Transcript specialised cells File

Candidates should be able to:
 Define the term stem cell
 Define the term differentiation, with reference to the production of
erythrocytes and neutrophils derived from stem cells in bone marrow,
and production of xylem vessels and phloem sieve tubes from
cambium
 Explain the meaning of the terms tissue, organ and organ system.
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Cells make up TISSUES, groups of similar cells performing a
common function e.g. Xylem or phloem in plants, muscle or
nervous tissue in animals
Groups of different types of tissues are arranged together to
form ORGANS e.g. the stomach consists of epithelial,
muscular and glandular tissue
Organs are grouped into ORGAN SYSTEMS e.g. respiratory
system, reproductive system. Organ systems consist of a
number of organs working together to perform an overall life
function
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Stem Cells
Stem cells are genetically identical, undifferentiated
cells that carry a full set of genetic information, and
are capable of dividing to become genetically
identical new (daughter) cells, which can then
differentiate to become specialised into any of the
different cell types found in the organism.
 Stem cells have a unique ability to renew themselves and
give rise to the more specialized cell types that do the work
of the body.
 Stem cells remain unspecialized until a signal from the
body tells them to develop into specific cells of the body like
a heart, nerve, or skin cell
 Differentiation is achieved due to the switching on and off
of relevant genes
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 Totipotent
Embryonic stem cells from a 8 cell stage embryo (morula)– able
to differentiate into any type of cell, including embryonic cells
Totipotent stem cells have a wide range of clinical applications
 Pluriponent
From the inner cell mass of an embryo (blastocyst) and umbilical
cord blood – able to differentiate into most types of cells but not
embryonic cells
Narrow range of clinical applications
 Unipotent cells - adult stem cells
Able to differentiate into only one cell type – its own type
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Stem cells are unspecialised cells that have two key qualities
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Self renewal – they can continuously divide and replicate
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Potency – they have the capacity to differentiate into specialised cell types
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Erythrocytes and neutrophils perform different functions but contain the same
genetic information.
All blood cells are produced from undifferentiated stem cells (adult/unipotent) in
the bone marrow. Particular genes are switched on/off so they differentiate to
become specialised.
 Cells destined to become erythrocytes (red blood cells) lose their
nucleus, mitochondria, Golgi apparatus and rough endoplasmic reticulum.
 They are packed full of haemoglobin and their shape is changed to
become biconcave discs


Cells destined to become neutrophils retain their nucleus.
The cytoplasm of neutrophils makes numerous lysosomes and appears
granular
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•In plants meristem cells are like stem cells
•One type of meristem cell is the cambium
•The cambium in part of the vascular bundle and
differentiates into transport tissues (xylem and phloem)
•To form xylem vessels, the cambium cells elongate
•produce lignin to strengthen and waterproof their walls –
•which causes cell contents to die so cells become hollow
•To form sieve tubes (phloem) the cambium cells elongate and
multiply themselves ‘end to end’
•the membrane/wall at the end of cells partially break down to create
channels (for mass flow between cells) called sieve plates.
•To form companion cells (phloem), the cambium cells need to
differentiate into cells which produce lots of enzymes and
mitochondria (as cells does lots of reactions)
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When asked to describe ‘specialisation’ of
a cell you should:
NAME THE FEATURE e.g. Sperm cells
have a flagellum
EXPLAIN HOW THE FEATURE ENABLES
IT TO DO ITS ROLE e.g propels the sperm
along the oviduct to meet an egg cell
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Specialised Cells
Neutrophils (white blood cells; phagocytes)
Multi-lobed nucleus (flexible)
Specialised for defence against disease

Flexible shape – allows engulfing of foreign
particles or pathogens by the process of
phagocytosis (“cell eating”)

Migrates to and from the tissues, through
pores in the capillary endothelium

Multi-lobed nucleus – allows flexibility

Contains many lysosomes – contain
hydrolytic/digestive enzymes to break down
engulfed particles.

Contains large amounts of rough
endoplasmic reticulum – for protein (enzyme)
synthesis

Granular appearance – contains granules granules contain hydrolytic enzymes

Many receptor sites on the cell surface
membrane for attachment to cells and
pathogens (antigens)
Granular
(granules contain enzymes)
Phagocytosis
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Erythrocytes (red blood cells) - carry oxygen in the blood
Contain haemoglobin (an iron containing respiratory pigment)
to transport O2 to tissues (cells) from the lungs

Haemoglobin requires iron for its structure as a
respiratory pigment – O2 is carried, from the lungs to the
tissues bound to the iron in haemoglobin

Thin outer membrane - creates a short diffusion
distance – allows rapid diffusion of oxygen into
erythrocytes in the lungs (alveoli) and out of
erythrocytes in tissues

Bi-concave disc shape - increases the surface area
for diffusion of gases
Allows more haemoglobin to be packed around the
edge (in contact with capillary wall) – reduces the
diffusion distance

Flexible membrane framework – allows red blood
cells to squeeze through the narrow capillaries; ensures
maximum contact between red cell membrane and
capillary wall

No nucleus - there is more room for haemoglobin, with
the whole cell full of haemoglobin
Disadvantage – limits life span to ~ 120 days

Transports some CO2 – from tissues to lungs
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Sperm cell (male sex cell; male gamete)
Specialised to fertilise the ovum (female gamete)
Fertilisation – fusion of male and female gamete to
form a zygote – fusion of sperm and egg nuclei
Sperm (n) + Egg (n)
(haploid)
(haploid)
Zygote (2n)
(Diploid)

Nucleus contains half the number of chromosomes
of an adult somatic (body)cell in order to fulfil its
role as a gamete

Streamlined head and body – to reduce resistance
during movement through fluid

Head contains genetic information (DNA) in the
haploid nucleus, and an acrosome (lysosome) .
Acrosome contains hydrolytic (digestive) enzymes
– digests the egg cell membrane for the
penetration of the sperm head (nucleus)

Cell surface membrane in head region has
receptors for binding to egg cell surface
membrane

A flagellum (tail) to propel the sperm to the egg

Mid-piece is packed with mitochondria – to
generate energy (ATP) for movement of flagellum
Sperm head entering an ovum
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Leaf palisade mesophyll cell
Specialised to carry out photosynthesis

Packed with chloroplasts containing the light
absorbing pigment chlorophyll

Converts light (solar) energy to chemical energy
– i.e.
synthesis of glucose (organic) from
inorganic materials (CO2 and H2O) using
light energy of the sun

Regular shaped, closely packed columnar
palisade cells forming a continuous layer for
maximum absorption of sunlight.

Thin walled cells – for rapid diffusion of gases
(carbon dioxide and oxygen).

Chloroplasts can move within the cell, aided
by the cytoskeleton– for maximum light
absorption

Vacuole – membrane bound organelle
containing cell sap; helps to maintain turgidity
to support plant

Cellulose cell wall – protects the cell, confers
strength, and prevents the cell from bursting
Palisade mesophyll cells
Upper epidermis
Sunlight
Xylem
Phloem
Vascular
bundle
Air space
Lower epidermis
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Cross-section of leaf
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Guard cells
Specialised to open and close leaf pores (stomata) – used for gas exchange and transpiration
(loss of water vapour from leaves by evaporation)

Regulate the size of leaf pore – allow entry and exit of gases and water vapour

Change shape easily

Swell up when the vacuole is filled with water and become turgid (firm)

In light (photosynthesis) - K ions are moved into the guard cell actively – water follows
down a water potential gradient and – makes the guard cells turgid.
ATP for active transport
Contain mitochondria to generate ATP for active transport

This causes the thin outer walls to stretch and the thickened inner walls to bend outwards
– opening the stomata – allowing gas exchange for photosynthesis.

When flaccid (e.g. in the dark – when there Is no photosynthesis), the thickened inner walls
move inwards to close the stoma
Guard
cells
Stoma
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(pore)
Stomata on underside of leaf
Guard cells flaccid
(limp)
- at night (dark)
Guard cells
turgid (firm)
- during daylight
The thick inner wall ensures that only the outer wall stretches when the cell is turgid –
causing the inner wall to curve outwards, thus opening the pore

Potassium (K) ions are actively transported into
guard cells during daylight (photosynthesis)

Reduces the water potential inside the guard cells

Causes water to enter down a water potential
gradient by osmosis

Guard cells fill with water and become turgid

Stomatal pores open

In the dark (night), K ions are actively pumped out
of guard cells– causing water to leave by osmosis
– guard ells become flaccid and the pores are closed
Dark
Light
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Root hair cell
Numerous, long hair-like extensions of the cell wall and cell membrane of root epidermal
cells in young plants, extending into the soil
Specialised for absorbing water by osmosis and dissolved minerals by active transport and
facilitated diffusion from the soil into the root

Provide a large surface area for efficient
absorption of water by osmosis down a
water potential gradient

Minerals are absorbed by active transport
against a concentration gradient

Some minerals are transported down a
concentration gradient from the soil by
facilitated diffusion through channel
proteins

Cell wall of root hair cell is thin and
permeable – reduces diffusion distance

Large number of mitochondria in root hair
cells provide energy (ATP) for the active
transport proteins located in the cell
surface membrane
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 Water and dissolved minerals from
the
soil are taken up into root hairs

Water enters root hair cells by
osmosis

Mineral ions are taken up by active
transport and diffusion ( facilitated )
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Some therapeutic uses of stem cells
 Retinal cells – replace dead cells in retina to cure diseases like glaucoma
 Skin cells - graft new skin cells to replace damaged cells in burn victims
 Nerve cells - repair damage caused by spinal injuries to enable paralysed victims to
regain movement
 Blood cells – bone marrow transplants for cancer patients who are immuno-compromised
as a result of chemotherapy
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