Lecture 10 Biological Implications of Scaling 1 A valonia big unicellular like cell a As size increases and surface volume decreases cells begin to suffer from i ii iii Inefficient gas exchange and nutrient uptake Increased distance from periphery to nucleus limits diffusion Inability of external and internal supports to scale up 1 Horse example iv Result anoxia starvation slow response collapse v So multicellular had to find solutions following are solutions 2 Methods to get around constraints a Adaptations for gas waste nutrient exchange b Multinucleate c Structural support strategies 3 Adaptations for gas waste nutrient exchange a Branched or villous architecture Increases surface area i 1 Either whole organism fungus or key organs lungs roots ii Could grow flat to increase surface area but that is not typical iii Branching growth is crazy allometry allows surface area to almost scale linearly with volume If it grew isometrically it would stay the same shape just get bigger 1 2 Making a sheet does the same thing epithelium b Vasculature i Special cells and organs that move gas and fluid 1 Passive plant vascular elements 2 Active heart and vessels heart actively pumps so you don t have to wait for diffusion c Carriers i Molecules that transport important solutes between cells 1 Ex oxygen hemoglobin lipids sterol carriers metal binding proteins 4 Multinucleate a Pack multiple nuclei into a big cell problem goes away b NEW PROBLEM how does this organize mitosis with multiple nuclei i Solution 1 for growth don t require nuclear division for cytokinesis ii Solution 2 for sex make uninucleate phase for reproduction fungal fruiting 1 Ex mycelium of fungi are connected but spores are uninucleate bodies c Be multicellular i Link separate cells together by adhesion ii PROBLEMS 1 How to reproduce a Solution 1 budding fusion necessarily asexual subdividing a body b Solution 2 sexual make single cell spore or gamete often coupled with meiosis and sex 2 Who gets to reproduce a Solution tight control over mitotic and meiotic potential b Need dedicated reproductive cells basically non reproductive cells reproducing cancer d Supporting larger body i Option 1 stay quishy 1 Live in water or horizontally a Tough extracellular surface layer often present b Pressure from surrounding water holds up squishy organisms c Hydrostatic skeleton allows for movement nematodes ii Option 2 evolve an exoskeleton endoskeleton 1 Mineralized exoskeleton corals mollusks 2 Organic exoskeleton arthropods 3 Mineralized endoskeleton sponged bony fishes 4 Organic endoskeleton woody plants some fishes
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