BIOLOGY UNIT 2

Question	Answer
SPECIES?	1. Group of similar organisms / organisms with similar features / / organisms with same genes/chromosomes; 2. Reproduce / produce offspring; 3. That are fertile;
HIERARCHY?	1. Groups within groups; 2. No overlap (between groups);
PHYLOGENETIC GROUP	(Grouped according to) evolutionary links/history/relationships / common ancestry;
DNA helicase is important in DNA replication. Explain why.	1. Separates/unwinds/unzips strands/helix / breaks H-bonds; 2. (So) nucleotides can attach/are attracted / strands can act as templates;
Explain how water enters xylem from the endodermis in the root and is then transported to the leaves.	(In the root) 1. Casparian strip blocks apoplast pathway / only allows symplast pathway; 2. Active transport by endodermis; 3. (Of) ions/salts into xylem; 4. Lower water potential in xylem / water enters xylem by osmosis /down a water potential gradient; (Xylem to leaf) 5. Evaporation / transpiration (from leaves); 6. (Creates) cohesion / tension / H-bonding between water molecules / negative pressure; 7. Adhesion / water molecules bind to xylem; 8. (Creates continuous) water column;
Abdominal pumping increases the efficiency of gas exchange between the tracheoles and muscle tissue of the insect. Explain why.	1. More air/oxygen enters / air/oxygen enters quickly/quicker; 2. (So) maintains/greater diffusion or concentration gradient;
Abdominal pumping is an adaptation not found in many small insects. These small insects obtain sufficient oxygen by diffusion. Explain how their small size enables gas exchange to be efficient without the need for abdominal pumping.	Large(r) SA:VOL / shorter diffusion distance (to tissues);
An arteriole is described as an organ. Explain why	Made of (different) tissues / more than one tissue;
Explain why a lack of protein in the blood causes a build up of tissue fluid.	1. Water potential (in capillary) not as low/is higher/less negative / water potential gradient is reduced; 2. Less/no water removed (into capillary); 3. By osmosis (into capillary);
The fertility of cheetahs is low. The proportion of abnormal sperm cells produced is higher in cheetahs than in other members of the family Felidae. Suggest an explanation for this.	1. Mutation affecting sperm cell or production (in small population); 2. Errors during meiosis; 3. Inbreeding / closely related cheetahs breed; 4. High chance of inheriting allele / high frequency of allele (in the population);
Using x to treat diseases caused by other species of bacteria could increase the chance of the bacterium that causes tuberculosis becoming resistant to x. Use your knowledge of gene transmission to explain how	1. Resistance gene/allele; 2. On plasmid; 3. (Spread by) horizontal transmission; 4. (Involves) conjugation/pilus;
Explain how a larger body size is an adaptation to a colder climate.	1. (Larger birds have) a low(er) SA:VOL; 2. (So) less heat loss / more heat retained;
Describe how DNA is replicated.	1. Strands separate / H-bonds break; 2. DNA helicase (involved); 3. Both strands/each strand act(s) as (a) template(s); 4. (Free) nucleotides attach; 5. Complementary/specific base pairing / AT and GC; 6. DNA polymerase joins nucleotides (on new strand); 7. H-bonds reform; 8. Semi-conservative replication / new DNA molecules contain one old strand and one new strand;
Base pairing is important in DNA replication. Explain how	(Free) nucleotides bind to exposed strands; A to T and C to G; To produce identical copies of DNA;
DNA polymerase is involved in DNA replication. Explain how	Forms new strands of DNA (molecules); By joining together (single) nucleotides bound to existing strands;
The chromosome number is halved during meiosis. Describe how.	Homologous chromosomes/chromosomes form pairs; One (of each pair) goes to each cell produced;
It is important that gametes contain the haploid number of chromosomes. Explain why.	Restores diploid number at fertilisation; Maintain chromosome number (from one generation to next);
Explain how an allele of a gene may produce a non-functional protein	Base sequence different/named mutation; Comparison to functional allele/gene/DNA/mRNA; Leads to different sequence of amino acids; So enzyme/protein with different/non-functional shape;
The mass of DNA in cells from a tissue in which mitosis was occurring was measured. Some cells were found to have 9.4 units of DNA and others 4.7 units. Explain why these cells had different amounts of DNA.	Cells with 9.4 replicated DNA/chromatids joined together / late interphase/prophase/metaphase/before cell division; 1 Cells with 4.7 single chromatids/DNA is not replicated/telophase/early interphase;
Explain why the DNA base sequences of homologous chromosomes are almost the same.	Homologous chromosomes have same genes; At the same loci; Different alleles (usually) only small differences in base sequence;
Explain the importance of meiosis in the life cycle of organisms that reproduce sexually	Produces haploid cells (somewhere in the life cycle); (Allows for) diploid number to be restored when gametes fuse at fertilisation; Maintains/constant chromosome number from one generation to the next; genetic variation through crossing over/independent assortment
Apart from increasing genetic variation, explain why meiosis is important in organisms which reproduce sexually.	haploid cells produced/halves chromosome number; fertilisation/fusion of gametes, diploid number restored; chromosome number constant at each generation;
Many athletes eat food high in carbohydrate for three to four days before a race. This is known as ‘glycogen loading’ and improves performance. Suggest and explain one advantage of ‘glycogen loading’	More glycogen stored (in the liver/muscles) Releases glucose (for respiration);
Ions enter a root hair cell from the soil. Describe how	Active transport; Against Concentration gradient; ATP/ energy required; Facilitated diffusion; Using membrane proteins (membrane) carriers (award once only);
Describe and explain four ways in which the structure of a capillary adapts it for the exchange of substances between blood and the surrounding tissue.	Wall/endothelium one cell thick, reduces diffusion distance; Flattened/squamous cells, reduced diffusion distance; Narrow (lumen) / small diameter, reduces flow rate/ more time for diffusion / exchange; Narrow/small diameter, large SA/V ratio / short diffusion distance; Narrow/small diameter, RBC in contact with wall; Gaps in the wall between cells/fenestrations, faster filtration/movement out/large molecules through;
Describe and explain how tissue fluid is formed and how it is returned to the blood.	Arterial end blood high (hydrostatic) pressure; Fluid/water/soluble substances forced out; Proteins/large molecules remain behind; Water potential become more negative; Friction /resistance to flow; Reduces hydrostatic pressure; Water moves in my osmosis; Excess water taken up by lymph capillaries; Returned to blood stream (via blood vessels) in the neck/into vein;
In dry conditions, the rate of transpiration is affected by an increase in temperature. Describe and explain how.	Increase in transpiration/evaporation/diffusion; Higher kinetic energy / faster movement of molecules/ particles/steeper water potential gradient;
In some diseases, lymph vessels in the legs may become blocked. Explain how this leads to swelling of the tissues in the feet and ankles.	1) Swelling caused by fluid build up; 2) because fluid cannot be drained (into lymph vessels);
Give two differences between the structure of arteries and the structure of veins.	Arteries have thick(er) muscular walls; Arteries have more elastic tissue; Veins have (relatively) larger lumen; Veins have valves;
Describe how water is taken up by root hairs and reaches the xylem in the root.	1 Root hair cells have lower water potential (than soil); 2 Due to active uptake of ions; 3 So water enters root hair cells by osmosis; 4 Passes along apoplast pathway; 5 Through (water filled spaces of) cell walls; 6 Passes along symplast pathway; 7 Through plasmodesmata/cytoplasm; 8 Casparian strip forces water from apoplast into protoplasm/cytoplasm/ into symplast; 9 Water moves from cell to cell/enters xylem by osmosis; 10 Salts pumped into xylem to lower water potential;
Use your knowledge of the cohesion-tension theory to explain how water in the xylem in the roots moves up the stem.	water evaporates/transpires; reduces water potential / creates water potential gradient / increases osmotic gradient /moves via apoplast pathway; water drawn out of xylem; creates tension/pulling effect / creates negative pressure (in context); cohesive forces or H bonding between water molecules / water moves as a column;
Describe and explain how water in the mesophyll cells passes out of the leaf.	(pathway from cells) along cell walls / through spaces and out through stoma(ta); by diffusion (disqualify if osmosis mentioned); down a WP/diffusion/concentration gradient;
Explain how xylem tissue is adapted for its function.	long cells / tubes with no end walls; continuous water columns; no cytoplasm / no organelles/named organelle; to impede/obstruct flow / allows easier water flow; thickening/lignin; support / withstand tension / waterproof / keeps water in cells; pits in walls; allow lateral movement / get round blocked vessels;

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