Conclusively the AER dismantles, and is kept only over

if apoptosis isn’t functioning properly you will either have not enough cell
death which can lead to cancer, as the wrong cells are dying. In contrast too,
much cell death can lead to condition such as Alzheimer’s and Huntington’s
disease (Alberts et al., 2017).


first step if a normal cell wants to undergo aptosis, it’s going to separate
from other cells, so it’s essentially goes off on its own. Second step is where
the cell shrinks shrivels up, and the nucleus collapses also known as chromatic
condensation’s third step is the cell nucleus becomes very dark, this can be
called membrane blebbing. The DNA condenses tighter, the cell then falls apart
forming plebs which are fragments of the cell. An enzyme DNASE attacks the DNA
to break it down enabling other cells to absorb or remove the fragments of the
cell that underwent apoptosis. Caspaces are apoptotic enzymes that can be
released by internal, sub internal or even external signals to destroy the
cell. Internal signals in the cell instruct the cell to start the apoptosis
process, an external signal most commonly happens at the same time. A death
lygone binds to the receptor activating apoptosis, leading to death of the
cell. A cell will automatically start apoptosis if the DNA is permanently

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is the process which excess or damaged cells in the body are removed. Apoptosis
is an extensive continual process in our bodies, it’s the fine line between the
production of new cells and cell death that keeps the appropriate number of
cells in the tissue. Apoptosis is a genetical program and is very predictable
and an example of this; A human as an embryo is created with webbing between
their fingers, apoptosis then comes in causing cell death to define and
separate the fingers.

role that programmed cell death plays in the development process is through











elongation continues the forming of the cartilaginous models of the imminent
digital bones happen when the mesenchyme condenses into plates. Next the AER
dismantles, and is kept only over the tips of the imminent digits. A process
called cellular apoptosis then steps in and gradually sculpts the interdigital
spaces (TeachMeAnatomy,
2017), (, 2017).


zone of polarising activity (ZPA) located in the posterior base of the  bud controls the AER alongside making sure s
are mirror-symmetric. The
location of the EAR is essential since the border separates the dorsal and
ventral  ectoderm.
The ectodermal the abilities to apply an ‘dorsaling and ventralising’ impact
over the mesenchyme. An example of this; it can remove hair follicles from the
palms and soles of our feet.


the embryo development process right up until the baby is born, mitotic division
continues. Lim bud formation starts in the fourth week with help from the
mesenchymal cells which are the somatic layer of lateral plate mesoderm. Upon
the ventrolateral body wall initially, 
buds first appear then stretch ventrally. They comprise of a focal
center of undifferentiated mesenchyme with a layer of ectoderm, known as the
apical ectodermal ridge (AER). The AER stimulates outgrowth of the  by promoting mitosis. During proliferation of
the fundamental mesenchyme core, elongation happens where the AER has a vital
role in making sure the mesenchyme underneath remains undifferentiated. As
growth continues, the proximal mesenchyme lacks signals from the AER whilst
starting to differentiate into the essential tissues of the .


sperm has managed to get threw the zona pellucida, breaking through the plasma
membrane enabling a mix of its genetical material with your own genetical
materials. Now you are known as a zygote, however this zygote begins dividing
rapidly splitting without growth and doubling your cells is known as the
cleavage stage.


cell division is the combination of mitosis and cytokinesis; which is where the
cytoplasm of a eukaryotic cell divides forming two similar cells. Mitosis is
involved in the majority of cell division that takes place in your body.


In this
essay I am going to talk about the role of mitotic proliferation and programmed
cell death play in the development process using the example of how a healthy
human embryo develops an arm bud into a functional hand.


How a healthy human embryo develops the
arm bud into a functional hand




Q6. In 1000 words or less describe how a healthy human embryo develops
the arm bud into a functional hand. Your answer should cover the role that
‘mitotic proliferation’ and ‘programmed cell death’ play in the developmental


Part C (assessment criterion 2.3)
















This cell shows us that it is in the
cytokinesis stage also known as the division of the cytoplasm. The process
of cell division cell organelles mitochondria being one of them, get
distributed evenly amongst the cells. The intucking of the plasma membrane
at the equator of the spindle’ pinching’ the cytoplasm in half is how
animal cells divide (Clegg 2000).








This cell
image shows us it’s in telophase where at opposite ends of the cell a
nuclear membrane re-forms around both groups of chromosomes. Through
uncoiling the chromosomes decondense, turning into a chromatin again. In
every nucleus the nucleolus reforms (Burrows et al, 2015).







This image is a cell during anaphase where the centromeres
divide the spindle fibers, shorten them and the chromatids are dragged
away by their centromeres to opposite poles, On completion of separation
the chromatids are now known as chromosomes











This cell image shows that it’s in the
Metaphase, animal cells centrioles shift to the opposite ends of the cell.
Radiating out from the centrioles are microtubules of the cytoplasm which
begin to form into a spindle. On each pair of chromatids, microtubules fix
themselves onto the centromeres, these are then organised at the equator
of the spindle (,2017).





cell image shows it’s in the prophase stage where the chromosomes are
distinguished as long thin threads. Threw a process of coiling these long
thing threads become rapidly shorter and thicker. It is only visible at
the end of prophase that each thread is made up of two chromatids bound
together by at the centromere. Whilst this is taken place the nucleolus
progressively disappears; the nuclear membrane then collapses

For each of the pictures of
the different stages of mitosis below, name the stage and describe what is
happening to the chromosomes.


Q5. Identify
different stages in mitosis from photographs or from a slide of a root tip.
Annotate the stages to explain the behavior of the chromosomes.



The M phase
stands for the Mitosis phase which is a continual cell division process that is
broken down into four distinct stages; Prophase, Metaphase, Anaphase and
Telophase. After all the four processes have done their job the chromatids end
up as one-strand chromosomes in the daughter cell (Boyle
and Senior, 2008).


G2 is the second
growth phase, but shorter growth happens here enabling the proteins and enzymes
required for cell division to be synthesised ready to be divided by mitosis.


The S phase is
the process following on from the G1 stage which is where DNA is synthesised
You would expect a cell to only move into the s phase with the intention of
dividing. The restriction point is the beginning of the DNA replication. Next
the cell becomes constricted or sealed into an automatic arrangement that
certainly move on to cell division.

In the G1 stage protein synthesis begins
the amount of cytoplasm, along with the number or organelles grow dramatically.
The process is complex not only because few organelles mitochondria being one
of them, having their own DNA divide individually from the cell nucleus.
Furthermore, in the later G1 stage the cell adopts a more normal amount; whilst
the surrounding cytoplasm grows this makes the nucleus appear smaller (Boyle
and Senior, 2008).


G1 is the first growth phase, following on
from production using division of its parent. A new cell is in the initial
place of the first growth phase being G0. Cells that won’t divide stay in this
location in the cell cycle due to not needing to progress onto the next stage,
because at no point do they replicate their DNA. New cells are small in
appearance but has a fully-grown nucleus but has little cytoplasm.

Interphase has three stages within in; G1,S
and G2.


The Go is also the stage after mitosis
where the cell can leave the cell cycle, remain in a resting state or re-enter
the cell cycle later. Blood cells which are Labile cells don’t go into the Go
stage after mitosis however they continue cycling. In the GO phase permanent
tissue such as muscle/nerves are stuck in this phase and cannot continue onto
the mitosis stage. Hypertrophy can only occur to these tissues when dealing
with more stress and form fibrous unnecessary scars through the healing
process.Stable tissue is predominantly found in the GO phase, although once
given the right signals, can re-enter the cell cycle. A good example of a
stable tissue is liver cells as they can take part in replication because of
injury to the organ to help the healing process (Boyle and Senior, 2008).


Cell division takes place at the beginning
of the cycle and then again at the end of the cycle. The cell cycle is broken
into two stages called Mitosis and Interphase, the break between the divisions
where the cell fulfils its normal function.



Below is a diagram representing the cell cycle. Write a description of what
happens at each labelled stage (G0, G1, S, G2, M).


Part B (assessment criterion 2.2)





















This image shows this man has Klinefelter syndrome
which is, where
a genetically they were born as a boy just with an extra copy of the X
chromosome. Some people don’t even realise they have this extra copy, whereas
others it can cause varies problems such as developmental delay both physical
and mental, reduced facial and body hair around puberty and infertility (,















































This is a male as it has the Xy. It shows no










































Trisomy 18 refers to three
duplicates of number 18 chromosome. At the point when three duplicates of any
of the chromosomes are available, as opposed to the normal two, the result is
47 chromosomes in the cell, rather than the standard 46. Trisomy 18 is also
known as Edwards syndrome, its additional chromosome brings about congenital
malformations genuine formative and motor disabilities, and a high rate of
mortality (Trisomy 18, Trisomy 13 and Related Disorders, 2017).


This is an image of a male as
it has two
distinct sex chromosomes XY.























Q3 Interpret the following human karyotypes in terms of the
sex of the individual and any abnormalities in the chromosomes.











































Draw and annotate the structure of a chromosome















A lot of scientists believed it was
impossible for DNA strands to be separated due to the strength of a DNA
molecule, so they were skeptical of this proposed semi conservative
explanation. Mathew Meselson and Franklin Stahl decided to create an experiment
using the old DNA verses the new DNA, naming this experiment ” The most
beautiful experiment in biology’. The scientists grew bacteria in the presence
of different nitrogen isotopes then looked at the DNA of the bacteria and
noticed the amount of nitrogen isotopes in the different bacteria generations
concluding that semi-conservative was the only possible explanation validating
Watson and Crick’s theory, they published there results in May 1958 which can
be found in ”The replication of DNA in Escherichia Coli”(Burrows
et al., n.d. 2015).


In 1953 the question of how does DNA
replication happen still remained, they had three theories up until that date;
Conservative replication where a DNA molecule would be copied and make a second
new DNA molecule. Dispersive where the DNA molecule would be cut at varies
parts each of which would be copied and reattached to produce two new DNA
molecules. Semi-conservative where two DNA strands would separate and each one
would serve as a template to copy its second strand thus producing two DNA
molecules. This was Watson and Cricks explanation of how DNA replication took


First step of DNA replication begins with
an enzyme called topoisomerase which relaxes the super coiled double-stranded
DNA. An enzyme called helicase then unwinds this DNA which opens to two strands
in one place at a time. Nucleotides matching the bases are exposed by the
unwinding base pair with their match. Following, the enzyme DNA polymerase
combine these bases by catalysing the development of a bond between the phosphates.
The enzyme DNA polymerase at that point combines these bases by catalysing the
development of a bond between the phosphate of one nucleotide and the sugar
(deoxyribose) of a nearby nucleotide. This enzyme has an editing capacity,
amending any mistakenly included nucleotides. The enzyme moves more remotely
along, unwinding the following area of DNA so more nucleotides can join the
developing chain of the new DNA strand. The site where this is going on is
known as the replication fork. Since each strand of a twofold stranded DNA
molecule gets fused into one of the two last duplicates of new DNA atoms, the
procedure is called semi-conservative replication. DNA polymerase can just add
bases in the 5? to 3?direction, so replication continues contrastingly on the
two strands of DNA in the replication fork.