Life Process

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Q1. What is the main driving force for the transport of water in plants?

A. Root pressure only

B. Transpiration pull created by loss of water vapor from leaves

C. Diffusion of carbon dioxide into leaves

D. Pumping action of the heart in plants

Transpiration pull created by loss of water vapor from leaves

Transpiration pull is the primary force driving water upward from roots to leaves. As water evaporates from leaf mesophyll cells into the air spaces, it creates a negative pressure (tension) that pulls water columns upward through xylem. Root pressure contributes only a small amount, especially at night or in small plants, but is not the main driver.

Q2. Which plant tissue is responsible for the transport of water and minerals from roots to leaves?

A. Phloem

B. Xylem

C. Cambium

D. Parenchyma

Xylem

Xylem consists of tracheids and vessel elements that form continuous tubes for transporting water and dissolved minerals from roots to shoots. Phloem transports food, cambium is a meristematic tissue for growth, and parenchyma is for storage and basic metabolic functions.

Q3. Which plant tissue is responsible for the transport of food (sucrose and other organic nutrients) from leaves to other parts of the plant?

A. Xylem

B. Phloem

C. Epidermis

D. Cortex

Phloem

Phloem contains sieve tubes and companion cells that transport the products of photosynthesis (sucrose, amino acids) from source (usually leaves) to sink (roots, fruits, growing tips). Xylem transports water, epidermis provides protection, and cortex is for storage.

Q4. What is the direction of transport in xylem versus phloem?

A. Xylem transports in both directions; phloem transports only upward

B. Xylem transports only upward; phloem transports both upward and downward depending on the needs of the plant

C. Both xylem and phloem transport only downward

D. Xylem transports food; phloem transports water

Xylem transports only upward; phloem transports both upward and downward depending on the needs of the plant

Xylem transport is unidirectional (roots → shoots) due to transpiration pull. Phloem transport is bidirectional because sources (e.g., mature leaves, storage organs) and sinks (e.g., roots, fruits, young leaves) can be located above or below each other. The pressure flow hypothesis explains movement from source to sink regardless of direction.

Q5. What is transpiration?

A. The absorption of water by roots

B. The loss of water vapor from the aerial parts of the plant, mainly through stomata

C. The transport of food through phloem

D. The process of photosynthesis in leaves

The loss of water vapor from the aerial parts of the plant, mainly through stomata

Transpiration is the evaporation of water from leaf surfaces, mostly through open stomata (also through cuticle). It creates the transpiration pull and helps in cooling, mineral transport, and maintaining leaf structure. It is distinct from water absorption and photosynthesis.

Q6. How does water enter the root hairs of a plant?

A. By active transport using ATP

B. By osmosis because the concentration of water in soil is higher than inside root hair cells

C. By diffusion of water through the cell wall only

D. By transpiration pull directly

By osmosis because the concentration of water in soil is higher than inside root hair cells

Root hair cells have higher solute concentration (lower water potential) than soil water. Water moves passively by osmosis across the cell membrane. Active transport is for minerals, not bulk water entry. Transpiration pull acts on water already inside xylem, not at root hairs.

Q7. What is the role of the endodermis in the transport of water in roots?

A. It stores water for the plant

B. It contains a Casparian strip that forces water and minerals to pass through the cytoplasm of endodermal cells, allowing selective uptake

C. It transports food from roots to leaves

D. It produces root hairs

It contains a Casparian strip that forces water and minerals to pass through the cytoplasm of endodermal cells, allowing selective uptake

The endodermis is a single layer of cells surrounding the stele. The Casparian strip (made of suberin) blocks the apoplastic pathway, forcing water and dissolved minerals to enter the symplastic pathway (through the cytoplasm). This allows the plant to selectively control which ions reach the xylem.

Q8. What is translocation in plants?

A. The movement of water through xylem

B. The transport of soluble products of photosynthesis (sucrose, amino acids) through phloem from source to sink

C. The loss of water vapor from leaves

D. The absorption of minerals by roots

The transport of soluble products of photosynthesis (sucrose, amino acids) through phloem from source to sink

Translocation specifically refers to the movement of organic nutrients (assimilates) via phloem. Water movement in xylem is called ascent of sap. Transpiration is water loss, and mineral absorption is a separate root process.

Q9. What is the pressure flow hypothesis for phloem transport?

A. Water pressure from roots pushes food upward

B. Active loading of sugar into sieve tubes at the source creates high osmotic pressure, drawing water in; this high pressure pushes sap toward the sink, where sugar is unloaded

C. Transpiration pull draws food through phloem

D. Food moves by simple diffusion through phloem

Active loading of sugar into sieve tubes at the source creates high osmotic pressure, drawing water in; this high pressure pushes sap toward the sink, where sugar is unloaded

The pressure flow hypothesis explains phloem transport. At the source, sugars are actively loaded into phloem, causing water to enter by osmosis. The resulting hydrostatic pressure pushes sap to the sink, where sugars are unloaded, water leaves, and pressure drops. This bulk flow is bidirectional depending on source-sink locations.

Q10. What happens to the rate of water transport if a plant is placed in a very humid environment?

A. The rate increases because humidity helps transpiration

B. The rate decreases because transpiration pull is reduced when the air is already saturated with water vapor

C. The rate remains unchanged

D. The plant stops absorbing water completely

The rate decreases because transpiration pull is reduced when the air is already saturated with water vapor

Transpiration rate depends on the water vapor gradient between leaf interior and atmosphere. High humidity reduces this gradient, slowing transpiration and consequently reducing transpiration pull. Water transport decreases accordingly, though absorption does not completely stop.

Q11. What is excretion?

A. The process of taking in food and digesting it

B. The removal of metabolic waste products (like urea, carbon dioxide, uric acid, ammonia) from the body

C. The elimination of undigested food as feces

D. The production of energy from glucose

The removal of metabolic waste products (like urea, carbon dioxide, uric acid, ammonia) from the body

Excretion specifically refers to eliminating wastes generated by cellular metabolism (e.g., nitrogenous wastes, CO₂). Elimination of undigested food (feces) is called egestion, not excretion, because it never entered body cells.

Q12. Which is the primary nitrogenous waste product in human beings?

A. Ammonia

B. Uric acid

C. Urea

D. Creatinine

Urea

Humans are ureotelic, converting toxic ammonia (from protein breakdown) into less toxic urea in the liver via the urea cycle. Ammonia is excreted by fish, uric acid by birds and reptiles, and creatinine is a smaller waste from muscle metabolism.

Q13. How is urine produced in the human body?

A. By the liver filtering toxins from blood

B. By the kidneys through three processes: glomerular filtration, tubular reabsorption, and tubular secretion

C. By the heart pumping waste into the bladder

D. By the large intestine absorbing water from waste

By the kidneys through three processes: glomerular filtration, tubular reabsorption, and tubular secretion

Urine formation occurs in nephrons. Filtration produces a protein-free filtrate, reabsorption reclaims useful substances (glucose, water, ions), and secretion adds additional wastes. The liver processes toxins but does not produce urine; the heart and large intestine are not involved.

Q14. What is glomerular filtration?

A. The active transport of glucose into the blood

B. The passive filtration of blood under pressure in the glomerulus, where water and small solutes pass into Bowman’s capsule while blood cells and large proteins remain

C. The reabsorption of water from the collecting duct

D. The secretion of urea into the nephron

The passive filtration of blood under pressure in the glomerulus, where water and small solutes pass into Bowman’s capsule while blood cells and large proteins remain

Glomerular filtration is a passive, pressure-driven process. Blood pressure forces water, glucose, amino acids, ions, and urea through the capillary walls into Bowman’s capsule. Red blood cells, white blood cells, platelets, and large proteins (e.g., albumin) are too large to pass and remain in blood.

Q15. What is tubular reabsorption?

A. The movement of waste products from blood into the nephron tubule

B. The movement of useful substances (glucose, amino acids, most water, ions) from the nephron tubule back into the blood capillaries surrounding the tubule

C. The filtration of blood in the glomerulus

D. The storage of urine in the bladder

The movement of useful substances (glucose, amino acids, most water, ions) from the nephron tubule back into the blood capillaries surrounding the tubule

Tubular reabsorption is a selective process that reclaims valuable substances from the filtrate to prevent their loss. It occurs mainly in the proximal convoluted tubule and loop of Henle via active transport (glucose, amino acids) and osmosis (water).

Q16. What is tubular secretion?

A. The filtration of blood in the glomerulus

B. The addition of certain substances (hydrogen ions, potassium ions, ammonia, drugs) from the blood into the nephron tubule to be excreted in urine

C. The reabsorption of water from the collecting duct

D. The release of urine from the bladder

The addition of certain substances (hydrogen ions, potassium ions, ammonia, drugs) from the blood into the nephron tubule to be excreted in urine

Tubular secretion is the opposite of reabsorption. It actively transports additional wastes (H⁺, K⁺, NH₃, certain drugs, toxins) from peritubular capillaries into the tubule lumen. This helps regulate blood pH and eliminate substances not filtered initially.

Q17. What are the main parts of the human excretory system?

A. Liver, pancreas, and gallbladder

B. Kidneys, ureters, urinary bladder, and urethra

C. Lungs, skin, and large intestine

D. Heart, arteries, and veins

Kidneys, ureters, urinary bladder, and urethra

The urinary system consists of two kidneys (filter blood), two ureters (transport urine), one urinary bladder (stores urine), and one urethra (expels urine). Lungs and skin also excrete wastes (CO₂, sweat) but are not the main urinary organs. The liver is part of the digestive system.

Q18. What is the structural and functional unit of the kidney?

A. Neuron

B. Nephron

C. Alveolus

D. Villus

Nephron

Each kidney contains about 1 million nephrons. Each nephron consists of a glomerulus (filtration) and a renal tubule (reabsorption/secretion). Neuron is the unit of the nervous system, alveolus of the lungs, and villus of the small intestine.

Q19. What is the function of the urethra in the human excretory system?

A. To carry urine from the kidney to the bladder

B. To store urine until it is ready to be expelled

C. To carry urine from the bladder to the outside of the body

D. To filter blood and produce urine

To carry urine from the bladder to the outside of the body

The urethra is a muscular tube that conducts urine from the urinary bladder to the external urethral orifice. The ureters carry urine from kidneys to bladder, the bladder stores urine, and kidneys filter blood.

Q20. What is an artificial kidney (hemodialysis)?

A. A surgical procedure to replace a damaged kidney with a donor kidney

B. A machine that performs the function of a natural kidney by filtering waste products and excess water from the blood when kidneys fail

C. A medicine that repairs damaged nephrons

D. A diet that reduces urea production

A machine that performs the function of a natural kidney by filtering waste products and excess water from the blood when kidneys fail

Hemodialysis is a life-support treatment, not a cure. The machine uses a semipermeable membrane to remove urea, excess ions, and water from blood, similar to glomerular filtration. Kidney transplant is a surgical procedure, not an artificial kidney.

Q21. How does hemodialysis work?

A. By surgically implanting a new kidney into the patient

B. By using the principle of diffusion across a semipermeable membrane; blood flows on one side, dialysate on the other, and wastes move down their concentration gradient from blood into dialysate

C. By boiling the blood to remove impurities

D. By using a centrifuge to separate wastes from blood

By using the principle of diffusion across a semipermeable membrane; blood flows on one side, dialysate on the other, and wastes move down their concentration gradient from blood into dialysate

Hemodialysis relies on passive diffusion. Blood and dialysate flow in opposite directions across a semipermeable membrane. Wastes (urea, creatinine) diffuse from high concentration (blood) to low concentration (dialysate). Dialysate has no wastes but has normal electrolyte levels to prevent loss of essential ions.

Q22. Why is a patient with kidney failure put on hemodialysis?

A. To permanently cure kidney disease

B. To artificially remove nitrogenous wastes, excess water, and maintain electrolyte balance when the natural kidneys can no longer function

C. To increase the production of red blood cells

D. To digest food more efficiently

To artificially remove nitrogenous wastes, excess water, and maintain electrolyte balance when the natural kidneys can no longer function

Kidney failure means nephrons can no longer filter blood effectively. Without dialysis, urea and other toxins accumulate (uremia), leading to death. Dialysis is a temporary or long-term substitute but does not cure kidney disease; transplant is needed for a cure.

Q23. What are the main waste products excreted by plants?

A. Urea, uric acid, and ammonia

B. Oxygen, carbon dioxide, water vapor, and some organic compounds like tannins, resins, gums, and alkaloids

C. Only carbon dioxide and water

D. Feces and undigested food

Oxygen, carbon dioxide, water vapor, and some organic compounds like tannins, resins, gums, and alkaloids

Plants excrete O₂ (photosynthesis byproduct), CO₂ (respiration byproduct), water vapor, and various secondary metabolites. Tannins, resins, gums, and alkaloids are stored or shed. Unlike animals, plants do not excrete nitrogenous wastes like urea; they recycle nitrogen.

Q24. How do plants excrete carbon dioxide?

A. Through roots

B. Through stomata during respiration

C. Through the bark only

D. By converting it into oxygen

Through stomata during respiration

Plants respire continuously, producing CO₂. This CO₂ diffuses out mainly through open stomata (and also through lenticels in bark). During the day, net CO₂ exchange is negative (photosynthesis dominates), but respiration still occurs and CO₂ is released.

Q25. What happens to waste products like tannins, resins, and gums in plants?

A. They are excreted through urine-like fluid

B. They are stored in old leaves, bark, fruits, or seeds, and are removed when these parts fall off or are shed

C. They are converted back into glucose

D. They are excreted through stomata

They are stored in old leaves, bark, fruits, or seeds, and are removed when these parts fall off or are shed

Plants lack excretory organs. They sequester waste products in vacuoles of old leaves, bark, heartwood, fruits, and seeds. When leaves fall, bark peels, or fruits/seeds are dispersed, the wastes are eliminated. This is called “excretion by shedding.”

Q26. What is the role of the ureter in the human excretory system?

A. To store urine temporarily

B. To carry urine from the kidney to the urinary bladder by peristaltic contractions

C. To filter blood

D. To carry urine from the bladder to the outside

To carry urine from the kidney to the urinary bladder by peristaltic contractions

Each ureter is a muscular tube (about 25-30 cm long) that connects a kidney to the urinary bladder. Urine moves by peristalsis (rhythmic contractions) and gravity. The bladder stores urine, and the urethra carries it outside.

Q27. Why does the composition of urine change depending on the body’s needs?

A. Because the kidneys can adjust the amount of water reabsorbed (under the influence of ADH hormone) and the amount of ions reabsorbed or secreted

B. Because the liver produces different wastes at different times

C. Because the bladder mixes urine with different substances

D. Because the ureters add chemicals to urine

Because the kidneys can adjust the amount of water reabsorbed (under the influence of ADH hormone) and the amount of ions reabsorbed or secreted

Kidneys maintain homeostasis by varying reabsorption and secretion. ADH (antidiuretic hormone) increases water reabsorption (concentrated urine). Aldosterone increases Na⁺ reabsorption and K⁺ secretion. The liver produces relatively constant wastes; bladder and ureters are passive conduits.

Q28. What is the function of the urinary bladder?

A. To produce urine

B. To store urine temporarily until it is convenient to expel it

C. To filter urea from blood

D. To reabsorb glucose from urine

To store urine temporarily until it is convenient to expel it

The urinary bladder is a hollow, muscular organ that collects urine from the ureters and stores it. Its wall can stretch to accommodate 400-600 mL. When full, nerve signals trigger the micturition reflex, expelling urine through the urethra.

Q29. How do plants excrete excess salts?

A. Through kidneys like animals

B. By storing them in vacuoles of cells, especially in old leaves; some plants secrete salts through salt glands (e.g., mangroves)

C. By converting salts into gases

D. By excreting them through stomata as solid crystals

By storing them in vacuoles of cells, especially in old leaves; some plants secrete salts through salt glands (e.g., mangroves)

Plants cannot actively excrete salts like animals. They compartmentalize excess salts in vacuoles or deposit them in old leaves that are later shed. Halophytes (salt-tolerant plants like mangroves) have specialized salt glands on leaves that actively secrete salt crystals onto the leaf surface, which are then washed off by rain or wind.

Q30. What is the difference between excretion in plants and excretion in humans?

A. Plants have kidneys, humans do not

B. Plants do not have specialized excretory organs and often store wastes in vacuoles or shed parts; humans have specialized organs (kidneys, lungs, skin) to actively remove wastes from the body

C. Plants excrete only oxygen; humans excrete only urea

D. There is no difference

Plants do not have specialized excretory organs and often store wastes in vacuoles or shed parts; humans have specialized organs (kidneys, lungs, skin) to actively remove wastes from the body

Plants lack excretory systems; they store wastes in vacuoles, bark, or old leaves and shed them. Humans have specialized organs: kidneys (urine), lungs (CO₂), skin (sweat), and liver (bile). Plants also recycle nitrogen, while humans excrete it as urea.