Complete, clear and concise notes for Topic 1-6 of the IB Biology course by a 44 student (7 for biology), structured according to the syllabus requirements to ensure all necessary information is covered, and including all needed diagrams and possible long answers
Requirements from the official IB Biology guide; important points; definitions/equations; not needed
Topic 1: Cell Biology
1.1 Cell Theory
Understandings:
● According to cell theory, living organisms are composed of cells.
● Organisms consisting of only one cell carry out all functions of life in that cell.
● Surface area to volume ratio is important in the limitation of cell size.
● Multicellular organisms have properties that emerge from the interaction of their cellular components.
● Specialised tissues can develop by cell differentiation in multicellular organisms.
● Differentiation involves the expression of some genes and not others in a cell’s genome.
● 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.
Applications:
➔ Questioning the cell theory using atypical examples, including striated muscle, giant algae and aseptate fungal hyphae.
➔ Investigation of functions of life in Paramecium and one named photosynthetic unicellular organism.
➔ Use of stem cells to treat Stargardt’s disease and one other named condition.
➔ 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.
Skills:
➔ Use of a light microscope to investigate the structure of cells and tissues, with drawing of cells.
➔ Calculation of the magnification of drawings and the actual size of structures and ultrastructures shown in drawings or
micrographs. (Practical 1)
Cell Theory
According to cell theory, living organisms are composed of cells.
1. Cells are the smallest unit of life (basic unit of structure in all living things)
- They are the smallest structures capable of surviving on their own.
2. All living organisms are composed of cells
- Multicellular organisms are composed of many cells while unicellular organisms (like bacteria) are
composed of only a single cell
3. New cells can only be formed from pre-existing cells (biogenesis)
- New cells arise via the process of cell division, and a zygote forms from the fusion of an egg cell and a
sperm cell
Cells that don't fit into cell theory
Question the cell theory using atypical examples, including striated muscle, giant algae and aseptate fungal hyphae.
- Striated muscle cell - long elongated cell with multiple nuclei and only single membrane → cells do not always
function as autonomous units
- Giant algae - large unicellular existence that grows up to 0.5-10 cm → challenges simple structure and small in
size of cell notions
- Aseptate hyphae - fungi cells are not partitioned, continuous cell with multiple nuclei → cell is not discrete
Cells - relatively small, contain genetic material, surrounded by a membrane, have energy release system
(In human body) Largest cell is the egg cell, smallest cell is the sperm cell, longest cell is the nerve cell
Functions of life in unicellular organisms (MR GHREN)
Organisms consisting of only one cell carry out all functions of life in that cell.
The definition of a living organism is
1. Metabolism – Chemical reactions that occur in organisms in order for them to maintain life
2. Reproduction – Producing offspring, (binary fission, sexual reproduction)
3. Growth – Increase in size and mass
4. Homeostasis - Maintaining a stable internal environment
, 5. Response – Reacts to external and internal stimuli, interact with the environment
6. Excretion – Expels waste products, metabolic waste
7. Nutrition – Feeding on organic molecules (endocytosis) or synthesizing their own food
Investigation of functions of life in Paramecium and one named photosynthetic unicellular organism.
Function Paramecium Chlorella
Eukaryotic single-celled protozoa Eukaryotic single-celled green algae
Metabolism Produce enzymes - catalyze various chemical reactions within the cell, break down food and use the
molecules to produce ATP in cellular respiration
Reproduction Reproduce asexually (binary fission) and sexually (meiosis and gamete formation), genetic variety is
introduced by conjugation
Growth Increase in cell size and mass by intake of organic Increase in cell size and mass by photosynthesis
matter and minerals from food, will divide by fission and mineral absorption, will divide once it
once it reaches a certain size reaches a certain size
Homeostasis Osmoregulation - excess water is collected in Stores excess glucose as starch
contractile vacuole and expelled through membrane
Response Reacts to stimuli - changes direction with cilia when Reacts to stimuli - has light-sensitive eyespot,
hitting a solid, can detect warmth will move towards it
Excretion Expels metabolism waste products from cellular Expels metabolism waste products from
respiration, when digested food in contractile photosynthesis, through the entire cell
vacuole reaches anal pore membrane
Nutrition Heterotroph - Endocytosis - ingests smaller Autotrophs - produces own food through
organisms, engulfs food through oral groove photosynthesis
Surface to volume ratio
Surface area to volume ratio is important in the limitation of cell size.
- Surface to volume ratio is what limits cell size
- Cells exchange substance with surroundings through diffusion
- The rate of exchange is dependant on the surface area
- Food/oxygen enters while waste leaves through the surface of the cells
- Metabolic reactions in cytoplasm (produce heat, wastes, consume resources), with the rate proportional to the
cell volume
As cell size increases, it’s surface area to volume ratio (SA/V) falls (volume increases faster than sa)
- A larger cell has more metabolic activity which requires more food and oxygen and produces more waste
- Cell becomes less efficient since rate of material exchange is much lesser than rate of metabolic reactions
- Excess heat produced in the cell cannot be lost efficiently, can cause cell to overheat
- Eventually surface area can no longer serve the requirements of the cell, which will stimulate mitosis
- (Higher sa/v ratio - heats/cools quickly, lower sa/v ratio - heats/cools slowly)
- Thus cells are limited to a small size as smaller cells have a higher sa/v ratio than larger ones
Multicellular Organisms
Differentiation involves the expression of some genes and not others in a cell’s genome.
- Differentiation - process of a less specialized cell becoming a more specialized cell (eg. stem cells → nerve cells,
muscle cells, blood cells...)
Specialized tissues can develop by cell differentiation in multicellular organisms.
, - Multicellular organisms need differentiated cells to live and function efficiently, specialized tissues develop
through cell differentiation
- Controlled by gene expression in cells - only the specific genes relating to the cells function is turned on
(eg. brain cell contains entire genetic information but only genes for brain cells are expressed)
- Once a pathway of development begins in a cell, it is usually fixed and cannot change pathways
- Cell is said to be “committed”
Multicellular organisms have properties that emerge from the interaction of their cellular components.
Emergent properties - arise from interaction of component parts of a complex structure with multicellular organisms
“The whole is greater than the sum of its parts”
- To function properly, complex life systems need millions of small simple interactions that work together
(eg. different cells in eye retina respond to light giving us vision and color perception, when working together emergent
properties arise, like ability to respond to different objects in environment)
Stem Cells
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.
Stem cells divide through mitotic cell division and can differentiate along different pathways to become a diverse range
of specialized cell types
- Human embryos are made up entirely of stem cells
- During the early embryonic stages, the stem cells can still divide and have ability to become any type of cell
- This is until they express certain genes and differentiate into a specific type of cell
Four types of stem cell potency
(Toti - whole, Pluri - many, Multi - several, Uni - one)
The more potent, the more likely to mutate
- Totipotent - can differentiate into any/all types of cell that make up the body, even extraembryonic (placenta
and embryo cells) cells
- Pluripotent - can differentiate all types of cell that make up the body (in inner cell mass within a blastocyst)
- Multipotent - can differentiate into a few similar types of cells (body tissues - bone marrow, fat tissue, dental
pulp, heart tissue...)
- Unipotent - can regenerate only into their associated cell type (liver stem cells can only make liver cells, found in
liver)
(Induced pluripotent stem cells - regular cells that are induced to behave like pluripotent cells)
Stem cells constantly divide and produce new cells
Some new cells remain as stem cells while others go through a series of maturing stages, differentiating to form more
specific cells
Sources of stem cells - embryonic stem cells (during zygote), cord blood stem cells (from umbilical cord blood)
There is great potential for the use of embryonic (toti stem cells) in treating a variety of diseases
- The capacity to divide and differentiate along different pathways make them suitable for therapeutic uses
Application of stem cell therapy (Regenerative medicine)
Use of stem cells to treat Stargardt’s disease and one other named condition.
Stargardt's macular dystrophy
- Genetic disease that leads to blindness - affects a membrane protein needed for active transport in retina cells,
protein causes photoreceptor cells in the retina to degenerate which progressively worsens their vision
- Extraction of limbal stem cells from healthy donor or spared limbal area of patient to culture with growth factors
- stem cell differentiation into RPE (Retinal Pigment Epithelial) cells
- RPE stem cells are injected into the eyes, the cells adhere to the retina, then grow and develop into retina cells,
improving their vision
- Suitable for treatment as there is a low chance of rejection from the body
Leukemia
, - Cancer caused by mutation in genes that control cell division, produces abnormal amount of white blood cells in
bone marrow → greatest therapeutic uses of stem cells is for Leukemia
- Blood stem cells, extracted from bone marrow tissue of patient or donor with same blood type, multiply in cell
culture
- Original cancerous cells are killed through chemotherapy and radiation therapy along with normal blood cells
- Cultured stem cells are injected into patient and re-establish themselves in bone marrow, begin reproducing and
making healthy red and white blood cells
Lab meat - grown stem cells through cell culture into cultured meat
Ethical concerns of Stem cells
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.
Stem cells can be derived from three sources, each with its own pros and cons
- Embryos - may be specially created by IVF or therapeutic cloning
- Pro: embryos are produced deliberately and lack nervous system - no killing of life and will not feel pain
- Con: requires destruction of the embryo, higher risk of becoming tumor cells, excess embryos will be
killed, and health risks in treating women with hormones to produce embryos via IVF
- Umbilical cord blood or placenta of a new-born baby
- Con: need to be stored and preserved, leading to issues of availability and access
- Certain adult tissues - eg. the skin or bone marrow (unlike other two, cells are not pluripotent)
- Pro: adult stem cells are fully compatible with adult’s tissues - no chances of tumors
- Con: Adult tissues are limited in application scope as it it pluri, not totipotent
Can improve health and quality of life of patients, can cure serious/previously incurable diseases
Stem cell research pave the way for future discoveries - have led to many beneficial technologies
Alternative technologies could possibly fulfill similar roles although with additional cost and effort (eg. nuclear
reprogramming of differentiated cell lines)
Magnification
Calculation of the magnification of drawings and the actual size of structures and ultrastructures shown in drawings or
micrographs. (Practical 1)
Magnification = Size of the image / Actual size of the specimen
(1mm=1000μm (micrometer), 1μm=1000nm (nanometer))
Resolution - Smallest distance between two points that can still be distinguished as two separate entities, depends on
the wavelength of the illumination source, anything less than half the wavelength will not be visible
- Biggest difference is in resolution
Use of a light microscope to investigate the structure of cells and tissues, with drawing of cells.
- magnification provided by a light microscope is usually x500 and it has a resolution of about 200 nm, in color
- an electron microscope provides higher magnification and better resolution (0.1 nm, have much shorter
wavelengths) but in black and white, is much harder to use and only dead specimens can be seen through it
Electron microscopes have a much higher resolution than light microscopes.
1.2 Ultrastructure of cells
Understandings:
● Prokaryotes have a simple cell structure without compartmentalization.
● Eukaryotes have a compartmentalised cell structure.
● Electron microscopes have a much higher resolution than light microscopes.
Applications:
➔ Structure and function of organelles within exocrine gland cells of the pancreas and within palisade mesophyll cells of
the leaf.
➔ Prokaryotes divide by binary fission.
Skills:
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