Biology

• Structural unit: Cells provide the basic building blocks for all living things. Just like bricks are the building blocks of a house, cells are the building blocks of tissues, organs, and organ systems.
• Functional unit: Cells carry out all the necessary processes for life. They can take in nutrients, convert these nutrients into energy, and perform specialized functions.

Cells are highly organized and contain a variety of structures called organelles, which perform specific functions. All cells are surrounded by a membrane, which regulates the passage of substances in and out of the cell.

There are two main types of cells:

• Prokaryotic cells: These cells do not have a nucleus or other membrane-bound organelles. Bacteria and Archaea are examples of organisms with prokaryotic cells.
• Eukaryotic cells: These cells have a nucleus and other membrane-bound organelles. Plants, animals, fungi, and protists are examples of organisms with eukaryotic cells.

For more information, you can refer to these resources:

• Cells: The Fundamental Units of Life - NCBI Bookshelf
• Cell Biology - Nature Scitable

• Fungi: A kingdom of organisms that includes mushrooms, toadstools, yeasts, molds, and mildews. Fungi are characterized by having cell walls made of chitin and obtaining nutrients by absorption.
• Mushrooms: The fleshy, spore-bearing fruiting body of a fungus, typically produced above ground or on its substrate.
• Toadstools: Generally refers to poisonous or inedible mushrooms. However, there is no scientific distinction between mushrooms and toadstools; the term "toadstool" is often used to describe fungi that are considered undesirable for consumption.

For more information, you can refer to these resources:

• Britannica - Fungus
• Diffen - Fungus vs. Plant

• Nitrogen Fixation: Atmospheric nitrogen (N₂), which is unusable by most organisms, is converted into ammonia (NH₃) or ammonium (NH₄⁺). This process is primarily carried out by nitrogen-fixing bacteria in the soil and aquatic environments. Some nitrogen fixation also occurs through lightning.
• Nitrification: Ammonia or ammonium is converted into nitrite (NO₂^-) and then into nitrate (NO₃^-) by nitrifying bacteria. Nitrate is a form of nitrogen that plants can readily absorb.
• Assimilation: Plants absorb nitrate (NO₃^-) or ammonium (NH₄⁺) from the soil through their roots. This nitrogen is then incorporated into plant tissues, such as amino acids and nucleic acids. Animals obtain nitrogen by consuming plants or other animals.
• Ammonification: When plants and animals die, or when animals excrete waste, the organic nitrogen in their tissues is converted back into ammonia (NH₃) or ammonium (NH₄⁺) by decomposers (bacteria and fungi). This process returns nitrogen to the soil.
• Denitrification: Nitrate (NO₃^-) is converted back into atmospheric nitrogen (N₂) by denitrifying bacteria. This process occurs in anaerobic conditions (oxygen-poor environments) and completes the cycle by returning nitrogen to the atmosphere.

Human activities, such as the use of fertilizers and the burning of fossil fuels, can significantly alter the nitrogen cycle, leading to environmental problems like eutrophication and air pollution.

Sources:

• The Nitrogen Cycle: Processes, Players, and Human Impact - Nature
• The nitrogen cycle - Science Learning Hub

• Light Intensity: As light intensity increases, the rate of photosynthesis generally increases until it reaches a saturation point. Beyond this point, further increases in light intensity will not increase the rate of photosynthesis.
• Carbon Dioxide Concentration: Similar to light intensity, as carbon dioxide concentration increases, the rate of photosynthesis generally increases until it reaches a saturation point. Once saturated, further increases in carbon dioxide concentration will not increase the rate.

Heterotrophs are organisms that cannot produce their own food and must obtain nutrition from other sources. Herbivores are heterotrophs that specifically consume plants.