
- Kingdom (king)
- Phylum (prawn)
- Class (curry)
- Order (or)
- Family (fat)
- Genus (greasy)
- Species (sausages)
what are the kingdoms in Eukarya domain?
- Protoctista
- Fungi
- Plantae
- Animalia
what are differences between the three domain; bacteria, Archea and Eukarya
in which taxon do you start finding more closely related organisms?
phylum
what is the nomenclature (naming system) used for classification?
binomial system
how does the binomial system work?
- all organisms are given one internationally accepted scientific name in Latin that has two parts
- first part; its genus and begins with a capital letter
- second part; species and begins with a lower case letter
the binomial system helps to avoid the confusion of using common names
what is phylogeny?
the study of evolutionary history of groups of organisms.
phylogeny tells us whos related to whom and how closely related they are
what does the theory of evolution state?
the theory states that all organisms evolve from a single common ancestor
how does phylogentic classifcation work?
- phylogentic classification is based upon the evolutionary relationship between organisms and their ancestors
- classifies species into groups using shared features derived from their ancestors
- arranges groups into a heirarchy, in which the groups atre contained within a larger composite group with no overlap
why might scientists find it difficult to classify organism as a particular speices?
- species can evolve and change over time
- within a species there is lots of variation of physical features e.g dog breeds
- many species have become extinct but there is no fossil record to look at evolutionary relationships
- some species rarely reproduce seually e.g pandas
- isolation of populations of species so interbreeding with other members of the same specie may never occur e.g birds on island vs mainland
- population of the same species that are isolated may be classified as different species but may turn out to be of the same species when interbreeding occurs
- some organisms are sterile so fertile offspring can never be witnessed
what is courtship behaviour?
courtship behaviour is carried out by organisms to attract a mate of the right species
- it is species specific so only members of the same species will do and respond to that courtship behaviour which allows members of the same speciec to recognise each other
- because of this specificity, courtship behaviour can be used to classify organisms (the more closely related the organism the similar the courtship behaviour)
why is courtship behaviour necessary?
- to ensure recognition of the same species so to prevent interbreeding
- to identify a mate in who is sexually mature
- to identify a female who is producing eggs
- form a pair bond; needed for successful mating and upbringing pf the offspring
- makes reproduction successful e.g a horse x donkey is not successful as it does not lead to a fertile offspring
what are some examples of courtship behaviour?
- chemical/pherome release e.g moths/bees
- sound e.g male dear roaring
- visual displays e.g great tit puffing its chest
- building e.g birds creating nest
- dancing
why is production of a fertil offspring important?
ensuring that alleles are passed on to the next generation
how has genome sequencing been used to clarify evoolutionary relationships?
- advances in genome sequencing have meant the entire base sequence of an organism’s DNA can be determined.
- The DNA base sequence of an organism’s DNA can be determined
- the DNA base sequence of one organism can be compared to the DNA base sequence of another organism, to see how closely related they are.
- Closely related species will have a high percentage of similarity in their DNA base order e.g humans and chimps share around 94%, humans and mice share about 86%
how has comparing amino acid sequence been used to clarify evoolutionary relationships?
- Proteins are made of amino acids
- the sequence of amino acids in a protein is coded for by the base sequence in DNA
- related organisms have similar DNA sequences and so similar amino acid sequences in their proteins e.g. cytochrome C is a short protein found in many species
- the more similar the amino acid sequence of cytochrome C in two different species, the more closely related the species are likely to be
how has Immunological comparisons been used to clarify evoolutionary relationships?
similar proteins will also bing the same anitbodies e.g if anitbodies to a human version of a protein are added to isolated samples from other species, any proteins that’s like the human version will also be recognised by that antibody
how does developed gene technology allow us to measure genetic diversity directly?
-Different alleles of the same gene will have slightly different DNA base sequences.
comparing the DNA base sequence of the same gene in different organisms in a population allows scientists to find out how many alleles of that geen there are in that population
-different alleles will also produce slightly different mRNA base sequences, and may produce proteins with slightly different amino acids sequences so these can be compared
define biodiversity
the variety of living organism in an area
define habitat
the place where an organism lives
define community
all the populations of different species in a habitat
what is meant by local diversity?
the variety of different species living in a small habitat that’s local to you
what is meant by global diversity?
the variety of species on the earth
biodiversity varies in different parts of the world - greatest at the equator and decreases towards the poles
what is meant by species richness?
this is a measure of the number of different species in a community
what is meant by the index of diversity?
this describes the relationship between the number of species in the community and the number of individuals in each species
what is the eqaution for the index of diversity?
the higher the number the more diverse the area is
so if all the individuals are the same species the index is 1
what agricultural practice can reduce biodiversity?
- )Woodland clearance- done to increase are of farmland so directly reduces number of trees and sometimes number of different tree species -> so some specices lose their shelter and food sources -> species dies or migrates
- ) Hedgerow removal - done to increase area of farmland by turning lots of small fields to fewer large fields (so results are same as woodland clearance)
- ) Pesticides - chemicals that kill orgnisms that feed on crops -> reduces bd by directly killing pests -> species that feed on pests will lose a food source so numbers could decrease too
- ) Herbicides - chemicals that kill unwanted plants -> reduces plant diversity -> reduce number of organisms that feed on weeds
- ) Monoculture - when farmers have fields containing only one type of plant -> single type of plant reduces biodiversity directly and will support fewer organisms
all these things reduce biodiversity further
what are some examples of conservation schemes?
- Giving legal protection to endagered species
- Creating proteded areas such as SSSIs (sites of specific interest) sand AONBs (areas of outstanding natural beauty). These restrict further developement, including agricultural development
- the environmental stewardship scheme which encourages farmers to conserve biodiversity e.g by replanting hedgerows and leaving margins around fields for wild flowers to grow
what is meant by standard deviation
- the measure of the width of the curve
- it gives indication of the range of values either side of the mean
what is the formula for calculating standard deviation
what are the things to consider when a sample is to be model for the whole population?
the samples are representative
the samples are not biased so are random
statistical tests:
how do you calculate the percentage error of your measurements
percentage error= uncertainty/reading x 100
what does it mean when the standard deviation bars overlap?
it means that there is no statisitical significant difference
end of topic- ish
EQ: Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf.
4 marks
- (Carbon dioxide enters) via stomata; 2. (Stomata opened by) guard cells; 3. Diffuses through air spaces; 4. Down diffusion gradient;
EQ: Sugar beet plants have been selected for a faster rate of growth. Suggest how the faster rate of growth may increase profit for a farmer
1 mark
- Beet is ready quicker
- so can be harvested earilier
EQ: Sugar beet is a crop grown for the sugar stored in its root. The sugar is produced by photosynthesis in the leaves of the plant. Plant breeders selected high-yielding wild beet plants. They used these plants to produce a strain of sugar beet to grow as a crop.
Describe and explain how selection will have affected the genetic diversity of sugar beet.
2 marks
-reduces genetic diversity of sugar beet
because an allele is being selected
EQ: Explain how the standard deviation helps in the interpretation of these data.
2 marks
- shows the spread of data and how it varies
- if figures overlap then there is no significant difference between results
- low standard deviation means results are more reliable
EQ:
estimate whether the index of diversity for the wheat field would be higher or lower than the index of diversity for the wood. Explain how you arrived at your answer
2 marks
A journalist concluded that this investigation showed that farming reduces species diversity. Evaluate this conclusion.
2 marks
Diversity index would be lower (NO MARK)
- Fewer species / Beech aphid/Large white butterfly/7-spot ladybird absent /only three species / species diversity lower;
- Mostly one species / mostly birdcherry aphid;
- Fewer plant species;
For: 1. Data support the claim / evidence supports claim;
Against: 2. Only wheat field / only comparing with wood / one type of habitat /only insects considered;
EQ: Farmers were offered grants by the government to plant hedges around their fields. Explain the effect planting hedges could have on the index of diversity for animals.
2 marks
- Greater variety of plants;
- Another habitat / more habitats / places to live / niches;
- Another food source / more food types;
