Studied by 12 people
Outline the processes that occur in a cell during interphase, including those needed to prepare for mitosis.
4 marks
DNA replication
DNA transcription
enzyme/ protein synthesis
biochemical reactions/ example of a biochemical reaction
cell respiration
growth
organelles replicated
Outline the thermal, cohesive and solvent properties of water.
5 marks
Water has a high specific heat capacity;
a large amount of heat causes a small increase in temperature;
water has a high latent heat of vaporisation;
a large amount of heat energy is needed to vaporise/evaporate water;
hydrogen bonds between water molecules make them cohesive/stick together;
this gives water a high surface tension / explains how water rises up xylem;
water molecules are polar; this makes water a good solvent;
Describe the significance of water to living organisms.
5 marks
Each feature or property must be related to living organisms in order to receive a mark.
Features may include:
surface tension - allows some organisms (e.g. insects) to move on water's surface
polarity / capillarity / adhesion - helps plants transport water
(excellent) solvent - capable of dissolving substances for transport in organisms
(excellent) thermal properties (high heat of vaporisation) - excellent coolant
ice floats - lakes / oceans do not freeze, allowing life under the ice
buoyancy - supports organisms
structure - turgor in plant cells / hydrostatic pressure
habitat - place for aquatic organisms to live
Describe the use of carbohydrates and lipids for energy storage in animals.
5 marks
Answers must discuss both carbohydrates and lipids to receive full marks
Carbohydrates
stored as glycogen (in liver)
short-term energy storage
more easily digested than lipids so energy can be released more quickly
Lipids
stored as fat in animals
long-term energy storage
more energy per gram than carbohydrates
lipids are insoluble in water so less osmotic effect
Describe the genetic code.
6 marks
composed of mRNA base triplets called codons
64 different codons
each codes for the addition of an amino acid to a growing polypeptide chain
the genetic code is degenerate
meaning more than one codon can code for a particular amino acid
the genetic code is universal
meaning it is the same in almost all organisms
(AUG is the) start codon
some (nonsense) codons code for the end of translation
Explain briefly the advantages and disadvantages of the universality of the genetic code to humans.
4 marks
genetic material can be transferred between species/ between humans
one species could use a useful gene from another species
transgenic crop plants/ livestock can be produced
bacteria/ yeasts can be genetically engineered to make a useful product
viruses can invade cells and take over their genetic apparatus
viruses cause disease
Compare how pyruvate is used in human cells when oxygen is available and when oxygen is not available.
5 marks
aerobic cell respiration if oxygen available and an anaerobic if unavailable;
pyruvate enters mitochondria for aerobic respiration; whereas pyruvate stays in the cytoplasm for processing under anaerobic conditions;
pyruvate converted aerobically into carbon dioxide
and water; whereas pyruvate converted anaerobically to lactate
Large ATP yield when oxygen available/from aerobic
cell respiration; no (further) ATP yield without oxygen;
Explain the role of water in photosynthesis.
4 marks
water is a substrate / reactant / raw material / for photosynthesis / equation for photosynthesis
water is a source of electrons to replace those lost by chlorophyll / photosystem II
water is a source of H+ needed to produce NADPH + H
photolysis / splitting / breaking of water
water for non-cyclic photophosphorylation / ATP production
water is transparent so photosynthesis can take place underwater / light can penetrate to chloroplasts
Define the terms gene and allele and explain how they differ.
4 marks
gene is a heritable factor / unit of inheritance
gene is composed of DNA
gene controls a specific characteristic / codes for a polypeptide / protein
allele is a form of a gene
alleles of a gene occupy the same gene locus / same position on chromosome
alleles differ (from each other) by one / a small number of bases(s)/ base pair(s)
Describe the consequences of a base substitution mutation with regards to sickle cell anaemia.
7 marks
the sequence of nucleotide bases in DNA codes for the sequence of amino acids in proteins
DNA is transcribed into mRNA, which is translated into amino acids of protein
normal (ß chain) haemoglobin gene / DNA produces normal (ß chain) haemoglobin protein / amino acids
substitution= the replacement of one (or more) nucleotide base with another caused by a copying mistake during DNA replication
As a result of a mutagen / X-rays / chemical / UV radiation / other mutagen mutation in normal (ß chain) haemoglobin gene alters the sequence of nucleotide bases
normal nucleotide sequence = CTC altered to CAC
resulting in altered mRNA (GAG to GUG) during transcription
resulting in altered sequence of amino acids in (ß chain) haemoglobin protein
(glutamic acid to valine) during translation
causing red blood cells to change shape / sickle under low oxygen conditions
causing sickle cells anaemia when two copies of the mutated gene are inherited
producing a sickle cell carrier when one copy of the mutated gene is inherited
sickle cells anaemia reduces oxygen flow to organs, leading to their deterioration
Compare the processes of mitosis and meiosis.
6 marks
Answers must be pairwise comparisons to receive any marks.
Mitosis: one cell division & Meiosis: two divisions
Mitosis: chromosome number does not change & Meiosis: converts diploid to haploid cells
Mitosis: products genetically identical & Meiosis: products genetically diverse
Mitosis: separation of sister chromatids in anaphase & Meiosis: separation of homologous chromosomes in anaphase I and sister chromatids in anaphase II
Mitosis: no crossing over & Meiosis: crossing over in prophase I
Mitosis: no formation of tetrads / no synapsis & Meiosis: formation of tetrads /synapsis
Mitosis: produce cells for growth/repair/asexual reproduction & Meiosis: produce sexual cells / gametes for sexual reproduction
Mitosis: two cells produced & Meiosis: four cells produced
Mitosis: daughter cells with both copies of chromosomes/random assortment does not occur & Meiosis: random assortment of maternal/ paternal chromosomes
Mitosis: replication of DNA in interphase & Meiosis replication of DNA in interphase
Mitosis: four phases: prophase, metaphase, anaphase and telophase & Meiosis: same four phases twice
Outline one example of inheritance involving multiple alleles.
5 marks
multiple alleles means a gene has three or more alleles / more than two alleles
ABO blood groups
ABO gene has three alleles
IA IB and i shown
any two of these alleles are present in an individual
homozygous and heterozygous genotype with phenotypes (shown somewhere)
all six genotypes with phenotypes given (shown somewhere)
example / diagram of a cross involving all three alleles
Describe the inheritance of ABO blood groups including an example of the possible
outcomes of a homozygous blood group A mother having a child with a blood group O father.
5 marks
example of co-dominance
multiple alleles / 3 alleles
(phenotype) O has (genotype) ii
B can be IB IB or IB i
A can be IA IA or IA i
AB is IA IB
(P are) i i x IA IA
(gametes) i and IA
(F1 genotype) IA i
(F1 phenotype) blood group A
accept other notations if used consistently and if phenotype and genotype are clearly distinguished
Outline sex linkage.
5 marks
gene carried on sex chromosome / X chromosome / Y chromosome
inheritance different in males than in females
males have only one X chromosome therefore, only one copy of the gene
mutation on Y chromosome can only be inherited by males
women can be carriers if only one X chromosome affected
example of sex linked characteristics (e.g. haemophilia / colour blindness)
example of cross involving linkage
Explain, using a named example, why many sex-linked diseases occur more frequently in men than women.
9 marks
named example of sex-linked disease caused by recessive allele on the X chromosome
example of pair of alleles (e.g. X H and X h)
(reject if alleles do not correspond)
females are XX and males are XY
females have two alleles of the gene and males have only one
allele causing the disease is rare / uncommon
probability of females inheriting rare allele twice as low
calculation of squaring the gene frequency
female would have to inherit the allele from her father who would have suffered from the disease
so females can carry the gene but still be normal but males (with the gene) will have the disease
Discuss the definition of the term species.
8 marks
a species is a group of organisms
a species shares a common gene pool
showing similar morphology / characteristics
capable of interbreeding and producing fertile offspring
but dissimilar organisms sometimes interbreed eg. mule formed by crossing horse and donkey / other example of interspecific hybridization
interspecific hybrids are sometimes fertile
sometimes organisms that are very similar will not interbreed
Drosophila pseudoobscura and persimilis / other example of sibling species
reference to the problem of defining fossil species
reference to the problem of species that only reproduce asexually
reference to the problem of isolated populations gradually diverging
State what carbon fluxes and carbon sinks are and describe how carbon fluxes are measured
4 marks
a carbon flux is the rate of exchange of carbon between the various carbon sinks;
a carbon sink is a forest, ocean or other natural environment viewed in terms of its ability to absorb carbon dioxide from the atmosphere;
example of a carbon sink (lithosphere, hydrosphere, atmosphere, biosphere)
not possible to directly measure the size of carbon sinks and fluxes;
due to constant changes;
global carbon fluxes are very large and estimated in gigatonnes per year
Outline the events that occur within the heart, which cause blood to move around the body.
6 marks
blood is collected in the atria
blood is pumped from the atria to the ventricles
opened atrio-ventricular valves allow flow from the atria to the ventricles
closed semi-lunar valves prevent backflow from the arteries to the ventricles
blood is pumped out from the ventricles to the arteries
open semi-lunar valves allow flow from ventricles to arteries
closed atrio-ventricular valves prevent backflow to the atria
pressure generated by the heart causes blood to move around the body
pacemaker (SAN) initiates each heartbeat
Explain the relationship between the structure and function of arteries, capillaries and veins.
9 marks
(3 marks maximum for information on arteries.)
carry blood away from the heart
have thick walls to withstand high pressure / prevent bursting
have muscle fibres to generate the pulse / help pump blood / even out blood flow
have elastic fibres to help generate pulse / allow artery wall to stretch / recoil
(3 marks maximum for information on capillaries.)
allow exchange of oxygen/carbon dioxide/ nutrients/waste products from tissues/cells
have a thin wall to allow (rapid) diffusion / movement in / out
have pores / porous walls to allow phagocytes / tissue fluid to leave
are narrow so can penetrate all parts of tissues / bigger total surface area
(3 marks maximum for information on veins.)
carry blood back to the heart / from the tissues
have thinner walls because the pressure is low / to allow them to be squeezed
have fewer muscle / elastic fibres because there is no pulse / because pressure is low
have valves to prevent backflow
Discuss the benefits and dangers of vaccination.
(7 marks)
Benefits: 4 max
immunity results can limit pandemics/epidemics/spread of (infectious) diseases;
diseases can be eradicated/smallpox eliminated;
reduces mortality/deaths due to disease; can protect vulnerable groups/young/old/with other
conditions;
decrease crippling effects of diseases (such as polio);
decreased health care costs;
Dangers: 4 max
may produce (mild) symptoms of the disease;
human error in preparation/storage/administration of vaccine;
individual may react badly to vaccine / defective immune system / hypersensitive/allergic reaction;
immunity may not be life-long/booster required;
possible toxic effects of mercury-based preservatives
Describe the mechanism of ventilation in the human lung.
5 marks
consists of inhaling and exhaling air / exchanging stale air with fresh air (with the environment)
external intercostal muscles contract moving the rib cage up/out
diaphragm contracts
increase volume of thorax / lowers lung pressure relative to air pressure / pulls air in
diaphragm relaxes
abdominal muscles contract
internal intercostal muscles contract moving the rib cage down/in
force air out / decreases volume of thorax / raise lung pressure relative to air pressure
Describe the need for a ventilation system.
6 marks
(small) animals obtain oxygen (by diffusion) through skin / in humans (large)
animals skin is ineffective for ventilation
humans are large / have a small ratio of surface area:volume so need ventilation system to increase surface area
to maintain a concentration gradient in alveoli as oxygen is used in respiration (and carbon dioxide is produced)
gaseous exchange occurs between air in alveoli and blood capillaries
alveoli have high ratio of surface area:volume (to facilitate ventilation)
to bring in fresh air (and remove stale air)
Explain the need for, and mechanism of, ventilation of the lungs in humans.
8 marks
draws fresh air / oxygen into the lungs
removal / excretion of carbon dioxide
maintains concentration gradient of oxygen / carbon dioxide / respiratory gases
diaphragm contracts
(external) intercostal muscles contract
increased volume (of thorax / thoracic cavity)
decreasing air pressure in lungs
air rushes in down air pressure gradient
converse of the above causes exhalation
abdominal muscles contract during active exhalation
elastic recoil of lungs helps exhalation
Many processes in living organisms, including ventilation and gas exchange, involve moving materials. State the differences between ventilation and gas exchange in humans.
4 marks
ventilation:
2 max
movement of air
movement in and out of the lungs
caused by muscles
an active process
involves mass flow / involves flow along air passages
gas exchange
2 max
movement of carbon dioxide and oxygen
(occurs when) oxygen moves from lungs / alveoli to red blood cells / carbon dioxide moves to lungs / alveoli from red blood cells
(occurs when) oxygen moves from red blood cells to
tissues / carbon dioxide
moves to red blood cells from tissues
a passive process / diffusion
takes place across a surface
Outline the general organisation of the nervous system.
4 marks
formed of central nervous system
brain and spinal cord
peripheral nervous system divided into voluntary and autonomic nervous systems
autonomic nervous system consists of sympathetic and parasympathetic nervous system
voluntary nervous system has motor and sensory neurons
Outline the changes that lead to the depolarization of an axon as an action potential travels along a neuron.
5 marks
local currents / ions diffuse from adjacent depolarized section of axon
resting / membrane potential reduced
voltage-gated ion channels affected
sodium channels open
sodium diffuses in / moves in rapidly
therefore fewer positive charges outside and more inside / inside becomes positive relative to outside / membrane polarity reversed
before depolarization outside was positive relative to inside
when some sodium gates open entry of Na+ causes more sodium gates to open
membrane potential rises from -70mV to +40 mV ( -+10 mV)
(Award no marks for statements about potassium movement and repolarization)
Explain how the nerve impulse passes along a neuron.
8 marks
in resting potential
sodium is pumped out by the active transport and potassium in
a concentration gradient builds up electrical potential / voltage
negative inside compared to outside
when impulse passes / action potential must pass threshold level
sodium channels open and ions diffuse into neuron
membrane depolarized
potassium diffuse out across membrane through ion channels
active transport of ions once more
slower in unmyelinated neuron than in myelinated
an action potential in one part of the neuron causes the action potential to develop in the next section
Explain how a non-myelinated neuron can maintain a resting potential and undergo an action potential.
9 marks
resting potential is a charge difference across the membrane / -70mV
inside negative compared to the outside
active transport of ions across the membrane / pumps using ATP
positively charged sodium ions / Na+ are pumped out
fewer K+ are pumped in / 2 K+ compared to 3 Na+
neuron contains negatively charged organic ions
membrane allows little / no diffusion of ions
to create action potential sodium ion channels open
sodium ions move into the neuron
therefore there is depolarization / membrane polarisation is reversed
this causes similar changes further on along the neuron
reference to diffusion of ions / local currents
potassium ion channels open after the sodium ion channels
potassium diffuses out causing some repolarization
Describe the principles of synaptic transmission in the nervous system.
6 marks
nerve impulse reaches presynaptic knob / membrane
calcium ions / Ca+2 enter presynaptic neuron / knob
vesicles with neurotransmitter / acetylcholine release contents
neurotransmitter diffuses across synapse / synaptic cleft
binds to receptors on postsynaptic neuron / membrane
sodium ions / Na+ enter post-synaptic neuron / sodium channels open
depolarization / action potential / nerve impulse (in postsynaptic neuron)
calcium ions / Ca+2 pumped back into synaptic cleft/ synapse
neurotransmitter broken down by enzymes
Explain the process of synaptic transmission.
7 marks
presynaptic neurons pass stimulus / potential to postsynaptic neurons
presynaptic neuron releases neurotransmitter into synaptic cleft
process involves exocytosis
exocytosis requires Ca+2 entry into presynaptic neuron
neurotransmitter binds with postsynaptic membrane receptor
neurotransmitter binding can cause postsynaptic membrane ion channel to open /increase / change permeability of postsynaptic membrane
increase / change permeability of postsynaptic membrane
open channel allows specific ions to enter / exit postsynaptic membrane
depolarization / hyperpolarization can result in /initiate action potential
outcome depends on type of postsynaptic receptor and type of channel opened ; reference to excitatory and inhibitory synapses
Na+ passing to the inside of the postsynaptic neuron (usually) causes
depolarization
Cl- passing to the outside of the postsynaptic neuron (usually) causes hyperpolarization
(some) neurotransmitters are destroyed by enzymes
Describe homeostasis in relation to blood glucose concentration in humans.
6 marks
homeostasis is maintaining internal environment at constant levels/within narrow limits
homeostasis involves both nervous and endocrine systems
low blood glucose triggers glucagon release
glucagon is produced å-islet cells in pancreas
glycogen is converted to glucose
high blood glucose concentration triggers insulin release
insulin produced by ß-islet cells in pancreas
glucose taken up by (liver/muscle) cells
glucose converted to glycogen
blood glucose levels controlled by negative feedback
correct reference to lowering or raising blood glucose levels
Define, with examples, the term homeostasis.
4 marks
keeping conditions constant/ within narrow limits within the body/ internal environment
E.g. temperature in humans kept at 37 degrees C/ other example
E.g. blood sugar/ glucose in humans kept within limits/ other example
Explain how blood glucose concentration is controlled in humans.
9 marks
homeostasis maintains the internal blood glucose levels between narrow limits
70-110 mg glucose per 100 ml blood
blood glucose level is maintained by negative feedback
islets in pancreas monitor blood glucose levels
after meal blood glucose increases
high blood glucose stimulates release of insulin
(release of insulin) by pancreatic islets/ by ß-cells causes muscles/ adipose tissue and liver to store glycogen
glucose stored in the form of glycogen (in muscle/liver)
storage lowers blood glucose levels
if blood glucose levels drops glucagon secreted
secrete glucagon by pancreatic islets/ by å-cells
this causes liver to break down glycogen (to glucose)
glycogen breakdown causes blood glucose level increase
Describe how pancreatic cells directly affect blood glucose levels.
5 marks
α cells (of pancreas) produce glucagon;
glucagon promotes release of glucose/breakdown of glycogen by liver cells;
glucagon secreted when blood glucose levels are low/ raises blood glucose levels;
β cells (of pancreas) produce insulin;
insulin promotes glucose uptake/storage of glycogen by liver/body/muscle cells;
insulin secreted when blood glucose levels are high/ lowers blood glucose levels;
negative feedback mechanism;
Describe the response of the human body to low external temperatures.
4 marks
thermoreceptors/ sensory input
hypothalamus acts as a thermostat
metabolic rate increases
shivering / goosebumps / hairs raising / sweat glands inactive
vasoconstriction of skin arterioles
blood flow from extremities is reduced / blood flow to internal organs is increased
increased activity
heat is transferred in blood
Explain the functions of the parts of the female reproductive system.
4 marks
Ovary:
Produces eggs, oestrogen and progesterone;
Oviduct:
Collects eggs from ovary and carries them
to the uterus;
Uterus:
Provides protection, food, oxygen and removal of waste products during
pregnancy;
Cervix: Blocks entry to the uterus during pregnancy
and dilates during birth
Explain the functions of the male parts of the reproductive system.
5 marks
Penis:
Penetrates the vagina to deposit semen close to the cervix;
Urethra:
Transfers semen during ejaculation and passage of urine during urination;
Seminal vesicle:
Produces a sugar-rich fluid that provides sperm with a source of energy to help them move;
Sperm duct:
Transfers sperm during ejaculation;
Epididymis:
Stores sperm until ejaculation;
Testis:
Sperm and testosterone production
Prostate gland:
Produces an alkaline fluid, rich in proteins which,
together with seminal vesicles’ secretion and sperm, makes semen;
Explain the role of hormones in the regulation of the menstrual cycle.
8 marks
FSH (Follicle Stimulating Hormone) and LH (Luteinising Hormone) are produced by
the pituitary gland;
Oestrogen and progesterone are produced by the ovary;
FSH stimulates the ovary to promote development of a follicle;
The developing follicles secrete oestrogen, which inhibits FSH (negative feedback);
Oestrogen stimulates the growth of endometrium;
Oestrogen stimulates LH secretion (positive feedback)
LH stimulates follicle growth and triggers ovulation
The secondary oocyte leaves the ovary and follicle becomes corpus luteum
The corpus luteum secretes oestrogen and progesterone;
Oestrogen and progesterone maintain the endometrium;
Oestrogen and progesterone inhibit LH and FSH (negative feedback);
After two weeks, the corpus luteum degenerates and
the progesterone and oestrogen levels fall;
This triggers menstrual bleeding and the loss of the endometrium;
The pituitary gland secretes FSH and LH, as they are no longer inhibited;
Menstrual cycle continues;
Note 
Flashcard (25)