Studied by 85 people
Looks like no one added any tags here yet for you.
Give three characteristics of DNA molecules in prokaryotic cells.
In prokaryotic cells, DNA molecules are short, circular and not associated with proteins.
What is the process that condenses prokaryotic DNA?
Supercoiling is the process that condenses prokaryotic DNA.
Where are DNA molecules found in eukaryotic cells?
In eukaryotic cells, DNA molecules are found in the nucleus.
Give three characteristics of DNA molecules in eukaryotic cells.
In eukaryotic cells, DNA molecules are very long, linear and associated with proteins called histones.
Give two reasons why histones are necessary.
One reason why histones are necessary is because the DNA molecule is wound around the histones.
Another reason is that the histones support the DNA.
Which two things form a chromosome?
A DNA molecule and its associated proteins form a chromosome.
Which two organelles contain DNA that is like the DNA of prokaryotes?
What does this mean?
The mitochondria and chloroplasts contain DNA that is like the DNA of prokaryotes.
This means it is short, circular and not associated with protein.
What is a gene?
A gene is a base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA.
Give two types of functional RNA.
Two types of functional RNA are ribosomal RNA and tRNA.
What is a locus?
A locus is the fixed position a gene occupies on a particular DNA molecule.
Explain what a triplet is.
A triplet is a sequence of three DNA bases which codes for a specific amino acid.
Give three characteristics of the genetic code.
The genetic code is universal, non-overlapping and degenerate.
Explain why the genetic code is universal.
The genetic code is universal because the same base triplets code for the same amino acids in all living things.
Explain why the genetic code is non-overlapping.
The genetic code is non-overlapping because each base in a sequence is only part of one triplet.
Explain why the genetic code is degenerate.
The genetic code is degenerate because some amino acids are coded for by more than one base triplet.
Give one reason why much of the nuclear DNA does not code for polypeptides.
Much of the nuclear DNA does not code for polypeptides because there are non-coding multiple repeats of base sequences between genes.
What is an exon?
An exon is a sequence in a gene which codes for amino acid sequences.
What are exons separated by in a gene?
In a gene, exons are separated by one or more non-coding sequences called introns.
Define the term genome of a cell.
The genome of a cell is the complete set of genes in a cell.
Define the term proteome of a cell.
The proteome of a cell is the full range of proteins that a cell is able to produce.
Describe the structure of messenger RNA molecules. (mRNA)
mRNA molecules have a single linear polynucleotide strand.
In mRNA groups of three adjacent bases are called codons.
In mRNA, there are only exons and no introns.
Describe the structure of transfer RNA molecules. (tRNA)
tRNA molecules have a single polynucleotide strand that is folded into a clover leaf shape.
There are hydrogen bonds between complementary base pairs which hold the molecule in shape.
Every tRNA molecule has an anticodon on one end and an amino acid binding side at the other end.
Describe the first step of transcription.
In the first step of transcription, the hydrogen bonds between the two DNA strands are broken.
This separates the strands and the DNA molecule uncoils, exposing the bases.
Describe the second step of transcription.
In the second step of transcription, only one of the strands is used as a template to make an mRNA copy.
The RNA polymerase lines up free RNA nucleotides alongside the exposed bases on the template strand by complementary base pairing.
Describe the third step of transcription.
In the third step of transcription, RNA polymerase joins adjacent nucleotides together.
What molecule does transcription result in the production of in:
Prokaryotes?
Eukaryotes?
In prokaryotes, transcription results directly in the production of mRNA.
In eukaryotes, transcription results in the production of pre-mRNA.
Explain why pre-mRNA must be spliced.
Pre-mRNA must be spliced to remove the introns.
The exons are then joined together to form mRNA strands in the nucleus.
Explain why splicing is not needed in prokaryotes.
In prokaryotes, splicing is not needed because there are no introns.
Describe the first step of translation.
In the first step of translation, the mRNA attaches itself to a ribosome and tRNA molecules carry specific amino acids to it.
ATP provides the energy needed to form the bond between the amino acid and the tRNA molecule.
Describe the second step of translation.
In the second step of translation, the anticodon on a tRNA molecule attaches to the first codon on the mRNA by complementary base pairing.
A second tRNA molecule attaches itself to the next codon on the mRNA.
Describe the third step of translation.
In the third step of translation, a peptide bonds joins the two amino acids, formed using ATP.
The first tRNA molecule moves away, leaving its amino acid behind.
This process continues, producing a polypeptide chain until there is a stop signal on the mRNA molecule.
Describe the final step of translation.
In the final step of translation, the polypeptide chain moves away from the ribosome.
What do gene mutations involve?
Gene mutations involve a change in the base sequence of chromosomes.
When can gene mutations arise spontaneously?
Gene mutations can arise spontaneously during DNA replication.
What do gene mutations include?
Gene mutations include base deletion and base substitution.
Explain why not all base substitutions cause a change in the sequence of encoded amino acids.
Not all base substitutions cause a change in the sequence of encoded amino acids because the genetic code is degenerate.
Some substitutions will still code for the same amino acid.
What can mutagenic agents do?
Mutagenic agents can increase the rate of gene mutation.
Give four examples of mutagenic agents.
Four examples of mutagenic agents are ultraviolet radiation, ionising radiation, some chemicals, and some viruses.
How can mutations in the number of chromosomes arise?
Mutations in the number of chromosomes can arise spontaneously by chromosome non-disjunction during meiosis.
The chromosomes do not separate properly.
What does meiosis produce?
Meiosis produces four haploid daughter cells that are genetically different from each other, from a single diploid parent cell.
Describe the first step of meiosis.
In the first step of meiosis, the DNA unravels and replicates so there are two copies of each chromosome, called chromatids.
Describe the second step of meiosis.
In the second step of meiosis, 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.
Describe the third step of meiosis.
(meiosis I)
In the third step of meiosis, homologous pairs of chromosomes associate and form a bivalent.
The homologous chromosomes cross over, where the chromatids twist around each other, forming chiasmata.
Equal lengths of non-sister chromatids are exchanged, producing new combinations of alleles.
Explain how the chromosome number is halved during meiosis.
During meiosis, the homologous pairs are separate.
One of each pair goes to opposite poles to end up in each daughter cell.
This halves the chromosome number.
Describe the fourth step of meiosis.
In the fourth step of meiosis the centromere is divided, separating the pairs of sister chromatids that make up each chromosome.
This produces four haploid cells that are genetically different from each other.
Explain why the independent segregation of homologous chromosomes results in genetically different daughter cells.
The independent segregation of homologous chromosomes results in genetically different daughter cells because the chromosome from each pair randomly ends up in the daughter cells.
This means the daughter cells have different combinations of the maternal and paternal chromosomes.
Describe the difference in the cells produced by mitosis, compared to that of meiosis.
Mitosis produces two genetically identical daughter cells with the same number of chromosomes as the parent cell.
Meiosis produces four daughter cells with half the number of chromosomes as the parent cell, which are genetically different to each other and the parent cell.
Explain why mitosis produces genetically identical daughter cells. (unlike meiosis)
Mitosis produces genetically identical daughter cells because there is no pairing or separating of homologous chromosomes.
Hence there is no crossing over or independent segregation of chromosomes.
Explain why the random fertilisation of haploid gametes is necessary.
The random fertilisation of haploid gametes is necessary to further increase genetic variation within a species.
This produces zygotes with new combinations of alleles.
Define genetic diversity.
Genetic diversity is the number of different alleles of genes in a population.
Why is genetic diversity important?
Genetic diversity is important because it enables natural selection to occur.
Explain how mutations can lead to increased reproductive success.
Random mutations can result in new alleles of a gene.
Many mutations are harmful but, in certain environments, the new allele of a gene might benefit its possessor, leading to increased reproductive success.
Describe how an advantageous allele can lead to evolution by natural selection.
The advantageous allele is inherited by members of the next generation.
As a result, over many generations, the new allele increases in frequency in the population.
The population evolves by natural selection.
Define the term directional selection, giving an example.
Directional selection is where individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce.
One example of directional selection is antibiotic resistance in bacteria.
Describe the first step of antibiotic resistance.
In the first step of antibiotic resistance, some bacteria in a population have alleles that give them resistance to an antibiotic.
The population is exposed to the antibiotic, killing bacteria without the resistant allele.
Describe the second step of antibiotic resistance.
In the second step of antibiotic resistance, the resistant bacteria survive and reproduce without competition, passing on the allele that gives antibiotic resistance to their offspring.
After some time, most organisms in the population will carry the antibiotic resistance allele.
Define the term stabilising selection, giving an example.
Stabilising selection is where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce.
One example of stabilising selection is human birth weight.
Explain why babies with low birth weights are less likely to survive.
Babies with low birth weights are less likely to survive because they find it hard to maintain their body temperature.
Explain why babies with high birth weights are less likely to survive.
Babies with high birth weights are less likely to survive because there is a risk of injury during birth.
What does natural selection result in?
Natural selection results in species that are better adapted to their environment.
What are the three types of adaptations?
The three types of adaptations are anatomical, physiological or behavioural.
What is a species?
A species is a group of similar organisms able to reproduce to give fertile offspring.
What is courtship behaviour?
Courtship behaviour is a necessary precursor to successful mating.
Suggest why courtship behaviour is carried out.
Courtship behaviour is carried out to attract mates of the same species.
Suggest why courtship behaviour must be species-specific.
Courtship behaviour must be species-specific to prevent organisms of different species from reproducing: infertile offspring would be produced.
Describe the role of courtship behaviour in species recognition.
Courtship behaviour is used to recognise organisms of a certain species.
This is because organisms with more similar courtship behaviour are more closely related.
What does a phylogenetic classification system attempt to do?
A phylogenetic classification system attempts to arrange species into groups based on their evolutionary origins and relationships.
Describe the hierarchy used by a phylogenetic classification system.
A phylogenetic classification system uses a hierarchy in which smaller groups are placed within larger groups, with no overlap between groups.
What is each group in a phylogenetic classification system called?
Each group in a phylogenetic classification system is called a taxon (plural taxa).
What does this classification suggest about the evolutionary relationships between these organisms?
This classification suggests that the chimpanzee and bonobo have a more recent common ancestor and are more closely related.
Name the taxa in one hierarchy.
In one hierarchy the taxa are domain, kingdom, phylum, class, order, family, genus and species.
Describe how each species is universally identified.
Each species is universally identified by a binomial consisting of the name of its genus and species.
How can evolutionary relationships between organisms be clarified?
Evolutionary relationships between organisms can be clarified by advances in immunology and genome sequencing.
What is biodiversity?
Biodiversity is the variety of living organisms in an area.
Describe what biodiversity can relate to.
Biodiversity can relate to a range of habitats, from a small local habitat to the Earth.
What is a community?
A community is all the populations of different species in a habitat.
What is species richness?
Species richness is a measure of the number of different species in a community.
What does an index of diversity describe?
An index of diversity describes the relationship between the number of species in a community and the number of individuals in each species.
Give the formula for the calculation of an index of diversity (d).
The formula for the calculation of an index of diversity (d) is:
where N = total number of organisms of all species and n = total number of organisms of each species.
There is a field with only one species of daises.
Suggest a value for the index of diversity.
The value for the index of diversity is 1 because all the organisms are of the same species.
State the effect of farming techniques on biodiversity.
Farming techniques reduce biodiversity.
Name five farming techniques that reduce biodiversity.
Five farming techniques that reduce biodiversity are woodland clearance, hedgerow removal, use of pesticides, use of herbicides, and monoculture.
Describe how woodland clearance reduces biodiversity.
Woodland clearance reduces biodiversity because it directly reduces the number of trees and the number of different tree species.
It also destroys habitats, so some species lose their shelter and food source.
The species will die or migrate to another suitable area.
Describe how hedgerow removal reduces biodiversity.
Hedgerow removal reduces biodiversity because it directly reduces the number of hedges and the number of different hedge species.
It also destroys habitats, so some species lose their shelter and food source.
The species will die or migrate to another suitable area.
Describe how the use of pesticides reduces biodiversity.
the use of pesticides reduces biodiversity because it directly kills the pests that feed on crops. Any species that feed on the pests lose a food source, so they might die as well.
Describe how the use of herbicides reduces biodiversity.
The use of herbicides reduces biodiversity because it directly kills unwanted plants, such as weeds. It also reduces the number of organisms that feed on the weeds.
Describe how monoculture reduces biodiversity.
Monoculture reduces biodiversity because there is only a single type of plant. This supports fewer organisms as a habitat or food source.
True or false:
There is no need for a balance between conservation and farming.
False.
There is a need for a balance between conservation and farming.
Why is conservation important?
Conservation is important to protect biodiversity.
Give three examples of conservation schemes.
One example of a conservation scheme is giving legal protection to endangered species.
Another example is creating protected areas which restrict further development.
Another example is encouraging farmers to conserve biodiversity by replanting hedgerows and leaving margins around fields for wild flowers to grow.
The genetic diversity within, or between species, can be investigated by comparing which four things?
The genetic diversity within, or between species, can be investigated by comparing:
the frequency of measurable or observable characteristics
the base sequence of DNA
the base sequence of mRNA
the amino acid sequence of the proteins encoded by DNA and mRNA.
Suggest how gene technology has caused a change in the methods of investigating genetic diversity.
Gene technology has caused a change in the methods of investigating genetic diversity because inferring DNA differences from measurable or observable characteristics has been replaced by a direct investigation of the DNA sequence.
What three things do quantitative investigations of variation within a species involve?
Quantitative investigations of variation within a species involve collecting data from random samples, calculating a mean and standard deviation, and interpreting mean values and their standard deviations.
Suggest why data must be collected from random samples.
Data must be collected from random samples to make sure the sample is not biased.
