Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

BIOLOGY LONG QUESTION ANSWERS

TOPIC 1A – BIOLOGICAL MOLECULES
Suggest how glycogen acts as a source of energy don't include transport across membranes in your
answer (2marks)
*Hydrolysed to glucose *Glucose used in respiration to give energy
Describe how structure of starch & cellulose molecules are related to their function (5marks)
STARCH
*Helical shape= compact
*Large molecule/ insoluble so osmotically inactive & cannot leave cell
*Branched so glucose can easily be released for respiration
CELLULOSE
*Long, strong unbranched chains of B-glucose joint by hydrogen bonding
*To form micro fibrils= provide strength & rigidity
Compare & contract the sturucture & properties of triglycerides & phospholipids (5marks)
*Both contain Ester bonds, glycerol
*Fatty acids on both can be saturated or unsaturated
*Both insoluble in water and contain C, H and O
*Phospholipid has 2x fatty acid plus phosphate group
*Triglycerides are hydrophobic and phospholipid have hydrophilic and hydrophobic regions
*Phospholipids form monolayer on surface micelle/ bilayer in water but triglycerides don’t
Describe the structure of proteins (5marks)
*Polymer of amino acids
*Joined by peptide bonds, formed by condensation
*Primary structure is order of amino acids
*Secondary structure is folding of polypeptide chain due to hydrogen bonding
*Tertiary structure is 3-D folding due to hydrogen bonding and ionic/disulfide bonds
*Quaternary structure is two or more polypeptide chains
Use protein structure to explain why enzymes are specific and may be affected by non-competitive
inhibitors (6marks)
*Enzymes are specific, amino acid sequence- primary structure
*Folds in a particular way- tertiary structure specific
*Active site with unique structure which is complementary to substrate
*Inhibitor fits at site on enzyme other than active site
*Determined by shape
*Distorts active site therefore substrate no longer fit so no enzyme substrate complex formed
Describe competitive and non-competitive inhibition of an enzyme (6marks)
*Inhibitors reduce binding of enzyme to substrate / prevent formation of E-S complexes;
Competitive inhibition
*Inhibitor similar shape (idea) to substrate;
*(Binds) in to active site (of enzyme);
*(Inhibition) can be overcome by more substrate;
Non-competitive inhibition
*Inhibitor binds to site on enzyme other than active site;
*Prevents formation of active site / changes (shape of) active site;
*Cannot be overcome by adding more substrate;

BIOLOGY LONG QUESTION ANSWERS
A mutation can lead to the production of a non-functional enzyme
...
(6 marks)
*Change/mutation in base/nucleotide sequence (of DNA/gene);
*Change in amino acid sequence/primary structure (of enzyme);
*Change in hydrogen/ionic/disulphide bonds;
*Change in the TERTIARY structure/shape;
*Change in ACTIVE SITE;
*Substrate not complementary/cannot bind (to enzyme/active site) / no enzyme-substrate
complexes form;
Describe the biochemical test you would use to identify each of the following:
- Reducing sugars
- Non-reducing sugars
- Starch
- Proteins
- Lipids (6marks)
Reducing sugar
*Heat with Benedict’s reagent (blue);
*Brick red (orange/green/yellow) precipitate formed as positive result;
Non-reducing sugar
*Boil with acid (break glyosidic bonds); Heat with Benedict’s reagent (blue);
*Brick red (orange/green/yellow) precipitate formed as positive result;
Starch
*Add iodine / potassium iodide solution (orange/brown);
*Blue/black colour as positive result;
Proteins
*Add Biuret reagent (blue);
*Lilac/purple colour change as positive result;
Lipids
*Mix / crush / grind; with ethanol / alcohol; Then add water;
*Forms emulsion / goes white / cloudy as positive result;

BIOLOGY LONG QUESTION ANSWERS

TOPIC 1B – MORE BIOLOGICAL MOLECULES
Explain how the structure of DNA is related to its functions (6marks)
*Sugar-phosphate (backbone) & double stranded helix so provides strength, stability, protects bases
& hydrogen bonds;
*Long / large molecule so can store lots of information;
*Helix / coiled so compact;
*Base sequence allows information to be stored / base sequence codes for amino acids / proteins;
*Double stranded so replication can occur semi-conservatively, identical copies can be made;
*(Weak) hydrogen bonds for replication allow unzipping, strand separation
Describe and explain how the structure of DNA results in accurate replication
...
g
...
of H
bonds means it is not easily vaporised)
...
fluctuations);

BIOLOGY LONG QUESTION ANSWERS

TOPIC 2A – CELL STRUCTURE & DIVISION
Compare the structure of prokaryotic and eukaryotic organisms (6marks)
*Both bounded by cell membrane
*Both have ribosomes (although different sizes)
*Prokaryotic organisms have a cell wall, as well as eukaryotic, plants, fungi
*Prokaryotic organisms are much smaller in size than eukaryotic organisms
*Genetic material in prokaryotic organisms is a single loop of DNA that lies in the cytoplasm- in
eukaryotic organisms is in nucleus
*Prokaryotic cells have additional DNA- DNA in a ring called a plasmid (which are very rarely found in
eukaryotic organisms
Describe & explain how cell fractionation and ultracentrifugation can be used to isolate
mitochondria from a suspension of animal cells (5marks)
*Cell homogenisation to break open cells
*Filter to remove large debris/ whole cells
*Use isotonic solution to prevent damage to mitochondria/ organelles
*Keep cold to prevnt damage by enzymes
*Use buffer to prevent protein/ enzyme denaturation
*Centrifuge at lower speed to separate heavy oranelles like nuclei
*Re-spin supernatant at higher speed to get mitochondria in pellet
Describe how you could use cell fractionation to isolate chloroplast from leaf tissue (3marks)
*Cell homogenisation to break open cells, filter to remove large debris/ whole cell
*Use isotonic/cold/buffered solution to prevent damage
*Second pellet is chloroplast
Describe the appearance and behaviour of chromosomes during mitosis and explain how this
results in the production of two genetically identical cells
...
Explain how
...
(6marks)
*Hydrophobic tail, hydrophilic head;
*Head made from glycerol and phosphate;
*Tail made from two fatty acids; saturated / unsaturated fatty acid (in tail);
*Phospholipids form a bilayer; stability to membrane brought about by attraction between
hydrophobic tails / between hydrophilic heads and water;
*Phospholipid bilayer forms with heads in contact with water on both sides of membrane
*Hydrophobic tails found in centre (of bilayer) away from water;
*Phospholipids allow for membrane fluidity / flexibility;
*Fluidity / flexibility helps membranes to be (functionally) stable;
*Phospholipids with short fatty acids / unsaturated fatty acids are more fluid;
*Fluidity is important in breaking and remaking membranes (eg endocytosis / exocytosis);
List the functions of membrane proteins
...

*Carriers associated with facilitated diffusion
Explain how three features of a plasma membrane adapted for its functions (6marks)
*Phospholipid bilayer as barrier-forms a barrier to water soluble substances to pass bilayer is fluid
*Can bend take up different shapes for phagocytosis
*Channel proteins let water soluble substances through-facilitated diffusion
*Carrier proteins-through bilayer allow facilitated diffusion/ active transport
*Surface proteins-as antigens
*Cholesterol-regulates fluidity increases stability
Some substances can cross the cell-surface membrane of a cell by simple diffusion through the
phospholipid bilayer
...
Use ideas about osmosis
...
Lack of water can
cause plants to wilt
...

*The membrane is partially permeable as water is small enough to pass through the pores, however,
larger molecules such as sugar are too big to pass through the pores in the membrane
...

*Movement of water across the membrane occurs due to the random movement of water particles
...
This has resulted in a lack of turgor pressure in the cell
...
Eventually the cell contents will collapse away from the cell wall,
referred to as a plasmolysed cell
...
Explain how the
transport of sodium ions is involved in the absorption of glucose by epithelial cells
...
in cell is lower than in lumen (of gut);
*Sodium/Na+ ions enter by FACILITATED diffusion;
*Glucose absorbed with Na+ ions against their concentration/diffusion gradient / glucose absorbed
down an electrochemical gradient;

BIOLOGY LONG QUESTION ANSWERS
Oxygen and chloride ions can diffuse across cell-surface membranes
...
The diffusion of oxygen does not involve a membrane
protein
...
(5 marks)
*Chloride ions water soluble/charged/polar;
*Cannot cross (lipid) bilayer (of membrane);
*Chloride ions transported by facilitated diffusion OR diffusion involving channel/carrier protein;
*Oxygen not charged/non-polar;
*(Oxygen) soluble in/can diffuse across (lipid) bilayer;
Explain why a plant will wilt if not watered? (6marks)
*Water enters plant cells by osmosis
*When a plant is well-watered, the cells are turgid
*When a plant isn’t watered, it will lose water, as water will diffuse from the cells
*As water concentration is now lower outside the cell
*Cells will lose their turgidity
*The cell contents are no longer pushing against cell wall- the cell will become flaccid and the plant
will wilt
Describe how you would use a 1 moldm-3 solution of sucrose to produce 30cm3 of 0
...
5cm3 of 1
...
5cm3 distilled water
Describe how you would use the students results in table 3 to find the water potential of the
potato tissue (3marks)
*Plot the graph with concentration on x-axis and percentage change in mass on the y-axis
*Find concentration where curve crosses the x axis/ % change is zero
*Use another resource to find water potential of sucrose concentration where curve crosses x-axis
Explain how amino acids are transported from the ileum to the blood (4marks)
*Sodium ions and amino acids absorbed by co-transport via carrier proteins
*Sodium ions were removed from epithelial cells by active transport into the blood
*Maintains low concentration of sodium ions between small intestines and epithelial cells
*Sodium enters epithelial cells by facilitated diffusion taking amino acids with them from SI
*Amino acids move by facilitated diffusion into blood from epithelial cells
The scientists concluded that the cells in flask g took up ions by active transport explain how the
information given supports this conclusion (4marks)
*Negative gradient therefore doesn't go down concentration gradient
*Therefore requires energy so must be active transport
*Faster uptake in G due to ATP
*Sodium concentration goes to zero in flask G must be active transport or would reach an
equilibrium

BIOLOGY LONG QUESTION ANSWERS

TOPIC 2C – CELLS & THE IMMUNE SYSTEM
How does phagocytosis destroy pathogens (6marks)
*Phagocyte attracted by a substance / recognises (foreign) antigen;
*(Pathogen) engulfed / ingested;
*Enclosed in vacuole / vesicle / phagosome;
*(Vacuole) fused / joins with lysosome;
*Lysosome contains enzymes;
*Pathogen digested / molecules hydrolysed;
When a vaccine is given to a person, it leads to the production of antibodies against a diseasecausing organism
...
They secrete lots of antibodies specific to antigens
called monoclonal antibodies
Explain what an antibody is and why is suited to carry out its functions (4marks)
*Antibody- a protein immunoglobulin specific to an antigen
*Produced by B cells or secreted by plasma cells
...
(6marks)
*Leaves are broad, so there’s a large surface are for the exchange of gases and light absorption
...

*The lower surface/epidermis of leaves is full of stomata
...

*There are guard cells surrounding each stoma to control when it opens and closes
...

*There are air spaces in the spongy mesophyll layer
...

*There is a large internal surface are to volume ratio to provide a large area for gas exchange
...
This allows plant cells to make the most of the Sun’s energy by
absorbing as much of it as possible
...

*The upper epidermis is transparent to that light can pass through it to the chloroplasts in the
palisade mesophyll layer
...
Explain how the gills of a fish are adapted for
efficient gas exchange (6marks)
*Large surface area provided by lamellae / filaments increases diffusion / makes diffusion efficient;
*Thin epithelium / distance between water and blood;
*Water and blood flow in opposite directions / counter current;
*Maintains concentration gradient (along gill) / equilibrium not reached / as water always next to
blood with lower concentrations of oxygen;
*Circulation replaces blood saturated with oxygen;
*Ventilation replaces water (as oxygen removed);
Explain three ways in which and insects tracheal system is adapted for efficient gas exchange
(3marks)
*Thin walls short diffusion pathway
*Highly branched large surface area for gas exchange
*Large number of tracheal short diffusion pathway
*Fluid at end of tracheal faster diffusion

BIOLOGY LONG QUESTION ANSWERS
Explain the movement of oxygen into the gas exchange system of an insect when it’s at rest
(3marks)
Oxygen is used in respiration so concentration of oxygen gradient is established which leads to
diffusion
...
Explain relationship
between body mass and oxygen uptake (3marks)
*Small animals have a large surface area to volume ratio, lose more heat per gram of tissue, and
respire faster to maintain body temperature oxygen demand increase
...

*Vesicle is made by pinching off a piece of membrane; Fluidity of membrane allows this;
*Vesicles can be used to transport material around inside cells; proteins are transported in vesicles;
*From the rough endoplasmic reticulum to the Golgi apparatus; From the Golgi apparatus to the
plasma membrane;
*Formation of vesicle from plasma membrane allows material to be taken in;
*Endocytosis / pinocytosis / phagocytosis / phagolysosome is absorption of material using a vesicle;
*Fusion of vesicle with plasma membrane allows material to be secreted / passed out;
*Exocytosis is secretion of material using a vesicle; named example of endocytosis or exocytosis;
Describe how the fluidity of the membrane allows it to change shape, break and re-form during
endocytosis and exocytosis
...
called phagocytosis when solids / organisms are engulfed;
*Phagocytosis is called feeding in some unicellular organisms; called pinocytosis when solutions are
taken in (vesicles are much smaller); may be receptor-mediated (eg HIV); requires energy / active
process;
Different parts of the human digestive system help to break down molecules of fat so that they
can be absorbed into the body
...
(6marks)
*Mechanical breakdown in mouth / stomach
*Fats →fatty acids and / or glycerol by lipase (produced by) pancreas and small intestine
*Fat digestion occurs in small intestine
*Bile produced by liver neutralises acid from stomach produces alkaline conditions in intestine
*Increased surface area related to emulsification or chewing products are small molecules / watersoluble products absorbed by small intestine
Describe how proteins are digested in the human gut (4marks)
*Hydrolysis of peptide bonds
*Endopeptidases break polypeptides into smaller peptide chains
*Exopeptidases remove terminal amino acids
*Dipeptidases hydrolyse/break down dipeptides into amino acids
How epithelial cells are adapted to increase the rate of absorption (6marks)
*Villus intestinal wall has many folds to increase SA: Vol= microvilli
*Epithelial cells have numerous mitochondria to provide ATP for AT & thin layer cells= short
diffusion pathway
*Each villus has capillaries & a lacteal for transport of the products of digestion, helps keep steep
concentration gradient
*Villi maybe moved by the underlying muscle so enhancing diffusion gradient for uptake
Where does most digestion take place & what secretions does it receive (3marks)
Duodenum, pancreatic juice containing digestive enzymes & bile to neutralise stomach acid &
emulsify lipids
...

Procarboxypeptidase  Carboxypeptidase ~By membrane bound entropeptidase
Chymotrypsinogen  Chymotrypsin ~By membrane bound entropeptidase
Trypsinogen  Trypsin ~By membrane bound entropeptidase
Describe the absorption of glucose (4marks)
*Absorbed with Na, a co-transport protein carrier
*Na moves down its concentration gradient, bringing glucose up a concentration gradient
*Na gradient is kept by sodium potassium pump, actively removing Na from cell
*Glucose leaves cell by facilitated diffusion, carried away in the hepatic portal vein
Describe how the SI is adapted for digestion & absorption (5marks)
*Large SA provided by villi & microvilli
*Thin layer of cells= short diffusion pathway
*Rich network of capillaries (carrying sugars & amino acids) and lacteals (carrying products of fat
digestion)
*Maintain a steep concentration gradient
*Presence of protein carriers & channel in membrane allow for uptake of polar molecules
...
(6marks)
The oxygen dissociation curve of the foetus is to the left of that for its mother
...

*Association of oxygen at high p
...
of O2;
*In lungs haemoglobin has a high affinity for oxygen; Dissociates oxygen at low p
...
of O2;
*Unloading due to higher carbon dioxide concentration; Bohr Shift;
*Higher affinity, loads MORE oxygen at low / same / high PARTIAL PRESSURE / P
...
O2;
*(Therefore) oxygen moves from mother / to foetus;
Describe the two types of circulatory system and explain the advantage of a double circulatory
system over a single one
...
For this fish need a
two-chambered heart: one chamber to receive blood and one to pump blood to the gills and the rest
of the body
*A double circulatory system involves two circuits of blood vessels from the heart – one to the body
and one to the lungs
...
This allows the blood to be
pumped separately to, and received separately from, the lungs and the body
...

Blood is transported around the body in arteries, veins and capillaries
...
(6marks)
*Arteries carry blood away from the heart at high pressure, so the muscular walls are strong and
elastic to withstand this pressure
...

*Capillaries carry the blood close to every cell in the body in order to exchange substances with
them
...
This increases the rate of
diffusion by decreasing the distance over which it occurs
...
This means the walls don’t need to be as thick as in
arteries
...

*They also have valves to help keep the blood flowing in the right direction despite the low pressure
...
If the coronary arteries providing that
blood become narrowed or restricted, a person has a greater risk of suffering a heart attack
...
(6marks)
*Eating a diet high in saturated fat has been linked to high levels of cholesterol in the blood
...
This
causes plaques to form in the artery walls
...

*The coronary arteries can become narrowed through the formation of plaques
...
This is because blood flow to the heart is
restricted and the heart muscle receives less oxygen
...

*If the flow of blood to the heart is completely blocked, an area of the heart will be cut off from its
oxygen supply
...

Explain how nervous control in a human can cause increased cardiac output during exercise
(4marks)
*Coordination via medulla of brain/ cardiac centre
*Increased impulses along sympathetic nerve
*To S
...
node/ pacemaker
*More impulses/ increased rate of discharge sent from S
...
node/ pacemaker

BIOLOGY LONG QUESTION ANSWERS
Explain why increased cardiac output is an advantage during exercise (3marks)
*In exercise more energy release/ more respiration/ actively respiring mucles for aeorobic
respiration
*Higher cardiac output- increases O2, glucose supply to muscles
*Increased CO2, heat removal from muscles
Describe how muscles in the thorax cause air to enter the lungs during breathing (3marks)
*Diaphragm/intercostal muscles contract
*Increase volume of lungs
*Negative/lower pressure in lungs
Describe the difference in the composition of gases in inhaled and exhaled air explain how these
different gases are caused (4marks)
*Inhaled air contains more oxygen and air exhaled air less carbon dioxide and less water vapour
*Relative amount/percentage of nitrogen also changes
*Respiration and result in lower blood oxygen higher blood carbon dioxide
*Oxygen enters blood carbon dioxide and leaves blood in alveoli by diffusion water vapour diffuses
from the moist surface
Describe the transmission and course of infection of pulmonary TB (5marks)
*Bacteria transmitted in droplets
*Bacteria engulfed by phagocytes
*Bacteria encased in wall
*Bacteria aren’t active- not replicating
*If immuno suppressed bacteria activated
*Bacteria destroy alveoli leading to fibrosis and damage leads to less diffusion
*Also allows bacteria to enter blood spreading to other organs
Emphysema is another disease of the lungs
...

Explain why (5marks)
*Alveoli break down, less SA, loss of elastic tissue
*Alveoli cannot recoil, reduce diffusion gradient
*less O2 enters blood, less respiration= less energy (ATP) released
Apart from reduced elasticity, explain how to the lungs tissue reduce the efficiency of gas
exchange (4marks)
*Alveolar walls thicken= longer diffusion pathway
*Scarred/ fibrous tissue= reduced SA for gaseous exchange
Explain why a person with emphysema is unable to vigorous exercise (4marks)
*Not enough O2 for increased respiration for ATP needed for exercise
*Decreased SA of alveoli= longer diffusion pathway, less gas exchange of O2 into blood
Explain how oxygen in the red blood cells is made available for respiration in active tissues
(3marks)
*Low PH (more H+) due to increase CO2, increase respiration
*Increase dissociation of haemoglobin, low O2 tension in tissues/ plasma
*O2 diffuses from red blood cell tissues

BIOLOGY LONG QUESTION ANSWERS
When a person starts to breath out the % of O2 in the air first exhaled is the same as the % of O2
in the atmospheric air, why (2marks)
*Air is from nose/ trachea/ bronchi not been in alveoli, dead space
*Gas exchange diffusion only in alveoli not in these structures
Describe the cohesion-tension theory of water transport in the xylem (5marks)
*Water evaporates/ transpires from leaves
*Reduces water potential in cell, osmotic gradient across cells
*Water is drawn out of xylem- creates tension
*Cohesive forces between water molecules
*Water pulled up as a column
Explain how water enters the xylem from the endodermis in the root and is then transported to
the leaves (6marks)
*Active transport in the roots of ions/salts into the xylem lowers the water potential in the xylem
*Water enters the xylem down a water potential gradient by osmosis
*Water is transported through xylem to leaf where it evaporates through the process of
transpiration
*This contains a continuous stream of water cohesion due to the hydrogen bonding of water
molecules, this creates a negative pressure within the xylem
*Adhesion causes the water molecules to bind to the xylem which creates the continuous water
column
How are sieve cells adapted for mass transport?
*No organelles *Very little cytoplasm *Large vacuoles
*Large space/ thick walls= resist pressure  easier flow of water
How are companion cells adapted for transport of sugar between cells?
*Mitochondria release energy for active transport
*Ribosomes produce proteins which are linked to transport e
...
carrier proteins/ enzymes
Describe how a high pressure is produced in leaves (3marks)
*Water potential becomes lower (more –ve)
*Water enters phloem by osmosis
*Increase volume of water= increase pressure
Explain how xerophytic plants are adapted to reduce water loss (6marks)
*Thick waxy cuticle= waterproof/ impermeable
*Sunken stomata= saturated layer of still air outside
*Hairy= saturated layers of air still outside
*Leaves small needle shaped, rolled up in dry weather= stomata covered, reduced SA for water loss
*Reduced number stomata= reduced SA for water loss
*CAM (Crassulacean Acid Metabolism) = stomata open in dark & cool, closed in warm & light
Explain the relationship between the number of leaves removed from the plant shoot & the mean
rate of water uptake (3marks)
Increase number of leaves= decrease water uptake as decrease leaves= less stomata= decease SA=
decrease evaporation= decrease transpiration= decrease cohesion & tension

BIOLOGY LONG QUESTION ANSWERS
Mechanism of water movement (6marks)
*Energy from sun
*Water evaporates from spongy mesophyll cells and diffuse from tissues
*Decreases water potential in leaf cells
*Water moves out of xylem into tissues by osmosis, Decreases pressure in xylem
*Water sucked up xylem by cohesion tension, Decreases water potential in root system
*Water moves through root cells to xylem
*Decreases water potential in root epidermis cells
*Water moves into root hair cells from soil by osmosis
Describe the mass flow hypothesis for the mechanism of translocation in plants (6marks)
*In source / leaf sugars actively transported into phloem; By companion cells;
*Lowers water potential of sieve cell / tube and water enters by osmosis;
*Increase in pressure causes mass movement (towards sink / root);
*Sugars used / converted in root for respiration for storage;

BIOLOGY LONG QUESTION ANSWERS

TOPIC 4A – DNA, RNA & PROTEIN SYNTHESIS
Messenger RNA (mRNA) is used during translation to form polypeptides
...
Compare the two processes by
referring to where each takes place and the kind of products that are made
...
Describe how meiosis causes this variation and explain the advantage of
variation to the species (6marks)
*Crossing-over involves exchange of alleles between homologous chromosomes;
*Independent segregation; *Mutations
*Produces gametes which have a random combination of maternal and paternal alleles;
*Different adaptions, allows for coping in a changing environment
*Some survive, to reproduce; Pass on gene / allele;
Describe what happens to chromosomes in meiosis (6marks)
*Chromosomes shorten, thicken, condense;
*Chromosomes associate in homologous pairs, formation of bivalents;
*Crossing-over / chiasma formation;
*Join to spindle (fibres) / moved by spindle;
*(At) equator / middle of cell;
*(join via) centromere;
*(Homologous) chromosomes move to opposite poles and separate
*(Pairs of) chromatids separated in 2nd division;
Explain the importance of genetic variation in process of evolution (5marks)
*Causes variation in phenotype some organisms are better, have more favourable characteristics for
environment
*Natural selection, better adaptation organisms survive & reproduce passing on genes
*Selection due to different phenotypes being better suited to different environments
*Eventually leads to species change in/gene pool/ gene frequencies
Explain how crossing over occurs during meiosis 1 (2marks)
*Homologous pairs of chromosomes came together & pair up
*Chromatids twist around each other & bits of chromatids swap over
*The chromatids still contain the same genes but now have a different combination of alleles
Explain how crossing over can contribute to genetic variation (3marks)
*Sections of chromatids exchanged
*Sections have different alleles
*New combinations of linked alleles

BIOLOGY LONG QUESTION ANSWERS
Explain how each process contributes to genetic variation (5marks)
*Mutation
*Different/ new formed alleles sequence of genes changed
*Random fusion of gametes in fertilisation
*New combination of alleles
*Independent segregation of chromosomes
*Shuffling of maternal & paternal chromosomes
The emperor penguin is adapted to survive in extremely cold conditions
...

Explain how the adaptations described above help the penguins to survive in cold conditions
...
(6marks)
*A small surface area to volume ratio reduces heat loss through the surface of the skin
...
Warm blood flowing in arteries to
the feet transfers heat to cold blood returning to the heart in the veins
...

*The penguins might have e
...
a thick layer of blubber/thick feathers for insulation
...

*The penguins might migrate to warmer areas during the winter months to avoid having to cope
with the cold conditions
...
This saves energy as the penguin won’t
have to find food or keep itself as warm as if it was active
...
g
...
g
...
They thought that these
two species are closely related
...

*Compare DNA- sequence of bases,
*DNA hybridisation-Separate DNA strands, break hydrogen bonds, Mix DNA strands of different
species, Temperature required to separate hybrid strands indicates relationship
*Compare same named protein; Sequence of amino acids- primary structure;
*Inject seahorse with protein serum into animal, Obtain antibodies serum, Add serum from other
seahorse species, Amount of precipitate indicates relationship
Comparison of base sequences, how could base sequences provide evidence that 2 animals are
different?
*We expect species that are more closely related to show more similarity in their DNA base
sequences than those who are distantly related
...

*Amino acid sequence is the result of the base sequence
...

*Closer the amino acid sequence, closer the relationship
...

*DNA from one species is labelled by attaching a radioactive or fluorescent marker to it, mixed with
unlabelled
...

*Mixture is cooled to allow strands to combine with other strands that a have a COMPLEMENTARY
SEQUENCES OF BASES (allow H bonds to reform)
...

*Hybrid strands separated out, temp increased in stages
...

*Relationship is closer = more complementary bases, more base pairs
...

*The greater the number of hydrogen bonds, the stronger the hybrid strand
...

*The higher the temperature at which the strand splits = the more closely related
...


BIOLOGY LONG QUESTION ANSWERS
Immunological comparison of proteins
*Serum from species A is injected into species B
*Species B produces antibodies specific to all the antigen sites on species A
*Serum is extracted from species B, this serum contains antibodies specific to antigens in the serum
of A
*Serum is extracted from species C (the animal you want to find out how closely related Species A is
with)
...

*The antibodies respond to their corresponding antigens in the serum of species C
...

*Greater the number of similar antigens, the more precipitate is formed, the more closely related
the species are
...

Biologists can also use protein structure to investigate the relationship between different species
of crane
...
g
...

*Hierarchical based on SHARED CHARACTERISTICS, seen today

BIOLOGY LONG QUESTION ANSWERS

TOPIC 5A – PHOTOSYSNTHESIS & RESPIRATION
Basil thinks that his geranium shoots grow towards light
...

Method: I left one plant locked in a dark cupboard for one week
...
Look at the diagrams of the plants at the end
of the experiment
...
Is Basil right to draw this conclusion? Evaluate his method and
his conclusion
...

*Experiment was testing whether plant grows in light or dark
Evaluation of method:
*Not enough detail to allow method to be followed
*Condition of unidirectional light required/ should have blocked out light from all but one direction
*Not watering both batches equally
*Not leaving them to grow for the same length of time
*Not a ‘fair test’
*Not doing repeats / controlling variables
*Variables that were not controlled e
...
size of plant at the start
Use your knowledge of photosynthesis and respiration to describe and explain how the
concentration of carbon dioxide in the air changes:
- over a period of 24 hours
- at different heights above ground
...

Describe how crop plants use light energy during the light-dependent reaction
...

Explain how microorganisms in the soil produce a source of nitrates from these remains
...
(6 marks)
Excitation of chlorophyll molecule/electrons/ energy of (pairs of) electrons raised to higher energy
level;
Electron(s) emitted from chlorophyll molecule;
Electron(s) to electron transport chain;
Loss of energy by electron(s) along electron transport chain;
Energy lost by electron(s) is used to synthesise ATP;
From ADP + Pi;
In the presence of oxygen, respiration yields more ATP per molecule of glucose than it does in the
absence of oxygen
...
(5 marks)
Oxygen as terminal hydrogen/electron acceptor;
Operation of electron transport chain/ oxidative phosphorylation;
Fate of pyruvate;
Krebs cycle;
Significance of ATP formed in glycolysis;
The nettle leaves with the larger area had more chloroplasts, which produce ATP and reduced
NADP
...

(Reduced NADP and ATP) used in light-independent reactions;
To convert GP to triose phosphate / PGA  PGAL;
Reduction by reduced NADP / reduced NADP supplies hydrogen ions/atoms;
ATP supplies energy;
(Some) triose phosphate converted to hexose/glucose;
Explain why oxygen is needed for the production of ATP on the cristae of the mitochondrion
...

5C/RuBP combines with CO2; to form 3C compound / TP / GP;
using ATP;
and reduced NADP / eq;
2 molecules of 3C compound/ TP / GP form hexose;
all RuBP is regenerated;
10 molecules of 3C/TP/GP form 6 molecules of 5C/RuBP;

BIOLOGY LONG QUESTION ANSWERS
Describe the role of electron transport chains in the light-dependent reactions of photosynthesis
...
Describe what happens during photolysis
...
oxygen atoms
...

Glycerate 3-phosphate  (GP) Triose phosphate
This process requires two substances produced in the light-dependent reactions
...
Describe the role of each in the conversion of GP to triose phosphate
...
provides phosphate
...
Describe how
...
Energy from ATP;
Much of Indonesia is covered with forest
...

In these forests, nitrogen in dead leaves is made available to growing plants by the action of
bacteria
...
(5 marks)
Saprophytes; digest nitrogen-containing substances;
to produce ammonia;
Ammonia converted to nitrate ions; by nitrifying bacteria;
in an oxidation reaction
Describe how ATP is made in mitochondria
...
(4 Marks)
Releases energy in small / manageable amounts;
(Broken down) in a one step / single bond broken;
Immediate energy compound/makes energy available rapidly;
Phosphorylates/adds phosphate;
Makes (phosphorylated substances) more reactive / lowers activation energy;
Reformed/made again;
Explain why it is important for plants to produce ATP during respiration in addition to during
photosynthesis
...

Describe how
...
Some energy is lost from the
food web
...
(6marks)
*Energy enters the food chain from sunlight
*Energy trapped by banana plants/chlorophyll in leaves of banana plants by photosynthesis
*Energy trapped in food/sugar
*Energy transferred from one organism to another (from producer to primary consumer) by feeding
*Energy in banana plants transferred to root borers, banana aphids and banana skippers by feeding
*Energy transferred from primary consumers to secondary consumers/ants and wasps
*Energy transferred from secondary consumers to tertiary consumers/birds
*Energy is lost at each stage/trophic level as it is converted into less useful forms
*Examples of methods of energy loss from this food web includes excretion, heat from respiration
and egestion
...
(6 Marks)
Some light energy fails to strike/is reflected/not of appropriate wavelength;
Efficiency of photosynthesis in plants is low/approximately 2% efficient;
Respiratory loss / excretion / faeces / not eaten; Loss as heat;
Efficiency of transfer to consumers greater than transfer to producers/approximately 10%;
Efficiency lower in older animals/herbivores/ primary consumers/warm blooded
animals/homoiotherms;
Carnivores use more of their food than herbivores;
Describe the advantages and disadvantages of using biological agents to control pests
...
(5 Marks)
*Fertilisers/minerals/named ion (added to soil);
*Role of named nutrient or element e
...
nitrate/nitrogen for proteins
*Pesticides/biological control prevents damage/consumption of crop;
*Pesticides/weed killers /herbicides/weeding remove competition;
*Selective breeding / genetic modification (of crops);
*Glass/greenhouses enhance temp/CO2/ light;
*Ploughing aerates soil/improves drainage;
*Ploughing/aeration allows nitrification/decreases denitrification;
*Benefit of crop rotation in terms of soil nutrients/fertility/pest reduction;

BIOLOGY LONG QUESTION ANSWERS
Describe how the action of microorganisms in the soil produces a source of nitrates for crop
plants
...
(5 Marks)
*Variation/variety in pest population;
*Due to mutation;
*Allele for resistance;
*Reference to selection;
*Pests with resistance (survive and) breed / differential reproductive success;
*Increase in frequency of allele;
Explain how the decay of dead plants results in reduced oxygen concentration and increased
nitrate production
...

*These bacteria have to respire, this uses up oxygen
...
Nitrifying bacteria then
convert ammonium compounds
...

Describe the effect that an increased nitrate concentration may have in the river
...
Animals in the river will then die due to
lack of oxygen
...
These fields are separated from each other by hedges
...
Today the lake
has no fish and few plants or invertebrates
...
(5)
*leaching of nitrates;
*leads to increased growth of algae; death of plants;
*respiration of microorganisms uses up oxygen;
*fish die due to lack of oxygen
Use your knowledge of the nitrogen cycle to explain the potential benefit of applying a fertiliser
containing ammonium nitrate rather than one containing potassium nitrate
...

*decomposers/ saprotrophs;
*release enzymes and digest detritus, absorb products of digestion
*respired and CO2 released;
*used by plants in photosynthesis/ enters leaves;
In this food chain, the phytoplankton reproduce very rapidly
...

*Idea of rapid reproduction to replace population/standing crop / so they don’t become extinct;
*Idea of supplying energy/biomass to zooplankton;
*Idea of taking account of energy losses between trophic levels;
Explain the advantage of having both algae & bacteria in a purification pond (4marks)
*Breaks down organic matter
*Ammonia used by algae to make amino acids
*Algae photosynthesise
*Bacterial respiration uses O2 Respiration allows for reproduction
Purification ponds only work efficiently when they are shallow and warm
...

Carbon is present in a wide variety of compounds in the carbon cycle
...
(6 marks)
*photosynthetic material/plants will remove CO 2 from the atmosphere
*these plants will use the CO 2 to make glucose
*plant respiration will release CO 2 into the atmosphere
*animals will eat the plants which contain carbon
*animals and plants will eventually die and decay due to microbial/bacterial action releasing CO 2
*the combustion/burning of fossil fuels will release CO 2 into the atmosphere
*the burning of carbon based products made from trees will release CO 2 into the atmosphere

BIOLOGY LONG QUESTION ANSWERS

TOPIC 6A – STIMULI & RESPONSE
Describe the path taken by a nerve impulse in this reflex, from stimulus to response
...

*The impulse travels along a sensory neurone to the central nervous system/spinal cord
...

*These chemicals cause impulses to be sent along the relay neurone
...

*The impulse then reaches the muscle, which contracts to move your hand away from the course of
pain
...
Describe
how
...

Describe how
...
Explain what causes her heart rate to increase while she
exercises
...
Explain how impulses are transmitted in a reflex
arc to prevent a person from injuring themselves (6 marks)
*a reflex response is an involuntary response, doesn’t involve the brain
*involve sensory neurones, relay neurones & motor neurones in the spinal cord
*impulses travel along neurones as electrical signals
*the axon is insulated by the myelin sheath which ensures the electrical signal does not lose energy
at the junction between two neurones there is a synapse
*the message is carried across the synapse by neurotransmitters, travels from the stimulus along the
axon and dendron of the sensory neurone to the spinal cord
*the reflex arc is important to keep the body safe
...
(4 marks)
*membrane relatively impermeable / less permeable to sodium ions / gated channels are closed /
fewer channels;
*sodium ions pumped / actively transported out;
*by sodium ion carrier / intrinsic proteins;
*inside negative compared to outside / 3 sodium ions out for two potassium ions in;
Explain what causes the conduction of impulses along a non-myelinated axon to be slower than
along a myelinated axon
...
(4 marks)
*action potential arrives / depolarisation occurs;
*calcium ions enter synaptic knob; vesicles fuse with membrane;
*acetylcholine diffuses (across synaptic cleft); binds to receptors;
The binding of GABA to receptors on postsynaptic membranes causes negatively charged chloride
ions to enter postsynaptic neurones
...
(3 marks)
*inside becomes more negatively charged / hyperpolarised;
*stimulation does not reach threshold level / action potential not produced;
*depolarisation does not occur / reduces effect of sodium ions entering;
When the postsynaptic membrane is stimulated by acetylcholine, an action potential is less likely
if GABA is released at the same time
...
(4 marks)
*GABA opens K+ and Cl– channels so K+ passes out and Cl– passes in;
*Membrane potential more negative / hyperpolarised;
*Requires increased stimulation / must open more Na+ channels / allow more Na+ to enter;
*To reach threshold;

Receptor

Receptor
neurone

Central nervous
system
Relay
neurone

Effector

Effector
neurone
Synapse B
Point A

BIOLOGY LONG QUESTION ANSWERS
Describe and explain the events which occur in the effector neurone at point A during the passage
of a nerve impulse
...
D
...

*Increased permeability of (presynaptic) membrane to calcium ions;
*Ca 2+enter; vesicles fuse with membrane;
*exocytosis of release of acetylcholine
*diffuses across synaptic cleft; binds to receptors on postsynaptic membrane
*increased Na + permeability / opens sodium channels / depolarises membrane
*acetylcholine broken down by acetylcholinesterase;
Describe the role of calcium ions & ATP in the contraction of a myofibril (5 marks)
*Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum;
*(Calcium ions) cause movement of tropomyosin (on actin);
*(This movement causes) exposure of the binding sites on the actin;
*Myosin heads attach to binding sites on actin; Hydrolysis of ATP (on myosin heads) causes myosin
heads to bend;
*(Bending) pulling actin molecules; Attachment of a new ATP molecule to each myosin head causes
myosin heads to detach (from actin sites)
...

*Phosphocreatine allows the regeneration of ATP under anaerobic conditions
*it replenishes phosphate from ATP when the muscle is relaxes to it can release phosphate to join
ADP and form ATP
Endurance athletes, such as marathon runners, nearly always have a high proportion of slow fibres
in their muscles
...
(6 marks)
*Slow fibres contract more slowly and provide less powerful contractions over a long period of time
...

*Slow fibres are adapted to aerobic respiration as they have many mitochondria (the side of the
krebs cycle and electron transport chain) which produce large amounts of ATP and are also resistant
to fatigue
...
Describe the pattern of blood
circulation in a mammal that causes blood to return to the kidney
...
(6 Marks)
*High osmotic potential detected by osmoreceptors in hypothalamus
*More ADH secreted from pituitary into blood
*To collecting duct, becomes more permeable,
*Water absorbed due to low water potential in medulla
Explain the function of the Loop of Henle in osmoregulation
...
Describe the role
of the nephron and collecting duct in achieving this increase in concentration
...
g: glucose
*Pass through basement membrane acts as filter;
*Protein too large to go through so stays behind;
*Presence of pores in capillaries

BIOLOGY LONG QUESTION ANSWERS
Explain how a lack of insulin affects reabsorption of glucose in the kidney of a person
who doesn’t secrete insulin (4 Marks)
*High conc of glucose in blood, high conc in filterate
*Reabsorbed by facilitated diffusion requires proteins
*These are workings at saturation, not all glucose is reabsorbed (some lost in urine)
Some desert mammals have long loops of henle & secrete large amounts of ADH
...
(4 marks)
*GN and gn linked, GgNn individual produces mainly GN and gn gametes,
*Crossing over produces some / few Gn and gN gametes, So fewer Ggnn and ggNn individuals
...

(2 marks)
Chi squared test, Categorical data
...
(6 marks)
*4 year cycles, Predator-stoat
peaks after prey- lemming
*Lemmings increase due to low
numbers of stoats available food
*More food for stoats so
numbers increase
*increased predation reduces
number of lemmings
*Number of stoats decreases due
to lack of food

James Bay is a large ocean bay in northern Canada
...
One
species of lemming inhabits the eastern side of James Bay and another species of lemming
inhabits the western side
...
Explain how two species of lemming evolved from the original species
...
5 was calculated from these results
...
001
...
(3 marks)
*p less than 0
...
(3 marks)
*Use of random numbers to place quadrats, number of individuals counted in large number of
quadrats, little variation random, large variation - clustered

BIOLOGY LONG QUESTION ANSWERS

TOPIC 7B – POPULATION & EVOLUTION
Both species are now found in the UK but the two species cannot interbreed with each other
...
Suggest an
explanation for the development of these different species
...
(6marks)
*Speciation requires reproductive isolation
...

*Reproductive isolation could have been caused by the Congo River acting as a physical barrier,
making the populations to the north and south of the river geographically unable to interbreed
...

*Over a long period of time, beneficial features may have spread through the populations through
the process of natural selection
...

*Eventually, individuals into eh populations to the north and south of the river may have developed
such different features they were no longer able to interbreed to produce fertile offspring
...

On islands in the Caribbean, there are almost 150 species of lizards belonging to the genus
/Anolis/
...

Explain how the Caribbean species could have evolved
...

Scientists believe that these two species have evolved from a common ancestor
...
(6marks)
*Isolation splitting by geographical barrier
*There was variation-different alleles
*Different environmental conditions
*Natural selection acted on the isolated populations
*Only certain alleles passed on to offspring, different alleles passed on in different environments
so differences lead to inability to interbreed

BIOLOGY LONG QUESTION ANSWERS

TOPIC 7C – POPULATION IN ECOSYSTEMS
Describe & explain the changes which occur in the learning & stoat population (6marks)
*4 year cycles
*Predator/ stoat peaks after prey/ lemming
*Lemmings increase due to low number of stoats/ available food
*More food for stoats so numbers increases
*Increased predation reduces number of lemmings
*Number of stoats decreases due to lack of food/ starvation
Anolis sagrei is a species of lizard that is found on some of the smallest Caribbean islands
...
(4 marks)
*Capture/collect sample, mark AND release;
*Method of marking does not harm lizard/make it more visible to predators;
*Leave sufficient time for lizards to distribute before collecting a second sample;
*Population = number in first sample x number in second sample divided by number of marked
lizards in second sample
Describe the advantages and disadvantages of using chemical pesticides to control pests of crops
...
(5 marks)
ADVANTAGES *Specific to 1 pest *Only needs 1 application *Maintains low population
*Pests don’t develop resistance *Doesn’t leave chemical in environment (no bioaccumulation)
*Can be used in organic farming
DISADVANTAGES *Doesn’t get rid of pests completely *May become a pest itself
*Slow acting, time lags to reduce post population
Succession occurs in natural ecosystems
...
(6 marks)
*Colonisation by pioneer (species);
*Change in environment enables other species to colonise/survive;
*Change in diversity/biodiversity;
*Stability increases / less hostile environment;
*Climax community is reached
...
(4 marks)
*Two strands therefore semi-conservative replication
*base pairing, hydrogen bonds holds strands together weak- easily broken, allow strands to
separate;
*bases sequence act as template, complimentary copy;
*DNA one parent and one new strand;
Describe how altered DNA may lead to cancer (6marks)
*(DNA altered by) mutation; (mutation) changes base sequence;
*Of gene controlling cell growth / oncogene / that monitors cell division;
*Of tumour suppressor gene;
*Change protein structure / non-functional protein / protein not formed;
*(Tumour suppressor genes) produce proteins that inhibit cell division;
*Mitosis; Uncontrolled / rapid / abnormal (cell division); malignant tumour;
Explain how the methylation of tumour suppressor genes can lead to cancer
...

Explain how alterations to tumour suppressor genes can lead to development of tumours (3
marks)
*Increased methylation of tumour supressed gene
*Mutation in gene
*Gene to not be transcribed/ gene isn’t expressed
Some cancer cells have a receptor protein in their cell-surface membrane that binds to a hormone
called growth factor
...
Scientists have produced a
monoclonal antibody that stops this stimulation
...
(3 marks)
*Antibody has specific tertiary structure / binding site
*Complementary shape to receptor protein binds to receptor protein on GF
*Prevents GF binding (to receptor)
...
Describe the process of cloning
used to produce Dolly the sheep
...

*The nucleus of a sheep’s egg was removed
...

*Another nucleus was inserted in the egg cell
...

*The cell was given an electric shock to make it divide by mitosis
...
The embryo was Dolly the sheep – a clone
...
Suggest two reasons why
(4 marks)
*Only infected cells have HIV protein on surface- so siRNA can only enter these cells
*siRNA (base sequence) complementary one mRNA- so only infected cells contain mRNA of HIV
stops translation of this gene

BIOLOGY LONG QUESTION ANSWERS

TOPIC 8B – GENOME PROJECTS & GENE TECHNOLGY
The DNA probe the geneticist used was for an exon in the DNA, not an intron
...
Describe how the
PCR is carried out (6 marks)
*DNA heated to 95°C strands separate
*Cooled to 50°C, primers bind
*Nucleotides attatch by complementary base pairing
*Temp 72°C DNA polymerase joins nucleotides together
*Cycle repeated
Describe how gene probes are used to identify alleles (6 marks)
*DNA probes are short strands of DNA complementary base sequence to target allele
*DNA probe will hybridise the target allele
*DNA probe is either labelled radioactively or fluorescently marked
*Restriction enzymes digest the DNA sample- separate using gel electrophoresis
*DNA fragments are transferred to nylon membrane and incubated with fluorescently labelled
probe
*If allele present then DNA probe will hybridise with it
*Expose membrane to UV light, if gene is present there will be a florescent band
Evaluate re-combinant DNA technology (6 marks)
* Medicine & drugs
*Agriculture (nutrition & resistance)
*Increase crop yield
*Monoculture leads to less resistance to diseases besides the odd one
*Unknown risks, don’t know genetic effects- could cause chronic diseases
*Research could harm other animals- ethics
*Risks to ecosystems & biodiversity

BIOLOGY LONG QUESTION ANSWERS

PRACTICAL SKILLS
Describe how you would use a -metre × -metre quadrat frame and a 30-metre tape measure to
obtain data similar to the data shown in the diagram
...
(6marks)
*Use of tape measure to produce transect
*Placing of quadrats
*Transect placed across stream
*Score presence of each plant species
*Use quadrat at regular intervals along tape
*Repeat transect several times (≥ 3), along stream, at random or regular intervals
Describe how you would decide the number of quadrats to use in order to collect representative
data (2marks)
Calculate remaining mean when enough quadrats this shows little change if plotted like a graph
...

Describe aseptic techniques and justify the chosen method (6marks)
*Keep lid on Petri dish, open lid as little as possible; To prevent unwanted bacteria contaminating
the dish or avoid bacteria getting out;
*Wear gloves, mask and wash hands; prevent spread of bacteria outside the lab;
*Use sterile pipette or Flame the loop or the neck of the container of the culture; maintain a pure
culture of bacteria;
*Use Bunsen Burner to maintain upward movement of air; Helps to prevent contamination of
culture when lid is removed;



---