Download CELLS The cell is the basic unit of life. All living organisms are

CELLS
The cell is the basic unit of life. All living organisms are composed of cells and their products. Under a microscope, the
human body is seen to be composed of many different cells; muscle cells, brain cells, liver cells - all of which are quite
dissimilar. Yet the differences, while important, should not obscure the many similarities in structure(how something is
made) which exist. Virtually all living cells have an outer cell or plasma membrane (a thin structure), cytosol (fluid
content of the cell); many small structures called organelles and a quantity of DNA (deoxyribo nucleic acid) which
controls the activities of the cell.
In Unit 2 you will examine a variety of cells under a light microscope. It is important that you are able to identify the
various structures, which are present. You are not expected to know, in fine detail, what the function(what something
does) of the cellular structures you observe. This will be covered during Unit 3.
Cells are made up of a:

Nucleus a dense area inside the cell;

Cytosol a semi transparent fluid surrounding the nucleus;

Organelles(including the nucleus) and a

Cell membrane a thin covering which holds the cell together and separates it from other cells and from
the cell's environment.

Cytoplasm – This is the cytosol and all organelles excluding the nucleus.
PLANT CELLS
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Not all plant cells possess these structures.
ANIMAL CELLS
Animal cell viewed under an electron microscope
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Plant cell viewed under an electron microscope
STRUCTURE & FUNCTION(S) OF ORGANELLES / MEMBRANES
CELL STRUCTURE
Mitochondrion
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SKETCH &/OR DESCRIPTION
A cigar-shaped structure bound by a double
membrane, the inner one tucked and folded
inside.
FUNCTION
Spherical in shape containing DNA,
chromosomes and the nucleolus. Bound by a
double membrane. Found in virtually all living
cells.
Nucleus
A dense, solid structure found in the nucleus.
Nucleolus
CELL STRUCTURE
SKETCH &/OR DESCRIPTION
A membrane penetrated by holes (nuclear
pores).
Nuclear Membrane &
Nuclear pore
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FUNCTION
A network of tubes and flattened sacs
continuous with the cell membrane. 'Smooth' in
appearance. Often looking like a series of
channels.
Smooth Endoplasmic
Reticulum(SER)
A network of tubes and flattened sacs
continuous with the cell membrane. Ribosomes
are attached giving the structure a 'rough'
texture.
Rough Endoplasmic
Reticulum(RER)
Cell Wall
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Found in plant cells on the 'outside'. Composed
of cellulose.
A structure variable in shape and size
containing dense sets of membranes like a
stack of coins separated by loosely arranged
membranes.
Chloroplast
A set of paired rods enclosed by a belt of large
molecules. Difficult to see unless using an
electron microscope.
Centriole
CELL STRUCTURE
SKETCH &/OR DESCRIPTION
A membrane often tucked and folded and
leading off into the endoplasmic reticulum.
Cell/Plasma Membrane
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FUNCTION
A series of flattened disc-shaped sacs,
stacked one on top of the other and connected
to the endoplasmic reticulum. Vesicles(look
like small balloons) appear to pinch off from
the body.
Golgi Body/Apparatus
Small ‘grains’ when viewed under an electron
microscope. Difficult to detect their internal
structure. Found in the cytoplasm and on
rough endoplasmic reticulum(RER). Only
visible with an electron microscope. Unlike the
diagrams below, they are not truly spherical.
Ribosome
Generally spherical, thin-walled sac showing
little internal structure but often containing
fragments of material being broken down.
Lysosome
Vacuole
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Simple organelles that are simply membranebound sacs. They may occupy the majority of
plant cells. If present in animals they are
usually small.
Vesicle
Smaller than vacuoles but
similar in appearance. Often
seen 'pinching off' Golgi,
endoplasmic reticulum and
cell membranes.
Contains the cytosol(fluid within a cell) and all
organelles with the exception of the nucleus.
Cytoplasm
Plastids(chloroplasts,
chromoplasts and
leucoplasts)
Chloroplasts have already been discussed.
Leucoplasts are found in underground storage
organs of plants. They lack coloured pigments
(translucent). Chromoplasts are yellow, red or
orange in colour.
DIFFERENCES BETWEEN PLANT AND ANIMAL CELLS
Although there are many similarities between plant and animal cells there are some important differences.
Animal cells do not possess
Higher plants(not mosses) do not possess

Plastids(chloroplasts, leucoplasts
and chromoplasts.

Centrioles.

Cell walls

Asters

Large permanent vacuoles
COMPOUNDS IN CELLS
Carbohydrates(C, H & O)

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Monosaccharides = one sugar e.g. glucose.
 Disaccharides = two sugars e.g. sucrose = glucose + fructose.
maltose = 2 glucose molecules.

Polysaccharides = many sugars e.g. cellulose and starch in plants, glycogen in animals(all contain
many glucose molecules joined together).Cellulose is found in the cell walls of
plants. Other carbohydrates are found in the cytoplasm; little carbohydrate is found
with the vacuole.
Proteins(C, H, O, N & S + P in some proteins)

Made up of many amino acids.

Peptide linkages join the amino acids.

Examples of proteins: enzymes, some hormones and structural proteins(e.g. hair).

Proteins are found in the cytoplasm and in cellular membranes.
Lipids(Fats & Oils; C, H & O)

Possess a lower proportion of oxygen than carbohydrates.

Structural units = fatty acids and glycerol.

Found in the cytoplasm and membranes.
Nucleic acids




Genetic material of all organisms
2 types: DNA (deoxyribonucleic acid) & RNA (ribonucleic acid)
Both made of long chains of subunits call nucleotides.
Nucleotides made up of a phosphate group, sugar group and a base.
Vitamins
 Organic molecules required by animals in small amounts for normal functioning.
 Some vitamins can be synthesised by animals – others must be obtained in their diet.
 2 categories: water soluble and lipid soluble (water soluble must be consumed regularly as they
cannot be stored in the body).
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