Extended Response Eq

Question 1

Describe the structure of DNA. (5 marks)

Answer 1

1. Polymer of nucleotides;
2. Each nucleotide formed from deoxyribose, a phosphate, and an organic/nitrogenous base;
3. Phosphodiester bonds between nucleotides;
4. Double helix/2 strands held by hydrogen bonds;
5. Hydrogen bonds/pairing between adenine, thymine and cytosine, guanine;

Question 2

Name and describe five ways substances can move across the cell-surface membrane into a cell. (5 marks)

Answer 2

1. Simple diffusion of small/non-polar molecules down a concentration gradient;
2. Facilitated diffusion via protein carrier/channel;
3. Osmosis of water down a water potential gradient;
4. Active transport against a concentration gradient via protein carrier using ATP;
5. Co-transport of 2 different substances using a carrier protein;

Question 3

Describe the cohesion-tension theory of water transport in the xylem. (5 marks)

Answer 3

1. Water lost from leaf by transpiration;
2. Lowers water potential of mesophyll cells;
3. Water pulled up xylem, creating tension;
4. Water molecules cohere via hydrogen bonds;
5. Adhesion of water to xylem walls forms a continuous column;

Question 4

Describe the appearance and behaviour of chromosomes during mitosis. (5 marks)

Answer 4

1. Chromosomes coil/condense and become visible;
2. Appear as chromatids joined at centromere;
3. Line up at cell equator;
4. Spindle fibers attach at centromeres;
5. Chromatids pulled to opposite poles and uncoil during telophase.

Question 5

Describe and explain the processes that occur during meiosis that increase genetic variation. (5 marks)

Answer 5

1. Homologous chromosomes pair;
2. Independent segregation;
3. Shuffling of maternal and paternal chromosomes;
4. Crossing over exchanges chromatids between homologues;
5. New allele combinations created.

Question 6

Describe how vaccination can lead to protection against bacterial meningitis. (6 marks)

Answer 6

1.Antigen on bacteria binds to B cell;

2. B cell undergoes mitosis;
3. Stimulated by cytokines;
4. Plasma cells release antibodies;
5. Some B cells become memory cells;
6. Memory cells produce antibodies faster.

Question 7

Describe how a population of Neisseria meningitidis (Nm) can become resistant to antibiotics. (4 marks)

Answer 7

1. Mutation occurs in Nm;
2. Resistant allele forms;
3. Bacteria with this allele survive and reproduce;
4. Over time, resistance spreads to new strains.

Question 8

Describe the gross structure of the human gas exchange system and how we breathe in and out. (6 marks)

Answer 8

1. Structures: trachea, bronchi, bronchioles, alveoli;
2. Diaphragm contracts and intercostal muscles expand chest cavity;
3. Volume increase, pressure decrease;
4. Inhalation occurs;
5. Exhalation occurs as diaphragm and muscles relax.

Question 9

Compare and contrast the structure and properties of triglycerides and phospholipids. (5 marks)

Answer 9

1. Both have ester bonds and glycerol;
2. Fatty acids can be saturated or unsaturated;
3. Triglycerides have three fatty acids; phospholipids have two fatty acids plus a phosphate group;
4. Phospholipids have hydrophilic head; triglycerides are non-polar.

Question 10

Describe the light-independent reaction of photosynthesis. (6 marks)

Answer 10

1. CO2 binds to RuBP, catalyzed by Rubisco;
2. Two molecules of GP are formed;
3. GP reduced to TP using NADPH and ATP;
4. TP converted to glucose or regenerated to RuBP.

Question 11

Give two structural differences between a molecule of mRNA and a molecule of tRNA. (2 marks)

Answer 11

1. mRNA is linear while tRNA is cloverleaf-shaped;
2. mRNA has codons while tRNA has an anticodon.

Question 12

Starting with mRNA in the cytoplasm, describe how translation leads to the production of a polypeptide. (5 marks)

Answer 12

1. mRNA associates with a ribosome;
2. Ribosome moves to the start codon;
3. tRNA brings an amino acid;
4. tRNA anticodon pairs with mRNA codon;
5. Amino acids join by peptide bonds to form a polypeptide.

Question 13

Describe how you could estimate the size of a population of sundews in a small marsh. (5 marks)

Answer 13

1. Use a grid or divide area into squares;
2. Use random coordinates;
3. Count number in each quadrat;
4. Calculate mean per quadrat;
5. Scale up to estimate total population.

Question 14

Suggest and explain how digesting insects helps the sundew to grow in soil with very low concentrations of some nutrients. (2 marks)

Answer 14

1. Digesting proteins provides amino acids;
2. Amino acids are used to produce proteins like enzymes and DNA, enabling growth.

Question 15

Contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells. (6 marks)

Answer 15

1. TEM uses electrons;
2. Higher resolution;
3. Shows smaller organelles;
4. Requires dead samples;
5. No color;
6. Complex preparation needed.

Question 16

What is a gene pool? (1 mark)

Answer 16

The gene pool is the complete set of different alleles in a population.

Question 17

Suggest how the two species of palm trees on Lord Howe Island might have arisen by sympatric speciation. (5 marks)

Answer 17

1. Mutation causes different flowering times;
2. Reproductive isolation;
3. Separate gene pools;
4. Different alleles passed on;
5. Results in two species.

Question 18

Describe how the structures of starch and cellulose molecules are related to their functions. (5)

Answer 18

1. Helical/ spiral shape so compact;
2. Large (molecule)/insoluble so osmotically inactive;
   Accept: does not affect water potential/ψ.
3. Branched so glucose is (easily) released for respiration;
   Ignore: unbranched.
4. Large (molecule) so cannot leave cell/cross cell-surface membrane;

Cellulose (max 3)

5. Long, straight/unbranched chains of β glucose;
6. Joined by hydrogen bonding;

Note: references to ‘strong hydrogen bonds’ disqualifies this mark
point.

7. To form (micro/macro)fibrils;
8. Provides rigidity/strength;

Question 19

Describe the processes involved in the transport of sugars in plant stems. (5)

Answer 19

1.(At source) sucrose is actively (transported) into the phloem/sieve element/tube;
Accept: ‘sugar/s’ for sucrose but reject other named sugars e.g. glucose.
Accept: co-transport (with H+ ions).

2. By companion/transfer cells;
3. Lowers water potential in phloem/sieve element/tube and
   water enters by osmosis;
4. (Produces) high (hydrostatic) pressure;
   Accept: pressure gradient.
5. Mass flow/transport towards sink/roots/storage tissue;
   Accept: sieve element/tube.
6. At sink/roots sugars are removed/unloaded;
   5 max
   Accept: at sink/roots sugars are used in respiration/stored.

Question 20

Describe the structure of DNA. (5)

Answer 20

1.Polymer of nucleotides;

Accept ‘Polynucleotide’
Accept for ‘phosphate’. phosphoric acid

2. Each nucleotide formed from deoxyribose, a phosphate (group) and an organic/nitrogenous base;
3. Phosphodiester bonds (between nucleotides);
4. Double helix/2 strands held by hydrogen bonds;
5. (Hydrogen bonds/pairing) between adenine, thymine and cytosine, guanine;

Question 21

Name and describe five ways substances can move across the cell-surface membrane into a cell. (5)

Answer 21

1.(Simple) diffusion of small/non-polar molecules down a concentration gradient;
If no reference to ‘small/ non-polar’ for 1.
accept this idea from ‘large/charged’ given in description of

2. Facilitated diffusion down a concentration gradient via protein carrier/channel;
   Reject if active rather than passive
3. Osmosis of water down a water potential gradient;
   Active transport against a concentration gradient via protein carrier using ATP;
   Co-transport of 2 different substances using a carrier protein;