IB Biology Higher Level Summary 1.1

1.1 Revision notes


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The Cell Theory
All living organisms are composed of cells.
- Unicellular
- Multicellular

Movement
Respiration
Sensitivity
Homeostasis
Growth
Reproduction
Excretion
Nutrition



Atypical cells
Striated muscle cells: have multiple nuclei
Fungi: made up of hyphae, tube-like structure with many nuclei
Algae: unicellular – even if they are large


Unicellular organisms
Paramecium
- Movement: beating of cilia on outside wall move the cell through water in response to
environmental stimuli
- Respiration: Metabolic reactions occur in cytoplasm (release energy by respiration).
Enzymes in cytoplasm are catalysts for reactions.
- Sensitivity: reacts to stimuli (reverses direction when comes into contact with object)
- Homeostasis: Contractile vacuoles fill up with water and expel it through plasma
membrane to keep water content within limit
- Growth: increases in size and mass by accumulating organic
- Reproduction: nucleus can divide to produce an extra nucleus (asexual reproduction)
- Excretion: cell membrane controls flow of substances through diffusion (entry of oxygen
for respiration and excretion)
- Nutrition: (endocytosis) food vacuoles contain smaller organisms that cell has
consumed. Are digested and nutrients are absorbed into cytoplasm for energy.