Life Processes

Water enters roots from the soil and moves into the xylem. Evaporation of water from leaf stomata creates transpiration pull, which is transmitted through the continuous water column and is a major force lifting water upward. Root pressure can also push water from below, especially when transpiration is low. Thus option A is the best answer; the other choices involve processes that do not occur in xylem transport.

Stomata are pores controlled by guard cells that allow carbon dioxide entry but also permit water vapour to escape. When water availability is low, continued high transpiration can reduce cell water content and cause wilting. Closing the stomata limits diffusion of water vapour and conserves the remaining water, although it may also reduce carbon dioxide uptake and photosynthesis. Therefore option A is correct.

The governing concept is transport in vascular tissues. Xylem carries water and dissolved minerals mainly upward, from roots toward stems and leaves, driven by transpiration and related forces. Phloem translocates food, especially sucrose made in leaves, from a source to sinks such as roots, fruits, or growing tissues. Because sources and sinks can vary, phloem movement may be upward or downward. Therefore, option A is correct; the other choices confuse plant tissues and their functions.

The governing concept is pressure-flow translocation in phloem. Sugars produced at a source, usually a leaf, are actively loaded into sieve tubes using cellular energy. This lowers water potential, so water enters from nearby xylem and creates pressure. The pressure gradient helps move phloem sap toward a sink, where sugar is unloaded and used or stored. Thus option A is correct; the other choices describe unrelated or impossible processes.

The governing concept is selective reabsorption during urine formation. Filtration at the glomerulus is not perfectly selective, so small useful substances such as glucose, required salts, and much of the water may enter the filtrate along with wastes. The nephron returns needed materials to the blood while retaining excess water and wastes for excretion. Therefore option A is correct. The other options misunderstand the roles of blood, lungs, and bile.

The governing concept is osmoregulation, or maintenance of the body’s water balance. When the body is dehydrated, the kidneys conserve water by increasing its reabsorption from the nephron filtrate into the blood. Consequently, less water is lost and urine becomes smaller in volume and more concentrated. Option A is correct. Complete stoppage would worsen dehydration, while digestion and oxygen production are not nephron functions.

The governing concept is excretion of nitrogenous waste. During protein metabolism, the liver forms urea from toxic ammonia. Healthy kidneys filter urea from the blood and eliminate it in urine. If kidney function fails, filtration and removal decline, so urea accumulates in the bloodstream, a condition associated with harmful waste buildup. Option A is correct; the lungs, heart, and stomach do not perform this renal excretory role.

The governing concept is selective diffusion through a semipermeable membrane. In dialysis, blood is placed next to a dialysis fluid that lacks, or contains very little, urea and other wastes. Small waste molecules diffuse across the membrane down their concentration gradient. Blood cells and many large plasma proteins are retained because they cannot cross the membrane readily. Therefore option A is correct; the other choices describe impossible conversions.

The governing concept is detoxification of nitrogenous waste. Breakdown of amino acids can produce ammonia, which is highly toxic and cannot safely accumulate in body tissues. In the liver, ammonia is converted into urea through the urea cycle. Urea is much less toxic, dissolves readily in water, and can be transported in blood to the kidneys for urinary excretion. Thus option A is correct; the remaining options confuse urea with nutrition, respiration, or photosynthesis.

The governing concept is plant excretion without specialized excretory organs. Plants may remove gases by diffusion through stomata or other surfaces, lose excess water by transpiration, and store wastes in vacuoles, old leaves, bark, or substances such as gums and resins. When leaves or bark are shed, stored wastes are removed from the plant. Therefore option A is correct; plants do not possess animal-like hearts, lungs, or blood platelets.

The governing concept is photosynthesis and conversion of energy. Chlorophyll in green plants absorbs light energy, which powers the formation of glucose from carbon dioxide and water. The energy captured from sunlight is not simply lost; it becomes stored chemical energy in the bonds of glucose and later other food molecules such as starch. Hence option A is correct. The other choices describe conversions unrelated to autotrophic nutrition and biology.

The governing concept is digestion followed by absorption. Heterotrophic organisms obtain ready-made food, but nutrients such as starches, proteins, and fats are often large, complex molecules that cannot cross the intestinal lining efficiently. Enzymes break them into smaller soluble substances—sugars, amino acids, and fatty acids with glycerol—which can be absorbed and used for energy, growth, and repair. Therefore option A is correct; the other choices confuse digestion with plant transport or gas exchange.

The governing concept is saprophytic nutrition. Fungi usually grow on dead and decaying organic matter, but they do not ingest solid food as animals do. They secrete digestive enzymes onto the material; these enzymes break complex substances into soluble, simpler molecules. The fungus then absorbs those dissolved nutrients through its hyphae. Therefore, option A is correct; the other options describe organs or processes that fungi do not possess.

The governing concept is absorption in the digestive system. The large intestine removes a considerable amount of water and some salts from undigested material before faeces are expelled. If water absorption is impaired, the intestinal contents remain unusually watery, which can lead to loose stools and increased loss of body water. Therefore option A is correct. The other options concern unrelated functions of respiration or plants.

The governing concept is transport of respiratory gases. Carbon dioxide produced by cellular respiration diffuses into the blood. Most of it reacts with water in red blood cells, with the help of carbonic anhydrase, and is converted into bicarbonate ions. These ions are soluble and can be transported efficiently in plasma to the lungs, where carbon dioxide is released and exhaled. Hence option A is correct; coal, starch and bile are unrelated substances.

The governing concept is the complementary relationship between photosynthesis and cellular respiration. During photosynthesis, green plants use carbon dioxide and water in light to form glucose and release oxygen. During respiration, cells use glucose and oxygen to release usable energy, producing carbon dioxide and water. Thus the products of one process serve as reactants for the other in an ecosystem. Option A states this relationship accurately; the remaining options confuse unrelated substances and functions.

The governing concept is translocation through phloem. Leaves produce sugars, mainly sucrose, by photosynthesis, and the phloem transports these organic nutrients from source tissues to sinks such as roots, fruits and growing regions. If phloem is damaged, the movement of food to roots may be reduced or interrupted, limiting their growth and respiration. Therefore option A is correct. Xylem, not phloem, carries water, and roots neither pump blood nor form alveoli.

The governing concept is xylem transport and cell turgidity. Xylem vessels carry water and dissolved mineral ions upward from roots to stems and leaves. Leaf cells need water to maintain turgor pressure, support photosynthesis and prevent excessive loss of firmness. If xylem is blocked, the water supply falls, cells lose turgidity and leaves may droop or wilt. Hence option A is correct; the other choices refer to animal organs or unrelated substances.

The governing concept is removal of metabolic wastes. Cellular respiration produces carbon dioxide and water as end products. Carbon dioxide is transported to the lungs and removed during exhalation, while excess water may leave through the kidneys, skin or lungs. Excretion therefore helps maintain a stable internal environment by eliminating unwanted products. Option A is correct. The other choices confuse excretion with photosynthesis, digestion or a function limited to teeth.

Step 1: Normally muscles release energy in the presence of oxygen. Step 2: During heavy exercise, energy demand rises and oxygen may be insufficient. Step 3: Then anaerobic respiration can occur for some time, forming lactic acid.