Resumen biologia ib

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Topic 2: Cells
2.1 Cell Theory
2.1.1 Outline the Cell Theory
* Living organisms are composed of one or more cells
* Cells are the smallest unit of life
* Cells must come from pre-existing living cells
2.1.2 Discuss the evidence for the cell theory
The cell theory has amassed tremendous credibility through the use of the microscope in the following:
* Robert Hooke- studiedcork and found little tiny compartments that he called cells
* Antonie Van Leeuwenhoek- observed the first living cells, called them 'animalcules' meaning little animals
* Schleiden- stated that plants are made of 'independent, separate beings' called cells
* Schwaan- made a similar statement to Schleiden about animals
2.1.3 State that unicellular organisms carry out all of the functionsof life
* Metabolism; chemical reactions inside the cell, including cell respiration to release energy
* Response; perceiving and responding to changes in the environment
* Homeostasis; keeping conditions inside the organism within tolerable limits
* Growth; an irreversible increase in size
* Reproduction; producing offspring either sexually or asexually
* Nutrition;obtaining food, to provide energy and the materials needed for growth
Amoeba would be an example of a unicellular organism.
2.1.4 Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using the appropriate SI unit
nm = nanometer µm = micrometer
* Molecules - 1 nm
* Thickness of membrane - 10 nm
* Viruses - 100 nm
* Bacteria - 1 µm* Organelles - up to 10 µm
* Most cells - up to 100 µm (three dimensional nature/shape)
2.1.5 Calculate the linear magnification of drawings and the actual size of specimens in images of known magnifications
*  :Drawings should show cells and cell ultrastructure.
A scale bar: |------| = 1 µm
Magnification: ×250
To calculate magnification:
* Magnification = MeasuredSize of Diagram ÷ Actual Size of Object
but before this, both magnifications must be in the same measurement, either in mm, cm etc..
2.1.6 - Explain the importance of the surface area to volume ratio as a factor limiting cell size.
* A cell needs a large surface area in order to carry out metabolic functions (as chemical reactions require a surface). As a cell grows, it needs to carry outmore and more reactions. Therefore, since a cell has to maintain a certain surface area to volume ratio, its size is limited.
* The rate of exchange of materials (nutrients/waste) and energy (heat) is a function of its surface area.
Thus: As a cell grows in size (volume), the distance increases between the cytoplasm at the center of the cell and the cell membrane. The rate of chemical exchangewith the surrounding environment may hence become too low to maintain the cell. It is not able to excrete waste quickly enough or take in important minerals.
Volume of a cell determines requirements while surface area determines supply.
2.1.7 - State that multicelluar organisms show emergent properties
* Emergent properties arise from the interaction of component parts: the whole is greaterthan the sum of its parts
2.1.8 - Explain how cells in multicellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others.
* During the early development stages of multicellular organisms, cells undergo differentiation, becoming specialized in structure and function. These cells are then organized into tissues and organs. Cells ofmulticellular eukaryotes express only a small fraction of their genes, allowing them to perform highly specialized functions. Cells, such as those of muscle or nervous tissue, express only a tiny fraction of their genes.
2.1.9 - State that stem cells retain the capacity to divide and have the ability to differentiate along different pathways.
2.1.10 - Outline one use of theapeutic stem cells .
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