How DNA profiles are made from a small sample of DNA:1. Get DNA
sample from tissue, blood or semen as it will be easy to collect.2.
DNA must be cut into fragments using restriction endonucleases.3.
DNA fragments will underdo PCR alongside free nucleotides (Increase
temperature to 90'C to break the hydrogen bonds between DNA
strands, decrease temperature to 55'C to allow annealing of primers
to the DNA strands, Increase temperature to 75'C as this is the
optimum temperature for DNA polymerase to work as it will bind the
free nucleotides to the DNA fragments.4. This process must be
repeated several times to get many copies of DNA (many or multiple
are interchangeable here).5. Put the DNA fragments into agarose
wells.6. Apply a potential difference from the negative electrode,
causing the negatively charged DNA fragments to move towards the
positive electrode. (Longer fragments of DNA will travel a shorter
distance and shorter fragments of DNA will travel a longer
distance).7. This will produce a DNA profile with a series of bands
which may differ in size and width.8. Can be used to compare
different peoples DNA and see if there is a genetic relationship
between the two.
How DNA profiles of two species are compared: Compare total
number of bands, their position and width.
How phagocytosis and lysosome action leads to APC by
macrophages: Bacteria taken in my macrophage. Phagosome (vacuole
formed around a particle absorbed by phagocytosis) fuses with
lysosome. Enzyme e.g. protease from lysosome breaks down bacteria.
Part of the bacteria is presented on macrophages cell surface
membrane.
How macrophages present antigens to T helper cells: Macrophage
binds to T helper cell as the MHC on the macrophage binds to the
CD4 receptor on the T helper cell.
How evolutionary race between some bacteria affects antigen
presentation to T helper cells: A mutation has occurred in the DNA
of the bacteria. This has caused a change in the antigen of the
bacteria. The memory T helper cells wont recognise the new antigen.
Thus a new primary immune response is needed e.g. new antigen needs
to be presented to the T helper cell to activate another population
of T helper cells.
Two greenhouse gases are: Carbon dioxide. Methane.
First generation biofuels could reduce global warming instead of
petrol/diesel because: Burning fossil fuels releases carbon dioxide
which is a greenhouse gas. Carbon dioxide is taken in for
photosynthesis for carbon fixation during the production of plants
for biofuels thus there is no net change of carbon dioxide in the
atmosphere when biofuels are burnt. Biofuels are carbon
neutral!
Why cellulose has to be treated with enzymes before bacteria can
use it as an energy source: Bacteria cannot breakdown cellulose
fast enough so enzymes like cellulase are needed to break down
cellulose into beta glucose by hydrolysing 1,4 glycosidic
bonds.
The changes in distribution of organisms after glaciers
disappear are: As time increases, the biodiversity of organisms
increases. Primary succession occurs whereby pioneer species such
as lichens are the first organisms to colonise bare rock. These
pioneers improve the conditions for plants by changing rock into
soil. There will be competition, limiting the species currently
present e.g. newer species outcompete previous species.
What a niche is: The role of an organism within its ecosystem.
The specie the question is talking about is a producer (because its
a plant) and so it provides food for other organisms. It also
improves the soil e.g. holds soil structure together. It provides
shelter for organisms.
How to carry out a study of the distribution of X: Use transect
from ____. Sample along the transect using a quadrat. These sample
sites along the transect are selected using systematic sampling.
Estimate abundance e.g. through number of plants.
One abiotic factor that affects the abundance of the plant and
how it can be measured: Light affects it Can be measured using
light probe and reading should be taken at the height of the plant.
Take several readings and get an average.
Effect of temperature on decomposition (of leaves): Increase in
temperature would increase rate of decomposition up to an optimum
temperature. Enzymes are used in decomposition. Increased heat
results in an increase in the number of collision between enzymes
and substrates thus increase rate of reaction. Above a certain
temperature, the rate of decomposition would decrease as enzymes
become denatured.
The role of RUBISCO in the production of GALP in the
light-independent reaction is: RUBISCO is an enzyme in the Calvin
cycle. Its involved in carbon fixation to form GP. GP is converted
into GALP using ATP and reduced NADP.
How the membranes inside the chloroplast are involved in
photosynthesis: Thylakoid membranes are the site of light-dependent
reactions. Has chlorophyll, electron carrier proteins etc. within
its membrane. Also has ATPase in it. Provides space for the
accumulation of protons.
Structure of enzymes: Globular proteins with active site. Has
charged R groups on the outside that are hydrophilic.
How anti-viral drugs would work in people w/ HIV: Drugs would
prevent viral replication. T helper cells wouldnt be killed by the
virus particles leaving the cell. Inhibits reverse transcriptase so
that viral DNA cant be made from viral RNA. Inhibits integrase so
that viral DNA cannot integrate into host genome.
Division that occurs when T helper cell is cloned: Mitosis.
How a microscope slide could be prepared to observe cell
division in T helper cells: Make a slide of T cells from the blood.
Use a stain like acetic orcein. Heat stain using acid. Look at
mitotic features.
The role of T helper cells in the immune response: Cytokines
from T helper cells stimulate B cells. B effector cells
differentiate into plasma cells that produce antibodies. Also
activate T killer cells that destroy infected host cells.
How is Golgi apparatus involved in T helper cells: It packages
proteins like cytokines, CD4 receptors etc. These synthesised
proteins then leave by exocytosis.
Judging reliability by looking at graph: Long error bars
indicate low reliability. Overlapping error bars are less
reliable.
Why antibiotics cannot be used to treat infections caused by
viruses: Viruses are non-living and have no target sites for
antibiotics.
Two ways hospitals can reduce spread of infections caused by
viruses include: Use hand washes. Reduce proximity of patients to
each other (i.e. isolate them!).
NPP is: Rate of production of energy incorporated into biomass.
NPP = GPP R in producers.
The relationship between NPP and rainfall and
temperature:Temperature: NPP depends on photosynthesis; the higher
the temp the more NPP. Enzymes in photosynthesis can works faster
so more enzyme-substrates are formed.Rainfall: Increase in rainfall
increases NPP. Water is needed for light-dependent reaction as it
transports mineral ions/amino acids/sucrose.
Two structures that would classify an organism as eukaryotic:
Chloroplast. Nucleus.
How a colony of genetically identical cells could develop from a
single original cell: Mitosis. Followed by cytokinesis. Repeated
several times.
Why the following are important in production of carbohydrates
in photosynthetic cells:Thin lamina: Maximum gas exchange so more
carbon dioxide is used in Calvin cycle.
Vessels in midrib: Transport in xylem of water to leaves; water
for light-dependent reactions for photolysis as a source of
hydrogen ions Transport in phloem of sucrose away from leaves.
How GALP formed can be used to synthesise the cellulose in plant
cell walls: GALP converts to glucose, which is beta glucose.
Glycosidic bonds forms between carbon 1 and carbon 4 by
condensation. This forms straight chains of glucose.
Production of biofuels isnt carbon neutral because: Carbon
neutral means that carbon dioxide produced = carbon dioxide used.
Forests act as carbon sinks. Deforestation results in net increase
in carbon dioxide in the atmosphere. Less plants means less carbon
dioxide is removed by photosynthesis. Burning trees can produce
carbon dioxide. Increased decomposition produces carbon dioxide.
Using fossil fuels by lorries/machinery to clear the land produces
carbon dioxide.
How combustion products from burning fuels may lead to global
warming: It produces a greenhouse such as carbon dioxide. These
gases build up in the upper atmosphere. They absorb infrared
radiation reflected from earths surface. Increased levels of these
gases increases greenhouse effect so mean temperature of earths
surface increases.
GPP = 10400; efficiency of grassland is 45%; calculate NPP and
R: NPP = 0.45x10400 = 4680. 10400-4680 = R.
Relationship between GPP and NPP: NPP = GPP R 55% of GPP energy
is lost as heat to provide for active transport. NPP is stored
energy.
NPP values would be useful for a farmer who wants to use his
land for cattle because: Cattle are primary consumers therefore
gain energy available as NPP. So itll affect yield of meat/milk so
changing to a more NPP yielding crop may be useful.
Triplet code means: Each amino acid is coded for by three bases
e.g. 12 bases code for 4 amino acids.
Non-overlapping code means: That each triplet is discrete as
each base is only used once in a triplet e.g. AAT AAC CAG TTT give
4 distinct triplets.
Degenerate means: That more than one code can be used for a
particular amino acid e.g. stop code e.g. both AAT and AAC code for
leucine.
How translation of mRNA synthesises part of a polypeptide
molecule (i.e. transcription): Refer to the mRNA sequence of the
question. Ribosome is involved. Each tRNA molecule is attached to a
specific amino acid. Anticodons on tRNA bind to codons on mRNA and
hydrogen bonds between the bases of mRNA and tRNA form. Peptide
bonds form between adjacent amino acids.
Two differences between genetic material of bacteria and
viruses: Bacteria have DNA, viruses can have DNA/RNA. Bacteria have
circular genetic material, viruses has linear genetic material.
How macrophages ingest bacteria: Phagocytosis i.e. formation of
pseudopodia around bacteria to engulf it. Bacterium inside
vacuole.
Why treatment with antibiotics may not be effective against
dormant bacteria in tubercles: Bacteria are inside macrophages and
has waxy layer. Also may be resistant to these antibiotics.
How artificial active immunity develops following a vaccination:
Attenuated pathogens are put into the person, which stimulates an
immune response. T helper cell activates e.g. macrophages become
APCs as they engulf antigen by endocytosis. B cells activated as B
cells become APCs and cytokines from T helper cells stimulates. T
killer cells activate as they attack infected cells with APC and
are stimulated by cytokines. Memory cells produce.
Why activity of bacteria e.g. TB and inhibition of T cells can
lead to death: Further lung damage and severe breathing problems
e.g. cannot obtain enough oxygen. Mycobacterium gets into
blood/lump leading to organ failure that leads to death. Reduced
immune response due to loss of T cells. So no T helper cells that
produce cytokines, no T killer cells so infected cells wont be
destroyed and no B cells so no antibodies produced. Thus
opportunistic infections can arise and cause death.
Why viruses cant infect cells if they land on unbroken skin:
Skin is a barrier made out of keratin. There are also no receptors
for the virus.
Why a common cold virus cannot infect cells if they enter blood
through a cut in the skin: The virus only attached to specific
receptors that arent present on blood cells.
Why species dont interbreed: Reproductive isolation. Different
breeding times. Dont recognise courtship displays. Physically
incompatible e.g. different genitalia.
Why the rate of change in the appearance of species can be slow:
They share the same habitat so they experience the same
environmental conditions. Thus will have the same section
pressures. Also, both are well adapted to their environment so no
mutations may have occurred that improve their survival. Thus few
changes in allele frequency and gene pool remain stable. Also
theres very little change to an environment over time.
Why reproducing asexually and sexually is advantageous to
lichens: Advantage of sexual reproduction is greater gene pool.
Advantage of asexual reproduction is conserves advantageous
alleles.
How percentage cover of a species can be determined: Use quadrat
Systematic sampling of the area. Count number of squares containing
the species.
How light intensity can be measured at the surface of something:
Use light probe and take several measurements.
How whatever data collected could be used to show a
relationship: Plot a scatter graph of Y against X. Look for a
correlation Use a statistics test e.g. Spearmans rank.
How GP can be used to synthesise starch: GP converts to GALP
using ATP and reduced NADP. GALP converts to glucose which is an
alpha glucose. Glycosidic bonds form by condensation; these bonds
are 1-4 and 1-6 glycosidic bonds. Amylose and amylopectin are a
part of starch; amylose is straight chain and has 1-4 bonds whereas
amylopectin is branched and has both 1-4 and 1-6 bonds.
How forest fires can lead to global warming: Fire produces
carbon dioxide which is a greenhouse gas. These gases form a layer
in the upper atmosphere and absorb infrared radiation reflected
form Earth. This increases mean temperature of surface area of
earth. Less carbon dioxide is removed by photosynthesis as the
trees are GONE.
Biofuels are good because: They are possibly carbon neutral.
Plants are used for biofuels. Carbon dioxide is used by the plants
that are needed in biofuel production. Thus using biofuels can
replace fossil fuel use.
GPP means: Rate of energy incorporated into biomass in
plants.
Why NPP is less than GPP: Energy is lost as heat by
respiration.
Advantage for why most amino acids have more than one code:
Effects of mutations are reduced. Third base can be altered with no
effect on the resulting polypeptide.
Stop codons: Stop codons occur at the end of the gene on a DNA
and are transcribed as mRNA. Theyll be recognised by ribosome and
they signal end of the polypeptide during translation.
How amino acids are joined together in a polypeptide: Peptide
bonds between amine group and carboxyl group in a condensation
reaction.
How antibodies help a person recover: Antibodies bind to
bacteria and enhance phagocytosis as a result as they immobilise
bacteria.
Species: Organism that can interbreed to produce fertile
offspring.
Characteristic features of antibodies: Y shape of 4 peptide
chains with disulphide bridges between peptides. Produced by plasma
cells. Is a glycoprotein.
How scientists can develop a means of producing active immunity
to HIV infection: Artificial active immunity through vaccination
containing synthetic antigen. Humoral immune response to synthetic
antigen. Process of producing effector B cells e.g. clonal
expansion of B cells through cytokines released by T helper
cells.
Why data about HIV infections are often estimates: HIV infection
doesnt always produce symptoms. Test is needed to detect HIV and
only those suspect of having it would have a test.
Chemical reaction involved in digestion of cellulose by enzymes:
Hydrolysis.
Likely product of digestion of cellulose by bacteria:
Glucose.
What would happen if number of animals in a clear area in
forests decreased: Taller growing plants could develop in the clear
areas. Loss of clear zones. Different animals appear.
Reproductively-isolated populations are: No interbreeding
between species due to a geographical barrier. Different behaviours
and incompatible genitalia. Each population has a discrete gene
pool e.g. restricted gene flow, different mutations, different
alleles
How forensic entomology is used: Body dead for a while because
more than one species of insect is present. Succession of insect
species. Life cycle times of insects are used which depend on
temp.
How body temperature could determine time of death: Drop in body
temp is linked to time after death. Factors affecting temperature
drop e.g. ambient temperature, body size, clothing. Useful because
time of death can be calculated if ambient temperature is known.
Only useful for short period of time following a day e.g. 24h
How state of decomposition could determine time of death: Body
decomposes in a specific sequence with time. Factors affecting
decomposition e.g. wounds. Not useful if entire body had
decomposed.
Why DNA can be described as a double-stranded polynucleotide:
Because made of two strands that are joined by hydrogen bonds
between bases. Polynucleotides of many nucleotides linked by
phosphodiester bonds.DNA ProfilingPolymerase is the. enzyme used in
the Polymerase Chain Reaction to amplify DNA in a small sample of
blood taken from a crime scene.
Gel Electrophoresis is the process used to separate DNA
fragments to create a DNA profile
Describe how gel electrophoresis can be used to analyse DNA. (3)
*First, a DNA sample will be collected from blood, saliva or semen
etc; *these small samples of DNA can then be amplified by PCR. DNA
profiling then takes place which uses *restriction enzymes to break
the DNA and then *uses electro potential difference, with the DNA
in a gel, to draw the bands apart. *The DNA is stained so it can be
seen and will *show up as bands/bars. *The number of bands that
match indicates the similarity of the DNA.
Name substances X, Y and Z:Substance X ...........DNA
PrimersSubstance Y......... (mono)nucleotidesSubstance Z
..........DNA Strands
What are the temperatures for?T1: Heated to 9095 CT2: Cooled to
5560 CT3: Heated to 75 C
Using DNA profiling explain how a suspect is found guilty. (5)A
DNA match is needed, this means that *all of the bands in the
sample are the same as the ones shown in the evidence sample. *DNA
profiling assumes every individuals DNA is unique/different; *apart
from identical twins. *DNA profiling analyses the introns/noncoding
blocks/STR parts of DNA as the *non-coding areas are hypervariable
because *there are a large number of introns/non-coding blocks and
so there can be *many combinations of STRs at each locus.
Suggest how DNA profiling could be useful to scientists who
examine fossils of animals and plants. (2)*Comparisons could be
made between DNA from fossils and other organisms *to find genetic
relationships/how closely related they are. It may also be *used in
taxonomy/classification *to understand evolutionary lines/to
determine a common ancestor.
Explain how the results of DNA profiling of tissue samples from
the two sub-species could be used to provide evidence that they
share common ancestry. (3) DNA profiling will *produce bands that
will have spread to *certain positions. *Common/similar bands will
contain similar DNA fragments; *the more similar these patterns,
the closer the relationship/more likely the sub-species will have a
recent common ancestor. *There will still be very few differences
between the DNA of sub-species.
Suggest how DNA analysis could give further evidence for
evolution. (2)DNA analysis could show the *similarity (of DNA) and
indicate the closeness of a genetic relationship *because genes are
sections of DNA and these *genes are the codes for proteins.
Why cant species of plants be identified from woody (xylem)
material using PCR and DNA profiling? (2) Because *xylem/wood is
made of dead material/has no living material/cytoplasm/nuclei/
mitochondria, meaning *no DNA / nucleic acid is present in the
material.
Suggest why DNA polymerase from human sources is not suitable
for use in a PCR machine. (2)*Because human enzymes will not work
at high/ above 37oC temperatures due to *denaturation (change in
shape of active site) at the temperatures found in the PCR
(55-95C).Explain why evidence from DNA profiles may not be
absolutely conclusive. (2)*DNA profiling has several stages and
*artefacts/contamination can arise at any stage. Furthermore as
*only a few sequences/a small portion of DNA is analysed it is
*possible to get two identical profiles from unrelated individuals
or for *identical twins/closely-related individuals to show the
same profile. Thus the minimum amount to be analysed is 10STRs
Decomposition and forensicsThe first stage in the decomposition of
a cow pat is known as putrefaction. Explain how carbon dioxide and
ammonia are formed during this stage of decomposition. (4)
*Microorganisms/microbes/bacteria/fungi are decomposers that
*convert organic compounds to carbon dioxide and *nitrogen
compounds/proteins/amino acids/urea to ammonia. *Aerobic/ anaerobic
respiration *of the microorganisms/bacteria/fungi is the process
whereby this occurs.
Suggest why the time taken for a cow pat to decompose changes at
different times of the year. (3) *Because in the warmer times of
the year the process will be faster as more heat energy is
available and so kinetic energy is available for enzyme reactions/
to speed up the metabolism but less is available in the winter
months (temperature effect). *There will also need to be sufficient
water availability for the microorganisms to survive (*e.g. If
frozen it cannot be accessed) however *too much water can lead to
waterlogging which reduces oxygen availability and thus the amount
of energy produced for decomposition.There may also be *more
insects/decomposers in summer. The *rate at which the
microorganisms grow will also be a factor as it depends on how much
food is available and how long they will be there to decompose the
pat.
Suggest how woodlice are involved in the recycling of carbon.
(3) *The carbon/organic compounds in plant material are broken down
in *digestion to provide respiratory substrates, *carbon dioxide is
then released from them in respiration. *This carbon dioxide is
available for photosynthesis. The carbon consumed may also become a
part of the woodlices biomass until it is eaten or dies and
decomposes to release it.
Describe the role of microorganisms in the recycling of the
carbon from compounds in a dead animal. (3)
Decomposition/putrefaction occurs by microorganisms, they may
digest the carbon in the animal and then release the carbon into
the atmosphere by *respiration where the *carbon dioxide is used
for photosynthesis. *Methane is released in anaerobic conditions
and is *available as fuel.
Suggest three factors that could influence the rate at which a
body cools after death. (3)*(Body) mass/ BMI / weight;
*(subcutaneous) fat; *surface area; *ambient temperature,
*immersion in water; *age (of person at death); *skin colour;
*thickness of hair; *gender; *clothing; *blood loss; *humidity;
*air movement; *{core / body} temperature at time of death.
Suggest two environmental factors that influence the rate of
progress of rigor mortis in a muscle immediately after death. (2)
*Physical damage; *immersion in water; *(external) temperature;
*burning; *electrocution; *clothing; *wind/air movements;
*(Presence of drugs in the body: bio)
Suggest why a forensic scientist would need to consider rigor
mortis in several muscles of a body when estimating the time of
death. (4) Because *not all muscles will contract/relax/reach
(full) rigor mortis at the same time; *e.g. jaw muscle will
contract fully before the leg muscle. *Full contraction/rigor in
muscle does not last very long; for example the *leg is still
contracting while jaw is relaxing.
Suggest how the time of death of a white rhinoceros could be
determined if it is discovered several days after being killed. (5)
You could work out the time of death by looking at the *stage of
succession on the body (if it has been a long period of time). You
could also use *(forensic) entomology which involves identifying
*the life cycle stages/ species of insect on the body *e.g. fly,
beetle, wasp. You could also work out the time of death by looking
at the *decomposition of the body as there are *different stages of
decomposition. Decomposition involves *putrefaction (discolouration
of abdomen that spreads), liquefaction of tissue, bloating and
production of gases.*All of this information (insects, succession
etc) is used to determine time of death, each of these methods
conclusions are *influenced by an external factor such as
temperature that influences the rate of succession/insect
development/ decomposition.
Suggest how Body Temperature would be useful in determining the
time of death (2)*A drop in body temperature is linked to the
amount of time that has passed after death e.g. algor mortis, *many
factors affect the temperature drop e.g. environmental temperature,
body size, clothing. It is useful because *time of death can be
calculated if the (ambient) temperature is known however it is
*only useful for a short period of time following death e.g. 24
hours/a day.
Suggest how the state of decomposition would be useful in
determining the time of death (2)Because the *body decomposes in a
specific sequence over time it can be useful in determining time
after death but *many factors affect the rate of decomposition e.g.
environmental temperature or the presence of wounds. It will also
*not be useful if all the body has decomposed.Protein
SynthesisStatement True False? (3)AACTAGT TGGCAAGTGGTCACThis
sequence of bases could be used as a template during translation FA
strand of mRNA could be synthesised using this sequence TThis
sequence codes for 7 amino acids during protein synthesis T
Thymine cant be found in.. mRNAA cistron is..the sequence of
triplets on a section of DNA used to form a strand of pre-mRNA A
Peptide Bond.. links the amino acids in the primary structure of a
proteinReverse transcriptase is the enzyme is used to produce DNA
from viral RNA in an infected cell Transcription takes place In the
nucleusThe amino acids in a primary structure are linked together
in the ........RibosomeNucleotide is the.term used to describe each
of the sub-units in a molecule of RNAName and describe the
structures where the polypeptide chain of an enzyme would be
synthesised. (2) The polypeptide chain would be synthesised on the
*ribosomes attached to the membrane of the rough endoplasmic
reticulum. *The ribosomes consist of rRNA and are a protein
component of two sub-units/ a large and small sub-unit.
Explain why a molecule of DNA can be described as a
double-stranded polynucleotide. (3) *It is double-stranded because
it is made of two strands *joined by hydrogen bonds between the
bases and it is *a polynucleotide of many nucleotides that are
*linked by phosphodiester bonds.
Explain how pre-mRNA is formed during transcription in the
nucleus. (3) First the *DNA strands separate/unzip by the use of
*DNA helicase, *one DNA strand of 12bases is used as a template (to
form mRNA) *from free nucleotides via complementary base pairing
and the formation of hydrogen bonds between the bases.
RNA-polymerase catalyses the transcription process.
Describe how free nucleotides are bonded together in the correct
sequence in the formation of pre-mRNA. (3)*The sequence of
bases/nucleotides on DNA determines the sequence on (pre-)mRNA, the
codons will *bond in complementary base pairs (give example eg.
GTA= CAU) by the formation of *phosphodiester bonds in
*condensation reactions. This process is catalysed by
*RNA-Polymerase.
Explain how the translation of mRNA into the sequence of amino
acids in a ribosome occurs. (3) *A specific amino acid is attached
to tRNA (coded for by the anticodon). *The anticodon on tRNA binds
to the codon/triplet on the mRNA strand, only two tRNA molecules
are held in the ribosome at any one time. When a third tRNA comes
along the first tRNA detaches, after the *peptide bonds have formed
between the adjacent amino acids. *Peptidyl transferase catalyses
this process.
Suggest why the final triplet of nucleotides, on a strand of
mRNA involved in the synthesis of a sequence of amino acids, did
not correspond with any anticodon on tRNA. (2)Because it was a
*stop codon and is *used to end the sequencing/further attachment
of tRNA and signal the *release of the polypeptide from the
ribosome.
Explain the function of the codons at each end of a strand of
mRNA, during the process of translation. (2) *They function as
start/stop/nonsense codons. The *start (codon) is needed to begin
the Polypeptide/protein synthesis and *the stop/nonsense (codon) is
needed to end polypeptide synthesis.
Suggest why a variety of different protein structures could be
formed from the polypeptides synthesised using the mRNA molecules
from a single gene. (3) *Because there are many variations of
exons/mRNA which lead to *different primary structures of a
protein/sequence of amino acids. The *secondary and tertiary
structure of the proteins depends on the primary structure. There
will also be a variety because there are *different bonds, some are
hydrogen/ionic/disulphide bonds, the proteins formed will also have
*different 3D shapes.
Describe how the sequence of bases in a DNA molecule would be
used to form the primary structure of a protein. (5)*The sequence
of bases forming the genetic code determines the amino acid
sequence as *one triplet codes for an amino acid. *The DNA acts as
a template during transcription (e.g. DNA unzips by helicase and
mRNA is synthesised).*Post-transcriptional modification of mRNA
then occurs where introns (non-coding regions of DNA) are removed
by splicing using the enzyme spliceosome, leaving only exons behind
in the mRNA to join back together. After modification the *mRNA
moves from nucleus to the cytoplasm through a pore in the nuclear
membrane, so that *translation may occur on the ribosomes found
attached to the rER (ribosomes aid codon-anticodon interaction).
*tRNA then carries an amino acid to the ribosome and joins with its
complementary base pair, *forming peptide bonds between the amino
acids forming the primary structure of a protein this is the
sequence/order of amino acids specified in DNA.
Non-Specific Immune ResponseInterferon is the enzyme released in
secretions that interferes with protein synthesis of viruses.
Histamine is the.chemical released by white cells in connective
tissue that causes swelling
D = antigens / (glyco)proteins ;E = B {lymphocytes / cells} /
plasma cells ;F = antibodies / immunoglobulins ;G = macrophage /
phagocyte / eq ;H = enzymes / lysozyme ;
Explain why the processes shown in the flow diagram will only
happen in response to some types of bacteria. (3) Because the
protein nature of antigens/antibodies is different, the *antigens
are specific to each bacteria strain and the *antibodies need to be
complementary/specific to the antigen so that binding can take
place. *Some bacteria will have different/changed antigens to
another, they may also have different *slime/mucus capsules or be
*inside body cells, this changes the effectiveness of the
antibodies. This is also a *primary infection meaning some
antibodies are already present from passive immunity or breast
feeding.
Describe how the production and action of interferon differs
from the production and action of lysozyme. (3) *Interferon is
involved in viral infections, whereas lysozyme affects bacteria
only. *Interferon is produced only by infected cells, but lysozyme
is present in all secretions (i.e.
saliva/phagocytes/neutrophils/macrophages. They have different
roles, *interferon inhibits replication of viruses and lysozyme
kills/ destroys bacteria.
Suggest why the protein structure of lysozyme is important to
the way in which it acts against pathogens. (4)*lysozyme is an
enzyme and so it *has an active site with a specific shape for
binding with our cell membranes. *The lysozyme acts on the cell
wall *of bacteria so that cell lysis occurs.
Explain why an insect bite, which breaks the surface of the
skin, may lead to inflammation around the injury. (3)Because
*histamine is released as a result of damaged tissue/cells, *it is
released from mast cells/platelets. *Histamine causes the
arterioles to dilate (vasodilation), which increases blood flow and
makes the capillaries more permeable allowing phagocytes to reach
the site more easily. *Inflammation involves
oedema/swelling/redness/heat/pain at the site of injury.
In order to reduce inflammation, a cream containing
antihistamines might be applied to the skin, around an insect bite.
Suggest why applying this cream might be better than taking tablets
containing antihistamines. (3)Because inflammation is *only a local
reaction produced/that histamines produced around the bite area and
so *cream that has been applied to actual site of production of
histamine *will be more effective and have more rapid/ immediate
relief as it will create a *higher concentration of antihistamine
at the site. *The antihistamines will not be digested (by
enzymes)/destroyed (by acid or enzymes) if they are applied in a
cream and not tablet. The *tablets may lower the immune response
generally/lead to unpleasant side-effects.Specific Immune
Response
Natural passive Artificial passive Natural active Artificial
active
When MRSA enters the blood it can stimulate the production of
several different clones of plasma cells. These produce a variety
of antibodies (polyclonal antibodies). Suggest an explanation for
this. (4) Because the *bacterium is made of many different
polymers/chemicals *which can act as different antigens,
*individual B-lymphocytes will recognise specific
antigens/antibodies are specific and so only certain *B-lymphocytes
are activated by T-lymphocytes. These cells of *B-lymphocytes will
then divide by mitosis *to form genetically identical plasma cells
that secrete specific antibodies.
Suggest the advantage of using monoclonal antibodies, rather
than polyclonal antibodies, in the detection of antigens in the
blood. (3)Because a *specific antigen/virus/pathogen/bacterium can
be identified as the *specific/ monoclonal antibody binds to a
specific antigen. As a result *specific treatment can be given that
will *avoid unnecessary use of drugs/treatment and will be *more
likely to be effective.
State two characteristic features of antibodies. (2)*They have
glycoproteins in their cell walls; have a *specific (3D) shape, L
and H regions, Y-shape, 4 (peptide) chains, disulphide bridges
between peptides, hinge region; they also *have an antigen-binding
site/variable region; all antibodies *have a similar/constant
region; they are *produced by plasma cells/present on B cells;
*their role is opsonisation, immobilisation, agglutination, lysis
of foreign cells.AntibioticsBactericidal antibiotics is the name of
antibiotics, such as vancomycin, that kill bacterial cells
The epidermis is. a part of the skin that forms a physical
barrier against infection by pathogenic bacteria
What are bactericidal antibiotics? Antibiotics that kill/destroy
bacteria cells by weakening their cell walls so their cells burst
Ignore reference to stopping growth
Suggest how bacterial cells are killed by vancomycin
(antibiotic). (2) The antibiotic may *weaken the bacteriums cell
wall or not allow it to form properly *so the cell bursts easily,
perhaps *during division.
What are bacteriostatic antibiotics?Antibiotics that stop cells
from increasing in number/replicating by preventing cell
division.
Explain what is meant by the terms bacteriostatic antibiotic and
bactericidal antibiotic. (3) *An antibiotic is used to
control/kill/prevent reproduction of bacteria. *Bacteriostatic
antibiotics will prevent the
reproduction/division/multiplication/growth of bacteria whereas
*bactericidal antibiotics will destroy/kill the bacteria.
Suggest why antibiotics may be used as part of the treatment for
influenza. (2) Because *influenza may allow the development of
other diseases e.g. opportunistic infections and *the antibiotics
will kill/inhibit growth of these bacteria.
Suggest why health authorities in the USA are encouraging the
reduction in the number of prescriptions of antibiotics. (2)Because
*some bacteria are resistant to the antibiotics and this
*resistance is genetic and can be passed on. *MRSA, for example is
already resistant to many antibiotics.
Explain why doctors have been advised to limit the prescription
of antibiotics. (2)Because *antibiotics act as a selective
pressure, *some bacteria are already resistant to some antibiotics.
These *resistant bacteria survive and pass on the resistance gene
so that the antibiotic is no longer effective. *Some infections
cannot be treated with antibiotics (ie viral infections)
Describe how you could investigate the effect of different
antibiotics on bacteria. (4)*Bacteria could be distributed evenly
by lawn spreading, *multidisks or wells in the agar may then be
placed at known positions to see the effectiveness of the
antibiotic. The *same concentration of antibiotics must be used and
the petri dish must be set using a sterile/aseptic
technique/conditions. The dish must then be kept *incubated at a
suitable temperature (below 30C to prevent the growth of pathogens)
and *the lid of the petri dish not all the way fastened to prevent
the growth of anaerobic bacteria. You can measure the effectiveness
by measuring the clear area/inhibition zone around the antibiotic
area. The investigation should be *repeated with both the same
conditions and bacteria and *different bacteria to asses overall
effectiveness.
Suggest why medications, other than antibiotics, are needed to
treat the most severe cases of BRD (viral infection). (2) Because
the infection *involves both viruses (and bacteria via
opportunistic infections), and (usually) antibiotics are only
effective against bacteria/do not affect viruses. Thus *other
medication will be needed to deal with viruses.
Suggest why it might be advisable to change the antibiotic being
used, in the treatment of (cattle), once a pathogen has been
identified. (3)Because the specified *antibiotic used is the most
effective against the now known bacterium. *None of the antibiotics
are 100% effective/some bacteria may survive or *be resistant or a
*resistant strain may develop/be prevented by changing the
antibiotic.
Suggest how the constitution of blood may change if an ill
person is treated with antibiotic drugs. (2) There will be *fewer
lymphocytes as *the lymphocytes are no longer needed as the
*antibiotics have killed/destroyed the bacteria.
Or: There are *more lymphocytes as there has been a *clonal
expansion of lymphocytes because the *antibiotics have not killed
all the bacteria yet.
Suggest how the constitution of blood may change if an ill
person is given a placebo. (2) *A placebo has no effect on the
bacteria *so there will be more bacteria, and *thus more
lymphocytes due to *clonal expansion.Vaccinations and prevention.
Suggest how scientists may be able to develop a means of producing
active immunity to HIV infection using synthetic HIV antigens.
(5)*This will be a method of *artificial (active) immunity, perhaps
by using a *vaccine/vaccination *containing the synthetic
molecule/(synthetic) antigen/(synthetic) glycoprotein. *A
specific/humoral immune response to the synthetic antigen will be
stimulated, i.e. *Effector B cells will be produced by clonal
expansion of B cells, involving cytokines or T helper cells will
activate B cells. These will then *produce B memory cells that will
cause (2G12) antibodies to be produced faster/in greater
concentration on reinfection (secondary immune response).
Describe how a vaccine gives active immunity against PWMS. (3)
*You may use the virus as a vaccine, *which will contain a
modified/attenuated/ harmless/similar form of the virus that
*contains the virus antigen. The vaccine will stimulate the
*activation of (specific) B cell/T cell/lymphocytes and cause the
*production of B/T memory cells; this means that the *body is now
able to produce (specific) antibodies faster/at higher
concentration on another exposure to the virus.
State two ways in which the skin flora can help to protect a
person from infection by pathogenic bacteria. (2) *They provide
interspecific competition for nutrients and *for space. They also
*secrete chemicals/substances/lysozyme OR affects pH so the
pathogenic bacteria cannot survive there. They also *stimulate the
(skin) immune system.
Suggest why the rate of MRSA infection in different hospitals
differs. (3)*One hospital may have stricter hygiene practices such
as strict *hand washing regimes for doctors/nurses/medical
staff/visitors *particularly when dealing with open wounds. *The
nurses may also have to wear suitable clothing such as no ties or
long sleeves or have *antiseptic (solutions) readily available such
as *gels, pastes, alcohol rubs. Patients may also be *isolated if
they are a suspected cases of MRSA or screening of admissions to
ensure they are clean. Better hospitals may also monitors the use
of antibiotics or have *fewer patients/visitors passing in and
out.
In a study in a London hospital, it was found that pillows
contaminated with bacteria could spread infections between
patients. Suggest how this hospital could improve the prevention
and control of the spread of infections. (3)*Hospitals will have to
change a code of practice/protocol/policy/standards currently
present for dealing with hospital acquired infections. They may
introduce *clothing rules for hospital workers such as no long
sleeves or jewellery (reduces places pathogens can hide); they may
also *improve laundry services of bed linen e.g. increased washing
frequency/higher washing temperature. They may also *use special
pillow cases/treat the pillow cases e.g. microfilters, treated with
antibacterials,sterilisation, disposable pillow cases or they could
*use special procedures when carrying pillow cases/bed linen to the
laundry e.g. sealed plastic bags to prevent it spreading to the
workers. *Screening of patients/isolation of infected patients
could help as the infected can be isolated to reduce the spread of
infection. *Hand washing regimes before and after seeing patients
could also reduce the spread.HIV
Name two types of cell that HIV enters in the immune system.*T
helper/CD4 positive cell/lymphocytes; *phagocytic cells e.g.
macrophages, dendritic cell
State how the genetic material in HIV differs from the genetic
material in the Mycobacterium tuberculosis that causes TB. (2)*RNA
is found in HIV/ virus and DNA in the bacterium/TB, *the nucleic
acid in the bacterium is circular whereas it is linear in HIV.
*There are also plasmids in bacterium and no plasmids in HIV.
One of the ways in which HIV may enter the blood is through the
use of infected needles. Explain why unbroken skin is an effective
barrier against HIV infection. (2) *Keratin/protein in skin
surface/epidermis *forms a physical/impenetrable barrier to
HIV.
Suggest one effect that HIV causing T killer cells to destroy T
helper cells will have on one other component of the infected
persons blood. (1)*B cells/lymphocytes not activated resulting in
fewer antibodies and *T killer cells increasing due to demand for
use.
Describe the change in numbers of CD4 T-lymphocytes during the
first 6 weeks after infection with HIV. (2) *Overall numbers will
decrease. *There will be a small decrease in the first week/between
weeks 4-6; *however the decrease is greatest between weeks 1-3
Explain the change in numbers of CD4 T-lymphocytes during the
first 6 weeks after infection with HIV. (5)*The glycoprotein/gp120
on the virus *binds with receptors/CD4 *on (surface) membrane of
lymphocytes, the *viral RNA then enters the lymphocyte. Once inside
the *viral RNA is used to produce viral DNA (in the lymphocyte) *by
action of reverse transcriptase *allowing the formation of new
viruses. The *lymphocyte is then destroyed when new viruses bud out
of/leave the cell. The *T killer cells then destroy the infected T
helper cells/lymphocytes.
How is HIV able to enter the immune systems cells? (3)*First,
the HIV binds to (CD4) receptors on cell surface membrane (CD4
receptors are found on the lymphocytes) *using the
gp120/glycoproteins on the virus surface. *The virus envelope then
fuses with the hosts cell surface membrane allowing viral RNA to
enter the host cell. *Macrophages also have CD4 receptors and may
be infected in phagocytosis.
Describe the sequence of events following infection by HIV,
which may lead to the death of the patient. (6) The HIVs *viral RNA
is used in reverse transcription using the enzyme, *reverse
transcriptase, to *produce viral DNA using viral RNA as a copy.
*The viral DNA is then incorporated into the host cells DNA/genome
by the use of the enzyme *integrase. The hosts DNA can now be used
in the *production of more viruses/viral RNA and proteins, these
virus molecules may then bud out of the cell to *infect further (T
helper) cells and destroy the recent host cell by *cell lysis.
*THelper cells are needed in the immune response to produce
cytokines, activate B cells/ killer cells. *Meanwhile there is
destruction of infected (T helper) cells by T killer cells, which
also contributes to *lowering the immunity to other diseases.
*Death may be caused by e.g. opportunistic disease, pneumonia, TB,
Kaposis sarcoma, cancer, dementia, extreme weight loss, meningitis,
and toxoplasmosis.
Suggest why effective treatment of HIV in human populations will
require the continual development of a mixture of many new drugs.
(4) Because *HIV has many varieties of strains/antigens/protein
coats, *some of these strains are/will become resistant to a
specific/particular drug and so *would survive if only one/the same
drug was used. *A mixture of drugs has more chance of getting rid
of all/ more strains.*A concoction of drugs are used together
because viruses have a rapid rate of mutation and a *rapid rate of
multiplication.
Suggest why data about HIV infections are often estimates.
(2)*Because HIV infection does not always produce symptoms
(*especially in the latency period) or are *common of other
diseases and so can be confused. In some cases a *test is needed to
detect the symptomless HIV. *Only people who suspect they may have
contracted HIV would have a test, *some people may not want to be
tested/impossible to test everyone for statistics, especially as
*new cases are arising/HIV patients are dying all the time or as
*new strains of the virus are arising.TBState one characteristic
symptom of TB other than coughingTubercules; bloody sputum;
(general)body tissue wastage
Mycobacterium tuberculosis ..causes TB
Why is ingesting food containing TB unlikely to lead to its
development? (2) Because the *bacteria is killed in the
stomach/mouth/saliva/gastric juice *by HCL/lysozymes
Describe how the organisms that cause TB are taken up by
macrophages. (3) First the *bacterium is recognised as non-self by
the immune system, *they are labelled as such by B
lymphocytes/cells. They are taken up into macrophages by
*phagocytosis, the *process whereby phagocytes (macrophages or
neutrophils) engulf the foreign matter and *enclose it within a
vacuole where it is destroyed by enzymes contained in the
lysosome.Bacteria and Viruses
Suggest two reasons why bacteria that cause infection are not
visible in a photograph. (2) Because the *bacteria are too small
and magnification/resolution is too limited; the bacteria may *not
be stained or have been removed/destroyed e.g. by phagocytosis;
*the bacteria are not present in the blood shown e.g. only a small
region is shown and they may only be present at the site of the
infection.
Photosynthesis:Suggest reasons why 95% of the light hitting the
surface of a leaf is not used by the chloroplasts. (2)*Reflection;
*incorrect wavelength/colour/ frequency; *light doesnt hit the
chloroplast/ chlorophyll, it is transmitted; *light being in excess
e.g. at max. photosynthesis so no more light can be used.
The light dependent reactions The products of the
light-dependent reactions that are used in the light-independent
reactions are reduced NADP and.... ATP Oxygen is produced when
water molecules are split in the process of photolysis When light
is absorbed by chlorophyll, it excites electrons
Describe the structures in a chloroplast that are involved in
the LD reactions (3) The LD reactions involve the *thylakoids that
are arranged into stacks of granum. *The grana are connected by
lamellae. The *thylakoid membrane contains electron carriers,
proteins and *photosynthetic pigments such as chlorophyll which are
*arranged into photosystems/quantasomes; the membrane also has
*ATPase/ ATPase channels.
Explain how the energy from light is made available in ATP
molecules for the synthesis of organic materials. (6)*The light
dependent reactions occur in the thylakoids *in the granum in
*accessory pigments such as chlorophyll. The process begins when
*light energy raises the energy level of two electrons so that they
are excited, the electrons are then *released from the chlorophyll/
photosystem. They then travel down the *electron carrier chain,
travelling to each carrier molecule through a series of *oxidation
and reduction (redox) reactions, releasing energy/ *the electrons
energy level falls. The energy released is used to *synthesise ATP
from ADP and an organic phosphate ion *(phosphorylation); the
*enzyme synthase/ synthetase is needed to make the ATP. *Photolysis
of water produces 2 electrons which are used to replace those lost
from the chlorophyll.
Explain how oxygen is produced during the light-dependent
reactions of photosynthesis. (2) Using *energy from light the
*photolysis *of water occurs that produces/releases oxygen
The light independent reactions/ The Calvin CycleRuBP combines
with carbon dioxide in The light-independent reactions of the
Calvin cycle. RUBISCO is the enzyme that catalyses carbon fixation.
Carbon fixation takes place in.. the stroma of a chloroplast.
Explain why the light-independent stage cannot take place
without the light-dependent stage. (3) Because the *products of the
light-dependent stage are needed for/used in the light-independent
stage/Calvin cycle. *Thee products of the light-dependent stage are
reduced NADP and ATP, *rNADP is used in the reduction GP/carbon
dioxide whilst *ATP is used as a source of energy.
Suggest why the development of plants depends on the rate of
carbon fixation. (3) *Carbon fixation produces {GP / eq}, this
*product is converted to glucose/ starch/ eq. *The faster the C-
Fixation the faster the glucose/ starch production, as the *rate of
growth of a plant is dependent on the rate of C-Fixation, if this
increases so will the *GPP of the crop/plant.
Suggest how GALP may be used to synthesise cellulose. (5) *GALP
is a 3C molecule that is used in the formation of *glucose a 6C
sugar. *This synthesis involves enzymes; to make cellulose enzymes
are also needed. *Cellulose consists of -glucose molecules that are
joined by *1-4 *glycosidic bonds in *condensation reactions.
*Cellulose is a polysaccharide (long chain molecule) and is an
*unbranched molecule; each cellulose chain is then joined together
in condensation reactions with 1-6 hydrogen bonds.
The rate of carbon fixation is higher at 25C than at 14C for
each of the six varieties of maize. Suggest an explanation for
this. (2)*Temperature change affects the kinetic energy/movement of
molecules/particles *therefore this effects number of
collisions/enzyme-substrate complexes.Global Warming:Suggest one
reason why some countries may decide to drain their marshy peat
lands for the production of biofuels. (1) Producing Biofuels may
increase the *countrys income as they can *export more fuel and
*import less fossil/biofuels; the production of biofuels will also
make *more jobs available to the general public. *Biofuels are also
renewable whereas *fossil fuels are finite. *Using biofuels as an
alternative to fossil fuels will help countries reach their carbon
targets. Using peat lands will also make sure that there is *no
loss of farmland, reducing ethical issues.
Suggest why the continued draining and clearance of peatlands
may contribute towards global warming even though they may be used
to produce biofuels. (5)*The combustion of biofuels releases carbon
dioxide that has been recently removed from atmosphere therefore
*there is no (net) increase in carbon dioxide in the atmosphere.
This is a benefit as *carbon dioxide is a greenhouse gas *that
absorbs infra-red radiation that has been reflected from the Earths
surface, *it cannot escape into space, therefore the *carbon
dioxide will cause the mean surface temperature of the Earth to
increase. However, *clearing peat lands may release more carbon
dioxide as carbon was once trapped in peats thousands of years ago;
this *causes a net gain of carbon dioxide in the atmosphere. The
process of clearing the peat lands will *involve machinery that
releases carbon dioxide; the removal of any peat plants will also
*reduce photosynthesis and thus the amount of carbon dioxide
removed from the atmosphere
Suggest how scientists could use available data to predict
future climate change.(3) Scientists could *extrapolate data *to
use for modelling/investigation of correlations to help* provide
evidence for global warming. *Using this data along with other
sources will increase the predictions reliability.
Suggest why some scientists may not be convinced that data can
be used to predict future climate change. (3)Because *there is not
enough data to *confirm its reliability (*may be place specific).
The fact that there are *great fluctuations in most climate change
data suggest that there is no real trend (as scattered) and thus
*poor representation of raw data. *A scatter of results may show
poor reliability.In addition the method of* estimating temperature
from growth rings of trees is questionable as *other environmental
changes affecting the trees are not taken into account.
Scientists have estimated that.. will reduce CO2 production.
Suggest why the may be supported by organisations that are
concerned about global warming. (5) *The idea will result in less
carbon dioxide (or methane), *which are both greenhouse gases/
cause the greenhouse effect *as they absorb/ trap heat/ infrared/
longer wavelengths (of radiation) *reflected from the Earth. *A
reduction in these gases (CO2) will lead to a reduced greenhouse
effect, *this means the Earths surface temperature is less likely
to rise and that there is a *reduced possibility of climate change
which can have effects such as the ice caps melting or crop
failure.(If relevant) *methane has a greater greenhouse effect than
carbon dioxide.
Suggest why some scientists do not agree that a reduction in the
use of fossil fuels will prevent further global warming. (6)*It is
clear that carbon dioxide is produced by using fossil fuels,
however there is *no (direct) evidence that increased carbon
dioxide concentrations leads to global warming. *Carbon dioxide is
released from other processes such as respiration and the *removal
of carbon sinks increases the concentration too, so reducing fossil
fuels alone will not help. *Other greenhouse gases also have a
contribution, such as CFCs, water vapour and methane that come from
*other sources such as ruminant animals, paddy fields, melting ice,
clearance of peat land. *Natural cycles/events/ phenomena may also
be involved (in global warming) e.g. the suns solar cycle or
volcanoes.*Evidence for this comes from the past and *this is not
an indicator of future events/ limitations of climatic models.
*Scientists may also be biased in their research depending on what
country/ company employs them and their own
self-interest/promotion. *We do not yet have an alternative source
of energy that has no great problems associated with it (i.e.
biofuels).
Explain how temperature has been maintained by the presence of
carbon dioxide and methane in the upper atmosphere. (3)*Greenhouse
gases such as carbon dioxide and/or methane *absorb/trap
heat/infrared/long wave radiation *which is reflected/ (re)radiated
from the Earths surface. *These gases prevent heat/infrared/long
wave radiation from escaping. *Thus resulting in temperatures being
maintained higher than they would otherwise be.
Suggest why temperatures below 0 C or above 40 C would be
unsuitable for most organisms. (2) *At 0C metabolism/ named example
stops/ is slow as *enzymes are inactive and cells are disrupted,
this may be *because of water freezing or lower kinetic energy of
molecules in cells. *Above 40C enzymes denature/ change their 3D
shape, this means that *fewer enzyme-substrate complexes are
possible/ the active site has changed/ theres a change in
bonding.
Suggest how global warming may affect the distribution of
species (3) *Global warming will increase the temperature
(especially at the latitudes) *so that the temperature may become
too high for any of the current species. *This new temperature may
be above the maximum to be able to complete development/ above the
lethal temperature limit. *Species may also move north/ to cooler
regions or they may have a *change to their food source/predators/
competition.
Suggest why the lower and upper lethal temperatures limit the
range of latitudes inhabited by (different species of frog).
(2)*Temperature affects the
survival/development/growth/metabolism/cell division of animals and
*the development/growth/metabolism/cell division is affected by
enzymes which are *affected by temperature. *And so as different
frogs have different enzymes the will be able to survive in
different latitudes. Explain why body temperature affects the rate
of development of animals. (3)Because there is an *increase in the
metabolic rate/enzyme activity as temperature rises due to
*molecules having an increase in kinetic energy as the temperature
rises; this means that there will be an *increase in the amount of
enzyme-substrate complexes/collisions. *At lower temperatures there
is inactivation of enzymes but at high temperatures there is
denaturation of enzymes. *Thus temperature affects cell
differentiation/growth/division.The carbon cycleDescribe the role
of microorganisms in the recycling of carbon in the carbon cycle.
(3) Microorganisms would *help in the decomposition/ putrefaction/
decay of dead organisms/ faeces *by eating the organic material
through the process of external digestion and then *respiration.
*Respiration releases carbon dioxide into the atmosphere *for
photosynthesis. *They also will release methane in anaerobic
conditions *which is then available as a fuel. *The microorganisms
themselves will also, one day, be eaten or decompose.Ecosystems:The
difference between abiotic and biotic factors is that..biotic
factors involve organisms/living things whereas abiotic are
physical/chemical/non-living factors.A species consists of..
individuals who can interbreed to produce fertile offspring.Net
primary productivity is..*the rate at which energy is incorporated
into biomass/ organic material in *producers/ plants, *as there may
be losses due to respiration (GPP- R).The metabolic process that
best describes the process that accounts for most of the difference
between GPP and NPP in plants is.. Respiration
Suggest two biotic factors that may influence NPP in grassland.
(2) *Grazing by consumers/herbivores/named herbivore; *trampling;
*shading by other plants/named plant; *competition from other
plants; *disease.
Suggest how other animal populations of a habitat may be
affected by changes in a lizard population. (2)Their prey may
increase in number as *fewer are eaten by the lizard. *Other
carnivores may increase *because there is less competition for food
(from lizards), however the *lizards predator may decrease/eat
other prey/migrate.
Suggest why an increase in temperature may cause an increase in
NPP. (2) *The rate of (bio)chemical/metabolic/photosynthetic
reactions increases due to an *increase in movement/kinetic energy
of enzyme/substrate/molecules; *thus increasing the reaction rate
because of more enzyme substrate interaction/ collisions.What is
the unit J m2 year1? Joules/ energy per metre squared per year/
unit time.
Explain what is meant by the term niche, using the sea anemone
as an example. (3) *The role/ purpose/ interaction of *an organism/
sea anemone/ species in a community; due to its *trophic level,
i.e. if it is a *predator or *prey or provides a *shelter/ home for
some animals.
Suggest and explain why the anemones contract when exposed at
low tide. (3) Contracting *reduces surface area (to volume) ratio,
so there is *less water loss and a smaller chance of dehydration/
drying out. This will also *reduce its visibility (to predators)
*and so provides protection from predators/carnivores. As there is
no *need for the tentacles to be exposed *energy will be conserved
and not be wasted.
Suggest adaptations for bacteria living in a cows stomach. (3)
The cows stomach has a *low pH/ (hydrochloric) acid which normally
*destroys bacteria. The stomach may also have *low/no oxygen and
*so they will have to use anaerobic respiration. They will also
have to be *resistant to the stomachs enzymes, i.e. Protease,
perhaps *by having a cell wall thats resistant to digestion. *They
will also need to be adapted to the cows body
temperature.SuccessionSuccession is.. The sequence of changes to a
community/organism over a period of time.A climax community is..the
final stage/sere/community of succession, it is
self-sustaining/stable and has a dominant species or a few
co-dominant species.Reproductively-isolated populations are..where
*no (inter)breeding between (the population) can take place
*because of a (geographical/ physical) barrier. Physical barriers
include the populations having *different mating behaviour,
*incompatible genitalia and *each population having a discrete gene
pool, e.g. restricted gene flow, different mutation/alleles.
Describe what might happen if deflected succession stops (i.e.
forest clearing). (3)*Taller (growing) plants could develop/ grow
in the clear areas as they are no longer eaten, but there will be
*the loss of low-growing plants/ clear zones. *Different animals/
species will appear as *secondary succession takes place where a
*climax community of the taller plants is reached.
Suggest why/ how a community changes over time. (5)*Lichens and
mosses enter as the pioneer community; *they are able to grow in
little/no soil and *will break up (rock) fragments, with their
roots, to form thin/shallow soil *which is able to retain some
water/minerals. *Then short-rooted plants enter, they out compete
the pioneer plant, *these are able to grow in shallow soil and in
turn *will change the soil structure to enable trees/ shrubs to
grow, *these may also out-compete the other species by
interspecific competition for (a)biotic resources. *As the plants
continue to lose leaves and die/decay they will *increase the
amount of organic matter/humus.
Why is a climax community stable? (4)*A climax community is
where (both) animals and plants are present/has many species/has
high biodiversity; *there will be interaction between these species
but they *will have reached a balanced equilibrium of species.
*There may be a (co)dominant plant or animal species present.*This
is stable as long as theres no change to the environment/human
influence.Speciation and evolutionA gene mutation is.a change in
DNA due to the change/deletion/addition/duplication/substitution
bases/nucleotides.Genetic diversity in a species is..the variety of
alleles in a gene pool A gene pool is The total of all the alleles
in a population.Allele Frequency is. The proportion of one allele
within a gene pool/population
Explain why there is likely to be a greater genetic diversity in
a hybrid plant than in two separate species. (2)Because there are
*different alleles in each of the two populations as *each
population/ species is adapted to living in different environmental
conditions. *This means that there will be different mutations in
each population. *In a hybrid the alleles of the two different
species will mix and hybrids will receive alleles from both
species.
Suggest why scientists may classify organisms into sub-species
rather than two separate species. (2)*If the organisms were allowed
to interbreed and could *produce fertile and viable offspring they
could be considered as sub-species. *The hybrids/offspring can
flower and produce viable seeds.
Suggest how the two sub-species develop from a single ancestral
population, use boar. (5) First a *few ancestral boar reach the
island/ habitat from their original environment, there are now two
populations that have *geographical separation perhaps by the sea
or volcanic eruptions. *These populations are unable to interbreed
(reproductive isolation) and so the *gene flow between the
populations is restricted/ prevented. *There are only a small
number of boar, on the island (founder effect), for breeding
resulting in a *limited variety of alleles. *Mutations may then
occur (*increasing diversity) that are *acted on by different
environmental conditions/ selection pressures that are unique to
the island (not found on mainland) ie food, habitat; the boar will
*adapt to best suit these by natural selection, *those with the
mutation are more likely to survive and reproduce. These mutations
will *change the gene pool as they arise and possibly become more
common, so the two are now different, *changing the allele
frequency. *These changes will lead to phenotypic/
physiological/physical/ behavioural changes; as a result*
allopatric speciation may occur (can no longer interbreed)
Explain how the two different species of flower on an island may
have evolved from a single population of an ancestral species.
(6)*The original population was increasing in size and spreading
into a wider diversity of habitats where they were then
*reproductively isolated, *i.e. diversity in flowering times,
causing a *restriction of gene flow *between extremes of the
population. Each habitat would have different environmental factors
and so different selection pressures. *Mutations may then have
arisen (*causing a change in the allele frequency) and *other plant
features so that the *plants adapted to a specific region,
advantageous features/mutations would allow the plants to *survive
and reproduce, passing on new genes and creating *differences
between gene pools.
Suggest how ecological isolation contributes to speciation.
(2)*There may be different conditions /environments in each region,
i.e. a temperature difference, so *there will be different
selection pressures. The geographical isolation will mean that the
two populations are *reproductively isolated from one another
*causing a restricted gene flow/ separation of gene pools.
Suggest how genetic mutation may lead to speciation (2)*This
will give a rise to different alleles/ gene pool, leading to
*new/different phenotypes. This new *allele/gene may be
advantageous, and so will be passed onto offspring; it could also
be *disadvantageous.
Suggest why interbreeding does not take place between different
populations of species. (3) These different species are
reproductively isolated, meaning that they may have different
*breeding times/ seasons, *courtship
behaviour/rituals/displays/colour/songs. *Any offspring produced
between the species may be infertile or not viable.
Suggest how a distinct species evolves from another species. (5)
*Geographical isolation, e.g. a physical barrier between the
population occurs/allopatric speciation, this means there is
*reproductive isolation between the populations, *there is a
restriction of gene flow between but not within the populations.
*This creates two habitats that will contain different selection
pressures *e.g. different food sources, or different habitats.
*Mutations will have occurred, if they were advantageous they would
have *helped the species to adapt to the conditions, *these
alleles/genes would have been passed onto the offspring. This would
have caused *a change in the gene pool e.g. increasing frequency of
(mutation) alleles.
Suggest how the allele frequency for a plant eating mutation
could change as a forest develops. (4)*There will be a change in
frequency of either allele e.g. mutant increases/normal decreases
*due to the reproductive success of the mutant/non-photosynthetic
individuals. *As the trees develop the pond will be more shaded
this *(less light means) means less photosynthesis possible. *The
photosynthetic individuals die/nonphotosynthetic individuals
survive and *pass on the mutation/allele for using organic
compounds, *thus allowing more organic nutrients in pond.AS related
exam questionsPlantsPlant fibres that may be present in eaten
material are: sclerenchyma fibres, xylem vessels and cellulose
fibre.What plant tissue that would be the main source of the lignin
in a plant? Sclerenchyma/xylem.What material would be synthesised
to form the cell wall of seedlings? CelluloseWhat tissue would form
the vessels in a root, following differentiation? Xylemhydrogen and
glycosidic bonds are what would need to be broken to digest
cellulose.
Describe the chemical nature of cellulose. (3) Cellulose is a
*polysaccharide with an *unbranched/ straight chain. The cellulose
is made up of *B glucose joined by *1-4 glycosidic bonds between
the glucose molecules. Between each chain there are *intermolecular
hydrogen bonds to hold the structure together.
Suggest two advantages of growing crops of wheat in glasshouses
with artificial lighting rather than growing them in open fields.
(2) Because *crops can be grown out of season/all year round;
*plants photosynthesise 24 hours a day; *the crops will receive
less physical damage from weather/animals *as pest control is
easier. *You can also control other factors such as CO2,
temperature, humidity and water supplyCell divisionWhat is the
correct sequence of stages in mitosis? Prophase, Metaphase,
Anaphase, TelophaseTranscription takes place in the nucleus
DNA and stuffTriplet of bases that could not be found in mRNA
is.Adenine Thymine Guanine (etc)The sequence of triplets on a
section of DNA used to form a strand of pre-mRNA is a. cistron
Explain why a molecule of DNA can be described as a
double-stranded polynucleotide. (3) *It is double-stranded because
it is made of two strands *joined together by hydrogen bonds
between (the nucleotides) bases. *It is a polynucleotide as it is
made of many nucleotides * linked together by phosphodiester
bonds.Describe how the sequence of bases in a DNA molecule would be
used to form the primary structure of a protein. (5)*A sequence of
bases that form the genetic code determines the amino acid
sequence, *one triplet of bases codes for an amino acid. *The DNA
acts as a template when *transcription occurs (i.e. DNA unzips,
mRNA synthesised); *the mRNA synthesised then moves from the
nucleus to the cytoplasm, where *translation occurs (expand with
ribosomes, codon-anticodon interaction). *tRNA will carry an amino
acid and *peptide bonds form between the amino acids on different
tRNA molecules; this is the *sequence/ order of amino acids is the
primary structure of a protein.
How does mRNA form during transcription in the nucleus? (3)
First the *DNA strands unzip, *one side of the DNA strand is the
template strand that is used to from a mRNA strand *from free
nucleotides. The nucleotides join by *complementary base pairing,
*joined together by hydrogen bonds. *RNA- polymerase/ DNA Helicase
are the enzymes involved in these reactions.
Describe how free nucleotides are bonded together in the correct
sequence in pre-mRNA. (3) *The sequence of bases / nucleotides on
DNA determines sequence on (pre-)mRNA as the nucleotides can only
with their *complementary base pair e.g. AU / CG / GC / TA. *The
bonds between the nucleotides form in condensation reactions and
produce *phosphodiester bonds. *RNA-Polymerase is the enzyme that
catalyses this reaction.
Explain the function of the codons at each end of a strand of
mRNA, during the process of translation. (2)*The codons are either
Start/ Stop codons; *start codons are needed to begin polypeptide
synthesis and the Stop /Nonsense is needed to end polypeptide
synthesis.
Suggest why the final triplet of nucleotides, on the strand of
mRNA involved in the synthesis of this sequence of amino acids, did
not correspond with any anticodon on tRNA. (2) As it is the *stop
codon that is *used to end the sequencing/ further attachment of
tRNA; *signalling the release of the polypeptide/ ribosome.
Suggest why a variety of different protein structures could be
formed from the polypeptides synthesised using the mRNA molecules
from a single gene. (3) Different protein structures could be
formed as there are *variations of exons/ mRNA; this means that
each mRNA strand will have a *different primary structure due to a
different sequence of amino acids. *The secondary and tertiary
structure of proteins will depend on the primary structure/
sequence *due to different bonds *such as Hydrogen/ Ionic/
Disulphide bonds. Each protein will be developed into *different 3D
shapes as a result.
How does the translation of mRNA into the sequence of amino
acids in a ribosome occur? (3) First *a specific amino acid becomes
attached to tRNA *by the amino acid codon binding to the tRNAs
anticodon *e.g. tRNA with alanine has CGA anticodon which binds to
GCU on mRNA; only two tRNA molecules can be held on a ribosome at
any one time. The tRNA and the amino acid bond by the formation of
*peptide bonds using the enzyme *peptidyl transferase. *Only two
tRNA and amino acids can be held in a ribosome at any one time.
Name and describe the structures where the polypeptide chain of
an enzyme would be synthesised. (2)*On the ribosomes/poly(ribo)some
*which is made of rRNA/ribosomal RNA. OR *on the rRNA which is *a
ribosome attached to a membrane.
State two differences between fibrous proteins, such as actin
and myosin, and globular proteins, such as enzymes. DescriptionDNA
onlymRNA onlyBoth DNA and mRNA
Polymer formed from a single strand of nucleotides
Pentose present in thenucleotides
Adenine, cytosine, guanine and thymine present
Nucleotides linked byphosphodiester bonds
*Fibrous long/linear/straight chains and *Globular
compact/spherical; *Globular are folded and fibrous are not;
*Globular are soluble and fibrous are not; Fibrous are involved in
structural functions (keratine) and globular are not; *Globular are
involved in catalysis/metabolism (enzymes) and fibrous are not.
ConservationExplain how the work of zoos could be important to
the survival of endangered species. (2) Zoos may run
*captive-breeding programmes *which conserve alleles/genes/ the
gene pool of a species and may run *reintroduction programmes/
re-introduce species into suitable habitats in the environment.
Suggest why it is important to conserve rare and endangered
plants. (2 *This will conserve genetic diversity/genetic
variation/biodiversity. It may also *prevent extinction. Conserving
the plants may be good as they may be *useful as medicines/eq or
they may be *depended on by animals for food or as a habitat, there
may also be aesthetic reasons.
Suggest why many scientists consider that the use of protected
reserves is likely to be more successful for the conservation of
some animals than captive breeding programmes in zoos. (3) Reserves
will cause*less stress/trauma/discomfort/depressed for the animals
as *reserves provide a larger area for animals that require this.
Animals are *more likely to breed in their natural environment and
*larger numbers available will result in a wider gene pool. *There
are problems associated with releasing animals back into the wild
and these are avoided with reserves (I.e. habituation). *Disease is
less likely to wipe out the whole population. *reserves allow
natural interspecific relationships/communities to exist and
*natural family/social structure/behaviour,* i.e. because their
natural diet/food is available.MethodologyUsing a line of quadrats
to investigate the distribution of organisms is a transectQuadrats
may be divided up into smaller sections to... make it easier to
estimate/measure /count the organisms & so the results are more
preciseExplain the meaning of All other abiotic factors were
controlled.(2) *Abiotic factors are non-living/non-biological/do
not involve organisms.* If all other factors are controlled they
are kept constant/the same.
Explain how a quadrat would be used to obtain the mean density
of the two species in different areas. (3) *You will need to take
several/more than 2 using *random quadrat positions, *these can be
generated by a random number generator on your calculator (or other
suitable method).*You would then count the number of individuals in
each quadrat and then *calculate the mean density of the species
using the total number of each species divided by the total area
sampled (*you need to know the area of the quadrat to do this).
Suggest how results could be displayed in order to compare the
effect of temperature on the growth of seedlings of two species.
(3)You could use a *graph such as a *line graph with the *X&Y
axes correctly drawn (i.e. temp at bottom/Y and growth rate/time at
X). *You would use the same scale for the axes of both plants and
would *plot each temperature/ species of plant separately.
Suggest why seeds may be germinated at 18 C before being placed
in the experimental conditions. (2)*This was done to control
variables. *18C may be the optimum/ suitable temperature for
germination. * This technique makes sure that all the seeds are
viable OR can germinate *and so increasing the validity of the
investigation.
Suggest why taking photographs is a suitable method to count
invertebrates. (2) *As they move about a lot *they are difficult to
count *some might be counted more than once/missed out.
Why would it be difficult to determine which abiotic factor is
influencing the behaviour and distribution of a species?
(3)*Because for results to be (scientifically) valid *only one
factor can be varied, *other factors need to be kept constant.
*There will be many biotic factors in a habitat and these are
difficult to control. *It will be difficult to set test factor
values as a result.
Suggest how the scientists can have their results accepted by
other scientists. (2) *Work needs to appear in a (Scientific)
journal or being presented at a conference.*Peer review of work by
other scientists to *consider the studys validity or
reliability.
The temperatures used in this investigation were 0C, 10C, 20C,
30C, 40C and 50C.Suggest what the results of the investigation show
about the minimum temperature required for photosynthesis in
Elodea. Give a reason for your answer. (2)*The minimum temperature
is between 0oC and 10oC /above 0oC but less than 10oC, *no
photosynthesis occurs at 0oC as *water freezes at 0oC.*We know that
the minimum temperature is somewhere between 0 oC and 10 oC but
there are no measurements between these temperatures.
Enzymes control the rate of photosynthesis in Elodea. Discuss
how far the results of this investigation support her conclusion.
(4)Her conclusion is supported to some extent as *the shape of
graph is typical of an enzyme-temperature graph, i.e. *the rate
increases (up to 30 oC) *because more enzyme-substrate
complexes/collisions between enzymes and substrates and *the rate
decreases (after 30oC) due to enzyme denaturation. However it isnt
supported as *other factors could be affecting photosynthesis (e.g.
CO2 Concentration). *The gas/oxygen/carbon dioxide solubility also
changes with temperature. *The graph shows evidence of correlation
and not causation.
Describe and suggest explanations for the effects of these two
abiotic factors on the distribution of (A. elegantissima) on this
shore. (3) *There is no indication that temperature has an effect
e.g. little variation, only 2oC so *distribution must be influenced
by height above the low water mark *as the organism is more likely
to dry out at higher levels. There would also be *a difference in
food availability e.g. less at higher levels, more at lower levels
as it is *more likely to be eaten at lower levels.
Suggest how this data could be analysed to assess the
relationshipbetween these two abiotic factors and the distribution
of (A. elegantissima on this shore). (2)You could *plot graph(s) of
numbers of anemones against height and temperature/abiotic factors
and then look for a *correlation.You could also *use a statistical
analysis/test *such as the Spearmans Rank Correlation
Coefficient.
1. group A = 720 and group B = 662/662.4 2. units correct = {dm3
day-1 / dm3 per day};
Suggest two reasons why a suspension of cells of a unicellular
alga, in a solution, is more suitable for investigating CO2
production in photosynthesis than using leaves. (2)Because *samples
of cells can be taken easily and there will be *no damage to
plant/leaf /other cells during sampling; *The carbon dioxide level
(in water) can be adjusted/maintained/changed easily; *As alga is
single celled RuBP/GP/ products cannot pass into other cells/rest
of plant, the alga will also on have *one kind of cell and thats
the one that photosynthesises; You can *control the
mass/number/surface area of cells to ensure that isnt another
influencing factor; *genetically-similar cells will also be used
which will reduce variation and so other factors.
Suggest why it would be advisable to illuminate the cells at a
high light intensity during a photosynthesis and C02 experiment.
(3) *As light is needed for the light-dependent reaction keeping it
at a high intensity means *it will not be a limiting factor. *Thus
C02 concentration is the only limiting factor. *ATP/ rNADP are
produced during the light dependent reactions, *ATP/ rNADP/
light-dependent products are required for the light-independent
reactions/ Calvin cycle/ carbon-fixation.
Both *RuBP and GP levels remain constant until the carbon
dioxide is lowered; *these are used in the Calvin cycle. *At lower
carbon dioxide levels the RuBP increases and drops and then stays
constant, it *rises at 250seconds because it is being regenerated
and it falls at 310seconds as being used to fixate carbon dioxide
into GP. *The RuBP level remains constant once a (new) equilibrium
is reached.*At lower carbon dioxide levels the GP drops and then
stays constant, *it drops at 250 seconds because less carbon
dioxide is available to convert into GP/less carbon fixation
occurs. *It levels out at a lower level as carbon dioxide is still
available but at lower level. *credit manipulation of figures (i.e.
GP drops by 1au)
Compare the changes in mean environmental temperature between
the pre-monsoon and the post-monsoon periods from 1600 to 2000.
(3)*There is no/little change in pre-monsoon temperature but
post-monsoon has risen overall, although they *both fluctuate the
*fluctuations match each other; the fluctuations are within/less
than 1oC. *The range of (mean) temperatures is greater OR shows
greater fluctuations, in post-monsoon period. *Reference to a
particular change in both e.g. both decreased between 1800 to 1850.
*Credit correct manipulation of figures to compare with
units.Calculate the overall percentage increase in the mean NPP
from January to May. (3)*Correct readings from graph indicated e.g.
(11 and 1) *Correct subtraction e.g. (11-1 / 10) *Correct division
(by 1) x 100/1 to give 1000%
Using information from the graphs, describe and explain the
relative effects of temperature and hours of sunlight on NPP in
this grassland. (4)*Between January and April NPP increases as
light increases, there is a *correlation between NPP and light;
thus an *increase in light increases the rate of photosynthesis/ATP
and so the energy available for Calvin Cycle, this is because
*(credit correct details of photosynthesis) e.g. light results in
excitation of electrons. *The changes in NPP occur after the
changes in light/peak light is April and peak NPP is in May.But
there is *no real correlation between temperature and NPP/reference
to temperature fluctuating despite *temperature affecting how
quickly enzymes work, for example *NPP falls from May but the
temperature remains high. *Light and temperature are limiting
factors.
Use the data in the tables to suggest which of the two species
is better adapted for growth at a wide range of latitudes (distance
from the equator). Give reasons for your choice.(4)*Sea
plantain/Plantago maritima are better adapted. Because *different
latitudes have different mean temperatures and the *sea plantain
grows better in all threeTemperatures. Whereas *bog sedge/Kobresia
simpliciuscula does not grow very well at lower temperatures/10oC
and 14oC. *Credit appropriate comparative manipulated figures i.e.
Sea Plantain has 73g more dry mass after 50days in 10oC.
Give reasons for your answers. (4) *As the rate of growth is
linked to the rate of photosynthesis.*The top of the shore is
shallower and where most wavelengths are available/lower shore is
deeper where only green (and blue) wavelengths are available.*The
red weeds reflect/do not absorb red light OR green weeds reflect/do
not absorb green light, thus the *green seaweed has its highest
rates in red/blue light and is at its lowest in green light but
*would still grow well if all light waves were available. *The red
seaweed is at its highest rate of photosynthesis in green light
only and so *can only grow where only green light available.
*A. Because *in Central Europe temperatures never reach
25oC/data for 25oC is irrelevant/14oC is within the range/close to
the average temperature and *the mean temperature is 15.25/15.3oC.
*A has the highest rates of CO2 fixation at 14oC*therefore A will
grow well in the temperature range of Central Europe.*All others
would have relatively low yield at 14oC.
Suggest why the students were not able to draw valid conclusions
about the effect of saturation of the soil by water on the
distribution of the five plant species. (3)*Because saturation was
not measured/depth of water does not give saturation data, there
are *no data on other factors/variables that *may be affecting
distribution/notcontrolled/confounding *i.e.Temperature. *Only one
set of data is taken.
Mint
Common Duckweed
Soft Rush
Calculate the percentage of the mean GPP that remains as NPP
within plants on Earth.The mean GPP for plants on Earth is 24.4 106
J m2 year1.The plants use 3.7 106 J m2 year1 of this energy in
metabolic processes*24.43.7=20.7 *10024.4=4.09
Temperature
*The rate of growth increases as temperature increases between
13oC and 22oC/up to 22oC, it then *decreases between 22oC and
25oC/above 22oC *e.g. increases by 0.7a.u./4.5 times and decreases
by 0.1a.u. This is because *enzymes are involved in growth;
*molecules move about more/have more kinetic energy as the
temperature increases *therefore enzyme and substrate molecules
collide more/rate of enzyme-substrate complexes formation increases
as temperature increases.But after a fixed point there will be
*denaturation of some enzymes/protein molecules, *which decreases
the rate of growth/reactions as fewer enzyme molecules are
available.Suggest why it was important that this investigation was
carried out at a high light intensity. (3)*So that each temperature
has the same light intensity which *must be above the
threshold/compensation point *below which no net photosynthesis
takes place. This ensures that *light is not limiting factor/so
temperature is the only limiting factor.*Photosynthesis produces
material needed for growth.
Suggest two abiotic factors, other than light intensity, that
would need to be controlled in this (temperature)
investigation.*Wavelength/colour/frequency of light; *CO2
concentration; *pH of solution; mineral concentration