Section 1: Discovering Cells What are cells? How did the invention of the microscope contribute to knowledge about living things? What is the cell theory? How are the cells of multicellular organisms organized?

What Are Cells? All living things are made up of cells. Cells have many similarities between different species. Example: Mitochondria can be found in the cells of humans, dogs, spiders, trees, etc. Cells are the basic unit of structure and function in all living things.

Cell Structure Cells form parts of your organs. It gives your body its’ shape, size, strength.

Cell Function Cells perform all of an organism’s tasks and functions. obtain oxygen and food get rid of wastes allow you to grow and repair.

Cell Size Most cells are so small they are microscopic. Microscopic: can only be seen by the human eye with the help of a microscope. Approximately 100,000 skin cells fit in a square centimeter. Approximately 250 million red blood cells are found in a drop of blood.

Development of the Cell Theory The cell theory states the following: All living things are composed of cells. Cells are the basic units of structure and function in living things. All cells are produced from other cells.

Unicellular vs. Multicellular Unicellular, or single- celled, organisms include bacteria, the most numerous organisms on Earth. Multicellular organisms, like this dog, are composed of many cells. Unicellular Multicellular

Advantages of Being Multicellular In multicellular organisms, cells are often organized into tissues, organs, and organ systems. This allows our cells to perform specialized and unique tasks.

End of Section: Discovering Cells

Section 2: Looking Inside Cells What role do the cell wall and cell membrane play in the cell? What is the role of the nucleus in the cell? What organelles are found in the cytoplasm and what are their functions? How do cells differ?

Organelles (and other Cell Structures) Organelle: a tiny structure that has a specific function inside the cell, floating in the cytoplasm Found in Both Plant and Animal Cells Found Only in Plant Cells Animal Cells nucleus cell wall lysosomes cell membrane chloroplasts vacuoles (several small) cytoplasm vacuole (one large) endoplasmic reticulum ribosomes Golgi body mitochondria

Plant and Animal Cells

Cell Membrane NOT an organelle What is it? The “skin” of the cell, helping form a boundary that separates the inside of the cell from the outside. Why does the cell need it? To control what substances are allowed to enter or leave the cell. Where can it be found? In both plant and animal cells. NOT an organelle

Cell Wall NOT an organelle What is it? A rigid layer of cellulose that surrounds the cell membrane. Although it is very strong, it still allows materials like water and oxygen to pass through. Why does the cell need it? It helps to protect and support the cell. Where can it be found? In plant cells only. NOT an organelle

Nucleus What is it? The “control center” of the cell. It contains thin strands of DNA called chromatin that direct all of the cell’s activities. Why does the cell need it? The cell would not know how to function without the nucleus. Where can it be found? In both plant and animal cells.

Cytoplasm NOT an organelle What is it? The area between the cell membrane and the nucleus. Contains a gel-like fluid that is constantly moving inside the cell. Why does the cell need it? Allows organelles to move around the inside of the cell. Also, the fluid helps regulate the cell’s temperature and pH level. Where can it be found? In plant and animal cells. NOT an organelle

Mitochondria What is it? The “powerhouses” of the cell because they convert food molecules to energy the cell can use to carry out its functions (also called “cellular respiration”). Why does the cell need it? Without it, cells wouldn’t have the energy to function. Where can it be found? In both plant and animal cells.

Endoplasmic Reticulum (E.R.) Where can it be found? In plant and animal cells. What is it? Moves materials throughout the cell. When covered with ribosomes, it is called “Rough E.R.”. Without ribosomes, it is called “Smooth E.R.”. Why does the cell need it? Ribosomes help make proteins, hormones, and other materials. The E.R. helps move these materials to specific places after they have been made.

Medical School Version Ribosomes What is it? Tiny “protein factories” that are found floating in the cytoplasm or attached to the E.R. Why does the cell need it? Ribosomes read the message encoded in the cell’s DNA and translate these codes into proteins, hormones, and other structures. Without ribosomes, the DNA would be useless. Where can it be found? In both plant and animal cells. Middle School Version Medical School Version

Golgi bodies What is it? The “post office” of the cell. The Golgi bodies receive proteins and other newly formed materials from the E.R., package them, and distribute them to other parts of the cell. Why does the cell need it? Without it, many proteins would be incomplete or lost. Where can it be found? In both plant and animal cells.

Chloroplast What is it? Green organelles that capture sunlight and convert it into sugar, which is used as a food source. Why does the cell need it? Without it, plants would not have a food source. Also, animals depend on plants for food, either because they eat plants, or they eat other animals (which eat plants). Where can it be found? In plant cells only.

Vacuole Plant Cell Animal Cell What is it? Storage area of the cell. Mostly stores water, but sometimes stores food and waste. Why does the cell need it? Allows the cell to store materials. In plants, the vacuole gives the cell internal pressure (like air inflating a balloon). Where can it be found? In animal cells, there are several tiny vacuoles. In plant cells, there is only 1 large vacuole (called “the central vacuole”). Animal Cell

Lysosomes What is it? Where can it be found? The “clean-up crew” of the cell. Contains chemicals called enzymes that break down large food particles, trash, and even old organelles. Why does the cell need it? Without it, the cell would become cluttered with food particles that are too big for the mitochondria, toxic trash, and dead organelles. Where can it be found? In animal cells only.

End of Section: Looking Inside Cells

Section 3: Chemical Compounds in Cells What are elements and compounds? How is water important to the function of cells? What are the functions of carbohydrates, lipids, proteins, and nucleic acids?

Elements An element is any substance that cannot be broken down into simpler substances. Examples include carbon (C), nitrogen (N), hydrogen (H), and oxygen (O).

Compounds Carbon dioxide, which is found in gas bubbles, is a chemical compound made up of 1 carbon and 2 oxygen atoms. So is water (2 hydrogen and 1 oxygen).

Organic and Inorganic Molecules Inorganic Molecules: do not contain carbon (C); water (H20) and “breathable” oxygen (O2) are important inorganic molecules needed by living organisms. Organic Molecules: contain carbon; includes carbohydrates, lipids, proteins, and nucleic acids.

Carbohydrates Provides quick energy for the cell. Plants make “carbs” in the form of sugars and starches. The cellulose in a plant cell wall is a type of “carb”.

Lipids Provides slow-burning energy for the cell. Cells can store lipids to save energy for future use. Makes up most of the cell membrane. Found in fats, oils, and waxes.

Proteins Provides structures (like muscles) and chemicals (like hormones and enzymes) for your body. Found in meat, eggs, fish, nuts, and beans. Proteins are actually made up of tiny molecules called amino acids.

Nucleic Acids Contains the instructions that cells need to do their job and stay “alive”. 2 types of nucleic acids: DNA (instructions that can be passed on from parent to child) RNA (help make proteins).

End of Section: Chemical Compounds in Cells

Section 4: The Cell in Its Environment How do most small molecules cross the cell membrane? Why is osmosis important to cells? What is the difference between passive and active transport?

A Selective Barrier The cell membrane protects the contents of the cell and helps control the materials that enter and leave.

Diffusion In diffusion, molecules move from an area of HIGHER concentration to an area of LOWER concentration.

Osmosis In osmosis, water diffuses through the cell membrane using the power of diffusion.

Osmosis The picture in the middle shows blood with equal amounts of salt inside and outside the cell. As a result, water moves evenly inside and outside.

Osmosis The picture on the left shows blood surrounded by excessive salt. Water is attracted to this, so it leaves the cell and the cell shrivels like a raisin.

Osmosis The picture on the right shows a cell that is filled with salt. Water is attracted to this, so the cell swells up with water.

Passive and Active Transport Passive and active transport are two methods that allow materials (like food and waste) to pass through the cell membrane. Active transport requires the cell to use its own energy, while passive transport does not.

End of Section: The Cell in Its Environment