CH 2018

Question 1

Some young grass plants were grown with their roots in a mineral solution that contained nitrate ions. The plants were divided into two batches, N and P. Cyanide, which inhibits aerobic respiration, was added to the solution given to the plants in batch P.

explain why the absorption of nitrate ions by the plants in batch N differs from that in batch P [4]

Answer 1

• nitrates in batch P are absorbed only by diffusion as there is no energy for active transport [1] because cyanide inhibits respiration, which releases energy from the breakdown of glucose [1]
• ions in batch N are absorbed by active transport (and diffusion) [1]
• after 10 hours, there is no concentration gradient in P [1] as rate of assimilation = rate of absorption (so concentration in plant remains constant) [1]
• active transport continues in N against a concentration gradient after 10 hours.
  (reference to appropriate figs linked to an explanation of different absorption rates) [1]
  [max 4]

Question 1

After 60 hours, the mineral solution the plants were placed in was replaced by distilled water.
Explain why the mean quantity of nitrate ions in both batches of plants
decreased after 60 hours. [2]

Answer 1

• no ions in distilled water [1] R: low ions
• ions lost by diffusion due to concentration gradient [1] (only applies for plant affected by cyanide)
• ions used in amino acid synthesis/protein synthesis [1] A: ions assimilated R: used/utilized

Question 2

State two components of blood that do not pass through the filter. [1]

Answer 2

• red (blood) cells
• phagocytes / lymphocytes
• named plasma proteins (e.g. fibrinogen / insulin / glucagon / thrombin / antibodies / clotting factors)
• platelets

Question 3

Using the data in Table 4.1, describe and explain the effect of the two conditions that the student changed during the investigation on the rate of water uptake. [5]

temperature

wind speed

Answer 3

temperature
use of figs. (units required) to make a valid comparison [1] ref to kinetic energy / speed of movement of molecules and rate of evaporation / transpiration / diffusion [1]
warm air holds more water vapour / molecules than cold air / AW [1]

wind speed
use of figs. (units required) to make a valid comparison [1] (A: use figs. once only either for wind speed or temperature) air blowing over the surface of the leaf takes water vapour away [1]
so air, around leaf is less humid [1]
[max 5]

Question 4

Describe three features of a polypeptide molecule that are different from those found in a DNA molecule. [3]

Answer 4

• amino acids vs nucleotides [1]
• single strand vs double (helix) strand [1]
• peptide bonds vs phosphodiester bonds [1] R: peptide bonds between peptides / polypeptides
• 20 types of monomers vs only 4 types of monomers [1] R: 4 bases
• no phosphate / PO4 vs has phosphate / PO4 [1]

Question 5

Explain why the carbon dioxide concentration in the expired air of a woman who just finished excersise slowly decreases before remainng constant after the excersise is over. [6]

Answer 5

• removal of excess carbon dioxide [1]
• more energy used during exercise means higher rates of respiration [1]
• aerobic respiration releases carbon dioxide [1]
• oxygen not supplied fast enough to muscles, incurring an oxygen debt [1]
• anaerobic respiration in muscles produces lactic acid / lactate [1]
• lactic acid is broken down to produce carbon dioxide [1] R: removal of lactic acid
  any 6

Question 6

Explain why exercise is recommended for people with a high risk of developing coronary heart disease. [2]

Answer 6

• prevents blood clot / thrombus formation [1]
• lowers blood pressure [1]
• lowers cholesterol / reduces risk of fatty deposits [1]
• weight loss / using fats / avoids obesity [1]
• lowers stress [1]
• (heart) muscle stronger / lower (resting) pulse [1]