Download What is a cell?

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What is a cell?
A cell is the basic unit of life, from which larger structures
such as tissue and organs are made.
 Unicellular organisms,
such as bacteria, consist of
just a single cell.
 Multicellular organisms
consists of many cells –
humans are made from an
estimated 50 trillion cells!
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What is a eukaryote?
A eukaryote is any organism
consisting of one or more cells that
contain DNA in a membrane-bound
nucleus, separate from the cytoplasm.
Eukaryotes include:

animals

plants

fungi

a diverse group known as the
protists (or protoctists).
All eukaryotic cells contain a large number of specialized,
membrane-bound organelles.
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The organelles of protein synthesis
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Mitochondria
The mitochondrion is an energy-generating organelle.
It is surrounded by two membranes. The inner layer folds
inwards to form the cristae. The cristae project into a liquid
called the matrix.
outer membrane
cristae
matrix
inner membrane
The inner membrane is coated in enzymes, which catalyze
the reactions of aerobic respiration to produce ATP.
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Microtubules and the cytoskeleton
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Which organelle?
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Plant cells
Plant cells share all the common features of animal cells,
but also contain some additional organelles.
Plants gain all their energy from sunlight; cells in their leaves
contain many chloroplasts to convert this into a useful form.
chloroplast
vacuole
Every plant cell is
surrounded by a cell
wall, and contains
one or more
permanent vacuoles.
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cell wall
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Chloroplasts
Chloroplasts use carbon dioxide, water and light energy to
build sugars. They are present in all green plants.
The chloroplast is surrounded by a double membrane. It is
filled with a liquid called the stroma, and contains stacks
of thylakoid membranes called grana.
grana
stroma
thylakoid membrane
The thylakoid membranes are the site of photosynthesis.
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The cell wall
The cell wall of a plant cell gives it support and structure.
It is made of the polysaccharide cellulose, and can function
as a carbohydrate store by varying the amount of cellulose
it holds.
The cell wall does not seal off a
cell completely from its
neighbors. There are pores
within the walls called
plasmodesmata. These
connect two cells together by
their cytoplasm, enabling
substances to be exchanged
and transported between them.
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Eukaryotic organelles
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Animal or plant?
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What do cells contain?
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What are membranes?
Membranes cover the surface of every cell,
and also surround most organelles within
cells. They have a number of
functions, such as:
 keeping all cellular components
inside the cell
 allowing selected molecules to move in and out of the cell
 isolating organelles from the rest of the cytoplasm,
allowing cellular processes to occur separately.
 a site for biochemical reactions
 allowing a cell to change shape.
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The fluid mosaic model
The freeze-fracture images of cell membranes were further
evidence against the Davson–Danielli model.
E-face
They led to the
development of
the fluid mosaic
model, proposed
by Jonathan
Singer and Garth
Nicholson in 1972.
P-face
protein
This model suggested that proteins are found within,
not outside, the phospholipid bilayer.
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Exploring the fluid mosaic model
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