6th Grade Science- Chapter 10 Notes

Chapter 10, Lesson 1 Notes

*Organisms, or living things, are made of tiny particles that can join together, making larger structures.

*The levels of organization in an organism from smallest to largest are atoms, elements, molecules, compounds, cells, tissues, organs, and organ systems.

*Every living and nonliving thing is a type of matter.  Elements make up matter.  An element is any substance that cannot be broken down into simpler substances.

*Important elements in the body include carbon, hydrogen, oxygen, nitrogen, sulfur, phosphorus, calcium, and sodium.  The smallest unit of an element is particle called an atom.  Any single element is made up of only one kind of atom.

*Compounds form when two or more elements combine chemically.  The smallest part, or unit, of many compounds is a molecule.  Carbohydrates, lipids, proteins, water, and nucleic acids are molecules that all living things need.  Nucleic acids contain the instructions necessary to carry out all the functions of life.

*One important nucleic acid is DNA, the genetic material that carries information about an organism and is passed from parent to offspring.

*A cell is the basic unit of structure and function in living things.  If a living thing has only one cell, it is called unicellular.  Plants and animals are multicellular, which means “made of many cells.”

*All cells in a multicellular organism must carry out key functions to survive.  Specialized cells may perform specific functions that benefit the entire organism.  Specialized cells may differ in structure as well as in function.

*In multicellular organisms, cells are organized into tissues, organs, and organ systems.  A tissue is a group of similar cells that work together and perform a specific function.  An organ is made of different kinds of tissues that function together.  A group of organs that work together and perform one or more major functions is an organ system.  Organ systems work together in an organism.  The level of organization becomes more complex from cell to tissue to organ to organ system.

Chapter 10, Lesson 2 Notes

*Cells are the basic units of structure and function in living things.  Cells form the parts of an organism and carry out all of its functions.  Every organism is made out of one or more cells, and each cell can carry out the basic functions that let it live, grow, and reproduce.  Those functions can include obtaining food, water, and oxygen, secreting wastes, and reproducing by division.

*The cell theory explains the relationship between cells and living things.  It was developed about two hundred years after the invention of the microscope, an instrument that makes small objects look larger, and the discovery of cells.

*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

*Most cells are too small to be seen by the human eye, so the development of the cell theory depended on observations made through microscopes.

*Some microscopes focus light through lenses to produce a magnified image, and other microscopes use beams of electrons.

*A compound microscope uses two lenses and focuses light from a lamp or reflected from a mirror.  This type of microscope is often used in classrooms.  You can estimate the true size of an enlarged object by measuring the width of the circular field visible through the microscope and comparing the size of the object to the width of the field.

*Objects viewed through a microscope are also more detailed than when viewed with the naked eye.  Microscopes improve resolution: the ability to distinguish separate structures that are close together.  Electron microscopes have better resolution and magnification that light microscopes.

Chapter 10, Lesson 3 Notes

*Homeostasis is the maintenance of internal stable conditions that are necessary for life functions.  Entire organisms maintain homeostasis.  So do individual cells.

*In all cells, the processes that help maintain homeostasis include getting and using energy from food and removing wastes.

*Most organisms get energy from cell processes that break down foods.  During cellular respiration, cells break down glucose molecules in the presence of oxygen, releasing energy.  Waste products of this process include carbon dioxide and water.  Animals and some other organisms get food for energy by eating other organisms.

*Unlike animals, plants and some other organisms can make their own food.  The process by which cells capture the energy in sunlight and convert it to energy stored in food is called photosynthesis.  Often, the foods produced in photosynthesis are glucose or other sugars.  The raw materials for photosynthesis are carbon dioxide from the air and water.  Oxygen leaves the cell as a waste product.

*To maintain homeostasis, materials such as food and oxygen must move into cells.  At the same time, waste materials must exit.  Materials that move in or out of a cell must cross a structure called the cell membrane.

*The cell membrane surrounds a cell, separates it from the outside environment, and controls which substances enter and leave.

*One way materials move across the cell membrane involves collisions of molecules.  These collisions push molecules away from one another in a process called diffusion.  During diffusion, molecules move from an area of higher concentration to an area of lower concentration.  Eventually, the molecules spread evenly throughout a space.

*All multicellular organisms grow during some part of their lifetimes.  They also have structures that wear out or become injured and must be replaced.  Growth and repair can occur because cells reproduce, or make more cells.

*Cell division is a process in which one cell splits into two new cells that are genetically identical to the original cell.  Through cell division, your body replaces damaged skin cells and worn out blood cells.

*Reproduction of cells is one of the processes that helps multicellular organisms maintain homeostasis.  You grow as your body produces more muscle cells, bone cells, and other kinds of cells.  Growth and repair help your body maintain homeostasis.

Chapter 10, Lesson 4 Notes

*Cells contain a number of smaller structures that divide up the jobs inside the cell.  Each kind of cell structure has a different function within a cell.

*Every cell is surrounded by a cell membrane, which controls the movement of materials into and out of the cell.  Jobs inside the cell are handled by specialized organelles suspended in the cells gel-like cytoplasm: the nucleus directs the cells activities, lysosomes break down food into smaller particles, mitochondria convert the energy stored in food to energy the cell can use, ribosomes produce proteins, and the endoplasmic reticulum and Golgi apparatus modify proteins and move them around inside the cell.

*Vacuoles are structures where the cell can store water, food, or wastes.  Plant cells have two structures that are not found in animal cells: the cell wall, which surrounds the cell and helps support it, and chloroplasts, which capture the energy in sunlight to power the process the plant uses to make its own food.

Chapter 10, Lesson 5 Notes

*Cell division allows organisms to grow, repair damaged structures, and reproduce.  Many single-celled organisms reproduce simply through cell division.  Other organisms reproduce when cell division leads to the growth of new structures.

*Most organisms reproduce when specialized cells from two different parents combine, forming a new cell.

*The regular sequence of growth and division that cells undergo is known as the cell cycle.  During the cell cycle, a cell grows, prepares for division, and divides into two new cells, which are called “daughter cells.” The cell cycle consists of three main stages: interphase, mitosis, and cytokinesis.

*During interphase, the cell grows, makes a copy of its DNA, and prepares to divide into two new cells.  The process by which a cell makes an exact copy of the DNA in its nucleus is called replication.

*At the end of replication, the cell contains two identical sets of chromosomes, which are the threadlike structures made up of proteins and DNA found in the nucleus.

*Mitosis is the stage during which the cell’s nucleus divides into two nuclei and one set of DNA is distributed to each nucleus of each daughter cell.  There are four parts to mitosis: prophase, metaphase, anaphase, and telophase.

*The final stage of the cell cycle is cytokinesis, in which the cytoplasm divides.  When cytokinesis is complete, two new cells have formed, each having the same number of chromosomes as the original parent cell.

*During cytokinesis in animal cells, the cell membrane squeezes together around the middle of the cell, and the cell pinches into two cells.

*In plant cells, the rigid cell wall cannot squeeze together.  Instead, a structure called a cell plate forms across the middle of the cell and begins to form new cell membranes between the two daughter cells.  New cell walls then form around the cell membranes.