Cell Theory (2.1)
The cell theory (2.1.1 / 2.1.2)
Function of life (2.1.3)
1. The cell is the smallest unit of life
Remember: MRS GREN
2. All living things are made of cells (or cell products)
Movement
Reproduction
Sensitivity (to stimuli)
3. Cells arise from pre-existing cells
Evidence:
Growth
Respiration
Excretion
Nutrition
• With the invention of microscopes (Janssen)
scientists could see cells (Hooke, Leeuwenhoek)
• Pasteur demonstrated that cells couldn’t grow in
sterile conditions (disproved abiogenesis)
Cell size (2.1.4 - 2.1.6)
• The rate of metabolism (e.g. cell respiration) is a function of a cell’s volume
• The rate at which material is exchanged (needed for metabolism) is a function of a cell’s surface area
• When a cell grows, volume grows quicker than surface area and the cell must divide or die
• Many cells contains structures (e.g. microvilli) to increase their SA:Vol ratio
Calculating cell sizes:
• Magnification = Size of image (magnified) ÷ Actual size of object
Relative sizes:
• Eukaryote (10 - 100µm) > Organelle (~10µm) > Bacteria (1 - 5µm) > virus (100nm) > membrane (7.5nm)
Differential gene expression (2.1.7 / 2.1.8)
• Differentiation is the process by which newly-formed cells specialize as they mature
• Cells in multi-cellular organisms share identical genomes but differ in gene expression
• Chemical signals lead to differential gene expression and thus specialization of cells
• The combination of different cell types can give rise to emergent properties
Stem cells (2.1.9 / 2.1.10 / 4.4.12 / 4.4.13)
• Stem cells retain the capacity to divide and differentiate along different pathways
• Therapeutic cloning can be used to regenerate skin cells in burns victims
somatic cell
nucleus
Reproductive
cloning
fusion
surrogate
stem cells
egg cell
Therapeutic
cloning
enucleated
egg
tissue culture
Arguments For Therapeutic Cloning:
• May be used to cure diseases (e.g. diabetes)
• Stem cell research may promote future discoveries
• Cells cultured when embryos lack nervous system
Arguments Against Therapeutic Cloning:
• Involves creation and destruction of embryos
• Rapidly dividing cells may become cancerous
• At more cost, other technologies fulfill same role