Review: Cell Membrane Cell membrane – selectively permeable phospholipid bilayer Controls what enters and leaves a cell Cell communication (carbohydrate chains) Protective barrier for cell from its surroundings Provides anchoring (peripheral proteins) for the cytoskeleton

How does a Cell Maintain Homeostasis All cells/organisms require a certain internal environment to function properly This is called homeostasis Main concerns for homeostasis include: Temperature pH levels Ions/salinity Water levels Nutrient availability *these conditions can very minute-to-minute or hour-to-hour*

Most bodily functions aim at maintaining homeostasis, and the inability to maintain it leads to disease and often death Temperature Body prefers 98.6⁰ F Cold = shake; Pull blood and water into your core area Hot = sweat; Send blood and water to your skin (red color) Controlled by enzymes unless extreme temps (denatures the enzyme)

pH levels Acids = 0-6; Bases = 8-14 (7 = neutral) Blood pH level very narrow ( ) Maintained by buffers in the blood (proteins usually) Affected by oxygen levels Body pH maintained by lipid buffers, alkaline salts, calcium from bones and muscles, lymphatic system Buffers – substances that can balance out too acidic or basic environments **yeast, molds, fungus, parasites thrive in an acidic body lacking oxygen (anaerobic). They feed on your proteins and fats and poison us with their waste**

Ions, water, nutrients, and large particles are moved/controlled by cellular transport Two types of Cellular transport Passive transport – Does not require energy – Moves from area of high concentration to low concentration – Ex. diffusion, osmosis, facilitated diffusion Active transport – Requires energy (ATP) – Moves from an area of low concentration to high concentration – Ex. pumps, endocytosis, exocytosis, ion channels