Topic 1: CELLS

1.1 Introduction to cells

Date: 21/August/2014

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WHAT DO YOU KNOW ABOUT CELLS?

• 1665- Robert Hooke observes the first cells. He coined the word ‘cell.’

Why do you think he called them cells?

Monk Cell Remains in Sanchi, Madhya Pradesh, India

• He examined very thin slices of cork and saw a multitude of tiny pores that looked like the walled compartments a monk would live in

1700’s-Anton van Leeuwenhoek made a light microscope with higher quality lenses to observe smaller organisms (animalcules)

First to see organisms living in a drop of water

1864: Spontaneous generation of life persisted for almost two centuries, until Louis Pasteur disproved it.

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smithlifescience.com

1665- Robert Hooke observes the first cells. He came up with the word “cell” & said all living things are made of cells

1700’s- Anton van Leeuwenhoek made a light microscope with quality lenses to observe smaller organisms (animalcules) living in a drop of water

1855- Jewish Robert Remak discovers cell division

• All living things are composed of cells

• Cells are the basic unit of structure and function in living things

• All cells come from pre-existing cells

The Cell TheoryHistory of the Cell

1864: Spontaneous generation of life persisted for almost two centuries, until Louis Pasteur disproved it.

Whereas cells taken from an organism often survive for a time, smaller parts of an organism do not.

Stated in this way Cell Theory might be attributed to Schleiden

and Schwann (1800’s)• According to the cell theory, living organisms are composed of cells.

Are there limitations and exceptions to CELL THEORY? YES!

Questioning the cell theory using atypical examples, including striated muscle, giant algae and aseptate fungal hyphae.

Acetabularia sp.Giant algaeUp to 100 mm in lenght

All organisms exist in either a unicellular (one cell) or multicellular (many cells) form.

All organisms carry out the functions of life:– Metabolism: Chemical reactions– Growth: Size increase– Reproduction: Producing offspring– Responses: Reaction to changes in the environment– Homeostasis: Control of internal conditions– Nutrition: Synthesis or absorption of food

• Organisms consisting of only one cell carry out all functions of life in that cell.

Why do cells not grow to larger sizes?Because of the surface-area to Volume Ratio! (relación

superficie/area)

As the organism gets bigger, their volume and surface area both get bigger, but not by the same amount. The volume increases as the cube but the area of the surface only increases by the square.

The rate of exchange of substances depends on the organism's surface area that is in contact with the surroundings.

Surface area to volume ratio is important in the limitation of cell size.

Multicellular organisms show Emergent propertiesEmergence is the occurrence of unexpected characteristics or

properties in a complex system, which emerge from the interaction of the “parts” of the system.

Emergent properties are seen at every level of increasing complexity, from the atom to the molecule, to the cell to the

organism, to the biosphere.

Tungsten Metal cup Glass container.

When studied individually they do not allow the prediction of the properties of the light bulb.

• Multicellular organisms have properties that emerge from the interaction of their cellular components.

Specialised cells express particular genes that relate to these specialist functions, producing particular shapes, functions and adaptations within a cell.

Multicellular organisms are large and have to specialize parts of their structure to complete functions characteristic of life.

This differentiation process is the result of the expression of specific genes.

• Specialized tissues can develop by cell differentiation in multicellular organisms.

• Some cells have a diminished ability to reproduce once they become specialized, e.g.: Nerve and muscle cells.

• Other cells retain the ability to rapidly reproduce throughout their life, e.g.: epithelial cells (skin)

A stem cell:

• Retains the capacity to divide and has the ability to differentiate along different pathways.

• Is able to divide but has not yet expressed genes to specialize to a particular function.

• Can be obtained from a variety of different places including the blastocyte (adult bone marrow, embrionic tissue,

SOME FACTS ABOUT STEM CELLS:

The capacity of stem cells to divide and differentiate along different pathways is necessary in embryonic development and also makes stem cells suitable for therapeutic uses.

infocelulasmadre.blogspot.com

Good link that includes an explanation:

http://www.teachersdomain.org/asset/biot09_int_stemcells/

HOMEWORK:IT MUST BE IN YOUR NOTEBOOK

Investigation of functions of life in Paramecium and one photosynthetic unicellular organism (Chlorella or Scenedesmus).