Biology 203 1st Edition Lecture 16Outline of Last Lecture I. Flowering PlantsII. Spore and gamete productionIII. PollinationIV. Seed plant life cycle “looks” like gametic life cycleV. Dikaryotic fungi Outline of Current Lecture I. Limits to cell sizeII. Advantages to MulticellularityIII. What is necessary for multicellularity?IV. Organisms in-between unicellular and multicellularV. Complex cell differentiationCurrent LectureI. Limits to cell sizea. As length increases linearly, surface area goes up as the square of length, and volume goes up as the cube of lengthb. Surface area to volume ratio limits a cell’s sizec. Increased benefit of larger size must be balanced against the increased cost of supporting the additional surface area and volume:i. Surface area, is made from costly membrane lipids and covered with other molecules. ii. Cellular volume is made from very costly cytosol (full of sugars, proteins,organelles, etc.) d. If size continues increasing, the surface area can no longer keep up with the demand of the volume, and the center of the cell starves for nutrientsII. Advantages of multicellularitya. Size related:i. Increased nutrient accessii. Increase capacity to store reserves when nutrients become limitediii. Create an internal environment protected by an external layer of cells iv. Enhance motility for dispersal or foragingb. Simultaneous separation of functionsi. Vegetative (e.g. nutrient acquisition, growth)ii. ReproductiveThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.c. In multicellular individuals with one or more differentiated cell types, the two sets of functions take place in different spatial areas and can take place simultaneouslyi. Somatic cells – perform only vegetative functionsii. Reproductive cells (germ cells) – are specialized for reproductive functionsIII. What is necessary for multicellularity?a. A way to stick together (physical unity), generally referred to as inter-cellular adhesioni. Epithelial tissuresii. The middle lamella (plants)iii. Septa in mycelia (fungi)b. Inter-cellular communication and recognition among cells (to ensure physiological unity).i. Cell gaps (plants & animals)ii. Cell-Cell signaling (hormones)iii. Septa in mycelia (fungi)c. Regulation of cell growth, proliferation and differentiationi. Gene expressionii. Chromatin remodelingiii. RNA processingIV. Organisms in-between unicellular and multicellulara. Aggregative Developmenti. Cells life independently for most of their life cycles, but episodically associate to become multicellularii. Occurs in a few group of organisms, including myxobacteria, some ciliates,and cellular slime moldsb. Undifferentiated colonial forms (all cells have the same form and function)i. Multicellularity arises when cells stay connected to one another followingdivisionc. Differentiated colonial forms (some cells have the same form and function)i. Vegetative and reproductive cells are spatially distinctd. Multicellular but lacking true tissuesi. Porifera have a cellular level of organizationii. They lack germ layers iii. Bodies are masses of cells embedded in a gelatinous matrix stiffened by spiculesV. Complex cell differentiationa. The development of tissues (Eumetazoan animals)b. The development of tissues (vascular plants)c. The development of tissues