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IB Biology: Unit 1 - Cell biology
Clear and consise notes on unit 1 - cell biology of the IB SL biology course.
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Unit 1 - Cell Biology1.1 - Introduction to Cells
The evolution of multicellular organisms allowed cell specialization and cell replacement.
Cell theory:
1. All living things are made of 1 or more cells
2. The cell is the smallest unit of life (able to sustain life alone)
3. All cells come from preexisting cells
Exceptions:
1) Skeletal muscle
● Many nuclei
2) Fungal hyphae
● Many nuclei
3) Giant algae
● Gigantic size
● 3 distinct anatomical (resemble unique cells)
Functions of life:
● Metabolism: chemical reactions inside the cell
● Response to the environment
● Homeostasis: keeping balance
● Growth: irreversible increase in size
● Reproduction: often asexual cloning
● Excretion: expulsion of waste (the useless stuff)
● Nutrition: obtain food for energy/growth
Memonic: Mr. H. Green
examples:
1) Paramecium
● Metabolism
○ In the cytoplasm
● Response
○ Cilia (hair-like structures) move the cell towards food
● Homeostasis
○ Water levels (managed by vacuoles that store extra water)
● Growth
○ Increases in size until cell division
● Reproduction
○ Asexsual reproduction (cell division)
● Excretion
○ Waste diffuses (through cell membrane) such as CO2
● Nutrition
○ Absorbed through endocytosis
2) Chlorella
, ● Metabolism (same)
● Response (same but needs light not food)
● Homeostasis (same)
● Growth (same)
● Reproduction (same)
● Excretion (same)
● Nutrition
○ Food is made inside the cell through photosynthesis
Magnification:
i
m=
a
Where: m is magnification, i is image (on paper), a is actual (in real life)
Cell size and surface area (SA) to volume (V) ratio:
● Surface area (SA) determines how much can be
○ Absorbed
■ eg. food, oxygen, etc
○ Excreted
■ eg. waste
● Volume (V) determines how much
○ Nutrients is needed
○ Waste is created
● As V increases, SA decreases
○ These are in negative correlation but have positive correlation needs
○ Thus the smaller the cell the more efficient it is
■ Thus cells stay small
The parts don’t explain the whole:
● Organisms have properties that emerge from the interaction of their cellular components.
● Cells interact to produce a tissue/organ/organism that can do things none of the
individual cells could do
● Eg. the brain
○ Cannot be explain by neurons (their functioning) alone
Cell specialization:
● Specialized cells develop through cell differentiation
● Differentiation explained:
○ Every cell has the same genes
■ Some genes are expressed (active
■ Others are non expressed (inactive)
○ A group of differentiated cells becomes a tissue
● Differentiation happens due to outside factors:
○ Neighbouring cells
■ Hormones
Stem cells:
What are stem cells:
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