Biology
A pyrimidine is made of a single ring
True or false? (1 mark)
True
A strand of DNA containing four codons with base sequence ACT GTA CTC TAC mutates, changing the base sequence to ACT ATG CTC TAC. What type of mutation has occurred? (1 mark)
Substitution
What is the role of an aquaporin?
(1 mark)
Channel protein for water
Which hormone regulates the hours of sleep and wakefulness? (1 mark)
Melatonin
Why can taq polymerase be used in the polymerase chain reaction? (1 mark)
What two molecules are produced during the hydrolysis of a triglyceride molecule? (2 marks)
DNA is double stranded, RNA is single stranded
DNA has Thymine, RNA has Uracil
DNA has deoxyribose, RNA has ribose
What two molecules are produced during the hydrolysis of a triglyceride molecule? (2 marks)
Fatty acids
Glycerol
Explain the function of a reflex arc
(2 marks)
A. process that occurs in response to danger/threat;
B. bypasses the brain/involuntary process;
C. to enable a faster response;
D. to protect the body from harm;
State two membrane-bound organelles that are common to both plant and animal cells (2 marks)
Nucleus
Mitochondria
Golgi apparatus
RER
Smoother ER
Vacuole/vesicle
What happens to the diaphragm and pressure in the lungs during inhalation (2 marks)
Diaphragm contracts & pushes down
Pressure decreases in lungs
Outline the differences in cytokinesis in animal and plant cells (3 marks)
Award [1] each for the following.
animal cells:
pinching of cell membrane / form cleavage furrow;
centrioles;
plant cells:
cell plate formation;
cell wall built (during cytokinesis);
Outline the roles of different types of teeth (3 marks)
Any three of the following:
incisors are used for biting chunks of food
canines are used for tearing food
premolars OR molars are used for slicing and crushing food
molars are used for grinding food
Distinguish between totipotent, pluripotent and multipotent stem cells (3 marks)
Totipotent cells are the most versatile stem cells and are capable of giving rise to any cell type in an organism, including making more totipotent stem cells and the cells that become the placenta;
Pluripotent stem cells are able to develop into many different types of cells or tissues in the body, except for becoming placental cells or totipotent stem cells;
Multipotent stem cells can create, maintain and repair the cells of one particular organ or tissue.
Explain the reasons for food chains rarely containing more than four or five trophic levels (3 marks)
Energy is lost between the trophic levels;
Transfer between levels is only usually 10% efficient OR energy transformations take place in living organisms/the process is never 100% efficient;
Energy is lost by the organism/used in respiration/released as heat/movement;
Energy is lost as waste/faeces/urine/undigested food/uneaten parts;
As energy is lost between trophic levels, (higher levels) have less biomass/energy available for the next level.
Distinguish between the structure of arteries and veins (3 marks)
Artery has thick wall, vein has thin wall
Artery has muscles in wall, vein does not
Artery has elastic fibres in wall, vein does not
Artery has small lumen, vein has large lumen
Artery has no valves, vein has valves
Outline the roles of helicase and ligase in DNA replication (4 marks)
helicase:
a. unwinds/uncoils the DNA «double helix» ✔
b. breaks hydrogen bonds «between bases» ✔
c. separates the «two» strands/unzips the DNA/creates replication fork ✔
ligase:
d. seals nicks/forms a continuous «sugar-phosphate» backbone/strand ✔
e. makes sugar-phosphate bonds/covalent bonds between adjacent nucleotides ✔
f. after «RNA» primers are removed/where an «RNA» primer was replaced by DNA ✔
g. «helps to» join Okazaki fragments ✔
Explain the relationship between temperature and enzymes (4 marks)
As temperature increases, the rate of molecular motion increases
increasing the frequency of collision between enzyme and substrate;
increasing the rate of reaction;
until an optimum temperature is reached;
with further increase in temperature, enzymes denature;
Outline how neurons generate a resting potential (4 marks)
a. sodium-potassium pump
b. sodium /Na+ out and potassium /K+ in
OR
sodium/Na+ concentration higher outside and potassium/K+ higher inside
c. three Na+ pumped for every two K+ (hence negative inside)
OR
inside of axon holds negative ions/Cl- ions/negatively charged proteins/organic anions (hence negative inside)
d. by active transport / using ATP
e. inside (of axon/neuron) is negative in comparison to outside
OR
electrochemical concentration/charge difference (across the membrane) is the resting potential
f. resting potential is –70 mV
Explain how the hormone auxin controls phototropism in plant shoots (4 marks)
auxin promotes growth/bends towards (brightest) light/Sun;
auxin moves from lighter to shadier side (of shoot/stem tip/apex);
moved by auxin efflux pumps; auxin promotes cell elongation/cell growth;
auxin causes cell wall acidification/loosening;
more growth on shady side of stem (due to auxin concentration gradient);
Compare type 1 and type 2 diabetes (4 marks)
Type 1 diabetes (usually) develops in childhood and type 2 develops in adulthood/later life;
Type 1 is due to an autoimmune reaction/white blood cells destroying pancreas cells and Type 2 is a gradual decline in insulin production/not due to an immune reaction;
In type 1 (eventually) no insulin is produced and in type 2 less insulin is produced/there is insulin resistance;
Type 1 risk factors are largely genetic, and type 2 are largely obesity/environmental;
Type 2 can be (partially) reversed (by weight loss/diet etc) and Type 1 cannot be reversed;
Type 1 has to be treated with insulin and type 2 can be treated by lifestyle/insulin promoting drugs/other form of treatment;
Explain how a population changes by natural selection (6 marks)
a. variation exists within a population;
b. sexual reproduction/mutation leads to variation within a population;
c. more individuals are born than the environment can support, competition for resources occurs;
d. when environmental conditions change/example of a change, increased competition occurs/struggle for survival increases;
e. better adapted individuals have higher chance of survival/or converse;
f. traits to avoid predation/resistance to pests/ resistance to antibiotics/ improved feeding opportunities/ immunity to diseases may be favourable variations;
g. better adapted /surviving individuals have more chance of breeding/producing offspring;
h. heritable traits/characteristics are passed on to offspring;
i. when populations adapt to environmental conditions, the favourable allele/trait increases in the population /OWTTE;
Accept marking points when they are made with correct use of an example.E.g. Darwin’s finches
Discuss the impacts of eutrophication on water bodies due to agricultural practices (6 marks)
excess nutrients to the water bodies will cause algae to grow rapidly OR algal blooms
growth of algae will block sunlight to underwater plants (and reduce oxygen), causing them to die
plant and algae die under surface due to lack of light (and lower oxygen)
increase in nutrients OR dead organic matter leads to more algal growth
increase in dead organic matter decomposed
aerobic bacteria are decomposers = greater oxygen demand OR biochemical oxygen demand OR BOD
oxygen-depleted water can lead to fish OR other aquatic organisms dying
decrease in biodiversity OR diversity of organisms
shorter food chains
changes in fish communities
economic impacts on tourism OR, fisheries OR water treatment
Describe four types of membrane transport, including their use of energy (6 marks)
Simple diffusion is passive movement
Molecules/ions move along a concentration gradient;
Facilitated diffusion is passive movement of molecules/ions
Molecules move along a concentration gradient/down a concentration gradient through a protein channel (without use of energy);
Osmosis is the passage of water through a membrane from lower solute concentration to higher;
Osmosis is passive
Active transport is movement of molecules/ions against the concentration gradient
Active transport (through membrane pumps) with the use of ATP/energy;
Explain how the function of DNA is linked to its molecular structure
(6 marks)
a. DNA base sequence provides information;
b. gene expression / genes provides a template for the construction of a protein;
c. transcription occurs / mRNA is built using DNA as a template;
d. DNA nucleotide structure described/sugar and phosphate and base;
e. polymer of nucleotides makes a DNA strand;
f. DNA has two anti-parallel strands;
g. complementary base pairs/A pairs with T and C with G;
h. strands linked by hydrogen bonding between bases;
i. double helix shape / helix held by hydrogen bonds;
Explain the mechanisms involved in thermoregulation in humans (6 marks)
a. normal body temperature is 37oC;
b. peripheral thermoreceptors detect environmental temperature;
c. supporting conscious behaviour to avoid temperature extremes, e.g. wearing more clothing;
d. sends messages to hypothalamus/temperature control centre of the brain;
e. the hypothalamus sends messages to pituitary gland;
f. (pituitary) releases TSH;
g. stimulating thyroxin release from thyroid;
h. thyroxin controls metabolic rate / production of heat;
i. muscle random contraction/shivering to generate heat;
j. (brown) adipose tissue burns fat to generate waste heat;
k. vasoconstriction to conserve heat / vasodilation to exchange heat with the environment;