Transportation

Phloem translocation distributes sugars such as sucrose from a source, usually a photosynthesising leaf, to sinks such as roots, fruits, seeds, or growing tissues. Loading sugars into sieve tubes and maintaining the pressure gradient require metabolic energy, especially from companion cells. Transport can occur in different directions according to demand. Therefore A is correct; the other choices wrongly describe phloem as dead tissue or a water-only pathway.

The governing concept is the link between digestion, absorption, and transportation. Digestion breaks complex food into soluble substances such as glucose, amino acids, and fatty acids. These products are absorbed mainly through the small intestine into the blood or lymph. The circulatory system then distributes them to cells, where they support energy release, growth, and repair. Therefore option A is correct; digestion alone does not deliver nutrients to every tissue.

Xylem forms the conducting tissue that carries water and dissolved mineral ions from roots to stems and leaves. If xylem is blocked, this upward supply is rapidly reduced even if phloem can still transport sugars. Leaves may lose turgidity, mineral nutrition may decline, and photosynthesis can eventually slow because water is required. Therefore option A is correct; haemoglobin and urine formation are animal functions, and phloem transports food.

The governing concept is transport in vascular tissues. Xylem mainly carries water and dissolved minerals from roots towards the shoots, generally upward. Phloem translocates sugars made in leaves from a source to a sink, such as roots, fruits, or growing tissues. Because sources and sinks may occur at different positions, phloem transport can be upward or downward according to need. Thus option A is correct; the other choices wrongly assign water, food, or blood to these plant tissues.

Transpiration is the loss of water vapour from leaf surfaces, mainly through stomata. This loss lowers water potential in leaf tissues and produces tension, commonly called transpiration pull, in the continuous water column. Cohesion between water molecules helps transmit the pull downward and draws water upward through xylem. Therefore option A is correct; the other options misuse plant structures or deny the relationship.

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.