Cell structure & organisation

Cell Structure and Organisation
T H E M E O N E : P R I N C I P L E S O F B I O L O G Y
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• Identify the main organelles and membranes in
the cell.
• Explain the various functions of the different
organelles.
• Compare the structure of plant and animal cells.
• Describe the relationship between structure and
function as seen in root hair cells, xylem vessels
and red blood cells.
• Differentiate between the levels of organisation
in an organism.
Learning Outcomes

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• A light microscope uses light rays to produce
images; an electron microscope uses electron
beams.
• Magnification: degree to which the image is
enlarged.
1.1 Structure of Cells

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• Resolution: the smallest distance
needed for two points to be
distinguished.
• Depth of field: different tissues
lie on different planes.

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• Preparing slides for use with the light microscope:

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• Caring for the microscope:
– When shifting the microscope, hold on to the
microscope handle with one hand and support the base
with the other. Do not swing it around.
– Do not touch the lenses with your fingers and use only
lens paper to clean the glass.
– Before keeping the microscope, first rotate the
nosepiece to the low power objective, then lower it
until it nearly touches the stage.
– Be careful when working with the slides and cover slips.

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• Prokaryotes do not have a nucleus and are more
primitive.
• Eukaryotes like the animal cell (left) and plant
cell (right) have a nucleus where the genetic
material resides.

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Nucleus
• Chromosomes are uncoiled chromatin, visible
during nuclear division.
• A man has 46 chromosomes (i.e. 23 pairs of
chromosomes) in all his cells except the sex cells.

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Nucleus
• Nucleolus is the most visible part, responsible for
formation of ribosomes.

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Endoplasmic Recticulum (ER)
• Extension of the outer layer of nuclear membrane.

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Endoplasmic Recticulum (ER)
• Smooth ER:
– Without ribosomes
– Responsible for producing lipids and cholesterol.
– Where harmful substances are detoxified.
• Rough ER:
– With ribosomes.
– Where proteins are synthesised.

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Golgi Body
• Stack of membrane-enclosed sacs.
• Modify small vesicles from ER:
– Small vesicles fuse with one side of this complex.
– Finished products bud off from the opposite face.

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Mitochondria
• Double-membraned organelle.
• Cristae is the inner membrane, thrown into deep
folds.

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Mitochondria
• Energy extracted from sugar molecules is stored in
bonds of adenosine tri-phosphate (ATP) molecules.
• Bonds can be easily released with the help of
enzymes during respiration.

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Vacuole
• Fluid-filled sacs.

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• Vacuoles in animal cells are
called vesicles; they are
temporary and have
different functions such as:
– Storing sugars.
– Transporting products.
– Containing digestive enzymes
to digest invading bacteria.
– Helping the cell expel excess
water.
Vacuole

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• Plant cells have a large and
relatively permanent central
vacuole.
Vacuole

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Cytoplasm and Plasma Membrane
• The fluid in which all
organelles are suspended
is known as the cytosol
(in blue).
• The plasma membrane (in
orange) controls
substances entering or
leaving the cell.

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Cytoplasm
• Entire region of the cell between the nucleus
and the plasma membrane.
• Includes the organelles, various membrane and
cytosol.

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Plasma Membrane
• Transfers chemical messages from the outside of the
cell to the inside.
• Keeps the cell contents in place.
• Made of lipids and proteins.
• Constantly reforms to allow movement of materials
into and out of the cell.

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Cell Wall
• Only in plant cells.
• Presence of strong cellulose
fibrils for reinforcement.
• Functions:
– Protects the cell from
harmful external influences
– Helps the cell keep its shape
– Prevents the cell from
absorbing too much water
that it bursts.

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Cell Wall
• Plasmodesmata are channels
that allow small molecules
and water molecules to
move between plant cells.

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Central Vacuole
• Makes up 90% of the cell’s volume in a fully grown
plant.

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Central Vacuole
• Tonoplast is the membrane enclosing the cell sap
which is mainly water.
• Maintains turgidity of the cell.
• Stores nutrients, wastes, pigments and poisonous
substances.

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Chloroplasts
• Oval or spherical.
• Found only in plant cells.

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Chloroplasts
• Give plant cells their green colour.
• Give petals and fruits their colour.
• Others do not contain colour but act as centres of
starch grain storage or storage of oils and proteins.

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• The cell is the basic unit of all living organisms.
• All activities of the cell are controlled by
information stored in the nucleus.
• Mitochondria in the cell extract energy from
glucose and store it as ATP molecules.
• The energy stored in ATP is used by various
organelles in the cell such as the ribosomes,
which use the ATP to produce proteins for cell
repair or for export to other parts of the
organisms.

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• The plasma membrane controls the movement of
substances into or out of the cell.
• Plant cells are rigid because of the cell wall
surrounding the cell. The cell wall helps to
provide support for the plant.
• Unlike the temporary small vacuoles of animal
cells, plant cells usually have a permanent, large,
central vacuole. This helps to maintain the shape
of the cell as well as store various substances.
• The most characteristic feature of the plant cell
is the chloroplast which allows the plant to make
food in the presence of sunlight.

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Xylem Vessels
• Pipe-like columns.
• Provide support.
• Transport water
and mineral salts
from roots to
other parts.
1.2 Specialised Cells, Tissues and Organs

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Root Hair Cell
• Long narrow extension of the cell.
• Increases cell surface area.
• Increases the rate of diffusion of water and mineral
salts.

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Red Blood Cell
• Contains red pigment called haemoglobin.
• Supplies oxygen to other body cells.

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Relationship Between Structure and
Function of Red Blood Cell
• Haemoglobin combines easily with oxygen.
• Absence of nucleus – can pack more haemoglobin.
• Biconcave shape – increases surface area.
• Thin and elastic plasma membrane – able to squeeze
through narrow capillaries.

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Cell, Tissue, Organ and Organ System
• Similar cells work together as a tissue
to carry out a particular function.
• Organs contain a number of different
kinds of tissues.
• Several organs may work together in
an organ system.
• Each organ system serves a specific
function.

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• The structure of a cell is related to its function.
• Similar cells work together as a tissue to carry
out a particular function.
• Organs contain a number of different kinds of
tissue.
(a) (b) (c) (d)

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• Several organs may work together in an organ
system.
• Each organ system serves a specific function.
Most activities involve more than one organ
system functioning at the same time.

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Cell structure & organisation

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