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Life Science


The cell is the basic unit of structure of all living things, and sometimes, the cell is a total living organism in and of itself. Cells reproduce in two different ways. The first way is called meiosis and the second way is called mitosis.

Meiosis is the reproduction of sex cells.

Mitosis is the reproduction of somatic (body) cells.

There are two different kinds of cells: prokaryotic and eukaryotic. Prokaryotic cells do not have a nuclear membrane surrounding its organelles. For example, bacteria and blue-green bacteria are prokaryotes. Eukaryotic cells are most cells that make up all living organisms.

Homeostasis is a term that means cell balance or equilibrium. While there is a lot of molecular movement in and out of the cell, limits must be maintained in order to keep the proper cell equilibrium, or homeostasis.

DNA, deoxyribonucleic acid is the basic life chemical. It is a nucleic acid that contains the genetic instructions or blueprint that specify the biological development of all forms of life. DNA is responsible for the genetic propagation of most inherited traits


Reproduction is necessary to the continuation of life. During reproduction, DNA is replicated and transmitted to the offspring. Reproduction is not always sexual, there is also asexual reproduction. This happens when a cell spits and makes a copy of itself and is used by single celled or lower life organisms.

Proteins are the energy source for every cell. Every living thing needs carbon, nitrogen, hydrogen and oxygen to survive and to construct organic molecules. Protein is the supplier of nitrogen to support life within a cell or organism. The smallest unit of a protein is called an amino acid. The process of breaking down a protein into an amino acid is called protein degradation. Protein synthesis is the process through which amino acids are combined to make peptide chains to reconstruct proteins.


In 1809 a man named Jean Lamarck proposed a theory regarding the evolution of organisms. He said that organisms evolve in response to their environment by acquiring traits that help them live and adapt to their changing surroundings. In 1859, Charles Darwin came up with a different idea that said that individual traits of organisms are inherited from the parents, and not acquired individually. Members of a species who acquire these different adaptive traits are more likely to survive. Darwin called this process his theory of natural selection. Thus, in biology, evolution is seen as the change in traits of living organisms over generations, including the emergence of new species.

An allele is an alternative form of the same gene. Since the 1940’s, evolution has been more specifically defined as a change in the frequency of alleles in a specific population from one generation to the next.

Species that have not had these adaptive traits have become extinct over time due to changes in atmospheric content, climate, and environment. 

Fossils provide us with evidence that there were things living a long time ago. Fossils are usually found in sedimentary rock. The age of the fossils can be found by using a chemical process called carbon dating, in which radioactive isotopes are measured to see how much carbon is in the fossil.


What would Charles Darwin call the human process of breeding different dogs together in order to produce an offspring that combines the traits of the two different parents? For example, let’s say you bred a rat terrier for hunting with a golden retriever for size and disposition.

A. Natural selection

B. Clever human antics

C. Artificial selection

D. Negative selection

Answer: C. Since natural selection describes the above process happening without human intervention, intervention would thus make it artificial. Negative selection is the term for artificial selection with a negative or undesired outcome. This question tests your ability to analyze. The answer was not directly stated in a passage or in the information given. You had to figure out what the opposite of natural selection would be and pick the most appropriate answer.

Read the following chart and answer the question below:

Geological Evolution

Precambrian Era: Origination of unicellular organisms

Paleozoic Era: Origination of multicellular animals and ferns

Mesozoic Era: Origination of reptiles, some early mammals, birds, and flowering plants

Cenozoic Era: The radiation of mammals, reptiles, birds and flowering plants occurred


If the Mesozoic Era saw the origination of mammals, reptiles, birds and flowering plants, which of the following would have flourished at that time?

A. Rabbits

B. Orangutans

C. Dinosaurs

D. Squirrels

E. Zebras

Answer: C. Dinosaurs are reptiles. And of all the species mentioned in the chart, were the most prolific in the Mesozoic period. None of the other answer options would have existed at the time.


These are the 11 main systems that make up the human body


Eating and digesting


Urine and filtering






Muscles and strength


Nerves and brain


Breathing and lungs


Genitalia and procreation






Disease fighter, lymphatic system

 Example: The Digestive System

Read the following paragraph and answer the questions below:

The digestive system is responsible for the mechanical and chemical digestion of food that breaks it down into molecules to enter the cells. Mouth, teeth and tongue incite the process and saliva is added to help break down the food. Amylase, an enzyme, helps break down carbohydrates and starches. The esophagus is the passageway for food from the mouth to the stomach where more digestive enzymes and hydrochloric acid break down the proteins in the food. After the stomach churns the food, which is now a liquid, it moves into the small intestine where the villi moves it into the bloodstream. Here it is delivered throughout the cells of the body. Waste and unused food are carried to the large intestine where they mix with water and roughage and are excreted.

Question 1

1. Which of the following specifically helps to break down carbohydrates and starches in food?

A. amylase

B. villi

C. saliva

D. small intestine

E. hydrochloric acid

Answer: A

Question 2

2. Why does only some of the food move from the small intestine into the large intestine to be excreted?

A. Because the rest of it was churned up in the stomach

B. Because the rest of it is moved by the villa into the bloodstream to be distributed throughout the cells in the body

C. Because only water is excreted

D. Because the rest of the food remains in the stomach for further digestion

Answer: B. Both of these questions were comprehension questions. The skill being tested is the ability to read and understand the information given and then answer a question that requires full comprehension. At this point in the course, you should feel fairly comfortable answering this kind of question, as we have practiced it multiple times and it requires no outside information. If you are still having trouble, or if you have more trouble with one subject than another, it may be that you feel insecure or unprepared specifically about a subject matter. If so, study up on that subject and remember that the skill being tested is the same for any subject and you have the ability to do it!


The study of interactions between organisms and their environment is more commonly referred to as “ecology.” Ecology is made up of chains: the food chain, the energy chain, and the water chain. These chains link up to create and support life. Ecology is the foundation of all of life’s support systems.

The life on earth exists in a biosphere. There are individual biomes of land and water that are determined by climate. For example, there are two water biomes: freshwater and marine or saltwater. These different biomes support different kinds of life.

Example: Population growth

Read the following paragraph and answer the questions below:

The size of a population at any given time is determined by its growth rate. This is determined by birth rate, death rate, immigration and emigration. Natural disasters, food availability, and disease also have an effect on population. Also, overcrowding of organisms can spread disease, reduce the amount of food available and interfere with reproduction. In these circumstances, competition for an environment’s limited resources happens between members of the population and between different species in the same area. This kind of competition can limit population size as well.

Question 1

1. Which of the following is NOT a population inhibitor?

A. disease

B. overcrowding

C. birth

D. limited food

E. competition

Answer: C. While birth rate was listed above as being a determinant of population growth rate; it was not listed as necessarily having a positive or a negative effect. If the birth rate is high, it increases population, if it is low, it inhibits population. The answer choice, however, simply says “birth,” which is always increases population. This kind of question requires you to read the question and answer choices very carefully as the answer is given, but it is not quite as simple as it seems.

Click on the link below to move on to Lesson 3.

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