Cell membranes

Osmosis, Diffusion and Molecular movements

Reviewing Some Basics

• Solution– Mixtures of 2 or more substances (in any

combination of solids, liquids or gasses)

• Solute– The dissolved substance (i.e. salt in water)

• Solvent– The substance the solute is dissolved in ( i.e.

the water in which the salt is dissolved)

Cell size? Why care?

Cell size (cont)

Cell size (continued)• Its all about surface to volume ratios• Notice that the larger cube has more surface area

and more volume but less surface area for each cubic centimeter of volume.  

• For any given geometric object (cubes, spheres, etc.), smaller objects have a greater surface to volume ratio (surface:volume) than larger objects of the same shape.

• Every cell is surrounded by a plasma membrane• Most cells are very small and therefore have a high

ratio of plasma membrane surface to cell volume. 

?

• How do larger multicellular organisms manage to solve this problem for a successful survival?

Diffusion

• http://www.biologycorner.com/resources/diffusion-animated.gif

More

Osmosis• Osmosis is the

movement of water (red dots) through a semipermeable membrane to a higher concentration of solutes (blue dots).

• Water easily moves through cell membranes by osmosis.

Active transport

• Active transport describes what happens when a cell uses energy to transport something. We're not talking about phagocytosis (cell eating) or pinocytosis (cell drinking) in this section. We're talking about the movement of individual molecules across the cell membrane. The liquids inside and outside of cells have different substances. Sometimes a cell has to work and use some energy to maintain a proper balance of ions and molecules.

Endocytosis/Exocytosis

Phagocytosis(food)/Pinocytosis (liquid)same process

• Cell interior

Cell wall

• Cell walls are the rigid structure found surrounding plant cells. They provide support for the plant

• The cell membranes are different than cell walls.

• Cell membranes line the inside of cell calls in plants.

• Cell membranes are the gatekeeper of all cells.

Cell membrane vs cell wall

Cell (plasma) Membrane• The plasma membrane (cell

membrane) is made of two layers of phospholipids.

• The membrane has many proteins embedded in it.

• The plasma membrane regulates what enters and leaves the cell.

• Many molecules cross the cell membrane by diffusion and osmosis.

• It”s formed and broken down as needed by the cell

Cell animation

Membranes etc.

• http://www.bioclips.com/

Plasma membrane

Isotonic solution

Hypotonic solution

Hypertonic solution

Factors affecting Osmosis/Diffusion

• Molecular size

• Concentration gradient

• Molecular charge

• Temperature

• Pressure

Egg lab(Change in gms)

• Period Control DH2O Glucose___________________________________• 1 -.2 +2.3 -3.1• 2 -.4 +3.1 -3.3• 3 -.1 +3.3 -2.9• 4 -.3 +3.0 -3.7• 5 -.1 +2.9 -3.5• 6 -.2 +4.1 -4.0

Elodea cells lab

Cell model lab

http://www.phschool.com/science/biology_place/labbench/lab1/osmosis.html

But what about the glucose?

Molecular size

• Water very small

• Iodine very small

• Glucose medium

• Starch very large

Blood cells

What happened and why?

• Egg lab?

• Elodea lab?

• Cell model lab?

• Beer, pretzels and a workout?

Cell Theory

• All organisms are composed of cells, and a cell is the smallest unit of living matter.

• Cells come only from preexisting cells.

Robert Virchow put all these ideas and facts from Robert Hooke, Leeuwenhoek, Schleiden and Schwann together and essentially compiled what is known today at the cell theory: – all living things are assemblages of different

kinds of cells. – each of these cells maintains its own

independent existence. – new cells can arise only from the growth and

reproduction of preexisting cells.

Evolutionary connections

Endosymbiotic theory

• Simply stated, the theory of endosymbiosis is the concept that mitochondria and chloroplasts are the result of years of evolution initiated by the endocytosis of bacteria and blue-green algae which, instead of becoming digested, became symbiotic.

Evidence?

• Organelles same size as prokaryotes

• Organelles have their own DNA

• Organelles have similar structure to prokaryotes

• Organelles reproduce like prokaryotes

• Membrane structure is like prokaryotes

• Double membrane makes sense

Lynn Margulis• Her hypothesis originally proposed that:• mitochondria are the result of endocytosis of

aerobic bacteria • chloroplasts are the result of endocytosis of

photosynthetic bacteria • in both cases by large anaerobic bacteria who

would not otherwise be able to exist in an aerobic environment.

• this arrangement became a mutually beneficial relationship for both cells (symbiotic).

Lynn Margulis