Grade 10 Transportation and Excretion in Plants and Animals

Transportation and Excretion in Plants and Animals

I. Transportation

Transportation is the process by which substances absorbed or synthesized in one part of an organism are carried to other parts of its body.

A. Transportation in Plants

Plants require transportation for water, minerals, and food (synthesized during photosynthesis).

  • Vascular Tissues: Plants have specialized vascular tissues for transportation:

    • Xylem:

      • Transports water and dissolved minerals from the roots to the aerial parts of the plant (leaves, stem).

      • Movement is unidirectional (upwards).

      • Composed of non-living cells: tracheids, vessels, xylem parenchyma, and xylem fibres.

      • Driving forces for water movement:

        • Root Pressure: Pressure developed in the roots due to continuous absorption of water, pushing water up a short distance. Effective for short plants.

        • Transpiration Pull: The most significant force for tall plants. Water lost as vapour from the leaves (transpiration) creates a suction pull (transpiration pull), drawing water upwards through the xylem. This is due to:

          • Cohesive forces: Water molecules sticking to each other.

          • Adhesive forces: Water molecules sticking to xylem walls.

    • Phloem:

      • Transports food (sugars, primarily sucrose) synthesized in the leaves (photosynthesis) to all other parts of the plant, including storage organs (roots, fruits, seeds) and growing regions.

      • The process is called translocation.

      • Movement is bidirectional (upwards and downwards), depending on the plant's needs.

      • Composed of living cells: sieve tubes, companion cells, phloem parenchyma, and phloem fibres.

      • Requires energy (ATP) to create osmotic pressure gradients for the movement of food.

  • Absorption of Water and Minerals:

    • Root hairs absorb water and minerals from the soil through osmosis and active transport respectively.

B. Transportation in Animals

Animals have a more complex system for transportation, primarily the circulatory system.

  • Human Circulatory System (Closed Circulatory System):

    • Components: Blood, Blood Vessels, Heart.

    • Blood: A fluid connective tissue.

      • Plasma: Liquid matrix, transports water, salts, proteins, digested food, hormones, and waste products.

      • Red Blood Cells (RBCs) / Erythrocytes: Contain haemoglobin, an iron-containing pigment that binds with oxygen and transports it from the lungs to tissues and carbon dioxide from tissues to lungs.

      • White Blood Cells (WBCs) / Leukocytes: Part of the immune system, fight infections.

      • Platelets: Help in blood clotting at the site of injury.

    • Blood Vessels:

      • Arteries: Thick-walled, elastic vessels that carry oxygenated blood away from the heart to various body parts (except pulmonary artery, which carries deoxygenated blood to lungs). Blood flows under high pressure.

      • Veins: Thin-walled vessels that collect deoxygenated blood from various body parts and carry it back to the heart (except pulmonary vein, which carries oxygenated blood from lungs to heart). They have valves to prevent backflow of blood, as blood pressure is low.

      • Capillaries: Extremely thin (one-cell thick) and narrow blood vessels that connect arteries and veins. They form a network throughout the tissues, facilitating the exchange of gases, nutrients, and waste products between blood and body cells.

    • Heart: A muscular, four-chambered pumping organ.

      • Chambers: Two atria (upper chambers: Right Atrium, Left Atrium) and two ventricles (lower chambers: Right Ventricle, Left Ventricle).

      • Function: Pumps blood throughout the body, ensuring segregation of oxygenated and deoxygenated blood.

      • Working (Double Circulation):

        • Pulmonary Circulation: Deoxygenated blood from the body enters the Right Atrium, then Right Ventricle, which pumps it to the lungs via the pulmonary artery for oxygenation. Oxygenated blood returns from the lungs to the Left Atrium via the pulmonary vein.

        • Systemic Circulation: Oxygenated blood from the Left Atrium enters the Left Ventricle, which pumps it to the rest of the body via the aorta. Deoxygenated blood from the body returns to the Right Atrium.

        • Valves: Present between atria and ventricles, and at the exit of ventricles, to prevent backflow of blood.

      • Ventricles have thicker muscular walls than atria because they have to pump blood to greater distances.

  • Lymphatic System:

    • Lymph (Tissue Fluid): A colourless fluid that leaks out from capillaries into the intercellular spaces. It is similar to plasma but lacks large proteins.

    • Function: Transports digested and absorbed fat from the intestine and drains excess fluid from extracellular space back into the blood. Also plays a role in immunity.

    • Lymphatic Vessels: Collect lymph and return it to the bloodstream.

    • Lymph Nodes: Filter lymph and contain immune cells.

II. Excretion

Excretion is the biological process of removal of harmful metabolic waste products from the body.

A. Excretion in Plants

Plants do not have specialized excretory organs or a complex excretory system like animals. They use various strategies to get rid of waste products.

  • Gaseous Wastes:

    • Oxygen (during photosynthesis) and Carbon Dioxide (during respiration) are released through stomata (on leaves) and lenticels (on stems).

    • Excess water is also released as water vapor through stomata during transpiration.

  • Storage of Solid and Liquid Wastes:

    • Many waste products are stored in vacuoles of cells, especially in older xylem, where they remain without harming the plant.

    • Waste products are also stored in leaves and bark, which are eventually shed (e.g., autumn leaf fall).

    • Some wastes are stored as gums, resins, and latex in specific parts of the plant. These are often commercially valuable.

  • Excretion into Soil:

    • Some waste substances are excreted by plants into the surrounding soil through their roots.

B. Excretion in Animals (Human Excretory System)

Animals, especially complex multicellular organisms, have specialized excretory systems to remove nitrogenous waste products.

  • Human Excretory System:

    • Components: A pair of kidneys, a pair of ureters, a urinary bladder, and a urethra.

    • Kidneys:

      • Bean-shaped organs located on either side of the backbone in the abdomen.

      • Main excretory organs.

      • Filter blood to remove nitrogenous waste products like urea and uric acid, along with excess salts and water, forming urine.

      • Also play a crucial role in osmoregulation (maintaining water and ionic balance).

      • Each kidney contains millions of microscopic filtering units called nephrons.

    • Nephron (Functional Unit of Kidney):

      • Consists of a Bowman's capsule (a cup-shaped structure) and a long coiled renal tubule.

      • Urine Formation involves three main steps:

        1. Glomerular Filtration (Ultrafiltration): Blood enters the glomerulus (a tuft of capillaries within Bowman's capsule) under high pressure. Water, salts, glucose, amino acids, urea, etc., are filtered from the blood into the Bowman's capsule, forming the filtrate. Large molecules like proteins and blood cells are retained in the blood.

        2. Tubular Reabsorption: As the filtrate passes through the renal tubule, essential substances like glucose, amino acids, most of the salts, and a major portion of water are selectively reabsorbed back into the blood capillaries surrounding the tubule. This process is highly regulated.

        3. Tubular Secretion: Some waste products like excess ions (K⁺, H⁺) and certain drugs are actively secreted from the blood capillaries into the renal tubule, further ensuring removal of unwanted substances.

    • Ureters: Two tubes that carry urine from each kidney to the urinary bladder.

    • Urinary Bladder: A muscular, elastic sac that stores urine temporarily until it is expelled from the body.

    • Urethra: A tube that carries urine from the urinary bladder to the outside of the body. The opening is controlled by sphincters.

  • Other Excretory Organs in Humans:

    • Lungs: Excrete carbon dioxide and water vapour during respiration.

    • Skin: Excretes small amounts of salts and urea through sweat produced by sweat glands. Sweat also helps in regulating body temperature.

    • Liver: Converts toxic ammonia into less toxic urea.


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