Life Processes

The governing concept is that green plants synthesize glucose by photosynthesis using light energy, carbon dioxide, and water; excess glucose is commonly stored as starch. When a plant is kept in darkness, the light-dependent stage cannot provide the required energy, so new food and starch formation become very limited or stop. Therefore option A is the best reason. Roots, oxygen uptake, and the absurd claim about blood do not explain the starch test.

The governing concept is the source and method of obtaining food. Autotrophic organisms, such as green plants, manufacture organic food from inorganic raw materials, usually using light energy, carbon dioxide, and water. Heterotrophic organisms cannot synthesize sufficient food from these materials and obtain it from other organisms or their products. Thus option A states the real distinction; blood colour, body size, and movement speed are unrelated characteristics.

Saliva has both a physical and a chemical role in digestion. Its water and mucus moisten and lubricate food, making it easier to form a bolus and swallow. Salivary amylase then begins the chemical digestion of starch into simpler sugars in the mouth. Therefore option A correctly gives both effects. Saliva does not convert fat into bile, form blood or urine, make oxygen, or direct food into the lungs.

The governing concept is the location and function of the first digestive enzymes. Salivary glands release saliva into the mouth, and saliva contains salivary amylase, which begins the digestion of starch before food reaches the stomach. If these glands malfunction, this initial starch digestion is directly affected first. Thus option B is correct. Most fat digestion occurs later with bile and lipase, major protein digestion begins in the stomach, and water is absorbed rather than digested.

The governing concept is protection during digestion. The stomach releases hydrochloric acid and digestive enzymes, but its inner lining is protected by a mucus layer. If mucus is deficient, acid can directly irritate and erode the lining, possibly causing inflammation or ulcers. Therefore option A is correct. The other options concern blood oxygen, bile production, or plant transport tissues and are unrelated to mucus protection in the stomach.

The governing concept is emulsification of fats. Bile contains no digestive enzyme, but its bile salts break large fat globules into many tiny droplets. This increases the surface area on which lipase can act and also helps provide an alkaline medium in the small intestine. Thus option A is correct. Bile does not digest starch directly, alter haemoglobin, or transform urine into blood.

The governing concept is water reabsorption during digestion. The large intestine removes a considerable amount of water and some salts from undigested material, helping faeces become more solid before elimination. If this absorption is greatly reduced, excess water remains in the intestinal contents, so the faeces may be loose or watery. Thus option A is correct; the other options describe impossible changes or unrelated functions.

The governing concept is alcoholic fermentation by yeast. In the absence of oxygen, yeast breaks down glucose only partially. The products are ethanol and carbon dioxide, and a small amount of energy is released. This process is used in baking and brewing. Therefore option A is correct. Oxygen and water are associated with aerobic respiration, whereas urea, bile, starch and saliva are not the products of yeast fermentation.

Haemoglobin is the oxygen-carrying pigment present in red blood cells. It binds oxygen in the lungs and transports it to body tissues. If haemoglobin is deficient, the oxygen-carrying capacity of blood decreases, so cells receive less oxygen for aerobic respiration and energy release. Therefore, option A is correct. B concerns digestion, while C and D describe unrelated plant or digestive structures.

Platelets are small cell fragments in the blood that gather at an injured site and help initiate clot formation. A clot forms a temporary seal over a damaged blood vessel, reducing blood loss and supporting repair. If platelet numbers are low, clotting becomes slower or inadequate, so bleeding may continue for longer after an injury. Therefore option A is correct; the other choices are unrelated effects involving oxygen, digestion, or plant stomata.

The urinary system has two ureters, each carrying urine from one kidney to the urinary bladder. The urethra is a separate tube that carries urine from the bladder to the exterior during urination. Therefore option A states the correct difference. Food travels through the alimentary canal, air through the respiratory tract, blood is pumped by the heart, and bile is produced by the liver, so the other options are incorrect.

Excretion removes metabolic wastes produced by cellular activities, such as carbon dioxide, urea, and excess salts or water. Egestion is different: it is the elimination of undigested and unabsorbed food from the alimentary canal as faeces. Thus option A gives the correct distinction. Neither process produces oxygen, makes food, pumps blood, or opens stomata; those statements confuse unrelated functions.

A unicellular organism consists of only one cell, and that cell is directly surrounded by its environment. Its large surface-area-to-volume ratio and short internal distances allow oxygen, water, nutrients, and wastes to move across the cell membrane mainly by diffusion. Therefore option A is correct. Such organisms do not require a heart, lungs, or xylem; those structures belong to specialised multicellular systems.

Chlorophyll is the green pigment that absorbs light energy needed to drive photosynthesis. In its absence or severe deficiency, the leaf cannot efficiently convert carbon dioxide and water into glucose, so food formation is affected directly and first. Transpiration, water transport and mineral absorption may continue through other structures, although plant growth can later suffer. Therefore option A is correct.

Water used in photosynthesis is mainly absorbed from the soil by root hairs. After absorption, it moves upward through the xylem, helped by root pressure, cohesion and transpiration pull, and reaches the leaves where photosynthesis occurs. The water is a raw material in glucose formation. Thus option A is correct; plants do not normally obtain their main supply directly from air or manufacture it in flowers or stems.

Photosynthesis initially produces glucose, a soluble sugar that can be used immediately in respiration or converted into other substances. When present in excess, plants commonly join glucose units to form starch, an insoluble storage carbohydrate. Starch can later be broken down when energy is needed. Therefore option A is correct; proteins, fatty acids and urea are not the usual direct storage form of extra glucose.

Amoeba performs nutrition by engulfing food with temporary extensions called pseudopodia. The captured food becomes enclosed in a food vacuole, where digestive enzymes break it into simpler soluble substances that can be absorbed by the cytoplasm. The vacuole therefore serves both ingestion and intracellular digestion. Option A is correct; the other choices are not functions of a food vacuole and Amoeba does not form blood.

Salivary amylase is an enzyme secreted by the salivary glands and mixed with food in the mouth. Its substrate is starch, a complex carbohydrate. The enzyme begins hydrolysing starch into simpler sugars such as maltose, although digestion continues elsewhere in the alimentary canal. Therefore option A is correct; fats require lipases, proteins require proteases, and minerals do not need enzymatic digestion.

The governing concept is pressure in the circulatory system. Arteries carry blood away from the ventricles, where it is pumped at relatively high pressure. Their thick, elastic and muscular walls withstand this pressure and help maintain blood flow. Veins return blood at much lower pressure and therefore have thinner walls. Options B, C and D describe functions that blood vessels do not perform. Thus, option A is correct.

The governing concept is one-way blood flow. Veins carry blood toward the heart, but the pressure inside them is relatively low, especially in vessels returning blood from the lower parts of the body. Valves open when blood moves toward the heart and close if it tends to reverse direction. Therefore, option A is correct. The other options are unrelated because valves neither change blood colour, make food, nor produce oxygen.

The governing concept is exchange between blood and body tissues. Capillaries have extremely narrow diameters and walls only about one cell thick, so the diffusion distance is very small. Oxygen and nutrients can move from blood to cells, while carbon dioxide and other wastes move into the blood. Thus option A is correct. Colour change, chewing and bone hardening are not functions of capillary walls.

The governing concept is the light-dependent requirement of photosynthesis. Chlorophyll absorbs light energy, which powers the reactions that produce energy-rich molecules and ultimately helps convert carbon dioxide and water into glucose and oxygen. At night, sunlight is absent, so these light-driven reactions usually stop in most plants. Water and xylem do not suddenly disappear, and chlorophyll is not always destroyed. Thus option A is correct.

The governing concept is that mitochondria are the main sites of aerobic cellular respiration, where food molecules are broken down to release usable energy in the form of ATP. A cell with high energy demands, such as a muscle cell, generally needs more mitochondria to produce sufficient ATP. Vacuoles mainly store materials, the cell wall provides support, and the nuclear membrane encloses the nucleus; none is the primary site of energy release.

The governing concept is cellular respiration. In body cells, glucose is broken down to release energy; during aerobic respiration, carbon dioxide is produced as a waste product. The blood transports this carbon dioxide, mainly in dissolved or chemically combined forms, to the lungs, where it is exhaled. Chewing, blood clotting, and water absorption do not produce carbon dioxide as their main function.

The urinary system has separate tubes with different functions. Urine is produced in the kidneys, and each ureter is a muscular tube that carries urine from a kidney to the urinary bladder, where it is temporarily stored. The vessel carrying blood from the heart to the lungs is the pulmonary artery, food travels through the oesophagus, and air travels through the trachea. Thus option A is the only correct description.