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Cells and Cell Cycles to Study for the AP Biology Exam

As you're studying for the AP Biology exam, keep these facts about cells and cell cycles close at hand and review them often. You never know, you may end up memorizing them all, which will help you ace [more…]

DNA Techology: Copying a Gene with PCR

The polymerase chain reaction (PCR) is a process that can turn a single copy of a gene into more than a billion copies in just a few hours. It gives medical researchers the ability to make many copies [more…]

Biology Basics: The Basics of Muscles

Muscle tissues are extremely important to your body — and not just because they help you look good at the pool. Muscles do many things to keep you alive and going strong: [more…]

Ten Tips for Getting an A in Biology

Science classes, like biology, may be among the most challenging classes you'll ever take. Getting an A in biology means looking at some of the major issues you'll face and having tips for dealing with [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…]

Human Biology: Fertilization through Birth

Fertilization, the joining of sperm and egg, typically occurs in the fallopian tube, after sperm have made the long swim up through the vagina, past the cervix, and through the uterus. Fertilization brings [more…]

Neurons and Nerves

Neurons are cells that form the core of nervous systems because they have the ability to receive and transmit signals. Neurons have a unique elongated shape and consist of three main parts: [more…]

Microbes and Pathogens

Microbes are things like bacteria and viruses that are too small to see with the naked eye. They exist on every surface and in every environment on Earth. They’re in the air, in the water, in the soil [more…]

The Parts of the Female Reproductive System

The female reproductive system produces eggs and supports the developing fetus. The reproductive process begins when a sperm cell from a male joins with an egg cell from a female in a process that scientists [more…]

Innate Immunity: Built-In Defenses

You’re usually unaware of all the microbes roaming the world because you can’t see them and because your innate immunity keeps most of them from bothering you. [more…]

The Human Digestive System

Humans have a complete digestive tract: Food enters at one end and wastes exit from the opposite end. Digestion begins in the mouth and continues as food moves through your system: [more…]

The Urinary System

Your body releases wastes that are filtered from your blood and tissue fluids as part of your urine. In particular, urine helps you flush out nitrogenous wastes [more…]

The Inner Workings of the Human Kidney

Like most organs in the human body, the function of a kidney is closely tied to its structure. The outer covering on each kidney, called the capsule, is made of stretchy collagen fibers that help anchor [more…]

Animal Respiration

Respiration is the exchange of life-sustaining gases, such as oxygen, between an animal and its environment. Gas exchange occurs by diffusion, moving necessary gases like oxygen into animals and taking [more…]

Animal Circulatory Systems

Every animal alive possesses a circulatory system that’s in charge of bringing nutrients to cells and removing wastes so they don’t cause disease. While they move fluids around the body, circulatory systems [more…]

Navigate the Human Heart and Circulatory System

The heart and circulatory system of a human, as well as some other mammals, are complex. These large animals need to have a higher blood pressure to push the blood throughout their entire bodies. This [more…]

The Heart and the Cardiac Cycle

Your heart is an impressive little organ. Even though it’s only as big as a clenched adult fist, it pumps 5 liters of blood throughout your body 70 times a minute. Your heart never stops working from the [more…]

Animal Movement with Friction and Gravity

Every type of locomotion, movement from one place to another, requires animals to use energy to overcome the forces of friction and gravity that would otherwise hold them to Earth. [more…]


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