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149 Cards in this Set

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A ribosome:

-assembled in the nucleus from ribosomal DNA and protein.

-Made up of 2 sub units.

-A groove, in which the length on mRNA can fit and read the code to assemble the amino acid.

Why is the sequence of Amino acids are critical?

- forms primary structure of a protein which determined the tertiary structure which allows a protein to function.

- If tertiary shape is altered:- protein can no longer function because the substrate molecule will not fit or won't allow an ion to pass to the membrane.

What is an anti-codon?

A sequence of three nucleotides forming a unit of genetic code in a transfer RNA molecule, corresponding to a complementary codon in messenger RNA.

What are the type of mutations?

Point mutations (substitutions):- one base pair replaces another.

insertion/deletion mutations: one or more bases are inserted or deleted. This causes a frame shift.

Example of a genetic disorders caused by mutations:-

- Sickle cell anaemia and cystic fibrosis.

Sickle cell anaemia results from a point mutation on codon 6 of the gene for the beta polypeptide chain of haemoglobin. This causes the amino acid valine to be inserted, at this point of the polypeptide, in place of glutamic acid.

Type of effects from mutations: Neutral effects.

Neutral effects:- produces no change to the organism if: mutation is in the non-coding region of the DNA. It is a silent mutation. (still codes for same amino acid.)

What are the lac system genes from an operon?

Structural genes: Z codes for the enzyme B galactoside and Y codes for enzyme lactose permease.

Each consists of a sequence of base pairs that can be transcribed into a length of mRNA.

What are the lac system genes from an operon?(Part II)

The operator region: O, is a length of DNA next to the structural genes. It can switch them on and off.

The promoter region: P, is a length of DNA to which the enzyme RNA polymerase binds to to begin the transcription of structural genes.

What is the role of (1)B galactosidase and (2)lactose permease?

(1)catalyses the hydrolysis of lactose to glucose and galactose.

(2) transports lactose into the cell.

Sequence of events when lactose is absent from the growth medium:

- The regulator gene is expressed.

- repressor protein is synthesised (it has two binding sites, one that binds to lactose and another than binds to operator region)

- Repressor protein binds to the operator region. It covers the promoter region so RNA polymerase cannot attach so structural genes cannot be transcribed into mRNA.

- Genes cannot be transcribed and enzymes cannot be synthesized.

Sequence of events when lactose is present in the growth medium:

1. Lactose molecule binds to repressor protein, this causes repressor protein to change shape so the repressor dissociates.

2. RNA can now bind and initiate transcription of mRNA for genes Z and Y.

3. Operator-repressor-inducer system acts as a molecular switch. It allows the transcription and translation of structural genes, Z and Y, into the lac enzymes.

What is apoptosis?

programmed cell death that occurs in multi cellular organisms. It leads to an orderly and tidy cell death. In contrast to necrosis which releases hydrolytic enzymes.

How is apoptosis controlled?

Cell signals include cytokines made by cells of the immune system, hormones, growth factors and nitric oxide. Nitric oxide can induce apoptosis by making the inner mitochondrial membrane more permeable to hydrogen ions and dissipating the proton gradient. Protons are released into the cytosol. This protein binds to apoptosis inhibitor proteins and allows the process to take place.

How does meiosis increase genetic variation:

1.crossing over, during prophase 1.

2. Genetic re-assortment due to random distribution and subsequent segregation of maternal and paternal chromosomes in homologous pairs.

3. genetic reassortment due to random distribution and segregation of sister chromatids at meosis II.

4. Random mutation.

3. fertilisation.

Process of crossing over:-

Occurs in P1.

Non-sister chromatids wrap around each other very tightly and attach at points called the chiasmata. The chromosomes may break at this point.

The broken ends of the chromatids rejoin the ends of non-sister chromatids being swapped over.

Reassortment of chromosomes:

-consequence of random distribution of maternal and paternal chromosomes on the spindle equator at metaphase I and the subsequent segregation into two daughter nuclei at anaphase I.

Reassorment of chromatids:

Result of random distribution on the spinder equator, of the sister chromatids, at metaphase II.

Why is sex linkage most likely to be on the X chromosome??

Because the Y chromosome has very few genes.

What is epistasis?

interaction if different gene loci so that one gene locus masks of suppresses the expression of another gene locus.

Recessive epistasis:

-Two gene loci on different chromosomes are involved.

-9:3:4 ratio suggests recessive epistasis

- When the recessive allele of one gene masks the effects of either allele of the second gene.

Dominant epistasis:

When the dominant allele of one gene masks the effects of either allele of the second gene.

12:3:1 or 13:3 ratio.

Epistasis working in a complimentary fashion:

One gene codes for an intermediate colourless pigment and the second locus codes for an enzyme that converts the intermediate compound to the final purple pigment.

What is discontinuous variation:

describes the qualitative differences between phenotypes. They fall into clearly distinguishable categories.

Different alleles at a single gene locus have large effects on the phenotype.

Different gene loci have different effects on the phenotype.

What is continuous variation?

Describes quantitative differences between phenotypes. There is a wide range of variation with no distinct categories.

Controlled by two or more genes.

Different alleles at each gene locus have small effect on the phenotype.

A large number of different genes may have a combined effect on the phenotype. They are know as polygenics and the characteristic they control is known as polygenic.

What are the assumption when using a Hardy Weinberg principle?

- Population is very large.

-mating is random.

-no selective advantage for any genotype.

-no mutation, migration or genetic drift.

What is a homeobox gene?
controls the development of the body plan of an organism, including the polarity and positioning of the organs
What is a selection pressure?
an environmental factor that confers greater chances of survival to reproductive ago on some members of the population.
What isolating mechanisms are there?

geographic barriers (ecological).

Seasonal (temporal) barriers such as climate.

Reproductive mechanisms such as breeding seasons or mating calls.

What is a carrying capacity?
Maximum amount that an environment can sustain
What is abiotic and biotic?
abiotic is a cause of non living components and biotic is caused by living organisms.
What is a genetic drift?
Variation in the relative frequency of different genotypes in small populations owing to the chance disappearance of particular genes as individuals die and do not reproduce.
The biological species concept
group of similar organisms that can interbreed and produce fertile offspring.
What is the phylogenetic species?
group of organism that have similar morphology, physiology, embryology and behaviour, and occupy the same biological niche.
What is a monophyletic group?
one that includes an ancestral organism and all descendant species.
stages of artificial selection:

-humans select organisms with useful characteristics.

-humans allow those with useful characteristics to breed and prevent ones without the characteristics from breeding.

-Thus humans have a significant effect on the evolution of these populations.

Increasing milk yield by artificial selection:

-Each cows milk yield is measured and recorded.

-Progeny of the bulls is tested to find which bulls have reproduced daughters with high milk yields.

-Only a few good quality bulls need to be kept.

- some elite cows are given hormones to produce many eggs.

-Eggs are fertilized in-vitro and then implanted into surrogate mother.

- These are cloned and divided into identical offspring.

What are the advantages of sexual reproduction?

-It's quick, allow individuals to reproduce rapidly and take advantage of their resources.

-possible is sexual reproduction fails or isn't possible.

-all offspring have genetic information to enable them to survive in their environment.

Disadvantage of sexual reproduction:
doesn't produce any genetic variety so any parental weaknesses will be in all the offspring.
Steps of callus tissue culture:

-Tissue taken from the plant called ex plant.

-placed on nutrient growth medium

-cells divide form callus.

-callus placed on growth medium containing hormones that encourage shoot growth

-Transferred to one where they encourage root growth.

-transferred to a greenhouse

Nuclear transfer:
nucleus of a differentiated adult cell can be taken and placed in an egg cell which has its own nucleus removed. Using genetic information, the cell goes through stages of development.
The advantages of cloning cells

-being genetically identical to individuals own cells means they wont be rejected.

-Could end problem of waiting for donor organs.

-cloned cells can be used to generate any cell type.

-less dangerous than major operation.

What are the precise growing conditions of microorganism culture?

temperature: too hot and enzymes will denature and cool.

type and time of added nutrients: Time of nutrient added can be manipulated depending on if the process is designed to produce primary or secondary metabolites.

Oxygen concentration: a lack will lead to unwanted products of anaerobic respiration and a reduction in growth rate.

pH: can reduce activity of enzymes and so reduce growth rates.

What is a batch culture?
Where organism starter population is mixed with a specific quantity of nutrient solution, then allowed to grow for a fixed period, with no further nutrient added. At the end of the period, the products are removed and the tank is emptied. (PENICILLIN)
What is a continuous culture?
Where nutrients are added to the fermenter and products removed from the fermenter tank at regular intervals. (INSULIN)
Effects of a contaminant:

-compete with microorganisms for nutrients and space.

-reduce yield of useful product.

-cause spoilage.

- may produce toxic chemicals.

-may destroy the culture microorganisms and their products.

The advantages of immobilising enzymes.

-Purification costs are lower.

-Enzymes immediately available for re-use.

- more stable because immobilising matrix protects the enzyme molecule.

Disadvantage of immobilising enzymes

-requires additional time, equipment and material so is more costly.

-can be less active because do not mix freely with substrate.

-Contamination is costly because whole system would need to be stopped.

Outline of Gene sequencing:

-Genome is mapped (to identify which part of the genome they come from)

-Samples of the genome are broken into smaller sections by the shotgun approach.

-These sections are played into BAC's and transferred to E.Coli cells.

-Cells grow in culture so many copies of the gene is produced.

- Cells referred to as clone libraries.

What is comparative gene mapping?
Knowing the sequence of genes in one organism and being able to compare genes for the same (or similar) proteins across a range of organisms is known as comparative gene mapping.
What are the applications of comparative gene mapping?

-Shows evolutionary relationships.

-Modelling the effects of changes to DNA/genes can be carried out.

-Comparing genomes from pathogenic and similar but non pathogenic organisms can be used to identify the genes or base pair sequences that are most important in causing the disease. (leads to vaccines and diseases)

- DNA analysis can reveal mutant alleles or those associated with risk of particular disease.

What are the techniques for sequencing DNA?

-DNA cut into smaller fragments by restriction endonuclease enzymes.

-Fragments separated by size using electrophoresis.

-Can be replicated to many copies using PCR.

-DNA fragments can be sealed together by using Ligase enzyme.

-DNA probes used to locate specific sequences.

Stages of Electrophoresis:

-DNA samples treated with restriction enzymes to cut them into fragments.

-DNA samples placed into wells at one end of the gel.

-Gel immersed in a tank of buffer solution and an electric current is passed through the solution.

-DNA positive charge attracted to the negative electrode so start to diffuse

-Shorter move faster.

-Position of fragments can be shown by dye that stains the DNA molecule.

Southern Blotting technique:

-Nylon or nitrocellulose sheet is placed over the gel, covered in paper towels, pressed and left overnight.

-DNA fragments are transferred to the sheet and can be analysed.

-DNA strands not visible so mark with radioactive marker before sample are run.

-placing photographic film over the nitrocellulose sheet shows position of the DNA samples in the finished gel.

DNA probes:

short, single stranded piece of DNA that is complimentary to the DNA being investigated.


-RADIOACTIVE MARKERS: location revealed by using photographic film.

-FLOURESCENT MARKER: emits a colour on exposure to UV light.

What is annealing?
The binding of a probe by complimentary base pairing.
How are probes useful in locating specific sequences?

-to locate a specific, desired gene that is wanted in genetic engineering.

-To identify the same gene on a variety of different genomes, from separate species when conducting genome comparison studies)

-to identify a presence or an absence of an allele for a particular genetic disease.

DNA probes and disease diagnosis:
Analysing the patients DNA using DNA probes. Probes are made that are complimentary to sequences found in faulty alleles of particular genes.
What is a DNA microarray?
Fixed probes are in wells. These probes are specific for sequences found in disease alleles. DNA samples are labelled with fluorescent markers. Where a test subject and a reference marker both bind to a particular probe, the scan reveals fluorescence of both colours indicating the presence of a particular sequence in the DNA
What is the polymerase chain reaction?
artificial DNA replication. Carried out on tiny samples of DNA in order to generate multiples copies of the sample. Particularly useful in investigations where DNA is taken from crime scenes.
What does PCR reaction rely on?

That DNA is:

-made up of antiparallel backbone strands.

-made up of strands that have a 5' and a 3' end.

-grows only from the 3' end.

-base pairs pair up according to complimentary base pairing rules.

Why is PCR not identical to a natural DNA replication?

-can only replicate relatively short sequences of DNA.

-primer molecules required for the process to start.

-A cycle of heating and cooling is used in PCR.

Method of PCR:

-DNA sample mixed with nucleotides and DNA polymerase.

-Mixture heated to 95- makes sample single stranded.

-Primers are added.

-Temp reduced to 55, allowing primers to bind making double stranded sections.

-DNA polymerase can bind to these double stranded sections.

-Temp raised to 72 and the enzyme extended the double stranded section by adding free nucleotides.

The enzyme polymerase:
It's described as thermophilic because it's not denatured by extreme temperatures used in processes. The enzyme is derived from a thermophilic bacterium.
Steps involved in sequencing a genome:

-Primer anneals at the 3' end of the template strand, allowing DNA polymerase to attach.

-DNA adds free nucleotides according to base-pairing rules so strand grows.

-If a modified nucleotide is added, polymerase is thrown off and the reaction stops.

In each case the final added nucleotide is tagged with a specific colour.

-Separated in length order by electrophoresis and the laser reads the colour sequence.

How do modified nucleotides work ?

They lack a 3-OH group required for the formation of a phosphodiester bond between 2 nucleotides.
Why can't polymerase initiate replication?
because DNA polymerase needs a free 3 hydroxyl group to add its nucleotide to. It's active site is not capable of initiating polymerization itself.
What is genetic engineering?
Genetic engineering is a broad term used to describe a number of different processes for obtaining a specific gene and placing that gene in another organism. The organism receiving the gene expresses the new gene product through the process of protein synthesis. Such organism are described as transgenic.
What steps are necessary in genetic engineering?

-required gene is obtained.

-copy of the gene is placed in a vector

-vector carries the gene to a recipient cell

-vector expresses the gene through protein synthesis.

What is a sticky end?
formed when DNA is cut using restriction enzymes. It is a short run of unpaired, exposed bases seen at the end of the cut section. Complementary sticky ends can anneal as part of the process for recombining DNA fragments.
Methods for obtaining the gene to be engineered (genetic engineering)

1) mRNA from the transcription of genes can be obtained from cells where the gene is expressed. The mRNA can be used as a template to make a copy of the gene.

2) DNA probe can be used to locate the gene on DNA fragments and the gene can be cut to form a DNA fragment using restriction enzymes.

Methods for placing a gene in a vector: (genetic engineering)

1) gene can be sealed into a bacterial plasmid using DNA ligase.

2) genes may be sealed into virus genomes or yeast cell chromosomes.

3) Vectors often have to contain regulatory sequences of DNA. These ensure that the inserted gene is transcribed in the host cell.

What is a regulatory sequence?
A regulatory sequence is a segment of a nucleic acid molecule which is capable of increasing or decreasing the expression of specific genes within an organism. Regulation of gene expression is an essential feature of all living organisms and viruses.
Method for getting the gene into the recipient cell: (genetic engineering)

-Electroporation: a high voltage pulse is applied to disrupt the membrane.

-Viral transfer: The vector is a virus; this method uses virus's mechanism for infecting the cell by inserting DNA directly.

-Microinjection: DNA is injected using a fine micropipette into the host cells nucleus

-Liposomes: DNA is wrapped in a lipid molecule. These are fat soluble and can cross the lipid membrane by diffusion.

What are restriction enzymes?
A restriction enzyme are used to cut through DNA at specific points. A particular restriction enzyme will cut DNA wherever a specific base sequence occurs. This sequence is called the restriction site and is usually less than 10 base pairs long. The enzyme catalyses a hydrolysis reaction that breaks the phosphate sugar backbone in different places, producing a staggered cut. To join together DNA fragments from different sources, both need to be cut by same restriction enzyme.
What is DNA ligase?
Enzyme used to catalyse a condensation reaction which joins the phosphate sugar backbone of the DNA double helix together.
Why do we genetically engineer an organism

1. Improving a feature of the recipient organism.

e.g. inserting a gene in crop plants to give them resistance to herbicides.

Inserting a growth controlling gene to promote muscle growth in animals.

2.Engingeering organisms that can synthesize useful products.

E.g. inserting the gene for insulin so mass production can take place.

Inserting a pharmaceutical gene in goat milk so its ,more easily obtainable

How do bacterial cells take up plasmid DNA?

Large quants of plasmids are mixed with bacterial cells, some of which will take up the recombinant plasmid.

The addition of calcium salts and heat shock increases the rate at which they are taken up. Less than 1% take up the plasmid, which are known as transformed bacteria. They have new DNA and so are transgenic.

What is heat shock and how does it work?
Temperature of the culture is lowered to around freezing then quickly raised to around 40C
What is bacterial conjunction?
Where genetic material may be exchanged. Copies of plasmid DNA are passed between bacteria, sometimes even of different species.
Genetic engineering to produce human insulin:

-Separate the right length of mRNA

-Reverse transcriptase used to synthesize a complimentary strand of DNA.

-Adding DNA polymerase and a supply of DNA nucleotides means that the second strand is built using the copied DNA (Like in DNA replication) This produces a copy of the original gene.

-Unpaired nucleotides are added at each end to give sticky end, complimentary to those on the cut plasmid.

-Plasmids are cut open with restriction enzyme and mixed with cDNA genes.

-Some plasmids take up the gene. DNA ligase enzyme seals the plasmids which become recombinant

What are the different types of colonies that may grow in genetic engineering of insulin.

-Some bacteria that do not take up a plasmid

-^ that have taken up a plasmid that has not sealed in a copy of the gene but has sealed up on itself to reform the original plasmid.

-^ that have taken up the recombinant plasmid.

Method of identification of transformed bacteria by replica plating:

Bacteria are grown on a standard nutrient agar, so all bacterial cells form colonies.

Some cells from the colonies are transferred onto agar that have been made with ampicillin, so only those that have taken up a plasmid will grow.

Some cells from these colonies are transferred onto agar that has been made with tetracycline so only those that have taken up a plasmid that does not have an insulin gene will grow.

We know that any bacteria that grow on the ampicillin agar, but not on the tetracycline agar, must have taken up the plasmid with the insulin gene.

What is replica plating by definition?
The process of growing bacteria on an agar plate, then transferring a replica of the growth to other plates, usually containing different growth promoters or inhibitors. Analysis of growth patterns on the replica plates gives information about the genetic properties of the growing bacteria.
What is gene therapy?
The techniques of molecular genetic technology used to treat some genetic disorders. If we can get a working copy of a gene into cells that have a dysfunctional copy, then transcription of that gene will mean that the person may not longer have symptoms associated with disease.
What is augmentation:
gene therapy by adding genes. Engineering a functioning copy of the gene into the relevant and specialized cells means that the polypeptide is synthesized and the cell can function properly
Description of gene therapy by killing specific cells
cancers can be treated by eliminating certain populations of cells. Using genetic techniques to make cancerous cells express genes to produce proteins that make the cell vulnerable to attack by the immune system.
Germline cell gene therapy:
Engineering a gene into a sperm, egg, zygote or into all the cells of an early embryo means that as the organism grows, every cell consists of a copy of the engineered cell. This gene can then function within any cell where the gene is required.
Why has germline cell gene therapy been considered as inappropriate?

-An inadvertent modification of DNA introduced into the germline could create a new human disease or interfere with human evolution.

-permanent modifications to the human genome in this way raise difficult moral, ethical and social issues that need to be fully debated.

What is a xenotransplantation?
refers to the transplantation of cell tissues or organs between animals or different species whereas allotransplantation refers to transplants between animals of the same species.
How are ecosystems dynamic?

Community of living things interact with each other and with their physical environment. Any small changes in one can affect the other. For example, if a predators population size goes up, the population size of the prey will go down.

The nitrogen fixing plant would grow successfully in nitrogen deficient soil, but they would affect their environment by increasing the nitrogen soil levels. This change would help other plants grow well.

Food webs
Within an ecosystem, living organisms are usually members of more than one food chain and often feed at different trophic levels in different chains. Drawing food webs helps us understand how energy flows through the whole ecosystem.
Pyramids of biomass:
areas of bars is proportional to the dry mass of all the organisms at the trophic level. obtaining dry mass is destructive so ecologists obtain wet mass of the organisms and calculate the dry mass on the basis of previously published data.
Pyramids of energy:
involves burning the organisms in something called a calorimeter and working out how much heat energy is released per gram- this is calculated by the temperature rise of a known mass of water. (destructive so revert to pyramid of biomass)
Productivity: limitations of the pyramid of energy

-They only take a snapshot of an ecosystem at one moment in time.

-Because population sizes can fluctuate over time, this may provide a distorted idea of the efficiency of energy transfer.

What is productivity?
The rate of energy flow and gives an idea of how much energy is available to the organisms at a particular trophic level, per unit area. Measures in mega joules.
What is GROSS primary productivity and NET primary productivity:

Gross primary productivity:- rate at which plants convert light energy into chemical energy

Net primary productivity: remaining energy available to primary consumer, after energy loss has taken place.

What is succession?
directional change in a community of organisms over time.
How does succession happen?

-algae and lichens begin to live on bare rock. This is a pioneer community.

-Erosion of rock and build up of dead and rotting organisms, produces enough soil for larger plants like mosses and ferns to grow (succeed the algae)

-larger plants succeed the smaller plants until a climax community is reached.

What is a quadrat?
a square frame used for studying ecosystems. It helps determine the abundance (number of individuals) and distribution (presence or absence of species) of the species.
Point frame:
Estimating the percentage cover is difficult so using a point frame can help with the estimate. The number of needles that touch each species is proportional to the percentage cover of that species.
What are the things you should determine before starting to sample?
-Provide a sample representative of the whole field.

-Work out how many are needed.

-how big your quadrats should be.

How to make sure your quadrat sample is representative:

(1) randomly position the quadrats across the habitat, using random numbers to plot co-ordinates for each one.

(2) take samples at regular distances across the habitat.

How to work out how many quadrats are needed:

take random samples from across the habitat and make cumulative frequency table. Plot the cumulative frequency across the quadrat number. The point where the curve levels off tells the minimum number of quadrats to use. (x2)

How to work out how big the quadrats need to be:

count the number of species you find in larger and larger quadrats. Plot the quadrat area of the x axis against the number of species you find in each, on the y axis. Optimal quadrat size at the point where curve starts to level off.

what is the equation that estimates the number of species in a whole habitat?

mean number of individuals of the species in the quadrat /fraction of the total habitat area covered by a quadrat.

What is a transect and what types are there?

Helps look for more systematic changes in vegetation across a habitat.

-Line transect: at regular intervals, make a note of which species touches the tape.

-Belt transect: at regular intervals, place a quadrat next to the line, moving it along the line.

How do you carry out a random sample?

lay out two tape measures on two edges of the study site. Use your calculator or a random number table to generate pairs of numbers. Use these as co-ordinates to place your quadrats.

How do Saproptrophs digest food?

secret enzymes onto dead and waste material, these digest the materials into smaller molecules, which are then absorbed into organisms body. Having been absorbed, the molecules are respired to release energy.

What would happen is bacteria and fungi did not break down dead organisms?

energy and valuable nutrients would remain trapped within the dead organism. By digesting dead and waste material, microbes get a supply of energy and the trapped nutrients are recycled.

What does nitrogen fixation consist of?

Occurs when lightning strikes or through the Haber process.

Nitrogen fixing bacteria live inside root nodules and provide the plant with fixed nitrogen, by using enzyme nitrogen reductase to reduce nitrogen gas to ammonium ions under anaerobic conditions. (proteins absorb oxygen)

What does Nitrification consist of?

Happens when chemoautotrophic bacteria in the soil absorb ammonium ions. They obtain their energy by oxidising ammonium ions to nitrites or by oxidising nitrites to nitrates. (Needs oxygen)

What does denitrification consist of?

Bacteria convert nitrates to nitrogen gas. They use nitrates as a source of oxygen gas for their respiration and produce nitrogen gas and nitrous oxide.

Describe the features of a population growth curve:

lag phase: few individuals, rate of reproduction is low and growth in population size is slow.

Log phase: conditions are good and resources are plentiful, rate of reproduction exceeds morality.

Stationary phase: population size levels out at a carrying capacity. Habitat cannot support a larger population. Population size stays stable.

Relationship between predator and prey:

1. when predator population gets bigger, more prey are eaten.

2. prey pop gets smaller: less food for predator.

3. fewer predators can survive, pop size red.

4. fewer predators; fewer prey eaten: pop size increases.

5.More prey, predator gets bigger- CYCLE.

What is intraspecific competition?

Happens between individuals of the same species. As factors such as food become limiting, individuals compete for them. This slows down population growth and population enters stationary phase.

-If population size drops, competition reduces, population size increases.

-vise versa.

What is inter specific competition?

between individuals of different species and can affect both population size and distribution of species. More over lap between two species niches would result in more intense competition while if they had the same one then one species would be out competed by another- with one becoming extinct.

Why might inter specific competition not lead to extinction?

- could simply result in one population being much smaller than another.

-In the wild, a wide range of variables may act as limiting factors for the growth of different populations. These variables may change on a daily basis, or course of a year.

What is coppicing?

approach to sustaining a sustainable wood supply.

Harvests wood while keeps the tree alive. Involves cutting the trunk of a deciduous tree, close to the ground. New shoots start to grow again and the cycle continues.

What is pollarding?

involves cutting the trunk higher up so that deer do not eat the emerging shoots.

What is rotational coppicing?

Woodland managers divided a wood into sections and cut one section each year until all been cut. By the time want to coppice a section, the new stems have matured and are ready to cut. In some sections, some trees are left to grow larger without being coppiced: these are called standards and used for larger pieces of timber.

Why is rotational coppicing beneficial?

Because it's good for biodiversity. Left unmanaged, woodlands goes through a process of succession, blocking out light to the floor of the woodland so reducing number of species that grow there. By using rotational coppicing, different areas provide different types of habitats, increasing diversity of species.

How to manage large scale timber production?

Involves clear felling all the trees in one area:

Can destroy habitats on larger scales and can reduce soil mineral levels and leave soil susceptible to erosion. Soil may run off into water polluting them. This is because:

-trees remove water from soil and stop soil being washed away.

-maintain soil nutrient levels through the trees' role in the carbon and nitrogen cycles.

What principles does sustainable forestry work on?

- any tree which is harvested is replaced by another tree.

-Forest as a whole must maintain its ecological function, regarding biodiversity, climate mineral and water cycles.

-locals should derive benefit from the forest.

How do foresters sustain-ably manage woods?

-Control pests and pathogens.

-Only plant particular tree species where they know they will grow well.

-position trees an optimal distance apart.

What is conservation?

involves the maintenance of biodiversity, including diversity between species, genetic diversity within species and maintenance of a variety of habitats and ecosystems.

How does the human population threaten biodiversity.

-Over exploitation of wild populations for food, sport, commerce. Species harvested faster than replenished.

- Habitat disruption and fragmentation as a result of intensive agricultural practices, increased pollution, or widespread building.

-Species introduced may out compete native species.

The ethics of conservation:

Every species has:

value in its own right.

right to survive.

humans have responsibility to look after them.

Economic and social reasons for conservation:

-species provide valuable food source. Genetic diversity in wild strains may be needed in future to breed for disease resistance, etc.

-Natural environment are a source of beneficial resources.

-Natural predators of pests can act as biological control agents.

-Many species have indirect value, some are responsible for polluting crop plants, maintain water quality, protect soil and break down waste products. Ecotourism also depends of maintenance of biodiversity.

What is preservation?

protecting land as unused by humans in their untouched form.

What is a stabilising selection?

Stabilizing selection (not the same thing as negative selection) is a type of natural selection in which genetic diversity decreases and the population mean stabilizes on a particular trait value.

What is an evolutionary force?

There are four forces of evolution: mutation, gene flow, genetic drift, and natural selection. A mutation is a random change in a gene or chromosome that can make for a physical or behavioral difference in an individual.

What is environmental resistance?

Factors in an environment such as predators, competition, climate, and food availability, that keep its various populations from reaching their maximum growth potential.

What is natural selection?

Those organisms best adapted to their environment are more likely to survive and reproduce, to pass on the favourable characteristics to their offspring. In this case, nature is doing the selecting.

What does polyploidy mean?

An organism with more than two sets of chromosomes. Having more than two complete sets of chromosomes. Many plants that are polyploid, such as dandelions, are sterile but can reproduce by apomixis or other asexual means. Other polyploidplants are fertile

Link between variation and selection:

When the environment changes, those that are well adapted will survive and reproduce, passing on their advantageous alleles to their offspring. This is the basis for evolution by natural selection.

What does monogenic mean?

involving or controlled by a single gene.


1. Enzymes break down the cell cytoskeleton.

2. cytoplasm becomes dense, organelles tightly packed.

3. cell surface membrane changes and blebs form.

4. chromatin condenses and nuclear envelope breaks. DNA breaks to fragments.

5. Cell breaks into vesicles that are taken up by phagocytosis. Cellular debris is disposed of and doesn't damage cells.

Why is it important that apoptosis is balanced?

too much leads to formation of tumours.

too little leads to cell loss and degeneration.

What is an operon?

A length of DNA, made up of structural genes and control sites. The structural genes code for proteins, such as enzymes. The control sites are the operator region and a promoter region. The operator and promoter are both genes as they are lengths of DNA but do not code for polypeptides.

What is the difference between DNA mutations and Chromosome mutations?

DNA mutations involve changes to genes due to changes in nucleotide base sequences but Chromosome mutations involve changes to parts of a whole chromosome.

What is the difference between mutations which occur during mitosis and those that occur during meiosis?

Mutations associated with mitosis are somatic mutations and are not passed on to offspring but may contribute to ageing process or to cancer. Mutations associated with meiosis and gamete formation can be inherited.

What is transfer RNA?

made in the nucleus and passes to the cytoplasm. Lengths of RNA that fold into hairpin shape and have three exposed bases at one end where an amino acid can bind. At the other end are three unpaired nucleotide bases known as anti codons- can bind temporarily to its complementary codon.

What is translation?

the assembly of polypeptides at ribosomes.

What is transcription?

creation of a single stranded mRNA copy of the DNA coding strand.

The genetic code:

-A triplet codon codes for an amino acid.

-Its a degenerate code- all but methionine have more than one code.

-some codes correspond 'stop'- an end to polypeptide chain.

-Widespread but not universal.

What is vegetative propaganda?

production of structures in an organism that can grow into new individual organisms. These offspring contain the same genetic information and so are clones of the parent.

What are the two main methods for vegetative propaganda?

-Cuttings: a section of the stem is cut between leaf nodes. The cut end of the stem is treated with hormones to encourage root growth and is planted to produce a clone.

-Grafting: shoot section of a wooded plant is joined to an already growing root and stem. The graft grows and is genetically identical to the parent plant.

What is tissue culture?

A more modern method of artificial propaganda.

Refers to the separation of cells of any tissue type and their growth in a nutrient medium. In plants, the undifferentiated callus tissue is grown in nutrient medium containing plant hormones that stimulate development.

What are some of the uses of microorganisms in biotechnology?

- grow rapidly in favourable conditions, with a generation time as low as 30 minutes.

-often produce proteins or chemicals that can be harvested.

-can be genetically engineered to produce specific products.

-grow well at relatively low temperature.

-can be grown anywhere in world and are not dependant on climate.

-can generate products of a more pure form.

-can often be grown using nutrient materials that would often be useless or otherwise toxic.