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Transport system

The Need for Transport

Multicellular organisms need the transport systems to supply nutrients to their cells as well as get rid of waste products. Plants transport substances through xylem and phloem while the mammalian heart makes use of blood vessels.
Transport systems
An increase in the size of an organism leads to a corresponding decrease in the surface area to volume ratio.
This implies that it has comparatively less surface area on hand for substances to diffuse through, so the rate of diffusion may not be swift enough to meet up the requirements of the cells.
Big multicellular organisms therefore cannot depend on diffusion alone to provide their cells with materials like food and oxygen and to eliminate waste products.
Large sized multicellular organisms therefore need specialized transport systems.
The box on the left hand side has a surface area of 6 square units and a volume of 1 cubic unit. Its surface area to volume ratio is 6:1.
The box on the right hand side has a surface area of 24 square units and a volume of 8 square units. Its surface area to volume ratio is 24:8 which equals 3:1.
The box has two times the height, length and breadth of the smaller box, but only has half the comparative surface.
Therefore the larger SA/V ratio of the smaller box would permit more effective diffusion and exchange of materials.

Transport system in plants

Plants need transport systems to transport water, dissolved food and other substances just about their structures in order to be alive.
Plants need water for two main reasons:
•For photosynthesis. In the majority of flowering plants it occurs in mesophyll cells of the leaves.

•To transport materials, like minerals.
Water absorbed by the roots of a plant is transported from one side of the plant to the leaves where a few of it is expelled out into the air. The stages involved in the process are:
1. Soil to xylem
•Water is been drawn up by the root hair cells. These are minute hairs enveloping the tip of the ends of the smallest roots. They make available a large surface area for the absorption of water by the process of osmosis.
•Water therefore passes from cell to cell via the root cortex by osmosis down a concentration gradient. This implies that every cell possess a lower water concentration than the one it is following.
•In the centre of the root, the water sips through the xylem vessels. These are vein-like tissues that transport water and minerals up a plant.
2. Xylem to leaf to air
Water molecules creeps up the xylem vessels to the leaves where they stay and are transferred from cell to cell.
Water passes from the xylem vessels into the mesophyll cells where it can be made use of for photosynthesis.
Some of the water disappears into the surrounding air spaces at the interior part of the leaf and subsequently diffuses out through the stomata into the adjoining air.
The opening and closing of the stomata is handled by guard cells in the epidermis.
The loss of water from the leaves of a plant is known as transpiration, and the resulting flow of water via the plant is known as the transpiration stream. The transpiration stream is significant because:
•It transports water for photosynthesis to the mesophyll cells. The mesophyll cells are the upper layer of cells where photosynthesis majorly occur place in the leaves.
•The water carries vital mineral salts dissolved in solution.

The xylem transport system

Water and minerals are carried up via the stem in xylem vessels. Xylem is a tissue made up of dead, hollowed-out cells that outline a system of pipes.
The walls of xylem cells are lignified. This means that they are strengthened with a substance known as lignin which permits the xylem to withstand the changes in pressure as water passes through the plant.

The phloem transport system

Sugar manufactured through the process of photosynthesis in the leaves is transported up and down the plant to the meristems and other tissues in living phloem cells.
Companion cells make available the energy for the sieve cells. The end walls of the sieve cells possess pores through which sugar is transported from cell to cell.
Animal transport and exchange systems
In mammals, nutrients like glucose and amino acids, oxygen and carbon dioxide are transported just about the body in the blood.
Oxygen is transported in red blood cells. Red blood cells are special cells that carry oxygen because:
•They have large quantities of a protein known as hemoglobin, which can react with oxygen.
•They possess no nucleus and therefore there is more room for hemoglobin.
•They possess a biconcave disc shape, which maximizes the surface area of the cell membrane for oxygen to disperse across.
•They are minute and stretchy and therefore can press through the narrowest blood capillaries to transport oxygen.


Haemoglobin reacts with oxygen in body parts where the oxygen concentration is high -in the lungs and forms oxyhaemoglobin.
Blood with a high concentration of oxygen is termed oxygenated blood. This is illustrated in the equation below:
The presence of oxygen in the blood makes it a bright red colour.
In places where the oxygen concentration is small-body tissues, the haemoglobin gives out oxygen as illustrated in the equation below.
The oxygen then passes through into the cells. Blood that has a low oxygen concentration is dark red colour and is termed a deoxygenated blood.

Transport system In Humans

The human transport system is made up of a system of tubes with a pump and valves to make sure blood flows one way.
We require a transport system to supply oxygen, nutrients and other substances to every part of our body cells, and remove waste products from them.
The oxygenated blood ie blood that is high in oxygen, red in color enters the heart from the lungs in the pulmonary vein; the heart pumps the blood to the aorta which is an artery and from there to the entire body parts.
The deoxygenated blood goes back to the heart from the body in the vena cava which is a vein and from there the heart pumps it to the lungs to eliminate the carbon dioxide.
•Oxygenated Blood: Red color, high oxygen low Carbon dioxide.
•Deoxygenated Blood: Blue color, low oxygen high Carbon dioxide.
You would observe that during one circulation, the blood passed through the heart two times, this is why it is referred to as double circulation.
When the blood is flowing away from the heart, it has an extremely high pressure, when it is flowing towards the heart it has a lower pressure.

The Blood:

The blood is a fluid that is made up of many types of cells afloat in a liquid known as plasma.
Red Blood Cells:
These are among the tiniest cells in your body; they are round with a hollow in the center. The shape is termed a Biconcave disc.
The function of the red blood cells is to convey oxygen from the lungs to the body cells.
A red protein known as Haemoglobin, when the blood reaches the lungs, oxygen passses from the alveoli to the red blood cells and reacts with haemoglobin to form an unstable compound known as oxyhaemoglobin.
When the blood reaches the body cells, the oxyhaemoglobin is readily divided into oxygen and haemoglobin again, the oxygen passses through the blood plasma to the cells.
Red blood cells are entirely tailored to their function due to the following features it possesses:
•Biconcave disc shape offers it gives it large surface area to carry more oxygen
•Haemoglobin that combines with oxygen
•No nucleus that occupies space.
White Blood Cells:
White blood cells are one of the substances that are afloat in the blood plasma. They are entirely different in function from the red blood cells. White blood cells are part of the body’s Immune System.
They are very significant and play a huge role in the body’s protection usually by killing bacteria which cause disease, also referred to as pathogens.
White blood cells can be differentiated from the red blood cells quite readily because they are very much bigger than the red blood cells and possess a nucleus, and are available in fewer amounts.
Types Of White Blood Cells:
They eliminate bacteria from the body by engulfing them, taking them in the cell and subsequently kill them by digesting them through the use of enzymes; this process is known as phagocytosis.
The majority of white blood cells are the phagocyte type.
As opposed to phagocytes, lymphocytes posses a large nucleus. They are produced in the lymph nodes-in the lymphatic system.
Lymphocytes get rid of bacteria by secreting antibodies and antitoxins which directly kill the pathogens or make it easier to get them killed.
Every one of the pathogens could be killed by a specific type of antibody.

The Platelets:

Platelets are minute cell fragments that inhibit bleeding when the skin is cut, and it prevents bacteria from passing into our systems via the wound.
This functions through blood clotting, when the skin is cut, a few reactions occur which leads to the platelets manufacturing a protein, this protein will alter the fibrinogen- another soluble protein in the plasma to insoluble fibrin.
The fibrin produces the long fibres that clot together covering the cut, thereby preventing any bleeding. This process is referred to as blood clotting.

Blood Plasma:

This makes up the majority of the blood. It is majorly water with a few substances dissolved in it; these embrace carbon dioxide, hormones, food nutrients, urea and other waste products.
The blood plasma transports substances from place to place.

Functions of the blood:

•To transport the red blood cells, white blood cells, oxygen, food nutrients, hormones, and waste products.
•Defend the body against disease, by white blood cells, a process known as phagocytosis and production of antibodies.
•Providing cells with glucose to respire and maintain a constant temperature.
Blood Vessels (Vascular System):
This is a number tubes that carry the blood away from and to the heart and other organs. The major types of are Arteries, Veins and Capillaries.
Their function of the arteries is to transport blood away from the heart to the lungs or other organs of the body.
The blood in the arteries always comes with a high pressure.
The heart pumps the blood swiftly into the arteries, leading in the pressure, every time the ventricle of the heart contracts, the pressure in arteries increase, when the ventricle relaxes, the pressure falls.
The lumen of arteries is as very narrow, making the pressure to be higher.
The structure is uncomplicated, apart from the narrow lumen it possesses; the arteries possess a strong thick wall to endure the pressure. Their walls are as well elastic and stretchable.
Concise explanation of characteristics of arteries:
•To carry blood away from the heart
•Blood that passes here are constantly in a high pressure
•They have rigid but stretchable walls
•Narrow lumen
The function of the veins is to transport blood to the heart from the body.
The veins always have a low blood pressure because when the blood with high pressure reaches the veins, it loses the majority of the pressure it has.

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