biology paper 2 not being tested Flashcards
what do automatic control systems in your body do?
regulate your internal environment
what are the three main components that make up all your automatic control systems?
cells called receptors, coordination centres, and effectors
what are 3 examples of coordination centres?
brain, spinal cord and pancreas
what are the 4 parts of the nervous system?
- the central nervous system (CNS)
- sensory neurones
- motor neurones
- effectors
what does the central nervous system (CNS) consist of in vertebrates?
the brain and spinal cord only
how is the CNS connected to the body in mammals?
by sensory neurones and motor neurones
what are sensory neurones?
the neurones that carry information as electrical impulses from the receptors to the CNS
what are motor neurones?
the neurones that carry electrical impulses from the CNS to effectors
what are effectors?
all your muscles and glands, which respond to nervous impulses
what are receptors?
the cells that detect stimuli
what are 2 different types of receptors?
taste receptors on the tongue and sound receptors in the ears
give an example of receptors forming part of a large, complex organ
the retina of the eye is covered in light receptor cells
what do effectors do?
respond to nervous impulses and bring about a change
what do muscles do in response to a nervous impulse?
contract
what do glands do in response to a nervous impulse?
secrete hormones
what does the CNS do?
it receives information from the receptors and coordinates a response. The response is carried out by effectors
what is a synapse?
the connection between two neurones
how is the nerve signal transferred across a synapse?
by chemicals which diffuse across the gap. These chemicals then set off a new electrical signal in the next neurone
what are reflexes?
rapid, automatic responses to certain stimuli that don’t involve the conscious part of the brain - they can reduce the chances of being injured
give two examples of reflex actions
- if someone shines a bright light in your eyes, your pupils automatically get smaller so that less light gits into the eye - this stops it getting damaged
- if you get a shock, your body releases the hormone adrenaline automatically - it doesn’t wait for you to decide that you’re shocked
what is a reflex arc?
the passage of information in a reflex (from receptor to effector)
where do the hormones in reflex arcs go through?
the spinal cord or through an unconscious part of the brain
what happens when a stimulus is detected by receptors?
impulses are sent along a sensory neurone to a relay neurone in the CNS. It travels along the relay neurone and across the synapse to the motor neurone. The impulses then travel along the motor neurone to the effector
what are the two hormones that can be used to reduce fertility?
oestrogen and progesterone
why can oestrogen be used as a method of contraception?
it can be used to prevent the release of the egg. This may seem strange (as it naturally stimulates release of eggs), but if oestrogen is taken every day to keep the level of it permanently high, it inhibits the production of FSH, and after a while egg development and production stop and stay stopped
how does progesterone reduce fertility?
it stimulates the production of thick mucus which prevents any sperm getting through and reaching an egg
what is the pill?
an oral contraceptive containing oestrogen and progesterone (known as the combined oral contraceptive pill)
how effective are oral contraceptives?
over 99% effective at preventing pregnancy
what are some downsides to oral contraceptives?
they can cause effects like headaches and nausea and they don’t protect against sexually transmitted diseases
why do some people use a progesterone-only pill?
it has fewer side effects and is just as effective
name 4 methods of contraceptives (other than oral contraceptives) that use hormones
- the contraceptive patch
- the contraceptive implant
- the contraceptive injection
- an intrauterine device (IUD)
what is the contraceptive patch?
a small (5cm x 5 cm) patch containing oestrogen and progestone that’s stuck to the skin
how long does a contraceptive patch last?
each patch lasts 1 week
how does a contraceptive implant work?
it is inserted under the skin of the arm. It releases a continuous amount of progesterone, which stops the ovaries releasing eggs, makes it hard for sperm to swim to the egg, and stops any fertilised egg implanting in the uterus.
how long can a contraceptive implant last for?
three years
what hormone does the contraceptive injection contain?
progesterone
how long does a contraceptive injection last?
2 to 3 months
what is an intrauterine device (IUD)?
a T-shaped device that is inserted into the uterus to kill sperm and prevent implantation of a fertilised egg.
what are the 2 types of IUDs?
plastic IUDs that release progesterone and copper IUDs that prevent the sperm surviving in the uterus
what is DNA and what does it contain?
DNA is the chemical that all of the genetic material in a cell is made up from. it contains coded information - basically all the instructions to put an organism together and make it work
what does your DNA determine?
- what inherited characteristics you have
- what proteins a cell produces (e.g. haemoglobin, keratin) which in turn determines what type of cell it is, e.g. red blood cell, skin cell
where is DNA found?
in the nucleus of animal and plant cells, in really long structures called chromosomes
what shape does DNA have?
a double helix
is DNA a monomer?
no - it’s a polymer
what is a gene?
a gene is a small section of DNA found on a chromosome, and it codes for a particular sequence of amino acids which are put together to make a specific protein
how many different amino acids are used to make proteins?
20
what do genes tell cells?
what order to put the amino acids together
what is a genome?
the entire set of genetic material in an organism
have scientists worked out the complete human genome?
yes, but it took them a long time
give 3 reasons why understanding the human genome is a really important tool for science and medicine
- it allows scientists to identify genes in the genome that are linked to different types of disease
- knowing which genes are linked to inherited diseases could help us to understand them better and could help us to develop effective treatments for them
- scientists can look at genomes to trace the migration of certain populations of people around the world. all modern humans are descended from a common ancestor who lived in africa, but humans can now be found all over the planet. the human genome is mostly identical in all individuals, but as different populations of people migrated away from africa, they gradually developed tiny difference in their genomes. by investigating these differences, scientists can work out when new populations split off in a different direction and what route they took
does sexual reproduction produce genetically identical or different cells?
genetically different cells
what is sexual reproduction?
sexual reproduction is where genetic information from two organisms (a father and a mother) is combined to produce offspring which are genetically different to either parent
in sexual reproduction, by what process do the mother and father produce gametes?
by meiosis
how many chromosomes does each gamete contain in humans?
23
what happens in fertilisation?
the egg (from the mother) and the sperm cell (from the father) fuse together to form a cell with the full number of chromosomes (half from the father, half from the mother)
what does sexual reproduction involve?
sexual reproduction involves the fusion of male and female gametes. because there are two parents, the offspring contain a mixture of their parents genes
why does sexual reproduction result in the offspring inheriting features from both parents?
the offspring has received a mixture of chromosomes from its mum and its dad. this mixture of genetic information produces variation in the offspring.
can plants sexually reproduce?
yes - they also have egg cells, but use pollen instead of sperm
does asexual reproduction produce genetically identical or genetically different cells, and why?
genetically identical - there’s only one parent so the offspring are genetically identical to that parent
what process does asexual reproduction happen by?
mitosis
describe asexual reproduction?
in asexual reproduction there’s only one parent. there’s no fusion of gametes, no mixing of chromosomes and no genetic variation between parent and offspring. the offspring are genetically identical to the parent - they’re clones
what reproduces asexually?
bacteria, some plants and some animals
what happens after two gametes have fused during fertilisation?
the resulting new cell divides by mitosis to make a copy of itself. mitosis repeats many times to produce lots of new cells in an embryo.
what happens to the cells in an embryo as the embryo develops?
they start to differentiate into the different types of specialised cell that make up a whole organism
what is the 23rd pair of chromosomes labelled as, and what do they control?
they are labelled XY or XX, and they’re the two chromosomes that decide your sex
is XY female or male?
is XX female or male?
XY = male XX = female
when are the X and Y chromosomes drawn apart in meiosis?
the first division
how likely is it for a sperm cell to get an X chromosome compared to a Y chromosome?
50% chance of each
what chromosome (X or Y) do all egg cells have?
X
what are genetic diagrams?
models that are used to show all the possible genetic outcomes when you cross together different genes or chromosomes
what are some things that are controlled by a single gene?
mouse fur colour and red-green colour blindness in humans
are most characteristics controlled by one gene or several genes interacting?
several genes interacting
how many alleles do you have for every gene in your body?
two - one on each chromosome in a pair
what does homozygous mean?
having two alleles for a particular gene that are the same
what does heterozygous mean?
having two alleles for a particular gene that are different
what is a dominant allele represented by in genetic diagrams?
a capital letter
what is a recessive allele represented by in a genetic diagram?
a lowercase letter
what is an example of a genetic diagram?
a punnett square
what is a gentoype?
all the genes and alleles an organism has
what is your phenotype?
what characteristics you display
can you be a carrier of a disease caused by a dominant allele?
no
is cystic fibrosis caused by a dominant or recessive allele?
recessive
what is cystic fibrosis?
a genetic disorder of the cell membranes. it results in the body producing a lot of thick sticky mucus in the air passages and in the pancreas
roughly what ratio of people are carriers of cystic fibrosis?
1 in 25 people are carriers
can a child get cystic fibrosis from just one carrier parent?
what about if one parent has the disorder?
no - both parents have to either be carriers or have the disorder themselves
how likely is it for a child to get cystic fibrosis if both parents are carriers?
there’s a 1 in 4 chance
is polydactyly caused by a dominant or recessive allele?
dominant
what is polydactyly?
a genetic disorder where a baby’s born with extra fingers or toes
can polydactyly be inherited if just one parent carries the defective allele?
yes - it is caused by a dominant allele
is it possible to be a carrier of polydactyly?
no
how likely is it for a child to get polydactyly if one parent has one dominant allele?
there’s a 50% chance
what does IVF stand for?
in vitro fertilisation
what happens in IVF?
embryos are fertilised in a laboratory, and then implanted into the mother’s womb
how can genetic disorders be detected in embryos?
using embryonic screening - in IVF, before being implanted, it’s possible to remove a cell from each embryo and analyse its genes. it’s also possible to get DNA from an embryo in the womb and test that for disorders
why is embryonic screening controversial?
because of the decisions it can lead to - for embyos produced by IVF, embyos with ‘bad’ alleles after screening would be destroyed. for embryos in the womb, screening could lead to the decision to terminate the pregnancy
what are three arguments against embryonic screening?
- it implies that people with genetic problems are undesirable - this could increase prejudice
- there may come a point where everyone wants to screen their embryos so they can pick the most ‘desirable’ one, e.g. they want a blue-eyed, blond-haired, intelligent boy
- screening is expensive
what are three arguments for screening?
- it will help to stop people suffering
- treating disorders costs the government (and the taxpayers) a lot of money
- there are laws to stop it going too far. at the moment parents cannot even select the sex of their baby (unless it’s for health reasons)
what can influence your phenotype?
your genotype, and interactions with your environment
what is most variation in phenotype determined by?
a mixture of genetic and environmental factors
what is a mutation?
a rare, random change in an organism’s DNA that can be inherited
do mutations occur continuously or sporadically?
continuously
what can mutations lead to?
mutations mean that the gene is altered, which produces a genetic variant. as the gene codes for the sequence of amino acids that make up a protein, gene mutations sometimes lead to changes in the protein that it codes for
what is a genetic variant?
a different form of a gene
do most genetic variants have a large effect or very little effect on the protein the gene codes for?
most have very little or no effect. some will change it to such a small extent that its function is unaffected. this means that most mutations have no effect on an organism’s phenotype
how can a gene variant only slightly alter an individual’s characteristics?
some characteristics, e.g. eye colour, are controlled by more than one gene. a mutation in one of the genes may change the eye colour a bit, but the difference might not be huge
give an example of an instance when a genetic variant has such a great effect it determines phenotype
cystic fibrosis is caused by a mutation that has a huge effect on phenotype. the gene codes for a protein that controls the movement of salt and water into and out of cells. however, the protein produced by the mutated gene doesn’t work properly, leading to excess mucus production in the lungs and digestive system, which can make it difficult to breathe and digest food
what can happen if the environment changes and a new phenotype caused by a genetic mutation makes an individual more suited to the new environment?
that mutation can become common throughout the species relatively quickly by natural selection
what is the theory of evolution?
all of today’s species have evolved from simple life forms that first started to develop over three billion years ago
what is meant by ‘survival of the fittest’
the organisms (roarganims) with the most suitable characteristics for the environment would be the most successful competitors and would be more (roar) likely to survive. the successful roarganisms that survive are roar likely reproduce and pass on their genes for the characteristics (charoarcteristics) that make them more successful to their offspring. over time beneficially characteristics become more common in the population and the species changes (it evolves)
why wasn’t Darwin’s theory perfect?
because the relevant scientific knowledge wasn’t available at the time, he couldn’t give a good explanation for why new characteristics appeared or exactly how individual organisms passed on beneficial adaptations to their offspring
how did the discovery of genetics support Darwin’s idea?
it provided an explanation of how organisms born with beneficial characteristics can pass them on (i.e. via their genes) and showed that it is genetic variants that give rise to phenotypes that are suited to the environment
what are two things that provided evidence for evolution?
- fossils of different ages (the fossil record) - they allowed us to see how changes in organisms developed slowly over time.
- the discovery of how bacteria are able to evolve to become resistant to antibiotics
what is speciation?
the development of a new species
what is the development of a new species called?
speciation
when does speciation happen?
when populations of the same species change enough to become reproductively isolated - they can’t interbreed to produce fertile offspring
what is extinction?
when no individuals of a species remain
what are 5 reasons species become extinct?
- the environment changes too quickly (e.g. destruction of habitat)
- a new predator kills them all (e.g. humans hunting them)
- a new disease kills them all
- they can’t compete with another (new) species for food
- a catastrophic event happens that kills them all
why are dodos now extinct?
humans hunted them, introduced other animals which ate all their eggs, and destroyed the forest where they lived
what is selective breeding?
when humans artificially select the plants or animals that are going to breed so that the genes for particular characteristics remain in the population
what are organisms selectively bred to develop?
features that are useful or attractive
what are some examples of features that organisms are selectively bred to develop?
- animals that produce more meat or milk
- crops with disease resistance
- dogs with a good, gentle temperament
- decorative plants with big or unusual flowers
what are the 4 steps to the basic process involved in selective breeding?
- from your existing stock, select the ones which have the characteristics you’re after
- breed them with each other
- select the best of the offspring, and breed them together
- continue this process over several generations, and the desirable trait gets stronger and stronger
what can selective breeding be used for in agriculture?
to improve yields
how long have humans been using selective breeding?
thousands of years
how did we get edible crops from wild plants, and domesticated animals like cats and dogs?
selective breeding
what is the main drawback to selective breeding?
a reduction in the gene pool
what is a gene pool?
the number of different alleles in a population
why does selective breeding result in a reduction of the gene pool?
the farmer keeps breeding from the “best” animals or plants, which are all closely related. this is known as inbreeding.
why can inbreeding cause health problems?
because there’s more chance of the organisms inheriting harmful genetic defects when the gene pool is limited
why can selective breeding cause problems when a new disease appears?
there’s not much variation in the population. all the stock are closely related to each other, so if one of them is going to be killed by a new disease, the others are also likely to succumb to it
what is the basic idea of genetic engineering?
to transfer a gene responsible for a desirable characteristic from one organism’s genome into another organism, so that it also has the desired characteristic
what are the 3 steps to genetic engineering?
- a useful gene is isolated (cut) from one organism’s genome using enzymes and is inserted into a vector.
- the vector is usually a virus or a bacterial plasmid depending on the type of organism the gene is being transferred to
- when the vector is introduced to the target organism, the useful gene is inserted into its cell(s)
what are 4 ways scientists have used genetic engineering?
- bacteria have been genetically modified to produce human insulin that can be used to treat diabetes
- genetically modified (GM) crops have had their genes modified, e.g. to improve the size and quality of their fruit, or make them resistant to disease, insects and herbicides (chemicals used to kill weeds)
- sheep have been genetically engineered to produce substances, like drugs, in their milk that can be used to treat human diseases
- scientists are researching genetic modification treatments for inherited diseases caused by faulty genes, e.g. by inserting working genes into people with the disease. this is called gene therapy
what are 3 cons of GM crops?
- some people say that growing GM crops will affect the number of wild flowers (and so the population of insects) that live in and around the crops - reducing farmland biodiversity
- not everyone is convinced that GM crops are safe and some people are concerned that we might not fully understand the effects of eating them on human health
- people worry that transplanted genes may get out into the natural environment. for example, the herbicide resistance gene may be picked up be weeds, creating a new ‘superweed’ variety
what are 3 pros of GM crops
- the characteristics chosen for GM crops can increase the yield, making more food
- people living in developing nations often lack nutrients in their diets. GM crops could be engineered to contain the nutrient that’s missing
- GM crops are already being grown in some places, often without any problems
what are fossils?
the remains of organisms from many thousands of years ago, which are found in rocks. They provide the evidence that organisms lived so long ago.
what can fossils tell us?
fossils can tell us a lot about how much or how little organisms have evolved over time
what are the three ways that fossils can form in rocks
- from gradual replacement by minerals
- from casts and impressions
- from preservation in places where no decay happens
what is the most common way for fossils to be formed?
from gradual replacement by minerals
how are fossils formed from gradual replacement by minerals?
- things like teeth, shells, bones etc., which don’t decay easily, can last a long time when buried
- they’re eventually replaced by minerals as they decay, forming a rock-like substance shaped like the original hard part
- the surrounding sediments also turn to rock, but the fossil stays distinct inside the rock and eventually someone digs it up
how are fossils formed from casts and impressions?
- sometimes, fossils are formed when an organism is buried in a soft material like clay. The clay later hardens around it and the organism decays, leaving a cast of itself. An animal’s burrow or a plant’s roots (rootlet traces) can be preserved as casts
- things like footprints can also be pressed into these materials when soft, leaving an impression when it hardens
name 3 places where fossils can be formed from preservation in places where no decay happens, and explain why no decay can happen there
- in amber and tar pits there’s no oxygen or moisture so decay microbes can’t survive
- in glaciers it’s too cold for decay microbes to work
- peat bogs are too acidic for decay microbes
what is amber?
a clear yellow ‘stone’ made from fossilised resin
describe two hypotheses suggesting how life first came into being
- the first life forms came into existence in a primordial swamp (or under the sea) here on Earth.
- simple organic molecules were brought to Earth on comets - these could have then become more complex organic molecules, and eventually very simple life forms
why can’t the hypotheses for the origin of life on Earth be supported or disproved?
there’s a lack of good, valid evidence:
- many early forms of life were soft-bodied, and soft tissue tends to decay away completely - so the fossil record is incomplete
- fossils that did form millions of years ago may have been destroyed by geological activity, e.g. the movement of tectonic plates may have crushed fossils already formed in the rock
how do antibiotic strains of bacteria form?
like all organisms, bacteria sometimes develop random mutations in their DNA. These can lead to changes in the bacteria’s characteristics, e.g. being less affected by a particular antibiotic. This can lead to antibiotic-resistant strains forming as the gene for antibiotic resistance becomes more common in the population.
do bacteria evolve quickly or slowly? why?
bacteria can evolve quite quickly because they are so rapid at reproducing
how does the population size of antibiotic-resistant bacteria increase/the gene for antibiotic resistance become more common in the population?
through natural selection: for the bacterium, the ability to resist antibiotics is a big advantage. It’s better able to survive, even in a host who’s being treated to get rid of the infection, and so it lives for longer and reproduces many more times. This increases the population size of the antibiotic resistant bacteria.
why are antibiotic-resistant strains a problem for people who become infected with these bacteria?
they aren’t immune to the new strain and there is no effective treatment. This means that the infection easily spreads between people. Sometimes drug companies can come up with a new antibiotic that’s effective, but ‘superbugs’ that are resistant to most known antibiotics are becoming more common
what is MRSA?
a relatively common ‘superbug’ that’s really hard to get rid of. It often affects people in hospitals and can be fatal if it enters their bloodstream
why is the problem of antibiotic resistance getting worse?
because of the overuse and inappropriate use of antibiotics, e.g. doctors prescribing them for non-serious conditions or infections caused by viruses
why is it important that doctors only prescribe antibiotics when they really need to?
the more often antibiotics are used, the bigger the problem of antibiotic resistance becomes
do antibiotics actually cause resistance? why?
no - they don’t CAUSE resistance, they just create a situation where naturally resistant bacteria have an advantage and so increase in numbers
why is it important that you take all the antibiotics a doctor prescribes to you?
taking the full course makes sure that all the bacteria are destroyed, which means that there are none left to mutate and develop into antibiotic-resistant strains
how are antibiotics used in farming? how can this be a problem?
in farming, antibiotics can be given to animals to prevent them becoming ill and to make them grow faster. This can lead to the development of antibiotic-resistant bacteria in the animals which can then spread to humans, e.g. during meat preparation and consumption.
what has increasing concern about the overuse of antibiotics in agriculture led to?
some countries restricting their use
why can’t we just develop new antibiotics that are effective against the resistant strains?
the increase in antibiotic resistance HAS encouraged drug companies to work on developing new antibiotics that are effective against the resistant strains. Unfortunately, the rate of development is slow, which means we’re unlikely to be able to keep up with the demand for new drugs as more antibiotic-resistant strains develop and spread. It’s also a very costly process
what do humans use land for?
things like building, quarrying, farming and dumping waste
what are some examples of when the way we use land has a bad effect on the environment?
deforestation, or the destruction of habitats like peat bogs and other areas of peat
what is deforestation?
the cutting down of forests
what are two reasons for deforestation?
- to clear land for farming (e.g. cattle or rice crops) to provide more food
- to grow crops from which biofuels based on ethanol can be produced
what are 2 problems that deforestation can cause?
- more carbon dioxide in the atmosphere
2. less biodiversity
name 4 reasons deforestation increases CO2 levels in the atmosphere?
- cutting down lots of trees means that the amount of carbon dioxide during
what do humans use land for?
things like building, quarrying, farming and dumping waste
what are some examples of when the way we use land has a bad effect on the environment?
deforestation, or the destruction of habitats like peat bogs and other areas of peat
what is deforestation?
the cutting down of forests
what are two reasons for deforestation?
- to clear land for farming (e.g. cattle or rice crops) to provide more food
- to grow crops from which biofuels based on ethanol can be produced
what are 2 problems that deforestation can cause?
- more carbon dioxide in the atmosphere
2. less biodiversity
name 4 reasons deforestation increases CO2 levels in the atmosphere?
- cutting down lots of trees means that the amount of carbon dioxide during
