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Chapter7
Looking at cells
Where does cork come from?
• The bark of an oak tree that grows in Spain and Portugal
• The bark is dead• All that is left are the
cell walls enclosing air
Microscopes reveal cell structure
• Robert Hooke , an English scientist, invented the microscope in the 1600’s to view cork
• He named the “little boxes” he saw, “cells”
Anton van Leeuwenhoek
• 10 years after Hooke’s findings
• Used a microscope to view pond water
• He named the single-celled organisms he discovered “animalcules”
The Cell Theory
• All living things are made of cells
• Cells are the basic units of structure and function in organisms
• All cells arise from existing cells
Measuring the size of cell structures
• Measurements are in metric units
• International System of Measurements (SI)
• Based on powers of 10• Micrometers are one-
millionth of a meter ( the size of a bacterial cell)
Cells must be small
• Lower surface area to volume ratio = inability to move substances across the membrane in large enough numbers
• Higher surface area to volume ratio = greater ability to exchange substances
Small is good! Big is bad!
Common features of all cells
• Cell membrane
• Cytoplasm
• Cytoskeleton
• Ribosomes
• Genetic material
Prokaryotes do not contain internal compartments
• No nucleus
• Smaller
• Ex: bacteria
Characteristics of bacteria• Prokaryotes
• All have a cell wall surrounding the cell membrane
• Some have flagella for movement
• DNA is circular instead of linear
• Some have a capsule for clinging
Eukaryotic cells are organized
• Have a nucleus
• Have other membrane enclosed organelles
• Some have flagella or cilia for movement
Eukaryotes
• Larger
• More complex
• Many are highly specialized
• Plants, animals, fungi, and many protists
Cell Organization
• Two divisions:– Nucleus- eukaryotes only– Cytoplasm- fluid portion of the cell outside the
nucleus• Eukaryotes and prokaryotes
Organelles
• Specialized structures
• “Little organs”
Nucleus• Controls cell functions
• Surrounded by a double membrane with nuclear pores
• Contains DNA wound around proteins
• Wind up into chromosomes before division takes place
Nucleus
• Nucleolus- where ribosomes are made
• Nuclear pores- allow materials in and out
Vacuoles
• Large, saclike, membrane-enclosed structures that store materials such as water, salts, proteins, and carbohydrates
Vacuoles
• Plants- large central vacuole, helps keep leaves and flowers rigid
• Found in some unicellular organisms and animals– Contractile vacuole in paramecium
Vesicles
• In almost all eukaryotic cells
• Used for storage and movement
Lysosomes
• Small organelle filled with enzymes
• Digest old organelles, cellular “junk,” lipids, proteins, and carbohydrates
• Type of vesicle, found in animal and some plant cells
Ribosomes
• Made of RNA and protein
• Produce proteins
• Found in the cytoplasm (free) and rough ER (attached)
Endoplasmic Reticulum (ER)• A system of internal membranes that moves
proteins and other substances through the cell• Rough ER- has ribosomes on the surface that
create exported proteins • Smooth ER- no ribosomes, makes lipids for the
cell membrane – Detoxifies drugs
Golgi Apparatus
• Stack of flattened sacs
• Modifies, sorts, and packages proteins made from the rough ER
• Sent into or out of the cell
Sources of Energy
• Mitochondria- animal and plant cells
• Chloroplasts- plant cells
Chloroplasts
• Converts sunlight into food energy in a process called photosynthesis
• Double membrane
• Contains a green pigment called chlorophyll
Mitochondria
• In eukaryotic cells
• Power plant of the cells
• Converts food energy into smaller units the cell can more easily use
• Double membrane
Mitochondria
• Inherited only from your mother
• A way to trace the maternal lines of animals
Endosymbiotic Theory
• Chloroplasts and mitochondria have their own DNA and double membranes
• Theory states:– These may have been independent
organisms at one time– Create their own energy– May have been beneficial once absorbed and
found to be beneficial
Unique features of plant cells
• Cell wall -surrounds the cell membrane, supports and protects the cell
• Chloroplasts- green structures that absorb sunlight and produce glucose
• Central vacuole- stores water and other substances, when full makes a cell rigid
Cytoskeleton
• Network of protein filaments
• Gives cells their shape and internal organization– Helps to transport materials inside the cell
• Protein filaments– Microtubules– Microfilaments
Microfilaments
• Threadlike structures made of protein called actin
• Make up a tough flexible framework that helps support the cell
• Help cells move– Amoebas- assemble and disassemble to help
them move
Microtubules
• Hollow structures
• Made of protein tubulin
• Maintains cell shape
• Centrioles– Makes spindle during mitosis to separate
chromosomes
Microtubules
• Make up cilia and flagella– Used for swimming
• Arranged in a 9+2 pattern
• Small bridges between aid in movement
Cell Boundries
• Cell wall
• Cell membrane
Cell Wall
• Prokaryotes, plants, algae, fungi– Animal cells do not
• Outside the cell membrane
• Strong supporting layer
• Porous- allows water, carbon dioxide and oxygen to pass through
Cell Membrane
• Protects and supports cell
• Regulates what enters and leaves
• Phospholipid bilayer- to layers of lipids
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