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CBSE Class 7 Science Chapter 7 Transportation in Animals and Plants — Notes

CBSE Class 7 Science Chapter 7 Transportation in Animals and Plants introduces students to one of the most vital life processes: the movement of materials within organisms. Every cell in your body needs a constant supply of oxygen and nutrients, and must expel waste products like carbon dioxide and urea — tasks handled by specialized transport systems. Similarly, a banyan tree standing 20 metres tall must lift water from deep roots to the topmost leaves while distributing the food prepared in those leaves to the roots below. This chapter from the NCERT Class 7 Science textbook unpacks the circulatory system in humans, the excretory system, and the vascular tissues in plants. Understanding these mechanisms is essential not just for CBSE exams but for grasping how life sustains itself at scale.

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Key takeaways

✓The human heart is a four-chambered muscular organ that pumps blood in a double circulatory loop — one through lungs, another through the body.
✓Blood contains red blood cells (oxygen carriers), white blood cells (infection fighters), platelets (clotting agents), and plasma (liquid component).
✓Excretion in humans occurs mainly through kidneys, which filter blood to produce urine containing urea, excess salts, and water.
✓Xylem vessels transport water and dissolved minerals unidirectionally from roots to leaves using root pressure and transpiration pull.
✓Phloem sieve tubes translocate prepared food (sugars) bidirectionally from leaves to all growing and storage parts of the plant.
✓Transpiration — water loss through stomata — creates a suction force that pulls water upward in tall trees, sometimes over 100 metres.
✓CBSE Class 7 Science Chapter 7 Transportation in Animals and Plants accounts for roughly 5–6% of the annual theory paper weightage.

Why Transportation Systems Are Essential in Living Organisms

Single-celled organisms like amoeba live in water and obtain oxygen and nutrients directly from their surroundings through simple diffusion. Waste products diffuse out just as easily because distances are microscopic. However, multicellular organisms — from a Class 7 student to a mango tree — have billions of cells arranged in tissues and organs located far from the external environment. Diffusion alone cannot meet the demands of cells buried deep inside. A specialized transport system becomes necessary. In animals, the circulatory system uses blood as the transport medium, pumped by the heart through a network of blood vessels. In plants, xylem and phloem tissues form a vascular system that moves water, minerals, and food. The NCERT Class 7 Science curriculum emphasizes this transition from simple to complex transport as organism size and complexity increase. CBSE Class 7 Science Chapter 7 Transportation in Animals and Plants builds this concept step-by-step, showing students that transport is not optional but a prerequisite for survival in large organisms.

Diffusion works only over short distances (a few micrometres), inadequate for multicellular bodies
Circulatory systems deliver oxygen and nutrients rapidly to trillions of cells
Transport systems also collect and remove metabolic wastes like CO₂ and urea
Plants require transport to connect non-photosynthetic roots with photosynthetic leaves

The Human Circulatory System: A Double-Loop Highway

The human circulatory system is a closed, double circulatory system, meaning blood travels through the heart twice in one complete circuit. Loop one is the pulmonary circulation: oxygen-poor blood flows from the right ventricle to the lungs, picks up oxygen, and returns to the left atrium. Loop two is the systemic circulation: oxygen-rich blood is pumped from the left ventricle to all body organs and returns oxygen-depleted to the right atrium. This design keeps oxygenated and deoxygenated blood separate, maximizing oxygen delivery — a key efficiency feature in mammals and birds. The NCERT Class 7 Science textbook explains that fish have a single-loop system (heart → gills → body → heart), which is less efficient. CBSE Class 7 Science Chapter 7 Transportation in Animals and Plants devotes significant attention to this double-loop architecture because it underpins why humans can sustain high metabolic rates and active lifestyles. Students must be able to trace the path of blood and explain why the left ventricle has thicker walls than the right (it pumps blood to the entire body, not just the nearby lungs).

Pulmonary loop: right ventricle → pulmonary artery → lungs → pulmonary veins → left atrium
Systemic loop: left ventricle → aorta → body organs → vena cava → right atrium
Double circulation prevents mixing of oxygenated and deoxygenated blood
Ensures efficient oxygen supply to energy-demanding tissues like brain and muscles

Structure and Function of the Human Heart

The heart is a fist-sized muscular organ located slightly left of the chest center, protected by the rib cage. It has four chambers: two upper atria (thin-walled, receive blood) and two lower ventricles (thick-walled, pump blood). The right atrium receives deoxygenated blood from the body via the superior and inferior vena cava. This blood moves to the right ventricle, which pumps it to the lungs. The left atrium receives oxygenated blood from the lungs via pulmonary veins, and the left ventricle pumps it out through the aorta. Valves between atria and ventricles (tricuspid on the right, bicuspid/mitral on the left) and at the exits (semilunar valves) ensure one-way flow, preventing backflow. The heart beats roughly 72 times per minute in a resting adult, driven by electrical impulses from the sinoatrial (SA) node. CBSE Class 7 Science Chapter 7 Transportation in Animals and Plants requires students to draw and label a diagram of the heart, identify each chamber and major vessel, and explain the flow direction. A common exam question asks 'Why is the wall of the left ventricle thicker than the right?' — the answer being that it must generate higher pressure to pump blood throughout the body.

Four chambers: right atrium, right ventricle, left atrium, left ventricle
Valves (tricuspid, bicuspid, semilunar) maintain unidirectional blood flow
Cardiac muscle contracts rhythmically, about 100,000 times per day
SA node acts as the heart's natural pacemaker, initiating each heartbeat

Blood Vessels: Arteries, Veins, and Capillaries

Blood travels through three types of vessels. Arteries carry blood away from the heart under high pressure, so their walls are thick, muscular, and elastic — the aorta and pulmonary arteries are the largest. Arteries branch into smaller arterioles and then into capillaries, the tiniest vessels with walls just one cell thick. This thinness allows oxygen, nutrients, and waste to diffuse between blood and tissues. Capillaries then merge into venules and veins, which return blood to the heart. Veins operate under low pressure and have thinner walls than arteries; many contain valves to prevent backflow, especially in the legs where blood must travel upward against gravity. A common misconception is that all arteries carry oxygenated blood — not true, because the pulmonary artery carries deoxygenated blood to the lungs. Similarly, pulmonary veins carry oxygenated blood, breaking the 'veins carry deoxygenated blood' rule. CBSE Class 7 Science Chapter 7 Transportation in Animals and Plants emphasizes these distinctions. Students should memorize: arteries = away from heart; veins = toward heart, regardless of oxygen content.

Components of Blood and Their Roles

Human blood is a specialized connective tissue comprising roughly 55% plasma (liquid) and 45% formed elements (cells and cell fragments). Plasma is a straw-coloured fluid containing water (90%), proteins (albumin, globulins, fibrinogen), nutrients (glucose, amino acids), hormones, and waste products (urea, CO₂). Red blood cells (RBCs or erythrocytes) are biconcave discs packed with haemoglobin, the iron-containing protein that binds oxygen. An adult has about 5 million RBCs per microlitre of blood. RBCs lack a nucleus in mammals, maximizing space for haemoglobin. White blood cells (WBCs or leukocytes) are fewer (about 7,000 per microlitre) but crucial for immune defense — they engulf pathogens, produce antibodies, and clean up dead cells. Platelets (thrombocytes) are cell fragments that initiate blood clotting when a vessel is injured, forming a plug to prevent blood loss. CBSE Class 7 Science Chapter 7 Transportation in Animals and Plants expects students to list these components and state each function clearly. A typical 2-mark question: 'Name the component of blood responsible for clotting and the component that fights infection.' Answers: platelets and WBCs.

Plasma: transports nutrients, hormones, waste; helps regulate body temperature
Red blood cells: carry oxygen via haemoglobin; give blood its red colour
White blood cells: defend against infections; include lymphocytes and phagocytes
Platelets: essential for blood clotting; prevent excessive bleeding from injuries

Excretion in Humans: Removing Metabolic Waste

Excretion is the biological process of removing metabolic waste products from the body. Cellular respiration produces carbon dioxide, protein breakdown yields urea and ammonia, and excess salts accumulate from diet. If not removed, these substances become toxic. The human excretory system includes kidneys, ureters, urinary bladder, and urethra. The two kidneys, located in the lower back, filter about 180 litres of blood daily, producing roughly 1.5 litres of urine. Each kidney contains about one million nephrons — the functional units that filter blood. A nephron has a glomerulus (a knot of capillaries) surrounded by Bowman's capsule, followed by a long tubule. Blood pressure forces water, glucose, salts, and urea into the capsule (filtration). As this filtrate moves through the tubule, useful substances like glucose and most water are reabsorbed into the blood (reabsorption), leaving concentrated urine containing urea, excess salts, and water. Urine drains via ureters into the bladder, stored until expelled through the urethra. CBSE Class 7 Science Chapter 7 Transportation in Animals and Plants covers excretion as part of the broader transport and removal theme. Students should know the path: kidney → ureter → bladder → urethra.

Kidneys filter blood, removing urea, excess water, and salts to form urine
Nephron is the basic filtration unit; each kidney has ~1 million nephrons
Useful substances (glucose, amino acids, most water) are reabsorbed in the tubule
Bladder stores urine temporarily; an adult bladder can hold about 400–500 mL

Transport in Plants: The Roles of Xylem and Phloem

Unlike animals, plants do not have a circulatory system with a heart. Instead, they possess vascular tissues — xylem and phloem — that form a continuous network from roots to leaves. Xylem is responsible for transporting water and dissolved minerals absorbed by root hairs from the soil. This movement is unidirectional: upward from roots through stem to leaves. Xylem vessels are made of dead, hollow cells with lignified walls, forming long tubes that offer little resistance to water flow. Phloem, on the other hand, translocates food (mainly sucrose) prepared in the leaves during photosynthesis to all parts of the plant — roots, stems, flowers, fruits, and storage organs. Unlike xylem, phloem is composed of living cells (sieve tube elements and companion cells), and transport is bidirectional depending on where food is needed. CBSE Class 7 Science Chapter 7 Transportation in Animals and Plants dedicates multiple sections to these tissues because understanding plant transport clarifies how a 30-metre coconut tree can lift water from soil to the crown and distribute sugars from leaves to roots. Students must differentiate xylem and phloem by structure, function, and the direction of transport.

How Water Moves Up Xylem: Root Pressure and Transpiration Pull

Water movement in xylem is driven by two main forces. Root pressure is generated when root cells actively transport minerals into the xylem, creating a lower water potential. Water from soil enters root hairs by osmosis, building pressure that pushes water upward. However, root pressure alone can lift water only a few metres, insufficient for tall trees. The dominant force is transpiration pull. Transpiration is the evaporation of water from stomata (tiny pores) on leaf surfaces. As water molecules evaporate, they pull adjacent molecules upward through the xylem due to cohesion (water molecules sticking to each other via hydrogen bonds) and adhesion (water sticking to xylem walls). This creates a continuous column of water from roots to leaves, like a chain being pulled from the top. On a hot day, a large tree can transpire hundreds of litres, creating a powerful suction. The NCERT Class 7 Science textbook illustrates this with a simple experiment: placing a leafy stem in coloured water shows the dye rising through the stem, marking the xylem path. CBSE Class 7 Science Chapter 7 Transportation in Animals and Plants expects students to explain both root pressure and transpiration pull and identify which is more significant in tall plants.

Root pressure: osmotic entry of water into roots pushes sap upward (works up to ~2 metres)
Transpiration pull: evaporation from leaves creates suction, pulling water up xylem (dominant in tall trees)
Cohesion-adhesion theory: water molecules cling to each other and xylem walls, forming an unbroken column
Stomata regulate transpiration; they close in dry conditions to conserve water

Translocation of Food in Phloem: From Source to Sink

Phloem translocates the products of photosynthesis — mainly sucrose and amino acids — from leaves (the source) to areas of growth or storage (the sink), such as roots, fruits, or developing buds. Unlike xylem transport driven by physical forces, phloem translocation requires energy. The process involves active loading of sugars into sieve tubes at the source, raising solute concentration. Water enters by osmosis, increasing pressure. At the sink, sugars are actively unloaded, reducing pressure. This pressure gradient pushes the sap from high-pressure source to low-pressure sink — a mechanism called the pressure flow hypothesis. Sieve tubes are living cells with perforated end walls (sieve plates) that allow sap to flow. Companion cells, connected to sieve tubes, provide metabolic support and energy. Phloem transport can reverse direction seasonally: in spring, sugars stored in roots move upward to support new leaf growth, making the roots the source and shoots the sink. CBSE Class 7 Science Chapter 7 Transportation in Animals and Plants includes phloem translocation to show that plant transport is not passive but an active, energy-dependent process. Students should contrast this with the passive, transpiration-driven xylem flow.

Sugars produced in leaves are actively loaded into phloem sieve tubes
Water follows by osmosis, creating high pressure at the source
At the sink (roots, fruits), sugars are unloaded, lowering pressure
Pressure gradient drives sap flow from source to sink

Stomata and the Regulation of Transpiration

Stomata are microscopic pores on leaf surfaces, primarily on the underside, each surrounded by two guard cells. These guard cells can change shape to open or close the stomatal pore, regulating gas exchange and water loss. During the day, when photosynthesis occurs, guard cells take up water, become turgid, and curve apart, opening the stomata to allow CO₂ in and O₂ out. At night or in dry conditions, guard cells lose water, become flaccid, and close the pore to conserve water. Transpiration through open stomata cools the plant and drives water uptake, but excessive water loss can lead to wilting. The NCERT Class 7 Science textbook describes a simple starch-iodine test to show that photosynthesis occurs mainly where stomata are present. CBSE Class 7 Science Chapter 7 Transportation in Animals and Plants emphasizes stomatal regulation as a balancing act: the plant must allow enough transpiration to pull water and minerals upward but avoid dehydration. Students should know that stomata open in light and close in darkness or drought, and that desert plants often have fewer stomata or sunken stomata to reduce water loss.

Guard cells swell when turgid (high water), opening stomata for gas exchange
Guard cells shrink when flaccid (low water), closing stomata to prevent water loss
Most stomata are on the underside of leaves to reduce direct sun exposure and water loss
Opening and closing are controlled by light, CO₂ concentration, and water availability

Comparing Transport in Animals and Plants: Key Differences

Though both animals and plants require transport systems, the mechanisms differ fundamentally. Animals use a circulatory system with a muscular pump (heart), blood as the medium, and vessels forming a closed loop. Blood carries oxygen, nutrients, hormones, and waste, and the system supports high metabolic rates and rapid responses. Plants lack a pump and circulatory fluid analogous to blood; instead, xylem and phloem are passive or semi-active conduits. Xylem relies on evaporation (transpiration) and root pressure; phloem uses osmotic gradients and active transport. Animals require rapid transport to sustain movement and homeostasis, while plants, being sessile, operate at a slower pace. Another difference: animals have a dedicated excretory system (kidneys, etc.), whereas plants store some waste in vacuoles or shed leaves. CBSE Class 7 Science Chapter 7 Transportation in Animals and Plants draws these comparisons to help students appreciate the diversity of life strategies. An exam question might ask, 'Why do plants not need a heart?' The answer: plants rely on transpiration pull and diffusion over short distances within tissues; a pump is unnecessary given their stationary lifestyle and lower metabolic demands.

Common Diagrams and Labelling Expected in CBSE Exams

CBSE Class 7 Science Chapter 7 Transportation in Animals and Plants frequently appears in exams through diagram-based questions worth 2–3 marks each. Students must practice drawing and labelling the human heart (four chambers, valves, aorta, vena cava, pulmonary artery and vein), a diagram showing the path of blood through the double circulation, a cross-section of an artery and vein for comparison, and a simplified nephron. For plants, common diagrams include a transverse section of a stem showing xylem and phloem arrangement, a stomatal apparatus with guard cells, and a schematic of water transport from root hair to leaf via xylem. NCERT Class 7 Science includes these diagrams, so students should redraw them multiple times for muscle memory. Examiners award marks for correct labels, neatness, and accuracy of structure. A typical question: 'Draw a labelled diagram of the human heart and indicate the flow of oxygenated and deoxygenated blood using arrows.' Practicing these diagrams boosts confidence and secures easy marks in the CBSE Class 7 annual exam.

Human heart: label all four chambers, major vessels, and valves; use arrows for blood flow direction
Artery vs. vein cross-section: show wall thickness, lumen size, presence/absence of valves
Stomatal apparatus: draw guard cells, stomatal pore, and surrounding epidermal cells
Xylem and phloem in stem: indicate position and direction of transport with arrows

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Frequently asked questions

How many marks does CBSE Class 7 Science Chapter 7 Transportation in Animals and Plants carry in the annual exam?+

This chapter typically carries 6–8 marks in the CBSE Class 7 Science annual examination. Questions include 2-mark short answers (e.g., functions of blood components), 3-mark diagram labeling (heart, nephron, xylem-phloem), and occasionally a 5-mark long answer explaining the circulatory or transport process in detail.

What is the difference between xylem and phloem in plants?+

Xylem transports water and minerals from roots to leaves in one direction using dead, hollow vessels; the driving force is transpiration pull. Phloem translocates prepared food (sugars) bidirectionally from source (leaves) to sink (roots, fruits) using living sieve tube cells and active transport, requiring energy.

Why does the left ventricle of the heart have a thicker wall than the right ventricle?+

The left ventricle pumps oxygenated blood to all body organs and tissues through the systemic circulation, requiring high pressure to overcome resistance in the long vascular network. The right ventricle only pumps blood to the nearby lungs (pulmonary circulation), needing less pressure, so its wall is thinner.

How do kidneys filter blood and produce urine?+

Each kidney has about one million nephrons. Blood enters the glomerulus under pressure; water, salts, glucose, and urea are filtered into Bowman's capsule. As filtrate flows through the tubule, useful substances (glucose, most water) are reabsorbed into blood. The remaining waste (urea, excess salts, water) forms urine, which drains to the bladder.

What is transpiration and why is it important for plants?+

Transpiration is the evaporation of water from stomata on leaves. It creates a suction force (transpiration pull) that draws water and minerals up the xylem from roots to leaves, even in tall trees. It also cools the plant and helps maintain turgor pressure in cells. However, excessive transpiration can cause wilting.

Do all arteries carry oxygenated blood and all veins deoxygenated blood?+

No. The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs, and the pulmonary veins carry oxygenated blood from lungs to the left atrium. The defining feature is direction: arteries carry blood away from the heart; veins carry blood toward the heart, regardless of oxygen content.

What are the main components of blood and their functions?+

Blood has four main components: plasma (liquid part that transports nutrients, hormones, waste), red blood cells (carry oxygen via haemoglobin), white blood cells (fight infections and disease), and platelets (help in blood clotting to stop bleeding from injuries). Together they maintain homeostasis and defend the body.

How does water enter the roots and travel up to the leaves?+

Water enters root hairs from soil by osmosis (moving from high water concentration in soil to lower concentration in root cells). Root pressure pushes it into the xylem. Transpiration pull — suction created by water evaporation from leaves — is the dominant force that pulls water upward through xylem vessels to the leaves and other parts.

Why do plants not need a circulatory system like animals?+

Plants are stationary and have lower metabolic rates than animals. They produce their own food via photosynthesis and do not need rapid delivery of oxygen or nutrients. Water and minerals move passively through xylem by transpiration, and food moves through phloem by osmotic pressure, eliminating the need for a heart or complex circulatory system.

What role do stomata play in plant transport and why do they close at night?+

Stomata allow gas exchange (CO₂ in, O₂ out) for photosynthesis and are the primary sites of transpiration. They close at night because photosynthesis stops in the absence of light, so CO₂ intake is unnecessary. Closing stomata prevents water loss, conserving water when it is not needed for photosynthesis.

Will my child need to memorize all the parts of the heart and blood vessels for CBSE Class 7 exams?+

Yes, CBSE Class 7 Science exams regularly ask students to draw and label the human heart, showing all four chambers, major blood vessels (aorta, vena cava, pulmonary artery and vein), and valves. Students must also trace the path of blood. Repeated diagram practice from the NCERT textbook is essential for scoring full marks on these questions.

How is food transported in plants different from water transport?+

Water transport (xylem) is unidirectional (roots to leaves), driven by passive forces (transpiration pull, root pressure), and occurs in dead cells. Food transport (phloem) is bidirectional (leaves to roots or growing parts), driven by active transport and osmotic pressure gradients, and occurs in living sieve tube cells. Both systems are independent but complementary.

Related resources

CBSE Class 7 Science Chapter 7 Transportation in Animals and Plants Worksheet with Answers Important Questions: CBSE Class 7 Science Chapter 7 Transportation in Animals and Plants Class 7 Science Chapter 7 Transportation in Animals and Plants — Formulas & Key Points NCERT Solutions for CBSE Class 7 Science Chapter 7: Transportation in Animals and Plants AI Tutor for Class 7: The Smart Alternative to Tuition AI Tutor for Class 7 Science: Learn Faster with Instant Help Online Class 9 Science Tutor in Mumbai – 24/7 CBSE-Aligned AI Coaching CBSE Class 9 Mathematics Chapter 1 Number Systems — Notes

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