An Introduction to Biology

• The cell theory is an in-depth explanation, supported with scientific data, to prove a cell is a living thing and has unique characteristics.
• Cells are the basic building blocks of life. Coming in various sizes and shapes, cells have specialized functions.
• Two broad types of cells are prokaryotic and eukaryotic cells.
• Prokaryotes are single-celled organisms that lack a nucleus, while eukaryotes are multicellular organisms that contain a nucleus and other organelles.
• Organelles are specialized structures with a specific cellular function.
• Both animal and plant cells are types of eukaryotic cells, both having similar organelles such as ribosomes, mitochondria, and an endoplasmic reticulum.
• Cell walls and chloroplasts are only found in plant cells. Cell walls provide protection and support to plant cells, giving them rigidity in their shape. Chloroplasts harness energy from the sun for plants through the process of photosynthesis.
• Living things can be classified as autotrophs or heterotrophs based on how they obtain energy. Plants are autotrophs which rely on photosynthesis to produce energy while heterotrophs such as animals must consume and metabolize food into energy.

An Overview of Plants

• Plants are classified as the kingdom plantae in the Linnaean taxonomic system.
• Plants may be categorized as angiosperms, gymnosperms, ferns, or bryophytes. Angiosperms produce flowers and seeds, gymnosperms produce cones and seeds, while ferns and bryophytes release spores. Bryophytes do not have a vascular system.
• Plants have a root system and shoot system. The root system may have a core taproot with various roots to complete the system.
• Roots will hold a plant in place and absorb water and nutrients from the soil.
• The shoot system consists of the plant structures above the ground or soil. The stem, leaves and budding flowers, cones, or spores are a part of the shoot system.
• The shoot system allows for the plant to absorb energy from the sun and complete cellular respiration and photosynthesis.
• Both the roots and shoots contain vascular tissues that allow for water and nutrients to travel throughout the plant.
• Vascular tissues consist of xylem and phloem cells. Xylem cells allow one-way flow of water and minerals from the soil through the shoot system. Phloem cells allow for two-way flow of water and minerals throughout the plant.

Cellular Respiration and Photosynthesis

• Cells are powered by cellular respiration and/or photosynthesis.
• Cellular respiration is the process where mitochondria of a cell break down glucose (sugar molecules) to produce energy in the form of ATP. The general equation for cellular respiration is: \(O_{2} + C_{6}H_{12}O_{6} → CO_{2} + H_{2}O + ATP\)
• Reactions during cellular respiration go from glycolysis to the citric acid cycle to the electron transport chain.
• Photosynthesis is the process plants use to make a food source from energy. Chloroplasts contain chlorophyll, which helps plants absorb light from the sun.
• Photosynthesis is considered the reverse of cellular respiration. The general equation is: \((ATP) + CO_{2} + H_{2}O → C_{6}H_{12}O_{6} + O_{2}\)
• The reaction involves two distinct phases: light reactions and dark reactions. Light-dependent reactions require light to produce ATP and NADPH. The dark reactions, also known as the Calvin Cycle, do not require light and use ATP and NADPH from the light reactions to produce glucose and oxygen.

Cellular Reproduction

• Cells are needed for growth, repair, and reproduction. Living things can reproduce asexually or sexually.
• Prokaryotes and some eukaryotes reproduce asexually, a process where a single parent cell copies its DNA and splits in half to reproduce. All offspring are genetically identical.
• Sexual reproduction is a process in which two gametes, otherwise known as reproductive cells, unite to create offspring with genetic characteristics from both parents, providing greater genetic diversity in the population.

• A chromosome is a rod-shaped structure that forms when a single DNA molecule and its associated proteins coil tightly before cell division. DNA can be found in the nucleus, a membrane-bound organelle unique to eukaryotes.
• The cell cycle regulates cellular division and can be divided into two phases: interphase and the M (mitotic) phase. The cell cycle consists of a \(G_{1}\) (growth) phase, S (DNA replication) phase, \(G_{2}\) (preparation) phase) and the M (mitotic) phase.
• Mitosis is a form of cell division where one parent cell divides into two identical daughter cells. It primarily consists of prophase, metaphase, anaphase, and telophase.

• Meiosis is a different cellular division process that is divided into two rounds of cell division: meiosis I and meiosis II.
• Meiosis I and Meiosis II involve the same phases as mitosis. The major difference is that DNA replication does not happen when meiosis I proceeds to meiosis II.
• Prophase I of meiosis includes a process of crossing over. This process increases genetic diversity because corresponding DNA from different parental chromosomes is exchanged.
• The products of meiosis are four haploid cells, or cells with half the number of normal chromosomes.
• The normal number of chromosomes is restored when two gametes, or haploid sex cells (sperm, egg) unite, forming a zygote, or diploid cell with a normal number of chromosomes.

Genetics

• Gregor Mendel is considered the father of genetics because of his Theory of Heredity. His theory revolves around the idea that parents do not transmit traits directly to their offspring. Rather, they pass on units of information called genes.
• A gene is a segment of DNA that transmits information from parent to offspring, also known as an allele.
• For each trait, an individual has two alleles: one from each parent. If the two factors have the same information, the individual is homozygous for that trait. If the two factors are different, the individual is heterozygous for that trait.
• The alleles determine the physical appearance, or phenotype. The set of alleles an individual has is its genotype.
• An allele may be dominant or recessive. A dominant allele guarantees a trait’s expression in the phenotype. The presence of a recessive allele does not guarantee that the trait will be expressed.
• Biologists can predict the probable outcomes of a genetic cross by using a diagram called a Punnett square.

DNA (Deoxyribonucleic Acid)

• Deoxyribonucleic acid is a long, thin molecule made of subunits called nucleotides that are linked together in a nucleic acid chain.
• Nucleotides consist of three parts: a phosphate group, a five-carbon sugar, and nitrogen base.
• There are four nitrogen bases: adenine, guanine, thymine, and cytosine. These bases occur in pairs on a DNA strand.
• Adenine pairs with thymine and guanine pairs with cytosine. These are the only possible pairings.
• Replication is the process of synthesizing a new strand of DNA. DNA will separate into two strands and build a complementary strand.
• Transcription is the first step in using DNA to direct the making of a protein. It is the process that “rewrites” the information in a gene in DNA into a molecule of RNA which will be used to code for proteins.
• Translation is the process of making proteins.

Designing an Experiment

• Recall that the scientific method uses seven steps to answer a question or solve a problem.
• A good experimental design properly defines all variables and considers how data will be analyzed.
• Correlations in data illustrates the cause-and-effect relationships between two variables.
• Positive and negative correlations can be displayed graphically by analyzing the slope of a line.
• Different devices are used to measure objects in an experimental study. For example, graduated cylinders can measure the volume of a liquid and a triple beam balance can be used to measure the mass of an object.
• Time, distance, volume, and mass can be measured in different units.
• The metric system is usually used when expressing the units of measured values.

Temperature and the Metric System

• The metric system is a universally accepted standard method that is used to determine the units of a given measurement.
• The English system is not universally accepted but provides a collection of measurements whose units are functionally unrelated.

• Meter (length), gram (weight), and liter (volume) are the most common types of SI base units.
• Metric prefixes are added to base units to describe the measurement of an object according to size.
• The metric staircase can be used for metric—metric conversions, and specific equivalent values are used for English—metric conversions.
• Scientific notation is used to make very large numbers and very small numbers easier to use.

• Three temperature scales, Celsius, Fahrenheit, and Kelvin, are used in science.
• Formulas are used to convert Celsius values to Fahrenheit or to Kelvin.