Living Things

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How a Human Kidney Works

In humans, the kidneys are the organs that produce urine. There are two kidneys, one on each side of your back, just below the ribs. Like most organs in the body, the function of the kidneys is closely [more…]

What's the Basic Structure of Nerves?

The nervous system sends messages from nerve endings to the brain and from the brain to cells, tissues, and organs. Cells of the nervous system sometimes secrete chemical messengers instead of neurotransmitters [more…]

What Are Stem Cells?

You’ve probably heard about stem cells in the news and may wonder exactly what that scientific term means. Stem cells are the body’s master cells. Stem cells can renew themselves [more…]

Explore Current Stem Cell Treatments

Scientists have been working with human adult stem cells — the stem cells found in specific tissues — for more than 40 years, compared to only a dozen years for human embryonic stem cells. As a result, [more…]

Stem Cell Research for Patient Treatment Plans

Stem cell scientists use stem cells to understand normal cell physiology, cell function, and development, as well as the mechanisms and progression of various diseases. Scientists hope to use this valuable [more…]

Stem Cells For Dummies Cheat Sheet

Scientists use various types of stem cells in the lab to gain a better understanding of how normal human development works and to look for new methods of treating a wide range of devastating human ailments [more…]

What Defines an Ecosystem?

The basic unit of study in environmental science is the ecosystem. An ecosystem consists of a biological community and its physical environment. Here are the most important things you need to know about [more…]

How to Characterize a Population of Living Things

Scientists who study living organisms examine them from different perspectives of complexity. The simplest level is the individual. Each individual is a member of a population. Each [more…]

Plant and Animal Facts to Remember for the AP Biology Exam

The following list contains some of the more challenging info on plants and animals that you might encounter on the AP Biology Exam. Study this list as long as you need to — if you remember this information [more…]

How Plants Pull and Transport Water

Several processes work together to transport water from where a plant absorbs it (the roots) upward through the rest of its body. To understand how these processes work, you first need to know one key [more…]

How Plants Send Sugars from Sources to Sinks

Plants use a special tissue called phloem to transports sap — a sticky solution that contains sugars, water, minerals, amino acids, and plant hormones. Sap moves through phloem via [more…]

How Plants Send Signals with Plant Hormones

Plant cells communicate with one another via messengers called hormones, chemical signals produced by one type of cell that travel to target cells and cause changes in their growth or development. Plant [more…]

The Parts and Types of Plants

Like animals, plants are made of cells and tissues, and those tissues form organs, such as leaves and flowers, that are specialized for different functions. Two basic organ systems exist in plants: [more…]

Types of Tissue in Plants

Plant organs are made of plant tissues, which are made of plant cells. All plants have tissues, but not all plants possess all three of the following types of tissues: [more…]

Plant Reproduction

Plants are very successful organisms, growing in almost every environment on Earth. Part of their success is due to the fact that they can reproduce both asexually and sexually. [more…]

Identify the Parts of the Male Reproductive System

Knowledge of the organ systems involved in human sexual reproduction helps you learn about the reproduction process. The following figure illustrates the male reproductive system: [more…]

Follow the Female Ovarian and Menstrual Cycles

Oogenesis (the egg-producing process), which includes the ovarian and menstrual cycles, begins very early in the life of a human female, when she’s still a developing fetus! In fact, a human female is [more…]

How Plants Take Elements from the Soil

Plants get all the carbon, hydrogen, and oxygen they need from carbon dioxide and water, which they use to build carbohydrates during photosynthesis. To build other kinds of molecules they also need elements [more…]


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