Plant hormones

What is a plant hormone and how does it differ from an animal hormone in terms of its site of production, transport, and target cells?

Name two plant hormones (for example, auxins, gibberellins, cytokinins, ethylene, or abscisic acid) and describe the main effect of each on the plant.

Name the five classical phytohormones (auxins, gibberellins, cytokinins, ethylene and abscisic acid) and associate each one with a characteristic process (stem elongation, fruit growth, cell division, ripening, dormancy and stomatal closure).

Define tropism and distinguish between phototropism, geotropism, and thigmotropism, stating the stimulus and an example of a response for each case.

What is gravitropism (geotropism)? Explain why the root grows downwards and the stem upwards even though the seed is sown in any position, indicating what the cells perceive (statoliths containing starch).

Went's experiment demonstrated the existence of auxin. Describe his set-up (coleoptile tips on agar blocks, asymmetric application of the block to decapitated stems) and explain what conclusion it allowed: the growth signal is a diffusible chemical substance.

Explain what phototropism is and discuss why it is a slow response of differential growth and not a rapid movement like that of Mimosa.

Distinguish between climacteric fruits (banana, apple, tomato) and non-climacteric ones (orange, grape, strawberry): what happens with ethylene and respiration in each group, what this implies for their harvesting, and how controlled-atmosphere chambers delay ripening.

In a laboratory bioassay, four batches of bean seedlings subjected to different treatments are analyzed: Batch 1 (intact control plant); Batch 2 (decapitation of the shoot apex); Batch 3 (decapitation of the apex and immediate placement of an agar block rich in indoleacetic acid on the cut surface); Batch 4 (decapitation and continuous topical application of cytokinins directly onto the basal axillary buds). a) Predict the development of lateral buds in each batch after two weeks and biologically justify your predictions based on the auxin/cytokinin balance. b) Explain the origin and transport direction of both phytohormones in an intact plant. c) Based on these mechanisms, physiologically justify why a gardener must carry out periodic pinching/heading-back pruning if they wish to achieve an ornamental hedge that is highly branched and dense from the base.

Define the dormancy of seeds and of buds, and explain which phytohormones maintain it (abscisic acid) and which break it (gibberellins), as well as its adaptive value (avoiding germinating in autumn).

Explain what abscission is and what role ethylene and the fall of auxins play in the formation of the abscission layer that makes leaves fall in autumn.

Abscisic acid is the "water stress hormone". Explain how it is produced in the root when the soil dries, which order it carries to the leaves (closing of stomata) and what advantage the plant has in anticipating dehydration even though it turns off the $\text{CO}_2$ tap.