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

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.

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).

Carries dissolved sugars (mainly sucrose) and other organic molecules from sources (leaves) to sinks (roots, fruits, growing tissues) bidirectionally as needed.

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.

Describe the cohesion-tension theory of water transport in plants, naming three properties of water that make it work. [3 marks]

A spirometer trace from a resting human shows tidal volume of 500 mL at 12 breaths per minute, while during exercise tidal volume rises to 1500 mL at 25 breaths per minute. Calculate minute ventilation in each state and explain how the alveolar surface meets the increased demand. [3 marks]