Scaling up Study Guide

Stem cells are unspecialised cells that have the ability to differentiate into many different 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 become any type of cell in the body. This extensive differentiation potential makes them valuable for research into treating diseases. Adult stem cells are found in tissues like bone marrow and skin. They are multipotent, meaning they can differentiate into a limited number of cell types to repair and replace damaged tissues within that specific organ system. For example, bone marrow stem cells can form various blood cells, but not skin cells. Meristems are the plant equivalent of stem cells. They are regions of undifferentiated cells found in plants, primarily at the tips of roots and shoots (apical meristems) and in the cambium (lateral meristems). These meristematic cells continuously divide and differentiate, allowing plants to grow throughout their lives, forming new roots, stems, leaves, and flowers. The ability of both animal stem cells and plant meristems to divide and specialise is crucial for growth, repair, and regeneration in multicellular organisms.

Plants absorb water through their roots, which then travels up the stem to the leaves in a continuous process called transpiration. The rate at which a plant takes up water is significantly influenced by various environmental factors. Understanding these factors is crucial for plant growth and survival. Light intensity affects the opening and closing of stomata, small pores on the leaf surface. In bright light, stomata usually open wider to allow carbon dioxide uptake for photosynthesis, which also increases water vapour loss, thereby increasing water uptake. Temperature also plays a key role; higher temperatures increase the kinetic energy of water molecules, leading to a faster rate of evaporation from the leaf surface (transpiration). This increased transpiration creates a stronger pull for water from the roots. Humidity, which is the amount of water vapour in the air, directly impacts the concentration gradient between the leaf and the surrounding atmosphere. Low humidity means a large concentration difference, causing more rapid evaporation from the leaves and consequently more water uptake. Conversely, high humidity reduces this gradient, slowing down transpiration and water uptake. Air movement, such as wind, removes humid air from around the leaves, maintaining a steep concentration gradient for water vapour. This removal of the 'boundary layer' of humid air allows for faster diffusion of water vapour out of the leaf, increasing the rate of transpiration and subsequent water uptake. Conversely, still air allows a layer of humid air to build up, slowing transpiration. Soil water availability is also critical; if there is insufficient water in the soil, the plant cannot absorb enough, regardless of other environmental factors, which can lead to wilting.