Revision: Busy at Work - Our Internal Organs Environmental Studies 1 SSC (English Medium) 5th Standard Maharashtra State Board

Difficulty or labored breathing, often described as shortness of breath.

It is a type of reflex whose stimulus is in the nasal passage which causes spasmodic contraction of expiratory muscles that forcefully expel the air through the nasal passage.

It is a type of reflex whose stimulus is any foreign particle, resulting from deep inspiration followed by strong expiration, which forcefully expels the air through the mouth.

The trachea is commonly called a windpipe. It is a tube supported by cartilaginous rings that connect the pharynx and larynx to the lungs, allowing the passage of air. The trachea divides into right and left bronchi and enters the lungs.

The process of conversion of glucose molecules in food into energy-rich molecules, carbon dioxide and water with the help of oxygen is known as respiration.

Eupnea is the medical and physiological term for normal, unlabored, and quiet breathing in a healthy individual at rest. It represents an efficient respiratory state where the body maximizes oxygen intake while minimizing muscular effort.

Apnea is defined as the temporary cessation of breathing, marked by the absence of respiratory muscle movement and airflow.

The exchange of gases through moist skin and blood capillaries underneath is called cutaneous respiration.

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.

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.

The circulatory system is a transport system moving substances throughout our body with the help of blood.

Veins are the blood vessels that carry deoxygenated (impure) blood from the body cells to the heart.

Arteries are the blood vessels in which oxygenated blood is going away from the heart to all parts of the body.

Neurons are the building blocks of the nervous system and transmit information throughout the body.

The neurons which carry impulses from the brain or spinal cord to the body parts are called motor or efferent neurons.

The neurons which carry impulses from the body parts to the spinal cord or the brain are called sensory or afferent neurons. For example, the optic nerve of the eye.

A stimulus is an agent or a sudden change in the external or internal environment that changes an organism or body parts. e.g., light, sound, heat, pain, hunger.

The path that an impulse takes in a reflex action is called a reflex arc.

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.

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.

• Two Parts — Upper (nasal cavities, pharynx, throat) | Lower (larynx, trachea, bronchi, bronchioles, lungs).
• Nasal Cavity & Pharynx — Nasal cavity is divided into 2 chambers by the mesethmoid cartilage. Pharynx: Nasopharynx → Oropharynx (common food & air) → Laryngopharynx.
• Larynx & Trachea — Glottis covered by epiglottis (prevents food entry). Trachea held by 16–20 C-shaped cartilage rings.
• Lungs & Alveoli — Right = 3 lobes, Left = 2 lobes, covered by pleural membranes. Alveoli = site of O₂/CO₂ exchange.
• Path of Air — Nasal cavity → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli (exchange) → reverse for CO₂.
• Gas Transport — O₂ carried by haemoglobin (RBCs) | CO₂ in dissolved form in plasma.
• Other Organisms — Plants: stomata | Fish: gills (breathe faster, less O₂ in water) | Terrestrial animals: lungs.

• 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.

• Receptors present in sense organs detect changes in the environment and send signals to the brain through neurons.
• A neuron has three parts — dendrites (receive signals), cell body (processes signals), and axon (transmits signals) — which work together to carry electrical impulses.
• The electrical impulse always travels in one fixed direction: dendrite → cell body → axon → axon terminal, ensuring a controlled flow of information.
• At the synapse, special chemicals called neurotransmitters are released to pass the impulse from one neuron to the next, or to a muscle or gland.
• The neuromuscular junction is where a nerve meets a muscle fibre; when the impulse reaches this point, it causes the muscle to contract and produce a response.

• 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.