Chapter 3: TRANSPORT OF MATERIALS IN LIVING ORGANISMS

Transport of materials is the movement of materials either from the environment into the

organisms or from one part to another part within the body of a living organism. Or

Transport of materials is the distribution of digested food and oxygen for growth,

respiration and reproduction in the body and removing of carbon dioxide and urine outside

the body. In other words; transport of materials occurs both within living organisms and

between the organism and its environment.

Organisms require transport system to carry out life processes such as nutrition,

respiration, excretion, coordination, growth and development. For instance; during

nutrition, food substances are taken from the environment are digested into different

nutrients and are transported to different parts of the body for being used and stored. The

by-products and waste are excreted from the organisms to the environment.

The Importance of Transport of Materials in Living Things

(i) It enables the distribution of nutrients and oxygen to the cells. materials

(ii) It facilitates the removal of waste products such as carbon dioxide and urea from

the body. If they accumulate in the body they become toxic and harm the body.

WAYS OF TRANSPORT OF MATERIALS

Life processes in organisms take place in the cell. Therefore, it is necessary for substances

to move in and out of the cells. The movement of materials is through the cell membrane.

There are two ways through which substances can move across the cell membrane;

(a) Active transport.

(b) Passive transport.

(a) Active transport occurs in the presence of energy in the form of ATP. During active

transport, substances move against concentration gradient from an area of low

concentration to an area of high concentration. Example; the uptake of glucose in the

small intestine of human being when the concentration of glucose in the blood become

higher than that of the small intestine.

(b) Passive transport occurs spontaneously without the need of energy to transport

materials through the cell membrane. Example; movement of oxygen from the lungs

to the blood stream and carbondioxide moving out of the blood stream into the lungs.

The passive transport of materials in the cells occurs through the following ways;

diffusion, osmosis and mass flow.

DIFFUSION

Diffusion is the passive movement of particles from an area of higher concentration to an

area of lower concentration. For example; a scent of flower and a colour of potassium

permanganate when a crystal is put in water. The difference in concentration of particles

between the more concentrated region and the less concentrated region is known as

concentration gradient or diffusion gradient.

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When the concentration gradient between the two point is high, diffusion is faster

and when the concentration gradient is low, diffusion is low.

When the particles are evenly distributed, they move at the same rate in either

direction.

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ROLES OF DIFFUSION IN LIVING THINGS

It helps in the movement of substances in the body, including;

(i)

Movement of oxygen gas from the alveoli to the blood capillaries.

Movement of oxygen gas from the blood capillaries to the tissue fluid.

(ii)

(iii) Movement of oxygen gas from the tissue fluid to the cell.

(iv) Movement of carbon dioxide gas from the cell to the tissue fluid.

(v)

Movement of carbon dioxide from the tissue fluid to the blood capillaries.

(vi) Movement of carbon dioxide from the blood capillaries to the alveoli.

(vii) Movement of air from the atmosphere to the leaves.

(viii) Movement of carbon dioxide gas from the intercellular space to the palisade cells.

(ix) Movement of oxygen gas from the palisade cells to the intercellular spaces of

spongy mesophyll.

(x)

Movement of oxygen gas from the intercellular spaces to the atmosphere.

(xi) Movement of water vapour from the leaves to the atmosphere.

(xii) Movement of digested food substances from the ileum to the blood circulatory

system.

Factors Affecting Rate of Diffusion

(a) Concentration gradient: When there is a great difference in concentration of

molecules between the two areas, high rate of diffusion occurs and vice versa

(b) Distance over which diffusion takes place: When the distance over which the

material is long, the rate of diffusion decreases. If the distance is short, diffusion

occurs faster because the materials do not have to travel far. For example, in a thin

layer of cells the rate of diffusion increases.

(c) Surface area to volume ratio: The larger the surface area to volume ratio, the

larger the number of particles that will be able to move in a given time hence, the

higher the diffusion rate.

OSMOSIS

Osmosis is the movement of water molecules from a region of high solvent (water)

concentration to a region of low solvent (water) concentration through a partially

permeable membrane. Or Osmosis is the movement of water molecules from region of low

concentrated solution to the region of high concentrated solution through a semi-

permeable membrane.

Osmosis is considered as a special form of diffusion because it involves movement of water

molecules through semi-permeable membrane. The partially permeable membrane is only

permeable to water. For osmosis to occur, there must be two solutions separated by a

semi-permeable membrane. One solution should have greater amount of water and less

quantity of solute than the other solution.

Figure 3.1: Movement of water molecules during osmosis

Types of solutions connected with Osmosis

(i) Isotonic solution: This refers to two solutions with the same concentration of water

and solute. That is, the two solutions have the same osmotic pressure

(ii) Hypotonic solution: is a solution that has lower solute potential or higher water

potential. Or Hypotonic solution is a solution containing less solute and more

water molecules compared to another. A hypotonic solution has lower osmotic

pressure and is generally termed as less concentrated. A cell placed in such a

solution gains water by osmosis.

(iii) Hypertonic solution: is a solution that has higher solute potential or lower water

potential. Or Hypertonic solution is a solution with more solutes and less water

molecules than another. A hypertonic solution has a higher osmotic pressure and

is generally termed as more concentrated solution. A cell placed in such a solution

loses water by osmosis.

Figure 3.2: Experimental set-up to demonstrate osmosis

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In (a), water molecules moved by osmosis to the potato hole hence the level of sugar

solution rose. The rise in the level of the sugar solution in the un-boiled potato hole

indicates that water molecules moved from the potato tissue to the hole containing

sugar solution. The potato tissue acts as a semi-permeable membrane.

In (b), no change was observed. The semi-permeable membrane of the potato hole

was destroyed by boiling and hence water molecules did not move. This indicates

that boiling potato killed all the potato tissue cells, and dead cells do not allow

osmosis to take place.

In (c), a very little amount of water entered the potato hole. There was very little

solute in the potato. In this hole, the solute potential was only due to the solutes

naturally present in the cells of the potato.