8th Grade Science Mrs. Christopherson The Cell: A Review 8th Grade Science Mrs. Christopherson

History of Cells 1665: Robert Hooke used a compound microscope to look at cork. 1674: Anton von Leeuwenhoek observes microorganisms in pond water 1838: Matthias Schleiden concludes all plants are made up of cells. 1839: Theodor Schwann concludes all animals are made up of cells. 1855: Rudolph Virchow proposes that all cells come from existing cells, completing the cell theory.

Cell Theory All organisms are composed of one or more cells Organisms can be unicellular or multicellular The cell is the basic unit of organization of organisms All cells come from pre-existing cells Cells reproduce to make exact copies of themselves

Two Types of Cells Prokaryotic Cells: No nucleus No organelles Mostly unicellular organisms Cell wall or membrane

Two Types of Cells Eukaryotic Cells: Nucleus Organelles surrounded by membranes Mostly multicellular organisms Cell wall or membrane

Cell Specialization Multicellular organisms have cells that do many different jobs. For example, there are blood cells, muscle cells, nerve cells, etc. These cells are said to be “specialized”. Specialized cells perform only their specific functions and cannot live on their own.

Levels of Organization Within Organisms In multicellular organisms, cells are grouped together in tissues. A tissue is a group of similar cells that do a specific job. An example is our skin. Tissues that work together form organs. An example of an organ is the heart. Organs and tissues working together from organ systems. Example: the digestive system The largest level of organization is the organism itself.

Cell Organelles Cell wall: Structure: a tough outer covering made of cellulose, small holes are present that allow materials to enter and exit the cell. Function: maintains shape, supports, strengthens Nickname: ? Only plant cells have cell walls. Can you guess why?

Cell Organelles Cell membrane: a protective covering that surrounds the cell. Materials entering the cell must pass thru the cell membrane. Some materials can easily enter while others cannot cross at all. Selectively permeable. Made of a phosopholipid bilayer: The heads of the lipids are hydrophilic (water loving) while the tails are hydrophobic (water fearing). Both plant and animal cells have cell membranes

Cell Organelles Cell membrane:

Cell Organelles Cytoplasm: Structure: gel-like material found inside the cell, made of water, salts, and organic materials. Function: holds the organelles, keeps them separate Nickname: ?

Cell Organelles Nucleus: Structure: round, large organelle. Surrounded by a membrane. Contains the DNA, nucleolus, and chromatin. Function: controls the cell Nickname: “brain” Nuclear membrane: surrounds and protects the nucleus.

Cell Organelles Endoplasmic Reticulum: Structure: made of membranes, flattened sacs Location: located next to the nuclear membrane Nickname: highway, subway system, … Smooth ER: does not contain ribosomes, makes lipids and membrane proteins, transports proteins Rough ER: contains ribosomes, makes proteins

Cell Organelles Ribosomes: Structure: made of RNA Function: produce proteins Location: attached to the endoplasmic reticulum. Nickname: food source

Cell Organelles Mitochondria: Structure: outer membrane is a phospholipid bilayer, inner membrane is permeable to oxygen, carbon dioxide, and water. Wrinkled appearance Function: transform the energy in food to energy the cell can use to drive chemical reactions. Nickname: “powerhouse” of the cell

Cell Organelles Vacuoles: Structure: cell membrane surrounding a fluid. Function: storage area Plant cells: very large organelle, contains pigments, waste, salts, water. Maintains turgor pressure Animal cells: smaller organelle, primarily responsible for general storage. Nickname: storage tank, …

Cell Organelles Lysosomes: Structure: sac filled with enzymes and liquids. Function: involved in digestion of old cell organelles as well as breaking large molecules into smaller ones. Location: found in all animal cells, rare in plant cells. Nickname: janitor, garbage person, stomach, …

Cell Organelles Golgi Body: Structure: stack of membranes. Function: packages proteins from the ER and distribute them around or outside of the cell. Nickname: UPS or shipping center, …

Cell Organelles

Movement thru the Cell Membrane Remember: The cell membrane provides support and protection for the cell. The cell membrane is made of a lipid bilayer that is selectively permeable. The lipid bilayer contains hydrophilic heads and hydrophobic tails. Proteins in the bilayer help materials pass into and out of the cell.

Movement thru the Cell Membrane: Diffusion Diffusion is the process of cells moving from areas of high concentration to areas of low concentration. Remember the scent diffusion lab from 7th grade? Occurs because molecules are constantly moving. This random movement causes the molecules to become evenly spread out.

Movement thru the Cell Membrane: Diffusion Molecules diffuse (move from high to low concentration) until the molecules are evenly spread out. This is called equilibrium. Diffusion doesn’t stop at equilibrium, the molecules just move in equal numbers. If one molecule enters an area, another molecule leaves.

Movement thru the Cell Membrane: Diffusion Cells use diffusion to get substances into and out of the cell. Example: During photosynthesis, oxygen is produced inside the cell. When this happens the concentration of oxygen becomes higher inside the cell than outside and oxygen diffuses out of the cell.

Movement thru the Cell Membrane: Osmosis Osmosis is the diffusion of water through a membrane. Water moves into an area with low concentrations and out of areas with high concentrations. Both diffusion and osmosis are forms of passive transport (they require no energy)

Movement thru the Cell Membrane: Active Transport Cells often need materials to move from areas of low concentration to areas of high concentration. This process requires energy! Active transport uses energy to move materials through a membrane. Endocytosis: moving a particle into the cell Exocytosis: moving a particle from inside the cell to outside.

Movement thru the Cell Membrane: Active Transport Endocytosis Exocytosis

Cell Growth and Division Multicellular organisms grow because cell division increases the number of cells in them. Cells become specialized during the development of an organism. Cells that are damaged or worn out are replaced by cell division.

Cell Growth and Division: The Cell Cycle Interphase: The part of the cell cycle when the cell is not dividing. This is the longest phase in the cell cycle. Cells grow and go about their daily routines in this part of the cycle. DNA (genetic material) replicates.

Cell Growth and Division: The Cell Cycle Mitosis: the part of the cell cycle where the nucleus divides. Occurs in non-reproductive cells and produces exact copies of the parent cell. Prophase: The chromosomes condense Metaphase: The chromosomes line up in the middle of the cell. Anaphase: The chromosomes separate and are pulled to either end of the cell. Telophase: The new nuclear membrane forms. Cytokinesis: The cell splits in half.

Cell Growth and Division: The Cell Cycle

Cell Growth and Division: The Cell Cycle Meiosis: The cell division that takes place within reproductive cells. Produces cells that only have one pair of chromosomes. Meiosis produces egg and sperm cells. Before meiosis begins, the chromosomes from the parent cell are copied.

Cell Growth and Division: The Cell Cycle Meiosis I: Pairs of chromosomes separate Prophase I: Chromosomes pair up Metaphase I: The chromosome pairs line up in the middle of the cell. Anaphase I: Chromosome pairs are pulled apart to opposite ends of the cell Telophase I: A new cell membrane forms around the chromosomes. Cytokinesis: The cell splits into two daughter cells

Cell Growth and Division: The Cell Cycle Meiosis II: Chromosomes separate Prophase II: In each daughter cell, there are two copies of a chromosome. Metaphase II: Each chromosome in each daughter cell lines up in the middle of the cell. Anaphase II: Each chromosome in each daughter cell is pulled apart to opposite ends of the cells. Telophase II: A new cell membrane forms, splitting each daughter cell into two new cells. Cytokinesis: The cells divide into four new cells.

Cells and Energy: Respiration Most chemical reactions that take place in cells require an energy source. Mitochondria in both plant and animal cells release this energy through respiration. Respiration is the process by which oxygen (O2) is combined with food (sugar) to release energy. Before respiration can occur in the mitochondria, sugar in the cytoplasm is broken down. This releases a small amount of energy.

Cells and Energy: Respiration If oxygen is not present in the environment, anaerobic respiration takes place. Fermentation: the process of cells releasing energy without oxygen. There are two types of fermentation: Alcoholic fermentation Lactic Acid fermentation

Cells and Energy: Respiration If oxygen is present in the environment, aerobic respiration can occur. After sugar in the cytoplasm is broken down, the smaller pieces travel to the mitochondria and are broken down even more. This produces energy, called ATP (adenosine triphosphate). Oxygen also enters the mitochondria and combines hydrogen to produce water. Glucose + Oxygen  Energy + Water + CO2

Cells and Energy: Photosynthesis Plant cells gain energy through the process of photosynthesis. Photosynthesis takes place in chloroplasts. Chloroplasts contain chlorophyll, the green pigment that captures sunlight for the plant. Carbon dioxide (CO2) and water enter the chloroplasts while the chlorophyll captures sunlight. The energy from the sunlight changes the CO2 and water into oxygen and sugar. CO2 + Water + Energy  Oxygen + Sugar