TRANSPORT SYSTEM

TRANSPORT SYSTEM

Transport system refers to the movement of metabolic materials from various parts of an organism where they are produced or obtained to parts where they are used, stored or removed from the body.

The Need for Transportation in Small and Large Organisms

1. Distribution of essential materials
2. Removal and disposal of metabolic wastes
3. Movement of hormones
4. Transport of substances to storage sites
5. Regulation of body temperature and distribution of heat
6. Distribution of water, mineral salt and manufactured food in plants

Need for Transport System in Large Organisms

The surface area to volume ratio (A/V) is too small. Many cells are situated far away from others. Materials need to move great distances. Materials to be distributed are too large in quantity. Hence, the need for efficient transport system.

Shape	Surface area	Volume		A/V ratio
A	6cm2	1cm3	6/1	6
B	10cm2	2cm3
C	16cm2	4cm3
D	24cm2	8cm3

Materials Transported in Animals

1. Oxygen
2. Carbon(IV)oxide
3. Water
4. Salts
5. Hormones
6. Antibodies
7. Food
8. Excretory products e.g. urea

Media of Transportation in Animals

1. Cytoplasm: used in lower organisms e.g. Amoeba, Paramecium
2. Blood: used in higher animals e.g. vertebrates
3. Lymph: used in higher animals
4. Cell sap or latex: used in plants

Composition and Function of Mammalian Blood

Blood is a tissue that contains cells.

1. Blood cells (corpuscles): contains red blood cell, white blood cell and blood platelets. This constitutes 45% of whole blood.
2. Plasma: the fluid portion of the blood. This constitutes 55% of whole blood. Plasma consists of proteins, food materials, mineral salts, hormones and excretory products.

Red blood cells (RBCs or Erythrocytes): these are tiny biconcave discs with no nucleus. There are about five million RBCs in each mm³ of blood. Red blood cells are produced in the bone marrow which is a spongy red tissue in bones. The lifespan of a red blood cell is about 120days. Old and worn out RBCs are destroyed in the spleen and liver. Red blood cells contain haemoglobin which helps it to transport oxygen from lungs to the cells and assist in the formation of blood clot.

White blood cells (WBCs or Leucocytes): these are colourless, irregular and amoeboid in shape. They are larger than RBCs and contain a nucleus. There are between 5,000 and 10,000 WBCs per mm³ of blood. They could be phagocytes which ingest bacteria or lymphocytes which produce antibodies. White blood cells keep the body healthy by fighting off disease.

Blood platelets are tiny fragments of cells which help in the formation of blood clot.

Plasma is the liquid component of blood. It contains soluble proteins (e.g. albumin, globulin), dissolved mineral salts, food substances, excretory products and hormones. Plasma help in transportation of substances dissolved in it.

General Functions of Blood

           1.      Transport medium

a.       For digested food to all parts of the body

b.      Excretory products

c.       Hormones

d.      Oxygen

e.       heat

           2.      Defence against diseases and infections

a.       Phagocytosis

b.      Production of antibodies

c.       Clotting of blood

           3.      Regulation of body temperature

           4.      Homeostasis

ASSIGNMENT: Describe the process by which blood clot forms during an injury

Circulatory System in Mammals

The mammalian circulation consists of heart (a pump) and blood vessels (arteries, veins and capillaries).

Structure of Mammalian Heart

The Mammalian Heart

The human heart is a hollow, conical, muscular organ which keeps blood circulating around the body throughout the life of a person. The heart is protected by a membrane called pericardium.

The muscles of the heart are called cardiac muscles. There are four (4) chambers in the mammalian heart: the right and left auricles or atria (singular- atrium) and the right and left ventricles. A thick septum separates the heart into two (2) sides. The right auricle communicates with the right ventricle by the tricuspid valve while the left auricle communicates with the left ventricle by the bicuspid valve. The valves ensure blood flows only in one direction.

The heart beats at about 70-75 times per minute. During a heartbeat, the resting period is known as diastole while the period the heart contracts is known as systole. The cycle between systole and diastole is known as pulse and takes about 0.8seconds.

Arteries

An artery is a blood vessel which carries blood away from the heart e.g. aorta. The walls are thicker, more elastic, has a small lumen and are more muscular than those of veins. The pressure in arteries is usually high and they are situated deep in muscles. Arteries carry oxygenated blood except for pulmonary artery. They branch out to arterioles and do not have valves.

Veins

Veins are blood vessels that return blood to the heart e.g. vena cava, pulmonary vein. The walls are less muscular, thinner, has a larger lumen and are less elastic compared to arteries. The pressure in veins is relatively lower and they are superficially located close to the skin surface. Veins carry deoxygenated blood except for pulmonary vein. They have valves.

Capillaries

These are microscopic blood vessels that form a network of linking arterioles to venules. Exchange of materials between tissues takes place in capillaries. Their walls are only one cell thick in order to facilitate diffusion of materials between the cells and the blood.

The diagram below shows the direction of blood flow in the body.

Types and Mechanisms of Circulation

     A.    Open and Closed Circulation

Open blood circulatory system is found in most invertebrates e.g. roundworms, insects and molluscs. The heart pumps blood into haemocoel, the organs and tissues are bathed in the blood (which is colourless) while the blood is returned to the heart through paired ostia. There is no system of blood vessels. Fluid flow in open circulation is slow.

Closed circulatory system occurs when blood leaves the heart in closed blood vessels and capillaries and circulates around the body and returns to the heart without being exposed. The blood flows from the heart to the arteries which branch out into arterioles, then capillaries where the exchange of material takes place with the body cells. The capillaries then form venules which connect together to form veins which return the blood to the heart.

     B.    Single and Double Circulation

In the single circulatory system, blood flows through the heart once in one cycle. This occurs in organisms such as fish which has a two-chambered heart (one atrium and one ventricle). Blood flows from the ventricle to the gills through the aorta, the blood picks oxygen which is distributed to various organs of the body through arteries which branch out to all parts of the body.

In the double circulatory system, blood flows through the heart twice in one cycle. This occurs in mammals.

The amphibians, the atrium is divided into right and left chambers. However, the ventricle is just one.

The mammalian heart is completely divided into right and left chambers, oxygenated blood does not mix with deoxygenated blood.

    C.    Pulmonary and Systemic Circulation

Pulmonary circulation involves the movement of blood between the heart and the lungs. From the right ventricle, deoxygenated blood is pumped into the pulmonary artery which branches to the right and left lungs. From the lungs, oxygenated blood is returned to the left atrium through the pulmonary vein.

Systemic circulation involves the movement of blood between the heart and all other parts of the body. Oxygenated blood collected by the left atrium is forced into the left ventricle, then to the aorta to be distributed around the body. The superior and inferior vena cava returns the deoxygenated blood from the body to the right atrium.

Coronary circulation involves the supply of blood to the muscles of the heart.

TRANSPORT SYSTEM IN PLANTS

The major materials transported in plants are gases, CO₂, oxygen, water, mineral salts, manufactured food, pigments and hormones.

The main transport media in plants are cytoplasm, cell sap and latex.

Transportation in Lower Plants

Lower plants use their cytoplasm for movement and distribution of materials. Gases enter the lower plants mainly by diffusion while water enters by osmosis

Transportation in Higher Plants

Vascular bundles are conducting vessels of plants and they consist of xylem and phloem.

Phloem tissues consist of thin-walled living cells with dense cytoplasm and have perforated cross-walls. Phloem translocates manufactured food from the leaves to living cells and storage organs. Xylem tissues consist of dead cells with lignified walls. Xylem vessels are responsible for upward conduction of soil nutrient and water from root to the leaves.

Translocation

This is the transport of manufactured food from the leaves to other parts of the plant where they are needed or stored.

EXPERIMENT: (Ringing Experiment)

AIM: To show that translocation takes place in phloem tissue.

MATERIALS: Two potted plants, knife

METHOD: use the knife to remove the bark of one of the potted plants together with the phloem tissues. The other plant is left untouched. Both plants are observed for a period of 2-5 weeks.

OBSERVATION: the potted plant with the removed bark and phloem tissues show swellings just under the part where the tissues have been removed. The other plant remains unchanged.

CONCLUSION: the swelling observed at the top of the ringed region is as a result of the accumulation of food which have passed down from the leaves. This shows that phloem is responsible for translocation of food from the leaves to other parts of the plant.

Transpiration

This is the loss of water vapour from the shoots of plants through the stomata of the leaves to the atmosphere. Water-loss from the stomata is known as stomatal transpiration, water-loss from the cuticles of plants are known as cuticular transpiration while water-loss through the lenticels is known as lenticular transpiration.

Measurement of Transpiration

1. Weighing method
2. Use of photometer
3. Use of cobalt chloride paper

EXPERIMENT

AIM:	To show that plants lose water from their leaves by transpiration
MATERIALS:	Two polythene bags, two bell jars, two potted plants (one having its stem cut), white copper(II)tetraoxosulphate VI (CuSO4) and crucible
METHOD:	Place the CuSO4 in a crucible along with the potted plants covering the soil with the polythene bag. Repeat the same procedure with the potted plant with the cut stem which serves as control. Cover the setups with bell jars
OBSERVATION:	The white anhydrous CuSO4 in the main test experiment changes colour to blue due to the water released by the plant while the CuSO4 in the control experiment did not
CONCLUSION:	Colour change from white to blue is due to water given off during transpiration of the leaves

Factors Affecting Transpiration

           A.    Plant factors

1)      Leaf area

2)      Leaf structure

3)      Root system

          B.     Atmospheric factors

1)      Sunlight

2)      Humidity

3)      Temperature

4)      Wind

          C.     Soil factor

1)      Availability of water

2)      Temperature

Importance of Transpiration

1. Cooling effect
2. Translocation of mineral salts
3. Good growth of plants

Absorption of Water and Mineral Salts

1. Uptake of soil water: the root hairs absorb water from the soil by osmosis.
2. Uptake of mineral salts: mineral salts are absorbed into the root hairs by active transport

Transport of Water in Xylem Tissue

Transport of water in xylem tissue is due to root pressure, capillary action and transpiration pull.

Root pressure: as the root accumulate water absorbed by root hairs, pressure is developed which causes water to move across root cells up the xylem vessels.

Capillary action: xylem vessels form fine capillary tubes. Water rises up along the tubes as a result of attraction between water molecules and the wall of xylem vessels.

Transpiration pull: as water evaporates from the leaves by transpiration and more sugar molecules are produced by photosynthesis, the osmotic pressure increases, and this causes water to flow into the leaf cells from xylem vessels.