Chapter 2 Questions
1) Figure 23 shows the structure of a membrane:
a. Distinguish between I and II
I is the hydrophilic phosphate head (polar) and II is the hydrophobic fatty
acid tail (non-polar).
b. Compare III and IV
III shows integral proteins (which are embedded in the plasma membrane),
whereas IV shows peripheral proteins (which are on the surface of the plasma
membrane). Both proteins have hydrophobic and hydrophilic parts.
c. Identify V and VI
V is a glycoprotein and VI is a cholesterol molecule.
d. State the thickness of VII
The thickness of VII is 10 nanometers.
2) Particles can enter or leave cells by diffusion, active transport, osmosis, endocytosis or
exocytosis. Identify which method is used in each of these examples.
a. water entering a root cell from the soil
Osmosis
b. antibodies being absorbed from milk in the stomach of a newborn baby
Endocytosis
c. oxygen entering a cell in the gill of a salmon
Diffusion
d. proteins being secreted from gland cells in the pancreas
Exocytosis
e. glucose from digested foods entering cells in the lining of the small intestine.
Active transport
3) In human secretory cells, for example in the lung and the pancrease, positively
charged ions are pumped out, and chloride ions follow passively through chloride
channels. Water also moves from the cells into the liquid that has been secreted. In the
genetic disease cystic fibrosis, the chloride channels malfunction and too few ions move
out of the cells. The liquid secreted by the cells becomes thick and viscous, with
associated health problems.
a. State the names of the processes that:
i. move positively charged ions out of the secretory cells
Active transport
ii. move chloride ions out of the secretory cells
Facilitated diffusion
iii. move water out of the secretory cells
Osmosis
b. Explain why the fluid secreted by people with cystic fibrosis is thick and
viscous.
The fluid secreted by people with cystic fibrosis is thick and viscous because
4) Table 6 shows the area of membranes in a rat liver cell.
a. Calculate the total area of membranes in the liver cell.
98130 µm2
b. Calculate the area of plasma membrane as a percentage of the total area of
membranes in the cell. Show your working.
Area of Plasma Membrane
1780
=
» 1.8%
Total Area of Membranes in Cell 98130
c. Explain the difference in area of the inner and outer mitochondrial
membranes.
The area of the inner mitochondrial membrane is greater than that of the
outer membrane because the inner membrane is folded back on itself, so more would
be needed. On the other hand, the outer membrane simply surrounds the
mitochondria.
d. Using the data in the table, identify two of the main activities of liver cells.
Protein synthesis and ATP production.
5)
a. Draw and label a diagram to show the structure of membranes.
b. Outline way in which proteins help cells receive and send messages.
Proteins help cells receive and send messages by means including hormone
binding sites and cell-to-cell communication.
c. Explain how cells use vesicles to transport materials.
Cells use vesicles to transport materials to and from the cell, and also within
the cell. In endocytosis, the plasma membrane is pulled and a section is pinched off.
This forms a vesicle that contains extracellular fluid, and the vesicle moves through
the cytoplasm to lysosomes. In exocytosis, vesicles (formed from the Golgi apparatus)
containing completed proteins fuse with the plasma membrane and release their
contents. Vesicles are also used for intracell transportation, such as between the
rough endoplasmic reticulum and the Golgi apparatus.