Biology A2 Flashcards
Which two factors affect genetic variation in populations? and how?
genetic drift and natural selection. Genetic drift occurs in small populations. Natural selection occurs to enhance the survival and fitness of offspring
What is genotype?
the genetic constitution of an organism
What is phenotype?
The expression of the genetic constitution of an organism and its interaction with the environment
What test is used to compare observed with expected ratios?
chi-squared
What is a population?
a group of organisms of the same species occupying a particular space at a particular time that could potentially interbreed
What is the Hardy-Weinberg equation?
p^2+2pq+q^2=1
What is the primary source of genetic variation? Name another source.
Mutation. Random fertilisation of gametes
What leads to differential survival and reproduction (i.e. natural selection)?
predation, disease and competition
What is a gene pool?
the complete range of alleles present in a population, how often the allele occurs is the allele frequency
What is stabilising selection?
Where individuals with alleles for characteristics toward the mid-range are more likely to survive and reproduce, it occurs when the environment is not changing and reduces the number of possible phenotypes, narrows the bell curve.
What is directional selection?
Where individuals with alleles for a single extreme phenotype are more likely to survive and reproduce, this could be in response to an environmental change. Bell curve moves towards the left or right.
What is disruptive selection?
Where individuals with extreme phenotypes are more likely to survive and reproduce, it is the opposite of stabilising selection because characteristics towards the mid range are lost. This occurs when the environment favours more than one phenotype.
What is speciation?
The development of a new species from an existing one.
When does speciation occur?
When populations become reproductively isolated so the allele frquency changes in the phenotype so they can no longer interbreed to produce fertile offspring.
What causes reproductive isolation?
A physical barrier - allopatric
Or random mutation which prevents interbreeding - sympatric
Describe the process of allopatric speciation
geographical isolation
separate gene pools
differential selection
allele frequencies change as mutations will occur independently in each population
Over time they become so different that they cannot interbreed
Describe the process of sympatric speciation.
Not geographically isolated
reproductive isolation due to mutation
gene pools kept separate
changes in allele frequency
cannot interbreed to produce fertile offspring.
What is genetic drift?
When chance dictates which alleles are passed on rather than environmental factors
Describe the process of genetic drift.
Individuals within a population show variation in their genotypes
By chance the allele for one genotypes is passed on to more offspring than others so the allele frequency of that allele increases
If by chance the same allele is passed on again and again it can lead to evolution as the allele becomes more common in the population
When is genetic drift more likely?
small populations
Why do individuals within a population of a species show variation?
Differents alleles
Mutations may occur
Variation in the environment like food or climate.
Why is genetic drift only important in small popualtions?
Chance has a greater influence whilst in larger populations chance factors would even out across the whole population
How does speciation lead to greater diversity?
To start with there was one species
Over time the population experienced reproductive isolation and evolved into separate species, the new species then divided again, and this happened over a long period of time.
What is the difference between a population and an ecosystem?
An ecosystem contains non-living components
What is carrying capacity?
The size of the population of a species that an ecosystem can support.
Why may population size vary?
abiotic factors
interactions between organisms: interspecific and intraspecific competition and predations
How can the size of a population be estimated?
Randomly placing quadrates or quadrats along a belt transect for slow-moving, non-motile organisms.
OR mark-release-recapture for motile organisms.
What assumptions are made for the mark-release recapture method?
the marked sample has had enough time and oppourtunity to mix back in with the population
Marking has not affected the individuals chance of survival
There are no changes to the environemnt due to births, deaths or migration
What equation is used to work out population when mark-release-recapture is used?
(number caught 1st x number caught 2nd)/ marked number in second sample
Ecosystems are ?
dynamic - meaning constantly changing
What is succession?
The process by which an ecosystem changes over time.
Describe the process of primary succession.
Pioneer species that cope with harsh conditons grow.
The pioneer species change the abiotic conditons to make the conditions less hostile. Pioneer species may die and decompose to form soil. New species may make the environment less suitable for the pioneer species. At each stage, different plants and animals that are better suited for the environement move in and out compete plants and animals wthat are still there. Eventually, this results in a climax community which is when the ecosystem supports the largest and most complex community of lants and animals it can.
What is a pioneer species?
The first species to colonise the area
What is a climax community?
When the ecosystem is supporting the largest and most complex community of plants and animals
What is secondary succesions?
When land is cleared of plants and animals but soil still remains.
What does the conservation of habitats by humans frequently involve?
Management of succession e.g. mowing a lawn prevents shrubs from growing.
Describe some human conservation methods.
Seed banks
Captive breeding breeding near extincion in controlled environements and reintroducing. HE, reintroducing may lead to diseases being introduced to the natural environment.
Fishing quotas limit the amount of each fish species that a fisherman can fish, reduce the amount that can be fished. HE, limit potential income, some already dead fish are thrown back
Protected areas such as national park restrict urban development.
WHat is homeostasis in animals?
Physiological control systems that maintain the internal environment within certain limits
Why is it important to maintain a stable body temperature and blood pH?
enzyme activity
Why is it important to maintain blood glucose levels?
So there is good availability of respiratory substrates and to maintain the water potential of the blood.
What is the role of negative feedback systems?
restores systems back to their original level
A mechanism that amplifies a change in a way that normal levels change is a …
Positive feedback mechanism
How may blood glucose concentration increase?
After eating food containing carbohydrate
How may blood glucose concentration decrease?
After exercise as more glucose is used in respiration to release energy
What is glycogenesis and what is the liver’s role?
Glycogenesis is when glucose is converted into glycogen. Enzymes in the liver may aid in this process. Insulin works here,
What is glycogenolysis, what is the liver’s role?
Glycogenolysis is when glycogen is broken down into glucose. The livers role is that glucagon binds to specific receptors on cell membranes of liver cells.
What is gluconeogenesis
When non-carbohydrates form glucose.
Describe the action of insulin (3)
insulin attaches to receptors on the surface of target cells
controls the uptake of glucose by regulating the inclusion of channel proteins in the cell surface membrane of target cells.
activates enzymes involves in glycogenesis (glucose to glycogen)
Describe the action of glucagon?
Attaches to receptors in the surface of target calls
activates enzymes involves in glycogenolysis (glycogen to glucose)
activates enzymes involved in gluconeogenesis (glycerol and amino acids into glucose)
Describe the role of adrenaline?
attaches to receptors on the surface of target cells
activates enzymes involved in the conversion of glycogen to glucose (glycogenolysis)
What activates glycogenolysis inside a cell? How?
adrenaline and glucagon bind outside of the cell. By the secondary messenger model as the binding of these hormones activates an enzyme in the cell membrane which then produces a chemical known as a secondary messenger. This secondary messenger activates other enzymes in the cell to bring about a response
Describe how glycogenosis is activated?
Adrenaline and glucose have specific tertiary structures which allow them to bind to complementary receptors
this activates adenylate cyclase (enzyme)
activated adenylate cyclase converts ATP into cyclic AMP (cAMP) which is the secondary messenger.
cAMP activates protein kinase A which is an enzyme
protein kinase A activates a cascade that breaks glycogen into glucose.
How is type 1 diabetes controlled?
injecting insulin
How is type 2 diabetes controlled?
manipulation of diet
How is water potential of the blood monitored?
osmoreceptors in the hypothalamus, when the water potential of blood decreases water will move out of osmoreceptors by osmosis this causes the cell to decrease in volume, this sends a signal to other cells in the hypothalamus which sends a signal to the posterior pituitary gland which causes ADH to be released.
What is the role of the kidneys?
Filter the blood and produce urine, this removes harmful waste products and controls the water potential of the blood
What is the first step of blood filtration?
Ultrafiltration, forms glomerular filtrate as urea, ions, glucose and water pass through the basement membrane to form glomerular filtrate
What is the second step of blood filtration?
Selelctive reabsorbtion in the proximal convoluted tubule of glucose by active transport and facilitated diffusion and active transport. And water by osmosis.
What adaptations does the proximal convoluted tubule have?
Mitochondria, Co-transport proteins, microvilli
What is the third step of blood filtration?
Loop of Henle Counter Current Mechanism, Sodium ions are actively transported out of the ascending limb into the medulla, this causes water to move out of the descending limb. Loss of sodium ions causes the water potential of the filtrate to gradually increase up the ascending limb while the loss of water causes the water potential of the filtrate to increase down the descending limb. This maintains the water potential gradient along the loop of Henle.
What is the fourth step of blood filtration?
glomerular filtrate moves into the distal convoluted tubule and the collecting duct where water is reabsorbed by osmosis depending in the body’s needs.
Where are osmoreceptors found?
Hypothalamus
What do osmoreceptors detect?
decrease or increase of blood water potential
Where is ADH stored?
posterior pituitary gland
What releases ADH into the blood?
posterior pituatary
How does ADH increase water absorption?
increasing the permeability of the distal convoluted tubule and the collecting duct to water.
What kind of feedback system is the control of blood water potential?
negative feedback
What happens when osmoreceptors detect an increase in blood water potential?
reduce simulation of the posterior pituitary so less ADH produced
What happens when blood glucose concentration is too low?
cells cannot respire and will die
What happens when blood glucose concentration is too high?
Water potential of the blood is too low and too much water will move out of cells
What do beta calls in the islets of Langerhans release?
insulin
How does insulin deacrease blood glucose concentration (not in the liver)?
causing vesicles to increases the number of channel proteins on the cell membrane for glucose after binding to complimentary receptors
What happens when insulin binds to complementary receptors on liver cells?
Activates enzymes which simulate glycogenesis which produces glycogen from glucose
Which cells release glucagon?
Alpha cells in the islets of langerhan
What happens when glucagon binds to complementary receptors on liver cells?
activate enzymes that stimulate glycogenolysis
and enzymes that convert glycerol and amino acids into glucose (gluconeogenesis)
How does glucose move into the blood?
facilitated diffusion
Where does adrenaline bind?
complimentary liver cells
What does adrenaline do?
activates enzymes involved in glycogenolysis in the second messenger model
What is the first messenger?
glucagon and adrenaline
What happens when first messengers bind? (2)
Activate adenylate cyclase
which converts ATP into cAMP
What happens to the second messenger?
cAMP binds to protein kinase and activates it to cause glycogenolysis
How does type one diabetes occur?
immune system attacks beta cells so insulin cannot be produced
How is codominance written?
gene then allele on top
What is DNA sequencing?
finding the nucleotide sequence for a gene or the whole genome
Give an example of a genome project
the human genome project 2003
Why is it important to identify the proteome?
to identify antigens for vaccines
Why might it be different to determine the proteome of complex organisms?
non-coding DNA and regulatory genes
What is gel electrophoresis used for?
to seperate DNA, RNA or Proteins
How are different molecules seperated in gel electrophoresis?
DNA and RNA by mass and proteins by mass or charge (determined by R group)
How does gel electrophoresis work?
sample added to well, there is a negative electrode at the start and a positive one at the end with an external power source with agar gel.
the lighter more positive molecules move faster
What is gel electrophoresis used for?
genome sequencing
genetic fingerprinting
What is recombinant DNA?
the combined DNA of two or more organisms
What issues are associated with recombinant DNA?
costs, side effects and ethics
How are DNA fragments prepared in in vivo cloning?
using restriction endonucleases
What is the DNA fragment inserted into?
a plasmid in a vector usually in bacteria
What is the difference between a promotor and terminator region
one stimulates transcription and the other inhibits it as one acts as a binding site and the other a detachment site
What is transformation, what does it require?
when the recombinant plasmid is inserted into the vector, this is easier with calcium ions and heat shock
How do the two conditions help recombinant plasmids enter?
Calcium ions brings it closer to the cell surface membrane
heat shock creates gaps in the cell surface membrane
What is needed for invitro cloning
Nucleotides Taq polymerase Primers and the DNA frangment
What are primers?
short single stranded pieces of DNA which signal where DNA polyermase should add nucelotides
What are the stages of PCR?
Heat to 95 degrees celcius so hydrogen binds between adjecat nucleotides break so DNA strands seperate, the cool to 55 degrees celcius so DNA primaer can anneal increas again to 72 degrees celcius so taq polymerase can join adjacent nucleotides to form the complementary strand
What is an advantage of invitro gene cloning?
faster
what is an advantage of invivo gene cloning?
does not multiply contamination DNA because restriction endonucleases are only complimentary to certain recognition sites
Where are calcium ion stored in muscles?
sarcoplasmic reticulum
Where are calcium ion release from in muscles?
T-tubules
How does muscle contraction occur?
Calcium ions trigger tropomysoin to moce away from actin binding sites
Myosin head attached to binding site on myosin forming an actinomyosin head
ADP and Pi are released from the mysoin head triggering the power stroke (this moved actin towards the M line)
ATP binds to myosin head causing it to detach from the actin
ATP is hydrolysed so mysosin head returns to starting position
