unit 5 topics past paper questions Flashcards
explain the advantage of preventing self-pollination [2]
- preventing inbreeding / (increase) GENETIC (variation/diversity) / larger gene pool
- increases chances of survival (of plant species) / selective advantage / adapt to changing environment
a leaf cell contains 20 chromosome. for this plant, state the number of chromosomes found in:
- female gamete
- primary endosperm nucleus
- petal cells
[2]
- 10
- 30
- 20
a plant appeared independently in edinburgh in 1974. originally there were 102 plants in three populations surrounded by parental plants growing on derelict land
- suggest one reason why the species became extinct in edinburgh by 1993 [1]
- outcompeted / not isolated so able to breed with parental plants / loss of habitat or description of
- as maize seeds germinate they produce the enzyme amylase which hydrolyses the starch in the endosperm into maltose
- this can be demonstrated in the laboratory using the following method:
• maize seeds are soaked in water
• seeds are cut in half and placed onto starch agar
• after 24 hours the seeds are removed and iodine solution added to the starch agar
• clear zones around the position of the seeds indicate amylase activity
• boil then cooled seeds are set up as a control - describe how you would develop and refine this practical procedure to determine whether treatment of seeds with a 0.1mmoldm^-3 solution of gibberellic acid increased production of amylase [4]
- soak some seeds in gibberellic acid
- measure clear area / compare size of clear zone
- same type/variety / age / size / mass of seed
- soaked for same time
- same conc / depth starch agar
- same temperature / light
- a group of scientists studied the sand dune ecosystem at Ynyslas, Ceredigion
- they cleared a 10m by 10m section of land in the dunes to expose the soil
- each year, they randomly select 20 1m^2 areas in the study area and identified the different species present
- they noted how many plants of each species were pleasant.
- describe how and explain why the sites are selected at random [3]
- lay out grid
- random number generator to give coordinates
- avoids bias / better representation of the whole area / avoid user generated influence
- many species were found in the cleared 1m^2 area after five years.
- in the first year, the scientists only found four different species in the area
- identify the type of succession that had taken place in the five years of the study and explain why the number of plant species increased [3]
- secondary succession
- colonised prior to being cleared, so (seeds/nutrients) already present
- (secondary succession) changes environment and allows other species to grow
explain why trees are unable to survive in waterlogged soils [2]
- (waterlogged soils/conditions) lack oxygen
- roots unable to respire aerobically / active transport of minerals stops
what is nitrogen used by plants for?
- making amino acids / proteins / DNA / nucleic acids
how do you know if something shows a continuous variation (rather than discontinuous)?
- (bell-shaped curve)
- not discrete / there are intermediates
state the difference between the term mean value and modal value [2]
- mean = average of a group of values
- mode = most (frequent / common) value
- one hundrred years ago the sweet vernal grass was unable to survive on the mine sites but now colonises them.
- use ur understanding of natural selection to explain this observation [4]
- (variation due to) MUTATION
- so the tolerant plants have a selective advantage
- (survive and) reproduce
- pass on alleles (for tolerance to offspring)
- repeated over several generations AND allele frequency for toleration increases
what are some factors for which plants compete for?
- space
- light
- water
- minerals/nutrients
state the function of the tapetum [1]
- (provide (nutrients/nourishes) for (developing cells / pollen / tetrad) / (provides waterproof / outer coat) for pollen grains / protects pollen grain from drying out
explain the appearance of the tetrad [2]
- (pollen mother cell divides by) meiosis
- forming four (haploid) (cells/nuclei)
describe the function of the tube nucleus in the growth of the pollen tube [2]
- (controls / directs) pollen tube
- (controls synthesis of / codes for) (enzymes / hydrolytic enzymes)
describe the role of mitosis and meiosis in the formation of the female gametes [3]
- MEGASPORE (mother cell) undergoes meiosis
- forming four haploid (cells/nuclei)
- one undergoes three mitotic divisions
- one of these (cells/nuclei) becomes the (gamete / oosphere / egg cell / ovum)
explain why fertilisation in plants is referred to as double fertilisation [3]
- first (male gamete / nucleus) (enters embryo sac) fuses with (gamete / oosphere / egg cell / ovum)
- to produce a (DIPLOID / 2N) zygote
- second male gamete fuses with (two) polar nuclei
- to produce (TRIPLOID / 3N) endosperm (nucleus)
define proto-oncogene: [1]
- genes which can mutate to (oncogenes which) cause (uncontrolled cell division / mitosis / cancer)
suggest how cancer cells switch off suppressor genes [3]
- remove acetyl groups (from histones)
- so DNA becomes tightly coiled
- RNA polymerase can’t access (gene/DNA)
- cannot be transcribed
in some humans, tumour suppressor genes can become permanently switched off in ALL CELLS in the body. explain the consequences of such a change [2]
- INCREASED (risk of) cancer / INCREASED (risk of) tumour formation
- passed onto next generation
two alleles:
I I A I I a B I I b I I I I
explain why a cross between AaBb and AaBb in the above could produce a phenotypic ratio of 3:1 [2]
- (genes / alleles) (completely) linked / linkage too close for chiasmata to form between them / no crossing over occurs
- only 2 types of gametes / only AB and ab / no Ab or aB
explain why two individuals, both with genotype AaBb, may not be phenotypically identical for these characteristics [1]
- environmental factors / epigenetics
give one reason why not all of the solar energy falling on the producers is used to form biomass [1]
- reflected / not absorbed (by chloroplast) / (transmitted/passes) through leaf
- wrong wavelength for (photosynthesis/photosystem)
- energy loss due to respiration
explain why ONLY the fertilised ovules develop into kernels. state the advantage to the plant [2]
- no (zygote/fertilisation of egg cell / fertilisation of polar nuclei) means no stored food
- saves plant (resources/energy) / energy used for other processes
- following a forest fire, given time, the forest will regenerate
- give the full name of the biological process involved in forest regeneration [1]
secondary succession
using relevant technical terms, describe and explain the process of forest regeneration [3]
- presence of (soil/spores/seeds)
- pioneer species are the first to return
- (presence alters conditions) allowing other species to grow
- seres/seral stages + the sequential progression of species to form intermediate communities
- climax community + remain (stable / in equilibrium) / final stage of succession
an investigation was carried out to determine the flower structure of a primrose.
the technician requested a materials list prior to the investigation
apart from safety glasses, list three items of apparatus which would be needed to carry out this investigation [1]
- tile or cutting mat
- razer blade / scalpel
- needle / pins
- forceps / tweezers
- scissors
- hand lens / microscope
what is the function of petals? [1]
attracts (insects/pollinators)
what is the function of the anthers? [1]
- (produces / contains) (pollen / male gametes)
what is the function of the sepal / calyx? [1]
- protects (FLOWER when in bud / flower bud)
what is the function of the ovary? [1]
- (site of development of / produces) (egg (cell) / female gamete / embryo) / contains ovules / site of fertilisation
how to tell if pollen from insect pollinated flower or wind?
wind pollinated :
- (smooth / no sculptured)
- is (small/light) easily blown in wind
insect pollinated :
- (rough / sculptured) to attach to insect
- large / heavy
the production of seeds requires sexual reproduction which involves meiosis. one way for a plant grower to produce plants with the same phenotype as the parent plant is to take cuttings.
using your knowledge of cell division explain why the same phenotype would be retained [3]
- asexual reproduction
- genetically identical/same genetic make-up / clone / same DNA
- produced by mitotic cell division / no (meiosis / gametes / crossing over)
in the capture/recapture method, suggest why clipping off one toe from the frogs caught might have affected the estimate of the frog population [1]
- removing part of toe might affect (ability to survive / increase chance of recapture)
describe how the production of amylase was triggered in the barley seeds [4]
- (absorption/entry) of water / imbibition
- gibberellins (released by embryo) / proteins / food reserves) (hydrolysed / mobilised)
- caused release of amino acids from aleurone layer / triggers (transcription/translation/protein synthesis) to release amino acids
- amino acids used to synthesise amylase
what does homogenise mean?
to mash it up
- students carried out an investigation to determine how amylase activity in barley seeds changes during germination
- the method:
- 100 barley seeds were soaked in 50cm³ of distilled water for 24 hours. they were then removed from the water and allowed to germinate
- after one day of germination, 10 of the barley seeds were homogenised in 5 cm³ of distilled water
- three discs of filter paper were soaked in the barley seed extract and placed on the surface of a starch agar plate
- the plate was incubator for 24 hours at 25°C
- the paper discs were removed and the surface of the agar covered with iodine/potassium iodide solution
- the maximum diameter of the clear area around each disc was measured and the mean diameter calculated
- steps 2 to 6 were repeated for barley sees after 2,4,5,8,9 and 10 days of germination
explain why it was important that the same concentration of agar and the same concentration of starch were used in all petri dishes [2]
- (agar) no effect on rate of diffusion / same resistance for amylase to diffuse
- (starch) same number of molecules to digest
- both are controlled variables / so the results are due to amylase activity only
example of table:
left hand column = time after germination (days)
right hand column = maximum diameter of clear area (mm) + clear area 1, clear area 2, clear area 3, mean
REMEMBER TO WRITE ‘MEAN’ FOR DEPENDENT VARIABLE ON GRAPH
explain why range bars are drawn on a graph [2]
- (range of results around / variation of results from) the mean / from maximum to minumum
- (provide information on) (repeatability/reliability/consistency) of the data/overlap of data
NOT ACCURACY
- an image shows barley grains at different stages of germination
- using your understanding of germination in endospermic seeds, suggest a reason for the decrease in amylase activity after eight days of germination [3]
- (leaves/shoot) appears (at 8 days/above soil)
- which are able to photosynthesise
- so plant can produce its own glucose
- therefore less starch needs to be broken down / most starch already broken down
how could you make data more reliable [1]
- repeat
- AND calculate a (mean/average)
design an experiment to investigate the effect of pH on the growth of pollen tubes [4]
- (place pollen grains in range of (pH (solutions) / pH (buffers) / pHs by adding acid or alkali
- measure lengths at a set time / time intervals / every 20minutes
- same species/type of plant
- same concentration of solution
- (same/control) temperature
- same (mass/volume/amount/age) of pollen grains
- light intensity
the photomicrographs below show pollen tubes. photomicrograph A shows a clear zone near the tip, this is a vesicle. electron micrograph B shows organelles present in a region further back from the tip.
describe the roles of the vesicle and the labelled organelles in the passage of the pollen tubes through the style of a flower [4]
- (secretory) vesicles (contains/releases) (digestive/hydrolytic) enzymes / (secretory) vesicle (contains/releases) protease / exocytosis
- (the enzymes digest/hydrolyse) a path through (the tissues) of the style
- mitochondria provide ATP/energy
- (rough ER/ribosomes) synthesize the (enzymes/protein)
- golgi bodies - formation of vesicles (processing/modifying/packaging) protein
describe the part played by mitosis and meiosis in the formation of the male gametes in flowering plants, explaining the biological significance of each type of cell division [5]
- mitosis produces diploid pollen mother cells
- meiosis produces (a tetrad of/four) haploid cells from the pollen mother cell
- mitosis splits (haploid) nucleus into the generative + pollen tube nuclei / generative nucleus into two gametes
- mitosis is significant (because retains chromosome number / daughter (cells/nuclei) are GENETICALLY identical / large number of pollen produced / allows double fertilisation
- meiosis is significant because it halves chromosome number to (create the correct number/ offset doubling) at fertilisation
- meiosis increasing genetic variation
explain what is meant by the term pure breeding [1]
two organisms of the same phenotype only produce offspring of the same phenotype when bred together / homozygous
name the male reproductive organs and explain how their removal would encourage cross-pollination [2]
- stamens/anthers
- pollen has to come from another flower/plant / no pollen available from the same flower / impossible to self fertilate
suggets how mendel could have prevented cross pollination [1]
(enclose/isolate) the flower (in a bag) to prevent transfer of pollen from another flower
what is the test for starch?
- add iodine
- from (yellow/)brown to blue/black
an image shows the structure of a rice grain. what is the structure that would stain blue-black on application of iodine solution [1]
the endosperm
what is the source of gibberellins during germination of a rice grain [1]
the embryo
what is the main source of amino acids for a germinating rice grain [1]
aleurone layer
if talking about water entering say BY OSMOSIS
remember draw range bars unless says otherwise
name a suitable stain for preparing plant cell chromosomes to be viewed in a light microscope [1]
- methylene blue
to view root tip chromosomes in the light microscope using a x40 objective, a root fragment must be squashed. explain why a specimen must be very flat to be viewed in the microscope [1]
- (there are too many layers of cells / it is too thick) to let the light through
in order to measure the lengths of A and B, the microscope must be calibrated. apart from a microscope, name two other pieces of microscopy equipment that are required to carry out the calibration [2]
- eyepiece graticule
- stage micrometer
why/when would you use a log scale?
- when you have a huge/large range of data / values that have a large range
- so convert to log10 so can read data points off graph accurately
do logs have units?
no
- so if asked, write units of original data
- e.g (time / seconds)
hazards/risk factors + how to minimise them:
- rocks/algae slippy (when wet) / uneven rocks = wear suitable footwear
- allergy to shellfish = wear gloves
- holly is sharp and can pierce skin = wear protective gloves/long sleeves
- wasp sting/allergy to holly = wear gloves/long sleeves
- plants have sharp thorns = scratches on skin WHEN CARRYING OUT THIS FIELDWORK = wear gloves/cover skin
- methylene blue is an irritant = can cause irritation to skin when being drawn into/using syringe = cover skin/wear gloves
- needle is sharp + can puncture skin when drawing up liquid
suggest two precautions that should be taken to reduce the risk of harm to individual dogwhelks (snails) or their habitat [1]
- measure dogwhelks on site / do not remove from site / replace where found
- avoid stepping on eggs/adults
- avoid stepping on other living organisms
- replace (rocks/seaweed)
- minimise (litter/pollution)
how to improve accuracy of data?
- measure to 0.1mm rather than nearest mm / smaller divisions on (ruler)
state two ways of improving the strength of evidence in this investigation [2]
- increase size of sample / measure more objects
- take samples from more sites on same beach
- make sure all dogwhelks are (same species/adults)
- measure at same time of year
a photomicrograph of a transverse section of a root and a low power plan to show the distribution of the tissue in the root are shown below.
state why individual xylem vessels are not shown on the plan [1]
- low power plan because no cells shown / tissue layers only
chi squared test conclusion:
- critical value = ____
- reject/accept null hypothesis
- calculated value of x^2 is greater/less than the critical value at 5%/0.05
- differences are/are not due to chance alone
- there is/is not a significant difference between the observed and expected results
how could investigation be more valid?
- have larger sample of leaves
- repeat investigation using another tree/same tree
- ensure leaves all observed within a short time/same time of year
- same age of tree
two environmental factors that should be kept constant?
- air temperature
- soil temperature
- humidity
- soil pH
- mineral/nutrient availability
- water availability/volume of water
- concentration of carbon dioxide
- same altitude
- same distance from sea
state two density dependent factors that may give different results for the population at the two different sites [2]
- air temperature
- soil temperature
- humidity
- soil pH
- mineral/nutrient availability
- water availability/volume of water
- concentration of carbon dioxide
why were measurements taken from leaves of the same age?
- same period of exposure / comparable stages of (development/growth) / same size / different ages may have different thickness of leaves
explain why leaves grown at low light intensities might be thicker than those grown at high light intensity in some species [3]
- (more/larger/multiple layers) of palisade cells
- so more (chloroplasts/chlorophyll/photosystems)/ higher concentration of photosynthetic pigments
- so more light can be absorbed
explain why the structures in image 2 appear to be a different shape from structure a in image 1?
- its cut in a different plane
explain why an electron microscope, rather than a light microscope, is needed to show the internal detail of structure a [1]
- size of structure (is below the level of resolution of the light microscope / too small) / electron microscope able to use a higher magnification
explain why fur and jawbones are found in an owl pellet, but muscle and fat are not [1]
- (fur/bone) are indigestible / (muscle/fat) are (digested/broken down/hydrolysed)
sampling in woodland often involves placing a 0.25m^2 quadrat at randomly chosen coordinates. use the information above and your knowledge of biology to suggest one reason why this is NOT a suitable sampling method for collecting owl pellets [1]
- pellets are not randomly distributed / are only found where owls live
give one reason why the x^2 test is a suitable statistical test for this study [1]
- (categorical / discontinuous) data / compare observed and (predicted/expected) (no of rodents)
explain what is represented by n in this study [1]
- number of species / number of (classes/categories) of data
explain why this type of woodland: ash and coniferous woodland, are described as a biotic factor?
- trees/woodland/plants are living organisms
why should students carry out the experiment between ash and coniferous woodland at the same time of year?
- so the study is not affected by any other factors
e.g temperature/food availability/ day length/ behaviour e.g breeding season
why should students carry out the experiment between ash and coniferous woodland at the same time of day?
- (birds/mammals) may be active at different times of the day
explain the meaning of p=0.05 in this experiment [1]
- the level of significance at which you’re testing the hypothesis
- 5% chance that the difference in results are due to chance
changes in land use and altered farming practices have reduced the amount of nitrate and ammonium ions in many soils. farmers, therefore, often use a high concentration of chemical fertiliser. use your knowledge of the nitrogen cycle to explain why a farmer may use less fertiliser if legumes, such as peas, are grown rather than green cabbage [4]
- legumes have root nodules
- which contain nitrogen fixing bacteria / Rhizobium
- convert (atmospheric) nitrogen to ammonium (ions)
- legumes use ammonium to make (nitrogen containing compounds)
describe a method the group could use to randomise the position of the quadrats [2]
- mark out a grid (using wood/tape measure at right angles)
- use random number generator/dice/table to pick coordinates
what is the functional caecum in a non-ruminant herbivore?
- is the site of cellulose digestion
- (e.g a rabbit, has a high cellulose diet)
explain how rabbits (non-ruminants) are able to digest cellulose without their cells being able to produce the necessary enzyme [1]
- enzyme/cellulase being produced by (bacteria/microorganisms)
reagent for the test of starch?
iodine
reagent for the test of reducing sugars?
benedict’s reagent
with reference to the relative positions of the main organs of the digestive system, and the fact that soft faeces of rabbits contain MORE reducing sugars than hard faeces, explain the reason for the nutritional difference between the two types of faeces [4]
- small intestine comes before the caecum in the digestive system
- (when eating grass) cellulose digestion takes place after absorption so sugar is (not absorbed/passed out in soft faeces)
- when eating soft faeces the food is passing through the alimentary canal a second time
- after eating the soft faeces the (sugar/nutrients) can then be absorbed
explain what is meant by an endangered species [1]
- (a species that is seriously) at risk of EXTINCTION
state why nitrogen and phosphorus are needed for plant growth
- nitrogen = needed for amino acid/protein/nucleotide/chlorophyll/ATP/DNA/RNA/ nucleic acid
- phosphorus = needed for phospholipids/nucleic acid/DNA/RNA
give an example of a biological molecule that contains sulfur [1]
protein/enzyme/cystein
field trials were carried out by a fertiliser company to determine the effect of the four macronutrients on grass growth.
what control would have been used in these field trials?
- only water applied
- no fertiliser added
what are the main advantages of hair-tube surveys to determine population numbers of the two species of squirrel? [2]
- can be certain that the two species do not get mixed up
- doesn’t rely on visual ID/difficult to ID from a distance / DNA/hair is more accurate to identify grey vs red
- can be monitored at any time/ can collect fur when convenient / do not need to stay on-site to monitor
- DNA will give number of individuals/gene pool/genetic diversity / DNA would mean they arent counted twice
- no harm/disturbance to species
describe how you would set up a transect so that the distribution of cone cores could be easily assessed [3]
- at regular intervals place a quadrat/description of belt transect
- count the number of cone CORES in each quadrat / along belt transect
- visit each transect/ quadrat at regular intervals (around every 2-3weeks)
- repeat in different areas
if a human eats a diet low in nutrients, amino acids from muscle tissue can be used as an alternative respiratory substrate. the amino acids, when processed, produce nitrogenous waste.
describe the production of nitrogenous waste and state where this takes place [3]
- removal of amino/amine/NH2 group / deamination
- combining of amino group with carbon dioxide / formation of urea (amino/amine/NH2 group)
what is the name given to the study of the control of gene expression by factors other than changes in the DNA sequence? [1]
epigenetics
the addition of methyl groups to DNA molecules is known to interfere with the ability of the molecules to take part in the formation of mRNA. it has been suggested that methylation of the inserted sequence of bases could be responsible for the range of colours seen in the mice with the genotype A^vy a.
explain how the addition of an increasing number of methyl groups to the inserted sequence of bases results in mice with a range of coat colours [3]
- methylation makes DNA tighter/more tightly wound (around histones)
- the more methylation, the LESS blocking molecule (ABNORMAL RNA) / more regulator protein) is made
- the more the gene is switched on and off
- the more methylation, the (more agouti the colour)
explain how the low levels of nitrates are brought about in these meadows [2]
- anaerobic conditions
- nitrates converted to atmospheric nitrogen
explain fully how the change in agricultural practices has led to the loss of this type of meadow [3]
- use of fertilisers
- ploughing increasing aeration/increasing aerobic/decrease anaerobic conditions
- nitrification increases
- more nutrients in flood water increasing nitrate levels
describe the technique you would use to carry out an assessment of the abundance of two plant species across a moderately trampled footpath [3]
- use of transects AND use of quadrats
- estimate % cover/number/frequency of each species
explain the observation: males with the f allele always suffer Fabry disease but females can have the f allele without suffering.
- females have two X chromosomes/alleles and males only have one
- ONLY females can be carriers/heterozygous / males have no equivalent allele on the Y chromosome
state two assumptions that must be made when using the capture-recapture technique to estimate snail population numbers [2]
- there are few/no births/deaths in the population / population size is constant/unchanged
- there is no immigration/emigration
- the proportion of marked:unmarked individuals in the second sample is the same as the proportion in the population as a whole
- marked individuals from the first sample distribute themselves evenly amongst the rest of the population / have sufficient time to spread out / all snails have an equal chance of being captured and recaptured
- the method of marking is non toxic/doesnt rub off/is lost/ not make them more conspicuous to predation
- organisms are spread evenly within its geographical range
a saltmarsh is an extreme environment for organisms trying to survive.
identify three abiotic factors which cause this to be an extreme environment for plant survival [6]
- high salt content/low water potential - (rooted) plants will have problems getting water/water would leave the plant (roots)
- watterlogging of soil - roots need oxygen for respiration/active uptake of minerals
- high fertiliser run off - eutrophication
state why denitrification is classed as a biotic factor?
- involves denitrifyijg bacteria which are LIVING organisms
identify two factors affecting denitrification [3]
- waterlogging/anaerobic conditions + more denitrification
- temperture affects rate of denitrification (higher in summer/ so more bacterial divisions/higher rate of reaction)
- nitrate levels in mud - higher denitrification in summer as more farming runoff (with use of fertiliser)
describe a practical method which you could carry out on the saltmarsh to investigate the change in vegetation over time [5]
- mark out a PERMANENT/same area each time
- 10m x 10m / transect
- method of sampling - use of quadrats
- reviewed periodically
- all species (identified/counted/frequency) /measure species diversity
- minimise damage to area
species density:
the number of individuals of a given species in a given area
species frequency:
- a measure of the probability of finding a given species with any one placement of a quadrat in a given area
- quick and easy method of assessing biodiversity, but the values depend on the size of the quadrats and values depend on the spatial distribution of the organisms e.g organisms found in clumps may have a high density but a low frequency
species cover:
- a measure of the proportion of ground occupied by a given species
when is preliminary work usually required?
to determine the minimum number of quadrats that need to be used to ensure that all species living in a habitat are sampled
(this involves placing quadrats randomly and recording the cumulative number of species. when there is no further increase in the number of species recorded in the habitat, this indicates the minimum number of quadrats to use
if a species occurs once in every 10 quadrats, what is its frequency?
10%
what is the ACFOR scale?
- an estimate of abundance
A= abundance
C= common
F= frequent
O= occasional
R= rare - this is only semi-quantitative and subjective
to increase the repeatability of your data when using a transect, what would you need to do?
- repeat the study at several points across the same study area
line transect = run a line across area being studied, at evenly spaced points, identity the species of the organism toughing the transect (good method for long distance) BUT only provides information on presence of species not abundance
belt transect = run a transect across the area studied, place a quadrat at even distances along the tape measure and estimate the density, % frequency or % area cover (time consuming unless for short distance) enables you to collect data on abundance
kite diagrams are useful when studying communities of organisms and how they change due to effect of changing environmental factors
mark release recapture:
- in sampling area, capture organisms you find of one species
- mark them in a way that doesnt make them more visible to predators or impede their movement. count how many you have marked and record it
- release the marked organisms and leave them long enough to remix with the population
- return to the sampling area and capture all the organisms of the species you can find. record how many you caught and how many of those are marked
- the calculation is based on the assumption that the marked to unmarked organisms in the second sample are in the same proportion as your first sample was to the whole population
populations of squirrels were surveyed and monitored for 20 years.
consider when the hair samples were collected explain why there was little confidence in this estimate [3]
- too much time left
- immigration/emigration/deaths/births can have occurred
- marked individuals may have been more vulnerable to predators
- population may not have been limited geographically
data on the number of pine trees could be collected using randomly positioned quadrats.
suggest the size of quadrats that would be suitable for collecting data on tree numbers [3]
- 10m x 10m
- most trees are large and so a smaller area would only have part of a tree in it, or only 2
- to get a representative sample
what are the units for GPP?
kJ m^-2 yr^-1
the students used quadrats to estimate the number of plants of the species found on the two sites.
explain the steps the students should have taken to ensure their sampling methods produced representative totals [3]
- use of random number generator
- use many/large enough number of quadrats (to ensure a consistent number of species)
- carry out both sites at the same time of year / repeat investigation at different times of year
name a mathematical value that each team could have calculated to indicate the variability of its results and the aspect of reliability of the experiment that would be assessed by this value. describe how this aspect could have been improved?
- mathematical value =
- aspect of reliability =
- improvement =
- standard deviation/variance
- repeatability
- increase number of repeats
explain why the ecologists worked upstream from the first sample [2]
- uncaught organisms (dislodged from stream bed) would flow downstream
- (working upstream) would prevent more organisms being caught than would be actually present in the sample area
suggest why the quadrats were placed in the middle of each stream [1]
- to minimise effects of banks/ similar flow of water / similar light
identify one other abiotic factor (apart from temperature) which is affected by altitude and explain why this may reduce your confidence in your conclusion [2]
- higher altitudes, lower oxygen levels
- not enough oxygen available for respiration
state what is meant by the term linkage and explain why mendel’s law of independent assortment only applied if the genes are not linked [2]
- linkage = genes present on same chromosome
- (if on same chromosome) (more likely to be segregated together/cannot be segregated independently) / can only segregate independently if on different chromosomes
what is meant by a climax community?
- the final stage of succession
- in which the species composition remains relatively stable
explain why the microscope would need to be recalibrated before calculating actual size when using an objective lens of a different magnification [1]
- eyepiece graticule is a fixed scale but values of 1 epu differ at different magnifications / number of smd per epu will change (at different magnifications / stage micrometers appear to have different sizes at different magnifications
state what is meant by an X linked condition [1]
(carried on) X chromosome
apart from dead tissue, name two other processes carried out by herbivores and carnivores that would also transfer energy to decomposers? [2]
- excretion
- egestion
state two types of organisms which act as decomposers [1]
- bacteria
- fungi
in the uk, most plants die or shed their leaves in the autumn. using your knowledge of the nitrogen cycle, explain why you would expect the nitrogen content of soil to increase during the winter but then decrease during the spring and summer months [4]
- in winter:
- decomposers convert nitrogenous compounds to ammonium ions/carry out ammonification
- nitrifying bacteria / Nitrosomonas / Nitrobacter
- convert ammonium ions into nitrites/nitrates
- in spring/sunmer:
- as more leaves grow (ammonium ions/nitrates) absorbed (from soil/by plants
- to make proteins/amino acids/nucleic acids (in new plant tissue)
pollen from a pure bred plant with glossy leaves was transferred to the stigma of a pure-bred plant with rough striped leaves. al of the F1 generation had glossy green leaves.
give three practical precautions that should be taken to ensure that the offspring produced are only from the desired cross [3]
- (anthers/stamen) removed
- pollen transferred by hand
- recipient flower is isolated / method of isolation e.g in a bag
- the male and female parts are separated
with reference to the results of the cross, explain why the actual ratio of phenotypes obtained was different from the expected ratio [4]
- the genes are (linked/on the same chromosome) / autosomal linkage
- (large number / more) of (non-recombinants)
- (small number/mess) of recombinants
- from crossing over in meiosis 1/prophase I
- between homologous chromosomes
state three factors that are required for the germination of seeds [1]
- water
- oxygen
- suitable temperature
explain why it was important that the seedlings were grown for 10 days before the total leaf surface area was recorded [1]
- leaves grow large enough to measure / give time for leaves to develop/grow
explain why the method of weighing 1cm^2 of leaf, weigh all leaves then divide mass of leaves by mass of 1cm^2, a more accurate estimate of the total leaf surface area than drawing around each leaf on a piece of graph paper and then estimating the area covered by the leaf [2]
- leaves are irregular/not flat so difficult to draw around/estimate area
- leaves may not be flat so drawing around not representative of actual area
- counting squares (needs judgement so) open to human error
- (weighing leaf gives) (quantitative data)
what stage of nitorgen cycle only takes place in aerobic conditions?
nitrification
