Chapter 7 Cell Structure
Objectives
Microscopes are used to make cells
look bigger
The Compound Microscope
The first person to discover
microscopic life was a Dutch man cal
led Antonie van Leeuwenhoek.
In 1665 Robert Hooke first used
the word 'Cell'.
Cells are measured in
micrometers
The symbol
µm is used.
There are 1000 micro
meters in 1mm.
An animal cell is abou
t 25µm in length.
Microscopes
A compound microscope has two lenses:
an eye piece lens and an objective lens
Total magnification = eye piece lens X objective lens
e.g. 10 X 4 = 40
Plant Cells
These cells are usually rectangular in shape.
They have a large central vacuole and have green Chloroplasts.
Chloroplasts are small factories that make food.
They catch sunlight and mix it with carbon dioxide and water to turn it into sugar.
Chlorophyll is the green pigment (chemical) in the chloroplast that catches sunlight.
An example of a plant cell is the onion cell.
Compulsory Experiment
Experiment Results
Note: If iodine stain is not used it is very difficult
to see the onion cells clearly.
Only the cell wall and nucleus
are visible in the cell you will
not be able to see the other
parts of the cell at x400
Animal Cell
An animal cell has no cell wall
and no chloroplasts.
An example of an animal cell is
the cheek cell.
Methylene blue stains the
nucleus of the cell.
Experiment to view a cheek cell under a light microscope
1. Rub the inside of your cheek with a clean
Finger
2. Smear your finger on a clean dry glass slide.
3. Apply a few drops of methylene blue stain.
4. Leave for a few minutes and allow excess
stain to drain down the sink.
5. Apply a cover slip carefully to avoid air
bubbles.
6. View under low, medium and high power under
the microscope.
Cell Ultra structure
Nucleus
The nucleus is the control centre of the cell.
The nucleus has numerous small holes in its
surface called nuclear pores.
The nucleus contains strands of DNA
(deoxyribonucleic acid).
DNA is arranged into structures called
Chromosomes. Every organism has a
definite number of chromosomes. E.g.
46 chromosomes in humans.
Genes are located randomly along
chromosomes.
Genes control features e.g. eye colour,
production of enzymes etc.
Genes are the units of inheritance.
Nuclear Pores
Nuclear pores allow a type of RNA (ribonucleic
acid) called mRNA (messanger RNA) to pass
in/out of the nucleus.
Nucleolus
The nucleolus is an area in the nucleus that stains very
darkly and is responsible for making ribosomes.
Cytoplasm
Jelly like liquid that surrounds the nucleus in a cell.
A number of organelles (small structures) e.g.
chloroplasts, mitochondrion etc. are suspended in the
cytoplasm.
Mitochondria (Singular is Mitochondrion)
Mitochondria supply energy to the cell. They are the sites of
respiration in the cell.
The DNA in mitochondria is inherited
along the female line in the family from
mother to daughter.
Chloroplasts
Chloroplasts are only found in plant
cells.
They are green structures in plants in
which photosynthesis takes place.
They are surrounded by a double
membrane. They have membrane
stacks, which contain the green pigment
chlorophyll. They also have a loop of
DNA. Chloroplasts are involved in
photosynthesis in the cell.
Cell Wall
The function of the cell wall is to support
and strengthen the cells.
Cell walls in plant cells are made of the
polysaccharide cellulose.
Cell walls are fully permeable (they allow all substances
into/out of the cell).
Ribosomes
Ribosomes are very tiny, bead like structures found in
cells. The are made of RNA (ribo nucleic acid) and protein.
The function of ribosomes is to make proteins.
Generalised Plant
and Animal Cells
Differences between Plant & Animal Cells
Plant Cells
Animal Cells
Have a cell wall
Do not have a cell wall
May have chloroplasts
containing chlorophyll
Do not have chloroplasts or
chlorophyll
Have a large vacuole
Do not have a large vacuole
Prokaryotic & Eukaryotic Cells
Living things (organisms) are divided into two
categories depending on the structure and complexity
of their cells.
a) Prokaryotes
b) Eukaryotes
Prokaryotic cells do not have a nucleus or membrane
enclosed organelles.
Prokaryotic organisms are:
Single celled
Have a circular loop of DNA (not surrounded by a
membrane and do not have a nucleus.
Have small cells.
Do not have a membrane and enclosed structures such
as chloroplasts and mitochondria.
Include bacteria.
Eukaryotic Cells have a nucleus
and cell organelles, all of which
are enclosed by membranes
Eukaryotic organisms:
• Have a nucleus (i.e. DNA
enclosed by a membrane)
•May have membrane-enclosed
organelles such as mitochondria
and chloroplasts.
•Have large cells.
•Include animal, plant and fungi
•Are more advanced than
prokaryotes.
• Life originated with prokaryotic
cells and has evolved into
eukaryotic cells.