4,5,6 markers Flashcards
(17 cards)
Describe the structure of proteins
- 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;
Accept alpha helix / pleated sheet - Tertiary structure is 3-D folding due to hydrogen bonding and ionic /
disulfide bonds; - Quaternary structure is two or more polypeptide
Explain how the structure of DNA is related to its functions
Sugar -phosphate (backbone) / double stranded / helix so provides strength / stability / protects bases / protects hydrogen bonds;
Must be a direct link / obvious to get the mark
Neutral: reference to histones
2. Long / large molecule so can store lots of information;
3. Helix / coiled so compact;
Accept: can store in a small amount of space for ‘compact’
Base sequence allows information to be stored / base sequence codes for amino acids / protein;
Accept: base sequence allows transcription
5. Double stranded so replication can occur semi-conservatively / strands
can act as templates / complementary base pairing / A-T and G-C so accurate replication / identical copies can be made;
6. (Weak) hydrogen bonds for replication / unzipping / strand separation / many hydrogen bonds so stable / strong;
Accept: ‘H-bonds’ for ‘hydrogen
Describe and explain the processes that occur during meiosis that increase genetic variation
(b) 1. Homologous chromosomes pair up;
- Independent segregation;
Maternal and paternal chromosomes are re-shuffled in any combination;
- Crossing over leads to exchange of parts of (non-sister) chromatids / alleles
between homologous chromosomes; - (Both) create new combinations of
Describe and explain how the structure of the mammalian breathing system enables
efficient uptake of oxygen into the blood.
- alveoli provide a large surface area;
- walls of alveoli thin to provide a short diffusion pathway;
- walls of capillary thin / close to alveoli provides
a short diffusion pathway; - walls (of capillaries / alveoli) have flattened cells;
- cell membrane permeable to gases;
- many blood capillaries provide a large surface area;
- intercostal / chest muscles / diaphragm muscles / to ventilate lungs /
maintain a diffusion / concentration gradient; - wide trachea / branching of bronchi / bronchioles for efficient
flow of air; - cartilage rings keep airways open;
(reject moist and thin membranes)
(a) exchange / diffusion across body surface / skin;
Explain sympatric speciation
Occurs in the same habitat/environment/population;
2. Mutation/s cause different flowering times;
3. Reproductive separation/isolation
OR
No gene flow
OR
Gene pools remain separate;
4. Different allele/s passed on/selected OR
Change in frequency of allele/s;
5. Disruptive (natural) selection;
6. Eventually different species cannot (inter)breed to produce fertile offspring;
Contrast how an optical microscope and a transmission electron microscope work
and contrast the limitations of their use when studying cells
- TEM use electrons and optical use light;
- TEM allows a greater resolution;
- (So with TEM) smaller organelles/named cell structure can be observed
OR
greater detail in organelles/named cell structure can be observed; - TEM view only dead/dehydrated specimens and optical (can) view live specimens;
- TEM does not show colour and optical (can);
- TEM requires thinner specimens;
- TEM requires a more complex/time consuming preparation;
- TEM focuses using magnets and optical uses
Explain three ways in which an insect’s tracheal system is adapted for efficient gas
exchange
Tracheoles have thin walls so short diffusion distance to cells;
2. Highly branched/large number of tracheoles so short diffusion distance to cells;
3. Highly branched/large number of tracheoles so large surface area (for gas exchange);
4. Tracheae provide tubes full of air so fast diffusion (into insect tissues);
5. Fluid in the end of the tracheoles that moves out (into tissues) during exercise so faster diffusion through the air to the gas exchange surface;
OR
Fluid in the end of the tracheoles that moves out (into tissues) during exercise so larger surface area (for gas exchange);
6. Body can be moved (by muscles) to move air so maintains diffusion/concentration gradient for oxygen/carbon dioxide;
Compare and contrast the structure and properties of triglycerides and phospholipids.
- Both contain ester bonds (between glycerol and fatty acid);
- Both contain glycerol;
- Fatty acids on both may be saturated or unsaturated;
- Both are insoluble in water;
- Both contain C, H and O but phospholipids also contain P;
- Triglyceride has three fatty acids and phospholipid has two fatty acids plus phosphate group;
- Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region;
- Phospholipids form monolayer (on surface)/micelle/bilayer (in water) but triglycerides don’t;
5 max
Describe the gross structure of the human gas exchange system and how we breathe
in and out.
- Named structures – trachea, bronchi, bronchioles, alveoli;
- Above structures named in correct order OR
Above structures labelled in correct positions on a diagram; - Breathing in – diaphragm contracts and external intercostal muscles contract;
- (Causes) volume increase and pressure decrease in thoracic cavity (to below atmospheric, resulting in air moving in);
- Breathing out - Diaphragm relaxes and internal intercostal muscles contract;
- (Causes) volume decrease and pressure increase in thoracic cavity (to above atmospheric, resulting
Explain 5 properties that make water important
A metabolite in condensation/hydrolysis/ photosynthesis/respiration;
2. A solvent so (metabolic) reactions can occur OR
A solvent so allowing transport of substances;
3. High heat capacity so buffers changes in
temperature;
4. Large latent heat of vaporisation so provides a cooling effect (through evaporation);
5. Cohesion (between water molecules) so supports columns of water (in plants);
6. Cohesion (between water molecules) so produces surface tension supporting (small) organisms;
Biochemical tests confirm lipid, non reducing sugar and amylase in a sample
Lipid
1. Add ethanol/alcohol then add water and shake/mix
OR
Add ethanol/alcohol and shake/mix then pour into/add water;
2. White/milky emulsion
OR
emulsion test turns white/milky;
Non-reducing sugar
3. Do Benedict’s test and stays blue/negative;
4. Boil with acid then neutralise with alkali;
5. Heat with Benedict’s and becomes red/orange (precipitate);
Amylase
6. Add biuret (reagent) and becomes purple/violet/mauve/lilac;
7. Add starch, (leave for a time), test for reducing sugar/absence of starch;
Describe gene mutation and explain how it can have
- no effect
- a positive effect
Definition of gene mutation)
1. Change in the base/nucleotide (sequence of chromosomes/DNA);
2. Results in the formation of new allele;
(Has no effect because)
3. Genetic code is degenerate (so amino acid sequence may not change);
OR
Mutation is in an intron (so amino acid sequence may not change);
4. Does change amino acid but no effect on tertiary structure;
5. (New allele) is recessive so does not influence phenotype;
(Has positive effect because)
6. Results in change in polypeptide that positively changes the properties (of the protein)
OR
Results in change in polypeptide that positively changes a named protein;
7. May result in increased reproductive success OR
May result in increased survival (chances);
Describe the cohesion-tension theory
Water lost from leaf bc of transpiration
- Lowers water potential of mesophyll / leaf cells;
- Water pulled up xylem (creating tension);
- Water molecules cohere / ‘stick’ together by hydrogen bonds;
- (forming continuous) water column;
- Adhesion of water (molecules) to walls of xylem
Describe the mass flow hypothesis for the mechanism of translocation in platns
SuGARS actively transported into phloem
By companion cells;
3. Lowers water potential of sieve cell / tube and water enters by
In source / leaf sugars actively transported into phloem;
osmosis;
4. Increase in pressure causes mass movement (towards sink /
root);
5. Sugars used / converted in root for respiration for storage.S
Describe the role of receptors and nervous system in increasing heart rate
Chemoreceptors detect rise in CO2/H+/acidity/carbonic acid/fall in pH
OR
Baro/pressure receptors detect rise in blood pressure;
2. Send impulses to cardiac centre/medulla;
3. More impulses to SAN;
4. By sympathetic (nervous system for chemoreceptors/CO2)
OR
By parasympathetic (nervous system for baro/pressure receptors/blood pressure);
E
HIC REPLICATION once inside helper T cells
RNA converted into DNA using reverse transcriptase;
2. DNA incorporated/inserted into (helper T cell) DNA/chromosome/genome/nucleus;
3. DNA transcribed into (HIV m)RNA;
4. (HIV mRNA) translated into (new) HIV/viral proteins (for assembly into viral particles);
