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I. Cell Theory & Cell Structure

Chapter 5Cell Structure and Function

The Cell Theory

• All living things are composed of cells.• Cells are the basic unit of structure

and function in living things.• All cells come from preexisting cells.

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Cell Size

• Cells can range in size from 5 to 50µmin diameter.

• Human cells generally range from 5 to20µm in diameter.

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Cell Membrane

• The cell membrane function– Support– Protection– Selectively permeable - Regulates the

flow of substances into and out of the cell• Messengers• Waste• Nutrients

Cell Membrane• The cell membrane structure

– Phospholipid bilayer– Proteins

• Transportation of molecules andinformation.

– Carbohydrates• Cell identification• Attached to proteins

• Fluid mosaic model– The cell membrane is fluid.– The lipids, proteins and carbohydrates

are free to move.

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Cell Wall

• Plant cells and animal cells both havecell membranes BUT plant cells alsohave a cell wall.

• Animal cells DO NOT have a cell wall.• The cell wall surrounds the cell

membrane

Cell Wall

• Cell wall function.– Protection & support.

• Cell wall structure.– Cellulose (primary cell wall)

• Plants that are not woody have an elastic cell wall made upof cellulose.

• Examples: Grass, dandelion, daisy, leaves on trees….– Cellulose and Lignin (secondary cell wall)

• Plants that are woody.• Provides excellent support and strength.• Examples: Trees and shrubs.

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The Nucleus

• Function of the nucleus.– The nucleus is the information center of the

cell. The function of the cell is directed bythe nucleus.

– The nucleus contains all of our geneticinformation DNA!

• The DNA can form chromosomes.Chromosomes are structures which carry ourgenetic information.

• Eye color, hair color, height…..

The Nucleus• Structure of the nucleus.

– The nucleus is surrounded by two membranes which formthe nuclear envelope.

– Molecules pass in and out of the nucleus by way of nuclearpores which line the nuclear envelope.

– A small nucleolus is found inside of the nucleus.• Made up of RNA and proteins.• The nucleolus makes Ribosomes.

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The Nucleus

• Eukaryotes (True Nucleus) – Organismswhose cells contain a nucleus.– Eukaryotes can be unicellular or multicellular.– Multicellular Examples – Humans, insects, plants,

fungus……– Unicellular Examples – amoeba, protozoa,

diatoms.• Can a eukaryotic cell function without its

nucleus? No!

E. The Nucleus - Eukaryotes

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The Nucleus

• Prokaryotes – organisms whose cellslack a nucleus.– Unicellular (one cell)– Bacteria and cyanobacteria (blue – green

algae)• Prokaryotes may lack a nucleus but

they still have DNA.

E. The Nucleus - Prokaryotes

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Cytoplasm

• The cytoplasm is the area between thenucleus and the cell membrane.

• The cytoplasm is a semi-fluid substance.• Structure and function of the cytoplasm.

– Contains cellular organelles.– Contains proteins, sugars and amino acids which

the cell uses to carry out its everyday activities.