Cell theory, differentiation, stem cells Topic 1.1 Biology SL
Cytology is the study of all aspects of a cell.
Cell Theory
1. All organisms are composed of one or more cells
2. Cells are the smallest units of life
3. All cells come from pre-existing cells
Louis Pasteur
➢ Performed an experiment that supports the principle that all cells come from
pre-existing cells
➢ He sterilized chicken soup and showed that living organisms wouldn’t
spontaneously reappear. Only after exposure to pre-existing cells was life able to
re-establish itself in the sterilized chicken broth.
The Cell
➢ All organisms are either uni- or multi- cellular
➢ All organisms carry out the 7 functions of life
1. Metabolism
■ All chemical reactions in cells
■ Energy being converted from one form to another
2. Growth
■ Can be limited but is always evident
3. Reproduction
■ Either asexual or sexual
■ Hereditary molecules being passed to offspring
4. Response to stimuli
■ Organisms adapt to their environment
■ Different organisms respond differently to their environment
■ Essential for the survival of the organisms
5. Homeostasis
■ Organisms maintain a constant internal environment or at least close
to optimal state
6. Nutrition
■ Compounds with many chemical bonds that can be broken down to
provide energy so the organism can maintain life
7. Excretion
■ Unusable or toxic compounds need to be disposed of
■ Essential for the organism
1
,Cell theory, differentiation, stem cells Topic 1.1 Biology SL
Paramecium
➢ A single-cell organism, member of protista, found in sweet-water lakes
➢ In the video of paramecium eating yeast, we can see the following:
○ Response to stimuli => it is moving toward the food
○ Metabolism => it is eating the food
○ Homeostasis => the yeast was acidic (red) and the cell converted it to neutral
(black), since that was a more suitable pH for paramecium
Chlorella
➢ A single-cell organism, found in fresh-water lakes
➢ It has chloroplasts
○ Convert the energy in sunlight into carbohydrates, a chemical form of energy,
which are a major nutritional source (photosynthesis)
➢ Since it carries out photosynthesis (produces its own food), it doesn’t need to
move around a lot
➢ The population can grow a lot if they find ideal conditions
Cell Reproduction and differentiation
➢ Multicellular organisms depend on differentiation
○ Every cell contains the complete genetic information needed to produce the
whole organism. However, not all genes of the cell’s genome will be
expressed
○ This means that each cell will become a specific type of a cell depending on
which DNA segment (gene) becomes active
➢ Some cells can keep dividing after differentiation
○ For example, skin cells divide in order to heal wounds
○ Die very often and replace themselves
➢ Some are unable to do that
○ For example, nerve and muscle cells
○ Don’t die, until you die
○ Difficult to be repaired
Limiting cell size
➢ Most cells can only be seen by using a microscope
○ Cells are so small due to a principle called “the surface area to volume ratio”
■ As cells increase in volume, their surface area also increases, but at a
much slower rate
2
, Cell theory, differentiation, stem cells Topic 1.1 Biology SL
➢ Smaller cells are more efficient in transporting nutrients and waste than bigger cells,
because their surface area is big compared to their volume
○ Big cells have large volume, but relatively small surface area. Therefore, they
need a lot of nutrition and have a lot of waste
But not all cells follow this norm
➢ Some cells have evolved into different shapes
○ Cells that are large in size have modifications that allow them to function
efficiently
■ Changes in shape, in- or out- foldings => increase of surface area
○ Some atypical examples
■ Striated muscles => flat and long rather than spherical
■ Giant algae => interconnected with each other with small openings
■ Acetate fungal hyphae => the roots of a certain fungi, physically
connected with each other, however they have their own organelles
Stem cells
➢ Stem cells are the cells that retain their ability to divide and differentiate into various
types of cells
➢ Plants have also stem cells in regions of meristematic tissue (near roots and stem
tips)
➢ Stem cells cannot be distinguished by their appearance. They need to be isolated
from other cells on the basis of their behaviour
➢ There are 2 types
○ Embryonic stem cells
■ Come from undeveloped embryos
■ When they divide to produce a tissue they also produce daughter cells
that stay stem cells
○ Pluripotent
■ Can differentiate into any kind of cell and even create a complete
organism
○ Adult stem cells or tissue-specific stem cells
■ Can turn into one type of tissue
■ For example, blood cells can turn into red or white blood cells or
blood platelets
Pluripotent stem cells
➢ Could heal many diseases
○ Alzheimer’s, Parkinson’s and diabetes
3
Cytology is the study of all aspects of a cell.
Cell Theory
1. All organisms are composed of one or more cells
2. Cells are the smallest units of life
3. All cells come from pre-existing cells
Louis Pasteur
➢ Performed an experiment that supports the principle that all cells come from
pre-existing cells
➢ He sterilized chicken soup and showed that living organisms wouldn’t
spontaneously reappear. Only after exposure to pre-existing cells was life able to
re-establish itself in the sterilized chicken broth.
The Cell
➢ All organisms are either uni- or multi- cellular
➢ All organisms carry out the 7 functions of life
1. Metabolism
■ All chemical reactions in cells
■ Energy being converted from one form to another
2. Growth
■ Can be limited but is always evident
3. Reproduction
■ Either asexual or sexual
■ Hereditary molecules being passed to offspring
4. Response to stimuli
■ Organisms adapt to their environment
■ Different organisms respond differently to their environment
■ Essential for the survival of the organisms
5. Homeostasis
■ Organisms maintain a constant internal environment or at least close
to optimal state
6. Nutrition
■ Compounds with many chemical bonds that can be broken down to
provide energy so the organism can maintain life
7. Excretion
■ Unusable or toxic compounds need to be disposed of
■ Essential for the organism
1
,Cell theory, differentiation, stem cells Topic 1.1 Biology SL
Paramecium
➢ A single-cell organism, member of protista, found in sweet-water lakes
➢ In the video of paramecium eating yeast, we can see the following:
○ Response to stimuli => it is moving toward the food
○ Metabolism => it is eating the food
○ Homeostasis => the yeast was acidic (red) and the cell converted it to neutral
(black), since that was a more suitable pH for paramecium
Chlorella
➢ A single-cell organism, found in fresh-water lakes
➢ It has chloroplasts
○ Convert the energy in sunlight into carbohydrates, a chemical form of energy,
which are a major nutritional source (photosynthesis)
➢ Since it carries out photosynthesis (produces its own food), it doesn’t need to
move around a lot
➢ The population can grow a lot if they find ideal conditions
Cell Reproduction and differentiation
➢ Multicellular organisms depend on differentiation
○ Every cell contains the complete genetic information needed to produce the
whole organism. However, not all genes of the cell’s genome will be
expressed
○ This means that each cell will become a specific type of a cell depending on
which DNA segment (gene) becomes active
➢ Some cells can keep dividing after differentiation
○ For example, skin cells divide in order to heal wounds
○ Die very often and replace themselves
➢ Some are unable to do that
○ For example, nerve and muscle cells
○ Don’t die, until you die
○ Difficult to be repaired
Limiting cell size
➢ Most cells can only be seen by using a microscope
○ Cells are so small due to a principle called “the surface area to volume ratio”
■ As cells increase in volume, their surface area also increases, but at a
much slower rate
2
, Cell theory, differentiation, stem cells Topic 1.1 Biology SL
➢ Smaller cells are more efficient in transporting nutrients and waste than bigger cells,
because their surface area is big compared to their volume
○ Big cells have large volume, but relatively small surface area. Therefore, they
need a lot of nutrition and have a lot of waste
But not all cells follow this norm
➢ Some cells have evolved into different shapes
○ Cells that are large in size have modifications that allow them to function
efficiently
■ Changes in shape, in- or out- foldings => increase of surface area
○ Some atypical examples
■ Striated muscles => flat and long rather than spherical
■ Giant algae => interconnected with each other with small openings
■ Acetate fungal hyphae => the roots of a certain fungi, physically
connected with each other, however they have their own organelles
Stem cells
➢ Stem cells are the cells that retain their ability to divide and differentiate into various
types of cells
➢ Plants have also stem cells in regions of meristematic tissue (near roots and stem
tips)
➢ Stem cells cannot be distinguished by their appearance. They need to be isolated
from other cells on the basis of their behaviour
➢ There are 2 types
○ Embryonic stem cells
■ Come from undeveloped embryos
■ When they divide to produce a tissue they also produce daughter cells
that stay stem cells
○ Pluripotent
■ Can differentiate into any kind of cell and even create a complete
organism
○ Adult stem cells or tissue-specific stem cells
■ Can turn into one type of tissue
■ For example, blood cells can turn into red or white blood cells or
blood platelets
Pluripotent stem cells
➢ Could heal many diseases
○ Alzheimer’s, Parkinson’s and diabetes
3
