Review: Cell MembraneCell 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 HomeostasisAll 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 (7.35-7.45)• 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