Overview of the cell

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OVERVIEW OF THE CELLBiology 20

Paramecium Human Cheek Cells Onion Cells

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Before we could see cells.. There had to be

the microscope! Early lens

makers (often physicists) allowed for the study of microbiology

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The first people to see cells... Robert Hooke - He

was looking at cork and noted that he saw a “great many boxes” (1665).

Anton van Leeuwenhock – observed living cells in pond water. He called these “animalcules”. (1673)

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The first people to see cells... Theodore Schwann-

observed that the tissues of animals had cells (1839)

Mattais Schleiden– observed that plants contained cells (1845)

Rudolf Virchow – every living thing is made up of cells (1850)

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The Cell Theory1. Every living organism is made of one

or more cells.

2. The cell is the basic unit of structure and function. It is the smallest unit that can perform life functions.

3. All cells arise from pre-existing cells.

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Question for you... Why is the Cell Theory called a Theory

and not a Fact?

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Main Points All organisms are made up of cells.

They can be:• Unicellular (1 cell)• OR multicellular (many cells)

In unicellular organisms all life functions are carried out by a single cell.

In multicellular organisms, cells specialise to perform specific functions – division of labour.

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Cells as seen with a microscope

Living protoplasm surrounded by surface membrane (& non-living cell wall in plants).

The living material between the nucleus and the cell surface membrane is known as cytoplasm.

Cytoplasm contains variety of cell organelles.

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Two main types of cells

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Prokaryotic Cells Very simple cells, probably

first to inhabit the earth. Do not contain a

membrane bound nucleus. Their nucleus material (DNA) lies free in a region known as nucleoid.

Example: Bacteria. DNA of bacteria is circular.

The word "prokaryote" means "before the nucleus"

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Eukaryotic Cells More advanced cells. Possess true nucleus

and nucleus material are found inside the nucleus surrounded by the two membranes, i.e nucleus envelope.

Example: plant cell, animal cell.

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Eukaryotic Cells4 main parts:

• cell membrane - outer boundary

• cytoplasm - jelly-like fluid interior

• nucleus - the "control center”, contains the cell's DNA (chromosomes)

• organelles - "little organs" that carry out cell functions

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Organelles in Animal & Plant CellsAnimal Cell Plant Cell

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Diagram Cell Part FunctionMitochondria Energy center or

"powerhouse" of the cell. Turns food into useable energy

Ribosomes Make protein

Golgi Apparatus Processes, packages and secretes proteins. Like a factory.

Lysosome Contains digestive enzymes, breaks things down

Endoplasmic Reticulum

Smooth ER - no ribosomesRough ER - ribosomes

Transport, "intracellular highway". Ribosomes are positioned along the rough ER, protein made by the ribosomes enter the ER for transport.

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Diagram Cell Part FunctionNucleolus Located inside the

nucleus, makes ribosomes

Vacuole Stores water or other substances, plant cells contain a large central vacuole.

Chloroplast Uses sunlight to create food, photosynthesis (only found in plant cells)

Cell Wall Provides additional support (plant and bacteria cells)

Microtubules Part of the cytoskeleton, function in supportAlso make up cilia and flagella (cell movement)

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Differences in Animal & Plant Cells

Lysosomes Cell Wall Chloroplasts Chromoplasts/

Amyloplasts

Found only in Animal Cells Found Only in Plant Cells

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Prokaryotic versus Eukaryotic Cells

Prokaryotic cell Eukaryotic cellNucleus material are not enclosed by nuclear membrane

Nucleus material are enclosed by nuclear membrane

Contains few organelles Contains many organellesNo membrane bounded organelles such as; chloroplast and mitochondria

Has membrane bounded organelles

DNA is circular and lies free in cytoplasm

DNA is linear and enclosed in nucleus

No mitosis or meiosis, divide by binary fission

Mitosis and meiosis occur

It contains 70s ribosome (smaller) It contains 80s ribosome (larger)Mainly unicellular Mainly multi-cellular