Question 23M.2.HL.TZ1.8
| Date | May 2023 | Marks available | [Maximum mark: 15] | Reference code | 23M.2.HL.TZ1.8 |
| Level | HL | Paper | 2 | Time zone | TZ1 |
| Command term | Describe, Explain, Outline | Question number | 8 | Adapted from | N/A |
Fluids inside unicellular and multicellular organisms allow materials to be moved.
Explain how vesicles are used by cells to move materials.
[5]
- fluidity of membranes allows vesicles to bud off membranes/fuse with membranes;
- materials taken into cells by endocytosis/vesicle formation;
- Paramecium takes in food / phagocytes engulf pathogens / another example;
- materials released from cells by exocytosis/by vesicle fusing with plasma membrane;
- neurotransmitter released at synapses / protein secretion / secretion from gland cell / another example;
- movement/transport of materials (inside vesicles) within cells/through the cytoplasm/between organelles/from an organelle to the (plasma)membrane/from the (plasma) membrane to an organelle;
- movement of proteins from the rough ER to the Golgi / another example;
The best answers here described endocytosis, exocytosis and the movement of vesicles within cells. Common misconceptions were that vesicles pass out through membranes and can then go on to move materials from one part of the body to another.
Describe the transport of carbon compounds such as sucrose and amino acids in phloem.
[7]
- transport/translocation in (phloem) sieve tubes;
- flow of sap through pores in end walls/sieve plates;
- sugar/amino acids are transported dissolved in water/sap;
- loaded into phloem (companion cells/sieve tubes) by active transport;
- protons pumped out and sucrose then enters by cotransport;
- high solute concentration created in phloem/sieve tube;
- water enters (sieve tube) by osmosis;
- hydrostatic pressure in sieve tube increases;
- unloading from sieve tubes in sink/in roots;
- water leaves by osmosis lowering the hydrostatic pressure;
- sap movement (in phloem) from higher to lower pressure;
- movement from source/leaves to sink/roots;
There were excellent answers to this question showing comprehensive understanding of phloem transport, but also answers showing little or no understanding. A familiar misunderstanding is over the nature of bidirectional transport in phloem. Despite some candidates thinking that a sieve tube can transport sap both up and down the stem simultaneously, phloem transport is only bidirectional in the sense that the direction can be reversed if the location of sources and sinks within a plant changes.
Outline how food is moved from the stomach to the large intestine.
[3]
- by muscles (contracting);
- peristalsis/waves of muscle contraction followed by relaxation;
- longitudinal muscle pushes food along the intestine when it contracts;
- circular muscle constricts the intestine to ensure movement only onwards/not back to stomach;
- movement (from stomach to large intestine) via the small intestine/duodenum/ileum;
Most candidates knew that food reaches the large intestine via the small intestine, but many failed to mention muscle contraction or peristalsis and very few answers distinguished between the role of circular and longitudinal muscle fibres.