Which type of transport takes place when molecules move from high to low concentration diffusion or active transport?

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Video explaining the differences

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Need to move something really heavy?

If you did, it would take a lot of energy. Sometimes, moving things into or out of the cell also takes energy. How would the cell move something against a concentration gradient? It starts by using energy.

In contrast to facilitated diffusion, which does not require energy and carries molecules or ions down a concentration gradient, active transport pumps molecules and ions against a concentration gradient. Sometimes an organism needs to transport something against a concentration gradient. The only way this can be done is through active transport, which uses energy that is produced by respiration (ATP). In active transport, the particles move across a cell membrane from a lower concentration to a higher concentration. Active transport is the energy-requiring process of pumping molecules and ions across membranes "uphill" - against a concentration gradient.

The active transport of small molecules or ions across a cell membrane is generally carried out by transport proteins that are found in the membrane.
Larger molecules such as starch can also be actively transported across the cell membrane by processes called endocytosis and exocytosis.

Homeostasis refers to the balance, or equilibrium, within the cell or a body. It is an organism’s ability to keep a constant internal environment. Keeping a stable internal environment requires constant adjustments as conditions change inside and outside the cell. The adjusting of systems within a cell is called homeostatic regulation. Because the internal and external environments of a cell are constantly changing, adjustments must be made continuously to stay at or near the set point (the normal level or range). Homeostasis is a dynamic equilibrium rather than an unchanging state. The cellular processes discussed in both the Diffusion andActive Transport concepts all play an important role in homeostatic regulation. You will learn more about homeostasis in other concepts.

Active transport is the energy-requiring process of pumping molecules and ions across membranes against a concentration gradient.
Active transport processes help maintain homeostasis.

Use this resource to answer the questions that follow.

Active Transport at www.northland.cc.mn.us/biolog...ns/active1.swf.

What is the role of ion pumps?
Why is ATP necessary with ion pumps?
What is cotransport?
Why must one molecule be pumped across the membrane during cotransport?

What is active transport?
Explain how cell transport helps an organism maintain homeostasis.

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Active and passive transport are biological processes that move oxygen, water and nutrients into cells and remove waste products. Active transport requires chemical energy because it is the movement of biochemicals from areas of lower concentration to areas of higher concentration. On the other hand, passive trasport moves biochemicals from areas of high concentration to areas of low concentration; so it does not require energy.

Active Transport versus Passive Transport comparison chart

	Active Transport	Passive Transport
Definition	Active Transport uses ATP to pump molecules AGAINST/UP the concentration gradient. Transport occurs from a low concentration of solute to high concentration of solute. Requires cellular energy.	Movement of molecules DOWN the concentration gradient. It goes from high to low concentration, in order to maintain equilibrium in the cells. Does not require cellular energy.
Types of Transport	Endocytosis, cell membrane/sodium-potassium pump & exocytosis	Diffusion, facilitated diffusion, and osmosis.
Functions	Transports molecules through the cell membrane against the concentration gradient so more of the substance is inside the cell (i.e. a nutrient) or outside the cell (i.e. a waste) than normal. Disrupts equilibrium established by diffusion.	Maintains dynamic equilibrium of water, gases, nutrients, wastes, etc. between cells and extracellular fluid; allows for small nutrients and gases to enter/exit. No NET diffusion/osmosis after equilibrium is established.
Types of Particles Transported	proteins, ions, large cells, complex sugars.	Anything soluble (meaning able to dissolve) in lipids, small monosaccharides, water, oxygen, carbon dioxide, sex hormones, etc.
Examples	phagocytosis, pinocytosis, sodium/potassium pump, secretion of a substance into the bloodstream (process is opposite of phagocytosis & pinocytosis)	diffusion, osmosis, and facilitated diffusion.
Importance	In eukaryotic cells, amino acids, sugars and lipids need to enter the cell by protein pumps, which require active transport.These items either cannot diffuse or diffuse too slowly for survival.	It maintains equilibrium in the cell. Wastes (carbon dioxide, water, etc.) diffuse out and are excreted; nutrients and oxygen diffuse in to be used by the cell.

There are two types of active transport: primary and secondary. In primary active transport, specialized trans-membrane proteins recognize the presence of a substance that needs to be transported and serve as pumps, powered by the chemical energy ATP, to carry the desired biochemicals across. In secondary active transport, pore-forming proteins form channels in the cell membrane and force the biochemicals across using an electromagnetic gradient. Often, this energy is gained by simultaneously moving another substance down the concentration gradient.

Example of primary active transport, where energy from hydrolysis of ATP is directly coupled to the movement of a specific substance across a membrane independent of any other species.

There are four main types of passive transport: osmosis, diffusion, facilitated diffusion and filtration. Diffusion is the simple movement of particles through a permeable membrane down a concentration gradient (from a more concentrated solution to a less concentrated solution) until the two solutions are of equal concentration. Facilitated diffusion uses special transport proteins to achieve the same effect. Filtration is the movement of water and solute molecules down the concentration gradient, e.g. in the kidneys, and osmosis is the diffusion of water molecules across a selectively permeable membrane. None of these processes require energy.

Three different mechanisms for passive transport in bilayer membranes. Left: ion channel (through a defined trajectory); center: ionophore/carrier (the transporter physical diffuses through with the ion); right: detergent (non-specific membrane disruption).