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Transportation in Animals and Plants for Class 7: The Complete CBSE Guide (2026-27)

Every living organism needs a system to move nutrients, oxygen, hormones, and waste products from one part of the body to another. In Class 7 Science, the chapter on Transportation in Animals and Plants reveals how nature has engineered elegant solutions for this challenge. Animals, including humans, rely on a circulatory system where the heart pumps blood through an intricate network of vessels. Plants, lacking a pump, use physical forces like transpiration and root pressure to move sap through specialized tissues called xylem and phloem. Understanding these mechanisms is crucial for CBSE students, as this chapter appears in every term exam and lays the groundwork for advanced Biology in Classes 9 and 10.

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Key takeaways

  • ✓The human circulatory system consists of the heart (a muscular pump), blood (the transport medium carrying oxygen, nutrients, and waste), and blood vessels (arteries, veins, capillaries).
  • ✓The human heart has four chambers (two atria and two ventricles) that work in a synchronized rhythm to pump oxygenated and deoxygenated blood separately, preventing mixing.
  • ✓Excretion in humans primarily occurs through kidneys, which filter blood to remove urea and excess water, forming urine stored in the bladder before discharge.
  • ✓Xylem tissue in plants transports water and dissolved minerals unidirectionally from roots to leaves through hollow, lignified tubes, driven by transpiration pull.
  • ✓Phloem tissue moves prepared food (sucrose solution) bidirectionally from leaves to all growing and storage parts of the plant via living sieve tubes and companion cells.
  • ✓Transpiration — evaporation of water from leaf stomata — creates a suction force that pulls water columns upward through xylem, enabling tall trees to defy gravity.
  • ✓CBSE Class 7 Science awards approximately 8–10 marks to Transportation in Animals and Plants in the final exam, with 2–3 short-answer and 1 long-answer question typical.

Why Transportation Systems Are Essential in Living Organisms

Transportation in Animals and Plants Class 7 begins by addressing a fundamental question: why do multicellular organisms need specialized transport systems? Single-celled organisms like Amoeba can rely on simple diffusion because every part of their body is close to the external environment. However, in larger organisms — a human body with trillions of cells or a banyan tree spreading across 100 meters — diffusion alone is too slow. Cells deep inside the body cannot access oxygen or nutrients directly from the environment. Hence, animals evolved circulatory systems and plants developed vascular tissues. In humans, blood carries oxygen from lungs to the brain in seconds; in a mango tree, xylem vessels lift water 15 meters high against gravity. Without these systems, internal cells would starve and suffocate. This section sets the biological context that makes transportation a necessity, not a luxury, for complex life forms.
  • Diffusion works only over short distances (a few micrometers) — insufficient for large organisms.
  • Human cells, located centimeters or meters from the skin or gut, need a dedicated delivery network.
  • Plants cannot move; they must transport water from underground roots to sunlit leaves several meters above.
  • Transportation systems also collect and remove metabolic waste (CO₂, urea) to prevent toxicity.

The Human Circulatory System: An Overview

The circulatory system in humans is a closed, double-loop network comprising the heart, blood, and blood vessels. 'Closed' means blood always flows inside vessels, never spilling into body cavities. 'Double loop' refers to two distinct circuits: the pulmonary circuit (heart → lungs → heart) that oxygenates blood, and the systemic circuit (heart → body organs → heart) that delivers oxygen and collects waste. The NCERT Class 7 Science textbook emphasizes that this separation ensures efficient oxygen delivery. The system operates 24/7: an average adult heart beats around 72 times per minute, pumping roughly 5 liters of blood per minute at rest. During exercise, this can triple. This continuous circulation maintains homeostasis — stable internal conditions — by distributing heat, hormones (like insulin), nutrients (glucose, amino acids), and immune cells (white blood cells) wherever needed. Students must visualize the circulatory system as the body's highway network, with the heart as the central pumping station.
  • Closed system: blood confined to vessels (unlike insects, which have open systems).
  • Double circulation: separate pathways for oxygenation (lungs) and distribution (body).
  • Continuous operation: the heart never rests during a person's lifetime.
  • Multi-functional: transports gases, nutrients, hormones, waste, and heat.

Blood: Composition and Functions

Blood is the liquid connective tissue that serves as the transport medium in the circulatory system. It constitutes about 7–8% of body weight (roughly 5–6 liters in an adult). Blood has four main components as per Transportation in Animals and Plants Class 7 curriculum. Plasma (55% by volume) is a straw-colored liquid composed of 90% water, 7% proteins (albumin, globulins, fibrinogen), and 3% dissolved substances (glucose, salts, hormones, urea, CO₂). Red blood cells or erythrocytes (45%) contain hemoglobin, an iron-rich protein that binds oxygen in lungs and releases it in tissues; their biconcave disc shape maximizes surface area for gas exchange. White blood cells or leukocytes (<1%) defend against infections — some engulf bacteria (phagocytes), others produce antibodies. Platelets or thrombocytes (<1%) are cell fragments that initiate clotting to seal wounds and prevent blood loss. Each component plays a distinct role, making blood a multifunctional tissue essential for survival.

Structure and Function of the Human Heart

The human heart is a muscular, fist-sized organ located slightly left of the chest midline, between the lungs. It has four chambers: two upper atria (singular: atrium) that receive blood, and two lower ventricles that pump blood out. The right atrium receives deoxygenated blood from the body via the vena cava; this blood moves to the right ventricle, which pumps it to the lungs through the pulmonary artery. In the lungs, CO₂ is released and O₂ is absorbed. Oxygenated blood returns to the left atrium via pulmonary veins, flows into the left ventricle, and is pumped to the entire body through the aorta, the largest artery. Critically, the left and right sides never mix, thanks to a muscular wall called the septum. Valves (tricuspid, bicuspid, semilunar) prevent backflow, ensuring unidirectional blood flow. The heart's rhythmic contraction (systole) and relaxation (diastole) produce the heartbeat. NCERT Class 7 Science introduces students to this four-chambered design, which is far more efficient than the three-chambered hearts of amphibians or the two-chambered hearts of fish.
  • Right side handles deoxygenated blood (body → lungs).
  • Left side handles oxygenated blood (lungs → body).
  • Septum: wall separating left and right, preventing mixing.
  • Valves: tricuspid (right atrium-ventricle), bicuspid/mitral (left atrium-ventricle), semilunar (ventricles to arteries).
  • Heartbeat: one complete cycle of contraction (systole) and relaxation (diastole), ~72 beats/min at rest.

Blood Vessels: Arteries, Veins and Capillaries

Blood vessels form the tubular network through which blood travels. There are three types, each with distinct structure and function. Arteries carry blood away from the heart. They have thick, elastic, muscular walls to withstand high pressure from ventricular contractions. The aorta and pulmonary artery are major arteries. Veins carry blood toward the heart. Their walls are thinner with less muscle, because blood pressure is lower on the return journey. Veins contain one-way valves that prevent backflow, especially in limbs where blood must travel upward against gravity. The vena cava and pulmonary veins are major veins. Capillaries are microscopic vessels, one cell thick, forming a dense network in tissues. Their thin walls allow exchange of gases (O₂, CO₂), nutrients (glucose, amino acids), and waste (urea) between blood and tissue fluid. Every cell in the body lies within ~0.1 mm of a capillary. Understanding these three vessel types is central to Transportation in Animals and Plants Class 7, as they illustrate how structure suits function — a recurring theme in Biology.

Excretion in Humans: The Role of Kidneys

Excretion is the biological process of removing metabolic waste from the body. In humans, the primary excretory organs are the kidneys, two bean-shaped structures located on either side of the spine, just below the ribcage. Each kidney contains about one million filtering units called nephrons. Blood enters the kidney via the renal artery; in the nephron, a tuft of capillaries called the glomerulus filters blood under pressure, allowing water, urea, salts, and glucose to pass into the Bowman's capsule while retaining blood cells and large proteins. As this filtrate travels through the nephron's tubule, useful substances (glucose, most water, essential salts) are reabsorbed into the blood. The remaining liquid — now called urine, composed of water, urea, uric acid, and excess salts — flows into collecting ducts, then to the ureter, and is stored in the urinary bladder until excretion through the urethra. Healthy kidneys filter about 180 liters of blood daily, producing ~1.5 liters of urine. Besides the kidneys, skin (via sweat containing urea and salts) and lungs (exhaling CO₂ and water vapor) also contribute to excretion. This topic, covered in Transportation in Animals and Plants Class 7, helps students understand that transportation and waste removal are interlinked — the circulatory system both delivers nutrients and collects waste for disposal.
  • Nephron: functional unit of kidney, performs filtration and reabsorption.
  • Filtration: blood pressure forces water, urea, salts, glucose into Bowman's capsule.
  • Reabsorption: tubule reclaims glucose, essential salts, and 99% of water.
  • Urine composition: water (95%), urea (2%), uric acid, salts, creatinine.
  • Urinary pathway: kidney → ureter → bladder → urethra → outside.

Transport of Water and Minerals in Plants: The Role of Xylem

Plants, being stationary, have evolved specialized vascular tissues for transport. Xylem is responsible for upward movement of water and dissolved minerals from roots to stems, leaves, and flowers. Xylem tissue comprises hollow, tube-like cells: tracheids and vessels, whose walls are reinforced with lignin (a hard substance) to prevent collapse under negative pressure. Roots absorb water from soil through root hairs by osmosis — water moves from soil (higher water concentration) into root cells (lower concentration due to dissolved salts). Once inside, water enters the xylem and travels upward. But how does water reach the top of a 30-meter coconut tree without a pump? Three forces are at work. Root pressure: active uptake of minerals by roots creates osmotic pressure, pushing water upward (minor role, ~1–2 atmospheres). Capillary action: adhesion (water sticking to xylem walls) and cohesion (water molecules sticking to each other) help water climb narrow tubes (minor role). Transpiration pull: the primary driver. Water evaporates from leaf stomata (transpiration), creating a suction that pulls water columns upward through xylem, like sipping through a straw. This pull can generate tensions of 15–30 atmospheres, sufficient to lift water to treetops. The NCERT Class 7 Science textbook emphasizes transpiration pull as the main mechanism, and students must understand that xylem transport is unidirectional (roots to leaves) and driven by physical forces, not metabolic energy.
  • Xylem structure: dead, hollow, lignified cells (tracheids, vessels) forming continuous tubes.
  • Water uptake: root hairs absorb water by osmosis from soil.
  • Root pressure: mineral absorption creates osmotic gradient, pushes water upward (weak force).
  • Capillary action: adhesion + cohesion in narrow xylem tubes (minor contributor).
  • Transpiration pull: evaporation from stomata creates suction, pulling water columns up (dominant force).
  • Unidirectional flow: always upward, no downward movement in xylem.

Transport of Food in Plants: The Role of Phloem

While xylem carries water upward, phloem transports food — primarily sucrose dissolved in water (called sap) — from sites of synthesis (mainly leaves, where photosynthesis occurs) to sites of use or storage (roots, fruits, seeds, growing shoots). Unlike xylem, phloem transport is bidirectional: sap can move upward to growing tips or downward to roots, depending on the plant's needs. Phloem tissue consists of sieve tubes (elongated living cells with perforated end walls called sieve plates) and companion cells (which provide metabolic support to sieve tubes). The movement of food through phloem is called translocation and occurs by a pressure-flow mechanism. At the source (e.g., a mature leaf), sugars are actively loaded into sieve tubes, increasing solute concentration and drawing water in by osmosis. This creates high turgor pressure. At the sink (e.g., a root or developing fruit), sugars are unloaded and used, reducing pressure. The pressure gradient causes sap to flow from source to sink. This process requires metabolic energy (ATP) for active loading and unloading, unlike xylem transport. Transportation in Animals and Plants Class 7 students must distinguish clearly between xylem and phloem: xylem is passive, unidirectional, carries water; phloem is active, bidirectional, carries food.

Transpiration: Process, Importance and Factors Affecting It

Transpiration is the loss of water vapor from aerial parts of plants, mainly through stomata (tiny pores on leaf surfaces). While it may seem wasteful — a large tree can lose hundreds of liters daily — transpiration serves several vital functions. It creates the transpiration pull that drives xylem transport, enabling water to reach great heights. It cools the plant, much like sweating cools humans; as water evaporates, it absorbs heat from leaf tissues, preventing overheating in direct sunlight. It facilitates the uptake of minerals; the constant upward flow of water carries dissolved nutrients from soil. Finally, it maintains turgidity in cells, keeping leaves and stems firm. However, excessive transpiration can cause wilting, so plants regulate it by opening and closing stomata via guard cells. Factors affecting transpiration rate include temperature (higher temperature increases evaporation), humidity (high humidity reduces the gradient, slowing transpiration), wind speed (wind removes water vapor, increasing transpiration), and light (stomata open in light, close in darkness). CBSE Class 7 Science students often perform a simple experiment: cover a potted plant with a transparent polythene bag, leave it in sunlight, and observe water droplets condensing inside — direct evidence of transpiration. Understanding this process is crucial for grasping plant water economy and the link between structure (stomata, xylem) and function (transport, cooling).
  • Definition: loss of water vapor from plant aerial parts, mainly via stomata.
  • Creates transpiration pull for xylem water transport.
  • Cools plant tissues by evaporative cooling.
  • Facilitates mineral uptake from soil.
  • Maintains cell turgidity, keeping plant firm.
  • Regulated by stomatal opening/closing via guard cells.
  • Rate increases with temperature, wind, light; decreases with high humidity.

Comparing Circulatory Systems Across Different Animals

While Transportation in Animals and Plants Class 7 focuses on humans and flowering plants, a brief comparative perspective enriches understanding. Simpler animals have simpler systems. Insects and many invertebrates have an open circulatory system: blood (hemolymph) is pumped by a tubular heart into body cavities, directly bathing organs, then re-enters the heart. This is less efficient but adequate for small-bodied organisms with low metabolic rates. Fish have a two-chambered heart (one atrium, one ventricle) and single circulation: blood flows heart → gills (oxygenation) → body → heart in one loop. Amphibians and most reptiles have three-chambered hearts (two atria, one ventricle), allowing partial separation of oxygenated and deoxygenated blood, supporting their dual aquatic-terrestrial lifestyle. Birds and mammals, including humans, possess four-chambered hearts and double circulation, completely separating oxygenated and deoxygenated streams. This is the most efficient system, supporting high metabolic rates, constant body temperature, and active lifestyles. By recognizing this evolutionary progression, students appreciate that the human circulatory system represents millions of years of optimization, not arbitrary design.
  • Insects: open system, hemolymph bathes organs directly.
  • Fish: two-chambered heart, single circulation via gills.
  • Amphibians/Reptiles: three-chambered heart, partial separation.
  • Birds/Mammals: four-chambered heart, complete separation, double circulation.
  • Complexity correlates with metabolic demand and lifestyle.

Common Misconceptions in Transportation in Animals and Plants Class 7

Students often harbor misunderstandings that impede mastery of this chapter. One frequent error is believing that arteries always carry oxygenated blood and veins deoxygenated. The correct definition is structural: arteries carry blood away from the heart, veins toward it. The pulmonary artery carries deoxygenated blood (heart to lungs), and pulmonary veins carry oxygenated blood (lungs to heart), reversing the usual oxygen status. Another misconception is that xylem and phloem are separate plants or that xylem carries food. In reality, both are tissues within the same plant: xylem transports water and minerals, phloem transports food. Students sometimes think transpiration is the same as evaporation. Transpiration is evaporation specifically from living plant parts, regulated by stomata, while evaporation is a purely physical process. Some believe the heart has only two chambers or that blood flows randomly. Emphasizing the four-chamber structure and the strict directional flow — facilitated by valves — corrects this. Another confusion arises around excretion versus egestion: excretion removes metabolic waste (urea from protein breakdown), while egestion removes undigested food (feces) that never entered cells. Clarifying these distinctions during revision significantly boosts exam performance.
  • Arteries carry blood away from heart; veins toward heart (not defined by oxygen content).
  • Xylem and phloem coexist in the same plant, serving different transport needs.
  • Transpiration is regulated evaporation from plants, not passive evaporation from any surface.
  • Heart has four chambers (not two or three), ensuring complete separation.
  • Excretion (metabolic waste) differs from egestion (undigested food waste).

Important Diagrams and Labeling for CBSE Exams

Diagram-based questions are a staple of Transportation in Animals and Plants Class 7 assessments. Students must be able to draw and label the following accurately. The human heart (sectional view): label right atrium, left atrium, right ventricle, left ventricle, septum, tricuspid valve, bicuspid valve, pulmonary artery, pulmonary vein, aorta, and vena cava. Mark the flow direction with arrows. A typical exam question awards 3 marks for a neat, labelled diagram plus 2 marks for describing one function. The structure of a nephron: label glomerulus, Bowman's capsule, proximal tubule, loop of Henle, distal tubule, collecting duct, renal artery, and renal vein. Understand the filtration and reabsorption steps occurring at each part. Transverse section of a leaf showing stomata and guard cells: label epidermis, stomatal pore, guard cells, mesophyll cells, xylem, and phloem in the vein. This illustrates the site of transpiration. A schematic of xylem and phloem structure: draw tracheids or vessels for xylem, sieve tubes and companion cells for phloem, labeling their distinguishing features. Finally, a diagram showing root hair absorbing water: label root hair cell, soil particles, water film, direction of water movement (osmosis into root hair). Practice drawing these diagrams within 3–4 minutes, ensuring clarity, proportion, and accuracy. Labeling should use pencil for diagrams and pen for labels and arrows, as per CBSE guidelines.
  • Human heart (sectional): 4 chambers, valves, major vessels, flow arrows.
  • Nephron structure: glomerulus, tubule, Bowman's capsule, blood vessels.
  • Leaf section: stomata, guard cells, xylem and phloem in veins.
  • Xylem and phloem tissue: cellular structure, sieve plates, lignified walls.
  • Root hair and water uptake: osmosis direction, soil-root interface.
  • Use pencil for outlines, pen for labels; keep diagrams large and clear.

Exam Strategy: Scoring Full Marks in Transportation in Animals and Plants Class 7

CBSE Class 7 Science allocates roughly 8–10 marks to this chapter in the annual exam, distributed across MCQs, short-answer (2–3 marks), and one long-answer (5 marks) question. To maximize scores, follow these strategies. For MCQs, pay attention to precise terminology: 'pulmonary artery carries deoxygenated blood' is correct, while 'all arteries carry oxygenated blood' is wrong. Eliminate obviously incorrect options first. For 2-mark questions asking 'What is the function of xylem?', give two distinct points: (i) Transports water and minerals from roots to leaves, (ii) Provides mechanical support due to lignified walls. Always write in points, not paragraphs, for short answers — easier to evaluate and less chance of missing a mark. For 3-mark 'differentiate' questions (e.g., arteries vs veins), present a table with at least three clear differences. For the 5-mark long answer (e.g., 'Describe the structure and functioning of the human heart'), organize your response: start with a one-sentence introduction, draw a labelled diagram (2 marks), explain structure (1 mark), describe blood flow through chambers (1.5 marks), mention valves and septum (0.5 mark). Budget 8–10 minutes for this question. Revise NCERT in-text questions and exercises thoroughly; CBSE often sources questions verbatim or with minor tweaks. Practice diagram drawing daily in the week before exams. Finally, use the correct scientific terms: write 'bicuspid valve', not 'left valve'; 'stomata', not 'small holes'. Precision in language signals mastery and earns full marks even when content is borderline.
  • Read questions carefully; keywords like 'only', 'always', 'never' in MCQs often indicate wrong options.
  • Write short answers in numbered points, not flowing paragraphs.
  • For 'differentiate' questions, use a table format with 3–4 clear distinctions.
  • In long answers, integrate a labelled diagram — it often carries 2 of 5 marks.
  • Underline key terms (xylem, phloem, nephron, atrium) to catch the examiner's eye.
  • Allocate time proportionally: 1 mark ≈ 1.5 minutes.

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Frequently asked questions

Why does the chapter emphasize transpiration pull over root pressure in xylem transport?+
Root pressure can generate only 1–2 atmospheres of force, sufficient to push water a few meters. Transpiration pull, created by evaporation from stomata, generates tensions of 15–30 atmospheres — enough to lift water to the top of 30+ meter trees. NCERT Class 7 Science identifies transpiration as the primary mechanism because it explains tall-tree transport, which root pressure cannot. Experiments confirm that cutting a leafy branch stops water uptake, proving leaves (transpiration site) drive the process.
What happens if a plant loses too many leaves to disease or pruning?+
Fewer leaves mean reduced transpiration surface, lowering the transpiration pull. This can decrease water uptake and slow mineral absorption, weakening the plant. However, plants compensate by closing stomata on remaining leaves to reduce water loss and by growing new leaves if conditions permit. Severe leaf loss (e.g., 70–80%) can cause wilting and stunted growth because phloem transport of food is also compromised, as leaves are the main food source.
Can you explain why the pulmonary artery carries deoxygenated blood despite being an artery?+
The definition of 'artery' is a vessel that carries blood away from the heart, not a vessel carrying oxygenated blood. The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs for oxygenation. After gas exchange in the lungs, oxygenated blood returns via pulmonary veins (toward the heart). This is a common confusion in Transportation in Animals and Plants Class 7; remembering 'artery = away' clarifies it instantly.
How do guard cells control stomatal opening and closing?+
Guard cells are kidney-shaped cells surrounding each stomatal pore. In the presence of light, guard cells actively take up potassium ions and synthesize sugars via photosynthesis, increasing internal solute concentration. Water enters by osmosis, guard cells become turgid (swollen), and their shape change opens the pore. At night or during water stress, potassium and water exit, guard cells become flaccid, and the pore closes, reducing transpiration. This mechanism balances gas exchange (CO₂ for photosynthesis) with water conservation.
Why do we feel thirsty and urinate less when we sweat heavily during summer?+
Sweating removes water and salts from the body. To maintain blood volume and prevent dehydration, the brain signals kidneys to reabsorb more water from the filtrate, producing less and more concentrated (darker yellow) urine. Simultaneously, thirst mechanisms activate, prompting you to drink water. This homeostatic response prevents dangerous drops in blood pressure and ensures that vital organs receive adequate circulation, illustrating the link between excretion and circulatory regulation.
What is the difference between blood plasma and tissue fluid?+
Blood plasma is the liquid component of blood, containing water, proteins (albumin, fibrinogen), nutrients, hormones, and waste. It stays inside blood vessels. Tissue fluid (interstitial fluid) is plasma that has filtered out of capillaries into spaces between cells, minus large proteins which cannot pass through capillary walls. Tissue fluid bathes cells directly, allowing nutrient-waste exchange, then re-enters capillaries or drains into the lymphatic system. Both are similar, but tissue fluid lacks large proteins.
If xylem vessels are dead, how does water move through them without living cell activity?+
Xylem transport is a physical, not metabolic, process. Transpiration creates negative pressure (suction) at the top of the plant, pulling water upward through the hollow xylem tubes. Cohesion (water molecules sticking to each other) and adhesion (water sticking to xylem walls) maintain the water column's integrity, preventing it from breaking under tension. No living cell activity is required inside the xylem; the process is driven by evaporation and intermolecular forces, demonstrating that not all biological transport requires energy expenditure.
Why is the left ventricle wall thicker than the right ventricle wall?+
The left ventricle pumps oxygenated blood to the entire body — from head to toes — requiring high pressure to overcome the resistance of long, branching systemic arteries. The right ventricle only pumps deoxygenated blood to the nearby lungs, which are close and have lower resistance. Greater force demands more muscle, hence the left ventricle has a much thicker muscular wall. This difference in structure reflects the difference in functional demand, a key principle in Transportation in Animals and Plants Class 7.
How does the body prevent blood from flowing backward in veins, especially in the legs?+
Veins have one-way valves — flaps of tissue that open to allow blood flow toward the heart and close if blood tries to flow backward due to gravity. In the legs, skeletal muscle contractions during walking squeeze veins, pushing blood upward; valves prevent it from falling back down. This is why prolonged standing (no muscle contractions) can cause blood pooling and varicose veins (valve failure). The combination of valves and muscle pumps ensures venous return despite low pressure and gravity.
Why do plants grown in waterlogged soil often show wilting despite ample water?+
Waterlogged soil lacks air spaces, reducing oxygen availability to root cells. Roots require oxygen for aerobic respiration to generate ATP, which powers active mineral uptake. Without minerals, osmotic gradients weaken, reducing water absorption. Additionally, roots may suffocate and die, losing the ability to absorb water altogether. Though surrounded by water, the plant cannot take it up efficiently, leading to wilting. This shows that water availability alone is insufficient; roots need oxygen too.
What role does the liver play in excretion, as it is not mentioned in the chapter?+
While Transportation in Animals and Plants Class 7 focuses on kidneys, the liver is crucial for excretion. It breaks down excess amino acids (from protein digestion) through deamination, converting toxic ammonia into less harmful urea, which kidneys then filter out. The liver also detoxifies drugs, alcohol, and metabolic by-products, converting them into excretable forms. Bile, produced by the liver, carries waste pigments (bilirubin from old red blood cells) into the intestine for egestion. Thus, the liver pre-processes waste for excretion, working upstream of the kidneys.
Can plants survive if phloem is removed but xylem is intact?+
No. While xylem would still supply water and minerals to leaves, enabling photosynthesis, the absence of phloem means food (sugars) produced in leaves cannot reach roots, stems, or other non-photosynthetic parts. Roots would starve, ceasing water absorption, and the plant would die within days. This demonstrates that both xylem and phloem are essential; one cannot substitute for the other. Their functions are complementary, not redundant, underscoring the integrated nature of plant transport systems.

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