Characteristics of Living Things

A. All living things must maintain homeostasis.

1. To maintain homeostasis, organisms carry out the same basic life functions: nutrition, excretion, transport, respiration, growth, synthesis and regulation. Know these terms!
2. All life processes make up an organism’s metabolism.
3. Failure to maintain homeostasis causes disease and death.

B. Nutrition:

1. Autotrophs (plants) make their own food, while heterotrophs eat other organisms.
2. Photosynthesis is carried out by plants, algae and blue-green bacteria (autotrophs). It takes the radiant energy of the sun and puts it in the bonds of sugar molecules. Photosynthesis occurs in the chloroplast of plant cells.

  • Plants have stomates, small holes in their leaves that let them exchange the gasses used in photosynthesis.
  • Guard cells open and close the stomates.

C. Respiration: Organisms get energy by breaking the bonds of sugar molecules. The released energy is used to make a molecule of ATP, which gives all organisms their energy.

1. Aerobic respiration requires oxygen, and yields more ATP (energy) for a molecule of sugar than anaerobic (no oxygen) respiration.
2. When humans are forced to get energy from anaerobic (no oxygen) respiration, we produce lactic acid that damages muscles (“the burn” you feel during exercise).
3. Photosynthesis and Aerobic Respiration are opposite reactions! They are also important in cycling oxygen, carbon, hydrogen and water through the environment.

D. Transport:

1. Diffusion: movement of molecules from high concentrations to low concentrations. Requires no energy (passive transport).
2. Active Transport requires the use of energy, usually moving molecules from a low concentration to a high concentration (against the flow of diffusion).
3. Osmosis is the diffusion of water into or out of the cell. If water diffuses into the cell, the cell swells (get larger) and may burst. If it loses water (being put in salt water for example) it will shrivel up.

E. Regulation: coordination and control of other life functions.

1. A stimulus is a change in the environment that you respond to.
2. A neuron is a nerve cell.
3. An impulse is the electrical signal carried by the nerves. Neurotransmitters are chemicals that help carry the impulse.
4. A hormone is a chemical signal secreted by different glands in the body. Examples of hormones include insulin, adrenaline, testosterone and estrogen.
5. Receptor molecules are proteins on the surface of the cell membrane that receive signals from the nervous and endocrine system. These are needed for your cells to communicate and work together.

F. Chemistry

1. The most common elements in living things are (in order) Carbon, Hydrogen, Oxygen and Nitrogen (CHON).
2. Organic Compounds have Carbon AND Hydrogen (ex: C6H12O6 is organic, H2O, CO2, and NO3 are not).
3. Carbohydrates are sugars and starches. All carbohydrates are made from simple sugars (like glucose) and they supply energy.
4. Lipids store energy and include fats, oils and waxes. They are made from fatty acids and glycerol.
5. Proteins are made from amino acids. Proteins also make hormones and many body and cell structures, so as far as your body is concerned, proteins are by far the most important of these three organic molecules.

a. It is the SHAPE of proteins (enzymes, hormones and antibodies) and how they fit together that determines what proteins can do.

b. Four specific jobs of proteins:

1) make enzymes
2) make receptor molecules on the cell membrane. These are used to receive chemical messages (like hormones).
3) make antibodies
4) make hormones

c. Enzymes are catalysts– they affect the rates of chemical reactions.

1) lock and key model– one type of enzyme fits one type of molecule. Change its shape and the enzyme will no longer work.
2) very high temperatures cause proteins and enzymes to lose their shape so that they no longer work properly (denature). This is why high fevers are dangerous.

6. pH: The pH scale measure the strengths of acids and bases. A low pH (0-6.9) is a acid, a high pH (7.1-14) is a base, and 7 is neutral (water).

G. Cells- Cells are the basic unit of life. All living things (except viruses) are made of cells.

1. You must know the cell theory (All living things are made of cells. Cells come from preexisting cells).
2. You must know the differences between plant and animal cells- cell wall and chloroplasts in plants and centrioles (animals).
3. You must know the following organelles and what they do: cell membrane (surrounds cell), cell wall (surrounds plant cells), nucleus (DNA storage), chloroplast (photosynthesis site), cytoplasm (fluid inside cell), ribosome (site of protein sythnesis), vacuole (storage), mitochondria (ATP synthesis).
4. The cell membrane is made of lipids and proteins.

  • The cell membrane is needed to control movement into and out of the cell
  • It shows selective permeability – that is only some molecules can pass through it (typically small molecules like water and oxygen).
  • Large molecules (like starch or protein) need to be moved by active transport.

H. Classification-

1. Organisms are classified mostly by evolutionary history. Those with common ancestors are grouped together.
2. Kingdoms are large groups of related organisms (fungi, bacteria, protists, animals, plants).
3. A species is able to successfully reproduce amongst its members.
4. A scientific name is made up of an organism’s Genus and species. The most similar genes are found between animals of the same Genus.

Maintaining Homeostasis in the Human Body:

A. Organization:

1. Cells are specialized into tissues.

a. Tissues are groups of cells specialized to do certain jobs such as muscle tissue and nerve tissue.
b. Specialization or differentiation occurs because only some genes in the nucleus of a cell are “turned on”. Almost every cells has a complete set of genes, but on those needed for the cells particular job are active.

2. Tissues work together to form organs (heart, lungs, kidney).
3. Organs work together in organ systems (digestive system, nervous system, etc).

B. Digestive System:

1. Food is broken down so that it is small enough to enter the body tissues/cells.
2. The digestive system is a one way passage through the body that includes the mouth, stomach and intestines.
3. Food is moved through the digestive system by muscular contractions (peristalsis) in the esophagus, stomach and small intestines.
4. Food is broken down mechanically and chemically. Chewing food is mechanical digestion and chemical digestion is done by enyzmes.
5. The large intestines absorbs water while waste moves through it.

C. Transport/Circulatory System.

1. Moves material (water, nutrients, hormones, wastes) through the body.
2. Red blood cells carry oxygen and are round in shape. White blood cells fight disease and are large with nuclei.
3. Plasma is the fluid of the blood. It transports everything except oxygen.
4. Platelets clot the blood and are quite small.

D. Immune System:

1. The job of the immune system is to protect the body against pathogens.

a. Types of pathogens include viruses, bacteria, and parasites.

2. White blood cells are the main components of the immune system. Different white blood cells have different roles.
3. Antigens such as pathogens, foreign tissues and toxic chemicals cause an immune response. Antibodies are proteins made by white blood cells to attack antigens. Each antibody attacks a specific antigen as determined by its shape.
4. Blood type O is a universal donor; type AB is the universal acceptor.
5. A vaccine is an injection of a dead or weakened pathogen. This causes the body to make antibodies against that pathogen. Vaccines only prevent diseases. They are not cures.
6. Antibiotics are drugs used to stop infections by bacteria. Antibiotics will not work against viruses.

E. Respiratory System:

1. Physical respiration (breathing) provides oxygen needed for chemical respiration (which releases energy from sugar).
2. The diaphragm is the muscle that allows breathing to occur.
3. You breathe faster when you exercise because CO2 builds up in the blood (not when you need oxygen).
4. The alveoli are very important because it is here that the oxygen enters the blood and CO2 leaves. The alveoli look like microscopic sacs surrounded by capillaries.

F. Excretory System:

1. Removes metabolic waste from your body.
2. Your body excretes salt, water, urea and CO2.
3. Lungs excrete CO2 and water and the skin excretes sweat.
4. The kidneys filter waste from blood and reabsorb nutrients.
5. The liver filters toxins and dead red blood cells from the blood.

G. Skeletal Muscle System

1. Know the function of bones, bone marrow, cartilage, tendons (muscle to bone) and ligaments (bone to bone).
2. Muscles only pull and must work in pairs.

H. The Nervous System

1. The nervous system regulates your body along with the endocrine system.
2. Know the three parts of the brain and what they do: cerebrum (thinking), cerebellum (balance), medulla (involuntary functions).
3. The spinal cord controls reflexes and brings impulses from the nerves to the brain.
4. To send impulses between nerve cells, the first nerve cell secrete neurotransmitters that move across the synapse and attach to receptor molecules on the second nerve cell.

I. Endocrine System:

1. Regulates the body along with nervous system, but slower but with longer lasting effects.
2. The pancreas makes insulin and glucagon which control blood sugar.
3. Adrenal glands make adrenaline when the body is under stress.
4. Testosterone (male), estrogen and progesterone (female) are the sex hormones.
5. Hormone levels are controlled by negative feedback.

J. Interaction between Systems:

Be able to explain how different systems of the body work together to maintain homeostasis.

  • Nutrients from the digestive system are transported to cells by the circulatory system.
  • Wastes from respiration are removed by the excretory system.
  • The nervous and endocrine systems work together to control the body.


A. Basically states that modern species evolved from earlier, different species and share a common ancestor. The less differientiation between two organisms the more recently they evolved apart.

B. Charles Darwin proposed that natural selection is the mechanism that causes species to change. The basic steps in natural selection are:

1. Overproduction of offspring with a variation of genes.
2. Competition for limited resources.
3. Survival of the fittest and reproduction OR death.

C. Organisms that are better adapted to their environment and able to reproduce successfully are considered “fit”.

  • Unfit organisms die, and their traits are eventually removed from the gene pool.
  • Evolutionary fitness has nothing to do with physical fitness. Stronger is not always better.

D. Evolution is usually driven by a change in the environment.

E. To evolve, variations must exist in a species BEFORE the environment changes. They do not get a trait just because it is needed.

F. Variations exist primarily as the result of sexual reproduction and mutation.

G. Species with more variation are better able to survive environmental changes.

H. Gradualism is a theory that says change occurs slowly. Punctuated equilibrium is a theory that says evolution happens in quick spurts. The closer two species are together on the evolution tree, the closer they are related.

I. Creation of new species usually requires geographic isolation which eventually results in reproductive isolation. The greater the isolation from the original population, the more a species will evolve.

J. Evidence in support of evolution comes from the fields of geology (fossil record and radioactive dating), genetics, biochemistry, anatomy and embryology (among others).


What You Absolutely Need to Know to Pass the Regents