Science Test Review [Introduction to Cells] (3 & 4)

Vocabulary

1. element - a pure substance that cannot be broken down into other substances by chemical or physical means
2. mixture - non chemical combination of different materials
3. compound - a substance made out of two or more elements chemically combined in a specific ratio, or proportion
4. carbohydrate - an energy-rich organic compound, such as a sugar or a starch, that is made of the elements carbon, hydrogen and, oxygen
5. lipid - an energy-rich compound, such as a fat, oil, or wax, that is made of carbon, hydrogen, and oxygen
6. protein - large organic molecule made of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur
7. enzyme - a type of protein that speeds up a chemical reaction in a living thing
8. nucleic acid - a very large organic molecule made of carbon, oxygen, hydrogen, nitrogen, and phosphorus, that contains the instructions cells need to carry out all the functions of life
9. DNA - deoxyribonucleic acid, the genetic material that carries information about an organism and is passed from parent to offspring
10. double helix - the shape of a DNA molecule; composed from many small molecules connected together
11. selectively permeable - a property of cell membranes that allow some substances to pass across it, while other cannot
12. passive transport - the movement of dissolved materials across a cell membrane without using cellular energy
13. diffusion - the process by which molecules move from an area of higher concentration to an area of lower concentration
14. osmosis - the diffusion of water molecules across a selectively permeable membrane
15. active transport - the movement of materials across a cell membrane using cellular energy
16. endocytosis - the process by which the cell membrane takes particles into the cell by changing shape and engulfing the particles
17. exocytosis - the process by which the vacuole surrounding particles fuses with the cell membrane, forcing the contents out of the cell

Elements

• An element is any substance that cannot be broken down into simpler substances
• Elements are pure substances found in nature, some elements are man-made
• The smallest unit of an element particle is called an atom
• A single element is made of a single kind of atoms
• Some examples of elements that can be found in your body are;
• carbon
• hydrogen
• oxygen
• nitrogen

Mixtures

• Mixtures are non chemical combinations of different materials
• Some examples of common mixtures include;
• salad dressing
• cement
• salad
• pizza

Compounds

• Compounds form when two or more elements combine chemically
• Most elements in our body are found in the form of compounds
• The smallest unit of most compounds is called a molecule; a molecule of carbon dioxide consists of one carbon atom and two oxygen atoms
• Some examples of compounds are;
• Water (H2O = two hydrogen atoms and an oxygen atom)
• Carbon Dioxide (CO2 = a carbon atom and two oxygen atoms)
• Carbon Monoxide (CO = a carbon atom and an oxygen atom)
• Many compounds in living things contain carbon
• Most compounds that have carbon are called organic compounds, these include;
• nylon
• polyester
• Some important groups of organic compounds that living things need are carbohydrates. lipids, proteins and nucleic acids
• Compounds that don't have carbon are called inorganic compounds; these include;
• water
• table salt
• Water is a necessary inorganic compound; it plays many important roles in cells

If you don't understand, watch the video

  Carbohydrates

• Carbohydrates are energy rich compounds made of carbon, hydrogen and oxygen
• Carbohydrates are important components of some cell parts (cellulose)
• When sugar molecules combine they form larger molecules called starches, or complex carbohydrates
• When you eat starches your body breaks them down into glucose, a sugar your cells can use to get energy
• Some foods where we can find carbohydrates are;
• cereals
• bread
• potatoes
• rice

  Lipids

• Lipids are compounds that are mostly made carbon and hydrogen and some oxygen
• Cell membranes consist mostly of lipids
• Lipids are classified into two groups; fats and oils, oils come from plants while fats come from animals
• Some examples of lipids are;
• fats
• oils
• waxes
• Fats and oils contain more energy than carbohydrates; cells store energy from fats and oils for later use

  Proteins

• Proteins, or polypeptide chains, are large organic molecules composed of carbon, hydrogen, oxygen, nitrogen and sulfur (sometimes)
• Proteins are made from the combinations of amino-acids
• There are twenty amino acids but only eight are essential in the formation of proteins
• Proteins are made through the following process:
• Coded message given to the mRNA
• Coded message taken to the ribosomes
• Coded message is decoded by the tRNA
• rRNA joins the amino acids and makes the protein

If you don't understand, watch the video

• A group of proteins known as enzymes speed up chemical reactions in living things
• Some examples of foods that are high in protein include;
• meat
• dairy
• fish
• nuts
• beans

  Nucleic Acids

• Nucleic acids are very long organic molecules that consist of carbon, oxygen, hydrogen, nitrogen and phosphorus; these contain the instructions that cells need to carry our all the functions of life
• Some nucleic acids include;
• DNA
• Is a nucleic acid that contains the cell's genetic code; it contains a type of sugar called ribose, nitrogenous bases, oxygen and nucleotides
• One of the most important components of DNA are the nitrogenous bases.
• There are four of them and are joined in a specific way.
• Adenosine = Thymine (AT or TA)
• Citosine = Guanine (CG or GC)
• RNA
• Ribonucleic acid, made by DNA; has specific tasks in the production of proteins; there are three types:
• mRNA (messenger)
• rRNA (ribosomal)
• tRNA (transfer or translator)
• Foods high in nucleic acids include;
• red meat
• shellfish
• mushrooms
• peas

Cell Membrane (Materials in & out of cells)

• To live and function cells must let certain materials enter and leave
• Every cell is surrounded by a cell membrane; the cell membrane controls how materials move into or out of a cell
• Molecules like lipids, proteins and carbohydrates play important roles in helping materials through the cell membrane
• While some materials move freely across the cell membrane, others can't because the cell membrane is selectively permeable, which means it only lets some substances pass

Passive Transport

• Passive transport is the movement of dissolved materials across a cell membrane without using the cell's energy; some examples of passive transport include:
• Diffusion
• Osmosis

  Diffusion

• Diffusion is the process by which molecules move from an area of higher concentration to one of lower concentration.
• This process uses no energy from the cell

  Osmosis

• Osmosis is the diffusion of water across a selectively permeable membrane
• Many cellular processes depend on osmosis, since they depend on water
• Osmosis uses no energy from the cell

  Facilitated Diffusion

• Oxygen and carbon dioxide diffuse freely across a cell membrane; other molecules (like sugar) don't
• Facilitated diffusion is when proteins in the cell membrane form channels through which sugars can pass; this provides a pathway for sugar to diffuse; it facilitates the process.
• Facilitated diffusion uses no cell energy

Active Transport

• Active transport occurs when molecules do the opposite of what they would do naturally (diffusion), they move from a place of lower concentration to one of higher concentration
• Cells have to supply energy to make active transport occur
• Active transport is the movement of materials across a cell membrane using cellular energy; it is a process by which molecules move from a low concentration area to a high concentration area, it requires a big amount of energy.
• Carrier proteins within the cell play a key role in active transport since they "pick up" specific molecules and carry them across the membrane using the cell's energy
• Substances carried into and out of cells by this process include;
• calcium
• potassium
• sodium
• When particles are too large and want to cross the membrane, like food, endocytosis or exocytosis may happen

  Endocytosis (enter)

• Endocytosis occurs when large materials want to come into the cell, it requires cellular energy
• In endocytosis, the cell membrane changes shape and engulfs the particle
• Once the food particle is engulfed, the cell membrane fuses, pitching off a vacuole within the cell and trapping the food large particles in the new vacuole
• Example: Amoeba & Food

  Exocytosis (exit)

• Exocytosis is the opposite of endocytosis; it occurs when large particles want to come out the cell, it requires energy from the cell
• During exocytosis a vacuole fuses with the cell membrane
• Then the cell membrane forms an opening to the outside and spills out the contents of the vacuole
• Example: Vesicles and Waste Products