Introduction to Biology (02:35)
Cells are the main components of living things; they work, grow, eat, and recycle. To understand cells and biology, students have to learn some basic chemistry; see vocabulary terms.
Elements and Atoms (02:45)
An element is a substance that can be broken down into a single atom and still be identified. An atom is made of protons, neutrons, and electrons; the number of protons determines the element. Protons have a positive charge and are located in a nucleus; negatively charged electrons orbit.
Atoms in a covalent bond share electrons. Each electron shell can hold a certain number of electrons; the second shell has to have eight electrons. Two or more atoms bonded together makes a molecule.
Importance of Water (02:14)
Cells are made mostly of water. Water consists of an oxygen atom bonded to two hydrogen atoms whose electrons are pulled closer to the oxygen. This makes it a polar molecule, attracting it to other water molecules; they bind together with hydrogen bonds.
Macromolecules are important for cell function. Carbohydrates provide energy and structure, proteins are chains of amino acids that do work in cells, nucleic acids store information, and lipids are hydrocarbons that store energy and create structure.
The Cell (03:53)
Scientists discovered cells and observed living cells in the 1600s, identifying them as the smallest unit of life. All living things have cells, cells divide to create new cells, and no two cells are identical.
Types of Cells and Nucleus (03:11)
Eukaryotic cells have a nucleus, while prokaryotic cells do not; animals, plants, and fungus have eukaryotic cells. The nucleus stores the genetic information in coiled DNA called chromosomes. DNA makes proteins through a transcription and translation process.
Inside the Cell (02:17)
Organelles are the cell organs. Rough endoplasmic reticulum makes proteins, while smooth E.R. makes lipids and detoxifies. The Golgi apparatus stores and moves proteins, lysosomes process waste, and the mitochondria create energy. The cytoskeleton gives structure while the plasma membrane protects the cell.
Plant Cells (01:06)
Plant cells have chloroplasts and cell walls. Chloroplasts contain chlorophyll which makes plants green. The cell wall provides a rigid structure.
Transport Across Membranes (05:38)
Cells often need materials from outside the cell to function. The cell membrane contains two layers of phosphorous and lipid molecules which regulate transport of substances. Diffusion is when molecules move from a highly concentrated to a less-concentrated solution. Active transport involves a transport protein which uses energy to bring something into the cell.
Plants use light and carbon dioxide to create chemical energy and oxygen in a mutually beneficial cycle with animals. The plant captures light to create ATP and NADPH, which are used alongside CO2 to create glucose, ATP, NADP, and RuBP.
Cellular Respiration (03:02)
Cells break down food and convert it to energy in the form of ATP. Aerobic respiration converts glucose and oxygen to carbon dioxide and ATP. Anaerobic respiration does not require oxygen, and uses fermentation to make ATP.
Credits: Molecules and Cells (00:16)
Credits: Molecules and Cells
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