There are two types of organisms: prokaryotes and eukaryotes

Prokaryotes are made up of a single prokaryotic cell.

Eukaryotes are made up of one or more eukaryotic cells.

Prokaryotic cells do not have a nucleus or membrane-bound, while eukaryotic cells do.

A cell’s structure is the arrangement of its parts.

A cell’s function us the activity the parts carry out.

All eukaryotic cells have a nucleus, membrane-bound organelles and parts that protect and support the cell.

The cell membrane acts as a barrier between the inside of a cell and the cell’s environment. It protects the cell and regulates what enters and leaves the cell.

The cytoplasm is the region between the cell membrane and the nucleus that includes fluid and all of the organelles.

The cytoskeleton is a network of protein filaments that gives shape and support to cells and is also involved in cell division and movement.

The cytoskeleton may help parts within the cell to move, or it may form structures that help the whole organism to move.

Deoxyribonucleic acid (DNA) is stored in the nucleus.

DNA is genetic material that contains information needed for cell processes.

The instructions for how to make proteins are stored in the DNA and sent out of the nucleus through pores in the nuclear membrane.

The nuclear membrane is a double layer where each layer is similar in structure to the cell membrane.

Cells get energy by breaking down food using a process called cellular respiration.

Cellular respiration occurs in an organelle called the mitochondria.

In cellular respiration, cells use oxygen to release energy stored in food. Cells break down the sugar glucose to release the energy stored in the sugar. The mitochondria then transfer the energy to a molecule called adenosine triphosphate or ATP.

Cells use ATP to carry out cell processes.

Mitochondria have their own DNA and they have two membranes. The outer membrane is smooth, the inner membrane has many folds. Folds increase the surface area inside the mitochondria where cellular respiration occurs.

Proteins control most chemical reactions of cells and provide structural support for cells and tissues.

Some proteins are even exported out of the cell for other functions throughout the body.

Making, packaging and transporting proteins requires many organelles.

The ribosome is the organelle that makes proteins by putting together chains of amino acids using instructions encoded in the cell’s DNA.

An amino acid is any of the about 20 different carbon-based molecules that are used to make proteins.

Almost all cells have ribosomes, which are the smallest organelle.

Ribosomes are not enclosed in a membrane. In prokaryotes, the ribosomes are suspended freely in the cytoplasm.

In eukaryotes, some ribosomes are free, others are attached to the endoplasmic reticulum.

The endoplasmic reticulum is a system of membranes near the nucleus.

The ER assists in the production, processing and transport of proteins as well as the production of lipids.

Rough ER has ribosomes attached to its membrane, while smooth ER does not.

Ribosomes on the rough ER make many of the cell’s proteins.

Some of the proteins move through the ER to different places in the cell.

The smooth ER makes lipids and breaks down toxic materials that could damage the cell.

The membrane-bound organelle that packages and distributes materials such as proteins is called the Golgi Complex.

The Golgi complex is a system of flattened membrane sacs.

Lipids and proteins from the ER are delivered to the Golgi complex where they may be modified to do different jobs. The final products are enclosed in a piece of the Golgi complex’s membrane. This membrane pinches off to form a small bubble, or vesicle. This vesicle transports its contents to other parts of the cell or out of the cell.

The cell wall is a rigid structure surrounding the cell membrane in plants.

Cell walls provide support and protection to the cell.

Plants don’t have a skeleton like many animals do, so they get their shape from the cell wall.

The vacuole is a fluid-filled vesicle found in the cells of most animals, plants and fungi.

A vacuole may contain enzymes, nutrients, water, or wastes.

Plant cells also have a large central vacuole that stores water.

Central vacuoles full of water help support the cell. Plants may wilt when the central vacuole loses water.

Plants and some protists can make their own food using photosynthesis.

Chloroplasts are the organelles where photosynthesis occurs.

Photosynthesis is the process by which plants use sunlight, carbon dioxide, and water to make sugar and oxygen.

Chloroplasts are green because they contain a green pigment called chlorophyll.

Chlorophyll absorbs the energy in sunlight. This energy is used to make sugar, which is then used by the mitochondria to make ATP.

Chloroplasts have two outer membranes.

Lysosomes contain digestive enzymes, which break down worn-out or damaged organelles, waste materials, and foreign invaders in the cell. Some of these materials are collected in the vacuoles.

A lysosome attaches to the vacuole and releases the digestive enzymes inside. Some of these materials are recycled and reused in the cell.

An organism is a living thing that can carry out life processes by itself.

Unicellular organisms do not have levels of cellular organization.

Multicellular organisms are grouped into different levels of organization, including tissues, organs, and organ systems.

The cells that make up a multicellular organism are specialized to perform specific functions.

Many multicellular organisms reproduce through sexual reproduction, during which a male sex cell fertilizes a female sex cell. The single cell that results from fertilization divides repeatedly. This cell division forms the basic tissues of an embryo, which further develops into all the specialized tissues and organs within a multicellular organism.

A tissue is a group of similar cells that perform a specific function.

There are four types of animal tissue: nervous, epithelial, connective and muscle.

Nervous tissue acts as a messaging system within the body.

Epithelial tissue is protective and forms boundaries, such as skin.

Connective tissue holds part of the body together and provides support and nutrients to organs, it includes bones and blood.

Muscle tissue helps produce movement.

There are three types of plant tissue: transport, protective and ground.

Transport tissue moves water and nutrients through the plant.

Protective tissue protects the outside of the plant.

Ground tissue provides internal support and storage and absorbs light energy to make food in photosynthesis.

A structure made up of a collection of tissues that carries out a specialized function is called an organ.

Nervous tissue sends messages to the stomach’s muscle tissue to tell the muscle tissues to contract. When the muscle issue contracts, food and stomach acids are mixed, and the food breaks down.

A leaf is an organ that contains protective tissue to reduce water loss, ground tissue for photosynthesis, and transport tissue to move nutrients from leaves to stems.

Stems and roots are organs that function to transport and store water and nutrients in the plant.

An organ system is a group of organs that work together to perform body functions.

Organs in the digestive system include the stomach, esophagus and the small and large intestines.

The lungs are made up of millions of tiny air sacs called alveoli.

The large number of alveoli increases the surface area of the lungs to let enough oxygen and carbon dioxide move between the lungs and blood.

Xylem and phloem are tissues that make up the vascular system.

Xylem transports water from roots to cells.

Phloem transports nutrients made in leaf cells to all parts of the plant.

Complex organisms are made up of many systems .

These systems work together to perform actions needed by cells to work together properly.

A unicellular organism must perform all functions necessary for life, such as getting nutrients, exchanging gases, and removing wastes.

The functions must be performed by a single cell, because there is no opportunity for cell specialization.

Multicellular organisms face different challenges.

Multicellular organisms have different cell types that can work together in groups to perform specific functions.

Groups of tissues that work together for organs, and groups of organs that work together form organ systems.

Systems work with other systems.

In most animals, the digestive, respiratory, and excretory systems interact with the circulatory system to maintain healthy cells.

A circulatory system delivers nutrients to body cells and carries away wastes.

The digestive system in most animals breaks down food mechanically and chemically.

In most animals, the digestive system works with a circulatory system.

In the small intestine, nutrients are absorbed through thousands of finger-like projections in the wall of the small intestine, called villi, and then into the blood vessels of the circulatory system.

Once in the blood, the nutrients are delivered to cells throughout the body.

In animals, taking in oxygen is a function of the respiratory system.

Depending on the animal, oxygen enters a body through skin, gills, spiracles, or lungs.

There, it comes in contact with the circulatory system.

Oxygen enters the bloodstream and is carried to the cells of the body.

Once in the cells, oxygen is used to release energy from nutrients from digestion.

Skin, lungs , the digestive system and the kidneys all have processes for removing waste products from the body.

Sweat evaporates from the skin.

Solid wastes and some water move out as part of the digestive system.

In humans, the largest amount of excess water and waste products from cells is carried by the blood to the kidneys.

There, wastes are filtered out of the blood through a complex series of tubules in the kidneys and leave the body out as urine.