Chapter 11 — Transportation In Animals And Plants

What is meant by transport? Transport means movement of substances (oxygen, nutrients, water, minerals, hormones, salts and wastes) within an organism from one part to another so that every cell gets what it needs and waste products are removed.

Why organisms need transport

• Supply of raw materials: Cells need oxygen and nutrients (glucose, amino acids, ions) to make energy and build cell parts.
• Removal of wastes: Carbon dioxide and other metabolic wastes must be removed to avoid poisoning cells.
• Distribution of water and minerals: Plants need continuous supply of water and dissolved minerals from roots to leaves.
• Communication and control: Hormones and chemical signals must be moved to coordinate body functions.
• Temperature and internal environment: Transport helps distribute heat and maintain internal conditions (homeostasis).

Why diffusion alone is not enough for large organisms

Small or single-celled organisms are thin and small so substances can reach every part of the cell by diffusion. Diffusion is slow over long distances, so as size increases diffusion becomes inadequate. Two important ideas explain this:

• Surface area to volume ratio (SA:V): As an organism gets larger, its volume increases faster than its surface area. A smaller SA:V means less area per unit volume for exchange with the environment, so internal transport systems are required.
• Diffusion distance and time: Time taken by diffusion increases rapidly with distance. For larger distances diffusion becomes too slow to meet the needs of cells deep inside the body.

How larger organisms solve the problem

• Animals have specialised transport systems: blood, blood vessels and heart (circulatory system) to carry oxygen, nutrients and wastes rapidly to and from cells.
• Plants have vascular tissues: xylem (moves water and dissolved minerals up from roots) and phloem (moves food/sugars from leaves to other parts). Mechanisms include transpiration pull, root pressure and active loading of sugars into phloem.

Summary The need for transport arises because every living cell needs constant supplies and a way to get rid of wastes. Simple diffusion works for small cells but larger, multicellular organisms must have specialised transport systems (circulatory system in animals; xylem and phloem in plants) because of limits imposed by surface area to volume ratio and slow diffusion over long distances.

Overview
Unicellular organisms (e.g., amoeba, paramecium, euglena, bacteria, yeast) consist of a single cell that must obtain food and oxygen and remove wastes directly across its cell membrane. They do not have specialized transport systems (like blood vessels); instead, all transport occurs across the cell surface and within the cell.

Main modes of transport

• Diffusion: Passive movement of molecules (such as oxygen and carbon dioxide) from a region of higher concentration to a region of lower concentration across the cell membrane. Works well because the cell is small.
• Osmosis: Diffusion of water across a selectively permeable membrane from a region of higher water concentration to lower water concentration. Important for maintaining cell volume and shape.
• Active transport: Movement of ions and molecules against their concentration gradient using energy (ATP) via membrane proteins. Helps take up nutrients present in low concentration.
• Endocytosis and exocytosis: Large particles or liquid droplets are taken in by the cell (phagocytosis/pinocytosis) forming food vacuoles; undigested wastes are expelled by exocytosis.
• Contractile vacuole: In many freshwater protozoa (e.g., amoeba, paramecium) a contractile vacuole collects excess water entering by osmosis and periodically expels it to prevent bursting (osmoregulation).
• Intracellular transport: Movement of materials inside the cell is achieved by cytoplasmic streaming and by transport vesicles (after endocytosis) so nutrients reach all parts of the cell.

Why small size matters
Unicellular organisms are small so they have a large surface area to volume (SA:V) ratio. A large SA:V ratio allows faster exchange of materials per unit volume, which is why diffusion and osmosis alone are sufficient for many unicellular life-forms.

Examples of processes in specific organisms

• Amoeba: Engulfs food by phagocytosis (forms food vacuoles), uses contractile vacuole to remove excess water; gases and small solutes diffuse across membrane.
• Paramecium: Uses cilia to create water currents that bring food into the oral groove; forms food vacuoles; contractile vacuoles expel excess water.
• Euglena: Uses cell membrane for nutrient uptake; contains chloroplasts for photosynthesis (when light is available) and can absorb food from the environment.
• Bacteria/Yeast: Transport occurs through membrane proteins (diffusion, facilitated diffusion, active transport); nutrients enter and wastes leave across the membrane.

Key points to remember

• Unicellular organisms rely mainly on diffusion, osmosis and membrane transport proteins for exchange of materials.
• Contractile vacuoles and endo/exocytosis help handle excess water and large food particles.
• Large surface area to volume ratio is essential for efficient transport.

Why transport is needed

In multicellular animals, cells are deep inside the body and far from the external environment. Simple diffusion is too slow or insufficient to supply oxygen, nutrients and to remove wastes for all cells. Therefore animals have special transport systems (fluids, tubes and pumps) to carry substances quickly to and from cells.

Basic components of a transport system

• Transport medium: a fluid that carries substances (blood or hemolymph).
• Pumping organ: a heart or hearts that move the fluid.
• Vessels or channels: tubes (blood vessels, sinuses) that direct flow.

Types of circulatory systems

• Open circulatory system: The blood (hemolymph) is not completely enclosed in vessels; it bathes organs directly in body cavities (examples: most arthropods — insects, crustaceans). Advantage: energy efficient for small or low-activity animals. Disadvantage: slower transport and less control over flow.
• Closed circulatory system: Blood stays inside vessels and is pumped by a heart through arteries, capillaries and veins (examples: annelids like earthworms, all vertebrates including fish, amphibians, reptiles, birds, mammals). Advantage: faster transport, higher blood pressure, better control of distribution.

Circulation patterns in animals

• Single circulation: Found in fishes. Blood passes through the heart once per circuit (heart → gills → body → heart).
• Double circulation: Found in amphibians, reptiles (partial separation), birds and mammals (complete separation). Blood passes through the heart twice per circuit: one loop to the lungs (pulmonary) and one loop to the body (systemic). This maintains higher pressure in the body circuit.

Human circulatory system (overview)

• Heart: A muscular pump with four chambers — two atria (upper) and two ventricles (lower). Valves prevent backflow.
• Blood vessels:
  • Arteries: carry blood away from the heart (thick muscular walls, high pressure).
  • Capillaries: microscopic vessels where exchange of gases, nutrients and wastes happens (thin walls, one cell thick).
  • Veins: carry blood toward the heart (thinner walls, valves to prevent backflow).
• Blood: A fluid connective tissue made of plasma (liquid part), red blood cells (carry oxygen using haemoglobin), white blood cells (immunity) and platelets (clotting).

How transport works in humans

Deoxygenated blood from the body enters the right atrium → right ventricle → pumped to lungs (pulmonary circulation) → blood gets oxygenated in lung capillaries → returns to left atrium → left ventricle → pumped strongly to entire body (systemic circulation). Capillaries at tissues allow exchange: oxygen and nutrients leave blood, carbon dioxide and wastes enter blood.

Other transport aspects

• Lymphatic system: collects excess tissue fluid (lymph) and returns it to blood; also has immune functions.
• Regulation: Heart rate and blood vessel diameter change to meet demands (e.g., exercise increases heart rate and blood flow to muscles).

Common health notes

Good circulation is essential. Problems include anemia (low RBCs or haemoglobin), infections, blocked vessels, high blood pressure (hypertension) and clotting disorders.

Summary

• Transport systems solve the limits of diffusion in large animals.
• Systems vary: open vs closed; single vs double circulation.
• In humans, a four-chambered heart and closed double circulation ensure efficient oxygen and nutrient delivery.

What is the circulatory system? The circulatory system (also called the cardiovascular system) is the body system that moves blood, nutrients, gases and wastes to and from the cells. Its main parts are the heart, blood and blood vessels.

Main components and their roles

• Heart: A muscular pump located in the chest. It has four chambers — two atria (upper) and two ventricles (lower) — and valves that ensure one-way flow of blood.
• Blood: A fluid tissue made of plasma (liquid), red blood cells (carry oxygen), white blood cells (fight infection), and platelets (help blood clot).
• Blood vessels: Tubes that carry blood. Arteries carry blood away from the heart (usually oxygenated), veins carry blood toward the heart (usually deoxygenated), and capillaries are tiny vessels where exchange of gases, nutrients and wastes occurs.

How blood flows (basic sequence)

Double circulation: blood goes from the heart to the lungs (pulmonary circulation) to get oxygen, returns to the heart, and then is pumped to the rest of the body (systemic circulation). A simplified flow:

Body tissues (deoxygenated blood) → right atrium → right ventricle → pulmonary artery → lungs (oxygenated) → pulmonary vein → left atrium → left ventricle → aorta → body tissues.

Key features to remember

• Four-chambered heart keeps oxygenated and deoxygenated blood mostly separate — efficient for warm-blooded animals like humans.
• Valves (tricuspid, pulmonary, mitral/bicuspid, aortic) prevent backflow of blood.
• Capillaries are the sites of exchange: oxygen and nutrients leave blood and carbon dioxide and wastes enter it.
• Blood composition by volume: plasma ~55%, red blood cells ~45%, white blood cells & platelets <1% (buffy coat).

Functions of the circulatory system

• Transport of oxygen, carbon dioxide, nutrients and wastes.
• Distribution of hormones and heat — helps regulate body temperature and internal environment.
• Protection: clotting prevents excessive blood loss; white blood cells fight infection.

Simple measurements students can relate to

• Pulse/heart rate: count beats at wrist (radial artery) or neck (carotid) for 60 seconds to get beats per minute (bpm). Resting heart rate for children may be higher than adults but typical adult resting is 60–100 bpm.
• Blood pressure: a measure of force of blood on vessel walls (recorded as systolic/diastolic in mmHg). Normal adult resting is around 120/80 mmHg (values vary by age).

Health and lifestyle links (real-life relevance): exercise strengthens the heart and improves circulation; poor diet, smoking or inactivity can cause blockages (heart disease) or high blood pressure. Anemia (low red cells/hemoglobin) reduces oxygen transport and causes tiredness.

What is blood?
Blood is a fluid connective tissue that circulates through the heart and blood vessels. It transports oxygen, nutrients, hormones and waste products, helps fight infections and controls body temperature.

Main components of blood

• Plasma (about 55% of blood volume)
  • Liquid part of blood, pale yellow in colour.
  • About 90–92% water; the rest is dissolved substances: plasma proteins (albumin, globulins, fibrinogen), electrolytes (Na+, K+, Cl–), nutrients (glucose, amino acids, lipids), gases (dissolved CO2), hormones and metabolic wastes (urea).
  • Functions: transports cells, dissolved materials, maintains blood pressure and pH, and helps in clotting (fibrinogen).
• Formed elements (cells and cell fragments, about 45% of blood volume)
  • Red blood cells (RBCs / erythrocytes)
    • About 45% of blood (this percentage is called the hematocrit).
    • Biconcave discs without nucleus (in mammals) to increase surface area for gas exchange.
    • Contain hemoglobin — an iron-containing protein that binds oxygen in lungs and releases it in tissues.
    • Typical lifespan ≈ 120 days; removed by liver and spleen.
    • Function: transport O2 from lungs to tissues and CO2 from tissues to lungs (partly).
  • White blood cells (WBCs / leukocytes)
    • Make up <1% of blood by volume (in the buffy coat).
    • Several types: neutrophils, lymphocytes, monocytes, eosinophils and basophils.
    • Function: defend the body against infection, produce antibodies, remove dead cells.
  • Platelets (thrombocytes)
    • Cell fragments that help blood clotting.
    • Also part of the buffy coat (<1% by volume).

Typical values and simple facts

• Blood is roughly 55% plasma and 45% formed elements (approximate; varies with age, sex, hydration).
• Hematocrit = percentage of blood made up of RBCs.
• Normal platelet count: ~150,000–450,000 per microlitre. Normal WBC count: ~4,000–11,000 per microlitre. Normal RBC count: ~4–6 million per microlitre (varies by sex and age).

How composition changes in everyday situations

• Dehydration: plasma volume decreases → blood becomes more concentrated (higher hematocrit).
• Infection: WBC count increases (body fights pathogens).
• Injury: platelets and plasma proteins (fibrinogen) act to form clots and stop bleeding.

Summary
Blood consists of plasma (liquid) and formed elements (RBCs, WBCs, platelets). Each component has a clear role: plasma transports, RBCs carry oxygen, WBCs defend, and platelets clot.

What is blood? Blood is a red fluid that circulates in the heart and blood vessels. It is a connective tissue made of plasma (liquid) and formed elements (red blood cells, white blood cells, and platelets).

Major components (by volume)

• Plasma: ~55% — straw-coloured liquid (water, proteins like albumin and fibrinogen, nutrients, wastes, hormones, gases).
• Red blood cells (RBCs or erythrocytes): ~45% — contain haemoglobin; carry oxygen.
• White blood cells (WBCs or leucocytes) and platelets: <1% — WBCs fight infection; platelets help clotting.

Main functions of blood

• Transport
  • Oxygen: RBCs carry O2 from lungs to all body cells (haemoglobin binds oxygen).
  • Carbon dioxide: Carried from cells to lungs for removal (dissolved, as bicarbonate, or bound to haemoglobin).
  • Nutrients: Glucose, amino acids, vitamins from intestine to cells.
  • Excretory wastes: Urea and other wastes to kidneys for removal.
  • Hormones: Chemical messengers transported from glands to target organs.
• Regulation
  • Body temperature: Distributes heat produced by cells. Vasodilation (more blood to skin) cools the body; vasoconstriction conserves heat.
  • Water balance and ion balance: Plasma helps maintain osmotic balance and electrolyte levels.
  • pH buffering: Plasma proteins and bicarbonate system help keep blood pH near 7.4.
• Protection
  • Clotting: Platelets and plasma proteins (fibrinogen → fibrin) prevent excessive blood loss when vessels are damaged.
  • Immune defence: WBCs (phagocytes, lymphocytes) destroy pathogens and produce antibodies.

How these functions work together — simple examples

• During exercise: Muscles need more O2 and nutrients. Heart rate and blood flow increase; blood carries extra oxygen and removes CO2 and heat.
• When you get a cut: Platelets form a plug and clotting factors make fibrin threads to seal the wound and stop bleeding. WBCs prevent infection.
• In infection: WBC numbers rise and antibodies produced to neutralize pathogens; fever may occur as part of a regulated immune response.

Key points to remember

• Blood transports, regulates and protects the body — making life processes possible.
• Different components have specific roles: plasma for transport and medium, RBCs for oxygen delivery, WBCs for defence, platelets for clotting.
• Healthy blood composition and flow are essential for all organs to function properly.

What is the heart?
The heart is a muscular organ that pumps blood throughout the body. It lies in the chest cavity slightly to the left of the midline and is about the size of a closed fist. The heart works like a double pump to maintain circulation.

Layers and coverings

• Pericardium: a protective sac that surrounds the heart and contains fluid to reduce friction.
• Myocardium: thick cardiac muscle layer that does the pumping.
• Endocardium: inner lining that comes in contact with blood.

Chambers of the heart
The human heart has four chambers:

• Right atrium: receives deoxygenated blood from the body via superior and inferior vena cava.
• Right ventricle: pumps deoxygenated blood to the lungs through the pulmonary artery.
• Left atrium: receives oxygenated blood from the lungs via pulmonary veins.
• Left ventricle: pumps oxygenated blood to the whole body through the aorta; its wall is the thickest because it needs to generate high pressure.

Valves and septum

• Valves: prevent backflow of blood and ensure one-way flow.
  • Atrioventricular (AV) valves: tricuspid (between right atrium and right ventricle) and bicuspid/mitral (between left atrium and left ventricle).
  • Semilunar valves: pulmonary (between right ventricle and pulmonary artery) and aortic (between left ventricle and aorta).
• Septum: muscular wall that separates right and left sides of the heart so oxygen-rich and oxygen-poor blood do not mix.

Blood flow through the heart (step-by-step)

1. Body (deoxygenated blood) → superior/inferior vena cava → right atrium.
2. Right atrium → tricuspid valve → right ventricle.
3. Right ventricle → pulmonary valve → pulmonary artery → lungs (blood gets oxygen).
4. Lungs → pulmonary veins → left atrium.
5. Left atrium → mitral valve → left ventricle.
6. Left ventricle → aortic valve → aorta → body (oxygen delivered to tissues).

Cardiac cycle and sounds
The cardiac cycle has two main phases: diastole (relaxation and filling) and systole (contraction and pumping). The normal heart makes two sounds: "lub" (closure of AV valves) and "dub" (closure of semilunar valves).

Coronary circulation
The heart itself is supplied with blood by coronary arteries that branch from the aorta. These vessels supply oxygen and nutrients to the heart muscle.

Key functional points

• Left ventricle pumps to the whole body and has the thickest muscular wall.
• Right ventricle pumps to the lungs only (shorter distance, lower pressure).
• Valves ensure unidirectional blood flow and prevent mixing of oxygenated and deoxygenated blood.
• Heartbeat is controlled by electrical signals from the sinoatrial (SA) node (natural pacemaker).

Simple analogy
Think of the heart as a two-stage water pump: the right side pumps water to the filter (lungs) and the left side pumps cleaned water to the whole house (body).

What is the heart?
The heart is a muscular organ that pumps blood throughout the body. It is roughly the size of your fist and lies slightly left of the centre of the chest. Structurally the heart has four chambers: two upper chambers called atria (right atrium and left atrium) and two lower chambers called ventricles (right and left ventricles). Valves between chambers ensure one-way flow of blood.

Pathway of blood (double circulation)
Blood follows two circuits:

• Pulmonary circulation: Right atrium → Right ventricle → Pulmonary artery → Lungs (blood gets oxygenated) → Pulmonary veins → Left atrium.
• Systemic circulation: Left atrium → Left ventricle → Aorta → Body tissues (oxygen delivered) → Venae cavae → Right atrium.

The left ventricle has thicker muscle because it must pump blood to the whole body, while the right ventricle pumps only to the lungs.

Valves and their role
Valves prevent backflow: the atrio-ventricular (AV) valves — tricuspid (right) and bicuspid/mitral (left) — sit between atria and ventricles. The semilunar valves — pulmonary and aortic — sit at the exits of the ventricles.

How the heart works (sequence)
The cardiac cycle is the sequence of events in one heartbeat. It has two main phases: systole (contraction) and diastole (relaxation).

1. Atrial systole: Atria contract, pushing blood into the relaxed ventricles through open AV valves.
2. Ventricular systole: Ventricles contract. AV valves close (this makes the first heart sound "lub"). Pressure rises; when ventricular pressure exceeds pressure in the arteries, semilunar valves open and blood is ejected into the pulmonary artery and aorta. When ventricles finish contracting and arterial pressure becomes higher than ventricular pressure, semilunar valves close (the second sound "dub").
3. Diastole (complete relaxation): Both atria and ventricles relax. Blood returns to the heart filling the atria and partially the ventricles; the AV valves open and the cycle repeats.

Timing
At rest, one cardiac cycle lasts about 0.8 seconds for a heart rate of ~75 beats per minute (bpm). The exact timing of atrial systole, ventricular systole and diastole varies with heart rate.

Control of heartbeat
Heartbeats are initiated by the sinoatrial (SA) node (natural pacemaker) in the right atrium. The impulse spreads across atria causing atrial contraction, then to the atrioventricular (AV) node and along conduction fibres to ventricles causing ventricular contraction. The autonomic nervous system (sympathetic and parasympathetic nerves) and hormones (e.g., adrenaline) modify heart rate and strength of contraction.

Sounds and clinical signs
Heart sounds "lub-dub" correspond to valve closures (AV valves then semilunar valves). The pulse felt at wrist/neck is a pressure wave generated by ventricular contraction and corresponds to heart rate.

Why this matters
Efficient cardiac cycles ensure continuous supply of oxygen and nutrients and removal of waste. Changes in rate/strength happen during exercise, rest, emotions, or disease.

What are blood vessels?
Blood vessels are tubular structures that carry blood throughout the body. They form a closed network of tubes through which the heart pumps blood to supply oxygen and nutrients to cells and remove wastes.

Types of blood vessels

• Arteries: Carry blood away from the heart. Walls are thick, elastic and muscular to withstand high pressure. They have a relatively small lumen and no valves. Most carry oxygenated blood, except the pulmonary artery which carries deoxygenated blood to the lungs.
• Veins: Carry blood toward the heart. Walls are thinner and less elastic, lumen is wider. Many veins (especially in limbs) have valves to prevent backflow. Most carry deoxygenated blood, except the pulmonary vein which carries oxygenated blood from the lungs.
• Capillaries: Extremely thin walled (one cell thick) and very narrow. They connect arterioles and venules and form dense networks in tissues. Their thin walls allow exchange of gases, nutrients and wastes between blood and body cells.

Structure and function summary

• Artery walls: outer connective tissue, middle thick muscle and elastic layer, inner endothelium. Function: carry blood at high pressure and maintain pulse.
• Vein walls: thinner muscle layer, larger lumen, valves in many veins. Function: return blood to heart at lower pressure; valves help against gravity.
• Capillary walls: single layer of endothelial cells. Function: exchange of oxygen, carbon dioxide, glucose, salts and waste products by diffusion and filtration.

How they work together
Blood is pumped from the heart into arteries, then into smaller arterioles, then into capillary networks where exchange occurs, then into venules and veins to return to the heart. Blood pressure falls as blood moves from arteries to veins. The total cross-sectional area of all capillaries is very large, which slows blood flow and maximizes exchange.

Important notes and exceptions
Most arteries carry oxygen-rich blood and most veins carry oxygen-poor blood, but exceptions are the pulmonary artery and pulmonary vein. Valves are normally found in veins and in the heart, not in arteries.

Common disorders related to blood vessels
Varicose veins (dilated, twisted veins due to valve failure), atherosclerosis (narrowing of arteries by fatty deposits), hypertension (high blood pressure) and thrombosis (blood clots) are conditions that affect blood vessels and circulation.

What is lymph?

Lymph is a clear to pale yellow fluid that circulates through the lymphatic system. It is formed from the fluid that leaks out of blood capillaries into the spaces between cells (interstitial fluid). When some of this interstitial fluid enters lymphatic vessels, it is called lymph.

How is lymph formed?

• Blood plasma leaks out of the thin walls of capillaries into the surrounding tissue because of blood pressure. Most of this fluid returns to blood capillaries, but a portion remains as interstitial fluid.
• Some interstitial fluid enters blind-ended lymphatic capillaries; once inside these vessels it is called lymph.

Composition of lymph

• Mostly water
• Small amounts of dissolved salts and proteins (fewer proteins than blood plasma)
• White blood cells (mainly lymphocytes)
• Fats absorbed from the small intestine (in the form of chyle) after a fatty meal

Structure of the lymphatic system

• Lymphatic capillaries — tiny, blind-ended vessels that collect interstitial fluid.
• Larger lymphatic vessels — have valves to prevent backflow and move lymph toward the chest.
• Lymph nodes — small, bean-shaped structures located along lymphatic vessels that filter lymph and are centres for immune cells.
• Other lymphoid organs — tonsils, spleen, thymus and Peyer's patches in the intestine play roles in immunity and blood filtration.
• Major drainage — lymph ultimately drains into large veins (subclavian veins) near the heart and rejoins the blood circulation.

How lymph flows

• There is no central pump. Lymph moves slowly due to: contraction of nearby skeletal muscles, breathing movements (pressure changes in the chest), and valves in lymphatic vessels that prevent backflow.
• Physical activity increases lymph flow; immobility can slow it and lead to swelling.

Functions of lymph and the lymphatic system

• Returns excess tissue fluid and leaked plasma proteins back to the blood, helping maintain fluid balance.
• Transports absorbed fats from the small intestine (via lacteals) to the bloodstream.
• Defence against infections: lymph carries pathogens to lymph nodes where immune cells (lymphocytes, macrophages) trap and destroy them.
• Filters and removes cellular debris and foreign particles.

Clinical and everyday relevance

• Swollen, tender lymph nodes (e.g., in the neck) are a common sign of infection — nodes enlarge as immune cells multiply.
• Edema (swelling) can occur if lymphatic drainage is blocked (for example, after surgery, injury, or in diseases such as elephantiasis).
• Tonsillitis is inflammation of lymphoid tissue (tonsils) in the throat; they trap pathogens entering via mouth or nose.

Summary (flow diagram to include in visuals)

Blood plasma → some becomes interstitial fluid → part re-enters blood capillaries, rest enters lymphatic capillaries → lymphatic vessels → lymph nodes (filtering) → larger lymphatic ducts → subclavian veins → returns to blood.

Why transport is needed: Plants need a continuous supply of water, mineral salts and dissolved gases to every cell for photosynthesis, growth and metabolism. They also need to move the sugars produced in leaves to growing parts and storage organs. Because many plants are large and multicellular, diffusion alone is not sufficient; specialised transport tissues and mechanisms are required.

Main transport tissues:

• Xylem: Carries water and dissolved mineral salts from roots to stems and leaves. Made of vessels, tracheids and xylem fibres. Transport is generally unidirectional (root → shoot).
• Phloem: Transports organic nutrients (mainly sucrose) from leaves (sources) to roots, fruits and growing tissues (sinks). Made of sieve tube elements and companion cells. Transport (translocation) can be bidirectional depending on source–sink relations.

How roots absorb water and minerals: Root hair cells increase surface area and absorb water by osmosis (movement of water from higher to lower water potential) and take up mineral ions by active transport (using energy). Water moves across cortex by cell-to-cell, vacuolar or apoplast pathways and reaches the xylem.

Ascent of sap (water movement up the plant): The main driver is transpiration pull, explained by the cohesion–tension theory. Water evaporating from leaf air spaces (transpiration) creates negative pressure (tension) in the leaf xylem. Cohesion between water molecules and adhesion to xylem walls transmits this tension down to the roots, pulling a continuous column of water upward. Other supporting forces include capillarity (in narrow vessels) and root pressure (minor, pushes water up slightly).

Transpiration: Loss of water vapour from aerial parts, mainly through stomata (stomatal transpiration), and to a lesser extent through cuticle (cuticular) and lenticels (lenticel transpiration). Transpiration is important because it helps cool the plant, creates transpiration pull for water transport and enables mineral uptake, but excessive loss can cause wilting.

Transport of food (translocation): Sugars produced in leaves are loaded into phloem sieve tubes at source regions. According to the pressure-flow (mass flow) hypothesis, accumulation of solutes at the source lowers the osmotic potential, drawing water into phloem from xylem and creating high turgor pressure. At sink regions (growing organs or storage tissues) solutes are removed, water leaves phloem, lowering pressure there. The resulting pressure gradient drives bulk flow of sap from source to sink.

Factors affecting transport: Transpiration and water transport are influenced by light (opens stomata), temperature (increases evaporation), humidity (inverse effect), wind (increases evaporation), soil water availability (limits uptake), and stomatal behaviour (open/closed). Phloem transport depends on photosynthesis rate (sugar production) and sink strength (demand).

Summary: Transport in plants relies on specialised tissues (xylem and phloem) and physical mechanisms (osmosis, transpiration pull, cohesion–tension, pressure-flow). These systems keep water, minerals and food moving to support life processes throughout the plant.

What is xylem? Xylem is the vascular tissue in plants that conducts water and dissolved minerals from roots to stems and leaves and provides mechanical support. It is one of the two types of vascular tissues; the other is phloem.

Where is xylem found? Xylem is present in roots, stems and leaves as part of vascular bundles. In stems it lies toward the inner side of the bundle.

Structure (cell types and features)

• Xylem vessels (vessel elements): Long, tubular cells joined end to end with perforated end walls to form continuous tubes. Walls are thickened with lignin in patterns such as annular, spiral, or pitted. Found mainly in angiosperms. Cells are dead at maturity and lack protoplasm.
• Tracheids: Long, tapered cells with thick lignified walls and pits for lateral water movement. Present in all vascular plants and are the main water-conducting cells in gymnosperms.
• Xylem parenchyma: Living cells that store food and help in lateral transport of water and minerals.
• Xylem fibers: Thick-walled cells that provide mechanical strength.

Key structural features that help function

• Lignified walls prevent collapse under tension and give strength.
• Continuous tubular arrangement of vessels/tracheids allows efficient long-distance water flow.
• Pits permit water movement between adjacent elements.
• Most conducting elements are dead, providing hollow conduits with low resistance.

How xylem transports water and minerals

1. Absorption at roots: Root hairs absorb water and minerals from soil. Water enters root xylem via apoplast and symplast pathways.
2. Ascent of sap: Water moves upward through xylem vessels and tracheids. Main driving forces are:

• Transpiration pull (cohesion-tension mechanism): Water evaporating from leaf stomata creates a negative pressure (tension) in leaf air spaces. Cohesion between water molecules and adhesion to cell walls transmits this pull down the continuous water column in xylem, pulling water up from roots.
• Root pressure: Osmotic uptake of water into root xylem can push water upward a short distance, usually at night or when transpiration is low.
• Capillary action: Adhesion and small diameter of xylem elements help draw water up small distances, but this is a minor effect in tall plants.

Other functions of xylem

• Mechanical support because of lignified walls and fibers.
• Storage of water and food in xylem parenchyma.

Direction of flow Water and dissolved minerals move mostly unidirectionally from roots to leaves. Organic food is transported in phloem in both directions.

Simple experimental evidence If a cut stem is placed in colored water, colored solution appears in petals and leaves, showing that vessels conduct water. Removing bark (phloem) kills the upper part because sugars cannot move downward, but xylem continues to supply water temporarily.

What is phloem?
Phloem is the living vascular tissue in plants that transports organic nutrients (mainly sugars produced by photosynthesis) from leaves (sources) to other parts of the plant (sinks) such as roots, growing shoots, flowers and storage organs. This downward and upward transport of food is called translocation.

Structure of phloem
Phloem is a complex tissue made of several types of cells arranged together. Main components:

• Sieve tube elements (sieve tubes) — elongated living cells joined end to end. Their end walls have perforations called sieve plates that allow flow of phloem sap. Sieve tube cells have very little cytoplasm and, at maturity, often lack a nucleus.
• Companion cells — closely associated with sieve tubes via many plasmodesmata. They have a dense cytoplasm and a nucleus and help load and unload sugars into sieve tubes and maintain the metabolism of sieve-tube elements.
• Phloem parenchyma — cells that store food and help lateral transport.
• Phloem fibres (sclerenchyma) — provide mechanical support and protection.

In cross sections of stems and leaves, phloem is found in vascular bundles along with xylem. In stems phloem is usually located toward the outer side of the xylem.

How phloem works — Pressure-flow (Münch) hypothesis, simple steps

• Sugar loading: At the source (leaf), sucrose is actively transported into companion cells and then into sieve tubes. This raises the solute concentration inside sieve tubes at the source.
• Water influx and pressure build-up: Water moves into sieve tubes from adjacent xylem by osmosis, increasing hydrostatic pressure at the source.
• Bulk flow: The pressure difference between source (high pressure) and sink (low pressure) pushes phloem sap through sieve tubes toward sinks.
• Sugar unloading: At the sink, sugars are actively or passively removed from the sieve tubes into sink cells (roots, fruits, growing tips). Water then returns to xylem or is used by sink tissues, lowering pressure at the sink.

Key features of phloem transport

• Transport is typically from source to sink and can be upward or downward depending on where sugars are needed.
• Phloem transport is a living process and often requires metabolic energy (ATP) for loading and unloading of sugars.
• Phloem sap contains sugars (mainly sucrose), amino acids, hormones, and sometimes viruses and other organic molecules.

Importance
Phloem supplies energy and carbon skeletons to non-photosynthetic parts, supports growth of buds and roots, helps fill fruits and storage organs (e.g., tubers), and distributes signalling molecules (hormones) throughout the plant.

Comparison with xylem (brief)
Xylem transports water and minerals from roots to shoots (mostly passive, upward), is made of dead cells (tracheids, vessels). Phloem transports food (organic solutes) in living cells and transport can be in either direction depending on source and sink.

What is ascent of sap?
Ascent of sap means the upward movement of water and dissolved minerals (sap) from the roots to all parts of a plant, especially the stem and leaves, through the xylem vessels.

Why it is important
Plants need continuous supply of water for photosynthesis, transport of minerals, cell turgor and cooling. Water moves from soil → roots → stem → leaves where it is used or lost by transpiration.

How it happens — main mechanisms

• Transpiration pull (Cohesion–Tension theory): Evaporation of water from leaf surfaces (transpiration) creates a negative pressure (tension) in the leaf xylem. Because water molecules are cohesive (stick to each other) and adhesive (stick to xylem walls), they form an unbroken column that is pulled up from roots to leaves. This is the primary mechanism that explains how water can rise to great heights in tall trees.
• Root pressure: When root cells actively take up minerals from soil, water follows by osmosis into the xylem, generating a small positive pressure that can push sap upward a short distance. Root pressure is stronger at night or when transpiration is low. It can cause guttation (droplets on leaf edges).
• Capillarity: Narrow xylem vessels cause capillary rise due to adhesion between water and vessel walls and surface tension. Capillary action alone can lift water only a few centimetres and cannot explain ascent in tall plants, but it helps near the base.

Supporting features of xylem
Xylem vessels are long, narrow tubes with lignified walls that prevent collapse under tension. Their continuity, narrow diameter and smooth walls favour formation of continuous water columns and efficient upward flow.

Evidence for transpiration pull
Cut a stem and you may see continuous sap flow out under some conditions; experiments (potometer, colored-water uptake in celery) show water loss from leaves correlates with water uptake at the stem base. Guttation demonstrates root pressure at low transpiration.

Factors affecting rate of ascent
Light (increases transpiration), temperature (increases), wind (increases), humidity (high humidity decreases transpiration), soil water availability (limits supply), leaf area, and stomatal opening.

Simple measurement idea
Transpiration rate can be measured by mass loss of a potted plant or by water uptake in a potometer; water uptake roughly equals transpiration when growth and storage are small.

Definition: Transpiration is the loss of water vapour from the aerial parts of plants, mainly through tiny pores called stomata on the leaves. It is a continuous process that helps pull water and dissolved minerals from the roots to the leaves.

Where it occurs:

• Stomatal transpiration (major): through stomata on leaves.
• Cuticular transpiration: through the waxy cuticle (minor).
• Lenticular transpiration: through lenticels on stems (very small).

How it happens (simple mechanism):

1. Roots absorb water from soil by osmosis into root hairs and xylem vessels.
2. Water moves upward in xylem due to transpiration pull (cohesion and adhesion of water molecules).
3. In the leaf, water evaporates from the moist cell walls of mesophyll into the air spaces.
4. Water vapour diffuses out through open stomata into the atmosphere.

Importance of transpiration:

• Creates a transpiration pull that helps transport water and minerals from roots to leaves.
• Helps cool leaves and whole plant (like sweating in animals).
• Mantains cell turgor and drives nutrient flow required for growth.

Factors affecting transpiration: light (opens stomata), temperature (increases evaporation), humidity (high humidity reduces transpiration), wind (removes humid layer, increases transpiration), soil water availability, leaf area and stomatal number/opening.

Distinction: Transpiration is loss of water vapour; do not confuse with guttation, which is liquid water exuded from leaf edges under special conditions.

Simple classroom demonstration: Cover one leaf side with petroleum jelly (vaseline) or nail polish to block stomata and compare water loss with an uncovered leaf; or use a potometer to measure water uptake as an estimate of transpiration.

Transpiration is the loss of water vapour from plant parts, mainly leaves. Most transpiration occurs through stomata (tiny pores) and to a lesser extent through the cuticle and lenticels. The rate of transpiration depends on several environmental and plant factors that affect evaporation and stomatal opening.

Main factors and how they affect transpiration

• Light: Light makes stomata open (guard cells become turgid). More light → more stomata open → higher transpiration. Transpiration is low at night because stomata close.
• Temperature: Higher temperature increases the kinetic energy of water molecules and reduces relative humidity near the leaf, so transpiration increases with temperature (up to a limit).
• Humidity (moisture in air): When air humidity is high, the water vapour concentration difference between leaf interior and air is small, so transpiration decreases. Low humidity increases transpiration.
• Wind / air movement: Air movement removes the moist layer around the leaf (boundary layer). Faster wind → faster removal → increased transpiration (until stomatal control or water supply limits it).
• Soil water availability: If soil is dry, plant water potential falls, guard cells lose turgor, stomata close and transpiration decreases. Adequate soil water allows sustained transpiration.
• Leaf surface area and structure: Larger leaf area → larger surface for evaporation → greater transpiration. Thick cuticles, waxy surfaces, hairs, or reduced leaf area (adaptations in xerophytes) reduce transpiration.
• Number and behaviour of stomata: More stomata per unit area or wider stomatal opening increases transpiration. Different species have different stomatal densities and behaviours.
• Time of day / season: Transpiration generally peaks during the day (midday) when light and temperature are high and falls at night. Seasonal changes (dry season vs rainy season) also affect rates.

Mechanism (brief): Water moves from soil → roots → xylem → leaves due to a continuous column of water and transpiration pull. Evaporation from mesophyll cells creates negative pressure that pulls water upward. Factors above change how fast water evaporates from the leaf surface or how open stomata are.

Simple classroom methods to observe effects: Use potted plants or cut shoots with a potometer to compare mass loss or water uptake under different light, temperature, humidity, or wind conditions.

What is translocation? Translocation is the movement of organic solutes (mainly sugars like sucrose), amino acids and other nutrients through the phloem from regions of production or storage (called sources) to regions of use or storage (called sinks).

Phloem structure (brief): Phloem is made of sieve tube elements (long cells joined end-to-end with sieve plates) and companion cells. Sieve tubes transport the sap; companion cells help load and unload sugars and maintain the sieve tubes.

How translocation happens — Pressure‑flow (Mass flow) hypothesis (simple steps):

• At the source (e.g., photosynthesizing leaf), sugars are actively loaded into phloem sieve tubes. This raises the solute concentration inside the sieve tubes near the source.
• Water moves osmotically from surrounding xylem into the phloem because of higher solute concentration, increasing the hydrostatic (turgor) pressure in the phloem at the source.
• At the sink (e.g., growing root, fruit or storage organ), sugars are unloaded from the phloem into sink cells for respiration or storage. Solute concentration in the phloem near the sink becomes lower.
• Water leaves the phloem (often back to xylem) where solute concentration is lower, lowering the pressure at the sink.
• The resulting pressure difference (high at source, low at sink) drives bulk flow of phloem sap from source to sink through the sieve tubes.

Key points:

• Movement in phloem is generally from source to sink and can be upward, downward or lateral depending on plant needs.
• Translocation is an active process because sugars are actively loaded and unloaded (requires energy).
• The flow is continuous and can change with plant activity (e.g., growth, fruiting, season).

Evidence and experiments: Girdling (removing a ring of bark including phloem) causes sugars to accumulate above the girdle and stops sugar reaching the roots. Radioactive carbon experiments (using 14C-labelled CO2) show movement of labelled sugars from leaves to sinks, supporting the pressure‑flow idea.

Factors affecting translocation: rate of photosynthesis (sugar production), temperature (affects respiration and membrane transport), water availability (affects osmotic water flow), activity of companion cells (energy for loading/unloading), and developmental stage (growing fruits are strong sinks).

Importance: Supplies energy and building blocks to growing parts, stores food in roots/bulbs/seeds, and helps in healing and storage functions of plants.

Comparison with xylem transport: Xylem moves water and minerals mainly upward by transpiration pull and root pressure (passive). Phloem moves organic solutes in any direction between sources and sinks and requires metabolic energy for loading/unloading.

Diffusion is the movement of particles (atoms, ions or molecules) from a region of higher concentration to a region of lower concentration until they are evenly spread (equilibrium). It is a passive process (requires no energy) and happens because particles move randomly. Common classroom demonstrations: a drop of ink or potassium permanganate in water, or perfume spreading in a room.

Key points about diffusion:

• Direction: from high concentration to low concentration.
• Stops when concentrations become equal (equilibrium).
• Occurs in gases, liquids and (slowly) in solids.
• Affected by temperature (higher temperature → faster diffusion), concentration difference (larger difference → faster), and distance/path length (shorter distance → faster).

Osmosis is a special type of diffusion of water (solvent) through a semipermeable membrane from a region of lower solute concentration (more water) to a region of higher solute concentration (less water). The membrane allows water to pass but not the solute particles. Osmosis is also passive and continues until the concentration difference is balanced or pressure (osmotic pressure) stops net flow.

Key points about osmosis:

• Requires a semipermeable membrane.
• Water moves toward the side with higher solute concentration.
• Causes swelling (turgidity) of plant cells in dilute solutions and shrinkage (plasmolysis) in concentrated solutions.
• Important in living systems: plant root water uptake, water balance in animal cells, absorption of water by root hairs, and movement of water in and out of cells.

Differences (short): Diffusion applies to any substance moving down its concentration gradient; osmosis is specifically the movement of water across a semipermeable membrane.

Overview: "Experiments and Practical Observations" in the chapter Transportation in Animals and Plants deals with simple hands‑on activities that show how water, minerals and food are moved in plants and how blood and other fluids are transported in animals. These experiments help observe transpiration, absorption by roots, movement through xylem and phloem, and circulation-related changes (for example, pulse rate).

Key practicals and what they show:

1. Coloured water and cut stem (celery/white carnation) experiment: Place a fresh celery stalk or white carnation in water coloured with food dye. Observation: After a few hours to a day, coloured streaks appear in the stem and coloured spots in the petals/leaves. Interpretation: Water moves upward through xylem vessels, visually proving xylem transport (transpiration stream).
2. Transpiration demonstration with a plastic bag: Cover a leafy twig with a transparent plastic bag and seal it at the stem. Leave for a few hours in sunlight. Observation: Water droplets collect inside the bag. Interpretation: Water lost by leaves (transpiration) evaporates and condenses on the bag surface; stomata are the main exit points for water vapour.
3. Wilting and recovery (transpiration vs water supply): Keep one potted plant without water and another well-watered under the same conditions. Optionally, keep a wilted plant in shade or water it. Observation: The unstressed plant wilts; watering and providing cooler/shaded conditions restores turgor. Interpretation: Loss of turgor due to reduced water in cells causes wilting; transpiration and water uptake balance determines plant water status.
4. Stomata observation: Peel the lower epidermis of a leaf (e.g., Tradescantia) or use a clear nail-polish peel and view under a microscope. Observation: Kidney-shaped guard cells surrounding pores (stomata). Interpretation: Stomata open and close to regulate gas exchange and transpiration.
5. Transpiration rate experiments (simple mass method): Take similar potted plants or leafy shoots, subject each to different conditions (light vs dark, wind vs still, humid vs dry). Measure mass loss of pot+plant or water loss from cut shoot at fixed intervals. Observation: Higher water loss in light, wind, and dry air; lower in humid or dark conditions. Interpretation: Transpiration increases with light, temperature and wind, decreases with humidity and darkness.
6. Capillary action demo: Dip one end of a narrow glass tube or a strip of blotting paper into water containing dye. Observation: Water rises up the tube or along the paper against gravity. Interpretation: Adhesion and cohesion (capillary forces) help water rise in narrow xylem vessels.
7. Root hair absorption (simple observation): Germinate seeds on moist filter paper and observe root hairs under a microscope. Observation: Fine root hairs increase surface area. Interpretation: Root hairs increase water and mineral absorption from soil.
8. Pulse and exercise experiment (transport in animals): Measure your resting pulse (beats per minute) by feeling the radial pulse for 15 seconds and multiplying by 4. Then do light exercise (e.g., climb stairs for 2 minutes) and measure again. Observation: Pulse rate increases after exercise and gradually returns to resting rate. Interpretation: Muscles need more oxygen and nutrients during activity; heart pumps faster to transport these through blood.

How to record and interpret results: For quantitative experiments, record initial and final values (mass of plant/pot, volume of water, pulse counts) at set time intervals. Plot data (time on x-axis, water loss or pulse on y-axis) to compare treatments. Always include a control (for example, a plant in shade) and repeat trials for reliability.

Safety & tips: Use fresh cuttings for dye experiments; avoid damaging stem ends excessively. When observing stomata, handle glass slides and microscopes carefully. For pulse experiments, ensure mild exercise only and stop if you feel unwell.

Overview

Transport in living organisms means movement of water, minerals and food in plants and movement of gases, nutrients and wastes in animals. Different organisms have special structural and functional adaptations that make transport efficient according to their size, habitat and activity level.

Adaptations in Plants

• Root hairs: Long, thin extensions of root epidermal cells that increase surface area for water and mineral absorption from soil.
• Xylem vessels: Dead, tubular cells joined end-to-end forming continuous channels to carry water and dissolved minerals from roots to leaves. Their thick lignified walls provide strength (help in tall plants).
• Phloem (sieve tubes and companion cells): Living cells that transport sugars from leaves to growing parts and storage organs (translocation). Companion cells help load and unload sugars.
• Transpiration and cohesion-tension: Evaporation of water from leaf stomata (transpiration) creates a negative pressure that pulls water up the xylem. Cohesion (water molecules stick together) and adhesion (stick to xylem walls) help maintain a continuous water column.
• Leaf adaptations: Xerophytes (cactus) have thick cuticle, reduced leaves (spines), sunken stomata and many stomatal hairs to reduce water loss. Hydrophytes (water lilies) have large air spaces and flat leaves to float and exchange gases easily.
• Vascular bundle arrangement: In stems and roots, arrangement and number of vascular bundles give mechanical support and efficient transport.

Adaptations in Animals

• Simple organisms (amoeba, hydra): Very small or thin bodies so gases and food can move by diffusion across the body surface—no specialized transport system needed.
• Insects: Tracheal system—network of air-filled tubes (tracheae) that deliver oxygen directly to tissues; spiracles regulate airflow and reduce water loss.
• Earthworms: Closed circulatory system with blood confined to vessels (dorsal and ventral vessels) and heart-like muscular segments (aortic arches) to pump blood; blood contains respiratory pigments for oxygen transport.
• Fish: Gills with thin lamellae and large surface area perform gas exchange in water; counter-current flow of water and blood increases oxygen uptake.
• Amphibians: Use skin, lungs and mouth lining for gas exchange; partially divided heart supports mixed circulation.
• Birds and mammals: Double circulatory system (separate pulmonary and systemic circuits) and four-chambered heart ensure efficient oxygen delivery to meet high metabolic demands; lungs have adaptations (alveoli in mammals, air sacs and parabronchi in birds) for high gas exchange efficiency.
• Blood vessels and valves: Arteries have thick muscular walls for high pressure, veins have valves to prevent backflow and thin walls, capillaries are thin-walled for exchange between blood and tissues.

Why these adaptations matter

Small organisms rely on diffusion because it is efficient only over short distances. Larger or more active organisms need specialised pumps (hearts), vessels and respiratory structures to move materials fast enough to meet cellular needs.

Transportation in animals and plants is the movement of substances (water, minerals, gases, nutrients, hormones, wastes) from one part to another. It is essential for survival because it supplies cells with what they need, removes wastes, supports growth and reproduction, helps in temperature regulation and defence, and maintains internal balance (homeostasis).

Importance in animals

• Supplies oxygen and nutrients to all body cells and removes carbon dioxide and metabolic wastes, enabling respiration and energy release.
• Transports hormones that coordinate growth, development and responses to environment.
• Helps in immune defence by transporting white blood cells and antibodies.
• Maintains body temperature and fluid balance (blood circulates heat and plasma carries water and salts).

Importance in plants

• Xylem transports water and dissolved minerals from roots to leaves; water is needed for photosynthesis and turgor pressure.
• Phloem transports food (sugars) from leaves to growing regions and storage organs (roots, fruits).
• Transpiration (loss of water vapour) creates a pull that helps move water up tall plants and cools the plant surface.
• Transport systems help distribute plant hormones that control flowering, fruiting and responses to stress.

Applications (how this knowledge is used)

• Medicine: understanding blood circulation enables treatments such as blood transfusions, IV fluids, dialysis, heart surgery, pacemakers and design of artificial organs.
• Agriculture and horticulture: grafting uses knowledge of xylem and phloem; irrigation (drip, sprinkler) is planned using transpiration rates; nutrient solutions in hydroponics replace soil transport.
• Greenhouse and crop management: controlling humidity, light and temperature to manage transpiration and improve water use efficiency and yield.
• Environmental monitoring: measuring transpiration and water uptake helps schedule watering and conserve water in drought-prone areas.
• Food storage and transport: knowing phloem transport and ripening hormones (like ethylene) helps control fruit ripening during storage and shipping.