TRANSPORT

· the life function that involves the absorption (taking in) and circulation (moving around) of materials throughout an organism. We can talk about both absorption and circulation as separate processes.

I. ABSORPTION
* the process where digested (broken down) nutrients as well as other dissolved materials enter the cells of an organism
* the key organelle that is involved with this life function is the PLASMA (CELL) MEMBRANE

Remember. it is a double lipid layer with floating proteins...

We also can call the plasma membrane the fluid mosaic model. Fluid because the double layer moves around, it never is motionless. A mosaic because that is how it appears--a mosaic is a piece of art that is made up of lots of little pieces put together.

Now for a related topic...

A) DIFFUSION
* diffusion is where very small particles move from a region of high concentration (a large amount) to a region of lower concentration (a smaller amount).
* molecules move in straight lines in a random direction
* diffusion usually happens until the concentration is the same throughout; this is called EQUILIBRIUM (a balanced state--kinda like HOMEOSTASIS!)

B) VARIOUS TYPES OF ABSORPTION

1) Passive Transport (DIFFUSION):
* the movement of molecules through the plasma membrane from a high to a low concentration
* smaller molecules such as glucose (C6H12O6), oxygen (O2), amino acids, carbon dioxide (CO2), and water (H2O) can diffuse right through like air through a screen door

* larger molecules such as polysaccharides, proteins, and lipids cannot fit, because they are too big

* it is called passive transport because NO ENERGY IS REQUIRED!!!

***OSMOSIS--the diffusion of water through a membrane***

***OSMOSIS--the diffusion of water through a membrane***

2) Active Transport:
* a process where a cell USES ENERGY (active) to move molecules from a low concentration to a high concentration

* special proteins called carrier proteins are used to move molecules to one side of the membrane to the other

3) Pinocytosis:
* a process where very large (too big to go through the plasma membrane) particles are "sucked in" to a cell, forming a vacuole
* "cell drinking"--uses energy (active transport)

4) Phagocytosis:
* a process where a cell engulfs large undissolved particles, forming a vacuole
* "cell eating"--uses energy (active transport)

II. CIRCULATION
* the transport of materials within one cell and/or the transport of materials throughout a multicellular organism

* for unicellular organisms, intracellular (inside the cell) circulation is accomplished by the endoplasmic reticulum, Golgi complex, and CYCLOSIS (cytoplasmic streaming).

* for multicellular organisms, intercellular (between cells) circulation is accomplished by the diffusion or transport through vascular tissues (like xylem, arteries)

ADAPTATIONS FOR TRANSPORT

I. PLANTS

A) Bryophytes:
* ex. mosses, liverworts
* have no vascular tissues (roots, stems, or leaves)
* live in moist environments so water and other substances can diffuse right through the plasma membranes
* intracellular transport occurs via cyclosis

B) Tracheophytes:
* ex. trees, flowers, grasses
* have specialized vascular tissues (roots, stems, and leaves) to transport water and nutrients

DIFFERENT PARTS OF TRACHEOPHYTES

ROOTS- structures used for...

* roots have root hairs--elongated epidermal (skin) cells which increase the surface area of the root so it can absorb more nutrients
* root hairs absorb these nutrients by diffusion, osmosis, and active transport

This water is pulled up the plant by TRANSPIRATIONAL PULL (transpiration) up the xylem. Remember the meniscus when you use a graduated cylinder--that happens because water hangs on to each other very tightly. In plants, the water molecules pull each other up to the leaves as some of them evaporate through the stomate.

STEMS- vascular tissues (carries nutrients up and down) that is used as a support beam of some plants

LEAVES-continuation of vascular tissue to the cells that produce food; remember the cross section!

what exactly is transpiration?

II. ANIMALS

A) Humans
* many cells are not in direct contact with the environment; many, many cell layers
* food is absorbed by the intestine
* O2 (oxygen) is absorbed in the lungs

Once absorbed, these materials are circulated through a closed, internal circulatory system...

* the blood of an human has a protein called hemoglobin that carries O2
* the blood is moved within this closed, internal system
* the blood is pumped throughout the human by the heart of the circulatory system
* water and other dissolved materials are transported from the digestive system to the rest of the cells

More to come in packet #11--HUMAN TRANSPORT