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Cell Size: Surface Area to Volume Scale of the Universe Most cells are very small and can’t be observed with the naked eye. Bacteria are the smallest cells <10 µm o .2 µm diameters Eukaryotic cells are larger, most between 10-100 µm o Bird eggs are large cells o Muscle cells and nerve cells are very long What limits cell size? Function o Minimum size must be large enough to contain DNA, proteins and internal structures needed for survival and reproduction Resource needs o Maximum size must be based on the supply of nutrients and oxygen to the cell, as well as waste removal. Surface Area = 96 mm2 Volume = 64 mm3 What is the relationship between Surface Area and Volume? Surface Area = Length X Width X 6 (Number of sides) Volume = Length X Width X Depth Large cells have more surface area and volume than smaller cells Smaller cells, however, have larger surface area to volume ratios Is it better to be made out of 1 big cell or many smaller cells? Many small cells Larger cell has greater volume, which means: More chemical reactions Greater need for resources Greater waste production Greater heat production Smaller SA/V ratio makes it difficult to acquire necessary resources while removing waste and heat. http://www.youtube.com/watch?v=xuG4ZZ1GbzI Cells All cells share some common characteristics: 1. Plasma membrane – phospholipid bilayer that serves as the barrier between what is inside/outside the cell. 2. Genetic material – all cells have DNA for their heritable material 3. Ribosomes – organelles that build proteins based on the information stored in the DNA. 4. Cytoplasm – organelles and fluid inside the plasma membrane, excluding the nucleus. Prokaryotic Cells vs. Eukaryotic Cells Prokaryotic Cells - All Bacterial Cells Pro = Before Karyote = Kernel = Nucleus Prokaryotic cells lack membrane bound organelles Small Cells Generally range from 0-10 micrometers (µm) Nucleoid Region – Nucleus-like region where the DNA inside a prokaryotic cell is coiled. Not a nucleus, no membrane. Cell Wall – located beyond the plasma membrane. Helps protect and maintain the shape of the cell. Not made of cellulose. Capsule – located outside the cell wall of some prokaryotes. Sticky layer that adds protection and allows cells to stick to surfaces. Pili (Pilus)/Fimbriae – short projections that help cells attach to surfaces. Prokaryotic Flagella – long projections that propel the cell through its liquid environment. Eukaryotic Cells – Protist, Plant, Fungus and Animal Cells Eu = True Karyote = Kernel = Nucleus Eukaryotes have many different membrane bound compartments called organelles that carry-out specific functions for the cell. Cellular metabolism – chemical activities of the cell o Many take place in these compartments Many important molecules are embedded into the membranes of these organelles. Eukaryotic cells have organelles with and without membranes. Larger Cells Generally range from 10-100 micrometers (µm) Plant and Animal cells share many similar organelles: Nucleus Mitochondria Ribosomes Vesicles Peroxisomes Plants Cell wall Chloroplast Large Central Vacuole Smooth/Rough ER Lysosomes Golgi Apparatus Cytoskeleton Others Animals Centrioles Flagella*