Cells
24.1 What are Cells?
• Living organisms are made up of small building
units of life called cells.
• Cells come in different shapes and sizes.
• Unicellular organisms are made up of one cell.
• Multicellular organisms, such as human
beings, are made of many cells.
Amoeba is an unicellular
animal.
Onion is a multicellular
organism.
24.2 What’s Inside a Cell?
• A cell is made up of a tiny mass of
living matter called protoplasm.
• Protoplasm is made up of a nucleus,
cytoplasm and cell membrane.
An animal cell
Vacuoles
Cell membrane
Nucleus
• Fluid-filled spaces
Chromosome
• A thin membrane
• within
Usuallythe
thecytoplasm,
largest
• Long
thread-like
surrounding
the cell
structure in the
surrounded
by cell
structures found in
• Partially
permeable –
• membranes
Spherical in shape
the nucleus
allows only certain
• Store
water and
other
Responsible
for cell
• Made
up of proteins
substances
to pass
nutrients
needed for
reproduction
and
deoxyribonucleic
through
living cell
organism
to
acid (DNA)
• the
Controls
activities
• Serves as a boundary
survive
including repair of
• Presence
of genes
between the
cell and
• The
animal
cell
worn-out parts
which
contain
the external
contains
many
tiny
hereditary
materials
• Needed for cell to
environment
vacuoles
stay alive
•• Passed
down
from
Controls
substances
•• Usually
parents
to
their
Containssmall,
entering
or
leaving
numerous
and
offspring
chromosomes which
the cell
temporary
animal
are geneticinmaterial
Cytoplasm
cells
• Jelly-like substance
• Contains chemicals and other tiny structures that
carry out special functions
• Many chemical reactions take place herez
A plant cell
Cytoplasm
•Cell
Jelly-like
wall substance
•• Contains
chemicals
A thick layer
and
other tiny
surrounding
the cell
Cell
membrane
structures
that
carry
membrane
• A
membrane
outthin
special
functions
• Made
up
of
cellulose
surrounding
the cell
• Many chemical
•• Supports
the
and
Partially
–
reactionspermeable
takecell
place
gives
a regular
allows
certain
here itonly
shape
substances to pass
through
• Serves as a boundary
between the cell and
the external
environment
• Controls substances
entering or leaving
the cell
Chloroplast
• Contains the green
pigment chlorophyll,
which is needed for
Nucleus
the plant to absorb
from
Sun
• energy
Spherical
in the
shape
make food through
• to
Responsible
for cell
photosynthesis
reproduction
Vacuole
Chromosome
Controlsa most
•• Usually
singlecell
large
•
Similar
to
that
activities
including
space surroundedofby a
animal
cells
repair
of worn-out
membrane
parts
• Contains a liquid
• called
Needed
cellCell
to
cellfor
sap.
stayisalive
sap
made up of
• water
Contains
and dissolved
chromosomes
which
materials
such as
are genetic
material
sugars
and mineral
salts.
24.3 Division of Labour
• Division of labour is the breakdown
of workload into smaller and more
specific tasks for maximum efficiency.
Division of labour in cells
• Within each cell, there are many special
structures or organelles.
• Each organelle is specially designed to
carry out a specific job.
chloroplast
nucleus
Chloroplasts
In a green plant
in green
cell,
plant
the nucleus
cells allow
is the
cells
responsible
to carry for
out
photosynthesis
controlling normal
to cell
make
activities.
food for growth
and survival.
Division of labour in multicellular
organisms
• Multicellular organisms are made up of
different types of cells performing different
functions.
• The cells have different shapes, sizes and
structures, designed to perform specific
tasks.
• This allows the organism to function
efficiently as a whole.
Division of labour in multicellular
organisms
• In the human body:
Nerve
havecells
specialised
The cells
red blood
in
extensions
called
blood contain
thenerve
red fibres
thatpigment
help tocalled
transmit nerve
haemoglobin.
signals
to and from the central
Haemoglobin
nervous
system.combines
nucleus
nerve
cell
with oxygen, which is
transported around the
body.
nerve fibre
red blood cell
Division of labour in multicellular
organisms
• In plants:
Guardhair
Root
cells
cells
on leaf
are found
surfaces
on
the surface
control
gaseous
of roots.
exchange
They are
long, which
between
theincreases
leaf and the
their
surface area. This helps the
atmosphere.
plant to better absorb water
and mineral salts from the soil.
stoma
root hair cell
guard cells
24.4 Forming a Multicellular
Organism
• A human body is made up of different organs
such as the heart, liver and stomach.
• Each organ has several sets of tissues working
together to allow it to function.
• These organs work together and make the five
main organ systems in your body – the
digestive system, the circulatory system, the
respiratory system, the skeletal system and
the muscular system.
24.4 Forming a Multicellular
Organism
• A human body:
o Different types of cells have specialised
functions
Heart muscle cells:
A single heart muscle cell
contracts rhythmically.
24.4 Forming a Multicellular
Organism
• A human body:
o Cells of the same kind that perform the same
job are grouped together to form a tissue.
Some tissues have more than one type of
cell. These are called complex tissues.
Heart muscle tissue:
Formed by heart muscle cells,
this tissue contracts and relaxes
rhythmically at a steady rate.
24.4 Forming a Multicellular
Organism
• A human body:
o An organ is formed by several tissues
working together to perform a specialised
function.
Heart: An organ formed by
muscle tissue, blood vessels,
nerve tissue and connective
tissue. It pumps oxygen-rich
blood to all the cells in the body.
24.4 Forming a Multicellular
Organism
• A human body:
o Organs with related roles coordinate to
function efficiently. They work together for a
specialised purpose to form an organ
system.
Cardiovascular system:
The heart, arteries and veins
work together to transport
blood to all parts of the body.
24.4 Forming a Multicellular
Organism
• A human body:
o The different organ systems work
together to make up the entire
body of an organism.
Body: All the systems work
together to enable the body to
function properly.
24.4 Forming a Multicellular
Organism
• Like the human body, plants have organ systems
too.
• The main organ systems in a plant are the shoot
system and the root system.
• The shoot system consists of the part of the plant
above the ground.
• The organs which make up the shoot system are the
leaves, stems, buds and flowers (of flowering
plants).
• The root system consists of the parts of the plant
below the ground such as the main roots and
branched roots.
24.4 Forming a Multicellular
Organism
• A plant
o Guard cells: The guard cells allow gaseous
exchange to take place.
24.4 Forming a Multicellular
Organism
• A plant
o Epidermal tissue (Epidermis): The
epidermal tissue is made up of many closely
packed cells including the guard cells. This
tissue helps to reduce water loss. It also
enables gaseous exchange and the
absorption of water and nutrients.
24.4 Forming a Multicellular
Organism
• A plant
o Leaf: The leaf is an organ where food
substances are formed. Epidermal tissue
forms the outermost layer of the leaf.
24.4 Forming a Multicellular
Organism
• A plant
o Shoot system: The shoot system includes
the organs – leaves, stems, buds and flowers
(of flowering plants).
24.4 Forming a Multicellular
Organism
• A plant
o Plant: The shoot and root systems work
together to help the plant grow and function.
shoot system
root system
Miscellaneous
• http://www.cellsalive.com/
• http://www.forgefx.com/casestudies/prenticehall/
ph/cells/cells.htm
• http://www.northern.edu/ramsayj/etechWeb/cells
.htm
• http://web.jjay.cuny.edu/~acarpi/NSC/14anatomy.htm
• http://www.nelsonthornes.com/secondary/scienc
e/scinet/scinet/plants/cells/types.htm