3.1 Transport System in Organisms
A transport system is essential in complex organisms to transport nutrients, oxygen, water, and excretory products to and from body cells.
Comparison Between Simple and Complex Organisms
- Simple Organisms (e.g., Amoeba, Paramecium, Hydra): Do not possess a specialized transport system. Their small size provides a large surface area-to-volume ratio (SA/V), allowing oxygen and nutrients to diffuse directly across their plasma membranes from the environment into cells.
- Complex Organisms (e.g., Humans, Animals, Vascular Plants): Have a small surface area-to-volume ratio (SA/V), making direct diffusion through outer layers insufficient. They require a specialized transport system (circulatory/vascular system) to reach inner tissues.
3.2 Blood Circulatory System in Humans
The human circulatory system is a closed double circulatory system comprising the heart, blood vessels, and blood.
Structure and Function of the Human Heart
The human heart consists of four chambers: two upper atria (singular: atrium) and two lower ventricles.
- Right Atrium: Receives deoxygenated blood from the upper and lower body via the vena cava.
- Right Ventricle: Pumps deoxygenated blood to the lungs via the pulmonary artery.
- Left Atrium: Receives oxygenated blood from the lungs via the pulmonary vein.
- Left Ventricle: Has the thickest muscular wall to pump oxygenated blood to the rest of the body via the aorta under high pressure.
- Valves: Prevent the backflow of blood (Tricuspid valve on the right side, Bicuspid/Mitral valve on the left side, and Semilunar valves at the bases of the aorta and pulmonary artery).
- Septum: Muscular wall separating the left and right sides to prevent mixing of oxygenated and deoxygenated blood.
Types of Blood Vessels
- Arteries: Carry blood away from the heart under high pressure. Thick, muscular, elastic walls; narrow lumen; no valves (except semilunar valves at heart exits).
- Veins: Carry blood towards the heart under lower pressure. Thinner, less muscular walls; wide lumen; contain valves to prevent backflow.
- Capillaries: Microscopic vessels connecting arteries to veins. Walls are one cell thick to enable rapid exchange of gases, nutrients, and waste products via diffusion.
Double Circulatory System
- Pulmonary Circulation: Heart → Lungs → Heart (Right ventricle → Pulmonary artery → Lungs → Pulmonary vein → Left atrium).
- Systemic Circulation: Heart → Rest of Body → Heart (Left ventricle → Aorta → Body tissues → Vena cava → Right atrium).
3.3 Human Blood
Human blood is a tissue composed of liquid plasma (55%) and cellular components (45%).
Components of Blood
- Blood Plasma: Yellowish liquid consisting mainly of water, containing dissolved nutrients, plasma proteins, antibodies, hormones, excretory products ($CO_2$, urea), and mineral salts.
- Red Blood Cells (Erythrocytes): Biconcave disc shape without a nucleus to maximize surface area for oxygen binding. Contain hemoglobin (iron-rich pigment).
- White Blood Cells (Leukocytes): Irregular shape with a nucleus. Defend the body against pathogens (phagocytes engulf bacteria; lymphocytes produce antibodies).
- Platelets (Thrombocytes): Anucleated cell fragments involved in blood clotting to stop bleeding at wounds.
Human Blood Groups (ABO System)
Determined by antigens on red blood cell membranes and antibodies in blood plasma.
| Blood Group | Antigens on Red Blood Cells | Antibodies in Plasma | Can Donate Blood To | Can Receive Blood From |
|---|---|---|---|---|
|
A | A antigen | Anti-B antibody | A, AB | A, O |
|
B | B antigen | Anti-A antibody | B, AB | B, O |
|
AB | A and B antigens | Neither antibody | AB only | A, B, AB, O (Universal Recipient) |
|
O | Neither antigen | Anti-A and Anti-B | A, B, AB, O (Universal Donor) | O only |
3.4 Transport System in Plants
Vascular plants possess a specialized transport system comprising vascular bundles: xylem and phloem.
Vascular Tissues
- Xylem: Composed of dead hollow tubes made of lignin. Transports water and dissolved mineral salts upwards from roots to leaves. Provides mechanical support.
- Phloem: Composed of living sieve tubes and companion cells. Transports sucrose and amino acids (synthesized in leaves via photosynthesis) to all parts of the plant (process called translocation).
Transpiration and Factors Affecting Its Rate
Transpiration is the process of water loss in the form of water vapor from the aerial parts of plants, mainly through leaf stomata. It creates a suction force (transpiration pull) that draws water and minerals up from the roots.
- Light Intensity: Higher light intensity → Stomata open wider → Higher transpiration rate.
- Temperature: Higher temperature → Kinetic energy of water molecules increases → Higher evaporation rate → Higher transpiration rate.
- Air Movement (Wind): Faster wind speed → Sweeps away water vapor near leaves → Steepens concentration gradient → Higher transpiration rate.
- Relative Air Humidity: Higher air humidity → Air saturated with water vapor → Lower concentration gradient → Lower transpiration rate.
3.5 Comparative Circulatory Systems in Vertebrates
- Fish: Single circulatory system; 2-chambered heart (1 atrium, 1 ventricle).
- Amphibians & Reptiles: Double circulatory system; 3-chambered heart (2 atria, 1 ventricle) with partial mixing of oxygenated and deoxygenated blood (reptiles have a partial septum).
- Mammals & Birds: Double circulatory system; 4-chambered heart (2 atria, 2 ventricles) with complete separation of oxygenated and deoxygenated blood.