LIFE PROCESSES
Chapter Notes • Important Concepts • Labelled Diagrams • Flowcharts • Practice MCQs
1. Respiration and Glycolysis
Respiration is the process by which food is broken down to release energy. Depending on the availability of oxygen, respiration may be aerobic or anaerobic.
Anaerobic respiration
Organisms such as yeast perform anaerobic respiration. Glucose is broken down into ethanol, carbon dioxide and energy without using oxygen.
Aerobic respiration
In the presence of oxygen, pyruvate enters the mitochondria and is completely oxidised to carbon dioxide and water, releasing energy.
Glycolysis – the first stage
- Glycolysis is the first stage in the breakdown of glucose.
- One six-carbon glucose molecule is broken down into two molecules of the three-carbon compound pyruvate.
- It takes place in the cytoplasm and is common to both aerobic and anaerobic respiration.
(6-carbon)→Glycolysis
(cytoplasm)→2 Pyruvate
(3-carbon each)
Important question: Where does pyruvate break down in the presence of oxygen?
2. Respiration in Humans
Air enters the body through the nostrils and passes through the respiratory tract to the lungs.
Pathway of air
- Fine hairs and mucus in the nasal passage filter dust and other impurities from inhaled air.
- The trachea has incomplete C-shaped cartilage rings that prevent the air passage from collapsing during breathing.
- The trachea divides into two bronchi. Each bronchus branches into bronchioles that end in alveoli.
- Alveoli are thin-walled, balloon-like structures surrounded by an extensive network of blood capillaries.
Inhalation and exhalation
| Inhalation (inspiration) | Exhalation (expiration) |
|---|---|
| External intercostal muscles contract. | Inspiratory muscles relax. |
| Ribcage moves outward and upward. | Ribcage moves inward. |
| Diaphragm contracts and becomes flatter. | Diaphragm relaxes and becomes dome-shaped. |
| Chest cavity volume increases; pressure inside lungs decreases, so air enters. | Chest cavity volume decreases; lungs are compressed, forcing air out. |
- Haemoglobin in red blood cells has a high affinity for oxygen and transports it to body tissues.
- Carbon dioxide is transported mainly in dissolved form in blood; some is carried in combination with haemoglobin.
- Cilia and mucus in the upper respiratory tract help trap and remove germs and dust.
3. Transportation in Human Beings – The Heart
Blood transports salts, vitamins, hormones, digested nutrients and waste products. The transportation system consists of the heart, blood vessels, blood and lymph.
Double circulation
In humans, blood passes through the heart twice during one complete circulation through the body. This is called double circulation.
- The right side 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.
- Ventricles have thicker walls than atria because they pump blood under higher pressure. Valves prevent backward flow.
- Complete separation in mammals and birds supports a continuous oxygen supply to meet high energy demands and maintain a constant body temperature.
4. Blood Pressure and Blood Vessels
Blood pressure
- Blood pressure is the force exerted by blood per unit area on the walls of blood vessels. It is considerably higher in arteries than in veins.
- Contraction of the heart is called systole; relaxation is called diastole.
- Systolic pressure is measured during systole and diastolic pressure during diastole.
- A commonly used reference value is 120 mmHg systolic and 80 mmHg diastolic.
- Blood pressure is measured using a sphygmomanometer. Persistently high blood pressure is called hypertension.
Comparison of blood vessels
| Blood vessel | Direction / function | Structure |
|---|---|---|
| Arteries | Carry blood away from the heart to body organs. | Thick, elastic and muscular walls; blood flows at high pressure. |
| Veins | Carry blood from body organs back to the heart. | Thinner walls; contain valves for one-way flow. |
| Capillaries | Allow exchange of gases, nutrients and wastes between blood and cells. | Walls are only one cell thick. |
5. Maintenance by Platelets and Lymph
Platelets and blood clotting
- When a blood vessel is damaged, bleeding may begin and blood pressure may fall.
- Platelets collect at the site of injury and help form a clot, plugging the leak and minimising blood loss.
Lymph (tissue fluid)
- Some plasma and white blood cells pass through pores in capillary walls into spaces between cells, forming tissue fluid.
- Lymph resembles blood plasma but is colourless and contains less protein.
- Lymph enters lymphatic capillaries, which join to form larger lymph vessels that ultimately open into larger veins.
- Lymph carries digested and absorbed fats from the intestine and drains excess fluid from extracellular spaces back into the blood.
6. Transportation in Plants
Xylem
Transports water and minerals from roots to other parts of the plant. Vessels and tracheids form a continuous water-conducting system through roots, stems and leaves.
Driving forces: Root pressure and transpirational pull.
Phloem
Transports products of photosynthesis from leaves to other parts of the plant, including storage organs. It also transports amino acids and other substances.
Process: Translocation.
Translocation through phloem
- Translocation is the transport of soluble products of photosynthesis through phloem.
- It takes place through sieve tubes with the help of adjacent companion cells.
- Sucrose is actively transported into phloem using energy from ATP. This raises osmotic pressure, causing water to enter.
- The resulting pressure moves dissolved substances towards tissues where the pressure is lower. Translocation can occur in both upward and downward directions.
7. Excretion in Humans
Excretion is the biological process of removing harmful metabolic wastes from the body.
The human excretory system consists of a pair of kidneys, a pair of ureters, a urinary bladder and a urethra.
Functions of the kidneys
- Each kidney contains numerous filtering units called nephrons.
- Each nephron has a glomerulus (a cluster of thin-walled blood capillaries), Bowman's capsule and a long, coiled tubule.
- As filtrate flows through the nephron tubule, useful substances such as glucose, amino acids, salts and much of the water are selectively reabsorbed into surrounding blood capillaries.
- Kidneys remove soluble nitrogenous wastes such as urea from blood and carry out osmoregulation, maintaining the balance of water and ions.
- In a healthy adult, about 180 litres of initial filtrate are formed daily, but only about 1–2 litres of urine are excreted because most filtrate is reabsorbed.
- Haemodialysis is the process of purifying blood using an artificial kidney when the kidneys are not functioning properly.
- The urinary bladder is a muscular organ. Its filling and emptying are regulated by the nervous system.
8. Excretion in Plants
Plants use different strategies for excretion. Oxygen may be a waste product of photosynthesis when produced in excess. Plants exchange oxygen and carbon dioxide through gaseous pores and remove excess water by transpiration.
Waste management strategies in plants
- Many plant tissues consist of dead cells.
- Plants can lose parts such as leaves along with waste substances stored in them.
- Many 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 surrounding soil.
9. Test Your Understanding – MCQ Practice
Choose one answer for each question and select Check answers to see your score and explanations.
1. Where does the breakdown of pyruvate take place in the presence of oxygen?
2. What does the left side of the human heart receive?
3. Which blood vessels carry blood away from the heart?
4. What is the filtering unit of the kidney?
5. Which tissue transports products of photosynthesis in plants?
6. Which component of blood helps in clot formation?
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