Chapter 1 “Living Things” Life Science Chapter 1 “Living Things”

Lesson 1: “Cells” What are cells? An organism is a living thing. All organisms are made of cells. A cell is the smallest unit of living things that can carry out the basic life processes. Cells come from other cells. A unicellular organism consists of a single cell that carries out its life processes. These life processes include growing, responding to its environment, reproducing, and getting food. Two examples of unicellular organisms are Amoebas and Euglena.

Lesson 1: “Cells” What are cells? (Continued) Organisms that have many cells are called multicellular. Examples of multicellular organisms include frogs, trees, and you! In multicellular organisms, every cell carries out its own life processes while at the same time working together to take care of different functions for the organism. An example of this would be how heart muscle cells carry out their own life processes as they work together to keep the heart beating. Scientists estimate that there are more than 1 billion kinds of unicellular organisms.

Lesson 1: “Cells” What is inside an animal cell? All organisms are made of cells. Your own body has more than 200 different kinds of cells. Plant and animal cells have several basic structures called organelles. These organelles help them perform life processes that keep the cell alive. All animal cells are surrounded by a flexible wrapping called a cell membrane which wraps around the cell sort of like how your skin wraps around you. The cell membrane gives the cell its shape. The function of the cell membrane is to control what materials move into and out of the cell. Cells contain a gel-like liquid called cytoplasm. Cytoplasm fills the region between the nucleus and the cell membrane and is made mostly of water.

Lesson 1: “Cells” What is inside an animal cell? (Continued) A variety of organelles float in the cytoplasm. The cytoplasm supports all the cell’s structures while constantly moving through the cell in a stream-like motion. Some of the cell’s life processes take place in the cytoplasm. Most cells also have a nucleus which functions as the cell’s control center. The nucleus is a large, round organelle usually found in the center of the cell that is most often easy to see with a microscope. The nucleus has a membrane with pores, or openings, that allow certain materials to pass in and out. The nucleus sends signals to all other parts of the cell.

Lesson 1: “Cells” What is inside an animal cell? (Continued) Mitochondria are oval, membrane covered organelles that supply energy for the cell. The mitochondria break down food which releases energy for the cell to use. Each mitochondria is like a tiny power plant. Some cells, like muscle cells, require more energy so they usually have more mitochondria. A vacuole is a membrane-covered structure used for storage. A vacuole can store water, food and wastes. The nucleus can signal the vacuole to release whatever it is storing. Some cells may have many small vacuoles and some cells may have none.

Lesson 1: “Cells” What is inside an animal cell? (Continued)

Lesson 1: “Cells” What is inside a plant cell? Plant cells have many of the same structures and organelles as animal cells. Plant cells often have a boxlike shape and are a bit larger than animal cells. Plant cells also contain a cell membrane, a nucleus, cytoplasm, a vacuole, and mitochondria which all perform the same functions as they do in an animal cell. Plant cells have an additional outer covering called the cell wall. The cell wall is a stiff structure outside the cell membrane that provides the cell with strength and extra support. Unlike animal cells, plant cells usually have one large, central vacuole which stores water and provides extra support.

Lesson 1: “Cells” What is inside a plant cell? (Continued) The extra water stored in the vacuole(s) of the plant keep the plant from drying out. Plants make their own food in structures called chloroplasts. A chloroplast is a green structure where the energy from sunlight is used to produce food for the plant. Chloroplasts are green because they contain chlorophyll, a chemical that absorbs sunlight. Chloroplasts are mainly found in the leaves and stems of plants.

Lesson 1: “Cells” What is inside a plant cell? (Continued)

Lesson 1: “Cells” How are cells organized? For unicellular organisms, organization is simple because the organism has only one cell which performs all life functions. Multicellular organisms are more specialized. In a complex organism such as a salamander or human being, organization starts at the cell level. Similar cells working together at the same job, or function, form a tissue. A group of tissues that work together to perform a specific function form an organ. Organs that work together to perform a specific function make up an organ system.