AHSGE Review
J. Pollock
Spring 2007
Cell Structure and Function
What is homeostasis?
Homeostasis is the maintenance of the internal stability of a cell, organism, or population in its environment.
It is a characteristic of all living things. It allows organisms to survive in
extreme conditions.
How do cells maintain homeostasis?
The plasma membrane determines what will get in or stay out.
It is made of a combination of phospholipids and proteins.
Materials can enter and leave the cell through active or passive transport.
Compare active and passive transport. Active Transport
proton pumps, sodium-potassium pumps, coupled channels, endocytosis, and exocytosis
uses energy
Passive Transport does not use energy diffusion, osmosis, or
facilitated diffusion
Passive Processes
Diffusion is movement from high concentration to low concentration areas.
Osmosis a form of diffusion that involves polarity of molecules.
Facilitated diffusion involves transfer of specific particles through the cell membrane using channel proteins.
Passive Processes
Active Processes
Proton pumps move protons through internal plasma membranes of mitochondria and chloroplasts.
Sodium-potassium pumps move potassium into the cell and sodium out using ATP. It is the most important energy-using process in the human body.
Coupled channels use a sodium-potassium pump and a second channel to move sugar molecules.
Active Processes
Compare exocytosis and endocytosis. Exocytosis
dumping of excretions or waste
uses waste vaculoes to push matter outside cell
also involved in secretion of hormones
Endocytosis particle engulfed by
cell membrane requires energy pinocytosis
liquid with dissolved molecules
phagocytosis another cell or
fragment of organic matter
Endocytosis and Exocytosis
What are the functions of carbohydrates in cellular activities?
Carbohydrates are composed of hydrogen, carbon, and oxygen.
They store and transport energy for cellular activities.
Polysaccharides are linked carbohydrates that store and convert sugars. Starch is an example.
Carbohydrates
What are the functions of lipids in cellular activities?
Lipids do not dissolve in water. They are fats, oils, and waxes. They are components of the cell membrane and
store energy. Saturated fats contain the maximum number of
carbon and hydrogen molecules. Unsaturated fats have carbon-carbon double bonds
and contain fewer hydrogen atoms. Steroids are the hormones that control body
activities.
Lipids
What are the functions of proteins in cellular activities? Proteins have important structural functions. Collagen makes up skin, ligaments, tendons, and
bones. Enzymes assist in the chemical reactions of
metabolism. They speed up and slow down reactions without being used up themselves.
Amino acids are the building blocks of proteins. They make long chains called polypeptides.
Proteins also function as hormones and neurotransmitters to signal cells and regulate activity.
Proteins
What are the functions of nucleic acids in cellular activities?
Nucleic acids are long chains of nucleotides (5-carbon sugar with phosphate group and organic base).
They serve to store hereditary information that will later form new proteins.
Deoxyribonucleic acid (DNA) stores information in cells.
Ribonucleic acid (RNA) helps in the making of proteins.
DNA and RNA
Compare the reactions of plant and animal cells in various types of solutions.
Hypotonic Isotonic Hypertonic
Soluteconcentration in
environment lowerthan in cell
Soluteconcentration in
environment equalto that in cell
Soluteconcentration in
environmentgreater than in cell
Water moves intocell
Equal movement ofwater into and out
of cell
Water moves out ofcell
Cell bursts Volume maintained Cell shrivels
Explain how environment affects cellular activity. Protein receptors on the cell surface
signal the cytoplasm about the conditions of the cell’s environment.
The cytoplasm responds to the surface whether or not particles should be allowed into the cell.
The cell attempts to maintain homeostasis at all times.
How does fluid pressure affect biological systems?
Hypotonic Isotonic Hypertonic
Soluteconcentration in
environment lowerthan in cell
Soluteconcentration in
environment equalto that in cell
Soluteconcentration in
environmentgreater than in cell
Water moves intocell
Equal movement ofwater into and out
of cell
Water moves out ofcell
Cell bursts Volume maintained Cell shrivels
Describe the process of photosynthesis. Photosynthesis forms a continuous cycle
with cellular respiration. Carbon atoms are pulled from carbon
dioxide in the air and used to form carbohydrates and other organic compounds.
Hydrogen is extracted from water molecules, and oxygen is released as a by-product.
Describe the process of cellular respiration. Cellular respiration is the reverse of
photosynthesis. Hydrogen molecules from carbohydrates
are joined with oxygen to form water. Carbohydrates and organic molecules are
chemically broken down and used as energy sources.
Carbon dioxide is released as a by-product.
Photosynthesis and Cellular Respiration
What are the parts of the cell?
Who contributed to the cell theory? Robert Hooke discovered cells in 1665 while looking
at cork through a microscope. Anton van Leeuwenhoek discovered single-celled
protists in 1675 looking at pond water. In 1838 Matthias Schleiden determined that cells
compose all parts of a plant. Theodor Schwann applied this discover to animals one year later.
Rudolph Virchow determined that cells come only from other cells in 1858.
All of these individuals contributed to the cell theory.
Cell Theory
All living things are composed of one or more cells.
In organisms, cells are the basic units of structure and function.
Cells are produced only from existing cells.
Characteristics of Cells
Cell membrane or plasma membrane to separate contents from environment
cytoplasm (everything except genetic material)
ability to reproduce possession of genetic material
Compare prokaryotic and eukaryotic cells. Prokaryotes
single cell organisms no nucleus no internal membrane-
bound compartments very small few specialized
functions genetic material single,
circular molecule
Eukaryotes contain nucleus specific membrane-
bound organelles more complex function most multicellular contain highly
specialized cells
How are cells observed?
Cells are too small to be observed with the naked eye.
Cells must be small to accommodate the exchange of materials with the environment and the distribution of materials.
They are viewed using microscopes.
How do cells become more advanced structures? Single cells cluster into multicellular
organisms. Cells become more specialized, and a few
cells take over activities once performed by all cells.
Scientists believe eukaryotes developed from prokaryotes (bacteria) that were enveloped by larger cells. They eventually lost their ability to function separately.
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