MATERIALS MOVE ACROSS CELL’S MEMBRANES

Chapter 2.3C

Review

What is a cell membrane?? What is the purpose of a membrane? What are membranes primarily made up

of?

For the remainder of the powerpoint, copy words highlighted in ORANGE!

Diffusion

Molecules spread out from where there are many to where there are fewer

They keep spreading until they are evenly distributed

Examples: Smelling a scent Oxygen (needed for respiration) and carbon

dioxide (produced by respiration)

Concentration

The number of particles of that substance in a specific volume Example:

Dissolving 9 grams of sugar in 1 liter of water yields the concentration 9g/L

Diffusion in Cells

Materials are able to move into and out of the cell Example:

Photosynthesis: produces oxygen inside the cell Concentration of oxygen is higher on the inside

than the outside Oxygen cells move out of the cell by diffusion

**What are some daily examples of diffusion?

Types of Diffusion

Passive transport Active transport Osmosis Endocytosis Exocytosis

Passive Transport

Materials move without using the cell’s energy (moving from high concentration to low concentration)

Osmosis

Diffusion of water through a membrane Example:

Unwatered plants wither Water leaves the plant’s roots to go to the dry soil to

even out the concentration of water molecules When the plant is watered,

water molecules diffuse through the plant’s cell membranes to even out the concentration again

Active Transport

Process of using energy to move materials through a membrane (moving from low concentration to high concentration) Examples:

Marine iguanas Kidneys

Endocytosis

Moving materials too large to pass through a membrane INTO the cell Membrane folds inward, creating a pocket Membrane closes around the material,

forming a “package” “Package” breaks away from

cell membrane, bringing the material into the cell

Exocytosis

Moving materials too large to pass through a membrane OUT OF the cell “Package” carries materials to cell

membrane Attaches to membrane and merges

together Materials are pushed out of membrane

Cell Size (and shape) Affects Transport

As cell grows, surface area is not large enough to allow resources to travel to all parts of cell

As a result, the cell may: Stop growing Divide

Shape Thin and flat cells (single-celled organisms) have

increased surface area Long and skinny cells (nerve and muscle) have

increased surface area