Revision:Cell Theory

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Cell Theory

Discuss the theory that living organisms are composed of cells

• Cells are the building blocks of life.
• Cells have metabolism
• Cells are capable of independent existence.
• Cells can only avite from already existing cells.
• Cells contain hereditary materials (DNA)
• Skeletal muscle and some fungal hyphae are not divided into cells but have mulinucleate cytoplasm. Some biologists consider unicellular organisms to be acellular.

State that a virus is a non-cellular structure consisting of DNA or RNA surround by protein coat

A virus is a non-cellular structure consisting of DNA or RNA surrounded by protein coat.

State that all cells are formed by other cells

All cells are formed by other cells.

Explain three advantages of using light microscopes

Some advantages are:

• Colour images instead of monochrome
• A larger field of view
• Easily prepared sample material
• The possibility of examining living material and observing movement
• Cheaper equipment

Outline the advantages of using electron microscope

The advantages of using an electron microscope are that they have greater magnification, which means that they can magnify more than light microscope. This means that they can see things that are smaller than with using a light microscope. They also have a higher resolution, which means that they can also show the images as separated particles and clear instead of blurry.

Define organelle

An organelle is a discrete structure within a cell, and has a specific function.

Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using appropriate SI units=

Molecules can be up to 1 nm

Cell membrane thickness can be up to 10 μm

Viruses can be up to 100 nm

Bacteria can be up to 1 μm

Organelles can be up to 10 μm

Most cells can be up to 100 μm

Calculate linear magnification of drawings

Magnification = size of the picture multiplied with size of the real object

Size of the real object = size of the picture divided with magnification

Explain the importance of the surface area to volume ratio as a factor limiting cell size

The volume increases faster than the surface area when a cell grows. The surface to volume ratio thus decreases. In order to carry out metabolic functions (chemical reactions etc) the cell needs the surface area and when it grows, it needs to carry out more functions. The size is thus limited since the cell needs to maintain a certain surface area to volume ratio.

State that unicellular organisms carry out all the functions of life

Unicellular organisms carry out all the functions of life.

Explain that cells in multicellular organisms differentiate to carry out specialised functions by expressing some of their genes but not others

The multicellular organisms contain all the genes but they do not use all of them. The cells differentiate to carry out specialised functions because they only express some of their genes.

Define tissue, organ and organ system

Tissue: An integrated group of cells with common function and structure.

Organ: A body function centre that is specialised into one function and composed by different tissues.

Organ system: A group of organs that are specialised into a certain function together.

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