Introduction to Cells (1.1) IB Diploma Biology

C E L S come only from existing cells. 4-cell stage of a sea biscuit by Bruno Vellutini on Flickr (CC) http://flic.kr/p/daWnnS

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)

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

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

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

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

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…

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)

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

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: http://umanitoba.ca/Biology/BIOL1030/Lab1/biolab1_3.html#Ciliophora 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

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: http://www.algae.info/Algaecomplete.aspx 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.

Which dissolves faster: sugar cubes or sugar crystals? Why? Sugar Cubes by Uwe Hermann on Flickr (CC) http://flic.kr/p/cFMMc

What will go cold faster: French fries or a baked potato? Why? French Fries by Ian Britton on Flickr (CC) http://flic.kr/p/6RLQ8j

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

Big Cell Exceptions Caulerpa species of algae are one giant cell with many nuclei distributed throughout. http://en.wikipedia.org/wiki/Caulerpa

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)

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: http://www.ns.umich.edu/stemcells/022706_Intro.html

Emergent Properties more than the sum the whole is of its parts Photo by Stephen Taylor: http://www.flickr.com/photos/gurustip/9668701965/in/photostream

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