Common Unit 2 Questions Flashcards
Describe and explain how the structure of the mammalian breathing system enables efficient uptake of oxygen into the blood.(6)
- Alveoli provide a large surface area; 2. Walls of alveoli thin to provide a short diffusion pathway; 3. Walls of capillary thin/close to alveoli provides a short diffusion pathway; 4. Walls (of capillaries/alveoli) have flattened cells; 5. Cell membrane permeable to gases; 6. Many blood capillaries provide a large surface area; 7. Intercostal/chest muscles/diaphragm muscles / to ventilate lungs / maintain a diffusion/concentration gradient; 8. Wide trachea / branching of bronchi/bronchioles for efficient flow of air; 9. Cartilage rings keep airways open
Describe and explain how features you would expect in the leaves of a tree adapted to a dry environment helps the tree’s survival. (6)
Sunken stomata; water evaporation into pit creates local humidity; increased humidity reduces gradient for water evaporation; Close arrangement of stomata; diffusion shells of individual stomata overlap; interferes with water diffusion and slows evaporation; restriction of stomata to lower side of leaf; rate of air movement below leaf less/ heating effect of sun less; gradient for water evaporation reduced/ water molecules have less kinetic energy; Thick cuticle/wax/suberin (on upper surface); (wax/suberin )waterproof; water unable to diffuse onto surface to evaporate, Presence of trichomes/ hairs; surface traps water close to leaf surface; increased humidity reduces gradient for water evaporation; Reduced leaves/spines/small surface area to volume; less surface area for evaporation; more distance across leaf for water to diffuse; Rolled leaves; stomata enclosed in localised humidity; increased humidity reduces gradient for water evaporation;
Describe and explain ways in which a capillary adapts for exchange
- Permeable capillary wall/membrane; 2. Single cell thick/thin walls, reduces diffusion distance; 3. Flattened (endothelial) cells, reduces diffusion distance; 4. Fenestrations, allows large molecules through; 5. Small diameter/ narrow, gives a large surface area to volume/ short diffusion distance; 6. Narrow lumen, reduces flow rate giving more time for diffusion; 7. Red blood cells in contact with wall/ pass singly, gives short diffusion distance / more time for diffusion; (allow 1 mark for 2 features with no explanation)
Factors that increase genetic diversity are…..
Mutations (producing new alleles) Gene flow: alleles move between populations as individuals form one population reproduce with those form another.
Describe what happens to chromosomes in meiosis.(6)
- Chromosomes condense; 2. Chromosomes associate in homologous pairs (bivalents) 3. Crossing-over (chiasma formation) 4. Join to spindle (fibres) / moved by spindle ;(*) 5. (Join via) centromere 6. (At) equator/middle of cell 7. Independent assortment” 8. (Homologous) chromosomes move to opposite poles / chromosomes separate/move apart; (ALLOW ‘are pulled apart’) 9. (Pairs of) chromatids separated in 2nd division;
Photosynthesis generally takes place in a leaf. Describe how the leaf is adapted to allow this process to occur effectively.
Large surface area to collect solar energy; transparent nature of cuticle to allow light penetration; position of chlorophyll to trap light; stomata to allow exchange of gases; thin / max. surface area to volume ratio for diffusion of gases; spongy mesophyll / air spaces for carbon dioxide store; xylem for input of water; phloem for removal of end products
Describe the molecular structure of DNA
Long polymer of nucleotides; composition of a nucleotide (pentose sugar, phosphate and N containing base) 4 bases named (A, T, C and G) (Uracil (U) is a base in RNA that replaces T), A, G are purine bases (2 ring structure) T, C and U are pyrimidine bases (single ring structures) sugar-phosphate ‘backbone’; two (polynucleotide) strands; specific base-pairing; example e.g. A–T / C–G; there are 2 H bonds between A/t and three H bonds between C/G hydrogen bonding between bases
Explain how the structure of DNA is related to its function.(6)
sugar - phosphate backbone gives strength (coiling gives) compact shape; sequence of bases allows information to be stored; long molecule stores large amount of information; information can be replicated / complementary base pairing; (double helix protects) weak hydrogen bonds / double helix makes molecule stable prevents code being corrupted; chains held together by weak hydrogen bonds; chains can split for replication / transcription Complementary base pairing enables information to be replicated / transcribed; Many hydrogen bonds together give molecule stability; Hydrogen bonding allows chains to split for replication / transcription OR molecule unzips easily for replication / transcription.
Explain why standard deviation is more useful than range as a measure of variation within a population
Definition of range + SD / effect of outliers on range + SD; Ranges are similar in both areas; Suggests that variation within populations is similar; SD smaller in area of high light intensity; Shows that area of high light intensity is a more uniform population
Basic structure of glycogen
Glycogen is similar to amylopectin. It is polymer of (1-4) alpha glucose with 9% (1-6) branches, though more than starch. Because it is so highly branched, it can be mobilised (broken down by glycogen phosphorylase to produce glucose for energy) very quickly, reflects the grater metabolic demands of animal over plant Animal’s storage polysaccharide Found mainly in muscle and liver
Within each subspecies there is a range of phenotypes. Explain the factors that give rise to this variation. (4)
Phenotype depends on genotype and environment different local environments can produce variation; different selection pressures; mutations producing new alleles; meiosis produces new combinations of alleles/example; random fusion of gametes / sexual reproduction Independent assortment in meiosis Crossing over in meiosis
Describe how the structure of a chloroplast is adapted to its function in photosynthesis
Membrane is permeable to gases Disc shape gives a large surface area for absorption of light and gas Contains chlorophyll to absorb light Contains a range of pigments to increase the range of wavelengths that can be absorbed Stacking of the thylakoids (grana) maximises light absorption Stroma contains enzymes for the reactions of photosynthesis Stroma contains ribosomes (70s) and DNA for making enzymes needed in photosynthesis
Give the meaning and explain one possible cause of each of the following types of variation. Continuous variation and discontinuous variation
Range between extremes/no discrete types; strong environmental influence; polygenic/many genes involved; quantitative. 2 discrete types; little/no environmental influence/only genetic; (often alleles of) 1/2 gene; qualitative.
Explain how water enters a plant root from the soil and travels through to the endodermis.
Water enters root hair cells; by osmosis; because active uptake of mineral ions has created a WP gradient; water moves through the cortex; (by osmosis) down a WP gradient; through cell vacuoles and cytoplasms / symplastic pathway; through cell walls / apoplastic pathway;
Explain the importance of meiosis in the life cycle of a sexually reproducing organism.
Meiosis halves the number of chromosomes (formation of haploid gametes, eggs and sperm) Restoration of diploid number at fertilisation; Introduces variation
A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted for efficient gas exchange.
1 Large surface area provided by lamellae/filaments; 2 Increases diffusion/makes diffusion efficient; 3 Thin epithelium/distance between water and blood; 4 Water and blood flow in opposite directions/counter-current; 5 maintains concentration gradient (along gill)/equilibrium not reached; 5 Not enough to say gives steep concentration gradient 6 As water always next to blood with lower concentration of oxygen; 7 Circulation replaces blood saturated with oxygen; 8 Ventilation replaces water (as oxygen removed);
Describe two ways by which blood flow in the veins is maintained
Valves prevent backflow; effect of (skeletal) muscle contraction Residual blood pressure from heart; negative pressure from thorax; ‘suction effect’ from heart;
Explain the link between the size of an organism and the way in which its cells are supplied with oxygen.(6)
Small organisms have large surface/volume ratio; as, for example, single-celled organisms; diffusion/exchange over body surface/skin; (the need for) specialised respiratory/gas-exchange surfaces in larger animals; diffusion is a slow process; cells of larger organisms are a long way from gas exchange surface; must be supplied by transport system/circulatory system/blood;
Biologists can also use protein structure to investigate the relationship between different species of crane. Explain why
- More closely related (species) have more similarities in amino acid sequence/primary structure; 2. In same protein / named protein e.g. albumin; 3. Amino acid sequence is related to (DNA) base/triplet sequence; OR 4. Similar species have a similar immune response to a protein/named protein; 5. More closely related (species) produce more ‘precipitate’ / antibody-antigen (complexes) / agglutination;
Describe the principles on which the system of classification of living organisms is based. (4)
Hierarchy of 7 taxonomic groups (KPCOFGS); no overlap between groups; organisms placed in groups due to common structures / similar characteristics; reflecting evolutionary history (phylogeny) of organisms within a group; binominal nomenclature / example; definition of a species;
