The function l) The production of xylem vessels

The features and
differentiation of stem cells

 

Features
of a stem cell:

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Ø 
A
renewing source of undifferentiated cells – capable of differentiating
(specialising) into other cells

Ø 
In
animals, replace damaged cells (e.g. new skin or blood cells)

Ø 
In
plants, makes new shoots and roots. Stem cells also differentiate into xylem
and phloem

Ø 
Stem
cells produce more stem cells (self-renew)

Ø 
Can
be:

o  
Totipotent

§ 
Can
differentiate into any type of body cell including extra-embryotic cells (in
placenta and umbilical cord)

§ 
Can
form entire organism

§ 
In
zygote and early stage embryo

§ 
In
meristems and cambium (in plant)

o  
Pluripotent

§ 
Can
differentiate into any type of body cell (par extra-embryotic cells)

§ 
Embryotic
(embryo) cells are pluripotent

o  
Multipotent

§ 
Can
form more than one cell type but not all

§ 
Found
in bone marrow

 

Differentiation
of stem cells:

Ø 
The
development and changes in multicellular organism cells as they form
specialised cells which perform a specific function

Ø 
Needed
as all cells cannot do everything like unicellular organisms.

Ø 
Specialisation
by:

o  
Having
a specific size / shape (e.g. root hair cell)

o  
Having
a certain number of organelles (e.g. sperm cell with large number of
mitochondria)

o  
Having
specific cellular content (e.g. phagocytes have enzymes to break substances)

 

k) The production of
erythrocytes and neutrophils derived from stem cells in bone marrow

 

Bone
Marrow:

Ø 
Bone
marrow contains multipotent stem cells

Ø 
These
cells will specialise into erythrocytes and neutrophils (hematopoietic cells),
despite both cells have the same set of chromosomes

Ø 
Erythropoiesis
is needed as RBC does not have nucleus so cannot divide

 

Production
of erythrocytes (erythropoiesis):

Ø 
Lose
their nucleus, mitochondria, Golgi apparatus and Rough Endoplasmic Reticulum

Ø 
Produce
a lot more haemoglobin

Ø 
Shape
becomes bi-concave

 

Production
of neutrophils:

Ø 
Keep
nucleus but have indentations in nucleus (gives lobed structure)

Ø 
Produce
granular cytoplasm due to many lysosomes produced

Ø 
Lysosomes
contain hydrolytic enzymes which allow for its function

 

 

 

 

 

l) The production of
xylem vessels and phloem sieve tubes from meristems

 

Cambium:

Ø 
Contain
totipotent meristem cells

Ø 
Between
tissue of phloem and xylem

 

Production
of xylem vessels:

Ø 
Meristem
cells elongate and line up end to end

Ø 
Walls
reinforced and waterproofed by deposits of lignin

Ø 
Cell
contents (Inc. cytoplasm) and end walls are destroyed forming a continuous long
tube with a wide lumen

Ø 
Xylem
tissue is suited to transporting water and dissolved minerals up the plant

Production
of phloem sieve tubes:

Ø 
Meristem
cells elongate and line up end to end to form a long tube

Ø 
Consists
of two cell types sieve tube elements and companion cells:

Ø 
Sieve
tube elements

o  
Cell
end walls do not breakdown completely and form sieve plates

o  
Sieve
plates allow assimilates to move up and down the plant

Ø 
Companion
cells

o  
Very
metabolically active

o  
Lots
of mitochondria, membrane proteins

 

Ø 
Production
of both xylem and phloem stimulated by hormones

 

m) The potential uses of
stem cells in research and medicine

 

Ø 
Stem
cells can be induced to form specific types of cell in the correct conditions

Ø 
This
can be potentially being used to repair damaged cells in the body

Ø 
Additionally,
if a person’s own stem cells are used, there is a lower chance of rejection

Ø 
There
has been research and trials in curing diseases using stem cells:

 

Alzheimer’s Disease:

 

What is it:

Ø 
Alzheimer’s
Disease (AD) is the most common cause of dementia

Ø 
It
causes memory loss, difficulty thinking and speaking

Ø 
The
disease causes protein in the brain to form plaques and tangles which cause
death of nerve cells and loss of brain tissue

Ø 
It
is progressive so the symptoms get worse over time

 

Research
with stem cells:

Ø 
Scientists
are using Induced Pluripotent Stem cells (iPS)

Ø 
iPS
are ‘reprogrammed’ specialised cells (such as skin cells) to form other cells;
in this case neutrons are made which are otherwise hard to obtain

Ø 
Scientists
use skin cells from Alzheimer’s patients and from that made iPS stem cells to
make neurons; this allows scientists to study neurons similar to ones in brain
affected by Alzheimer’s to gain a better understanding of why the proteins form
and to search and test for drugs

Ø 
This
holds a great promise to expand our knowledge on Alzheimer’s (as not a lot is
known) and eventually find a cure

 

Parkinson’s Disease:

 

What is
it:

Ø 
A
progressive neurological disease

Ø 
It
occurs when cells in the brain producing dopamine die

Ø 
Dopamine
is released to control movement which includes talking, writing and walking

Ø 
As
more cells are lost, symptoms get worse such as tremors, memory issues, speech
problems, eating issues, bladder issues, slowness in movement

Ø 
The
cure for Parkinson’s is not found yet

 

Research
with stem cells

Ø 
The
cure for Parkinson’s is not found yet

Ø 
Embryonic
stem cells have been used to make dopamine producing cells for transplant in
the brain to replace those lost

Ø 
The
clinical trial was a success in rats; the stem cell produced dopamine cells
acted like native cells and restored the brain’s dopamine production

Ø 
A
human trial should be ready in 3 years by Lund University in Paris

 

Research into
Developmental biology

Ø 
Stem
cells are valuable in the study of the bodies development from a fertilised
egg, including the behaviour of cells and the cause of problems in development

Ø 
Embryonic
stem cells are the most useful for this as they can form every cell however
using surplus human embryos is controversial