Objectives

Chapter 7 Cell Structure

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 micrometersThe symbol µm is used.There are 1000 micrometers in 1mm.An animal cell is about 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 lense.g. 10 X 4 = 40

Plant CellsThese 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 CellAn 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

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

Differences between Plant & Animal Cells

Prokaryotic & Eukaryotic CellsLiving things (organisms) are divided into two categories depending on the structure and complexity of their cells.a)Prokaryotesb)Eukaryotes

Prokaryotic cells do not have a nucleus or membrane enclosed organelles.

Prokaryotic organisms are:Single celledHave 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.