Cell Biology: Cell Structure, Transport, and Division Homework

This document presents a comprehensive solution to a cell biology assignment. It begins with an examination of the ultrastructure of nerve cells (neurons) and red blood cells (RBCs), highlighting their key functional characteristics. The assignment then delves into cell membrane models, discussing the fluid mosaic model and the role of hydrophilic protein channels in selective substance transport. Further, the solution differentiates between osmosis, simple diffusion, facilitated diffusion, and active transport, explaining how large molecules are transported across cell membranes. The final section explores the necessity of mitosis and meiosis, contrasting their processes, stages, and outcomes, including the genetic variations introduced by meiosis. References to relevant sources are also included to support the analysis.

Introduction to cell biology

TABLE OF CONTENTS
QUESTION 1 ..................................................................................................................................1
PART 2 .......................................................................................................................................1
QUESTION 2...................................................................................................................................1
PART 1 .......................................................................................................................................1
PART 2 .......................................................................................................................................2
QUESTION 3 ..................................................................................................................................3
PART 1 .......................................................................................................................................3
PART 2........................................................................................................................................3
PART 3........................................................................................................................................4
QUESTION 4 ..................................................................................................................................4
PART 1 .......................................................................................................................................4
PART 2........................................................................................................................................4
PART 3........................................................................................................................................5
REFERENCES ...............................................................................................................................7

QUESTION 1
PART 2
A. Ultrastructure of nerve cell (Neuron)
Their key function of nerve cell is to transmit electrical and chemical signals through
central nervous system. These cells consist of dendrons, in which nucleus is surrounded by axon,
cell membrane and cytoplasm. The smaller extension of dendrons are called dendrites and they
received signals from other nerve cells. The dendrites are elongated and are extended outwards
which helps them to receive signals with ease. The axon is insulated with substance called
myelin. This insulated coating helps neurones to carry signals from one location to another in
body. Myelin is formed by various cells and consist of gap between sheath (Kohen, 2014). This
gap is essential for neuron functionality because it allows saltatory impulse propagation. Nerve
cell transmit signals from axon terminal via neurotransmitter. In order to enhance the
neurotransmitter secretion huge number of mitochondria are present at axon terminal.
B. Ultrastructure allowing red blood cell (RBC) to carry out its role
RBC is characterised by biconcave shape. Both side surfaces of RBC is curved inwards
similar to interior of sphere. This structure helps these cells to enters into tiny blood vessels also
for supplying oxygen. Identifiers present on the surface of RBC determines the blood type.
Haemoglobin present in these cells binds oxygen and absence of nucleus enhances the oxygen
carrying capacity. The biconcave shape of RBC optimize the surface area for rising oxygen
absorption efficiency and to squeeze through thinnest capillaries and narrow vessels (Alberts and
et.al., 2015).
QUESTION 2
PART 1
A. Cell membrane model as fluid
Cell membrane consist of number of molecules which floats along lipids. For example
cell membrane contains various proteins which are embedded in membrane. Different
constituents of cell cause lipid bilayer to float along lipid thus lipid bilayer acts as fluid. Due to
this reason cell membrane is described as the fluid model.
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B. Cell membrane model as a mosaic
Mosaic structure is formed by inlaying of small pieces of different coloured substances.
Fats and proteins constituents of cell membrane can be separate or bound with each other and
have different functionalities such as maintaining fluidity, adherence to cell and molecular
transportation (Nicolson, 2015). These elements are randomly distributed on cell membrane
surface which gives it mosaic appearance. Thus, membrane is explained as mosaic model.
PART 2
Membrane labelling
E. Role of hydrophilic protein channel
Channel protein allows the selective transportation of substances through membrane.
Hydrophilic protein channels can be described as the pores which are filled with water which
enable movement of ions through cell. The concentration gradient of this channel allows
molecules to flow from high to low concentration regions. Another significant characteristic of
channel protein is that a part of these molecules inside membrane is able to move closer to
hydrophilic pores (Ibarguren, López and Escribá, 2014).
Thus, the ion exchange process in cell membrane is executed in more controlled manner.
Usually the membrane serve as a barrier for these water friendly or hydrophilic ions or molecules
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cholesterol"
an intrinsic a
"hydrophilic protein channel.

and thus these molecules are restricted to enter into the cell region. Hydrophilic protein channel
provides a gateway to these molecules. The hydrophilic channel helps polar molecules to avoid
hydrophobic core so that speed of cell transportation mechanism is not slowed down.
QUESTION 3
PART 1
Osmosis and simple diffusion
Simple diffusion involves migration of molecules from high concentration to lower until
equilibrium is established. Uncharged and lipid soluble molecules can move through membrane
without any assistance from carrier molecule. It is known as simple diffusion. Due to kinetic
energy of particles at high speed collision occurs which causes diffusion.
On the other hand osmosis is flow of water molecules through semipermeable membrane
due to concentration gradient. Both diffusion and osmosis occurs due to concentration gradient.
The difference between both processes lies in the fact that osmosis involves only water
molecules while diffusion is the movement of particles except gas and water (Nicolson, 2015).
Diffusion can occur without membrane but osmosis essentially requires selective membrane.
PART 2
Active transport and facilitated diffusion
The movement of molecules due to concentration gradient with the support of energy is
known as active transportation. Energy can be in the form of ATP or electrochemical gradient
energy. On the other hand facilitated diffusion is uses a biological membrane carrier for
molecular movement instead of energy requirements. Cells used active transport for movement
against concentration gradient whereas for moving particles along the gradient passive transport
is employed by the cells (Rizzo, 2015). These different movements ensure proper cellular
functionality by keeping concentration of some molecules like amino acids or sugar higher in
certain cells. Facilitated diffusion and active transportation both transport sugar, salts and ions by
using proteins. However, the major difference between both of the mechanisms is the energy
requirements.
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PART 3
Transportation of large molecules
Large molecules cannot be transported by diffusion or osmosis thus they are carried
through protein channels. These channels are involved in facilitated diffusion and are situated
between phospholipid bilayer (Kohen, 2014). Large molecules may require energy for
facilitating their movement so energy is supplied by ATP. Their movement also involves vesicles
which permits the large molecules to move in and out of the cell because of plasma membrane
and vesicle fusion. Another process which can be used for exchange of these molecules is cell
drinking or pinocytosis. In this process membrane invagination causes particles to supspend
inside vesicle and thus particles are brought inside.
QUESTION 4
PART 1
Necessity of Mitosis and Meiosis
In the absence of Mitosis the cell division will not occur. Everyday cells are destroyed
and new cells are originated with this division. If this process will not occur then functions like
immunity towards diseases, production of reproductive cells and generation of new cells for
repairing tissues cannot be accomplished and thus survival will become impossible (Rizzo,
2015).
The reproduction and continuity of life by generation of new offspring is possible only
due to the cell division process called Meiosis. The evolution process can occur only by variation
and these genetic variations are introduced by Meiosis only (Duro and Marston, 2015). Its
inaccurate accomplishment can results in chromosome abnormalities which can make survival
difficult or impossible.
PART 2
Types of cell division
Mitosis Meiosis
What are the number of cell divisions? One Two
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What are the number of daughter cells
produce?
2 4
Is it identical to the parent cells? Yes No
Are polar body produced? No Yes
Where in the bodies does it occur? Somatic cells Germ cells
Is it haploids or diploid Diploid Haploid
PART 3
A. Mitosis stages and important processes in each stage
The various stages of Mitosis are as follows:
Stage Process
Interphase Normal functions are performed and new organelles are generated by
cell growth.
Prophase Nucleus and cytoplasm undergoes into changes. Chromosome is
condensed and visible
Pro-metaphase Interaction between spindle and chromosome begins and nuclear
membrane breaks (Vigneron and et.al.,2016).
Metaphase Alignment of copied chromosome in in-between of spindle occurs.
Anaphase Two identical groups results due to separation of chromosomes and
both of the groups are diverted towards opposite ends of spindle.
Telophase Around each set of chromosome nuclear membrane is formed and
spindle breaks down
Cytokinesis Parent cell is divided into 2 daughter cells with equal number of
chromosomes as in parent cell.
Distinguish process involved in Meiosis which are not present in Mitosis
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The crossing over process and independent assortment which occurs in meiosis leads to
genetic variations and does not occur in mitosis. The crossing over process occurs in the
prophase 1 of meiosis. However, this process does not occur in mitosis prophase. Meiosis
division divide cell two times and produces 4 haploids which are not identical. During metaphase
process in meiosis cell division chromatids are also aligned in random pattern and thus in
meiosis 1 chromatids are not divided into sitters. These processes distinguish between the two
types of cell divisions (Meiosis vs Mitosis: What’s the Difference?, 2014).
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REFERENCES
Books and Journals
Alberts, B., Roberts, K., and et.al., 2015. Essential cell biology. Garland Science.
Duro, E. and Marston, A.L., 2015. From equator to pole: splitting chromosomes in mitosis and
meiosis. Genes & development. 29(2). pp.109-122.
Ibarguren, M., López, D.J. and Escribá, P.V., 2014. The effect of natural and synthetic fatty
acids on membrane structure, microdomain organization, cellular functions and human
health. Biochimica et Biophysica Acta (BBA)-Biomembranes.1838(6). pp.1518-1528.
Kohen, E. ed., 2014. Cell structure and function by microspectrofluorometry. Academic Press.
Nicolson, G.L., 2015. Cell membrane fluid–mosaic structure and cancer metastasis. Cancer
research.
Rizzo, D.C., 2015. Fundamentals of anatomy and physiology. Cengage Learning.
Sherwood, L., 2015. Human physiology: from cells to systems. Cengage learning.
Vigneron, S., Robert, P. and et.al.,2016. The master Greatwall kinase, a critical regulator of
mitosis and meiosis. International Journal of Developmental Biology.60(7-8-9). pp.245-
254.
Online
Meiosis vs Mitosis: What’s the Difference?, 2014 [Online] Accessed through
<https://blog.udemy.com/meiosis-vs-mitosis/>
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