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381 Cards in this Set

  • Front
  • Back

How many pairs of chromosomes do humans have?

23

What kind of coding is DNA coding?

Triplet code/ degenerate code

What is transcription?

The process of turning a gene into a strand of mRNA

Describe the process of DNA transcription

DNA strand unwinds and unzips, H bonds break


Activated free nucleotides line up against complementary base pairs on the template strand


Sugar phosphate backbone forms between free nucleotides using RNA polymerase

What is translation?

The process of translating a strand of mRNA into a polypeptide chain

What happens after an mRNA strand is formed in the nucleus?

Leaves through a nuclear pore


Attaches to a ribosome


Translation begins

What happens when mRNA has left the nucleus?

Attaches to a ribosome- 6 bases at a time are exposed to the large subunit of the ribosome


Process of translation begins

Describe the process of translation

tRNA molecules carry amino acids to the ribosome- the first amino acid is always methionine. The tRNA's UAC anticodon is complementary to the first mRNA codon (AUG).


Using ATP energy and an enzyme, the tRNA molecule hydrogen bonds to the mRNA molecule.


A second tRNA molecule with a different amino acid binds to the second exposed codon with its complementary anticodon.


A peptide bond forms between the two adjacent amino acids using an enzyme in the small ribosome subunit.


The ribosome moves along the mRNA strand and the process continues until it reaches a stop codon

What is a stop codon?

A codon that doesn't code for an amino acid

What is always the first amino acid in a polypeptide chain and what is it's codon?

Methionine, AUG

How are some proteins activated by cAMP?

cAMP alters their 3D shape so that they are a better fit to their complementary molecules

What is an anticodon?

A sequence of 3 RNA bases that are specific to a certain amino acid and complementary to a codon on the mRNA molecule

What enzyme catalyses the formation of peptide bonds in the ribosome?

Peptidal transferase

What is a silent mutation?

A mutation where the bases change but it still codes for the same amino acid

What is a mis-sense mutation?

A mutation where the bases change and the amino acid it codes for is altered

What is a non-sense mutation?

A mutation where the bases change and change it to a stop codon, so it no longer codes for an amino acid

What is a mutation?

A random change to the sequence of bases

What are the two fundamental types of mutation?

DNA mutation


Chromosome mutation

What are the types of chromosome mutation?

Deletion, inversion, translocation

What can cause chromosome mutations?

Tar found in tobacco, UV light, X-Rays, gamma rays

When do mutations occur?

During DNA replication

What is the difference between mutations in meiosis and in mitosis?

Mutations in meiosis are called somatic mutations and can be passed on to offspring


Mutations in mitosis are non-somatic mutations and can't be passed on

What are the types of DNA mutations?

Point mutations, Insertion mutations, Deletion mutations

What can insertion and deletions cause? Explain what it is.

Frameshift


The bases all shift up or down by a certain number, causing the codons all the way along the DNA to be changed

What is sickle cell anemia caused by?

A point mutation on a gene for the beta polypeptide chains in haemoglobin, causing the wrong amino acid to be coded for (mis-sense), valine in the place of glutamic acid

What is sickle cell anaemia?

A disease caused by a genetic mutation that causes the red blood cells to become sticky and clump together, so that they can no longer fit through the narrow blood capillaries

What causes cancer?

Growth-promoting genes called protooncogenes can be changed to oncogenes by a point mutation which stops the gene being able to be turned off. This causes unregulated cell division which leads to a tumour.

What causes Huntington disease?

A stutter in the genetic code- a repeat of three nucleotides.

What is Huntington disease?

A disease caused by a genetic mutation, the symptoms of which manifest later in life and include dementia and loss of motor control

Give 3 examples of diseases caused by genetic mutations

Huntington disease, sickle cell anaemia, cystic fibrosis

What is cystic fibrosis usually caused by?

A deletion of a triplet of base pairs, which deletes one amino acid in a sequence of thousands in the normal polypeptide

Explain how a mutation can be beneficial using the example of skin colour in humans

Dark skin protects from damaging effects of UV light in Africa, and the sun is intense enough to allow them to synthesise enough vitamin D


A mutation causes some humans to have paler skin- these humans would have died in Africa because they would be burnt by the sun and suffer from skin cancer.


However, when humans migrated to colder climates, those with dark skin could not synthesise enough vitamin D and died in childbirth from narrow hips from the deficiency. Those with pale skin could synthesise enough vitamin D and survived more easily.



Why have inuit people not lost their dark skin, despite living in a less bright environment?

They can get a lot of vitamin D from the seal meat and blubber they have in their diet

Why is genetic mutation essential?

Without it, evolution would not be possible

What are structural genes?

Genes which code for protein with specific functions, aided by their structure

What are regulatory proteins?

Proteins that regulate transcription of DNA

Name the components of the lac operon

Regulatory gene (far away along the DNA)


Promoter region


Operator region


Structural gene for beta galactosidase


Structural gene for lactose permease

What does E-Coli usually use to respire? What can it also use?

Glucose, can use lactose using the lac operon

Describe how E-coli can use lactose in respiration

Normally, a repressor protein is bound to the operator region on the lac operon, and this also overhangs and obstructs the promoter region. This stops RNA polymerase binding to the promoter region so the structural proteins aren't synthesised.


When lactose diffuses into E-coli, it binds to another site on the repressor protein and changes its shape so it falls away from the operator region. RNA polymerase can now bind, and beta galactosidase and lactose permease are synthesised. These respectively break down lactose into glucose and galactose, and increase cells' permeability to lactose so more can be broken down.

What are homeobox genes?

Genes that control the development of the body plan of an organism, including where the head and tail go (polarity) and positioning of the organs

In which organisms are homeobox genes found?

ALL of them!

Why should pregnant women avoid too much vitamin A in early pregnancy?

It contains a substance that interferes with the morphogens (substances that control the pattern of tissue development) which can cause birth defects including cranial deformities

What is apoptosis?

Programmed cell death that occurs in multicellular organisms, leading to tidy an controlled cell death

What is necrosis?

An untidy and damaging cell death that occurs after trauma, releasing hydrolytic enzymes

Outline the sequence of events for apoptosis

Enzymes break down the cell cytoskeleton


The cytoplasm becomes dense


The cell surface membrane changes and small blebs form


Chromatin condenses and nuclear envelope breaks


DNA breaks into fragments


Cell breaks into vesicles which are phagocytosed

How is apoptosis controlled?

A range of different types of cell signalling including cytokines, hormones and nitric oxide

How does nitric oxide induce apoptosis?

Makes the inner mitochondrial membrane more permeable to hydrogen ions and dissipating the proton gradient

How is polydactyly caused?

Lack of apoptosis- joints are all joined by skin during limb development, and should be separated by apoptosis before birth, but sometimes this doesn't happen

Describe the events in Prophase I

Chromosomes form bivalents


Homologous chromosomes pair up


Maternal and paternal chromosomes cross over, forming a chiasma

What is a chiasma?

A chromosome with a new combination of alleles, created in crossing over

Describe what happens in Metaphase I

Homologous pairs of chromosomes line up on the equator


There is an independent/random assortment of homologous pairs (maternal/paternal chromosomes could be on either side of the equator)

Describe what happens in metaphase II

Chromosomes line up on the equator


There is an independent/random assortment of chromatids (chiasmata could be on either side of the equator)

Which stages in meiosis cause variation?

Prophase I, metaphase I, metaphase II


Can also be variation caused by chromosome mutation- if they don't split in anaphase II

How is fertilisation random?

Random mating


Random fusing of sex cells

Why are there twice the divisions in meiosis?

The sex cells need to have half as many chromosomes so that they can be used in fertilisation and sexual reproduction, and so that the zygote has a full set of chromosomes

What is an allele?

An alternative version of a gene

What is a phenotype?

An observable characteristic of an organism

What is a genotype?

The particular alleles present within the cells of an organism, for a particular organism, for a particular characteristic

What is a locus?

The specific position on a chromosome, occupied by a specific gene

What is meant by dominant?

An allele that will be expressed in the phenotype whether it occurs in the homozygous or the heterozygous condition

What is meant by recessive?

An allele that will only be expressed in the phenotype if it is in the homozygous condition

What is meant by codominant?

When two alleles are expressed equally in the phenotype

What is sex-linked inheritance?

When genes are on the sex chromosome (X or Y) and so are only inherited if the chromosome is inherited

What is haemophilia?

A sex-linked genetic disease which causes blood to not clot

How can you check the genotype of a phenotype?

Do a test cross with one that has the recessive phenotype

What is epistasis?

When different genes at different loci interact to affect one phenotype. One gene is epistatic (first locus) and suppresses the hypostatic gene (second locus)

How does recessive epistasis work?

The epistatic gene will suppress the hypostatic gene if the allele is in the homozygous recessive genotype. It does this because the homozygous recessive genotype causes a functional protein such as an enzyme inhibitor or a repressor protein

How does dominant epistasis work?

The epistatic gene will suppress the hypostatic gene if the epistatic allele is in the dominant form. It can be hetero or homozygous. The dominant allele will cause a functional protein to be produced which changes the phenotype.

What does a 9:3:4 ratio suggest?

Recessive epistasis
What does a 12:3:1 ratio suggest?
Dominant epistasis

What does a 13:3 ratio suggest?

Dominant epistasis

What does a 9:7 ratio suggest?

Complementary epistasis

How does complementary epistasis work?

The dominant allele for the first gene will cause a functional protein to be produced which will produce an intermediate compound (it might be colourless, or have a pigment). The intermediate compound will be converted into a different pigment if there is also a dominant allele for the second gene. E.G. if the final pigment was purple, the genotype would have to be A_B_
What does the chi squared test test?

The null hypothesis
What is the null hypothesis?
There is no significant difference between the observed and expected numbers, and any difference is due to chance
What is the chi squared test?

A statistical test to find out of the difference between observed categorical data and expected data is small enough to be due to chance

When can the chi squared test be used?

For categorical data


Where there is a strong biological theory that we can use to predict expected values


Large sample size


No zero scores

How do you calculate the degrees of freedom?

Number of categories-1

What is the critical value in a chi squared test?
The level at which we are 95% certain that the result is not due to chance

Compare continuous and discontinuous variation


Continuous has no discrete classes, non-continuous does


Continuous varies between limits, non-continuous has no intermediates


Continuous is plotted as a normal distribution curve, non-continuous is plotted as a bar chart


Continuous is quantitative, non-continuous is qualitative


Continuous alleles have small additive effects, non-continuous different alleles have large effects


Many alleles and genes involved in continuous (polygenic), fewer alleles and one gene in non-continuous

Give examples of continuous variation

Height, weight, fur length
Give examples of discontinuous variation
Eye colour, fur colour, blood group


What is the Hardy Weinberg principle?


A mathematical model to calculate allele frequencies in populations

What assumptions does the Hardy Weinberg principle make?


-The population is very large


-The mating in the population is random


-There is no selective advantage for any genotype


-There is no mutation, migration or genetic drift


What is the equation for finding frequency of genotypes?

p^2 + 2pq + q^2 = 1

What is the equation for finding frequency of alleles?


p + q = 1

What is meant by population?

A group of individuals of the same species that can interbreed

What is a gene pool?

The set of genetic information carried by a population

What can cause a population to become unstable?


Selection pressures, genetic drift, inbreeding

What is a selection pressure?

An environmental factor that gives greater chances of survival to reproductive age to some members of a population

What is genetic drift?

The change in allele frequency in a population, as some alleles pass on to the next generation and some disappear. This causes some phenotypic traits to become rarer or more common

What are the types of isolating mechanisms?


Geographic barriers, such as a river or mountain range


Seasonal (temporal) barriers such as climate change throughout a year


Reproductive mechanisms (incompatible genitals, breeding seasons, courtship behaviours)

What is stabilising selection?
When natural selection keeps things the way they are, because those organisms with mutations don't survive

What is directional selection?
When those organisms with a mutation are better adapted and natural selection causes an increase in the frequency of a phenotype in a population

What is the biological species concept?
A species is a group of similar organisms that can interbreed and produce fertile offspring

What is the phylogenetic species concept?

A species is a group of organisms that have a similar morphology (shape), physiology (biochemistry), embryology (stages of development) and behaviour, and occupy the same ecological niche


Two organisms are members of the same species if the differences in these factors are small enough to just be phenotypic variation within a species

What is a monophyletic group?

A group that contains an ancestral organism and all of its descendent species

What is cladistics?

The hierarchal classification of species, based on their evolutionary ancestry. It uses DNA and RNA sequencing, computer programmes and molecular analysis to classify species

What is a paraphyletic group?

A group that includes the most recent ancestor but not all of its descendants

What is polyploidy? What can it be used for?


A nucleus containing more than one diploid chromosomes


Used to create hybrid species like bread wheat, which is bigger because it has more chromosomes, so bigger nuclei, so bigger cells

What are the advantages of asexual reproduction?

Don't have to find a mate- useful when sexual reproduction fails


Offspring are genetically identical- can survive in a particular environment


Quick method of reproduction

What are the disadvantages of asexual reproduction?

Smaller gene pool


No genetic variation


Evolution is more slow


More susceptible to being wiped out by a disease or change in environment

What are the ways in which vegetables and fruit can reproduce asexually?

Using runners, basal sprouts or bulbs

What are runners in asexual reproduction?

Small growths from the plant with nodes of meristem cells which can grow new shoots and roots

What are basal sprouts in asexual reproduction?

Runners underground that grow outwards from the roots. They have nodes of meristematic tissue which can grow new shoots and roots

How can bulbs form new plants asexually?

They can split and form separate shoots

What is Dutch Elm disease? How does it cause trees to die?

It is a fungal infection that grows in the xylem. When infected, the tree tries to stop the spread of the disease by blocking the xylem with a sticky gum


This stops the movement of water and minerals up the xylem


No water or minerals for the leaves causes them to wilt and turn yellow, then fall off


Without leaves the tree can't photosynthesize so dies.

How is Dutch Elm disease spread?

A beetle which only lives in elm trees burrows into the dead infected trees and picks up fungal spores before flying to a new elm tree (uninfected), burrowing in that and infecting it with the fungal spores

Why is Dutch Elm disease such a big problem?

Elm trees reproduce asexually (not very successful at sexual reproduction) so they are all genetically identical- they are all susceptible to the disease so it spreads very quickly

Describe the process of artificial vegetative propogation

1. Cut the plant into pieces- explants


2. Sterilise the explants using alcohol, bleach or sodium hypochlorite


3. Place the explant on agar (which should contain glucose, amino acids, nitrates and phosphates)


4. The explant will grow into a mass of undifferentiated cells- callus


5. Treat the explant with auxins and cytokinins to encourage the growth of the callus


6. Separate the callus into groups of cells


7. Treat each group separately to produce roots and shoots


8. This will produce plantlets which should be placed in a greenhouse to grow

What are the advantages of artificial vegetative propogation?

Quick process


Can produce many copies of the same plant


--> can repopulate


You can predict results


Can grow lots in a small space


Only need a few cells


Can produce genetically modified plants easily- only need to modify one cell


Can be used for infertile plants



What are the disadvantages of artificial vegetative propogation?

Expensive process- labour intensive


All exactly the same- lack of genetic variation


--> small gene pool


All susceptible to the same diseases or pests


Its easy to become contaminated


Lack of genetic variation means if you repopulate they could all die out again for the same reasons

Describe the steps involved in embryo cell cloning

An embryo from two parents with desired characteristics is produced by IVF


Cells are separated


Cells multiply and divide into identical embryos


Embryos are placed into surrogate mothers


Offspring are clones of eachother

Describe the steps involved in adult cell cloning

A diploid adult cell of the organism to be cloned and an egg cell from another of the same species is taken.


The nucleus of both is removed


The nucleus from the adult cell to be cloned is placed inside the empty egg cell and fused with an electric shock


The cell divides and forms an embryo


The embryo is implanted into a surrogate mother

What are the advantages of animal cloning?

Can clone high value items


Can repopulate rare animals


Can repopulate extinct animals (deextinction)


Can produce a genetically modified organism

What are the disadvantages of animal cloning?

Reduces gene pool


Less genetic diversity


Welfare of animals is endangered because their value is considered more important


Unclear as to what the effects are

What is therapeutic cloning used for?

Cloning cells, tissues and organs for transplants in medicine

What is biotechnology?

Using (micro)organisms to make useful products

What is biotechnology used for?

Producing:


bread


alcohol


cheese/yoghurt


mycoprotein


antibiotics


enzymes/hormones e.g. insulin



Cleaning:


waste water


oil spills

Describe what happens to the graph in the lag phase

The number of microorganisms is just above zero to begin with


Does not increase


Slowly begins to increase towards the end of the lag phase

Explain the shape of the graph in the lag phase

There are a very small number of cells to begin with


Division is slow to begin with because the microorganisms are acclimatizing to their environment and starting to respire and synthesise specific enzymes and replicate DNA


Also in the lag phase the microorganisms are absorbing water to grow

Describe the shape of the graph in the log phase

The number of microorganisms increases rapidly and significantly

Explain the shape of the graph in the log phase

The population is doubling with each generation


There is a plentiful supply of minerals, oxygen, amino acids and glucose


There is lots of space to grow in


The rate of reproduction > the rate of death

Describe the shape of the graph in the stationary phase

The rate of increase slows down and plateaus- the number of microorganisms is constant

Explain the shape of the graph in the stationary phase

The rate of reproduction = the rate of death


Minerals, oxygen, amino acids, glucose and space become limiting factors


Concentration of waste products increases- CO2

Describe the shape of the graph in the death phase

Number of microorganisms decreases, there is a drop in the graph

Explain the shape of the graph in the death phase

Rate of death > rate of reproduction


Essentials for life are used up (if its a closed system)

What does the liquid medium in a fermenter contain?

Water, a carbon source (e.g. glucose, starch, lactose, fructose), nitrates and amino acids

Why is the liquid medium stirred in a fermenter?

So that the nutrients, heat and microorganisms are evenly distributed throughout the liquid

Why is air pumped into a fermenter?

It is needed for respiration

Why is the air pumped into a fermenter sterile?

Otherwise it would contaminate the fermenter with unwanted microorganisms

Why must the temperature in a fermenter be monitored?

To keep it at an optimum temperature for the enzymes, otherwise the enzymes will denature and the bacteria will die

How is the temperature in a fermenter controlled?

Cooling water around the tank- the tank usually gets to hot rather than too cold because respiration is exothermic

Why must the pH in a fermenter be monitored?

The wrong pH could denature enzymes and cause microorganisms to die

How is pH in a fermenter controlled?

Addition of acid or base

What are the two types of fermenters?

Batch and continuous

What is a metabolite?

A substance that is produced as part of the metabolism of an organism

What is a primary metabolite?

A substance which is produced as part of the metabolism of an organism and is directly linked to the organism's growth

What is a secondary metabolite?

A substance which is produced as part of the metabolism of an organism but is not produced in the main growth phase- usually after.

Which is better for primary metabolites- continuous or batch fermenters?

Continuous

Which is more productive- continuous or batch fermenters?

Continuous

Which requires more space- continuous or batch fermenters?

Batch

Which results in a bigger loss if contaminated- continuous or batch fermenters?

Continuous

Which type of fermenter is more complex and less versatile- continuous or batch fermenters?

Continuous

Which has more difficult downstream processing- continuous or batch fermenters?

Batch

Which has less consistent quality of products- continuous or batch fermenters?

Batch

Which is easier to monitor and control conditions- continuous or batch fermenters?

Batch

How are enzymes immobilised by adsorption?

Enzymes are mixed with and bind to an immobilising support with hydrophobic interactions and ionic links

How are enzymes immobilised by covalent bonding?

Enzymes are covalently bonded to a support (an insoluble material like clay) and to each other using a cross linking agent like sepharose

What is leakage with immobilised enzymes?

Enzymes becoming detached from a support

How does entrapment work to immobilise enzymes?

Enzymes are trapped in something like a gel bead or cellulose fibres

Why does entrapment slow down reaction rates?

Substrate molecules need to get through the trapping barrier- active site is less available

How are enzymes immobilised by membrane separation?

Enzymes are physically separated from the substrate mixture by a partially permeable membrane (permeable by substrates and products, not by enzymes)

What are the benefits of immobilising enzymes?

More stable- can use in higher temperatures and wider pH range


Don't have to separate enzyme from the reaction mixture- easier downstream processing- cheaper


Biodegradable and therefore less environmental pollution

What can immobilised enzymes be used for?

Making lactose free milk


Making high fructose corn syrup


For glucose test strips


Detecting pesticides


Capturing carbon

What are the disadvantages of using enzymes in industrial processes?

Highly sensitive to changes in physical and chemical conditions


Easily denatured by a small increase in temperature or change in pH


Mixture must be uncontaminated

Why is immobilised enzyme better than immobilised yeast?

Immobilised yeast- has to pass through two membranes (capsule and yeast cell)


Yeast produces waste materials which can contaminate your products

What is a genome?

All the genetic information of an organism or cell

What is BAC?

A cloning system to replicate DNA samples

What does PCR stand for?

Polymerase chain reaction

What is gel electrophoresis used for?

Separating DNA of different sizes

Describe the process for gel electrophoresis

Start with DNA sample


Treat with a restriction endonuclease enzyme (cut DNA into bits)


Load DNA into wells


Add blue dye to DNA


Switch on electrical current


DNA will move towards positive electrode

Describe the process of the polymerase chain reaction

DNA is mixed with a supply of DNA nucleotides and the enzyme DNA polymerase


Primer molecules are added to allow the process to start


The mixture is heated to 95°C to break the hydrogen bonds in DNA


The temperature is reduced to 55°C to allow the primers to bind


The DNA polymerase can then bind to the sections of DNA with primers attached. The temperature is raised to the optimum temp for DNA polymerase -72°C - which allows DNA polymerase to add free nucleotides. It moves all the way along to form a double stranded DNA molecule

What are the reasons PCR is better than BACs?

Quicker


Can use lower quality DNA like from forensics or fossils


Uses less space as DNA and enzyme is more compact than cells


Less labour intensive


Combines selection and amplification


Safer as no risk of contamination


Uses less equipment

What are the reasons BACs is better than PCR?

Less prone to mutation


Useful when cloning longer piece of DNA


Useful for searching for a new gene


Less expensive as materials are cheap


Less technically complex as conditions aren't critical

What property of DNA allows gel electrophoresis to work?

Negatively charged (due to phosphate)

How can you get a DNA fingerprint from gel electrophoresis?

Use southern blotting

Describe the process of southern blotting

Place nylon or nitrocellulose sheet on the gel


Place paper towels on top


Leave overnight


Will produce a DNA fingerprint

What are DNA probes?

Short, single stranded pieces of DNA which are about 50-80 nucleotides long and are complementary to the section of DNA being analysed

What happens when DNA probes are washed over DNA?

They anneal to complementary sections of DNA

What are the ways in which we can make DNA visible?

Use probes containing radio labelled phosphorus


Use photographic film to record the radio labelled parts of DNA


OR use a fluorescent marker to make it glow in UV light (although UV light damages DNA)

What are the uses of DNA probes?

Identifying genes for genetic engineering


Identifying a gene on different genomes


Presence or absence of diseased alleles

What is automated PCR?

PCR in which the binder causes each base to be a different colour

What is automated PCR used for?

Producing DNA fingerprints of bases in different colours, allowing you to read the DNA sequence

What is the DNA mixed with in automated PCR?

taq polymerase


Free nucleotides


Primers


Free nucleotides with coloured markers

What happens when a coloured nucleotide is added in automated PCR?

The taq polymerase is thrown off and the DNA strand stops growing- resulting in lots of different length strands of DNA

What are the ways in which a gene can be inserted into a recipient cell?

Electroporation


Microinjection


Viral transfer


Ti plasmid


Liposome

Describe the process of genetic engineering

mRNA is obtained after transcription


Gene is synthesised using automated polynucleotide sequencer


DNA probe is used to locate the gene and restriction enzymes


Copy of gene is inserted into a vector


Vector carries gene to recipient cell


Needs to be ensured that recipient expresses the gene through protein synthesis

What is electroporation?

Using a high voltage electric shock to pass something through a cell membrane

How can a liposome be used to pass a gene through a cell membrane?

The DNA is wrapped in lipids so can go through the membrane

How is the insulin gene extracted for use in genetic engineering?

mRNA for insulin is extracted from beta cells in the islets of langerhans in the pancreas. Enzyme reverse transcriptase is used to make a single stranded piece of DNA from the mRNA, then DNA polymerase is used to make double stranded DNA.

Describe the steps involved in putting the insulin gene into an E.Coli cell

Sticky ends are added to the insulin gene


Plasmid is extracted from E. Coli cell


Plasmid is treated with restriction enzymes to produce sticky ends which are complementary to the sticky ends on the Insulin gene


Insulin gene and plasmid are mixed together with DNA ligase to form a recombinant plasmid


This is added to E.coli cell by addition of Ca salts and heat shocking the bacteria to disrupt the membrane to allow the plasmid back in

What is replica plating?

Sterile velvet is used to lift off bacteria and leave an imprint on a new agar dish, so they grow an identical colony in the same position

Why was golden rice developed?

To combat vitamin A deficiency in the developing world

What does vitamin A deficiency lead to?

Blindness

What else do we need to include in our diet to get enough vitamin A?

Lipids- vitamin A is fat soluble so must have lipids to absorb it

Where did scientists get the genes they used for the first golden rice?

Daffodils and Erwina bacteria

Why was the first version of golden rice not very good?

Didn't supply enough vitamin A when consumed

Where do most humans get their vitamin A from?

Meat

Where do vegetarians get their vitamin A from?

Vegetables- beta carotene from veg can be converted to vitamin A

What are the arguments against golden rice?

Greenpeace believes it will lead to a reduction of biodiversity


The human food safety of engineered rice is unknown


The genetically modified rice could breed with wild types and contaminate wild rice populations

Why is Golden rice said to be biofortified?

It contains higher than normal concentrations of a particular nutrient

What is a GMO?

Genetically modified organism- an organism that has undergone genetic engineering

What is a transgenic organism?

An organism that has received an allele of a gene from another organism, often of a different species

What are liposomes?

Small spheres of lipid bilayer containing a functioning allele

What are liposomes capable of doing?

Passing through the bilayer of cells and acting as vectors to carry the allele into the cell

What is SCID?

Severe combined immunodeficiency (leads to complete disfunction of the immune system)

What are the drawbacks of somatic gene therapy?

Any treatment is short lived and and has to be repeated regularly


The cells carrying the gene will not pass on the new allele when they divide


Can't be passed on to children


Difficult to get the allele to work


Difficult to get the gene to the target location

What are the advantages of germline cell therapy?

The functioning allele is passed on when the cell divides


The functioning allele can be passed on to children

What is the major drawback of germline cell gene therapy?

Illegal!!!

What is xenotransplantation?

Transplantation of cell tissues or organs between animals of different species

Why is xenotransplantation being considered?

There is a shortage of organ donors


Other animals' genetics can be altered within the law


Organs can be engineered that will not trigger an immune response

What is xenotransplantation?

Transplantation of cell tissues or organs between animals of different species

Why is xenotransplantation being considered?

There is a shortage of organ donors


Other animals' genetics can be altered within the law


Organs can be engineered that will not trigger an immune response

Why might xenotransplantation of pigs' hearts not be a viable option?

Differences in organ size


The lifespan of pigs is about 15 years, so the heart might need to be replaced


Body temperature of pigs is 2°C above human body temperature


Ethical problems linked to killing animals to harvest their organs


Religious objections to eating pork


Medical concern about disease transfer between animals and humans

Why is human embryo genetic manipulation illegal?

Don't know how far it will go


Don't know long term effects


Risks 'killing a human'

What are the risks associated with using genetically engineered microorganisms?

May escape from containment and transfer genes


Uses antibiotic resistance as markers; these genes could be passed on to other microorganisms, leading to more antibiotic resistance

What are the risks associated with genetically engineering plants?

Genes introduced could pass to wild relatives- leading to less genetic variation and the production of less useful hybrids


Herbicide resistant genes could pass to weeds or unwanted species, forming 'super-weeds'


Modified plants my cause allergies or be toxic in humans


Plants resistant to pathogens could cause pathogens to evolve attack mechanisms more rapidly

What are the risks associated with genetically engineering animals?

Animal welfare issues; genetic manipulation could lead to animal suffering


Strong religious views about animals; cows are sacred to Hindus and pigs are considered unclean by orthodox Jews and Muslims

What are the risks associated with genetically engineering humans?

Mainly in germline cell gene therapy:


-effects of gene transfer are unpredictable-> further defects could be caused in the offspring


-offspring of patients will have had no say in whether their genetic material should have been modified


-concerns that it could be used to 'enhance favourable characteristics' resulting in 'designer babies'

What is a tropism?

A directional growth response in which the direction of the response is determined by the direction of the external stimulus

What are some examples of tropisms in plants?


Phototropism


-shoots grow towards light, roots away


Geotropism


-roots grow towards gravitational pull


Chemotropism


-pollen tubes grow down the style towards chemicals in the ovary


Thigmotropism


-shoots of climbing plants wind around other plants or structures for support

How can hormones travel around a plant?

Active transport


Diffusion


Mass flow in the phloem sap or in xylem vessels

What are the effects of auxins (e.g. IAA) on plants?


Promotes cell elongation


Inhibits the growth of side-shoots


Inhibits leaf abscission (leaf fall)

What is the effect of cytokinins on plants?

Promotes cell division

What is the effect of giberellins on plants?

Promotes seed germination and growth of stems

What are the effects of abscisic acid on plants?

Inhibis seed germination and growth


Causes stomatal closure when the plant is stressed by low water availability

What is the effect of ethene on plants?

Promotes fruit ripening

Where are apical meristems found and what are they for?

The tips or apices of roots and shoots


Responsible for making roots and shoots get longer

Where are lateral bud meristems found and what are they for?

In the buds
They can give rise to side shoots

Where are lateral meristems found and what are they for?

Found in a cylinder near the surface of roots and shoots


Responsible for making roots and shoots get wider

Where are intercalary meristems found and what are they for?

Found between the nodes of the stem


Responsible for the shoot getting longer

With reference to division and auxin, how does a shoot grow?

Cell division occurs in meristematic tissue, closest to the apex of the shoot. Auxins like IAA are produced at the apex and diffuse/ are actively transported to the cells just behind the apex in the zone of elongation and cause the cells to elongate, making the shoot grow

How does auxin make cells elongate?

It increases the stretchiness of the cell wall by promoting the active transport of hydrogen ions by an ATPase enzyme into the cell wall. The low pH is the optimum conditions for the wall loosening enzymes (expansins) to work


Expansins break bonds in cellulose so the walls are less rigid and can expand as the cell takes in water

Describe how plant hormones cause leaf fall (abscission)

Usually auxin inhibits abscission


Leaves get old and auxin production drops


This makes the cells in the abscission zone (the base of the leaf) more sensitive to ethene


The drop in auxin also increases ethene production


Ethene causes an increase in production of cellulase enzyme which digests the walls of the cells in the abscission zone, causing the leaf to fall off

What is the evidence for apical dominance being caused by auxin?

There is a high concentration of auxins in the shoot tip


When the shoot tip is cut off, lateral buds will grow


When a paste containing auxins is applied to the cut shoot, lateral buds did not grow

Why is the evidence for apical dominance being caused by auxin not viable?

The apical dominance could've been caused by something else; it might have been the exposure of the cut shoot to oxygen that caused the lateral buds to grow


While there is an association between auxin concentration and growth, it might not be a cause because there could be a third factor

What is apical dominance?

The growing apical bud at the tip of the shoot inhibits growth of lateral buds further down the shoot

How can auxins be used in taking cuttings?

Dipping the end of a cutting in rooting powder containing auxins before planting it encourages root growth

How can auxins be used in making seedless fruit?

Unpollinated flowers can be treated with auxins which stimulate the growth of the ovary, which triggers automatic production of more auxins in the fruit, which helps it to finish developing

How can auxins be used as herbicides?

They are taken up by the weeds and are transported to all parts of the plant. They then promote shoot growth so much that the stem cannot support itself so it buckles and dies

How can gibberellins be used in fruit production?

Delay ageing in citrus fruit, extending the time fruits can be left unpicked and extending the season the fruit is available in shops


Can be used with cytokinins in apples to elongate apples and improve their shape


Used on grapes to extend the stalks to allow more growth of the fruit

How can gibberellins be used in brewing?

Can be added to barley seeds to speed up the process of stored starch being broken down to maltose

How can gibberellins be used in sugar production?

They can be sprayed on sugar cane to stimulate growth between the nodes, making the stems longer so there is more sugar in each plant

How can gibberellins be used in plant breeding?

They can induce seed formation in young trees allowing them to be bred from a younger stage


They can induce seed formation and flower production in plants in their first year when they usually only do so in their second year

How can inhibiting gibberellin production in plants be useful?

Can keep flowers short and stocky when desired


Can keep stems of crop plants short to stop them growing too long and bending over, which makes them difficult to harvest

How can cytokinins be used in industry?

Can be used to prevent yellowing of lettuce leaves after they've been picked


Can be used in tissue cultures to promote bud and shoot growth

What are the commercial uses of ethene?

Speeding up fruit ripening in apples, tomatoes and citrus fruits


Promoting fruit drop


Promoting female sex expression in cucumbers so that they can't be pollinated (pollination makes cucumbers taste bitter)


Promoting lateral growth in plants, which makes compact flowering stems

How can inhibiting ethene production in plants be useful?

Prevents fruit ripening so fruits can be stored for longer


Can increase the shelf life of cut flowers

Describe the structure of the cerebrum

Divided into two hemispheres, which are joined by the corpus callosum
The outermost layer is called the cerebral cortex and is highly folded


What is the function of the cerebral cortex?

It is in control of the 'higher brain functions'


-conscious thought and emotional responses


-the ability to override some reflexes


-features associated with intelligence, such as reasoning and judgement

What are the areas of the cerebral cortex and what do they do?

Sensory areas receive impulses which come from receptors


Association areas compare input with previous experiences to interpret what it means and deliver an appropriate response


Motor areas send impulses to effectors

What does the cerebellum control?

The coordination of movement and posture


Fine motor control


Remaining balanced and upright


Judging the position of objects and limbs


Feedback on muscle position, tension and fine movements


Coordinating antagonistic muscles in contraction and relaxation

Where does the cerebellum process sensory information from?

The retina


The balance organs in the inner ear


Spindle fibres in muscles which give info about muscle tension


The joints

What is the function of the medulla oblongata?

Controls non-skeletal muscles


(effectively in control of the autonomic nervous system)


Has regulatory centres:


-cardiac centre for regulating heart rate


-respiratory centre for regulating breathing

What is the function of the hypothalamus?

Controls homeostasis


Receives input from temperature receptors and osmoreceptors and causes a response to regulate body temperature and blood water potential


Controls the endocrine system- regulates the pituitary gland

What are grey matter and white matter?

Unmyelinated nerve cells and myelinated axons and dendrons

What do somatic motor neurones do?

Carry impulses from the CNS to the skeletal muscles (voluntary)


What do autonomic motor neurones do?

Carry impulses from the CNS to the cardiac muscle, to smooth muscle in the gut wall and in glands (all involuntary)

How is the autonomic nervous system different to the somatic nervous system?

Most autonomic neurones are non-myelinated, most somatic neurones are myelinated


There are always more than one autonomic neurones connected to an effector- for somatic there is only one


Autonomic motor neurones occur in two types: sympathetic and parasympathetic

What are the features of the parasympathetic nervous system?

Most active in sleep and relaxation


Neurones are linked at a ganglion within the target tissue


-pre-ganglionic neurones vary considerably in length


Acetylcholine is the neurotransmitter between neurone and effector


Effects of action: dec heart rate, pupil constriction, dec ventilation rate, sexual arousal

What are the features of the sympathetic nervous system?

Most active in times of stress


Neurones are linked at a ganglion just outside the spinal cord


-pre-ganglionic neurones are very short


Noradrenaline is the neurotransmitter between neurone and effector

What are the effects of the action of the parasympathetic nervous system?

Decreased heart rate


Pupil constriction


Decreased ventilation rate


Sexual arousal

What are the effects of the action of the sympathetic nervous system?

Increased heart rate


Pupil dilation


Increased ventilation rate


Orgasm

What does the peripheral nervous system consist of?

All the sensory and motor neurones that are outside the central nervous system connecting the receptors and effectors to the CNS

What is the function of cartilage at a synovial joint?

Reduce friction as bones move

What is the function of the synovial membrane at a synovial joint?

Produces synovial fluid

What is the function of the synovial fluid at a synovial joint?

Lubricates the joint

What is the function of the ligament at a joint?

Holds the bones together to prevent dislocation

What is a neuromuscular junction?

A specialised synapse which occurs at the end of a motor neurone where it meets the muscle fibre

What happens at a neuromuscular junction that causes muscle contraction?

Actetylcholine (neurotransmitter) is released and stimulates the contraction of the muscle fibre

What is a motor end plate?

The end of a motor neurone

How can a stronger force be exerted by a muscle?

There are multiple motor neurones stimulating one muscle, so multiple impulses can be sent down multiple neurones, to go to multiple neuromuscular junctions, to contract multiple muscle cells. More contractions of more muscle cells results in a stronger force

Give some examples of where involuntary muscle is found in the body and its use

Walls of the intestine- peristalsis


Iris of the eye- to control the intensity of light entering the eye by contraction and relaxation or circular and radial muscles


Walls of arteries and uterus- contraction narrows diameter of the vessel

Which type of muscle is not striated?

Involuntary

Describe the structure of involuntary (smooth) muscle

Not striated


Spindle-shaped cells


Cells contain bundles of actin and myosin and a single nucleus

Describe the structure of cardiac muscle

Striated


Individual cells connected in rows


Dark areas called intercalated disks which are cell membranes which fuse together in a way that has gaps which allow free diffusion between cells so action potentials can pass through quickly and easily

Describe the structure of voluntary (skeletal) muscle

Cells form fibres of about 100µm in diameter


Multinucleated


Each cell is surrounded by a cell surface membrane called the sarcolemma


Cytoplasm is called the sarcoplasm


Many mitochondria


Lots of sarcoplasmic reticulum


Many myofibrils with thin actin and thick myosin

What is a sarcomere?

The smallest contractile unit of a muscle

What is a cross-bridge?

The attachment formed by a myosin head binding to a binding site on an actin filament

What happens to the widths of the:


1) sarcomere


2) I-band


3) A-band


4) H-zone


during a contraction?

1) decreases (gets smaller)


2) decreases


3) stays the same


4) decreases

What is the I-band?

The section with only thin filament

What is the A-band?

The section of thick filament (the entire length of it)

What is the H-zone?

The section with only thick filament

Describe the structure of the thin filaments in a muscle cell

Two strands, made mostly of F actin, coiled around each other


Each strand is made of G actin subunits


Tropomyosin molecules coil around the F actin to reinforce


A troponin complex with 3 binding polypeptides for actin, tropomyosin and calcium ions is attached to each tropomyosin molecule

Describe the structure of the thick filaments in a muscle cell

Bundles of myosin protein


Each myosin molecule consists of a tail and two protuding heads


The heads of the myosin stick out from opposite ends of the thick filament

Describe the 4 stages in muscle contraction

1. Myosin head groups attach to the surrounding actin filaments, forming a cross-bridge


2. The head group bends, causing the thin filament to be pulled along and so overlap more with the thick filament (the power stroke). ADP and Pi are released


3. The cross-bridge is broken as new ATP attaches to the myosin head


4. The head group moves backwards as the new ATP is hydrolyed to ADP and Pi. It can then restart the process with the thin filament further along

Why do muscles get smaller when they contract?

In contracting muscle several million cross-bridges are continuously being made and broken, causing the thin filaments to slide past the thick filaments and so shorten the sarcomere, which in turn shortens the whole length of the muscle

How do calcium ions trigger muscle contraction?

Normally the binding sites for the myosin head on the actin fibre are covered by the tropomyosin subunits so cross-bridges cannot form and muscle contraction doesn't occur


When an action potential occurs, calcium ions are released into the sarcomeres and diffuse through the sarcoplasm to bind with the troponin molecules


The shape of the troponin is changed which moves the tropomyosin away from the binding sites on the actin, so cross-bridges can form



How can muscle contraction be stopped?

Nervous stimulation stops, and calcium ions are actively transported back into the sarcoplasmic reticulum by carrier proteins on the membrane

What is the role of ATP in the power stroke?

Energy from ATP is required in order to break the cross-bridge connection between the myosin head group and the actin binding site and re-set the myosin head forwards

How is the ATP supply maintained in a contracting muscle cell?

Aerobic respiration in the muscle cell mitochondria (dependent on O2 and glucose supply)


Anaerobic respiration in the muscle cell sarcoplasm (quite quick but leads to lactic acid production)


Transfer from creatine phosphate in the muscle cell sarcoplasm

How can creatine phosphate be used to supply ATP?

The phosphate group from creatine phosphate can be transferred to ADP to form ATP very quickly by the enzyme creatine phosphotransferase

What is the 'fight or flight' response?

The full range of coordinated responses of animals to situations of perceived danger, using the combined nervous and hormonal responses

What is a stressor?

A stimulus that causes the stress response, and causes wear and tear on the body's physical or mental resources

What are the physiological changes in the fight or flight response? (9 things)

-Pupils dilate


-Heart rate and blood pressure increase


-Arterioles to the digestive system and skin are constricted whilst those to the muscle and liver are dilated


-Blood glucose levels increase


-Metabolic rate increases


-Erector pili muscles in skin contract, making hairs stand up


-Ventilation rate and depth increase


-Endorphins are released in the brain


-Sweat production increases

How does the 'fight or flight' response come about?

-The cerebral understanding of a threat activates the hypothalamus


-Stimulates increased activity in the sympathetic nervous system and triggers release of adrenaline from adrenal medulla


-Stimulates release of CRF into pituitary gland, which stimulates release of ACTH from anterior pituitary gland


-Stimulates release of hormones from adrenal cortex, which help the body to resist stressors

What is meant by behaviour?

The responses of an organism to its environment which increases its chances of survival

Compare how genetics and environment affect innate behaviours and learned behaviours

Innate behaviours are genetically determined and passed onto offspring, whereas learned behviours are determined by the genetic make-up of the individual and environmental influences and aren't passed on to offspring (apart from through teaching)

How do experiences affect innate and learned behaviours?

Innate- rigid and inflexible


Learned- can be altered by experience

Compare the variation within innate and learned behaviours

Innate- patterns of behaviour are sterotypical in all members of the species

Learned- considerable variety is shown between members of the species


How are innate behaviours 'unintelligent'?

The organism probably has no sense of the purpose of the behaviour

What is innate behaviour?

Any animal response that occurs without the need for learning


An inherited response that is similar in all members of the same species and is always performed in the same way in response to the same stimulus

Why are innate behaviours more suitable for invertebrates than learned behaviours?

They have very short life spans (little experience gained)


Live solitary lives and do not take care of their offspring (no teaching between generations)

What is an example of an invertebrate showing a reflex response?

Earthworms withdraw underground in response to vibrations on the ground to avoid predators

What is an example of an invertebrate showing a kinesis?

Woodlice will move around rapidly and randomly in response to dry/bright conditions until they are in more suitable conditions (damp and dark) in order to avoid predation

What is a kinesis?

A non-directional orientation behaviour where the rate of movement increases when the organism is in unfavourable conditions

What is a taxis?

A directional orientation response in which the direction of movement is described in relation to the stimulus which triggers the behavioural response

What is learned behaviour?

Animal responses that change or adapt with experience

What kind of animals benefit the most from learned behaviours?

Animals with:


-a longer lifespan and so time to learn


-time after birth with parental care of the young, and so learning from parents


-living for a part of time with other members of the species and so learning from them

Describe habituation

Animals learning to ignore certain stimuli because repeated exposure to the stimulus results in neither a reward nor a punishment e.g. birds learning to ignore scarecrows


Avoids wasting energy in making escape responses to non-harmful stimuli

Describe imprinting

Young animals becoming associated with (imprinting on) another organism (usually the parent) during a sensitive period (usually 36 hours after hatching in goslings). It is important so that they can learn skills from parents

Describe classical conditioning

Two unrelated stimuli are applied to an animal, one a 'normal response' (e.g. salivation in presence of food) and another unrelated (e.g. ringing a bell). After repeated exposure to both stimuli together the animal will eventually respond with the 'normal response' to the unrelated stimulus

Describe operant conditioning

Animals are given punishment or reward to reinforce the performance of a particular operation, resulting in them learning whether or not to perform an action


Famously 'Skinner box' where rats given food pellets for operating a lever

Describe latent (exploratory) learning

Animals exploring new surroundings and retaining information that is not of immediate use but may be essential to staying alive in the future e.g. rabbits exploring their burrows and environment, may help them escape a predator later in life

Describe insight learning

Thinking and using reason to solve a problem or deal with a situation, and learning the solution to the problem once solved. This means when the problem is next encountered, the problem can be solved immediately. E.g. gorillas learning to use crates to get to bananas

What is a hierarchy?

Where individuals in a group have a place in the order of importance within the group, often shown by individuals higher up in the hierarchy having more food or having rights to mate with others

What is social behaviour?

Organisms living together in groups with relatively defined roles for each member of the group

Describe the social behaviour of gorillas

All members of the group groom eachother


Female mother protects the baby gorilla for 2 years, and the baby learns from the mother in this period, and is protected


Juvenile gorillas play together and imitate adults


From 3-6 years the silverback teaches the juvenile gorilla new skills and protects it from other older males in the group


Communication by calls, displays, grunts, facial expressions

What are the advantages of social behaviour in primates?

Females only give birth to one (or very few) infants at a time- maternal care and group protection enhances the survival rate of the young


The young learn through observation of and play with other members of the group


The large brain size slows the maturation of primates- the security of the group enhances the survival of immature young


Knowledge and protection of food sources is shared


Greater ability to detect and deter predators achieved by working together

What are low levels of dopamine linked with?

Parkinson's disease

What are abnormally high levels of dopamine linked with?

Schizophrenia


Compulsive gambling

What is dopamine?

A neurotransmitter and hormone which acts as a precursor molecule for the production of adrenaline and noradrenaline

Why are there so many effects of dopamine?

There are many different dopamine receptors and lots of variation between them


Each of the 5 receptors (DRD1 to DRD5) is coded for by a separate gene

What is DRD4?

One of five genes that code for dopamine receptor molecules

How is DRD4 linked to ADHD?

In a number of studies, a particular variant of DRD4 has been shown to be more frequent in people with ADHD

What is psychosis?

A mental heath condition characterised by an impaired grasp on reality, diminished impulse control and disorder of perception (e.g. hallucinations)

What is a longtudinal study?

An investigation in which the same individuals are studied repeated over a long period of time in order to gather relevant data about progression of the factor under investigation

What is a habitat?

The place where an organism lives

What is a population?

All of the organisms of one species that live in the same place at the same time, and that can breed together

What is a community?

All the of the populations of different species that live in the same place at the same time, and can interact with each other

What are biotic factors?

Living factors that can affect other living things in an ecosystem e.g. food supply, predation, disease

What are abiotic factors?

The effects of the non-living components of an ecosystem- e.g. pH, temperature, soil type

What are decomposers?

Living things that feed on waste material or dead organisms e.g. bacteria, fungi, some animals

What is a niche?

The that each species plays in an ecosystem

What is trophic level?

The level at which an organism feeds in a food chain

What are the ways in which energy is lost at each trophic level in the food chain?

-Carrying out life processes- respiration releases energy from glucose as heat


-Energy remains stored in dead organisms and waste material, which is then only available to decomposers


-Undigestible food ends up as waste

How can the dry mass of a trophic level be measured? Why isn't it? What's the way around it?

All of the organisms are collected and put in an oven at 80°C until all the water has evaporated, then measure the mass. This isn't done in practice because it's very destructive. Instead wet mass is calculated and then dry mass can be calculated from previous data

How can a pyramid of energy be constructed?

Burning the organisms at each trophic level in a calorimeter and working out how much heat energy is released per gram (very destructive)

What are the limitations of a pyramid of energy?

They only take a snapchat of an ecosystem at one moment in time


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

What is productivity?

The rate at which energy passes through each trophic level in a food chain

What is the gross primary productivity?

The rate at which plants convert light energy into chemical energy

What is the net primary productivity?

The rate at which carbohydrate accumulated in the tissue of plants of an ecosystem and is measured in dry organic mass, such as kg ha^-1 yr^-1


How much of the sunlight energy reaching Earth is used for photosynthesis?

Less than 1%

Why is so little of the sunlight energy reaching Earth used for photosynthesis?

Reflected by clouds and the Earth's surface


Used to heat the Earth's atmosphere


Used to evaporate water


Wrong wavelength


Doesn't hit photosynthetic parts of the plant


Passes through the plant

How can primary productivity be improved?

Increase light levels


Irrigrating crops/ breeding drought-resistant crops


Warmer temperature


PLanting crops earlier to provide longer growing season


Crop rotation/ including a nitrogen-fixing crop/ breeding crops that are responsive to high levels of fertiliser


Breeding pest-resistant crops


Spraying crops with fungicides


Spraying weeds with herbicides

How can secondary productivity be improved?

Harvesting animals just before animals to minimise waste of food when the animal stops growing


Treating animals with steroids to make them grow more quickly (illegal in EU)


Selectively breeding breeds with faster growth rates, inc egg production or inc milk production


Treating animals with antibiotics to avoid unnecessary loss of energy to parasites or pathogens


Keeping animals in small enclosures to reduce energy loss from movement

What is succession?

A directional change in a community of organisms over time

Describe the process of succession

Starts from bare rock/sand/silt/lava


Pioneer plants like algae, lichen and sea rocket colonise the area first, stabilising or eroding the area they are growing on (improving the soil)


Larger plants can grow on improved soil


All organisms are growing and dying, increasing humus, water and minerals when they are broken down, improving soil further


Climax community is the final community, usually lower biodiversity because of competition between species

Describe one example of primary succession resulting in a climax community

On a sand dune:


pioneer plants like sea rocket colonise the sand just above the high water mark. These can withstand salt water spray, lack of fresh water and unstable sand


Sand builds up around these plants, forming mini sand dunes, in which dead and decayed plants accumulate nutrients. The mini dune gets bigger and is colonised by sea sandwort and sea couch grass. Underground stems help stabilise the sand


More stability and nutrients mean plants like marram grass start to grow- the marram grass traps sand in its shoots and make the sand dune grow


As the sand dune and nutrients build up, the climax community of bigger plants and legumes colonise the dunes and stabilise the dune

Why are all the stages of succession visible in a sand dune?

Because the sea deposits sand on the beach, the sand nearest to the sea is deposited more recently than the sand further away

How can you measure the distribution of a species?

See whether it is present or absent (using sampling techniques like using quadrats)

How can you measure the abundance of a species?

Estimate or count the number of individuals in that species (using sampling techniques like using quadrats)

What are saprotrophs?

Organisms that feed by secreting enzymes onto dead and waste material, which digests the material into small molecules, which are then absorbed into the organism's body and stored or respired to release energy.

How do ecologists work out how many quadrat samples are needed to properly sample a habitat?

Carry out a pilot study


Take random samples from across the habitat and make a graph of cumulative frequency against quadrat number. The point where the curve levels off is the minimum number of quadrats to use (usually do double)

How can you avoid biasing the sample when sampling with quadrats?

-randomly position the quadrats across the habitat using random numbers to get coordinates for each one


-take samples at regular distances across the habitat, so you sample every part of the habitat to the same extent

How do you use a quadrat and a point frame to estimate percentage cover?

Stand the quadrat firmly on the ground


Lower each needle downwards


Record the species that the tip touches on the way down


The number of needles that touch each species is proportional to the percentage cover of that species

How can ecologists work out how big a quadrat they should use?

Count the number of species you find in larger and larger quadrats


Plot the quadrat area on the X-axis, against the number of species you find in each one on the y-axis


The optimal quadrat size is where the graph starts to level off

How do you use a quadrat and a point frame to estimate percentage cover?

Stand the quadrat firmly on the ground


Lower each needle downwards


Record the species that the tip touches on the way down


The number of needles that touch each species is proportional to the percentage cover of that species

How can ecologists work out how big a quadrat they should use?

Count the number of species you find in larger and larger quadrats


Plot the quadrat area on the X-axis, against the number of species you find in each one on the y-axis


The optimal quadrat size is where the graph starts to level off

How can you use data from quadrats to work out the population size of a species?

Mean number of individuals of the species in each quadrat/fraction of the total habitat area covered by a quadrat

What is a transect?

A line taken across a habitat

What is a transect?

A line taken across a habitat

How can you use a line transect?

Make a note of which species is touching the tape at regular intervals

What is a transect?

A line taken across a habitat

How can you use a line transect?

Make a note of which species is touching the tape at regular intervals

How can you use a belt transect?

Place a quadrat at the line at regular intervals and study each quadrat (interrupted belt transect)


Place a quadrat at the line then move it along the line after looking at each quadrat (continuous belt transect)

At what stages in the nitrogen cycle are bacteria involved?

Ammonification


Nitrogen fixation


Nitrification


Denitrification

When does denitrification occur?

When the bacteria are growing in anaerobic conditions e.g. In waterlogged soils

What happens in denitrification?

Bacteria convert nitrates back into nitrogen gas


The bacteria use nitrates as a source of oxygen for their respiration and produce nitrogen gas and nitrous oxide

What are the bacteria involved in the nitrogen cycle? What are their roles?

Rhizobium live in root nodules of leguminous plants and fix nitrogen


Nitrosomonas obtain energy by oxidising ammonium ions to nitrites


Nitrobacter obtain energy by oxidising nitrites to nitrates

How is the relationship between Rhizobium bacteria and leguminous plants mutualistic?

The Rhizobium fixes nitrogen and provide the plant with organic nitrogen for growth


The plant provides the bacteria with glucose in return

Describe and explain a graph of population growth

At the beginning (lag phase) there are only a few individuals, acclimatising to their habitat, speed of reproduction is low, growth in population slow, graph has a low gradient


In the middle (log phase) resources are plentiful, conditions good, rate of reproduction is high and exceeds mortality, population size increases rapidly and graph steepens


Towards the end, the population size levels out, mortality rate = birth rate, has reached carrying capacity, graph levels off (plateaus)

Describe 'boom and bust' population growth

The population size increases so quickly that it can exceed the carrying capacity of the habitat before the limiting factors start to have an effect


The population then decreases rapidly because there are no longer enough resources for reproduction

What kinds of species is 'boom and bust' population growth characteristic of?

Species with short generation times (like bacteria)


Pioneer species

What is a limiting factor (in populations)?

Factors that limit the growth in population size
Often the factor in shortest supply

What are the limiting factors for population growth?

Availability of food, water, light, oxygen, nesting sites, shelter


Effects of parasites, predators


Competition with other organisms

Describe the pattern in predator and prey population sizes

1. When the predator population gets bigger, more prey are eaten


2. The prey population then gets smaller, leaving less food for the predators


3. With fewer predators, fewer prey are eaten, and population size increases


4. With more prey, the predator population gets bigger, and the cycle starts again

What is intraspecific competition?

Competition between individuals of the same species, for example competition for food.

How does intraspecific competition keep population sizes relatively stable?

If the population size drops, competition reduces and the population size then increases


If the population size increases, competition increases and the population size then drops

What is interspecific competition?

Competition between individuals of different species

Describe the experiment Gause carried out to show interspecific competition

Grew two species of Paramecium bacteria both separately and together. When together, there was competition for food, and Paramecium aurelia obtained food more effectively than Paramecium caudatum, so over time the population of Paramecium caudatum reduced and died out whereas the population of Paramecium aurelia increased until it was the only species remaining

What conclusion did Gause make from his experiment to show interspecific competition?

More overlap between two species niches would result in more intense competition. If two species had exactly the same niche, one would be out-competed by the other and die out




Known as the competitive exclusion principle

What is coppicing?

Cutting a deciduous tree trunk close to the ground to encourage new growth. Once cut, new shoots grow from the cut surface and eventually mature into stems of quite narrow diameter which can be cut regularly

What is pollarding?

Cutting a deciduous tree trunk high up off the ground so that new shoots grow from the cut surface. It is cut higher up so that deer in the area don't graze on the new shoots

What is rotational coppicing?

Woods are divided into sections and one section is cut every year until they've all been cut. By the time they need to coppice the first section again, the new stems are mature enough to be cut

Why is rotational coppicing good for biodiversity?

Stops the process of succession in woodland by opening up the woodland floor to light and increasing the number of species that can grow there. In rotational coppicing, different areas of the woodland have different levels of light so more different species can grow

What are 'standards' in sustainable timber production?

Trees that are left to grow without being coppiced and that are eventually harvested to supply larger pieces of timber

Why is clear-felling bad?

Leads to a massive loss in biodiversity


Causes a loss of stability of the soil because there are no trees to absorb water


The soil might become waterlogged and denitrification occur, no nitrates returned to the soil due to loss of tress, so the soil devolves into sand

What is selective cutting?

Removing only the largest, most valuable trees to result in the habitat being largely unaffected

What needs to be made sure of when replanting?

The trees are the right species for the environment


Disease needs to be monitored and stopped before it spreads


Need to be planted at correct distance from other trees