Gonit Vigyan

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Characteristics of Living Organisms

1. Introduction

Living organisms exhibit certain unique characteristics that differentiate them from non-living things. While some differences are evident, such as movement and respiration, others require scientific understanding at the molecular level.

2. How Do We Identify Living Organisms?

We commonly recognize living organisms by their visible activities, such as:

• A dog running
• A cow chewing cud
• A man shouting on the street

Even when an organism is asleep, we consider it alive because we observe signs like breathing. However, not all forms of life exhibit obvious movement.

3. Recognizing Life in Plants

Unlike animals, plants do not exhibit movement in a traditional sense. We generally associate green color with plant life, but:

• Some plants have leaves of colors other than green.
• Growth over time is a strong indicator of life.

Even if a plant is not visibly growing, it remains alive.

4. Movement as a Sign of Life

• We often associate movement with life.
• However, some living beings (e.g., certain animals during hibernation) may not show visible movement.
• Breathing movements are often observed, but some organisms breathe without any external movement.
• Even molecular movement, though invisible, is crucial for life.

5. Importance of Molecular Movement in Life

• At a microscopic level, living organisms maintain constant molecular activity.
• These molecular movements help in repairing and maintaining the structure of the organism.
• The highly organized structure of life, from cells to tissues to organs, must be constantly maintained.
• External environmental factors can lead to breakdowns in biological structures, which must be repaired.

6. Viruses: Are They Alive?

• Viruses do not exhibit molecular movement unless inside a host cell.
• They do not grow, respire, or perform metabolic activities outside a living host.
• This is why scientists debate whether viruses are truly living organisms.

7. Why is Molecular Movement Necessary?

• Living beings are composed of organized structures, from the cellular level to complete organisms.
• Over time, these structures face wear and tear due to environmental changes.
• To sustain life, continuous molecular movements are needed for:
  • Repair and maintenance of cells
  • Metabolic activities
  • Energy production and transportation of nutrients

8. Conclusion

The difference between living and non-living things is not always obvious. While visible movement is a common sign of life, true living organisms continuously exhibit molecular movement, ensuring their structure is maintained. Understanding these microscopic processes helps us define life beyond just movement or growth.

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Life Processes 

1. Introduction

Life processes are the essential biological functions that help organisms maintain and sustain life. These processes continue even when an organism is at rest, asleep, or not actively engaging in specific activities.

Definition of Life Processes:

The fundamental biological activities that ensure the survival and maintenance of living organisms are called life processes.

Importance of Life Processes:

• Maintain internal stability (homeostasis).
• Prevent damage and breakdown of body structures.
• Support growth and development.
• Ensure the survival of the organism.

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2. Major Life Processes

The primary life processes include:

1. Nutrition – Obtaining and utilizing food.
2. Respiration – Breaking down food to release energy.
3. Transportation – Movement of substances within the body.
4. Excretion – Removal of waste products.

Let’s explore each process in detail.

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3. Nutrition

Definition:

The process by which organisms obtain and utilize food for energy, growth, and repair.

Types of Nutrition:

1. Autotrophic Nutrition (Self-feeding)
   • Organisms synthesize their own food from simple inorganic substances (CO₂ and H₂O).
   • Example: Green plants, algae (Photosynthesis).
2. Heterotrophic Nutrition (Feeding on others)
   • Organisms depend on other organisms for food.
   • Types:
     • Holozoic – Ingestion of solid food (e.g., humans, animals).
     • Saprotrophic – Feeding on dead organic matter (e.g., fungi).
     • Parasitic – Feeding on a host organism (e.g., tapeworms, leeches).

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4. Respiration

Definition:

The biochemical process where food is broken down to release energy.

Types of Respiration:

1. Aerobic Respiration (With Oxygen)

   • Oxygen is used to break down glucose into CO₂, H₂O, and energy (ATP).
   • Equation:
     $C_6H_{12}O_6 + 6O_2 → 6CO_2 + 6H_2O + Energy (ATP)$
   • Example: Humans, most animals, plants.

2. Anaerobic Respiration (Without Oxygen)

   • Glucose is partially broken down to produce lesser energy.
   • By-products: Lactic acid (in animals), Alcohol & CO₂ (in yeast).
   • Example: Muscle cells during vigorous exercise, Yeast fermentation.

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5. Transportation

Definition:

The process of moving essential substances (food, oxygen, water) within the body of an organism.

Need for a Transport System:

• In unicellular organisms, diffusion is sufficient for transport.
• In multicellular organisms, diffusion alone is inefficient; thus, specialized transport systems are required.

Transport in Plants:

• Xylem – Conducts water and minerals from roots to leaves.
• Phloem – Transports food from leaves to other parts of the plant.

Transport in Animals (Humans):

• Circulatory System:
  • Heart pumps blood.
  • Blood vessels (arteries, veins, capillaries) distribute nutrients, gases, and hormones.
  • Blood carries oxygen (via hemoglobin in RBCs) and nutrients.

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6. Excretion

Definition:

The process of removing metabolic waste products from the body.

Need for Excretion:

• Waste products like CO₂, urea, and excess salts can be toxic.
• Excretion prevents the accumulation of harmful substances.

Excretion in Different Organisms:

• Unicellular organisms – Diffusion through the cell membrane.
• Plants – Excrete oxygen (from photosynthesis) and store waste in vacuoles.
• Humans (Excretory System) – Major excretory organs:
  • Kidneys – Filter blood, remove urea (urine).
  • Lungs – Remove CO₂.
  • Skin – Excretes salts and water (sweat).

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7. Summary of Life Processes

Life Process	Definition	Example
Nutrition	Obtaining and utilizing food	Plants (photosynthesis), Humans (eating)
Respiration	Breaking down food to release energy	Aerobic respiration in humans, Anaerobic respiration in yeast
Transportation	Movement of substances within an organism	Blood circulation in humans, Xylem and Phloem in plants
Excretion	Removal of waste products	Urination in humans, Oxygen release in plants

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8. Conclusion

Life processes are essential for survival and proper functioning of living organisms. While unicellular organisms use simple diffusion for these processes, multicellular organisms have specialized systems. Understanding these biological mechanisms helps in appreciating how life is sustained.

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QUESTIONS & ANSWERS

1. Why is diffusion insufficient to meet the oxygen requirements of multicellular organisms like humans?

Answer: Diffusion is insufficient for multicellular organisms because:

• In large organisms, body cells are far from the surface, making direct gas exchange inefficient.
• Diffusion is a slow process and cannot transport oxygen quickly to all cells.
• Multicellular organisms need a specialized transport system (like the circulatory system) to efficiently deliver oxygen to every cell.

2. What criteria do we use to decide whether something is alive?

Answer: We determine if something is alive based on these characteristics:

• Movement – Visible movement or molecular movement (e.g., breathing).
• Growth and development – Increase in size and complexity over time.
• Respiration – Release of energy from food.
• Response to stimuli – Reacting to environmental changes.
• Reproduction – Ability to produce offspring.
• Excretion – Removal of waste products from the body.

3. What are outside raw materials used for by an organism?

Answer: Outside raw materials used by an organism include:

• Food – Provides energy and essential nutrients.
• Oxygen – Required for respiration and energy production.
• Water – Helps in biochemical reactions and transportation of substances.
• Minerals – Used for growth, repair, and metabolic functions.

4. What processes would you consider essential for maintaining life?

Answer: The essential life processes for maintaining life are:

• Nutrition – Intake and utilization of food.
• Respiration – Breaking down food for energy.
• Transportation – Distribution of nutrients, gases, and wastes.
• Excretion – Removal of waste products from the body.
• Reproduction – Ensuring the continuity of species.

Nutrition

1. Introduction

• Definition: Nutrition is the process by which organisms obtain and utilize food for energy, growth, and maintenance.
• Importance of Nutrition:
  • Provides energy for all life activities.
  • Supplies raw materials for growth and repair.
  • Helps in the synthesis of essential biomolecules like proteins and enzymes.
• Different Modes of Nutrition:
• Autotrophic Nutrition (self-sustained food production).
• Heterotrophic Nutrition (obtaining food from other sources).

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2. Autotrophic Nutrition

Definition:

• Organisms synthesize their own food using simple inorganic substances like carbon dioxide and water.
• Example: Green plants, algae, and some bacteria.

Photosynthesis: The Key Process

Definition: The process by which autotrophs convert light energy into chemical energy (glucose).
Equation:

Steps in Photosynthesis:

1. Absorption of light energy by chlorophyll.
2. Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen.
3. Reduction of carbon dioxide to form carbohydrates.

Factors Affecting Photosynthesis:

• Light intensity – Higher intensity increases photosynthesis.
• Carbon dioxide concentration – More CO₂ leads to higher photosynthesis.
• Water availability – Required for the splitting process.
• Temperature – Enzymes work best at an optimum temperature.

Role of Stomata in Photosynthesis:

• Stomata are small pores on leaves that help in gas exchange.
• Guard cells control the opening and closing of stomata to reduce water loss.

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3. Heterotrophic Nutrition

Definition:

Organisms obtain food from other living or dead organisms.

Types of Heterotrophic Nutrition:

1. Holozoic Nutrition (Ingestion of solid food)
   • Food is ingested, digested, absorbed, and assimilated.
   • Example: Humans, Cows, Dogs.
2. Saprotrophic Nutrition (Feeding on dead matter)
   • Organisms secrete enzymes externally and absorb nutrients.
   • Example: Fungi (Mushroom, Bread Mould).
3. Parasitic Nutrition (Living on a host)
   • The organism derives nutrition from another living being (host).
   • Example: Lice, Tapeworm, Cuscuta (Amar-bel).

Nutrition in Unicellular Organisms

1. Amoeba:
   • Engulfs food using pseudopodia (finger-like extensions).
   • Food is digested in food vacuole and absorbed into the cytoplasm.
   • Waste is excreted by moving undigested material to the surface.
2. Paramecium:
   • Food enters through a fixed spot.
   • Cilia move food into the food vacuole.

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4. Nutrition in Human Beings

Human Digestive System

• Function: Converts complex food into simpler absorbable forms.
• Parts of the Alimentary Canal:

Part	Function
Mouth & Buccal Cavity	Food is chewed and mixed with saliva.
Oesophagus (Food Pipe)	Moves food to the stomach via peristalsis.
Stomach	Digests proteins; releases HCl & Pepsin.
Small Intestine	Complete digestion of food; absorption of nutrients.
Large Intestine	Absorbs water; prepares waste for excretion.
Anus	Expels undigested waste (egestion).

Process of Digestion in Humans:

1. Ingestion (Intake of Food):
   • Food is chewed and mixed with saliva, which contains the enzyme salivary amylase (breaks down starch into sugar).
2. Digestion in the Stomach:
   • Gastric glands release:
     • Hydrochloric Acid (HCl) – Creates acidic pH for enzyme activity.
     • Pepsin – Begins protein digestion.
     • Mucus – Protects the stomach lining from acid.
3. Digestion in the Small Intestine:
   • Liver secretes bile – Helps break down fats (emulsification).
   • Pancreas releases enzymes:
     • Trypsin – Digests proteins.
     • Lipase – Breaks down fats.
     • Amylase – Converts carbohydrates into glucose.
4. Absorption in the Small Intestine:
   • The villi increase the surface area for maximum nutrient absorption.
   • Absorbed food is transported through blood to all body cells.
5. Egestion (Waste Removal):
   • Large intestine absorbs water, and waste is expelled through the anus.

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5. Digestive Enzymes and Their Functions

Enzyme	Site of Action	Function
Salivary Amylase	Mouth (saliva)	Converts starch into maltose.
Pepsin	Stomach	Breaks proteins into peptides.
Trypsin	Small Intestine (Pancreas)	Completes protein digestion.
Lipase	Small Intestine (Pancreas)	Breaks fats into fatty acids & glycerol.
Maltase	Small Intestine	Converts maltose into glucose.

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6. Importance of a Balanced Diet

• Carbohydrates – Provide energy.
• Proteins – Essential for growth and repair.
• Fats – Store energy and insulate the body.
• Vitamins & Minerals – Regulate body functions.
• Water – Essential for metabolism.

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7. Dental Caries (Tooth Decay)

• Causes:
  • Bacteria break down sugar into acids, which erode enamel.
  • Formation of dental plaque (bacterial coating on teeth).
• Prevention:
  • Brushing teeth regularly removes plaque.
  • Reducing sugar intake prevents acid production.
  • Using fluoride toothpaste strengthens enamel.

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8. Summary of Nutrition

Type of Nutrition	Definition	Example
Autotrophic	Organisms make their own food using photosynthesis.	Green plants, Algae
Heterotrophic	Organisms obtain food from other sources.	Humans, Fungi
Holozoic	Ingesting, digesting, and absorbing food.	Humans, Amoeba
Saprotrophic	Feeding on dead organic matter.	Fungi, Bacteria
Parasitic	Feeding on a host organism.	Lice, Tapeworm

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9. Conclusion

• Nutrition is essential for providing energy and raw materials to organisms.
• Autotrophs use photosynthesis, while heterotrophs rely on other organisms for food.
• The human digestive system is highly specialized for food processing and nutrient absorption.
• A balanced diet is crucial for a healthy life.

QUESTIONS & ANSWERS

1. What advantage over an aquatic organism does a terrestrial organism have with regard to obtaining oxygen for respiration?

Answer:

• Terrestrial organisms breathe air, which contains more oxygen than water.
• Oxygen diffuses faster in air than in water, making it more readily available for respiration.
• Aquatic organisms extract dissolved oxygen from water, but its concentration is much lower than in air.
• Terrestrial organisms have efficient respiratory systems (lungs in mammals, trachea in insects) to take in more oxygen quickly, whereas aquatic organisms rely on gills, which need continuous water flow for oxygen exchange.

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2. What are the different ways in which glucose is oxidised to provide energy in various organisms?

Answer:
Glucose is oxidized in two ways: Aerobic respiration and Anaerobic respiration.

1. Aerobic Respiration (With Oxygen):
   • Occurs in most plants and animals.
   • Glucose is fully broken down into carbon dioxide (CO₂) and water (H₂O), releasing high energy (ATP).
   • Equation: $$C_6H_{12}O_6 + 6O_2 → 6CO_2 + 6H_2O + Energy (ATP)$$
2. Anaerobic Respiration (Without Oxygen):
   • Occurs in some microorganisms (like yeast) and human muscle cells under oxygen deficiency.
   • Glucose is partially broken down into lactic acid (in muscles) or ethanol and CO₂ (in yeast), releasing less energy.
   • Equation (Yeast Fermentation): $$C_6H_{12}O_6 → Alcohol + CO_2 + Energy$$
   • Equation (Muscle Fatigue in Humans): $$C_6H_{12}O_6 → Lactic Acid + Energy$$

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3. How is oxygen and carbon dioxide transported in human beings?

Answer:

• Oxygen Transport:

  • Oxygen enters the lungs during inhalation.
  • In the lungs, oxygen binds with hemoglobin in red blood cells (RBCs) to form oxyhemoglobin.
  • This oxygen-rich blood is transported to all body cells, where oxygen is released for respiration.

• Carbon Dioxide Transport:

  • Carbon dioxide (a waste product of respiration) diffuses from cells into the blood.
  • It is transported in three ways:
    1. As bicarbonate ions (HCO₃⁻) in plasma (70%).
    2. Bound to hemoglobin (carbaminohemoglobin) (20%).
    3. Dissolved directly in blood plasma (10%).
  • The lungs remove CO₂ from the blood, which is exhaled out of the body.

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4. How are the lungs designed in human beings to maximise the area for exchange of gases?

Answer:
The lungs are adapted for efficient gas exchange through the following features:

1. Millions of alveoli (air sacs):

   • Lungs contain millions of alveoli, increasing the surface area for gas exchange.
   • This allows more oxygen to diffuse into the blood and more CO₂ to be expelled.

2. Thin walls of alveoli:

   • The one-cell thick alveolar walls enable rapid diffusion of gases.

3. Rich blood supply:

   • Alveoli are surrounded by capillaries, ensuring continuous oxygen uptake and carbon dioxide removal.

4. Moist surface:

   • The inner surface of alveoli is moist, helping gases dissolve and diffuse easily.

5. Breathing mechanism:

   • The diaphragm and intercostal muscles help in expansion and contraction, facilitating continuous air exchange.

Transportation in Living Organisms 

1. Introduction

Transportation is the process by which nutrients, gases, water, and waste materials are carried throughout the body of organisms. Since diffusion alone is insufficient in complex organisms, specialized transport systems are required.

Why is Transportation Necessary?

• To deliver oxygen and nutrients to all body cells.
• To remove waste materials like CO₂ and nitrogenous wastes.
• To maintain homeostasis (internal stability).

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2. Transportation in Human Beings

2.1 Components of the Human Circulatory System

The circulatory system in humans consists of:

1. Blood – The transport medium.
2. Heart – The pumping organ.
3. Blood Vessels – Arteries, veins, and capillaries.

2.2 Blood and Its Components

Component	Function
Plasma	Transports nutrients, hormones, CO₂, and waste materials.
Red Blood Cells (RBCs)	Contain hemoglobin for oxygen transport.
White Blood Cells (WBCs)	Fight infections and provide immunity.
Platelets	Help in blood clotting to prevent excessive bleeding.

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2.3 Structure and Function of the Human Heart

• The heart is a muscular organ about the size of a fist.
• It has four chambers:
  • Left Atrium & Left Ventricle → Receive and pump oxygenated blood.
  • Right Atrium & Right Ventricle → Receive and pump deoxygenated blood.
• Valves prevent backflow of blood.

Steps of Blood Circulation:

1. Oxygen-rich blood from the lungs enters the left atrium.
2. It is pumped into the left ventricle and then to the rest of the body.
3. Deoxygenated blood from the body enters the right atrium.
4. It is pumped into the right ventricle and then to the lungs for oxygenation.

This double circulation ensures that oxygenated and deoxygenated blood do not mix, making oxygen transport highly efficient.

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2.4 Blood Pressure

• Definition: The force exerted by blood against the walls of arteries.
• Measured by: Sphygmomanometer.
• Types:
  • Systolic Pressure (120 mm Hg) – During heart contraction.
  • Diastolic Pressure (80 mm Hg) – During heart relaxation.
• Hypertension (High Blood Pressure): Caused by narrowing of arteries, leading to increased resistance and risk of internal bleeding.

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2.5 Blood Vessels

Type	Function	Features
Arteries	Carry blood away from the heart.	Thick, elastic walls due to high pressure.
Veins	Carry blood back to the heart.	Thin walls, contain valves to prevent backflow.
Capillaries	Allow exchange of gases, nutrients, and waste.	One-cell thick walls for diffusion.

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2.6 Blood Clotting

• Platelets help stop bleeding by forming blood clots at injury sites.
• Clotting prevents excessive blood loss and maintains blood pressure.

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2.7 Lymphatic System

• Lymph is a clear fluid that helps in:
  • Transporting fats from the intestine.
  • Draining excess fluid from tissues into the bloodstream.
  • Immunity (contains WBCs).
• Lymph flows through lymphatic vessels, which open into large veins.

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3. Transportation in Plants

Unlike animals, plants have two separate transport systems for:

1. Water and minerals (Xylem).
2. Food and organic substances (Phloem).

3.1 Transport of Water and Minerals (Xylem)

• Water and minerals move from roots to leaves through xylem.
• How does water move upwards?
  1. Root Pressure: Roots absorb water, creating a push effect.
  2. Capillary Action: Water moves up through narrow xylem tubes.
  3. Transpiration Pull: Loss of water from stomata creates a suction force, pulling water upwards.
  4. Cohesion and Adhesion: Water molecules stick to each other and to xylem walls, aiding movement.

Transpiration:

• The loss of water as vapour through stomata.
• Helps in:
  • Cooling the plant.
  • Maintaining water movement.

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3.2 Transport of Food (Phloem – Translocation)

• The phloem transports food from leaves to other parts of the plant.
• Movement occurs in both directions (upward & downward).
• Process of Translocation:
  1. Sucrose (sugar) is actively loaded into phloem using ATP.
  2. Water enters phloem, creating pressure that moves food to required parts.
  3. Food is delivered to storage organs (roots, fruits, seeds) or growing parts.

Difference Between Xylem and Phloem:

Feature	Xylem	Phloem
Function	Transports water and minerals	Transports food (sugars, amino acids, hormones)
Direction	Upward (roots to leaves)	Both directions (upward & downward)
Tissue Type	Dead (vessels & tracheids)	Living (sieve tubes & companion cells)

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4. Summary of Transportation in Living Organisms

Organism	Transport System	Function
Humans	Circulatory System (Blood & Lymph)	Transport oxygen, nutrients, and waste.
Plants	Xylem	Transports water & minerals from roots to leaves.
Plants	Phloem	Transports food from leaves to the rest of the plant.

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5. Conclusion

• Humans and animals rely on a circulatory system with blood, heart, and vessels.
• Plants use two transport systems:
  • Xylem for water and minerals.
  • Phloem for food and organic substances.
• The efficiency of transport systems allows organisms to grow, survive, and function properly.

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QUESTIONS & ANSWERS

1. What are the components of the transport system in human beings? What are the functions of these components?

Answer:
The transport system in human beings consists of:

Component	Function
Heart	Pumps blood to all parts of the body.
Blood	Carries oxygen, nutrients, hormones, and waste materials.
Blood Vessels	Transport blood throughout the body (arteries, veins, capillaries).
Lymphatic System	Transports white blood cells and drains excess fluid.

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2. Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?

Answer:

• Mammals and birds are warm-blooded and need a constant body temperature.
• They have high energy needs to maintain their metabolism.
• Separation of oxygenated and deoxygenated blood ensures an efficient supply of oxygen to all body cells.
• It prevents mixing of blood, ensuring that tissues receive only oxygen-rich blood for better respiration.

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3. What are the components of the transport system in highly organized plants?

Answer:
The transport system in plants consists of two vascular tissues:

Component	Function
Xylem	Transports water and minerals from roots to leaves.
Phloem	Transports food (sugars, amino acids) from leaves to other parts of the plant.

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4. How are water and minerals transported in plants?

Answer:
Water and minerals are transported from roots to leaves through xylem by:

1. Root Pressure – Water enters roots by osmosis, pushing it upward.
2. Capillary Action – Water moves up through narrow xylem tubes.
3. Transpiration Pull – Water evaporates from leaves, creating a suction force.
4. Cohesion and Adhesion – Water molecules stick to each other and to xylem walls, helping upward movement.

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5. How is food transported in plants?

Answer:
Food is transported in plants through phloem by a process called translocation.

• Sucrose (sugar) is actively loaded into phloem using ATP energy.
• Water moves into phloem, creating pressure differences.
• The food moves from high-pressure areas (leaves) to low-pressure areas (roots, fruits, and other growing parts).
• Unlike xylem, phloem transport occurs in both directions.

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Excretion 

1. Introduction

• Definition: Excretion is the process of removing metabolic waste products from the body to maintain internal balance (homeostasis).
• Importance of Excretion:
  • Eliminates toxic substances like urea and carbon dioxide.
  • Maintains water and salt balance in the body.
  • Prevents damage to tissues due to waste accumulation.

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2. Excretion in Human Beings

2.1 Human Excretory System

The human excretory system consists of:

Organ	Function
Kidneys (2)	Filter blood and produce urine.
Ureters (2)	Transport urine from kidneys to bladder.
Urinary Bladder	Stores urine temporarily.
Urethra	Releases urine from the body.

2.2 Structure and Function of the Kidney

• The kidney is the main organ of excretion, located on both sides of the backbone.
• It filters out nitrogenous wastes (urea, uric acid) from the blood and produces urine.

2.3 Structure of Nephron (Basic Unit of Kidney)

• Nephrons are the functional units of the kidney responsible for filtration.
• Each nephron consists of:
  • Bowman’s Capsule – Cup-shaped structure that collects filtrate.
  • Glomerulus – A network of thin-walled capillaries for filtration.
  • Renal Tubule – Reabsorbs useful substances (water, glucose, salts).
  • Collecting Duct – Sends urine to the ureter.

2.4 Steps of Urine Formation

1. Filtration:
   • Blood enters the glomerulus, and wastes are filtered into the Bowman’s capsule.
   • Filtrate contains water, urea, salts, glucose, and amino acids.
2. Reabsorption:
   • Useful substances (glucose, amino acids, and most water) are reabsorbed into the blood.
3. Excretion:
   • The remaining waste and excess water form urine, which is sent to the bladder for storage.

2.5 Artificial Kidney (Hemodialysis)

• Used in kidney failure to remove waste from the blood.
• A dialysis machine filters waste from blood, similar to a kidney.
• No reabsorption occurs in dialysis, unlike a normal kidney.

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3. Excretion in Plants

Plants have different excretion strategies compared to animals.

3.1 Waste Products in Plants

• Oxygen (O₂): Released as a waste product of photosynthesis.
• Carbon dioxide (CO₂): Removed during respiration.
• Water (H₂O): Lost through transpiration.

3.2 Methods of Excretion in Plants

Method	Description
Diffusion	Gases like O₂ and CO₂ diffuse out through stomata.
Transpiration	Excess water evaporates through leaves.
Storage in Vacuoles	Waste materials are stored in cell vacuoles.
Leaf Shedding	Toxic substances accumulate in old leaves, which fall off.
Excretion into Soil	Some plants release wastes into the surrounding soil.
Secretion of Gums & Resins	Wastes are stored in old xylem in the form of gums and resins.

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4. Organ Donation & Transplantation

• Organ donation is a process where an organ is taken from one person (donor) and transplanted into another person (recipient).
• Organs that can be donated:
  • While alive: Kidney, part of liver, lung, bone marrow.
  • After death: Heart, liver, pancreas, intestines, corneas, lungs, skin, tissues.
• Importance of Organ Donation:
  • Saves lives of patients with organ failure.
  • Improves the quality of life for recipients.
  • Promotes medical research and treatment advances.

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5. Summary of Excretion

Organism	Excretory System	Main Waste Products
Humans	Kidneys, Ureters, Bladder, Urethra	Urea, Uric Acid, Excess Water & Salts
Plants	Stomata, Vacuoles, Xylem, Phloem	O₂, CO₂, Water, Resins, Gums

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6. Conclusion

• Excretion is vital for removing metabolic waste and maintaining balance.
• Humans have a complex excretory system using kidneys and nephrons.
• Plants use diffusion, transpiration, and vacuoles for excretion.
• Artificial kidneys and organ transplants help patients with organ failure.

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Answers to the Questions:

1. Describe the structure and functioning of nephrons.

Structure of Nephrons:

• Nephrons are the structural and functional units of the kidney.

• Each kidney contains millions of nephrons, which help in filtering blood and producing urine.

• A nephron consists of the following parts:

  Part	Function
  Bowman’s Capsule	Cup-shaped structure that encloses the glomerulus and collects the filtrate.
  Glomerulus	A network of capillaries that filters waste, water, and small molecules from the blood.
  Renal Tubule	Long, coiled tubule where useful substances (glucose, amino acids, water) are reabsorbed.
  Collecting Duct	Carries urine from multiple nephrons to the ureter.

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Functioning of Nephrons (Urine Formation Process):

Nephrons filter blood and form urine through three major steps:

1. Filtration (Glomerular Filtration):

   • Blood enters the glomerulus, and high pressure forces water, salts, urea, glucose, and amino acids into the Bowman’s capsule.
   • Large molecules like proteins and blood cells remain in the blood.

2. Reabsorption (Selective Reabsorption):

   • The filtrate flows through the renal tubule, where useful substances are reabsorbed into the blood (e.g., glucose, amino acids, most water, and salts).
   • Only waste and excess substances remain.

3. Excretion (Urine Formation):

   • The remaining filtrate (urine) moves into the collecting duct, then to the ureter, and finally to the urinary bladder for storage.
   • Urine is expelled from the body through the urethra.

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2. What are the methods used by plants to get rid of excretory products?

Plants have different mechanisms for excreting waste products:

Method	Description
Diffusion	Gases like oxygen (O₂) and carbon dioxide (CO₂) are removed through stomata and lenticels.
Transpiration	Excess water evaporates through the leaves.
Storage in Vacuoles	Waste substances are stored in vacuoles inside plant cells.
Leaf Shedding	Toxic substances accumulate in old leaves, which fall off.
Storage in Old Xylem	Wastes are stored as resins and gums in dead xylem tissues.
Excretion into Soil	Some plants release excess waste into the soil through roots.

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3. How is the amount of urine produced regulated?

The amount of urine produced is regulated by:

1. Water Balance in the Body:

• More water in the body → More urine is produced.
• Less water in the body → Less urine is produced to conserve water.

2. Hormonal Control:

• The antidiuretic hormone (ADH) (also called vasopressin) plays a key role.
• When water is low in the body, ADH increases water reabsorption in the kidneys, reducing urine output.
• When there is excess water, ADH secretion decreases, leading to more urine production.

3. Salt and Waste Concentration:

• If there is high salt and waste concentration in the blood, the kidneys produce more urine to remove them.
• If the blood has low salt levels, urine production decreases to maintain balance.

4. Temperature and External Conditions:

• In hot weather or excessive sweating, less urine is produced as more water is lost through sweat.
• In cold weather, more urine is produced as sweating is reduced.

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Summary of Key Points:

Question	Key Answer
Structure & Functioning of Nephron	Nephrons filter blood and form urine through filtration, reabsorption, and excretion.
Excretion in Plants	Plants excrete wastes through diffusion, transpiration, vacuoles, leaf shedding, resins, and soil release.
Urine Regulation	Controlled by water balance, hormones (ADH), salt levels, and environmental conditions.

EXERCISES – QUESTIONS & ANSWERS

1. The kidneys in human beings are a part of the system for

(a) nutrition
(b) respiration
(c) excretion ✅
(d) transportation

Answer: The kidneys are part of the excretory system, responsible for removing nitrogenous wastes (urea, uric acid) from the blood and maintaining water balance in the body.

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2. The xylem in plants is responsible for

(a) transport of water ✅
(b) transport of food
(c) transport of amino acids
(d) transport of oxygen

Answer: Xylem transports water and minerals from the roots to the leaves in a unidirectional flow through the process of transpiration pull.

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3. The autotrophic mode of nutrition requires

(a) carbon dioxide and water
(b) chlorophyll
(c) sunlight
(d) all of the above ✅

Answer: Autotrophic nutrition requires carbon dioxide (CO₂), water (H₂O), sunlight, and chlorophyll to perform photosynthesis, which produces glucose and oxygen.

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4. The breakdown of pyruvate to give carbon dioxide, water, and energy takes place in

(a) cytoplasm
(b) mitochondria ✅
(c) chloroplast
(d) nucleus

Answer: Pyruvate is broken down in the mitochondria during aerobic respiration, releasing carbon dioxide (CO₂), water (H₂O), and energy (ATP).

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5. How are fats digested in our bodies? Where does this process take place?

Answer:

• Fats are digested in the small intestine.
• The liver secretes bile, which breaks down large fat molecules into smaller droplets (emulsification).
• The pancreas releases lipase, which converts fats into fatty acids and glycerol, which can be absorbed into the bloodstream.

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6. What is the role of saliva in the digestion of food?

Answer:

• Saliva, secreted by the salivary glands, contains salivary amylase, which converts starch into maltose.
• It moistens food, making it easier to chew and swallow.
• It helps in the initial digestion of carbohydrates before food enters the stomach.

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7. What are the necessary conditions for autotrophic nutrition and what are its by-products?

Answer:

• Conditions required:

  • Carbon dioxide (CO₂) from the air.
  • Water (H₂O) absorbed from the soil.
  • Sunlight as an energy source.
  • Chlorophyll present in leaves.

• By-products of photosynthesis:

  • Glucose (C₆H₁₂O₆) – Stored as starch in plants.
  • Oxygen (O₂) – Released into the atmosphere.

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8. What are the differences between aerobic and anaerobic respiration? Name some organisms that use the anaerobic mode of respiration.

Answer:

Feature	Aerobic Respiration	Anaerobic Respiration
Oxygen Requirement	Requires oxygen	Does not require oxygen
Location	Occurs in mitochondria	Occurs in cytoplasm
End Products	CO₂, H₂O, and ATP	Lactic acid (in muscles) / Alcohol & CO₂ (in yeast)
Energy Released	High (36-38 ATP)	Low (2 ATP)
Example Organisms	Humans, plants, animals	Yeast, some bacteria, muscle cells (during heavy exercise)

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9. How are the alveoli designed to maximise the exchange of gases?

Answer:

• Millions of alveoli increase surface area for gas exchange.
• Thin walls (one-cell thick) allow rapid diffusion of oxygen and carbon dioxide.
• Rich blood supply (capillaries) helps in efficient exchange.
• Moist lining facilitates the dissolution of gases.

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10. What would be the consequences of a deficiency of haemoglobin in our bodies?

Answer:

• Reduced oxygen transport, leading to fatigue and weakness.
• Increased breathing rate to compensate for low oxygen levels.
• Dizziness and pale skin due to less oxygen in blood.
• Severe cases lead to anaemia, affecting overall health.

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11. Describe double circulation of blood in human beings. Why is it necessary?

Answer:

• Double circulation means blood passes through the heart twice in one complete cycle.

• It includes:
  1. Pulmonary Circulation:

  • Oxygen-poor blood from the right ventricle is sent to the lungs for oxygenation.
  • Oxygen-rich blood returns to the left atrium.
    2. Systemic Circulation:
  • Oxygen-rich blood from the left ventricle is sent to the body.
  • Deoxygenated blood returns to the right atrium.

• Necessity:

  • Keeps oxygenated and deoxygenated blood separate.
  • Ensures efficient oxygen supply to all body cells.
  • Maintains higher metabolism in warm-blooded animals.

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12. What are the differences between the transport of materials in xylem and phloem?

Answer:

Feature	Xylem	Phloem
Function	Transports water and minerals	Transports food (sugars, amino acids)
Direction	Upward (roots to leaves)	Bidirectional (up & down)
Cell Type	Dead cells	Living cells
Mechanism	Passive transport (no energy needed)	Active transport (requires ATP)

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13. Compare the functioning of alveoli in the lungs and nephrons in the kidneys with respect to their structure and functioning.

Answer:

Feature	Alveoli (Lungs)	Nephrons (Kidneys)
Function	Exchange of O₂ and CO₂	Filtration of blood and urine formation
Structure	Tiny air sacs with thin walls	Tubular structures with filtration units
Process	O₂ diffuses in, CO₂ diffuses out	Filters waste; reabsorbs useful substances
End Product	Oxygenated blood	Urine (urea, salts, excess water)

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