Large animals- examples

https://www.youtube.com/watch?v=5m8XNwLl798

Smallest animals in the world

https://www.youtube.com/watch?v=NSBaxVidcqo

Do elephants and mice have the same size cells??

Why aren’t cells big?

Activity: Investigate Cell Size and Surface Area to Volume Ratios

Minimize diffusion time

No “donut holes” No poking holes into

cell Done when 100%

color gone Disqualified if cell

breaks apart mass/time ratio

identifies winner!

Design your own cell!

Print out or draw a picture of your cell (color)

Include a typed description of the cell, its function, and how it has overcome the SA:V ratio problem.

This should be on a piece of cardstock or printer paper

HW Find an example of acell that has overcome the SA:V problem.

Erythrocytes, also known as red blood cells (RBCs), function to transport oxygen in the blood. The shape of erythrocytes is ideal for this function. Seen from the top, erythrocytes appear to be circular, but a side view shows that they are actually biconcaved discs. This shape increases the surface area-to-volume ratio of the cell, thus increasing the efficiency of diffusion of oxygen into and out of the cell.

The Shape of A Red Blood Cell

Why aren’t cells big?

The evolution of life required a boundary…

BIG IDEA 2: Cell membranes are

selectively permeable due to their structure.

Membranes and Membrane Transport

Barrier Gate Keeper Communicator

Cell membranes:

Lipids, proteins and carbohydrates…

The molecules of a membrane

phospholipids

Fluid mosaic

Maintaining fluidity

oligosaccharides

Surface carbohydrates• Short, branched chains• Cell-cell recognition• Glycolipids• glycoproteins

Membrane proteinsIntegral:

embedded in phospholipid layerfor transport, carriers, and receptorsmay or may not be transmembrane

Peripheral:found on inner or outer membrane surfaceact as point of attachment for cytoskeleton

Cells must move materials through the membrane to maintain homeostasis.

How is the membrane semipermeable?

Some molecules can cross without help.

Transport proteins -help other molecules across cell membrane

Aquaporins allow water to diffuse across the membrane

Lab: Osmosis and Diffusion

- moves materials against a concentration gradient. - requires Energy (ATP).

Active Transport

Active Transport by membrane Proteins:

Globular proteins act as “ferries” for specific molecules shape change allows transport from one side of membrane to other

called protein pumps

Many models & mechanisms--uniports, symports, antiportsprimary vs. secondary active transport

The cell removes 3 sodium ions for every 2 potassium ions that enter the cell. This mechanism requires energy.

Sodium-Potassium pump

Example of Transport: Absorption of Nutrients in the small intestine

Passive transport• Water, fatty acids, glyderol, some vitamins by diffusionfructose by facilitated diffusion

Active (protein pumps) transport amino acids, glucose, some vitamins against concentration gradients across intestinal cell membranes

allows intestine to absorb much higher proportion of nutrients in the intestine than would be possible with passive diffusion

worth the cost of ATP!

Structure: Small IntestinesAbsorption through villi& microvilliincrease surface area

Gated channelsSome channel proteins open only in presence of stimulus (signal)stimulus usually different from transported moleculeex:ion-gated channels: when neurotransmitters bind to a specific gated channels on a neuron, these channels open = allows Na+ ions to enter nerve cellex:voltage-gated channels - change in electrical charge across nerve cell membrane opens Na+& K+ channels

Moving Large Molecules