Quick questions on Gas exchange and internal transport in plants and animals (QCE Biology Unit 1)

Stomata. Small pores in the leaf epidermis, mainly on the lower surface, bounded by two guard cells. Open during the day for CO2 to diffuse in (for photosynthesis) and O2 to diffuse out; close at night and during water stress to conserve water.

Plants have two vascular tissues, both organised into vascular bundles.

Transpiration is the loss of water vapour from the aerial parts of a plant, mostly through stomata. It is the engine that pulls water up the xylem.

Animals concentrate exchange at specialised surfaces with high SA:V, thin walls and good blood supply.

Open circulatory systems. A heart pumps blood (haemolymph) into the haemocoel, bathing tissues directly. Low pressure, slow flow. Adequate for small, slow-moving animals (most arthropods, most molluscs).

Small pores in the leaf epidermis, mainly on the lower surface, bounded by two guard cells. Open during the day for CO2 to diffuse in (for photosynthesis) and O2 to diffuse out; close at night and during water stress to conserve water.

Inside the leaf, palisade and spongy mesophyll cells expose a large moist surface area to the air spaces. Gases dissolve in the moist cell wall and diffuse into the cell.

Carries water and dissolved minerals from roots to leaves in one direction (upward). - Composed of dead, hollow, lignified vessel elements and tracheids. - No end walls in vessels (angiosperms); cell contents removed at maturity.

Carries dissolved sugars (mainly sucrose) and other organic molecules from sources (leaves) to sinks (roots, fruits, growing tissues) bidirectionally as needed. - Composed of sieve tube elements (living but lacking nuclei) connected end to end through sieve plates. - Each sieve tube element is supported by an adjacent companion cell that provides metabolic services.

Bronchi branch into bronchioles ending in millions of alveoli. Each alveolus is a single-cell-thick sac wrapped in capillaries. Total exchange surface around 70 square metres.

Stacks of filaments, each carrying many lamellae. Water flows over the lamellae in the opposite direction to blood flow inside (counter-current exchange), maintaining a steep oxygen gradient along the whole length of the lamella.

Air enters through spiracles and travels through branching tracheae and tracheoles directly to tissues. No blood is involved in gas transport; the haemolymph carries nutrients only.

A heart pumps blood (haemolymph) into the haemocoel, bathing tissues directly. Low pressure, slow flow. Adequate for small, slow-moving animals (most arthropods, most molluscs).

Blood is confined to vessels (arteries, capillaries, veins) and pumped at high pressure. Supports higher metabolic rates. Found in vertebrates, cephalopods and annelids.

A double closed circulation. - Pulmonary circuit. Right ventricle pumps deoxygenated blood through the pulmonary artery to the lungs, returns oxygenated blood via the pulmonary vein to the left atrium. - Systemic circuit. Left ventricle pumps oxygenated blood through the aorta to the body, returns deoxygenated blood via the venae cavae to the right atrium.