paper 2 mock specific Flashcards
why is homeostasis important?
your cells need the right conditions in order to function properly including the right conditions for enzyme action
what is homeostasis?
maintaining optimum internal conditions for enzyme action and all cell function
what are three things that are controlled in homeostasis?
body temperature, blood glucose level and your water content
what do automatic control systems in your body do?
regulate your internal environment
what are the two examples of automatic control systems?
nervous and hormonal communication systems
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 is reaction time?
the time it takes to respond to a stimulus - it’s often less than a second
what can reaction time be affected by?
factors such as age, gender or drugs
what are the 8 steps to measuring the effect of caffeine on reaction time?
- the person being tested should sit with their arm resting on the edge of a table (to stop their arm moving up or down)
- hold a ruler vertically between their thumb and forefinger. Make sure that the zero end of the ruler is level with their thumb and finger. Then let go without giving any warning
- the person being tested should try to catch the ruler as quickly as they can - as soon as they see it fall
- reaction time is measured by the number on the ruler where it’s caught. The number should be read from the top of the thumb. The further down the ruler it’s caught (i.e. the higher the number), the slower their reaction time
- repeat the test several times then calculate the mean distance that the ruler fell.
- the person being tested should then have a caffeinated drink (e.g. 300 ml of cola). After ten minutes, repeat steps 1 to 5.
- you need to control any variables to make sure that this is a fair test. For example, you should use the same person to catch the ruler each time, and that person should always use the same hand to catch the ruler. Also the ruler should always be dropped from the same height, and you should make sure that the person being tested has not had any caffeine (or anything else that may affect their reaction time) before the start of the experiment
- too much caffeine can cause unpleasant side-effects, so the person being tested should avoid drinking any more caffeine for the rest of the day
how can reaction time be measured using a computer?
simple computer tests can be used to measure reaction time. For example, the person being tested has to click the mouse (or press a key) as soon as they see a stimulus on the screen, e.g. a box change colour
why can computers give a more precise reaction time?
- because they remove the possibility of human error from the measurement
- computers can record the reaction time in milliseconds, which gives a more accurate measurement
- using a computer removes the possibility that the person can predict when to respond - using the ruler test, the catcher may learn to anticipate the drop by reading the tester’s body language
what are hormones?
chemical molecules released directly into the blood - they are chemical messengers sent in the blood
where are hormones carried to in the blood, and what do they effect?
they are carried in the blood to other parts of the body, but only affect particular cells in particular organs (called target organs)
what do hormones control?
things in organs and cells that need constant adjustment
where are hormones produced and secreted from?
endocrine glands
what do your endocrine glands make up?
your endocrine system
how long do the effects of hormones last?
a long time
name 6 endocrine glands
- the pituitary gland
- ovaries
- testes
- thyroid
- adrenal gland
- the pancreas
what does the pituitary gland do?
it produces many hormones that regulate body conditions. It is sometimes called the ‘master gland’ because these hormones act on other glands, directing them to release hormones that bring about change
what do ovaries produce?
oestrogen, which is involved in the menstrual cycle
what do testes produce? What does this do?
testosterone, which controls puberty and sperm production in males
what does the thyroid gland produce?
thyroxine, which is involved in regulating things like the rate of metabolism, heart rate and temperature
what does the adrenal gland produce? What does this do?
adrenaline, which is used to prepare the body for a ‘fight or flight’ response
what does the pancreas produce?
insulin, which is used to regulate the blood glucose level
what are 3 differences between nerves and hormones
- nerves have a very fast action, whereas hormones have a slower action
- nerves act for a very short time whereas hormones act for a long time
- nerves act on a very precise area, whereas hormones act in a more general way
what happens at puberty (hormone wise)?
at puberty, your body starts releasing sex hormones that trigger secondary sexual characteristics (such as the development of facial hair in men and breasts in women) and cause eggs to mature in women
what is the reproductive hormone in men? where is it produced? what does it do?
the main male reproductive hormone is testosterone. It’s produced by the testes and stimulated sperm production
what is the main reproductive hormone in women? where is it produced? what does it do?
in women, the main reproductive hormone is oestrogen. It’s produced by the ovaries. As well as bringing about physical changes, oestrogen is also involved in the menstrual cycle
how many stages does the menstrual cycle have?
four
what happens in stage 1 of the menstrual cycle?
Day 1 - menstruation starts. The uterus lining breaks down for about 4 days
what happens in stage 2 of the menstrual cycle?
the uterus lining builds up again, from day 4 to day 14, into a thick spongy layer full of blood vessels, ready to receive a fertilised egg
what happens in stage 3 of the menstrual cycle?
an egg develops and is released from the ovary at day 14 - this is called ovulation
what happens in stage 4 of the menstrual cycle?
the wall is then maintained for about 14 days until day 28. If no fertilised egg has landed on the uterus wall by day 28, the spongy lining starts to break down and the whole cycle starts again
what are the 4 hormones that control the menstrual cycle?
- FSH (follicle-stimulating hormone)
- LH (luteinising hormone)
- oestrogen
- progesterone
where is FSH produced?
in the pituitary gland
what does FSH cause/stimulate
it causes an egg to mature in one of the ovaries, in a structure called a follicle. It also stimulates the ovaries to produce oestrogen
where is oestrogen produced?
the ovaries
what does oestrogen cause/stimulate/inhibit?
it causes the lining of the uterus to grow. It also stimulates the release of LH and inhibits release of FSH
where is LH produced?
the pituitary gland
what does LH do?
it stimulates the release of an egg at day 14 (ovulation)
where is progesterone produced?
in the ovaries by the remains of the follicle after ovulation
what does progesterone do?
it maintains the lining of the uterus during the second half of the cycle. When the level of progesterone falls, the lining breaks down. It also inhibits the release of LH and FSH
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 happens if a woman has too low levels of FSH?
their eggs don’t mature, which means that no eggs are released and the woman can’t get pregnant
which hormones can be given to women in a fertility drug? how do they work?
the hormones FSH and LH can be given to women in a fertility drug to stimulate ovulation
what are the cons of fertility drugs?
- it doesn’t always work - some women may have to do it many times, which can be expensive
- too many eggs could be stimulated, resulting in unexpected multiple pregnancies (twins, triplets, etc.)
what does IVF stand for?
in vitro fertilisation
what does IVF involve?
- collecting eggs from the woman’s ovaries and fertilising them in a lab using the man’s sperm
- it can also involve a technique called intra-cytoplasmic sperm injection (ICSI), where the sperm is injected directly into an egg
what is intra-cytoplasmic sperm injection (ICSI)? when is it useful?
it’s a form of IVF where the sperm is injected directly into an egg. It’s useful if the man has a very low sperm count
what are the 4 stages of IVF?
- collecting eggs from the woman’s ovaries and fertilising them in a lab using the man’s sperm
- The fertilised eggs are then grown into embryos in a laboratory incubator
- once the embryos are tiny balls of cells, one or two of them are transferred to the woman’s uterus to improve the chance of pregnancy
- FSH and LH are given before egg collection to stimulate several eggs to mature (so more than one egg can be collected)
what are the cons of IVF?
- multiple births can happen if more than one embryo grows into a baby - these are risky for the mother and babies (there’s a higher risk of miscarriage, stillbirth…)
- the success rate of IVF is low - the average success rate in the UK is about 26%. This makes the process incredibly stressful and oftwn upsetting, especially if it ends in multiple failures
- as well as being emotionally stressful, the process is also physically stressful for the woman. Some women have a strong reaction to the hormones - e.g. abdominal pain, vomiting, dehydration
how have advances in microscopic techniques helped to improve the techniques (and therefore success rate) of IVF?
specialised micro-tools have been developed to use on the eggs and sperm under the microscope. They’re also used to remove single cells from the embryo for genetic testing. More recently, the development of time-lapse imaging (using a microscope and camera built into the incubator) means that the growth of the embryos can be continuously monitored to help identify those that are more likely to result in a successful pregnancy
why are some people against IVF?
- the process of IVF often results in unused embryos that are eventually destroyed. Because of this, some people think it is unethical because each embryo is a potential human life
- the genetic testing of embryos before implantation also raises ethical issues as some people think it could lead to the selection of preferred characteristics, such as gender or eye colour
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 process are gametes produced by?
meiosis
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
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
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
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
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
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
what type of data do scientists analyse to work out evolutionary relationships for extinct organisms?
they use information from the fossil record
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
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 resistant 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 are 2 ways to study the distribution of an organism?
- measuring how common an organism is in two sample areas (e.g. using quadrats) and compare them
- study how the distribution changes across an area, e.g. by placing quadrats along a transect
what type of data do quadrats give about the distribution of organisms?
quantative data (numbers)
what is a quadrat?
a square frame enclosing a known area, e.g. 1 m^2
how would you use quadrats to compare how common an organism is in two sample areas (e.g. shady and sunny spots in a playing field)
- place a 1m^2 quadrat on the ground at a random point within the first sample area. E.g. divide the area into a grid and use a random number generator to pick coordinates
- count all the organisms within the quadrat
- repeat steps 1 and 2 as many times as you can
- work out the mean number of organisms per quadrat within the first sample area
- repeat steps 1 to 4 in the second sample area
- finally compare the two means.
what does “abundance” mean?
the population size of an organism
how can you work out the population size of an organism in one area?
- work out the mean number of organisms per m^2
2. multiply the mean by the total area (in m^2) of the habitat
what can we use transects for?
to help find out how organisms (like plants) are distributed across an area - e.g. if an organism becomes more or less common as you move from a hedge towards the middle of a field
how can we use transects to help find out how organisms (like plants) are distributed across an area?
- mark out a line in the area you want to study using a tape measure
- then collect data along this line
- you can do this by just counting all the organisms you’re interested in that touch the line
- or, you can collect data by using quadrats. These can be placed next to each other along the line or at intervals, e.g. every 2 m
why might you want to work out the percentage cover of an organism in a quadrat?
if it’s difficult to count all the individual organisms in the quadrat (e.g. if they’re grass) it might be easier to work out the percentage cover
what does it mean to calculate the percentage cover?
estimating the percentage area of the quadrat covered by a particular type of organism, e.g. by counting the number of little squares covered by the organisms
how do you work out the percentage cover of an organism?
- count the number of small squares in a quadrat covered by the organism
- make this into a percentage - divide the number of squares covered by the organism by the total number of squares in the quadrat, and then multiply the result by 100
what is a transect?
a line used to help find out how organisms are distributed across an area
how could you estimate the number of organisms in a quadrat, if they are difficult to count?
by working out the percentage cover
what are the 8 stages of the water cycle?
- energy from the Sun makes water evaporate from the land and sea, turning it into water vapour
- water also evaporates from plants - this is known as transpiration
- the warm water vapour is carried upwards (as warm air rises). when it gets higher up it cools and condenses to form clouds.
- water falls from the clouds as precipitation (usually rain, but sometimes snow or hail) onto land, where it provides fresh water for plants and animals
- some of this water is absorbed by the soil and is taken up by plant roots. This provides plants with fresh water for things like photosynthesis. Some of the water taken up by plants becomes part of the plants’ tissues and is passed along to animals in food chains
- like plants, animals need water for the chemical reactions that happen in their bodies. Animals return water to the soil and atmosphere through excretion (processes that get rid of the waste products of chemical reactions, e.g. sweating, urination and breathing out)
- water that doesn’t get absorbed by the soil will runoff into streams and rivers
- from here, the water then drains back into the sea, before it evaporates all over again
how are elements cycled back to the start of the food chain by decay?
- living things are made of materials they take from the world around them. E.g. plants turn elements like carbon, oxygen, hydrogen and nitrogen from the soil and the air into the complex compounds (carbohydrates, proteins and fats) that make up living organisms. These get passed up the food chain
- these materials are returned to the environment in waste products, or when the organisms die and decay
- materials decay because they’re broken down (digested) by microorganisms. This happens faster in warm, moist, aerobic (oxygen rich) conditions because microorganisms are more active in these conditions
- decay puts the stuff that plants need to grow (e.g. mineral ions) back into the soil
- in a stable community, the materials that are taken out of the soil and used by plants etc. are balanced by those that are put back in. There’s a constant cycle happening
what is the constant cycling of carbon called?
the carbon cycle
what are the 8 stages of the carbon cycle?
- CO2 is removed from the atmosphere by green plants and algae during photosynthesis. The carbon is used to make glucose, which can be turned into carbohydrates, fats and proteins that make up the bodies of the plants and algae
- when plants and algae respire, some carbon is returned to the atmosphere as CO2
- when the plants and algae are eaten by animals, some carbon becomes part of the fats and proteins in their bodies. The carbon then moves up the food chain
- when the animals respire, some carbon is returned to the atmosphere as CO2
- when plants, algae and animals die, other animals (called detritus feeders) and microorganisms feed on their remains. When these organisms respire, CO2 is returned to the atmosphere
- animals also produce waste that is broken down by detritus feeders and microorganisms
- the combustion of wood and fossil fuels releases CO2 back into the air
- so the carbon (and energy) is constantly being cycled - from the air, through food chains (via plants, algae and animals, and detritus feeders and microorganisms) and eventually back out into the air again
what happens to the energy that green plants and algae get from photosynthesis?
it is transferred up the food chain
what is biodiversity?
the variety of different species of organisms on Earth, or within an ecosystem
why is high biodiversity important?
it makes sure that ecosystems are stable because different species depend on each other for things like shelter and food. Different species can also help to maintain the right physical environment for each other (e.g. the acidity of the soil). For the human species to survive, it’s important that a good level of biodiversity is maintained
name three human actions that are reducing biodiversity
- deforestation
- global warming
- waste production
why is the global population rising?
mostly because of modern medicine and farming methods, which have reduced the number of people dying from disease and hunger
why are our actions having a far more widespread effect in modern times?
- our increasing population puts pressure on the environment, as we take resources we need to survive
- but people around the world are also demanding a higher standard of living (and so demand luxuries to make life more comfortable - cars, computers, etc.). So we use more raw materials (e.g. oil to make plastics), but we also use more energy for the manufacturing processes. This all means we’re taking more and more resources from the environment more and more quickly
- unfortunately, many raw materials are being used up quicker than they’re being replaced. So if we carry on like we are, one day we’re going to run out
- we’re also producing more waste
what effect does our increasing population have on waste production? why is this important?
as we make more and more things we produce more and more waste, including waste chemicals. And unless this waste is properly handled, more harmful pollution will be caused. Pollution affects water, land and air and kills plants and animals, reducing biodiversity
how is water affected by our waste?
sewage and toxic chemicals from industry can pollute lakes, rivers and oceans, affecting the plants and animals that rely on them for survival (including humans). And the chemicals used on land (e.g. fertilisers, pesticides and herbicides) can be washed into water
how does our waste pollute the land?
we use toxic chemicals for farming (e.g. pesticides and herbicides). We also bury nuclear waste underground, and we dump a lot of household waste in landfill sites
how does our waste affect the air?
smoke and acidic gases released into the atmosphere can pollute the air, e.g. sulfur dioxide can cause acid rain
