Chapter Notes: Life Processes - 2
Science Class 10 | Respiration, Transportation, and Excretion
1. Respiration
Organisms such as yeast perform anaerobic respiration. In this process, glucose is broken down into ethanol, carbon dioxide and energy without using oxygen. The process is called anaerobic respiration because it takes place in the absence of oxygen.
C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + energy
During vigorous exercise, when the supply of oxygen to the muscles is insufficient, muscle cells perform anaerobic respiration. This produces lactic acid and releases a small amount of energy. The accumulation of lactic acid in the muscles during sudden activity may cause muscle cramps.
2. Glycolysis
Glycolysis is the first stage in the breakdown of glucose. A glucose molecule contains six carbon atoms and is broken down into two molecules of the three-carbon compound called pyruvate. Glycolysis takes place in the cytoplasm and is common to both aerobic and anaerobic respiration.
In the presence of oxygen, pyruvate enters the mitochondria and is completely oxidised. Each pyruvate molecule produces carbon dioxide, water and energy. Since this process takes place in the presence of oxygen, it is called aerobic respiration. The overall reaction for one glucose molecule can be represented as:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy
The energy released during cellular respiration is used to synthesise a molecule called ATP, or adenosine triphosphate. ATP provides energy for various activities of the cell.
For every glucose molecule, aerobic respiration releases considerably more energy than anaerobic respiration. ATP is hydrolysed when energy is required for cellular activities, including many energy-requiring reactions.
3. Respiration in Humans
In human beings, air enters the body through the nostrils. Fine hairs and mucus in the nasal passage help to filter dust and other impurities from the inhaled air.
From the nostrils, air passes through the pharynx and larynx and then enters the lungs through the trachea.
The trachea contains incomplete C-shaped rings of cartilage. These rings prevent the air passage from collapsing during breathing.
Inside the lungs, the trachea divides into two bronchi. Each bronchus branches repeatedly into smaller tubes called bronchioles, which end in thin-walled, balloon-like structures called alveoli.
The alveoli provide a large surface area for the exchange of gases. They have thin walls and are surrounded by an extensive network of blood capillaries. Oxygen diffuses from the alveoli into the blood, while carbon dioxide diffuses from the blood into the alveoli.
During inhalation, the chest cavity expands. The external intercostal muscles contract and move the rib cage outward and upward, while the diaphragm contracts and becomes flatter.
The increase in the volume of the chest cavity decreases the air pressure inside the lungs. As a result, air rushes into the lungs through the external nostrils. This process is called inspiration or inhalation.
During expiration or exhalation, air containing more carbon dioxide than inhaled air is expelled from the lungs.
Expiration occurs when the inspiratory muscles relax. The rib cage moves inward, and the diaphragm relaxes and becomes dome-shaped. This reduces the volume of the thoracic cavity and compresses the lungs, forcing air out.
The respiratory pigment haemoglobin in red blood cells has a very high affinity for oxygen and transports it to body tissues. Carbon dioxide is transported mainly in dissolved form in the blood; some carbon dioxide is carried in combination with haemoglobin.
The upper part of the respiratory tract has small hair-like structures called cilia. Cilia, along with mucus, help trap and remove germs and dust from inhaled air.
4. Transportation in Human Beings
Blood transports substances such as salts, vitamins, hormones, digested nutrients and waste products. The transportation system in human beings consists of the heart, blood vessels, blood and lymph.
Our Pump: The Heart
The heart is a muscular organ approximately the size of a fist. A mammalian heart has four chambers. The two upper chambers are called auricles or atria, and the two lower chambers are called ventricles.
Double circulation occurs in human beings. This means that blood passes through the heart twice during one complete circulation through the body.
The right side of the heart receives deoxygenated blood and pumps it to the lungs. The left side receives oxygenated blood from the lungs and pumps it to the rest of the body. A septum separates the two sides and prevents mixing of the two types of blood.
Deoxygenated blood from the body returns to the right auricle through two large veins called the superior vena cava and inferior vena cava.
When the right atrium contracts, the right ventricle is filled with blood. The right ventricle then contracts and pumps the blood to the lungs through the pulmonary artery for oxygenation.
Oxygenated blood returns from the lungs to the left atrium through the pulmonary veins. It then passes into the left ventricle.
Contraction of the left ventricle sends oxygenated blood to the whole body through the aorta, the largest artery.
The walls of the ventricles are thicker than the walls of the atria because the ventricles pump blood under higher pressure. Valves prevent the backward flow of blood during contraction.
In mammals and birds, the complete separation of the left and right sides of the heart prevents the mixing of oxygenated and deoxygenated blood. This is advantageous for these warm-blooded animals because they require a continuous supply of oxygen to meet their high energy demands and maintain a constant body temperature.
Fish have a two-chambered heart consisting of one auricle and one ventricle. In single circulation, blood is pumped from the heart to the gills for oxygenation and then directly to the body. Thus, the blood passes through the heart once during one complete circulation.
5. Blood Pressure
Blood pressure is the force exerted by blood against the walls of blood vessels. It is considerably higher in arteries than in veins.
The contraction of the heart is called systole, while its relaxation is called diastole. The pressure during systole is called systolic pressure, and the pressure during diastole is called diastolic pressure. A commonly used reference value is 120 mm Hg systolic pressure and 80 mm Hg diastolic pressure.
Blood pressure is measured with an instrument called a sphygmomanometer. Persistently high blood pressure is called hypertension. Narrowing of the arterioles can increase resistance to blood flow and contribute to hypertension. Severe hypertension may damage blood vessels and increase the risk of internal bleeding.
6. Blood Vessels
Arteries carry blood away from the heart to various body organs. Because blood leaves the heart at high pressure, arteries have thick, elastic and muscular walls.
Veins carry blood from the body organs back to the heart. They have thinner walls because the blood pressure inside them is lower, and they contain valves that ensure one-way flow of blood.
As arteries reach organs and tissues, they divide into smaller vessels. The smallest vessels are called capillaries. Their walls are only one cell thick, which allows the exchange of gases, nutrients and waste products between the blood and surrounding cells.
Capillaries join to form larger vessels, which become veins. These veins carry blood away from the organ or tissue and back to the heart.
7. Maintenance by Platelets
What happens if this system of tubes develops a leak?
When we are injured, blood vessels may be damaged and bleeding may begin. The loss of blood from the circulatory system must be minimised.
A leak would also cause a loss of blood pressure and reduce the efficiency of the pumping system.
To prevent excessive blood loss, the blood contains platelets. Platelets collect at the site of injury and help to form a clot, thereby plugging the leak.
8. Lymph
Another important fluid involved in transportation is lymph, also called tissue fluid. Some plasma and white blood cells pass through the pores in capillary walls into the spaces between cells, forming tissue fluid.
Lymph resembles blood plasma but is colourless and contains less protein. It enters lymphatic capillaries from the spaces between cells. These capillaries join to form larger lymph vessels, which ultimately open into larger veins.
Lymph carries digested and absorbed fats from the intestine and drains excess fluid from the extracellular spaces back into the blood.
9. Transportation in Plants
Xylem transports water and minerals from the roots to other parts of the plant. Phloem transports the products of photosynthesis from leaves to other parts of the plant, including storage organs.
Xylem contains vessels and tracheids that form a continuous system of water-conducting channels through the roots, stems and leaves.
Water and minerals are conducted from the roots to other parts of the plant due to root pressure and transpirational pull.
The transport of soluble products of photosynthesis is called translocation. It takes place through the phloem. Phloem also transports amino acids and other substances to storage organs.
Translocation of food and other substances takes place through the sieve tubes with the help of adjacent companion cells. It can occur in both upward and downward directions. Substances such as sucrose are actively transported into the phloem using energy from ATP. This raises the osmotic pressure of the phloem, causing water to enter it. The resulting pressure moves the dissolved substances towards tissues where the pressure is lower.
10. Excretion in Humans
The biological process of removing harmful metabolic wastes from the body is called excretion. Different organisms use different strategies for excretion. In complex multicellular organisms such as human beings, specialised organs carry out this function.
The human excretory system consists of a pair of kidneys, a pair of ureters, a urinary bladder and a urethra. The kidneys are situated in the abdomen, one on each side of the backbone. Urine produced in the kidneys passes through the ureters to the urinary bladder, where it is stored until it is expelled through the urethra.
Functions of the Kidneys
Each kidney contains numerous filtering units called nephrons, which are closely packed together.
Each nephron has a cluster of thin-walled blood capillaries called the glomerulus, associated with the cup-shaped Bowman's capsule, followed by a long, coiled tubule.
As the glomerular filtrate flows through the nephron tubule, useful substances such as glucose, amino acids, salts and a major amount of water are selectively reabsorbed into the surrounding blood capillaries.
In a healthy adult, the initial filtrate formed in the kidneys is about 180 litres daily, but only about one to two litres of urine are excreted because most of the filtrate is reabsorbed by the kidney tubules.
The kidneys remove soluble nitrogenous compounds, such as urea, from the blood as waste products.
The kidneys perform two important functions: (i) filtering nitrogenous wastes from the blood, and (ii) carrying out osmoregulation, which maintains the proper balance of water and ions in the body.
An artificial kidney is used to filter the blood of patients whose kidneys are not functioning properly. The process of purifying blood using an artificial kidney is called haemodialysis.
The urinary bladder is a muscular organ. Its filling and emptying are regulated by the nervous system, which helps control the urge to urinate.
11. Excretion in Plants
Plants use strategies for excretion that differ from those of animals. Oxygen can be considered a waste product of photosynthesis when it is produced in excess of the plant's requirements. Plants also exchange oxygen and carbon dioxide through gaseous pores, and they remove excess water by transpiration.
Waste Management Strategies
Plants make use of the fact that many of their tissues consist of dead cells.
Plants can lose some of their parts, such as leaves, along with the waste substances stored in them.
Many plant waste products are stored in cellular vacuoles.
Waste products may be stored in leaves that later fall off.
Other waste products are stored as resins and gums, especially in old xylem.
Plants also release some waste substances into the soil around them.
No comments:
Post a Comment