Transportation

The governing concept is the comparison of forces involved in xylem water transport. Root pressure develops when roots actively absorb ions and water enters by osmosis, producing a positive push from below. Transpiration pull develops when evaporation from leaves creates negative pressure that pulls the continuous water column upward. Thus option A states the key difference; the other options concern digestion, excretion, or lungs and are irrelevant.

The governing concept is phloem translocation from a source to a sink. A mature leaf may act as a source by producing sugars, while roots, growing shoots, flowers, seeds, or fruits may act as sinks by using or storing them. Since different sinks may lie above or below a source at different times, phloem transport can occur in either direction in different sieve tubes. Therefore option A is correct; xylem and the remaining choices are unrelated.

Transpiration is the loss of water vapour from the aerial parts of a plant, mainly through stomata. As water evaporates from leaf surfaces, it creates tension or a transpiration pull in the continuous water column of the xylem. Cohesion between water molecules helps transmit this pull downward, drawing more water upward from the roots. Thus option A is correct; the remaining processes belong to animal physiology or digestion.

Phloem is the living conducting tissue that transports sugars and other organic nutrients made in photosynthetic leaves to growing or storage regions, such as roots, fruits, and young shoots. This movement is called translocation and can occur in different directions according to the source and sink. Damage to phloem therefore most directly disrupts food distribution. Water transport is mainly a xylem function, so option A is correct.

The governing concept is phloem translocation from a source to a sink. Mature leaves commonly produce sugars, but growing roots, fruits, seeds, stems, and buds may require them at different times. Phloem can therefore move dissolved food from the producing region to the region of use or storage, either upward or downward according to need. Option A is correct; xylem mainly transports water and minerals, not food.

Haemoglobin is the iron-containing pigment in red blood cells that binds oxygen in the lungs and transports it to body tissues. If haemoglobin concentration falls, the blood carries less oxygen, so cells may receive insufficient oxygen for respiration; tiredness and weakness can result. Option A is correct. Taste, starch production and stomatal opening are unrelated to haemoglobin-dependent oxygen transport in humans.

The governing concept is transpiration pull. Water evaporates from moist cell surfaces inside leaves and exits through stomata as water vapour. This loss lowers water pressure in the leaf and creates tension in the continuous water column. Cohesion between water molecules and adhesion to xylem walls help pull water upward from the roots. Hence option A is correct; the other choices do not describe transpiration.

Food prepared in leaves is transported through phloem by translocation. Depending on the location of the source and the current sink, sugars may move toward roots, stems, fruits, seeds, or growing buds. Consequently, the direction is not permanently fixed: movement can be upward in one part and downward in another, or change with the plant’s needs. Thus option A is correct; the one-way alternatives incorrectly describe phloem transport.

Human blood circulation is driven primarily by the muscular heart, which creates pressure to move blood through vessels. In plants, xylem transports water and minerals upward without a heart; evaporation from leaves produces transpiration pull, assisted by cohesion and sometimes root pressure. Thus option A identifies the main difference. The other options wrongly give plants a heart or assign haemoglobin and photosynthesis to xylem or blood.

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.