1. Introduction to Cells (1.1)
IB Diploma Biology

4. C E L S come only from existing cells.
4-cell stage of a sea biscuit by Bruno Vellutini on Flickr (CC)

7. According to the cell theory, living organisms are composed of cells
Cells vary in many ways within and between organisms, but some things are common to all cells…
Surrounded by a membrane
Contain genetic material (DNA)
Contain enzymes to catalyze chemical reactions within the cell
Have an energy-release system (or metabolism)

8. Organisms consisting of only one cell carry out all functions of life in that cell

9. Question the cell theory using atypical examples, including striated muscle, giant algae and aseptate fungal hyphae

10. Exception #1: Muscle Fiber
Muscle fibers are much larger than normal animal cells and may have as many as several hundred nuclei per “cell”

11. Exception #2: Fungal Hyphae
In some fungi, each hypha is a single, long tube structure with many nuclei

12. Exception #3: Giant Algae
Can grow as large as 100mm (!) yet only has one nucleus
An organism this size would be expected to be made up of many cells…

13. All cellular organisms carry out the following functions of life:
Organisms consisting of only one cell carry out all functions of life in that cell
All cellular organisms carry out the following functions of life:
Metabolism (chemical reactions that release energy for cellular use)
Reproduction (either asexual or sexual)
Homeostasis (maintain stable internal conditions)
Growth
Response to the environment
Excretion (removal of waste)
Nutrition (Obtaining food needed for energy & growth)

14. Membrane maintain homeostasis, takes in nutrients, and excretes wastes
Investigate functions of life in Paramecium and one named photosynthetic unicellular organism
Nucleus replicates for asexual reproduction once cell grows large enough
Membrane maintain homeostasis, takes in nutrients, and excretes wastes
Metabolic reactions occur in the cytoplasm where enzymes are
Contractile vacuoles maintain stable water levels in cell
Flagella and cilia allow for movement in response to environment

15. Metabolism – most metabolic pathways happen in the cytoplasm
Excretion – the plasma membrane control the entry and exit of substances including expulsion of metabolic waste
Homeostasis – contractile vacuole fill up with water and expel I through the plasma membrane to manage the water content
Response – the wave action of the cilia moves the paramecium in response to changes in the environment, e.g. towards food.
Source:
Metabolism – most metabolic pathways happen in the cytoplasm
Nutrition – food vacuoles contain organisms the parameium has consumed
Growth – after consuming and assimilating biomass from food the paramecium will get larger until it divides.
Reproduction – The nucleus can divide to support cell division by mitosis, reproduction is often asexual

16. Metabolism – most metabolic pathways happen in the cytoplasm
Excretion – the plasma membrane control the entry and exit of substances including the difussion out of waste oxygen
Reproduction – The nucleus can divide to support cell division, by mitosis (these cells are undergoing cytokinesis)
Response – the wave action of the cilia moves the algae in response to changes in the environment, e.g. towards light.
Source:
Metabolism – most metabolic pathways happen in the cytoplasm
Homeostasis – contractile vacuole fill up with water and expel I through the plasma membrane to manage the water content
Nutrition – photosynthesis happens inside the chloroplasts to provide the algae with food
Growth – after consuming and assimilating biomass from food the algae will get larger until it divides.

17. Which dissolves faster: sugar cubes or sugar crystals? Why?
Sugar Cubes by Uwe Hermann on Flickr (CC)

18. What will go cold faster: French fries or a baked potato? Why?
French Fries by Ian Britton on Flickr (CC)

19. Surface are to volume ratio is important in the limitation of cell size

23. Big Cell Exceptions
Caulerpa species of algae are one giant cell with many nuclei distributed throughout.

25. 220 recognized, different highly-specialized cells types in humans
Specialized tissues can develop by cell differentiation in multicellular organisms
220 recognized, different highly-specialized cells types in humans
EX: Rod cells in retina of the eye are light-sensitive
EX: Red blood cells carrying oxygen and nutrients
Groups of similar cells form tissues (epithelial, muscle, connective, and nervous)

26. Key Concept: Structure v. Function
Differentiation involves the expression of some genes and not others in the cell’s genome
Differentiation (specialization) of cells:
All diploid (body) cells have the same chromosomes.
So they carry all the same genes and alleles. BUT
Not all genes are expressed (activated) in all cells.
The cell receives a signal.
This signal activates or deactivates genes.
Genes are expressed accordingly and the cell is committed.
Eventually the cell has become specialized to a function.
Key Concept: Structure v. Function
How do the structures of specialized cells reflect their functions? How does differentiation lead to this?
Screenshot from this excellent tutorial:

27. Emergent Properties more than the sum the whole is of its parts
Photo by Stephen Taylor:

28. Multicellular organisms have properties that emerge from the interaction of their cellular components