Summary of Chapter Concepts

Most terrestrial plants obtain nutrients and water from the soil. Soil nutrients include nitrogen, phosphorus, calcium, and potassium. The water-holding capacity of soil, known as its field capacity, depends on the particle sizes in the soil. The ability of plants to absorb this water requires that the osmotic potential of the roots be stronger than the matrix potential of the soil. This water moves up the plant stem to its leaves through a combination of osmotic pressure, the cohesion of water molecules, and the force of transpiration.

Sunlight provides the energy for photosynthesis. Within the full range of electromagnetic radiation produced by the Sun, only a narrow range of wavelengths is used by the photosynthetic pigments of plants. This solar energy is used to power the process of photosynthesis by splitting water molecules and producing molecular oxygen and sugar. There are three pathways of photosynthesis: C₃, C₄, and CAM. Each differs in how it captures CO₂ and each works best in particular environmental conditions. These different pathways are often associated with structural adaptations that help plants from arid regions conserve water.

Terrestrial environments pose a challenge for animals to balance water, salt, and nitrogen. Organisms attempt to achieve homeostasis in all of these compounds, typically through the use of negative feedbacks. Plants and animals both possess a number of adaptations to balance their concentrations of salt, water, and nitrogenous wastes.

Adaptations to different temperatures allow terrestrial life to exist around the planet. Organisms can gain and lose heat through radiation, conduction, convection, and evaporation. These processes combine to form an individual’s heat budget. Temperature can be regulated to different degrees by animals through the process of thermoregulation. Poikilotherms have variable body temperatures whereas homeotherms have relatively constant body temperatures. The body temperatures of ectotherms are largely determined by their external environment whereas endotherms can raise their body temperatures to be higher than the external environment. Additional adaptations to assist in thermoregulation include the shunting of blood and countercurrent circulation.