Science Notes Chapter 2 PDF

2.1 Unicellular Organisms Unicellular organisms are living things made of a single cell. ○ Ex. Phytoplankton live in oceans and contain chlorophyll to convert the Sun’s energy into food. They provide most of the oxygen in the Earth’s atmosphere and are the fou...

2.1 Unicellular Organisms Unicellular organisms are living things made of a single cell. ○ Ex. Phytoplankton live in oceans and contain chlorophyll to convert the Sun’s energy into food. They provide most of the oxygen in the Earth’s atmosphere and are the foundation of the ocean’s food chain. ○ Bacteria decomposers complete the cycling of matter by converting nitrogen in the soil around them into a form of nitrogen that can support plant life and the terrestrial food chain. A Single Cell is a Living Things Examples of unicellular organisms are the diatom, paramecium, amoeba, bacteria, and phytoplankton. ○ Diatoms live in glass-like shells which they make themselves. They make food through photosynthesis. They perform the same basic activities that complex plant and animal organisms perform. They move, eat, respond to stimuli, reproduce, and expel waste that results from cellular activity. How Unicellular Organisms Move Paramecia have tiny hairs that act like oars and propel the organism along. E.coli bacteria move by rotating a flagellum that looks like a tail. The organisms swim along. An amoeba moves by changing shape and forcing its cytoplasm into extensions called pseudopods. The Amoeba Microscopic. They thrive in water-based environments and are found in fresh and saltwater. They can also live in wet, decaying vegetation on the forest floor, in wet soil, or in other living organisms (including humans). Many species, Most are harmless, but some can be harmful and cause disease.  Body is surrounded by a selectively permeable cell membrane. Commonly visible organelles include one or more nuclei, cytoplasm, food vacuoles, and a special vacuole that pumps water out of the cell to prevent it from bursting. Water enters the amoeba by osmosis. Oxygen diffuses into the organism and carbon dioxide waste diffuses out of the organism. Amoebas can be carnivores, herbivores, or omnivores. They are predators that prey on organisms like algae and bacteria. They have the ability to change shape (from Greek, meaning change). The organism changes shape as it moves and captures the prey. The food it consumes becomes a vacuole. Chemicals called enzymes digest the food, the nutrients are absorbed by the organism, and the vacuole. Waste products are eliminated through the cell membrane. 2.2 Multicellular Organisms and Cell Specialization Multicellular organisms rely on a variety of types of cells to perform cellular functions. Specialized cells perform specific functions, such as digestion or movement and must interact with other types of cells in the organism in order to carry out their tasks successfully. More Cells for Bigger Organisms Unicellular organisms are usually micro-sized because cellular activities are performed most efficiently at that size. The limitation is related to the processes of diffusion and osmosis. The processes that deliver gasses and water to cells and remove wastes are effective across very short distances. ○ Ex. An oxygen particle can diffuse over a distance of 0.01 mm in a fraction of a second. To diffuse over a distance of 1 mm would take 100 times as long. The large increase is because in a bigger cell, even though the surface area of the selectively permeable cell membrane would increase as the cell’s size increases, the cell’s volume would increase even more. ○ For a cell to be bigger in the same proportion, gasses and water would have to travel much farther to reach all of the organelles in the cytoplasm. If a unicellular organism were many times bigger than 1 mm, diffusion and osmosis could take up several minutes instead of fractions of a second. The increase of volume is why the organelles in a huge cell would have trouble accessing the resources they need. Larger living things tend to be made up of more than one cell. In organisms made up of a dozen, millions, billions, or even trillions diffusion and osmosis can still happen in a second. Specialized Cells in Multicellular Organisms One type of cell cannot do all of the different jobs in a complex organism. Multicellular organisms are made up of specialized cells rather than cells that are exactly the same. While the specialized cells have the same kinds of organelles as other plant or animal cells, the organelles may be better adapted to performing the cell’s tasks. Specialized Animal Cells Hydra is a simple multicellular organism. It has skin cells on the outside and digestive cells on the inside. The skin cells protect the inside front of the outside environment and act as gatekeepers to control the substances that can get into and out of the organism in the same way that the cell membrane protects a cell. A human has skin, digestion, muscle, nerve and brain, blood, storage, and cells in the eyes. Specialized Plant Cells Leaf cells transform the Sun’s energy into sugars, Stem cells transport food and water to the rest of the plant, store some food, and support the plant. Root cells store food, absorb water from the soil, and transport water and nutrients to the stem. 2.3 Plant and Animal Cellular Processes Transforming Energy Mitochondria provides energy for the cell by transforming oxygen and sugar into carbon dioxide and water. This process is called cellular respiration. Occurs in both plant + animal cells. In photosynthesis, the chlorophyll in chloroplasts captures the Sun’s energy so the chloroplast can convert carbon dioxide and water into sugar and oxygen. Energy is  transformed from sunlight into sugar in plants and then sugar is consumed to release usable energy in both plant and animal cells. Processing and Transporting Materials Materials move through the cytoplasm to the various organelles. The endoplasmic reticulum makes proteins from raw materials that come into the cell and passes them to the Golgi apparatus. The Golgi apparatus processes protein molecules and secretes them outside the cell to be used elsewhere in the organism. Lysosomes break down food and digest wastes. All of this is controlled by the nucleus. Reproducing Amoebas live for approximately two days. Human brain cells live between 30 to 50 years. Human red blood cells live for 120 days. Skin cells live for 20 days. In the average human body, approximately 3 billion cells die every day. Cells die because they have been damaged, not received enough water or food, or because they have reached the end of their lifespan. Before they die, they create a replacement for themselves through cell division. During cell division, the cell’s nucleus splits into two. Then the membrane begins to pinch near the middle to divide the cytoplasm, including its organelles, and ensure that each new cell has a nucleus. The two new cells are identical. ○ For a plant cell - instead of pinching in half after the nucleus divides, a new cell plate develops across the cell to create a new cell wall between the two nuclei.