Transport in Living Things

🟢 Lite — Quick Review (1h–1d)

Rapid summary of transport systems for NABTEB biology.

Living organisms need transport systems to move materials (nutrients, oxygen, waste) to and from all cells, since simple diffusion is too slow for large organisms.

In Humans — The Circulatory System:

The human circulatory system is a double circulation system:

• Pulmonary circulation: Heart → Lungs → Heart (collects oxygen, removes carbon dioxide)
• Systemic circulation: Heart → Body → Heart (delivers oxygen, collects waste)

The Heart:

• Four chambers: Right atrium, right ventricle, left atrium, left ventricle
• Right side pumps deoxygenated blood to lungs
• Left side pumps oxygenated blood to body
• The left ventricle has the thickest wall (pumps blood furthest — around entire body)
• Heart rate: 60–80 beats per minute at rest
• Cardiac output = stroke volume × heart rate

Blood Vessels:

Vessel	Function	Structure
Arteries	Carry blood away from heart	Thick elastic walls
Veins	Carry blood to heart	Thin walls, valves present
Capillaries	Exchange materials	One cell thick, walls permeable

Blood Composition:

• Plasma (55%): Water, dissolved nutrients, waste, hormones, proteins
• Red blood cells (RBCs): Carry oxygen using haemoglobin; no nucleus (biconcave shape increases surface area)
• White blood cells (WBCs): Part of immune system; some produce antibodies
• Platelets: Cell fragments; essential for blood clotting

Blood Groups:

• ABO system: A, B, AB, O
• Rh factor: Positive (+) or Negative (−)
• O negative is the universal donor; AB positive is the universal recipient

⚡ NABTEB Exam Tip: Arteries have thick walls because blood is under high pressure (pumped directly from the heart). Veins have valves to prevent backflow of blood. These are the most commonly tested distinguishing features.

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🟡 Standard — Regular Study (2d–2mo)

For NABTEB students who want thorough understanding of transport systems.

The Cardiac Cycle:

The heart beats in a coordinated sequence:

1. Diastole — Heart relaxes, blood fills the atria and ventricles
2. Atrial systole — Atria contract, forcing blood into ventricles
3. Ventricular systole — Ventricles contract, forcing blood out (left ventricle contracts first, then right)
4. Cardiac cycle — The whole sequence repeats ~72 times per minute

Blood Pressure:

• Systolic pressure (higher): when ventricles contract — normal ~120 mmHg
• Diastolic pressure (lower): when ventricles relax — normal ~80 mmHg
• Written as 120/80 mmHg

Blood Clotting:

When blood vessels are damaged:

1. Platelet plug forms at injury site
2. Thrombokinase enzyme is released
3. Prothrombin → Thrombin (catalysed by thrombokinase + Ca²⁺)
4. Thrombin converts fibrinogen → Fibrin threads
5. Fibrin threads form a mesh that traps blood cells
6. Clot forms, preventing further blood loss

Vitamin K is needed for the synthesis of prothrombin and fibrinogen.

Transport in Plants:

Plants have two transport systems:

1. Xylem — transports water and minerals (root to leaves)

   • Made of dead cells
   • Vessel elements and tracheids
   • Water moves upward by transpiration pull (cohesion-tension theory)

2. Phloem — transports dissolved sugars (leaves to all parts)

   • Made of living cells
   • Sieve tube elements and companion cells
   • translocation

Transpiration:

• Loss of water vapour from plant leaves through stomata
• Creates suction force that pulls water up through xylem
• Rate increases with: higher temperature, lower humidity, stronger wind, more sunlight
• Rate decreases with: stomata closing (at night, in drought)

The cohesion-tension theory:

• Water molecules stick together (cohesion) due to hydrogen bonding
• Water column is pulled upward by surface tension at evaporating surfaces
• Adhesion to xylem walls helps prevent breakage

⚡ NABTEB Exam Tip: Don’t confuse xylem and phloem. Xylem transports water UP (think “xylem = water = upward”). Phloem transports sugars (food) in ALL directions.

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🔴 Extended — Deep Study (3mo+)

Comprehensive coverage of transport for thorough NABTEB preparation.

Detailed Heart Structure:

Chambers:

• Right atrium: Receives deoxygenated blood from body via superior and inferior vena cava
• Right ventricle: Pumps blood to lungs via pulmonary artery (only artery carrying deoxygenated blood)
• Left atrium: Receives oxygenated blood from lungs via pulmonary veins (only veins carrying oxygenated blood)
• Left ventricle: Pumps blood to body via aorta (thickest wall — works hardest)

Valves:

• Tricuspid valve: Between right atrium and right ventricle (3 flaps)
• Bicuspid (mitral) valve: Between left atrium and left ventricle (2 flaps)
• Semilunar valves: Aortic valve (left ventricle-aorta) and pulmonary valve (right ventricle-pulmonary artery)

Valves prevent backflow of blood during the cardiac cycle.

Coronary Circulation: The heart muscle itself needs oxygen and nutrients. Coronary arteries branch from the aorta and supply the heart wall. Blockage leads to heart attack.

The Lymphatic System:

A secondary transport system that:

• Returns excess tissue fluid to the bloodstream
• Absorbs fats from the small intestine (via lacteals in villi)
• Plays a role in immunity (lymphocytes in lymph nodes)

Circulatory Patterns in Different Organisms:

Organism	Circulatory System	Features
Single-celled	None	Diffusion directly with environment
Hydra	None	Gastrovascular cavity distributes nutrients
Earthworm	Closed	Blood travels in vessels; 5 hearts/aortic arches
Fish	Single	2-chambered heart; 1 circuit; blood flows to gills then body
Mammals	Double	4-chambered heart; pulmonary + systemic circuits

Translocation (Phloem Transport):

Unlike xylem (passive), phloem transport requires energy:

• Sugar is actively loaded into phloem sieve tubes at source (leaves)
• Water follows by osmosis, increasing pressure
• Sugar is actively unloaded at sink (roots, fruits, growing regions)
• Pressure flow hypothesis explains movement

Mineral Ion Transport in Plants:

Mineral ions are absorbed by root hairs through:

• Active transport: Requires ATP; against concentration gradient
• Passive diffusion: Along concentration gradient

Ions may also move in xylem with the transpiration stream.

Water Potential:

Water moves from high water potential to low water potential:

• Pure water: 0 kPa
• Solutions: negative values
• Root hair cells have lower water potential than soil (due to dissolved minerals) — water enters by osmosis

Calculations — Blood:

Blood clotting time: 3–8 minutes (if time is much longer, could indicate haemophilia or vitamin K deficiency)

Heart Rate Factors:

• Exercise increases heart rate (to deliver more oxygen to muscles)
• Emotions (fear, excitement) increase heart rate (adrenaline release)
• Athletes have lower resting heart rate (more efficient heart)

Disorders of the Circulatory System:

1. Atherosclerosis: Fatty deposits (plaques) in arteries; increases blood pressure
2. Hypertension: Chronically elevated blood pressure (>140/90 mmHg)
3. Heart attack: Blocked coronary artery; part of heart muscle dies
4. Stroke: Blocked or burst blood vessel in the brain
5. Varicose veins: Veins become swollen due to faulty valves

⚡ NABTEB Quick Reference:

• Double circulation: pulmonary + systemic circuits
• 4 heart chambers: RA, RV, LA, LV
• Arteries: thick walls, no valves (except semilunar in heart)
• Veins: thin walls, have valves
• Capillaries: 1 cell thick, exchange site
• Xylem: water + minerals; UP only
• Phloem: sugars; ALL directions
• Transpiration pull: cohesion-tension theory
• Blood groups: ABO + Rh
• Platelets: blood clotting