Revision: Organ Systems in Animals Science SSLC (English Medium) Class 9 Tamil Nadu Board of Secondary Education

The organisms which feed upon other animals and animal products.

Examples - tiger, lion, cat, etc.

It is the breaking down of complex insoluble food components into simple soluble substances.

The organisms which feed on all kinds of plant and animal food are called omnivores.

Examples - Cockroach and human beings.

These are the organisms which prepare organic food in their body from simple inorganic materials like carbon dioxide, water, etc.

Example - green plants and certain protests.

The organisms that feed on plants only are termed as herbivores.

Examples - sheep, cow, goat, etc.

Peristalsis is the rhythmic contraction and relaxation of the muscles of the alimentary canal that pushes the food along the gut.

Pylorus is the passage at the lower end of the stomach that opens into the duodenum.

Omnivores are organisms that consume both plants and animals.

Absorption of substances which are built into other compounds in the organisms. 

A kilocalorie is a unit of energy. It is the energy required to raise the temperature of 1 kg of water by 1 Celsius.

Egestion — The process of removal of the undigested food from the body is defined as egestion.

Digestion — The process of breaking the food into smaller and simpler substances so that they can be easily used by the body is called digestion.

The process by which all organisms obtain or synthesize their food and convert it into simpler substances, so that it can be absorbed and utilized by the cells of the body is called nutrition.

Assimilation — The process of using the digested food by the body is called assimilation.

The process of converting complex food substances into simpler and smaller units so that they can be easily utilised by the body is defined as digestion.
E.g. proteins are converted to amino acids.

Holozoic nutrition is a mode of nutrition in which an organism takes complex organic food materials into its body by ingestion; the ingested food is digested and then absorbed into the organism's body cells.

The organisms which cannot prepare their own food and depends on ready-made food synthesized by green plants are called heterotrophs.

Examples - animals and human beings.

A nutrient can be defined as a substance which an organism obtains from its surroundings and uses as a source of energy or for the biosynthesis of its body constituents (like tissues and organs).

Assimilation — The process of using the digested food by the body is called assimilation.

The organisms which feed upon other animals and animal products.

Examples - tiger, lion, cat, etc.

It is the breaking down of complex insoluble food components into simple soluble substances.

The organisms which feed on all kinds of plant and animal food are called omnivores.

Examples - Cockroach and human beings.

These are the organisms which prepare organic food in their body from simple inorganic materials like carbon dioxide, water, etc.

Example - green plants and certain protests.

The organisms that feed on plants only are termed as herbivores.

Examples - sheep, cow, goat, etc.

Peristalsis is the rhythmic contraction and relaxation of the muscles of the alimentary canal that pushes the food along the gut.

Pylorus is the passage at the lower end of the stomach that opens into the duodenum.

Omnivores are organisms that consume both plants and animals.

Absorption of substances which are built into other compounds in the organisms. 

A kilocalorie is a unit of energy. It is the energy required to raise the temperature of 1 kg of water by 1 Celsius.

Egestion — The process of removal of the undigested food from the body is defined as egestion.

Digestion — The process of breaking the food into smaller and simpler substances so that they can be easily used by the body is called digestion.

The process by which all organisms obtain or synthesize their food and convert it into simpler substances, so that it can be absorbed and utilized by the cells of the body is called nutrition.

The process of converting complex food substances into simpler and smaller units so that they can be easily utilised by the body is defined as digestion.
E.g. proteins are converted to amino acids.

Holozoic nutrition is a mode of nutrition in which an organism takes complex organic food materials into its body by ingestion; the ingested food is digested and then absorbed into the organism's body cells.

The organisms which cannot prepare their own food and depends on ready-made food synthesized by green plants are called heterotrophs.

Examples - animals and human beings.

A nutrient can be defined as a substance which an organism obtains from its surroundings and uses as a source of energy or for the biosynthesis of its body constituents (like tissues and organs).

Kidneys are the primary excretory organs, eliminating nitrogenous wastes (chiefly urea) from the blood and throwing it out in the form of urine.

During different metabolic activities taking place in our body, the body produces many substances of which some are useful and some are useless.
If retained in the body the unwanted substances may become poisonous and cause much harm and in severe cases, even death. The organs which remove these unwanted and toxic substances from the body are called excretory organs.

During different metabolic activities taking place in our body, the body produces many substances, of which some are useful and some are useless.
The process of removing useless and harmful metabolic waste substances is called excretion.

The process of removal of chemical wastes (Mainly Nitrogenous) from the body is known as ''excretion''. It plays an important role in maintaining the homeostatic (steady-state) condition of the body.

The apex of each pyramid in the medulla of the kidney that projects into the pelvis is called the papilla.

The kidney is composed of an enormous number of minute tubules called uriniferous tubules or nephrons or renal tubules or just kidney tubules. These are the structural and functional units of the kidney. 

Bowman's capsule is a thin-walled, cup-shaped structure in the nephron that surrounds the glomerulus and collects the filtrate from the blood.

The glomerulus is a knot-like network of blood capillaries located inside the Bowman's capsule, where blood filtration occurs.

The Malpighian capsule is the combined structure of the Bowman's capsule and glomerulus, forming the filtration unit of the nephron.

Inside the kidney, there are millions of microscopic tubes called renal tubules or nephrons. It is the structural and functional unit of the kidney.

Selective absorption is the process by which only useful substances like glucose, some salts, and water are absorbed from the renal tubule back into the blood, without disturbing its normal concentration.

The blood flows through the glomerulus under great pressure which causes the liquid part of the blood to filter out from the glomerulus into the renal tubule. This filtration under high force is called Ultrafiltration.

Glomerular filtration rate is the amount of glomerular filtrate formed in all the nephrons of both kidneys per minute. In a healthy individual, it is about 125 ml/minute.

The artificial process which cleans and filters the blood in a person where one or both the kidney may stop working properly is called dialysis.

Tubular secretion is the active transfer of certain substances, such as ions and drugs, from the blood into the renal tubule during urine formation.

Glomerular filtrate is the fluid formed after ultrafiltration that enters the renal tubule and contains water, urea, salts, glucose, and other small molecules.

Ultrafiltration is the process in which blood is filtered under high pressure in the glomerulus, allowing water and small solutes to pass into the Bowman’s capsule.

An artificial kidney is a dialysis machine that removes urea and excess salts from the blood when both kidneys fail, and returns the purified blood back into the body.

Dialysis is a medical process in which nitrogenous wastes and toxic substances are removed from the blood using an artificial machine when the kidneys fail to function properly.

• Digestion is the conversion of complex food into soluble forms that can be absorbed into the blood.
• The digestive system has two main components: the alimentary canal (mouth to anus) and associated digestive glands.
• The alimentary canal is a long muscular tube about 9 m in adults, including mouth, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus.
• Salivary glands, liver and pancreas are accessory digestive glands that open into this canal and secrete juices needed for digestion.
• Different organs of the digestive system act in sequence; each stage of digestion occurs in a specific organ that performs a specialised mechanical or chemical role.

• The stomach is a muscular J‑shaped sac in the upper left abdomen, between oesophagus and small intestine.
• It has four regions: cardiac, fundus, body and pyloric, each with specific roles in food storage and mixing.
• The body region mainly stores food, churns it and mixes it with gastric juice to form chyme.
• The pyloric region opens into the duodenum and its pyloric sphincter controls the release of chyme.
• The cardiac (lower oesophageal) and pyloric sphincters prevent backflow and regulate movement of food, so regurgitation is avoided.

• The large intestine has a wider diameter than the small intestine.
• It is the terminal part of the alimentary canal.
• It is divided into three main parts: caecum, colon and rectum.
• The rectum opens to the outside through the anus.
• Only minimal digestion occurs here, but water and electrolytes are absorbed efficiently.

• Digestion is the conversion of complex food into soluble forms that can be absorbed into the blood.
• The digestive system has two main components: the alimentary canal (mouth to anus) and associated digestive glands.
• The alimentary canal is a long muscular tube about 9 m in adults, including mouth, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus.
• Salivary glands, liver and pancreas are accessory digestive glands that open into this canal and secrete juices needed for digestion.
• Different organs of the digestive system act in sequence; each stage of digestion occurs in a specific organ that performs a specialised mechanical or chemical role.

• Absorption of nutrients occurs via passive and active transport across the intestinal mucosa.
• In the mouth/buccal cavity, certain drugs that contact the mucosa (e.g., under the tongue) are absorbed directly into blood capillaries.
• In the stomach, a small amount of water, simple sugars, electrolytes, alcohol and some drugs (like aspirin) are absorbed.
• The small intestine is the main site of absorption; final products of digestion such as glucose, fructose, fatty acids, glycerol and amino acids enter blood and lymph here.
• Lipids and fat‑soluble vitamins (A, D, E, K) are absorbed via micelles, converted to chylomicrons in intestinal mucosa, taken up by lacteals in villi and then released into the bloodstream.
• The large intestine absorbs most of the remaining water, some minerals and certain drugs.

• The large intestine has a wider diameter than the small intestine.
• It is the terminal part of the alimentary canal.
• It is divided into three main parts: caecum, colon and rectum.
• The rectum opens to the outside through the anus.
• Only minimal digestion occurs here, but water and electrolytes are absorbed efficiently.

• The human excretory system consists of a pair of kidneys, two ureters, a urinary bladder and a urethra.
• Kidneys are dark red, bean-shaped, retroperitoneal structures located from the 12th thoracic to the 3rd lumbar vertebra. Size: 10-12 cm × 5-7 cm × 2-3 cm; weight: 150 g (males), 135 g (females).
• Ureters are narrow tubular structures made of transitional epithelium that carry urine from the kidneys to the urinary bladder.
• The urinary bladder is a pear-shaped, hollow, muscular organ in the pelvic cavity, lined by transitional epithelium, and acts as a reservoir of urine.
• Two sphincters exist between the bladder and the urethra: the internal sphincter (involuntary, detrusor muscles) and the external sphincter (voluntary, striated muscles).
• The urethra is a canal-like structure that opens to the exterior via the urethral orifice, much longer in males than in females.
• The aorta supplies oxygenated blood to the kidneys; the inferior vena cava carries deoxygenated blood away from the kidneys.

• Humans have two bean-shaped kidneys located on either side of the vertebral column (from the 12th thoracic to the 3rd lumbar vertebra).
• Kidneys help in maintaining homeostasis by regulating water balance (osmoregulation) and pH of body fluids.
• They also secrete erythropoietin, a hormone important for red blood cell production.
• Each kidney has an outer cortex and an inner medulla; the medulla contains conical structures called renal pyramids.
• Cortex extends into medulla, forming renal columns (columns of Bertini), and pyramids open into minor calyces through renal papilla.
• Kidneys are protected by renal capsule, adipose capsule (fat layer), and renal fascia, and contain nephrons, which are functional units for urine formation.

• Nephrons are the structural and functional units of the kidney, each consisting of a glomerulus and a renal tubule, and measuring about 4–6 cm in length.
• The Malpighian corpuscle (glomerulus + Bowman’s capsule) is the site of ultrafiltration, where blood enters through the afferent arteriole and leaves via the efferent arteriole.
• The proximal convoluted tubule (PCT), lined with cuboidal cells and microvilli, is the main site of selective reabsorption of water, ions, and nutrients.
• The loop of Henle extends into the medulla and helps in concentration of urine; its descending limb is permeable to water, while the ascending limb is impermeable to water but allows movement of electrolytes.
• The distal convoluted tubule (DCT) carries out tubular secretion and regulation of ions, and opens into the collecting duct, which reabsorbs water and transports urine to the renal pelvis.
• Nephrons are of two types: cortical nephrons with short loops of Henle and juxtamedullary nephrons with long loops that play a key role in urine concentration.
• The kidneys receive rich blood supply and filter large volumes of blood daily, with most filtrate reabsorbed and about 1–1.5 litres of urine excreted per day.

1. Kidneys are the main excretory organs that remove urea and other nitrogenous wastes from the blood in the form of urine.
2. Skin eliminates small amounts of urea, salts, and water through sweat, mainly for body cooling.
3. Lungs excrete carbon dioxide through exhaled air, playing a key role in gaseous waste removal.
4. Liver helps in detoxification by converting ammonia to urea and breaking down toxins like alcohol and drugs.