Science Knowledge Organiser: Plant Biology and Electrical Physics and Electricity
Plant Tissues and Cellular Anatomy
The plant structure is organized into specific tissues designed for protection, photosynthesis, and gas exchange. The epidermis refers to the outermost cells of a plant, acting as a protective barrier. Within the leaf, the palisade mesophyll is the tissue found in the uppermost layers, characterized by its high concentration of chloroplasts where a significant amount of photosynthesis takes place. Directly below the palisade layer is the spongy mesophyll. This tissue contains internal air spaces specifically designed to allow the diffusion of gases throughout the leaf.
Plant Organs and Specialized Growth Areas
The root serves as the primary plant organ responsible for the absorption of water and minerals from the surrounding soil. For growth and development, the plant relies on the meristem, which is identified as the source of stem cells. These undifferentiated cells allow the plant to grow in length and girth and differentiate into specialized tissue types as required by the organism's life cycle.
Systems of Transport and Atmospheric Conditions
Plants possess specialized vascular tissues for the internal transport of essential substances. The xylem is the tissue responsible for carrying water and minerals upwards from the roots to the leaves. Conversely, the phloem carries glucose produced during photosynthesis from the leaf to other parts of the plant where it is needed for energy or storage. The environmental condition known as humidity refers to high levels of water vapour in the atmosphere, which directly affects the rate of transpiration and evaporation from these tissues.
Mechanisms of Particle Movement
Substances move into and out of plant cells through specific physical processes. Diffusion is defined as the movement of particles from an area of high concentration to an area of low concentration. A specialized form of this movement is osmosis, which is the movement of water from a high concentration to a low concentration specifically through a partially permeable membrane. Both processes are vital for nutrient uptake and the maintenance of turgor pressure within the plant.
Fundamentals of Electrical Currents and Potential Difference
In physics, frequency is defined as the number of waves to pass a specific point in one second. When discussing electrical systems, potential difference (PD) and current can behave in two distinct ways. Direct potential difference is a PD that always flows in one direction, leading to a direct current, which is a current that flows in one direction only. In contrast, alternating potential difference refers to a PD that changes direction many times each second, resulting in an alternating current, which is a current that constantly changes direction.
UK Mains Electricity Standards and Safety Wiring
The domestic electricity supply in the United Kingdom operates under specific standardized parameters. The UK PD (Potential Difference) is established at , and the UK Frequency is set at . Electrical safety and functionality in appliances are maintained through a three-wire system. The live wire is color-coded brown, the neutral wire is blue, and the earth wire is distinguished by yellow and green stripes. Each wire serves a specific purpose in completing the circuit or providing a safety path for electrical current to prevent shocks or fires.