Scaling up Study Guide

Plants use two essential transport processes: transpiration and translocation. Transpiration is the process by which water vapour evaporates from the leaves of plants, primarily through small pores called stomata. This evaporation creates a pulling force, or tension, that draws water up from the roots through the xylem vessels to replace the lost water. This continuous flow of water is known as the transpiration stream. Transpiration is vital for transporting water and dissolved mineral ions from the soil to all parts of the plant and also helps to cool the plant, similar to sweating in animals. Factors such as temperature, humidity, light intensity, and air movement can affect the rate of transpiration.

Translocation, on the other hand, is the movement of dissolved sugars (produced during photosynthesis in the leaves) and other organic substances from the 'source' (e.g., leaves) to 'sink' areas where they are needed for growth or storage (e.g., roots, fruits, growing shoots). This transport occurs through specialized tissue called phloem. Unlike the unidirectional flow of water in xylem, translocation in the phloem can be bidirectional, moving sugars both upwards and downwards depending on the plant's needs. The movement of substances in the phloem is an active process, meaning it requires energy from the plant's respiration to load and unload sugars against a concentration gradient. Both transpiration and translocation are crucial for the survival and growth of plants, enabling them to distribute resources efficiently throughout their structure.

Stem cells are unique, unspecialised cells with the remarkable ability to divide and develop into many different specialised cell types. In animals, there are two main types: embryonic stem cells and adult stem cells. Embryonic stem cells are found in early embryos and are pluripotent, meaning they can differentiate into almost any cell type in the body. This makes them highly versatile for growth, development, and potential therapeutic uses like repairing damaged tissues or growing new organs. Adult stem cells, found in specific tissues like bone marrow, skin and the gut, are multipotent or oligopotent, meaning they can only differentiate into a limited range of cell types relevant to their tissue of origin. Their primary function is to replace dead or damaged cells and repair tissues throughout an organism's life. This ongoing repair and maintenance is crucial for tissue homeostasis.

In plants, similar roles are performed by meristems. Meristems are regions of unspecialised cells capable of cell division and growth. Apical meristems are located at the tips of roots and shoots, responsible for primary growth, which increases the length of the plant. Lateral meristems, such as the vascular cambium, contribute to secondary growth, increasing the girth (width) of stems and roots by producing new vascular tissue and bark. Meristematic cells continuously divide to produce new cells, which then differentiate to form all the specialised tissues of the plant, including leaves, stems, roots, and flowers. This continuous growth throughout a plant's life is a key characteristic that distinguishes it from animal growth patterns.