Transportation

Most oxygen in human blood is transported by binding reversibly to haemoglobin, the iron-containing respiratory pigment present in red blood cells. In the lungs, haemoglobin combines with oxygen to form oxyhaemoglobin; in tissues, oxygen is released for respiration. Therefore option A is correct. Saliva and bile aid digestion, while urea is a nitrogenous waste, not an oxygen carrier.

Blood is the principal transport fluid in the human body. Its plasma carries dissolved nutrients, hormones, carbon dioxide, urea and other substances, while red blood cells transport most oxygen through haemoglobin. Blood also distributes heat and helps protect the body. Therefore option A is correct. Saliva and bile support digestion, whereas sweat mainly helps cooling and excretion rather than general internal transport.

The governing concept is transport in vascular plants. Roots absorb water and dissolved mineral ions from the soil, and xylem conducts them mainly upward to the stem and leaves. Therefore option A, xylem, is correct. Phloem transports sugars and other organic nutrients, while epidermis provides a protective covering and cork forms protective tissue; neither is the main water-conducting tissue.

The governing concept is water loss in plants. Transpiration is the loss of water vapour from the aerial parts of a plant, especially leaves, mainly through microscopic stomata. Therefore option A is correct. It is not the taking of food, the formation of soil by roots, or blood production by flowers; those choices describe unrelated or biologically incorrect processes.

The governing concept is transpiration pull. When water evaporates from leaf surfaces, especially through stomata, it creates tension in the continuous water column inside xylem. This helps draw water and dissolved minerals upward from roots toward leaves, so option A is correct. Digestion, oxygen binding in blood, and urine formation are animal processes and are unrelated to plant transpiration.

The governing concept is transportation, which distributes essential materials and removes wastes. Digested nutrients and oxygen must reach cells, while carbon dioxide and other wastes must be carried away to suitable organs. In plants, xylem and phloem transport water, minerals, and food. Therefore option A is correct; the other options describe no general life-process function.

Haemoglobin is the iron-containing respiratory pigment inside red blood cells. In the lungs, it combines reversibly with oxygen to form oxyhaemoglobin, allowing oxygen to be carried efficiently through the blood; in tissues, oxygen is released for cellular respiration. Bile helps digest fats, saliva begins digestion, and urea is a nitrogenous waste, so none of these transports oxygen. Therefore option A is correct.

The governing concept is transpiration pull in plant transport. When water evaporates from leaf surfaces through stomata, it creates negative pressure in the continuous water column inside xylem. Cohesion between water molecules helps transmit this pull downward, assisting the upward movement of water and dissolved minerals from roots to leaves. Therefore option A is correct. The other options refer to animal digestion, circulation or excretion, not transport through plant xylem.

The governing concept is transport in plants. Roots absorb water and mineral ions from the soil, and xylem tissue carries them mainly upward through vessels and tracheids to stems and leaves. Transpiration pull, along with root pressure and cohesion, supports this movement. Phloem transports food, stomata regulate gas exchange and chlorophyll absorbs light, so option A is correct.

The governing concept is transportation in living organisms. Cells in different parts of an organism need materials such as digested food, water, minerals, and oxygen, while carbon dioxide and other wastes must be carried away. Blood transports substances in animals, and vascular tissues such as xylem and phloem perform comparable functions in plants. Thus option A states the main importance; cooling, taste, and sleep are not the primary purposes of transport.

Transport is necessary because essential materials and wastes are not always located where they are needed. In animals, blood carries oxygen, digested nutrients, hormones, and wastes between organs. In plants, xylem transports water and minerals, while phloem distributes food. Therefore option A expresses the governing purpose. The other options would prevent, rather than support, cellular activities and do not describe transport.

Xylem is the conducting tissue that transports water and dissolved mineral salts from the roots toward the stem, leaves, and other aerial parts of a plant. This movement is supported by root pressure, capillary effects, and transpiration pull. Phloem transports prepared food, epidermis mainly provides protection, and meristem produces new cells through division. Thus, option A is correct.

The heart is a muscular organ that pumps blood to the lungs and the rest of the body through rhythmic contraction and relaxation. The lungs add oxygen to the blood and remove carbon dioxide, but they do not pump blood. Exam tip: Remember that the heart pumps blood, while gas exchange occurs in the lungs.

Stomata are tiny pores in the epidermis of leaves. They allow carbon dioxide to enter for photosynthesis and allow oxygen and water vapour to leave; hence, they are mainly involved in gas exchange and transpiration. Water is absorbed from the soil by root hairs, not by stomata. Exam tip: remember stomata as guard-cell-controlled pores of leaves.

Haemoglobin is a protein present in red blood cells. It binds oxygen in the lungs to form oxyhaemoglobin and carries it to body tissues. Only a very small amount of oxygen is dissolved in blood plasma, so plasma is not the main carrier. Exam tip: Remember that oxygen is mainly carried by haemoglobin, whereas most carbon dioxide is transported as bicarbonate ions.