Life Processes

The thin walls of alveoli reduce the distance across which respiratory gases must diffuse. Because the alveoli are also moist and closely associated with blood capillaries, oxygen can enter the blood and carbon dioxide can leave it rapidly. Therefore option A is correct. Digestion occurs in the alimentary canal, blood cells are formed mainly in bone marrow, and urine is produced by the kidneys.

The heart is a muscular organ that contracts rhythmically to pump blood through the pulmonary and systemic circulations. The right side sends deoxygenated blood to the lungs, while the left side pumps oxygenated blood to the body. Therefore option A is correct. Lungs exchange gases, the stomach digests food and the liver performs metabolic and processing functions; none acts as the main blood pump.

The governing concept is the structure of the human circulatory system. The human heart is divided into two upper chambers, called atria, and two lower chambers, called ventricles. Adding them gives 2 + 2 = 4 chambers. Therefore, option C is correct. Two and three are incomplete counts, while five is more than the actual number of chambers in the normal human heart.

The governing concept is the direction of blood flow through blood vessels. Arteries generally carry blood away from the heart to body tissues; this definition is based on direction, not on whether the blood is oxygen-rich. Thus option A is correct. Veins usually return blood toward the heart, whereas the stomach, kidney, and lungs are not the general destinations described by the term artery.

The governing concept is the direction of circulation in veins. Veins generally carry blood from body tissues back toward the heart, so option B is correct. This directional rule applies even though pulmonary veins carry oxygenated blood; they still move it toward the heart. Option A describes the usual direction of arteries, while options C and D are not definitions of venous transport.

The governing concept is the microscopic organization of the excretory system. A nephron is the structural and functional unit of a kidney; each nephron filters blood, reabsorbs useful substances and water, and helps form urine. Thus option A is correct. Alveoli belong to the lungs, villi increase absorption in the small intestine, and stomata are pores in plant leaves.

Urine formation is a part of excretion, a life process that removes metabolic wastes from the body. Blood enters the kidneys, where nephrons filter it and selectively reabsorb useful substances and some water. The remaining wastes, excess salts and water form urine. Therefore, option A is correct; chewing, air entry and light capture belong to digestion, respiration and photosynthesis, not urine formation.

The urinary system has a definite sequence: kidneys form urine, ureters carry it to the urinary bladder, and the urethra carries it from the bladder to the outside. Thus, the tube connecting a kidney with the bladder is the ureter, making option A correct. The urethra has a different direction and function, while the trachea and oesophagus belong to the respiratory and digestive systems.

The kidneys continuously produce urine as they remove wastes from the blood. The urinary bladder is a muscular storage sac that holds urine temporarily until it is released through the urethra during urination. Therefore, option A correctly states its main function. Pumping blood is performed by the heart, digestion occurs in the digestive tract, and oxygen is not produced by the urinary bladder.

Plants do not have specialised excretory organs like animal kidneys, so they use several methods to handle wastes. Some wastes are stored in forms such as gums and resins, especially in older tissues, and may later be removed when leaves or bark are shed. Therefore, option A is correct. Haemoglobin, muscles and the heart are animal structures and are not normal plant storage forms.

Photosynthesis requires water and carbon dioxide as raw materials, along with light energy and chlorophyll. Roots absorb water from the soil, and xylem transports it upward to the leaves, where photosynthesis occurs. Thus, option A is correct. Carbon dioxide usually enters through leaf stomata, while starch is a product of photosynthesis and protein is not the raw material identified here.

Carbon dioxide is a gaseous raw material needed to make glucose during photosynthesis. Tiny pores called stomata, found mainly on leaf surfaces, open and close to regulate gas exchange; carbon dioxide diffuses through them into the leaf tissues. Therefore, option A is correct. Roots absorb water, while petals and seed coats are not the main pathways for photosynthetic gas exchange.

Digestion breaks complex food into soluble, simple substances such as glucose, amino acids and fatty acids. These products pass through the wall of the small intestine into the blood or lymph; this movement is called absorption. Hence option A is correct. Swallowing only moves food into the alimentary canal, excretion removes wastes, and respiration releases energy rather than transferring digested nutrients into blood.

After digestion and absorption, nutrients such as glucose and amino acids enter the bloodstream from the small intestine. The circulatory system then transports these dissolved nutrients to tissues and body cells, where they are used for energy, growth and repair. Therefore, option A is correct. Hair, teeth and nails do not form a transport system for digested food; teeth only help mechanical digestion.

Cellular respiration is the controlled oxidation of food inside cells. In the usual school-level description, glucose is broken down in the presence of oxygen to release usable energy, with carbon dioxide and water as products; without oxygen, partial breakdown can occur. Thus option A is correct. Sand, iron and glass are not cellular respiratory fuels and cannot replace glucose in this process.

During normal breathing, air first enters through the nose and then moves through the nasal cavity, pharynx, larynx and trachea toward the lungs. Nasal hairs and mucus help trap dust, while the moist lining warms and humidifies incoming air. Therefore, option A is correct. The stomach and small intestine belong to digestion, and the kidney belongs to excretion, so none of them begins the respiratory pathway.

The governing concept is the coordinated set of life processes. Nutrition supplies materials, respiration releases usable energy, transportation distributes substances, and excretion removes metabolic wastes. These functions support survival in both plants and animals. Thus option A gives the complete conclusion, whereas B omits respiration, C is scientifically false, and D wrongly excludes animals.

The governing concept is the definition of life processes. An organism must obtain or prepare food, release usable energy, distribute materials, and remove wastes in order to remain alive. Nutrition, respiration, transportation, and excretion are therefore grouped under this term. Option A is correct; heredity concerns traits, natural selection concerns evolution, and a reflex is a rapid response.

Photosynthesis is the process by which green plants use sunlight, carbon dioxide, and water to prepare food. The immediate main product is glucose, a simple carbohydrate that stores chemical energy. Some glucose is used in respiration, while some is converted into starch for storage. Urea, bile, and saliva are not products of photosynthesis, so option A is correct.

The governing concept is nutrition. Organisms that cannot prepare their own food from simple inorganic substances and obtain it from plants or other organisms are called heterotrophs. Humans, animals, and most fungi are examples. Autotrophs and producers generally make their own food, while green plants are typical autotrophs. Therefore, option A correctly identifies these dependent organisms.