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Chapter 7 – Cell Structure and Function
Microscopes and Cells
The typical cell measure 10 micrometers in length. Can you see it with your
eye? So then how do we know about cells?
Anton van Leeuwenhoek – Early 1600s Dutchman
- Placed several lenses at set distances and
realized he could MAGNIFY very small objects.
Instruments he used were some of the first
MICROSCOPES in history.
- The microscope used rays of LIGHT that bent
through the lenses to enlarge images.
- He looked at pond water under the microscope
and noticed tiny living things.
Robert Hooke – 1600s Englishman
- Saw under the microscope while looking at the woody parts of flowers
called CORK: tiny rectangular chambers he called CELLS. The shapes
reminded him of tiny rooms in a MONASTERY.
Picture of Hooke’s “cells”
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The work of early microscope pioneers led to the CELL THEORY:
1. All living things are made up of cells
2. Cells are the basic units of structure and function in living things
3. New cells are produced from existing cells
Some organisms may have as little as 1 cell, like Giardia.
Other organisms have millions of cells.
Modern Microscopes
Compound Light Microscope:
A microscope that allows LIGHT to pass through a specimen and uses __2____
lenses to form an image.
Can magnify image up to 1000 times.
The type we use in school is a COMPOUND LIGHT MICROSCOPE
Electron Microscope:
Uses a beam of ELECTRONS instead of light to examine a specimen
Can magnify up to 1000 times larger than a light microscope.
Same concept used for the television.
TEM - TRANSMISSION ELECTRON MICROSCOPE- TEM shines beam of
electrons through sample, then magnifies image on a fluorescent screen.
SEM - SCANNING ELECTRON MICROSCOPE - SEM collects the electrons that
bounce off the sample then forms image on a television screen.
Scanning Probe Microscope (developed in 1980s):
No lenses. Traces the surface of a sample with tiny tip known as a SCANNING PROBE
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CELL MEMBRANE:
- Role: Protects cell and regulates what comes in and out of cell.
permeable: lets some things in and out but not everything.
Semi-
- Phospholipid Bilayer: Cell membrane is made of a double layer of lipids
(a special type of lipid with a phosphate head)
PROTEINS in the cell membrane form channels and pumps to help move
material across the membrane. Many of the proteins have CARBOHYDRATES
attached to them that stick out like identification cards so other cells know
which cells are the organisms and which are foreign.
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Cell Wall:
- Found in PLANTS, ALGAE, BACTERIA (NOT found in animal cells)
- Helps to further support and protect cell in addition to cell membrane
- Tough but porous to let water, gases and other substances across
- Cellulose is a main component of cell walls.
How do substances get across the cell membranes?
Passive Transport:
Substances pass through cell membrane WITHOUT expending energy.
Diffusion: Molecules move from regions of HIGH to LOW concentrations.
Facilitated Diffusion: substances diffuse across cell membrane with a little
help from PROTEINS
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Osmosis: diffusion of WATER through a semi permeable membrane.
Osmotic pressure or turgor
The cytoplasm of cells is filled with salts, sugars and other substances. If
the cell is surrounded a mostly water solution than a gradient is
established and water will rush in to the cell where there is less water.
How do cells prevent this from happening?
What if you want to move substances in the opposite direction- from low to
high concentration? - ACTIVE TRANSPORT
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Active Transport – movement of substances against a gradient.
This process requires ENERGY. Moving from low to high concentration.
Endocytosis: pinching in of the cell membrane to let substances IN. A way to
get food and nutrients INTO THE CELL.
Exocytosis: reverse of endocytosis. A way to release materials and waste OUT
OF THE CELL. Think EXIT= Exocytosis
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Inside the Cell
The cell is like a factory: workers assemble items, package, transport, deliver,
needs power/energy, a control center to plan and operate the cell.
The cell has organelles: little organs that perform a special function for the
cell, and they have a specific structure.
Nucleus: a very important organelle
Large, dense structure usually near the center of cell.
Contains almost all of a cell’s genetic material (DNA)
Chromatin (DNA) is spread throughout the nucleus until the cell divides.
During cell division the chromatin condenses, coils up to form large
structures called chromosomes.
- Nucleus has two membranes together called the nuclear envelope
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- Nucleolus: small, dense region of nucleus. Place where ribosomes are
produced/made.
- EUKARYOTES : Cells that HAVE a nucleus (tiny single celled organisms to
very large organism).
- PROKARYOTES: Cells that DO NOT HAVE a nucleus (bacteria, other
single celled organisms)
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Cytoplasm: cyto means CELL, plasm means FLUID. Fluid filling the cell.
- Fills the cell outside of the nucleus. Other organelles are suspended in
the cytoplasm.
Endoplasmic Reticulum: Network of channels extending from the nucleus
into the cell.
- Role: TRANSPORT materials in the cell
- Rough ER: have ribosomes that dot the top of it, make it look rough.
- These ribosomes are sites where proteins are synthesized (made/
assembled). After a protein is synthesized at the ribosome in the Rough
ER, it travels through to the Smooth ER .
- Smooth ER: channels that Do NOT have ribosomes.
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After proteins are synthesized/assembled in the Rough ER, it travels on to the:
Golgi Apparatus: Sac-like structure where special enzymes attach
Lipids or carbohydrates to the proteins synthesized in the Rough ER.
- Modifies, packages and ships final product throughout the cell or outside
cell.
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Lysosomes: Clean-up crew
- Sac-like membranes filled with enzymes and chemicals that break down
and digest substances in the cell.
Vacuoles: Storage
- Store materials such as water, salts, carbohydrates, lipids, proteins
- In PLANT cells there is usually a large central vacuole that stores water
and dissolved salts.
Cytoskeleton: Internal support beams
- Made with strong proteins called MICROTUBULES (hollow tubes) and
MICROFILAMENTS (strandlike, ropelike).
- Proteins can attach to cytoskeleton and move organelles along.
- Hairlike structures called CILIA and FLAGELLA on surface of cells move,
propel cell or things around cell. Centrioles: organize microtubules
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Mitochondria: Power-house of cells
- Supplies ENERGY to the cell.
- Convert chemical energy of food into compounds the cell can use to do
work (make proteins, move molecules, synthesize, digest, etc)
- Has its own DNA, and double membrane.
Chloroplasts: Only found in PLANT cells.
- Use energy from the sun and converts into useable chemical energy
through a process called PHOTOSYNTHESIS.
- Has its own DNA, and double membrane.
Marguli’s Model – Endosymbiont Hypothesis: Eukaryotes have a nucleus,
Prokaryotes do not. Mitochondria and Chloroplasts have a double membrane
and reproduce separately from the rest of the cell with their own DNA.
Believed mitochondria and chloroplasts were once their own cells and later
became part of eukaryotic cells.
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ANIMAL CELLS VS PLANT CELLS
- Only Animal cells have Centrioles
- Only Plant cells have Cell Walls and Chloroplasts
- Plant cell vacuoles are much bigger than animal vacuoles
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Organization of Cells
How does the body get 100 trillion cells to work together and perform
different jobs? What are the levels of organization?
Cells  Tissues  Organs  Organ Systems  Organisms
Cell: basic unit of structure and function in living things. Cells have ways
of communicating and working with each other.
Specialized cells: a cell that is uniquely suited to perform a particular
function/job (muscle cell, White Blood Cell, heart cell, nerve cell, etc)
Tissues: a group of cells that perform a single function (muscle tissue)
Organs: a group of tissues that work together to perform a function
(stomach, skin, heart, liver,
Organ system: a group of organs that perform closely related functions.
We have 11 organ systems in our body – Digestive System, Nervous
System, Cardiovascular System, Muscular System, Skeletal System, Etc
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Using 1-3 words describe role of each organelle,
and draw a picture of its structure:
Cell Membrane:
Cell Wall:
Nucleus:
Nucleolus:
Ribosomes:
Chromatin/Chromosomes:
Cytoplasm:
Rough ER:
Smooth ER:
Golgi Body/Apparatus:
Lysosome:
Vacuole:
Mitochondria:
Chloroplast:
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LAB:
On one side of paper, draw a cell going through
passive transport of sugar across its membrane.
Include and label: lipids, proteins, sugar, high
concentration and low concentration, arrows.
On the other side of paper, draw a cell going
through active transport of sugar across its
membrane. Include and label: lipids, proteins,
sugar, high concentration and low concentration,
arrows and ENERGY.
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