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IB Business Management Unit 1 (Notes, Case Studies and Tools)
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IB Biology Topic 1: Cell Biologywritten by
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IB TOPIC 1 | CELL BIOLOGY
2016 | SYJ0014
Topic 1.1: Cell biology – Introductions to cells
The evolution of multicellular organisms allowed cell specialization and cell replacement.
• Understanding: According to the cell theory, living organisms are composed of cells.
Three tenets of the cell theory:
1. All living organisms are composed of one or more cells
2. The cell is the basic unit of structure and organization in organisms
3. Cells arise from pre-existing cells
• Understanding: Organisms consisting of only one cell carry out all functions of life in that cell.
Unicellular organisms: organisms composed of a single cell that carry out all of their life processes within that cell
Multicellular organisms: organisms composed of multiple cells that carry out functions of life by division of labour
Most cells in multicellular organism are much less complex than unicellular organisms as the latter needs to carry all functions of life while
the roles may be divided in the former.
Essential functions of life:
Metabolism: chemical reaction inside the cell (often uses ATP for energy)
Response: ability to react to environmental stimuli (as it appropriately perceives)
Homeostasis: maintenance of condition inside the organism (through measures such as phospholipid bilayer)
Growth: getting to full size and repairing old cells (via cell division)
Reproduction: ability to produce offspring (sexual or asexual)
Excretion: removal of waste products
Nutrition: obtaining food for energy and growth
• Understanding: Surface area to volume ratio is important in the limitation of cell size.
Surface area to volume ratio: ratio of surface area to volume (i.e. SA:V)
Ratio trend: ratio falls as cell size increases (as the cell size increases, volume increases faster than surface area)
To function efficiently a cell needs a large surface area relative to its volume (high SA:V ratio)
If the ratio is too small: waste products accumulates, cells may overheat
If the ratio is too big: cells may not be able to contain all the necessary organelles
• Understanding: Multicellular organisms have properties that emerge from the interaction of their cellular components.
Emergent properties: arise from the interaction of the component parts of a complex structure.
Alternatively expressed as: “the whole is greater than the sum of its parts”
• Understanding: Specialized tissues can develop by cell differentiation in multicellular organisms.
Specialized cells: cells modified (undergo differentiation) to carry out a particular function more efficiently
Division of labour: different cells perform different functions in multicellular organisms
Division of labour in human cells: humans have 220 distinctively different cell types
• Understanding: Differentiation involves the expression of some genes and not others in a cell’s genome.
Cell differentiation: process where a cell changes from one cell type to another to develop ideal structure for specific functions
Cause: different sequence of genes is expressed (used) while others are not for cells to differentiate
Result: differentiation give rise to different sets of genes being expressed despite identical genome
Advantage: epigenetic modifications to shut down the expression of irrelevant genes
Cells have genes required to specialize in every possible way, but all genes in a cell’s genome are not always used
Control of gene expression is therefore important for development in multicellular organisms
• Understanding: 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.
Characteristics of stem cells:
Undifferentiated: have not yet specialized into a certain type of cells and therefore all genes can be expressed
Self-sustaining: can divide and replicate for a long time to produce copious quantities of new cells
Cause of stem cell differentiation: stem cells are able to differentiate into a particular cell type when given a specific signal
Therapeutic use: stem cells are therefore useful to produce regenerated tissues and provide a means of healing certain diseases
Cell potency (stages and versatility of early stem cells):
Totipotent: can become any type of cells; constitutes in early zygotes
Pluripotent: can become almost any kind of cells; found and cultured in blastocysts
Multipotent: can become a limited number of particular cell types; found in umbilical cords or in bone marrow
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