Cell level systems Study Guide

Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize nutrients from carbon dioxide and water. The overall equation is Carbon Dioxide + Water + Light Energy → Glucose + Oxygen. Experiments designed to investigate photosynthesis typically focus on measuring the rate of one of the inputs or outputs, while carefully controlling all other variables to ensure a fair test. For example, to investigate the effect of light intensity on photosynthesis, an aquatic plant like pondweed (Elodea) can be used. The plant is placed in a test tube containing pond water enriched with sodium hydrogen carbonate (to provide carbon dioxide). A lamp is positioned at varying distances, and the number of oxygen bubbles produced per minute is counted. The dependent variable is the rate of oxygen production (number of bubbles/minute), the independent variable is the light intensity (controlled by distance from the lamp), and control variables include temperature, carbon dioxide concentration, and the type/amount of pondweed. Safety precautions include handling electrical equipment carefully near water and wearing eye protection. The results can be plotted on a graph, with light intensity on the x-axis and bubble count on the y-axis, to observe how the rate of photosynthesis changes with light intensity. Other experiments might involve measuring changes in pH (due to CO2 uptake) or the increase in biomass over time, always with careful control of conditions to isolate the effect of a single independent variable.

Deoxyribonucleic acid, commonly known as DNA, is the fundamental genetic material found in all living organisms. It carries the instructions for an organism's development, functioning, growth, and reproduction. The structure of DNA is often described as a double helix, resembling a twisted ladder. This complex molecule is a polymer, meaning it is made up of many repeating smaller units called monomers. In the case of DNA, these monomers are called nucleotides.

Each DNA nucleotide is composed of three main components: a deoxyribose sugar, a phosphate group, and a nitrogenous base. The deoxyribose sugar is a five-carbon sugar molecule that forms the backbone of the DNA strand. The phosphate group is attached to the sugar and links to the sugar of the next nucleotide, creating the sugar-phosphate backbone. There are four different types of nitrogenous bases found in DNA: adenine (A), guanine (G), cytosine (C), and thymine (T). These bases are attached to the deoxyribose sugar molecule.

It is the sequence of these bases along the DNA strand that encodes genetic information. The four different nucleotides are distinguished solely by the specific nitrogenous base they contain. So, you have an adenine nucleotide, a guanine nucleotide, a cytosine nucleotide, and a thymine nucleotide. While the sugar and phosphate components remain constant across all DNA nucleotides, the base component varies, leading to the diversity needed to store vast amounts of genetic information. The precise arrangement of these nucleotides in a specific order determines an organism's traits and characteristics.