ENDURING UNDERSTANDING 2.B GROWTH, REPRODUCTION AND DYNAMIC HOMEOSTASIS REQUIRE THAT CELLS CREATE AND MAINTAIN INTERNAL ENVIRONMENTS THAT ARE DIFFERENT FROM THEIR EXTERNAL ENVIRONMENTS. ESSENTIAL KNOWLEDGE 2.B.1 CELL MEMBRANES ARE SELECTIVELY PERMEABLE DUE TO THEIR STRUCTURE. BIG IDEA II BIOLOGICAL SYSTEMS UTILIZE FREE ENERGY AND MOLECULAR BUILDING BLOCKS TO GROW, TO REPRODUCE AND TO MAINTAIN DYNAMIC HOMEOSTASIS.

ESSENTIAL KNOWLEDGE 2.B.1: CELL MEMBRANES ARE SELECTIVELY PERMEABLE DUE TO THEIR STRUCTURE. Learning Objectives: (2.10) The student is able to use representations and models to pose scientific questions about the properties of cell membranes and selective permeability based on molecular structure. (2.11) The student is able to construct models that connect the movement of molecules across membranes with membrane structure and function.

CELL MEMBRANES SEPARATE THE INTERNAL ENVIRONMENT OF THE CELL FROM THE EXTERNAL ENVIRONMENT. Selective permeability is a direct consequence of membrane structure, as describe by the fluid mosaic model.

Fig. 7-2 Hydrophilic head WATER Hydrophobic tail WATER

Fig. 7-3 Phospholipid bilayer Hydrophobic regions of protein Hydrophilic regions of protein

Fig. 7-9 (a) Transport ATP (b) Enzymatic activity Enzymes (c) Signal transduction Signal transduction Signaling molecule Receptor (d) Cell-cell recognition Glyco- protein (e) Intercellular joining (f) Attachment to the cytoskeleton and extracellular matrix (ECM)

SELECTIVE PERMEABILITY

SELECTIVE PERMEABILITY OF THE CELL MEMBRANE

TYPES OF TRANSPORT PROTEINS Transport proteins allow passage of hydrophilic substances across the membrane 1.Some transport proteins, called channel proteins, have a hydrophilic channel that certain molecules or ions can use as a tunnel 2.Channel proteins called aquaporins facilitate the passage of water 3.Other transport proteins, called carrier proteins, bind to molecules and change shape to shuttle them across the membrane A transport protein is specific for the substance it moves – i.e. FORM FITS FUNCTION!!! Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

CELL WALLS The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. Cell walls provide a structural boundary, as well as a permeability barrier for some substances to the internal environments. It is located outside the cell membrane and provides these cells with structural support and protection, in addition to acting as a filtering mechanism. A major function of the cell wall is to act as a pressure vessel, preventing over-expansion when water enters the cell. Cell walls are found in plants, bacteria, fungi, algae, and some archaea. Animals and protozoa do not have cell walls. The material in the cell wall varies between species, and can also differ depending on cell type and developmental stage.

PLANT CELL WALLS

FUNGI CELL WALLS

BACTERIAL CELL WALLS