Ap Biology Lab Report

Aim:

The aim of this report is to investigate the responses of plants in regards to growth on the basis of varying directional sunlight. In order analyze this; pea plants will be used within a conducted experiment.

Introduction:

Introduction to plants:

Organisms of all ecosystems rely on the mechanisms that have evolved for the sustainability of survival (Source 7). This is particularly applicable for the Eukaryote Kingdom, Plantae, (plant), of which is sessile. Due to their dormant nature, plants must be proficient in subsisting with the changing biotic and abiotic factors. As plants have no nervous system, plants rely on hormones (Source 1). Plant hormones are chemical messengers that are transported between the cells of a plant (Source 1, Source 3), and are responsible for several operations such as the growth of stems, leaves, and seed germination (Source 1).

Introduction to plant hormones:

There are five main plant hormones, Auxin, Abscisic Acid (ABA), Cytokinins, Ethylene, and Gibberellins (Source 1). Plant hormones have individual roles, and functions, yet often require the

interrelation of two hormones to properly operate. The study of plant hormones has allowed an escalation of knowledge and therefore application to commercial industries around the world.

Auxin
Upon experimenting in 1881, Charles Darwin and son, Francis Darwin, observed the unilateral curvature of a canary grass’ coleoptile towards the light source (Source 9).

Having performed several further experiments, the Darwins’ stated when seedlings are exposed to a lateral source of light; an (unknown) inducer is transmitted from the upper part to the lower part of the plant, causing a curvature-like appearance (Source 9). Continuing onto Darwins’ discovery, Peter Boysen-Jensen and Arpad Paal determined the substance that caused the bending was due to a chemical present in the plant (Source 7). One year later, scientist F.W. Went concluded the initial discovery, calling the substance responsible for the bending in the plant, Auxin (IAA) (Source 9). Biologists have since recognized the extent of Auxin’s role in plant growth, as well as its location within the plant

itself.

Increasing the plasticity of the plant’s cell walls due to tugor pressure, Auxin is responsible for stimulating cell growth and cell expansion within a cell (Source 7). Situated in the coleoptile, Auxin is dispersed from the tip of the plant, in a downward motion towards the base of the plant (Source 3, Source 7). Due to the highest concentration of Auxin at the coleoptile, and lowest at the base, Auxin ensure apical dominance may be maintained therefore lateral buds may be removed (Source 3).

Auxin is also essential to the plant’s sustainability, as its curvature-like mechanisms allow the plant to reach sunlight, therefore the plant may photosynthesize (Source 12). Photosynthesis is the process by which plants containing chlorophyll use sunlight to synthesize the production of glucose from carbon dioxide and water (Source 15). The glucose is then converted into a compound called pyruvate, which is then released as adenosine triphosphate (ATP) (Source 15).

-Auxin is also involved in cellular respiration (Source 3). Cellular respiration is…
-Auxin however, is also used in conjunction with another plant hormone, called…

ABA
Abscisic Acid, or ABA, is recognized as the hormone that alerts the plant of water stress (Source 3).

Cytokinins
Produced in the root apical meristems, Cytokinins are responsible for growth stimulation (Source 6). With the combination of Auxin and Cytokinins, a stimulating result of cell division promotion and cell differentiation in plants occurs (Source 1).

Ethylene
Ethylene is the only gaseous hormone within plants (Source 3). Produced in the flowers, and leaves of a plant, Ethylene promotes the ripening of fruits (Source 1). This hormone is commonly used commercially, trough applying the Ethylene to fruit in need of ripening so that it may be sold to the genera public (Source 7). Ethylene is produced in conjunction with Auxin, when Auxin is transported down from the apical stem it consequently encourages the production of Ethylene (Source 7).

Gibberellins
Often working in conjunction with Auxin, Gibberellins offer a major role in the growth of a stem (Source 7). Discovered in the 1920’s by Japanese plant pathologist Eiichi Kurosawa, and further isolated for structural identification, the discovery of Gibberellins was not confirmed until 1954 by British chemists (Source 7). Named after the fungus Gibberella fujikuroi, Gibberellins promote stem elongation between nodes of a stem (Source 3). This hormone is synthesized in the meristem and roots of a plant (Source 6).

Tropisms
‘Tropisms are the natural responses of organisms to external stimuli’ (Source 5). The three primary tropisms, phototropism, gravitropism, and thigmotropism

Cellular Respiration