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
LAST EDITED 2017-03-13 | 1
, IB TOPIC 1 | CELL BIOLOGY
2016 | SYJ0014
• Application: Questioning the cell theory using atypical examples, including striated muscle, giant algae and aseptate fungal hyphae.
Striated muscle fibres Aseptate fungal hyphae Giant algae
Atypical character Size: larger than other most cells (has Septa: no septa (cross walls that divide Size: each algae cell can grow up to
an average length of 30mm) the hyphae) 100mm despite having single nucleus
Nucleus: one cell has more than one Nucleus: each hypha is an
nucleus (+100 nuclei per cell) uninterrupted tube like structure with
many nuclei spread along
• Application: Investigation of functions of life in Paramecium and one named photosynthetic unicellular organism.
Paramecium Chlamodomonas
Diagram
Function of life
Metabolism Metabolic reaction take place in the cytoplasm (where Metabolic reaction take place in the cytoplasm (where enzymes that
enzymes that causes these reaction is present) causes these reaction is present)
Reproduction Nucleus divide for asexual reproduction Nucleus divide for asexual reproduction. Nuclei can also fuse to
sexually reproduce
Homeostasis Contractile vacuoles fill up and expel water to maintain Contractile vacuoles fill up and expel water to maintain water content
water content
Growth Organism uses oxygen and nutrients to grow and Organism uses oxygen and nutrients to grow and reproduce
reproduce
Response Cilia is used to move the paramecium in response to Two flagella is used to move the Chlamodomonas in response to
changes in environment changes in light levels
Excretion Waste products are diffused through membrane Waste products are diffused through membrane and cell wall
Nutrition Smaller organisms are consumed and enter as food Photosynthesis occurs in the chloroplasts. However, in the dark,
vacuoles and are digested as food carbon compounds from other organisms can absorbed
• Application: Use of stem cells to treat Stargardt’s disease and one other named condition.
Stargardt’s Macular Dystrophy Leukaemia
Cause Genetic; recessive mutation that cause membrane Cancerous; production of abnormally large number of
protein in retina cells to malfunction white blood cells
Treatment procedure Injection: retina cells derived from embryonic stem cells Extraction: stem cells are extracted from the bone
are injected into the eyes marrow of the patient and are stored
Replacement: stem cells replace the original degenerate Chemotherapy: all remaining cells in the bone marrow is
retina cells then destroyed through chemotherapy
Improvement: there is an improvement in vision Replacement: there stem cells are then returned to the
patient’s body
Note There are no notably harmful side effects other than There are no notably harmful side effects other than
risks from rejection risks from rejection
• Application: Ethics of the therapeutic use of stem cells from specially created embryos, from the umbilical cord blood of a new-born baby
and from an adult’s own tissues.
Embryonic stem cells Cord blood stem cells Adult stem cells
Source In vitro fertilization (IVF) Umbilical cord of a new born baby Adult tissues such as bone marrow
Potential Totipotent (unlimited) Multipotent (limited) Multipotent (limited)
Ethical implication Removal of cells kills embryo Umbilical cord is discarded regardless Removal of cells does not the kill
stem cell collection adult (albeit painful)
Compatibility Genetically different from the adult Fully compatible with the tissues of Fully compatible with the tissues of
patient the adult the adult
Disadvantage More risk of become tumour cells Limited quantities of stem cells Difficult to obtain
Less chance of genetic damage Limited capacity to differentiate and Limited capacity to differentiate and
impacting therapeutic property hence reduced potential hence reduced potential
Further ethical arguments for and against embryonic stem cells:
1. Different opinions on the beginning of human personhood
2. Associated risk for IVF such as invasive surgical procedure and exploitation of vulnerable groups
3. Potential to allow methods of current incurable diseases and disability
LAST EDITED 2017-03-13 | 2
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
LAST EDITED 2017-03-13 | 1
, IB TOPIC 1 | CELL BIOLOGY
2016 | SYJ0014
• Application: Questioning the cell theory using atypical examples, including striated muscle, giant algae and aseptate fungal hyphae.
Striated muscle fibres Aseptate fungal hyphae Giant algae
Atypical character Size: larger than other most cells (has Septa: no septa (cross walls that divide Size: each algae cell can grow up to
an average length of 30mm) the hyphae) 100mm despite having single nucleus
Nucleus: one cell has more than one Nucleus: each hypha is an
nucleus (+100 nuclei per cell) uninterrupted tube like structure with
many nuclei spread along
• Application: Investigation of functions of life in Paramecium and one named photosynthetic unicellular organism.
Paramecium Chlamodomonas
Diagram
Function of life
Metabolism Metabolic reaction take place in the cytoplasm (where Metabolic reaction take place in the cytoplasm (where enzymes that
enzymes that causes these reaction is present) causes these reaction is present)
Reproduction Nucleus divide for asexual reproduction Nucleus divide for asexual reproduction. Nuclei can also fuse to
sexually reproduce
Homeostasis Contractile vacuoles fill up and expel water to maintain Contractile vacuoles fill up and expel water to maintain water content
water content
Growth Organism uses oxygen and nutrients to grow and Organism uses oxygen and nutrients to grow and reproduce
reproduce
Response Cilia is used to move the paramecium in response to Two flagella is used to move the Chlamodomonas in response to
changes in environment changes in light levels
Excretion Waste products are diffused through membrane Waste products are diffused through membrane and cell wall
Nutrition Smaller organisms are consumed and enter as food Photosynthesis occurs in the chloroplasts. However, in the dark,
vacuoles and are digested as food carbon compounds from other organisms can absorbed
• Application: Use of stem cells to treat Stargardt’s disease and one other named condition.
Stargardt’s Macular Dystrophy Leukaemia
Cause Genetic; recessive mutation that cause membrane Cancerous; production of abnormally large number of
protein in retina cells to malfunction white blood cells
Treatment procedure Injection: retina cells derived from embryonic stem cells Extraction: stem cells are extracted from the bone
are injected into the eyes marrow of the patient and are stored
Replacement: stem cells replace the original degenerate Chemotherapy: all remaining cells in the bone marrow is
retina cells then destroyed through chemotherapy
Improvement: there is an improvement in vision Replacement: there stem cells are then returned to the
patient’s body
Note There are no notably harmful side effects other than There are no notably harmful side effects other than
risks from rejection risks from rejection
• Application: Ethics of the therapeutic use of stem cells from specially created embryos, from the umbilical cord blood of a new-born baby
and from an adult’s own tissues.
Embryonic stem cells Cord blood stem cells Adult stem cells
Source In vitro fertilization (IVF) Umbilical cord of a new born baby Adult tissues such as bone marrow
Potential Totipotent (unlimited) Multipotent (limited) Multipotent (limited)
Ethical implication Removal of cells kills embryo Umbilical cord is discarded regardless Removal of cells does not the kill
stem cell collection adult (albeit painful)
Compatibility Genetically different from the adult Fully compatible with the tissues of Fully compatible with the tissues of
patient the adult the adult
Disadvantage More risk of become tumour cells Limited quantities of stem cells Difficult to obtain
Less chance of genetic damage Limited capacity to differentiate and Limited capacity to differentiate and
impacting therapeutic property hence reduced potential hence reduced potential
Further ethical arguments for and against embryonic stem cells:
1. Different opinions on the beginning of human personhood
2. Associated risk for IVF such as invasive surgical procedure and exploitation of vulnerable groups
3. Potential to allow methods of current incurable diseases and disability
LAST EDITED 2017-03-13 | 2
