Biology Study Guide Complete review of your notes • Vocabulary + concepts to know • No tables This guide covers the vocabulary, nitrogen cycle, phosphorus cycle, water cycle, energy transfer, food chains, organisms, and ecological processes from all your notes. I combined repeated information and clarified a few definitions to help you prepare for tomorrow’s test. Part 1: Vocabulary 1. Ecology and ecosystem organization Ecology — The study of interactions between organisms and their environment. Biosphere — All parts of Earth where life exists. Population — Members of the same species living in the same area. Community — Different populations living and interacting in the same area. Ecosystem — A community of organisms and the nonliving environment they interact with. Biomass — The total mass of living organisms in a particular area or trophic level. Trophic level — An organism’s feeding position in a food chain. 2. Types of organisms Autotroph — An organism that makes its own food using light energy or chemical energy. * Examples: plants, algae and some bacteria. * Autotrophs are also called producers. Heterotroph — An organism that obtains energy and nutrients by consuming or absorbing organic matter from other organisms. - Examples: animals and fungi. Producer — An organism that makes its own organic food. Consumer — An organism that obtains energy by eating other organisms. Herbivore — An organism that eats plants or other producers. Examples: deer, cows and caterpillars. Carnivore — An organism that eats other animals. Examples: lions, hawks and sharks. Omnivore — An organism that eats both plants and animals. Examples: humans, bears and crows. Scavenger — An organism that feeds on dead animals. Example: a vulture. Detritivore — A heterotroph that obtains nutrients by ingesting detritus. Detritus — Dead and decomposing plant and animal material, including organic waste. Decomposer — An organism that breaks down organic matter externally using enzymes and absorbs the released nutrients. - Examples: fungi, mushrooms and bacteria. Phytoplankton — Tiny photosynthetic organisms, including algae, that drift in aquatic environments and form the base of many aquatic food webs. 3. Food and energy vocabulary Food chain — A single pathway showing how energy passes from one organism to another. Food web — A network of interconnected food chains showing feeding relationships in an ecosystem. Energy transfer — The movement of energy from one organism to another. Photosynthesis — The process that uses light energy to make sugars from carbon dioxide and water. Cellular respiration — The process of breaking down molecules such as glucose to release usable energy. Chemosynthesis — The process of using energy from chemical reactions to make organic molecules. 4. Nitrogen cycle vocabulary Nitrogen fixation — The conversion of atmospheric nitrogen gas into usable nitrogen compounds. Assimilation — The process in which plants absorb nitrogen compounds and use the nitrogen to build organic molecules. Consumption — Animals obtain nitrogen and other nutrients by eating plants or other animals. Ammonification — Decomposers convert nitrogen in organic matter into ammonia or ammonium. Nitrification — Bacteria convert ammonium into nitrite and then nitrate. Denitrification — Bacteria convert nitrate into nitrogen gas, returning nitrogen to the atmosphere. Ammonia — A nitrogen-containing compound with the formula . Ammonium — A positively charged nitrogen ion with the formula . Nitrite — A nitrogen-containing ion with the formula . Nitrate — A nitrogen-containing ion with the formula , which plants can absorb. 5. Water cycle vocabulary Evaporation — Liquid water absorbs energy and changes into water vapor. Condensation — Water vapor cools and changes into liquid droplets. Transpiration — The release of water vapor from plants, mainly through their leaves. Precipitation — Water falling from clouds as rain, snow, sleet or hail. 6. Nutrients and other vocabulary Phosphorus — An essential nutrient used to build DNA, RNA, ATP and cell membranes. It also supports plant growth and root development. Limiting nutrient — A nutrient whose limited availability restricts the growth of organisms. Eutrophication — The process in which excess nutrients enter a body of water, promoting excessive algae growth and potentially reducing dissolved oxygen. Amino acids — The building blocks of proteins. Proteins — Molecules made of amino acids that perform many functions in living organisms. Nucleic acids — Molecules such as DNA and RNA that store and transmit genetic information. External digestion — The breakdown of food outside an organism’s cells or body using enzymes, as fungi do. Decomposition — The breakdown of dead organic matter and waste, returning nutrients to the environment. Part 2: Things You Need to Know 1. The nitrogen cycle The nitrogen cycle describes how nitrogen moves between the atmosphere, soil, water and living organisms. Nitrogen is essential for making proteins, amino acids and nucleic acids such as DNA and RNA. Although the atmosphere contains a lot of nitrogen gas, most plants cannot use atmospheric nitrogen gas directly. The main processes 1. Nitrogen fixation Atmospheric nitrogen gas () is converted into usable nitrogen compounds. * Mainly carried out by nitrogen-fixing bacteria. * Lightning also helps convert atmospheric nitrogen into compounds that enter the soil. 2. Assimilation Plants absorb nitrate () or ammonium () from the soil and use the nitrogen to make proteins and nucleic acids. 3. Consumption Animals obtain nitrogen by eating plants or other animals. 4. Ammonification Decomposers break down nitrogen-containing material in dead organisms and waste, releasing ammonia or ammonium into the environment. 5. Nitrification Bacteria convert ammonium into nitrite and then nitrate. NH_4^+ \rightarrow NO_2^- \rightarrow NO_3^- 6. Denitrification Bacteria convert nitrate into nitrogen gas, returning nitrogen to the atmosphere. Important things to remember * Nitrogen fixation starts with atmospheric nitrogen gas, . * Nitrogen fixation is carried out mainly by bacteria, but lightning also contributes. * Plants need nitrogen to build proteins and nucleic acids. * Animals obtain nitrogen through food. * Decomposers recycle nitrogen from dead organisms and waste. * Nitrification produces nitrite and then nitrate. * Denitrification returns nitrogen to the atmosphere. The nitrogen cycle is a cycle, so nitrogen can enter through several pathways. The processes do not always occur in one simple sequence. 2. Nitrogen formulas to memorize * = nitrogen gas * = ammonia * = ammonium * = nitrite * = nitrate Pay special attention to the difference between ammonia, ammonium, nitrite and nitrate. 3. The phosphorus cycle Phosphorus is an essential nutrient that organisms need to survive. How it moves through the environment * Weathering breaks down rocks and releases phosphorus into soil and water. * Plants absorb phosphorus through their roots. * Animals obtain phosphorus by eating plants or other animals. * Waste and dead organisms are broken down by decomposers. * Phosphorus returns to soil and water, where it can be used again. Why phosphorus matters * It is needed to build DNA and RNA. * It is part of ATP, which cells use to transfer energy. * It is a component of cell membranes. * It helps plants grow and develop strong roots. * It is often a limiting nutrient in soils and aquatic ecosystems. Important difference: Unlike the nitrogen cycle, the phosphorus cycle does not have a major atmospheric gas phase. 4. Eutrophication Eutrophication happens when too many nutrients enter a body of water. This can occur when fertilizers or sewage enter lakes and rivers. Know the steps: * Excess nutrients enter the water. * Algae grow rapidly, creating an algal bloom. * Algae die and decomposers break down the dead material. * Decomposers use dissolved oxygen during decomposition. * Oxygen levels decrease, which can harm or kill fish and other aquatic organisms. Remember that the problem is not simply that algae grow. The decomposition of dead algae can use up the oxygen aquatic organisms need. 5. The water cycle The water cycle describes how water moves between Earth’s surface and the atmosphere. The four main processes * Evaporation: Liquid water absorbs heat and becomes water vapor. * Condensation: Water vapor cools and forms liquid droplets, helping create clouds. * Precipitation: Water falls from clouds as rain, snow, sleet or hail. * Transpiration: Plants release water vapor through their leaves. Water also collects in rivers, lakes and oceans, while some infiltrates the soil and becomes groundwater. Make sure you can explain the difference between evaporation and condensation: * Evaporation: liquid to gas. * Condensation: gas to liquid. 6. Photosynthesis, respiration and chemosynthesis Photosynthesis * Uses light energy to produce sugars. * Takes in carbon dioxide and water. * Releases oxygen in typical plant photosynthesis. * Stores energy in chemical bonds. Cellular respiration * Breaks down glucose and other molecules to release usable energy. * Happens in plants, animals and many other organisms. * Most of the energy organisms obtain is eventually released as heat. Chemosynthesis * Uses energy from chemical reactions instead of sunlight. * Allows certain organisms, such as some bacteria, to produce organic molecules. How they differ Photosynthesis uses light energy, cellular respiration releases usable energy from molecules, and chemosynthesis uses chemical energy to make organic molecules. 7. Carbon and energy in ecosystems Your notes include these important ideas about carbon and energy. * Carbon enters the atmosphere through processes such as respiration, decomposition and the burning of fossil fuels. * Vehicles release carbon dioxide when they burn gasoline or other fossil fuels. * Plants remove carbon dioxide from the atmosphere during photosynthesis. * Energy moves through food chains and food webs. * Most energy obtained by organisms is eventually released as heat. * Unlike nutrients, energy does not continuously recycle through an ecosystem; it flows through the ecosystem. 8. Food chains and food webs A food chain shows one pathway of energy transfer, while a food web shows many connected feeding relationships. For example: Grass — Producer Grasshopper — Primary consumer Frog — Secondary consumer Snake — Tertiary consumer Arrows point from the organism being eaten to the organism receiving the energy. Know these facts * Producers make their own food. * Primary consumers eat producers. * Secondary consumers eat primary consumers. * Tertiary consumers eat secondary consumers. * Food webs connect multiple food chains. * Less energy is available at higher trophic levels because energy is used for life processes and much is released as heat. 9. Autotrophs versus heterotrophs Autotrophs: * Make their own organic food. * Use light energy or chemical energy. * Include plants, algae and certain bacteria. Heterotrophs: * Obtain organic food from other organisms or organic matter. * Include animals and fungi. * Depend directly or indirectly on producers for energy. Remember that not every heterotroph eats another living organism. Decomposers, for example, absorb nutrients from dead organic matter. 10. Detritivores, decomposers and scavengers These three types of organisms are easy to confuse. Scavengers eat dead animals. Examples include vultures and some crabs. Detritivores ingest dead organic matter and waste. Examples include earthworms, woodlice and some aquatic organisms. Decomposers break down organic matter externally by releasing enzymes, then absorb the nutrients. Examples include fungi and bacteria. Where they live * Terrestrial means land-based. Examples of detritivores include earthworms and woodlice. * Aquatic means water-based. Some crabs and other aquatic organisms feed on detritus. Why they matter They help recycle nutrients back into the environment, allowing those nutrients to be used by other organisms. 11. Ecosystem organization Know the difference between these four terms: * Population: One species living in a particular area. * Community: Multiple populations living in an area. * Ecosystem: The community and its nonliving environment. * Biosphere: All parts of Earth where life exists. A community consists of different populations. An ecosystem includes both living and nonliving components. 12. Phosphorus transfer through food webs * Plants absorb phosphorus from soil or water. * Heterotrophs obtain phosphorus by eating plants or other animals. * Phosphorus moves between organisms through feeding. * Decomposition and waste return phosphorus to the environment. Phosphorus is important for plant growth and for building molecules that all living organisms need. Part 3: What to memorize before the test If you’re short on time, make sure you can answer these questions without looking at your notes. Final review checklist 0 of 13 Define ecology, biosphere, population, community and biomass. Explain the differences between autotrophs and heterotrophs. Distinguish herbivores, carnivores, omnivores, scavengers, detritivores and decomposers. Explain the nitrogen cycle processes and put them in context. Memorize N₂, NH₃, NH₄⁺, NO₂⁻ and NO₃⁻. Explain the phosphorus cycle and why phosphorus matters. Explain the steps of eutrophication and why oxygen decreases. Define evaporation, condensation, precipitation and transpiration. Compare photosynthesis, cellular respiration and chemosynthesis. Explain the difference between food chains and food webs. Explain why energy decreases at higher trophic levels. Explain how decomposers recycle nutrients. Describe how carbon enters and leaves the atmosphere. My advice for tonight: Study the vocabulary first, draw the nitrogen cycle from memory, and then explain eutrophication and the water cycle out loud. Finish by testing yourself on the checklist. If you can explain each item without looking, you’re in a good position for your test.

Photosynthesis

The process by which green plants and some other organisms use sunlight to synthesize foods with the help of chlorophyll.

Cellular Respiration

The metabolic process in which cells convert glucose and oxygen into energy, carbon dioxide, and water.

Homeostasis

The ability of an organism or a cell to maintain a stable internal environment despite changes in external conditions.

Mitosis

A type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus.

Meiosis

A specialized form of cell division that occurs in sexually reproducing organisms, resulting in four haploid cells, each with half the chromosome number of the parent.

DNA (Deoxyribonucleic Acid)

A molecule that carries the genetic instructions used in the growth, development, functioning, and reproduction of all known living organisms.

Chromosome

A thread-like structure composed of DNA and proteins that contains genetic information.

Natural Selection

The process where organisms better adapted to their environment tend to survive and produce more offspring.

Ecosystem

A biological community of interacting organisms and their physical environment.

Biodiversity

The variety of life in the world or in a particular habitat or ecosystem.