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Cells
What is a cell?
What is a cell?
A cell is the smallest unit of living things.
Cells are microscopic in size. The parts or
organelles that make up a cell can only be
observed using a microscope.
Animal and plant cells
The two kinds you need to be most familiar
with are ‘typical’ animal and plant cells.
Cell membrane
One part found in all cells is the cell
membrane.
Cell membrane
The cell membrane controls what chemicals can enter
and leave the cell.
Nucleus
Another part found in all cells is the nucleus.
Nucleus
The nucleus is the ‘control centre’ of the cell. It
contains DNA and controls all the activities of the
cell.
Cytoplasm
All cells also contain cytoplasm.
Cytoplasm
Cytoplasm is a jelly-like mixture of chemicals
where most of the chemical reactions we need to
keep us alive take place.
Mitochondrion (plural – mitochondria)
All cells also contain mitochondria.
Mitochondria
Mitochondria are the ‘power houses’ of the cell.
These are the sites where respiration taes place
and energy is released from our food.
Plant cell organelles
Plant cells may contain some extra parts.
Chloroplasts (plant cells)
Chloroplasts which are disc shaped and are the ‘sites
for photosynthesis’. They contain the green pigment
chlorophyll which is needed for photosynthesis.
Cell wall (plant cells)
A cell wall which is a rigid outer layer to support
the cell and give it shape.
Vacuole (plant cells)
Large permanent vacuoles are found in plant
cells. These store a liquid called cell sap (a
mixture of sugars, salts and water). These help to
support the plant structure.
A cell is like a city.
A plant cell compared to a city
The wall of a city provides a fixed boundary.
The cell wall acts like the wall of the a city. It
gives the plant cell a fixed shape.
A plant cell compared to a city
The border guard of a city controls who
enters or leaves the city.
The cell membrane controls what enters or
leaves the cell.
A plant cell compared to a city
The air, land and water provide a physical
environment where all the the components of
the city can exist.
The cytoplasm of the cell is the place where all
of the organelles are found.
A plant cell compared to a city
The office where the city’s leader is based
(e.g. city hall) controls what happens in the
city.
The nucleus controls the activities if the cell.
A plant cell compared to a city
The power plant provides electrical energy
for the city.
The mitochondria of the cell provide the
energy needed for the cells activities.
A plant cell compared to a city
The restaurants within a city make food for
the people in the city.
The chloroplasts are the sites where food is
made in plant cells.
A plant cell compared to a city
The reservoir of a city stores water.
The large permanent vacuole of a plant cell
stores cell sap.
Animal and plant cells
The two kinds you need to be most familiar
with are ‘typical’ animal and plant cells.
Unicellular Organisms
• A single cellular organism performs all
required functions in one cell.
• e.g. Amoeba.
Multicellular Organisms
• Multicellular organisms are made up of
more than one type of cell.
• Their bodies need to supply food and
nutrients, transport materials, remove
wastes and fight infection.
What do all of these cells have in common?
Cell Specialisation
The cells on the previous slide all have
typical structures such as:
–
–
–
–
–
cytoplasm
cell membrane
cell wall
nucleus
chloroplasts
However, the structure each type of cell is
different so that it can carry out a particular
function. This is known as cell specialisation.
Sperm cell
Head contains nucleus
and mitochondria
Tail
Sperm cells swim towards the egg to carry out
fertilisation. They have a tail to enable them to swim
and many mitochondia for producing energy.
Egg cell (ovum)
Cytoplasm containing
food store
• Made in the ovaries of
mammals.
• An egg cell is large
compared to sperm.
• Contains a food store in
the cytoplasm for
nourishing the embryo.
Nucleus
Ciliated cell
• Help to prevent dust and
bacteria entering lungs
nucleus
• Line the windpipe (trachea)
• Have tiny hairs called cilia
cilia
• Cilia sweep mucus with
trapped dust and bacteria
up to mouth to be swallowed
Nerve cell (neurone)
extension of the
cytoplasm (axon)
nucleus
• Longest cells in the body
•Transmit electrical nerve impulses in body
Red blood cell
• No nucleus
• Contain haemoglobin to carry oxygen
around the body
• “Biconcave” shape for large surface area
Palisade mesophyll cell
• Found in leaves of plants
nucleus
• Packed with chloroplasts
to trap light for
photosynthesis
chloroplasts
Root hair cell
• Root hair
increases
surface area for
uptake of water
and minerals
from soil
• Thin cell wall so
water can move
in easily
thin cell wall
root hair
cell membrane
vacuole
• Tissues are
groups of cells
that perform the
same function.
• Examples of
human tissues
include
epithelial tissue
and muscle
tissue.
Tissues
Epithelial tissue
• Epithelial tissue covers body surfaces and
lines cavities and tubes.
• These include the airways and digestive
tract.
• Some epithelial tissue is specialised to
form glands like oil and sweat glands in
the skin.
Muscle tissue
• Muscle tissue helps in body movement
because it can contract and relax.
• There are three different types of muscle
tissue:
- cardiac
- skeletal
- smooth
Plant tissues
• Plants also have different types of cells
that are grouped together into tissues.
• In each case, the structure of each cell is
related to its function.
• Plant tissues include epidermal, palisade
mesophyll and spongy mesophyll.
Epidermal tissue
• Epidermal cells fit together like a jigsaw
• From Greek word meaning “over-skin”
• Create a strong and protective layer on
the outside of leaves, roots and stems
epidermal
Palisade mesophyll tissue
• These cells have many chloroplasts to trap
light for photosynthesis
• Are column shaped so that they can be
densely packed near the surface of the
leaf
palisade mesophyll
Spongy mesophyll tissue
• These cells have a rounded shape
• This allows them to be loosely arranged
so that they can take up carbon dioxide by
diffusion
• Carbon dioxide can then be used for
photosynthesis
spongy mesophyll
Organs
• A group of tissues working together form
an organ.
• Examples of animal organs include the
heart, lungs, brain and kidneys.
• Examples of plant organs include roots,
stems, flowers, seeds and fruits.
Systems
• A group of related tissues and organs eg.
blood, heart, arteries, capillaries and veins
make up a system.
• The tissues an organs above make up the
circulatory system.
Systems
• Examples or organ systems in animals
include:
• skeletal
• muscular
• digestive
• respiratory
• nervous
• circulatory
Systems
• Examples of organ systems in plants
include the vascular system in the roots
and shoots.
• This includes xylem and phloem. You will
learn about these specialised cells later.
Summary
• Cells have different ___________ that allow
them to carry out a particular__________.
• These are known as cell specialisations.
• Many __________ cells working together form a
__________.
• A group of tissues that work together form an
___________.
• Organs are found in both _______ and plants. A
group of related tissues and organs form a
__________.
animal
specialised
organ
tissue
structures
function
system
Summary
structuresthat allow them
• Cells have different _________
function
to carry out a particular__________.
• These are known as cell specialisations.
specialised cells working together form a
• Many __________
______. tissue
• A group of tissues that work together form an
organ
_______.
animal and plants.
• Organs are found in both _______
• A group of related tissues and organs form a
system
__________.
Building cells
Refer to the attachment – ‘Cell Project’ to
find out about your group assignment on
cells.
Oh no!