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Characteristics of living organisms
• Are highly organized, complex entities
• Are composed of 1 or more cells
• Contain a blueprint of their characteristics (a genetic
program encoded in DNA)
• Acquire and use energy
• Carry out and control numerous chemical reactions
• Grow in size and change in appearance and abilities
• Maintain a fairly constant internal environment
(homeostasis)
• Reproduction
• Respond to changes in their environments
• May evolve into new types of organisms
Six kingdoms of life are recognized
Figure 1.6 The development of a scientific theory rests on a five-tiered foundation. The basic tier comprises
observations made of natural phenomenon. Observations lead to questioning. Does what we observe fit with
our expectations of what should occur? Especially if the answer is no, observations and questions lead to
tentative, testable alternative explanations, that is, to hypotheses. Now follows intense testing, conducted
ideally by both the framer of the hypothesis and others. Testing may lead to refinement of they hypothesis
and an eventual explanation of the hypothesis. Only after extensive testing and widespread acceptance
within the community of scientists can an idea in science reach the level of theory.
Six elements make up 99% of all living things
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Carbon
Hydrogen
Oxygen
Nitrogen
Phosphorus
Sulfur
There are four organic macromolecules (or
polymers) that are made from simple
building blocks (or monomers)
• Carbohydrates also known as
Polysaccharides (monosaccharides)
• Lipids (fatty acids)
• Proteins (amino acids)
• Nucleic Acids (nucleotides)
Carbohydrates (polysaccharides) are built from
simple sugars (monosaccharides)
Lipids are
built from
fatty acids
Proteins are
built from
amino acids
Nucleic Acids
(DNA and RNA)
are built from
nucleotides
Cells and Microscopes
• The cell was first named by Robert Hooke in 1665. He
remarked that it looked strangely similar to cellula or
small rooms which monks inhabited, thus deriving the
name. However what Hooke actually saw was the non
living cells from a cork (cork) . Hooke's description of
these cells was published in Micrographia. The cell walls
observed by Hooke gave no indication of the nucleus
and other organelles found in most living cells. The first
man to witness a live cell under a microscope was Anton
Van Leeuwenhoek, who in 1674 described the algae
Spirogyra and named the moving organisms
animalcules, meaning "little animals".
Cell Theory
• All organisms are composed of one or
more cells.
• The cell is the fundamental unit of life.
• Cells arise from preexisting cells.
 Credit for developing Cell Theory (1839-1858) is usually
given to three scientists, Theodor Schwann, Matthias
Jakob Schleiden, and Rudolf Virchow.
Examples of two
eukaryotic cells
Organelles and their functions
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Nucleus-control center of the cell
Nucleolus-synthesis of ribosomes
Endoplasmic recticulum-membrane tunnel system where many proteins and lipids
are made
Golgi bodies-modification, packaging, and distribution center for proteins
Ribosomes-sites of protein synthesis
Vesicles-storage and transport of cellular products and raw materials
Central vacuole-water, waste and food storage
Lysosomes-involved with intracellular digestion
Mitochondria-power pack of the cells; site of aerobic respiration; ATP formation
Chloroplasts-site of photosynthesis; production of food
Centrioles- facilitate division of the genetic material in the nucleus during cell
division and organization of the cytoskeleton
Cytoskeleton-system of microfilaments, intermediate filaments and microtubules
that provide internal cellular structure
Plasma membrane-regulates the movement of substances into and out of the cell
Flagella & cilia- plasma membrane projections; involved with cell movement
Cell wall-provides structural support and protection to the cell
Most biologists view viruses as
non-living as they are acellular.
How do molecules get into and
out of cells?
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Bulk flow
Diffusion
Osmosis
Facilitated diffusion (passive transport)
Active transport
Endocytosis and Exocytosis
Figure 4.17 Osmosis is the net diffusion of water across a selectively
permeable membrane. In this illustration, green protein molecules cannot
cross the membrane, but blue water molecules can. Water will move in both
directions, but there is a net movement from the left compartment of the
chamber to the right compartment. The left compartment is said to be
hypotonic relative to the right compartment. Conversely, the right
compartment is hypertonic relative to the left compartment.
Figure 4.19 Membrane transport involves specific transport proteins that are
embedded in the phospholipid bilayer. (a) Ion channels must be opened (step 1) before
the ion can pass through (step 2). Channels can be opened or closed in response to
various kinds of messages received by the cell. (b) In facilitated diffusion, substances
enter a protein carrier and change the shape of the protein (step 1). After the solute is
moved across the membrane, the protein resumes its original shape (step 2). For both
ion channels and facilitated diffusion, substances move from high to low concentration.
No energy is needed.
Figure 4.20 Active transport moves substances from low to high concentration-against their concentration gradient. In this illustration, sodium (Na+) outside of the
cell attaches to the protein (step 1). The protein gets energy when the ATP donates
a phosphate to the protein (step 2). This changes the shape of the protein and
pushes the sodium across the membrane (step 3). Potassium (K+) from outside the
cell binds to the altered protein (step 4) and is expelled into the cell when the
protein resumes its original shape (step 5).
Figure 10.7 Adenosine triphosphate (ATP) is an important nucleotide
in cellular metabolism. When the terminal phosphate on ATP is cleaved
leaving ADP and a free phosphate, a small packet of energy is
released that can be used by the cell to fuel metabolic processes.
Figure 4.21 Cells can transport substances in bulk across their membranes.
(a) In endocytosis, the membrane engulfs the substances and the movement is
into the cell. (b) In exocytosis, the movement is out of the cell.
Figure 12.16 (a) The
kidney, which has
about a million
nephrons. (b) The
nephron, which
includes a vascular
portion (the
glomerulus and the
peritubular capillaries,
in red and blue) and a
tubular portion (in
gold).