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 called Antonie van Leeuwenhoek. In 1665 Robert Hooke first used the word 'Cell'. Cells are measured in micrometers
The Compound Microscope
The first person to discover
microscopic life was a Dutch man called 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 micrometers in 1mm.
An animal cell is about 25µm in length.
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
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.
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
An example of an animal cell is the cheek cell.
Methylene blue stains the nucleus of the cell.
1. Rub the inside of your cheek with a clean
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
6. View under low, medium and high power under
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
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
Genes control features e.g. eye colour,
production of enzymes etc.
Genes are the units of inheritance.
Nuclear pores allow a type of RNA (ribonucleic acid) called mRNA (messanger RNA) to pass in/out of the nucleus.
The nucleolus is an area in the nucleus that stains very darkly and is responsible for making ribosomes.
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 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 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.
The function of the cell wall is to support
and strengthen the cells.
Cell walls in plant cells are made of the
Cell walls are fully permeable (they allow all substances into/out of the cell).
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.
Eukaryotic Cells have a nucleus and cell organelles, all of which are enclosed by membranes