Why is there no effective vaccine for HIV?
- high rate of mutations leads to genetic diversity
- HIV leads to fewer T cells - a vaccine may be produced but an immune response won’t happen
Explain the relationship between surface area: volume ratio and metabolic rate
- as SA:V increases, metabolic rate increases
- larger SA:V ratio = more heat loss
- therefore a higher metabolism is needed to replace the heat lost
What is the formula for percentage saturation of haemoglobin with oxygen?
oxygenated haemoglobin divided by max saturation x 100
How does the shape change of haemoglobin make it easier for other O2 molecules to bind?
- at a lower partial pressure, there is an increase in saturation as O2 increases
- then a rapid rise as it gets easier for O2 to bind
What is the advantage of haemoglobins change in affinity?
- more rapid uptake in the lungs and more rapid release to respiring tissues
Steps in cell fractionation
- homogenise mixture to break open the cells and release organelles
- filter to remove cell debris
- cold solution to prevent enzyme activity
- isotonic solution with an equivalent water potential to prevent osmosis
- buffered to prevent a pH change to stop enzymes from denaturing
- centrifuge at a low speed so highest density organelles eg. nuclei form a pellet at the bottom
How do bases stabilise DNA?
- hydrogen bonds between the 2 base pairs hold the strands together
- they collectively provide strength
What is the advantage of showing the genetic code as mRNA rather than DNA triplets?
because ribosomes assemble polypeptides using the mRNA code
What is the role of a stop codon?
results in the detachment of the polypeptide from the ribosome
How is an insects tracheal system adapted?
- highly branched tracheoles - large surface area and short diffusion distance
- tracheoles are lined with a single layer of cells - short diffusion distance
- fluid in tracheoles moves out during exercise as lactate is produced which lowers the water potential - faster diffusion
- abdominal pumping - concentration gradient is constantly maintained
How is starch broken down?
- amylase breaks down starch into maltose
- maltase breaks down maltose into glucose
- by breaking the glycosidic bond via a hydrolysis reaction
What are the disadvantages of using a quadrat?
- some species cannot be accurately counted due to abundance
- quadrat may be disproportionate to the area being measured
What are phylogenetic trees and what are the disadvantages?
- show evolutionary relationships, physical features and uses DNA/amino acid sequences to show genetic differences
- can be difficult to use as shared physical features may have different functions
- artificial system is less likely to change
How is O2 loaded and unloaded?
- o2 diffuses into the blood from alveoli
- haemoglobin has a high affinity in the lungs due to high partial pressure
- o2 binds to form oxyhaemoglobin
- haemoglobin has a low affinity in the respiring tissues due to low o2 partial pressure
- therefore o2 dissociates
What is o2 needed for in respiration?
needed to synthesise ATP
What does an overlap in standard deviations show?
the results are due to chance therefore are not significant
- point out that no other stats tests are used and only one variable was used/tested so cannot be certain
What is genetic diversity?
the number of different alleles of a gene in a population
What type of population is genetic drift most common in and why?
- most common in smaller populations as there is less genetic diversity
How does the lymphatic system regulate swelling?
- hydrostatic pressure at the venuous end is higher outside the capillary
- therefore tissue fluid is forced back into the capillary
- osmotic forces also pull tissue fluid back into the capillary
Describe the role of insulin in reducing blood glucose concentration
- pancreas detects high blood glucose and secretes insulin
- insulin binds to receptors on the cell surface membrane
- causes vesicles with GLUT 4 channel proteins to fuse with the membrane
- increases the diffusion of insulin into the cell
- stimulates the conversion of glucose to glycogen (glycogenesis)
Describe the myogenic simulation of the heart
- SAN releases a wave of electrical activity
- causing the atria simultaneously contract
- AVN passes electrical activity after a short delay via purkyne tissues in the bundle of His
- causing ventricles to simultaneously contract from the bottom upwards
How does a fall in pH lead to a reduction in the ability of calcium ions to stimulate muscle contraction?
- low pH causes tertiary structure of calcium ion receptor proteins to change
- therefore fewer calcium ions bind to tropomyosin
- so fewer tropomyosin molecules move away
- therefore fewer binding sites on actin are revealed
- so fewer cross-bridges form
Describe how the products of the light-dependent reaction are used in the light-independent reaction to produce triose phosphate
- ATP and reduced NADP
- ATP provides energy
- which reduces GP to triose phosphate
Why does a poor supply of phosphate ions result in poorer plant growth?
- needed to make ATP so less energy/respiration for growth
- needed to make nucleotides so less DNA for cell division/production of proteins therefore less growth
- needed to make phospholipids for membranes
- needed to make RUBP so less CO2 reduced into sugar
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Carbohydrates16
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Proteins and enzyme controlled reactions20
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Lipids11
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ATP12
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Nucleic acids15
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Water7
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Inorganic ions5
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Cell structure25
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Mitosis and replication14
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Transport across cell membrane21
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Immune system35
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Gas exchange and SA:V41
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Digestion and absorption43
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Mass transport in animals and plants53
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DNA, Genes and Chromosomes25
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DNA and protein synthesis7
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Mutation and meiosis20
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Species and taxonomy38
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Genetic diversity and adaptation11
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Photosynthesis19
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Respiration20
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Energy and ecosystems21
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Nutrient cycles21
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Detection and response33
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Nervous coordination29
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Skeletal muscles28
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Homeostasis32
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Inheritance18
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Populations and speciation17
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Populations in ecosystems25
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Control of gene expression and epigenetics46
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Genome projects10
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Gene technologies31
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Statistical tests7
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PPQs31
