Cells and Their Environment

Hooke and van Leeuwenhoek postulated:1. All living things are composed of cells2. Cells are the basic unit and function in

an organism3. Cells only come from the reproduction

of existing cells

Many forms of life are unicellular

For multicellular organisms:• Cells make tissues• Tissues make organs• Organs make organ

systems• Organ systems make

organisms

A cell is the smallest unit of life

All cells are surrounded by a membrane

Bipolar molecules Create

“Phospholipid Bilayer”

Hydrophobic (lipid) tail

Hydrophylic (phosphate) head

Older model Most recent model

1. Homeostasis is the ability to maintain a stable internal environment

2. Homeostasis, at a cellular level, is achieved by the cell membrane

3. The cell membrane regulates what leaves and enters the cells

1. A concentration gradient occurs when the concentration of molecules differ across a space

2. A molecule moves “down” the concentration gradient passively (no energy)

3. A molecule moves “up” the concentration gradient actively (with energy used)

1. When the concentration of molecules of a substance is the same throughout a space, a state of equilibrium exists.

2. Molecules in equilibrium move randomly

Certain substances can cross the cell membrane without any energy from the cell

There are 4 types:1.Diffusion2.Osmosis3.Facilitated diffusion4.Diffusion through ion channels

1. Both osmosis and diffusion are types of passive transport

2. Diffusion is the movement of particles from an area of higher concentration to an area of lower concentrationSimple Facilitated Ion channel

3. Osmosis is the diffusion of water (often when particles can’t cross the membrane)

1. Some molecules cannot move across the membrane without a carrier protein Too big Not soluble in lipids Example: Glucose

2. Carrier proteins are like special doors for specific substances and are embedded in the phospholipid bilayer

1. Involves movement of materials up (or against) the concentration gradient

2. Move from an area of low concentration to an area of high concentration

3. This requires energy from the cell (in the form of ATP)