Unit 2

Question 1

Explain how the structure and properties of phospholipids help to maintain the structure of cell membranes.

Answer 1

phospholipid structure

hydrophobic tail/hydrophilic head
head made from glycerol and phosphate
tail made from two fatty acids
saturated/ unsaturated fatty acid (in tail)
arrangement in membrane
phospholipids form a bilayer
heads face outside the membrane/ tails face inside the membrane/ hydrophic interior/ hydrophilic exterior of membrane

Question 2

Explain the role of vesicles in transportation of materials within cells

Answer 2

vesicles are membrane bound packages/droplets
formed by pinching off/budding off a piece from a membrane
can carry proteins
rough ER synthesizes proteins
proteins enter/accumulate inside the ER
transported to Golgi apparatus for processing
targeted to/transported to specific cellular organelles
fuse with membrane of organelle so contents of vesicle join the organelle
transported to the plasma membrane

Question 3

Describe the process of active transport.

Answer 3

uses/ requires energy/ ATP
goes against concentration gradient/ lower to higher concentration
requires a protein in the cell membrane/ pump/ carrier protein (reject channel)

Question 4

Outline the ways in which substances move passively across membranes.

Answer 4

diffusion (is a method of passive transport across the membrane)
pore/ channel proteins for facilitated diffusion/ to allow hydrophilic particles across
movement from high to low concentration/ down the concentration gradient
membrane must be permeable to the substance diffusing

Question 5

Distinguish between active and passive movements of materials across plasma membranes, using named examples.

Answer 5

passive: diffusion / osmosis / facilitated diffusion, whereas, active transport: ion pumps / exocytosis / pinocytosis / phagocytosis
a second passive method (from above), whereas, active transport: a second active method; (from above)
passive: does not require energy, whereas, active transport: requires energy/ATP;
passive: down concentration gradient, whereas, active transport: against concentration gradient;
passive: no pumps needed, whereas, active transport: requires protein pumps;
passive: oxygen across alveoli / other example, whereas, active transport: glucose absorption in ileum / other example;

Question 6

Outline, with an example, the process of exocytosis

Answer 6

esicles carry material to plasma membrane;
vesicle fuses with membrane;
(by joining of) phospholipid bilayers;
aided by the fluidity of the membrane;
material released/expelled from the cell;
membrane flattens;
name of example e.g. exocytosis of neurotransmitter / exocrine secretion/endocrine secretion / hormone secretion / release of cortical granules;
outline of example: (in the presence of calcium), neurotransmitter vesicles release their contents into the synapse / hormones released from one cell have an effect on another cell etc.;

Question 7

Explain the reasons for cell division in living organims

Answer 7

to increase the number of cells in an organism
to allow differentiation/ cell specialization
for greater efficiency
to replace damaged/ lost cells
example
binary fission
asexual reproduction of unicellular organisms
gamete/ spore formation
cells only arise from pre-existing cells

Question 8

Outline the processes that occur in a cell during interphase, including those needed to prepare for mitosis

Answer 8

DNA replication
DNA transcription
enzyme/ protein synthesis
biochemical reactions/ example of a biochemical reaction
cell respiration
growth
organelles replicated