Revision: Respiration and Circulation Biology HSC Science (General) 12th Standard Board Exam Maharashtra State Board

The breakdown of glucose in the presence of oxygen to produce carbon dioxide, water, and energy is called aerobic respiration.

It is a process of release of energy from food substances such as glucose and fats under the control of enzymes, to carry out life processes, by the living organisms.

The breakdown of glucose in the absence of oxygen to produce alcohol or lactic acid and a small amount of energy is called anaerobic respiration.

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

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 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.

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.

It is a breathing equipment that is used during surgery, therapy for serious lung disorders, or other cases where normal breathing fails.

A portal vein is one that starts with capillaries and also ends in capillaries.

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

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

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

The plasma from which the protein fibrinogen has been removed is called serum. 

Phagocytosis is a process in which most WBCs, particularly the neutrophils, engulf particle-like solid substances, especially bacteria.

The enzyme released by injured tissues and disintegrating platelets that initiates clotting is called thrombokinase (also known as Thromboplastin or Factor X or Stuart factor).

The solid mass left behind after clotting, formed by fibrin and trapped blood cells, is called clot or thrombus.

Diapedesis is the movement of white blood cells from lymph capillary walls to neighbouring tissues, often for immunological defence.

The heart is a hollow muscular vertebrate organ that pumps blood through rhythmic contractions.

A venule is the smallest branch of a vein formed by the union of capillaries. It has a thin muscular coat and gradually joins with other venules to form larger veins.

An ARTERY is a vessel that carries blood away from the heart towards any organ.

A VEIN is a vessel that carries blood away from an organ towards the heart.

The smallest or the final branch of an artery is called an arteriole.

A pulse is the rhythmic expansion and contraction of arteries (especially the radial artery at the wrist) due to the pumping action of the heart.

The sound or movement of the heart as it sends blood around the body is called heartbeat. Every heartbeat causes a pulse in the arteries.

Blood pressure is the pressure that the blood flowing through the arteries exerts on their walls.

Diastolic pressure is the lower limit of blood pressure, recorded when the heart is at rest and the pressure in the arteries drops after the pulse wave has passed.

Hypertension is a condition in which the blood pressure consistently remains above 140/90 mm Hg.

A sphygmomanometer is the instrument used to measure blood pressure in the arteries.

Lymph is the fluid formed from tissue fluid that enters lymph vessels. It helps in returning excess fluid to the blood and plays a role in immunity.

The breakdown of glucose in the presence of oxygen to produce carbon dioxide, water, and energy is called aerobic respiration.

It is a process of release of energy from food substances such as glucose and fats under the control of enzymes, to carry out life processes, by the living organisms.

The graphical recording of electrical variations detected at the surface of the body during their propagation through the heart wall is called electrocardiogram.

The breakdown of glucose in the absence of oxygen to produce alcohol or lactic acid and a small amount of energy is called anaerobic respiration.

1. Glucose is first broken down in the cytoplasm into a 3-carbon molecule called pyruvate, releasing some energy.
2. In the absence of oxygen, pyruvate is converted into ethanol and carbon dioxide (in yeast) or lactic acid (in muscles), releasing less energy.
3. In the presence of oxygen, pyruvate is broken down in the mitochondria into carbon dioxide and water, releasing a large amount of energy.
4. The energy released during respiration is used to make ATP, which is the energy currency of the cell and used for all life processes.

1. In plants, exchange of gases (O₂ and CO₂) occurs through stomata by diffusion, depending on day or night.
2. Aquatic animals like fish breathe faster because water has less oxygen; they absorb oxygen through gills.
3. In terrestrial animals, oxygen is taken from the air using special respiratory organs like lungs.
4. In humans, air enters through nostrils, passes through the trachea and bronchi, and reaches the lungs, where gas exchange happens in tiny sacs called alveoli.
5. Oxygen is carried by haemoglobin in red blood cells, and carbon dioxide is mostly transported in dissolved form in blood.

1. RBCs are biconcave, disc-shaped cells without a nucleus, mitochondria, or endoplasmic reticulum in their mature form.
2. They contain haemoglobin, which transports oxygen as oxyhaemoglobin and a small amount of CO₂ as carbaminohaemoglobin.
3. RBCs are produced in the bone marrow of long bones and have an average lifespan of about 120 days.
4. Old RBCs are destroyed in the spleen, liver, and bone marrow; their iron is retained, and the rest forms bile pigment.
5. RBC count is higher in newborns, during physical activity, and at high altitudes, and lower during sleep.
6. Abnormalities include polycythaemia (increased red blood cells) and erythropenia (decreased red blood cells).

1. WBCs are produced in red bone marrow, lymph nodes, and sometimes in the liver and spleen; their average lifespan is about two weeks.
2. Most WBCs are amoeboid and squeeze through capillary walls into tissues by diapedesis to fight infections.
3. They are classified into granular (neutrophils, eosinophils, basophils) and non-granular (lymphocytes, monocytes) types.
4. Neutrophils and monocytes perform phagocytosis, engulfing germs and damaged cells.
5. Lymphocytes produce antibodies to neutralise specific germs, forming the basis of immunity and vaccination.
6. WBC count increases during infection, stress, or leukaemia (leukocytosis) and decreases in viral illness or bone marrow disorders (leukopenia).

1. Platelets have a short lifespan of 3 to 5 days and are mainly destroyed in the spleen.
2. At the site of injury, platelets disintegrate and release thrombokinase (also called thromboplastin or Factor X), initiating clot formation.
3. Thrombokinase, in the presence of calcium ions, converts inactive prothrombin in the plasma into active thrombin.
4. Vitamin K is essential for the synthesis of prothrombin in the liver.
5. Thrombin converts soluble fibrinogen into insoluble fibrin, forming sticky threads at the wound.
6. The fibrin mesh traps blood cells, forming a clot that seals the wound and stops bleeding.
7. The clot contracts, squeezing out serum, and leaves behind a solid mass called a thrombus (clot).

1. Lymph is formed from tissue fluid and flows through lymph vessels due to the contraction of nearby muscles.
2. Lymph contains only WBCs (mainly lymphocytes) and is free from RBCs and platelets; it is made up of 94% water and 6% solids like proteins and fats.
3. It supplies nutrients and oxygen to areas where blood cannot reach, especially in deep tissues.
4. Lymph plays a role in draining excess tissue fluid and returning proteins and waste products to the bloodstream.
5. It helps in absorbing fats from the intestine and defending the body by removing bacteria and housing immune cells like lymphocytes.

1. Glucose is first broken down in the cytoplasm into a 3-carbon molecule called pyruvate, releasing some energy.
2. In the absence of oxygen, pyruvate is converted into ethanol and carbon dioxide (in yeast) or lactic acid (in muscles), releasing less energy.
3. In the presence of oxygen, pyruvate is broken down in the mitochondria into carbon dioxide and water, releasing a large amount of energy.
4. The energy released during respiration is used to make ATP, which is the energy currency of the cell and used for all life processes.

1. Control of Breathing
   Respiration is under dual control—nervous and chemical, and normal breathing is an involuntary process regulated by respiratory centres.
2. Respiratory Centres
   The respiratory centres are located in the medulla and pons and include the dorsal group (inspiration), ventrolateral group (inspiration and expiration), and pneumotaxic centre (limits inspiration).
3. Hering–Breuer Reflex
   Inflation of lungs stimulates stretch receptors which send impulses via vagus nerve to inhibit inspiration, initiating expiration; this reflex controls depth and rhythm of breathing.
4. Voluntary Control
   Respiratory centres are connected to the cerebral cortex, allowing voluntary control of breathing, but this is limited by rise in carbon dioxide levels in blood.