Cell Membrane Transport Analysis: Biology 101 Assignment

This biology assignment explores the mechanisms of cell membrane transport. The solution analyzes data on substance L's entry into cells, identifying the likely mode of transport as normal diffusion based on the relationship between external concentration and rate of entry. The assignment covers the flexibility and selective permeability of cell membranes, explaining how these properties are essential for cell survival and homeostasis. It discusses the role of membrane proteins and lipids in transport, including facilitated and simple diffusion of various molecules and ions. The solution also addresses the energy requirements for different transport processes, differentiating between passive and active transport based on concentration gradients.

Running head: BIOLOGY
QUESTION AND ANSWERS
Name of the Student
Name of the University
Author Note

1BIOLOGY
Answer 1
(a) After looking at the nature of the graph given in figure 1, it can be stated that the
movement of substance L occurs by a normal diffusion process. This is evident from the fact
that the rate of entry increases with the increase in the concentration of L outside the cell.
Thus, it can be stated that the substance is transferred from higher to lower concentration
without the application of any energy.
(b)
10 20 30 40 50 60 70 80 90 100
0
20
40
60
80
100
120
External concentration
Fig 1: Rate vs External concentration curve
Source: Microsoft Excel
Y axis= Rate of transfer
X axis= External concentration of the substance L
(c) The concentration of substance L resulting in one half of the maximal rate is= 55 mM
(d) The rate of entry will be decreased due to an increase in the total weight of the substance
and its effect on the concentration gradient followed.

2BIOLOGY
Answer 2
(a) The flexibility of the cell membrane is needed by the cell to survive in different
environments. For example, it has been observed that cells survive for long in the water. Cell
membranes are also selectively permeable and thus will allow only selected substances to
enter the cell only when they are needed by the cells. On the condition of absence of cell
membrane, any substance will enter the cell or be excreted from the cell at random which can
cause cell death either by lysis or flaccid condition. Selectively permeable membranes are
required for the maintenance of cellular homeostasis, electrolyte balance, fluid balance and
cellular health. Cell membranes also hold various proteins and lipids which together act as
transporters to allow the selective transfer of essential ions like sodium, chlorine, hydrogen
and potassium. Various transport mechanisms are maintained by cell membrane in order to
respond to sudden changes in the surrounding environment. Thus, it can be stated that these
are all the reasons which justify the biological need of a selectively permeable membrane in
cells.
(b) The model stated shows that black solid molecules (lipids) are only taken inside the cell in
a specific amount (7 out and 4 in). The model also shows the presence of membrane channel
protein or the membrane transporter as discussed in the previous answer. This transporter
selectively takes in only the water-soluble ions and leaves out the water-insoluble ions.
Transporters also send out the water-insoluble ions which make up the concentration gradient
for the transport of water-soluble ions inside the cell via diffusion also. All these functions
are the pieces of evidence for a selectively permeable nature of the cell membrane. Thus, it
can be stated that the model stated in figure 1 in the question, shows a selectively permeable
nature of the cell membrane.
(c) Plasma membrane containing lipid bilayer of the monolayer has several hydrophobic
chains at the inner side of the cell. These hydrophobic chains facilitate the transfer of small

3BIOLOGY
hydrophobic either by facilitated diffusion or by simple diffusion. This is because of the fact
that the hydrophobic core has been found to block the diffusion of hydrophilic ions and all
polar molecules. Thus, small hydrophobic molecules and gases can easily dissolve through a
lipid bilayer containing several hydrophobic fatty acid chains.
(d) The molecules which are being transferred from a lower concentration to a higher
concentration requires energy. This is because of the fact that the molecules across the cell
membrane move against the concentration gradient when they get transferred from a low
concentration to a higher one. Membrane transporter-mediated molecule transporter also
requires energy. Thus, it can be stated that, depending upon the concentration gradient, the
transport system uses energy in the form of ATP to send molecules either inside the cell or
outside the cell.

4BIOLOGY
Bibliography
Azan, A., Gailliègue, F., Mir, L.M. and Breton, M., 2017. Cell membrane electropulsation:
chemical analysis of cell membrane modifications and associated transport mechanisms.
In Transport Across Natural and Modified Biological Membranes and its Implications in
Physiology and Therapy (pp. 59-71). Springer, Cham.
Kulbacka, J., Choromańska, A., Rossowska, J., Weżgowiec, J., Saczko, J. and Rols, M.P.,
2017. Cell membrane transport mechanisms: Ion channels and electrical properties of cell
membranes. In Transport Across Natural and Modified Biological Membranes and its
Implications in Physiology and Therapy (pp. 39-58). Springer, Cham.
Liu, L., Cherstvy, A.G. and Metzler, R., 2017. Facilitated diffusion of transcription factor
proteins with anomalous bulk diffusion. The Journal of Physical Chemistry B, 121(6),
pp.1284-1289.
Staaf, E., Bagawath-Singh, S. and Johansson, S., 2017. Molecular Diffusion in Plasma
Membranes of Primary Lymphocytes Measured by Fluorescence Correlation
Spectroscopy. JoVE (Journal of Visualized Experiments), (120), p.e54756.
Sun, S.Y., Nie, X.Y., Huang, J. and Yu, J.G., 2020. Molecular simulation of diffusion
behavior of counterions within polyelectrolyte membranes used in electrodialysis. Journal of
Membrane Science, 595, p.117528.
Sweeney, D.C., Douglas, T.A. and Davalos, R.V., 2018. Characterization of Cell Membrane
Permeability In Vitro Part II: Computational Model of Electroporation-Mediated Membrane
Transport. Technology in cancer research & treatment, 17, p.1533033818792490.