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DIFFUSION, OSMOSIS, AND ACTIVE TRANSPORT

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Justin Lee

on 9 March 2015

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Transcript of DIFFUSION, OSMOSIS, AND ACTIVE TRANSPORT

DIFFUSION, OSMOSIS, AND ACTIVE TRANSPORT
Today, I shall be explaining what Diffusion, Osmosis and Active Transport are, how they work, and their role in both plants and animals.
OSMOSIS
Osmosis is the movement of water through na partially permeable membrane along a concentration gradient.

The partially permeable membrane is important in osmosis as it prevents some substances from diffusing across.

In short, osmosis is the diffusion of water across a partially permeable membrane.
OSMOSIS IN BIOLOGY
Osmosis is extremely important to living organisms as it plays a role in the distribution of nutrients and the removal of waste products.

As stated earlier, the partially permeable membrane - in this case, the cell membrane - is important here as it prevents toxic materials from diffusing into the cell.


DIFFUSION
Diffusion is the process in which molecules intermingle as the result of their kinetic energy of random motion.

More simply put, it is the spreading out of the particles of a gas or liquid in a solution.
DIFFUSION IN BIOLOGY
Diffusion plays an important role in biology as it is one of the ways that important substances can be transported throughout an organism.

For example, carbon dioxide diffuses into a plant leaf via the stomata on its underside, while oxygen and water vapour produced by photosynthesis diffuse out, also via the stomata.

Another example of diffusion in biology is the movement of oxygen from the air into our blood and the movement of glucose from the blood into our cells.


ACTIVE TRANSPORT
Active transport is the movement of molecules across a cell membrane against the concentration gradient, i.e from an area of lower concentration to an area of higher concentration.

In active transport, 'carrier' proteins on the cell membrane 'grab' useful molecules on the outside of the cell, before rotating and 'dropping' the minerals on the inside of the cell.

This process uses cellular energy because active transport moves molecules against the concentration gradient. Due to this, cells that undergo a lot of active transport usually have large amounts of mitochondria to provide energy.

DIFFUSION, OSMOSIS AND ACTIVE TRANSPORT
DONE BY: JUSTIN LEE KAI REN

HOW DOES IT WORK?
Diffusion is the result of Brownian motion, the result of particles colliding with each other, causing them to move. This is also known as random movement.

Diffusion results in the movement of particles from a area of high concentration to an area of low concentration down a concentration gradient, which is the difference in concentration between these areas.

If the concentration difference is large, then diffusion will be faster than if the difference in concentration was small.

Diffusion occurs until there is an even distribution of particles between the two areas. When this happens, then diffusion will stop as there is no concentration gradient due to both areas having the same concentration of particles.
FACTORS AFFECTING DIFFUSION
Diffusion takes place at a higher speed at higher temperatures because at these higher temperatures, molecules possess more energy and thus move faster.

The surface area of an object will speed up diffusion as there will be more surface area with which substances can enter.

The volume of an object also influences the rate of diffusion as it will take longer for any substances to evenly distribute themselves in the object.

This means that the most efficient diffusion occurs when an object has a high surface area to volume ratio - i.e. when an object has a large surface area but a small volume, like a cell.
THE CELL MEMBRANE
All cells, whether plant or animal, possess a cell membrane - a structure which serves an important purpose to the working of a cell. It not only isolates the cell from the environment, it also helps to identify the cell and enable it to communicate with other cells.

But the most relevant function of the cell membrane here is its ability to regulate the substances that enter or exit the cell.

The cell membrane is partially permeable, allowing some substances, such as water, to pass through while preventing the passage of others.

The cell membrane also contains proteins that can 'grab' molecules and pull them into the cell - important in active transport.
OSMOSIS IN PLANT CELLS
Osmosis is the way that plants obtain water - root hair cells absorb water from the ground via osmosis. The cell vacuole has a lower water concentration than the soil, so water enters the root hair cell via osmosis.

When a plant cell absorbs water via osmosis, it swells, causing it to press against the cell wall. When this happens, the cell becomes turgid, meaning it becomes firm. This helps support the plant as plants do not have skeletons.

However, when a plant cell loses water, the opposite happens - it becomes flaccid as the cell shrinks, causing the plant to wilt.
OSMOSIS IN ANIMAL CELLS
As we know already, animal cells do not have a cell wall. Therefore, they are vulnerable to damage as a result of absorbing or losing too much water to osmosis.

If an animal cell is in a solution of higher water potential, then it will absorb water. If it absorbs too much, it will burst open - this is called haemolysis.

In reverse, when an animal cell is in a solution of lower water potential, water will leave the cell and cause it to shrink and appear wrinkled - this is called crenation.
ACTIVE TRANSPORT IN BIOLOGY
Root hair cells utilise active transport to absorb minerals from the soil. This is because they cannot absorb them via osmosis as osmosis only affects water, and the concentration of minerals is small so they cannot absorb the minerals via diffusion.

Another example of active transport is during the digestion of food in the human gut. When food is being digested, the villi in the small intestine will absorb the food particles. After some time, the concentration will be high enough that the villi cannot use diffusion to absorb any more food. At this point, active transport is used instead.
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Graphical explanation
Graphical explanation
Graphical Explanation
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