B2.2 Organelles and compartmentalisation

Question 1

B2.2.1—Organelles as discrete subunits of cells that are adapted to perform specific functions

Answer 1

Students should understand that the cell wall, cytoskeleton and cytoplasm are not considered organelles,
and that nuclei, vesicles, ribosomes and the plasma membrane are.
NOS: Students should recognize that progress in science often follows development of new techniques.
For example, study of the function of individual organelles became possible when ultracentrifuges had
been invented and methods of using them for cell fractionation had been developed

Question 2

B2.2.2—Advantage of the separation of the nucleus and cytoplasm into separate compartments

Answer 2

Limit to separation of the activities of gene transcription and translation—post-transcriptional
modification of mRNA can happen before the mRNA meets ribosomes in the cytoplasm. In prokaryotes
this is not possible—mRNA may immediately meet ribosomes.

Question 3

B2.2.3—Advantages of compartmentalization in the cytoplasm of cells

Answer 3

Include concentration of metabolites and enzymes and the separation of incompatible biochemical
processes. Include lysosomes and phagocytic vacuoles as examples.

Question 4

B2.2.4—Adaptations of the mitochondrion for production of ATP by aerobic cell respiration

Answer 4

Include these adaptations: a double membrane with a small volume of intermembrane space, large
surface area of cristae and compartmentalization of enzymes and substrates of the Krebs cycle in the
matrix.

Question 5

B2.2.5—Adaptations of the chloroplast for photosynthesis

Answer 5

Include these adaptations: the large surface area of thylakoid membranes with photosystems, small
volumes of fluid inside thylakoids, and compartmentalization of enzymes and substrates of the Calvin
cycle in the stroma.

Question 6

B2.2.6—Functional benefits of the double membrane of the nucleus

Answer 6

Include the need for pores in the nuclear membrane and for the nucleus membrane to break into vesicles
during mitosis and meiosis.

Question 7

B2.2.7—Structure and function of free ribosomes and of the rough endoplasmic reticulum

Answer 7

Contrast the synthesis by free ribosomes of proteins for retention in the cell with synthesis by membranebound ribosomes on the rough endoplasmic reticulum of proteins for transport within the cell and
secretion.

Question 8

B2.2.8—Structure and function of the Golgi apparatus

Answer 8

Limit to the roles of the Golgi apparatus in processing and secretion of protein

Question 9

B2.2.9—Structure and function of vesicles in cells

Answer 9

Include the role of clathrin in the formation of vesicles.