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CHAPTER 2 – LESSON 1
7th Science
Cells and Life
Cell Theory: States that all living things are made of one or more cells, the cell is the smallest unit of life, and all new
cells come from some preexisting cells.
Basic Cell Substances: These substances, called MACROMOLECULES, form by joining many small molecules together.
Main ingredient in any cell is water. It makes up more than 70 percent of a cell’s volume and is essential for
life.
Structure of water molecule makes it ideal for dissolving many other substances.
Substances must be in a liquid to move into and out of cells.
Water molecule has two areas:
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An area that is more negative (-), called the negative end; this end can attract the positive part
of another substance.
An area that is more positive (+), called the positive end; this end can attract the negative part
of another substance.
The positive and negative ends of a water molecule attract the positive and negative parts of another
substance, similar to the way magnets are attracted to each other.
Macromolecules: are large molecules that form when smaller molecules join together. Four types of
macromolecules in cells-each type has unique functions:
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Nucleic acids – are macromolecules that form when long chains of molecules called nucleotides join
together.
Proteins – are long chains of amino acid molecules and are the macromolecules necessary for nearly
everything cells do.
Lipids – a large macromolecule that does not dissolve in water. Lipids play roles in energy storage and in
cell communication.
Carbohydrates – one sugar molecule, two sugar molecules, or a long chain of sugar molecules. They
store energy, provide structural support, and are needed for communication between cells. Sugars and
starches are carbohydrates that store energy.
LESSON 2 – THE CELL
Cells come in many shapes and sizes. The size and shape of a cell relates to its job or function.
Cell Membrane: a flexible covering that protects the inside of a cell from the environment outside a cell.
Cell Wall: A stiff structure outside the cell membrane.
Cell Appendages: Arms, legs, claws, and antennae are all types of appendages, Cells can have appendages too.
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Flagella – long tail-like appendages that whip back and forth and move a cell.
Cilia – short hair-like structures that can move a cell or move molecules away from a cell.
Cytoplasm: a fluid inside a cell that contains salts and other molecules.
Cytoskeleton: a network of threadlike proteins that are joined together – protein framework inside a cell.
CELL TYPES – Two types
1. Prokaryotic Cells: The genetic material in a prokaryotic cell is not surrounded by a membrane.
2. Eukaryotic Cells: Plants, animals, fungi, and protists are all made of eukaryotic cells. Eukaryotic cell has genetic
material that is surrounded by a membrane.
a. Organelles: Every Eukaryotic cell also has other structures, called organelles, which have specialized
functions. Most organelles are surrounded by membranes.
i. CELL ORGANELLES
1. Nucleus – the part of a eukaryotic cell that directs cell activities and contains genetic
information stored in DNA.
a. DNA is organized into structures called chromosomes.
b. Nucleolus – the nucleolus makes ribosomes-organelles that are involved in the
production of proteins.
2. Manufacturing Molecules
a. Endoplasmic Reticulum (ER) – spreads from the nucleus throughout most of the
cytoplasm.
i. Rough Endoplasmic Reticulum – site of protein production.
ii. Smooth Endoplasmic Reticulum – site of lipid production.
3. Processing Energy
a. Mitochondria – surrounded by two membranes. Energy is released during
chemical reactions that occur in the mitochondria. This energy is stored in highenergy molecules called ATP (adenosine triphosphate).
i. ATP is the fuel for cellular processes such as growth, cell division, and
material transport.
b. Chloroplasts – membrane-bound organelles that use light energy and make
food-a sugar called glucose-from water and carbon dioxide in a process known
as photosynthesis. The sugar contains stored chemical energy that can be
released when needed.
4. Processing, Transporting, and Storing Molecules
a. Golgi apparatus – prepares proteins for their specific jobs or functions. It
packages the proteins into tiny, membrane-bound ball-like structures called
vesicles. VESICLES transport substances from one area of a cell to another area.
LESSON 3 – MOVING CELLULAR MATERIAL
Passive Transport: the movement of substances through a cell membrane without using the cell’s energy. This mode
depends on the amount of substance on each side of a membrane.
Diffusion: the movement of substances from an area of higher concentration to an area of lower concentration. Usually
diffusion continues through a membrane until the concentration of a substance is the same on both sides of the
membrane (called equilibrium).
Osmosis is the diffusion of water molecules only through a membrane.
Facilitated Diffusion – is when molecules pass through a cell membrane using special proteins called transport proteins.
Two types of transport proteins
1. Carrier proteins – carry large molecules through the membrane, such as glucose (sugar molecule)
2. Channel proteins – form pores through the membrane – atomic particles such as sodium ions pass
through the cell membrane by channel proteins.
Active Transport is the movement of substances through a cell membrane only by using the cell’s energy. Cells can take
in needed nutrients from the environment through carrier proteins by using active transport.
Endocytosis and Exocytosis: Some substances are too large to enter a cell membrane by diffusion or by using a
transport protein. These substances can enter a cell using another process.
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Endocytosis – the process during which a cell takes in a substance by surrounding it with the cell membrane.
Exocytosis – the process during which a cell’s vesicles release their contents outside the cell.