NEX EXAM STUDY GUIDE
SCIENCE
BIO
Cell Structure and Function
The cell is the basic unit of life. Cells vary in complexity, but all cells have
cytoplasm (the fluid inside the cell), DNA (deoxyribonucleic acid, the
molecule that contains directions for making proteins), ribosomes (the
structures that translate the code in DNA to make proteins), and a plasma
membrane (the barrier that surrounds the cell). The plasma membrane is
selectively permeable, or semipermeable, which means that it only allows
certain materials to enter the cell. The space between cells contains fluid
known as interstitial fluid.
The Cell
The structures that make up a cell are known as organelles (“little organs”).
They each carry out an important cellular process. Organelles involved in
energy acquisition are chloroplasts and mitochondria. Chloroplasts are
found in plants and other organisms that can carry out photosynthesis.
They capture solar energy and use it to make food in the form of glucose.
Glucose is broken down in the mitochondria, releasing energy in the form
of adenosine triphosphate (ATP). Organisms such as plants, bacteria, and
fungi have a cell wall that supports and protects the cell. Other organelles
include the vacuole, which stores water, food, or waste, and the lysosome,
which breaks down waste.
The Nucleus
Complex cells contain a nucleus that stores DNA. The code in DNA is used
to make proteins that carry out various functions. The endoplasmic
reticulum (ER) typically surrounds the nucleus, and helps in protein
synthesis. Proteins then travel to the Golgi complex, which packages and
modifies proteins to be used either inside or outside the cell.
Cell Division
Cells divide to create more cells for growth, tissue repair, or reproduction.
Each new cell needs a complete copy of the original DNA, since that
contains all the directions for making new cell parts.
,Mitosis is the division of nuclear material that produces two identical
“daughter” cells from an original “parent” cell. In preparation for mitosis,
the parent cell makes a copy of its DNA. The DNA then condenses from
chromatin (loosely coiled strands) into chromosomes (tightly wrapped and
organized). The chromosomes are separated from each other so that each
cell has a copy. During meiosis, the chromosomes divide twice to create
sex cells that have only half the original DNA of the parent cell. During
fertilization, two sex cells will combine to make a zygote, the first cell of a
new organism.
Organization Levels
Some organisms exist as a single cell, which must carry out all of the
functions of life. In multicellular organisms, cells often differentiate and
become specialized in carrying out specific tasks. The cells of multicellular
organisms are organized into various levels.
Tissue
A tissue is a bundle of cells that perform a similar function. Humans have
four main tissue types:
muscle tissue—This tissue is composed of flexible cells that contract and
relax to cause movement. The three types of muscle tissue are cardiac,
skeletal, and smooth.
nervous tissue—This tissue is made up of neurons and is found in the
brain, spinal cord, and other nerves.
connective tissue—This tissue serves to connect, anchor, and support
other tissues found throughout the body.
epithelial tissue—This tissue is made of stacked layers of cells and has a
role in protection, absorption, and secretion. The skin and the stomach
lining are made of this type of tissue.
Organ
A group of tissues that perform a particular function make up an organ.
Examples of organs in the human body include the heart, stomach, brain,
uterus, and femur. Each of these is composed of various tissue types that
work together to help that organ carry out its job.
Organ System
,Organs are typically part of an organ system, a larger network of organs
that all work together to perform a specific function. The heart, for
example, is part of the circulatory system, which delivers nutrients and
removes waste products from all of the body’s tissues. The femur is part of
the skeletal system, which supports and protects the body and works with
the muscular system to produce movement.
Organism
All of the organ systems of the body combine to create the organism, an
individual living thing. Complex organisms, such as humans, are organized
into levels as described in this section. Other organisms, such as fungi,
algae, and sponges, may only have specialized cells or tissues that carry
out their life functions.
Cell Functions
One important function in cells is the passage of materials in and out of
the cell. This occurs through the cell membrane, the flexible barrier
surrounding the cell. It has special components that aid in this essential
function.
Methods of Transport
The transport of materials into and out of the cell can be differentiated
based on whether the cell uses energy to move materials. In passive
transport, materials cross the membrane without the use of energy.
Diffusion and osmosis are types of passive transport. In active transport,
the cells must use energy to move substances through the membrane.
Diffusion
Diffusion is the movement of substances from high concentration to low
concentration. They continue diffusing until the concentration on both
sides of the membrane is the same. Some substances can pass directly
through the membrane itself. Some substances, such as glucose, must use
special passageways in the membrane.
Osmosis
Osmosis is the diffusion of water. The movement of water through the
membrane depends on the concentration of solutes inside and outside of
the membrane. Terms related to differences in concentration include:
, isotonic—Concentration of solutes inside and outside the cell are equal. In
this case water will move into and out of the membrane equally, and there
is no net movement of water.
hypertonic—Concentration outside the cell is greater than inside the cell.
Water will move out of the cell until isotonic conditions are reached.
hypotonic—Concentration outside the cell is less than inside the cell. Water
will move into the cell until isotonic conditions are reached.
Filtration
In general terms, filtration is the passage of certain substances through a
barrier under pressure. In cells, filtration occurs when substances pass
through the cell membrane due to pressure from an outside source. This is
a type of passive transport. An example in humans would be kidney cells
filtering toxins from blood, aided by the pressure applied by the
cardiovascular system.
Cellular Respiration
Cellular respiration is the chemical reaction that breaks down glucose for
energy. Aerobic respiration occurs when oxygen is available. After oxygen
is delivered to individual cells, it is used to break down glucose (a food
molecule) for energy. The waste products of this reaction are water and
carbon dioxide. If needed, cells can break down glucose without oxygen in
a process called anaerobic respiration. It is not nearly as efficient as
aerobic respiration, and it produces lactic acid as a byproduct.
Genetics
Genetics is the study of how traits are inherited and expressed. In this
section, you will learn about some of the patterns and rules of inheritance,
as well as the cellular mechanism that turns a sequence of DNA into a
physical trait.
Basic Genetic Theory
A gene is a section of DNA that codes for a specific trait. One version of a
gene is known as an allele. Each organism has two copies of each gene,
one inherited from the mother and one from the father. If the two alleles
are identical, they are homozygous for that trait. If they are different, they
SCIENCE
BIO
Cell Structure and Function
The cell is the basic unit of life. Cells vary in complexity, but all cells have
cytoplasm (the fluid inside the cell), DNA (deoxyribonucleic acid, the
molecule that contains directions for making proteins), ribosomes (the
structures that translate the code in DNA to make proteins), and a plasma
membrane (the barrier that surrounds the cell). The plasma membrane is
selectively permeable, or semipermeable, which means that it only allows
certain materials to enter the cell. The space between cells contains fluid
known as interstitial fluid.
The Cell
The structures that make up a cell are known as organelles (“little organs”).
They each carry out an important cellular process. Organelles involved in
energy acquisition are chloroplasts and mitochondria. Chloroplasts are
found in plants and other organisms that can carry out photosynthesis.
They capture solar energy and use it to make food in the form of glucose.
Glucose is broken down in the mitochondria, releasing energy in the form
of adenosine triphosphate (ATP). Organisms such as plants, bacteria, and
fungi have a cell wall that supports and protects the cell. Other organelles
include the vacuole, which stores water, food, or waste, and the lysosome,
which breaks down waste.
The Nucleus
Complex cells contain a nucleus that stores DNA. The code in DNA is used
to make proteins that carry out various functions. The endoplasmic
reticulum (ER) typically surrounds the nucleus, and helps in protein
synthesis. Proteins then travel to the Golgi complex, which packages and
modifies proteins to be used either inside or outside the cell.
Cell Division
Cells divide to create more cells for growth, tissue repair, or reproduction.
Each new cell needs a complete copy of the original DNA, since that
contains all the directions for making new cell parts.
,Mitosis is the division of nuclear material that produces two identical
“daughter” cells from an original “parent” cell. In preparation for mitosis,
the parent cell makes a copy of its DNA. The DNA then condenses from
chromatin (loosely coiled strands) into chromosomes (tightly wrapped and
organized). The chromosomes are separated from each other so that each
cell has a copy. During meiosis, the chromosomes divide twice to create
sex cells that have only half the original DNA of the parent cell. During
fertilization, two sex cells will combine to make a zygote, the first cell of a
new organism.
Organization Levels
Some organisms exist as a single cell, which must carry out all of the
functions of life. In multicellular organisms, cells often differentiate and
become specialized in carrying out specific tasks. The cells of multicellular
organisms are organized into various levels.
Tissue
A tissue is a bundle of cells that perform a similar function. Humans have
four main tissue types:
muscle tissue—This tissue is composed of flexible cells that contract and
relax to cause movement. The three types of muscle tissue are cardiac,
skeletal, and smooth.
nervous tissue—This tissue is made up of neurons and is found in the
brain, spinal cord, and other nerves.
connective tissue—This tissue serves to connect, anchor, and support
other tissues found throughout the body.
epithelial tissue—This tissue is made of stacked layers of cells and has a
role in protection, absorption, and secretion. The skin and the stomach
lining are made of this type of tissue.
Organ
A group of tissues that perform a particular function make up an organ.
Examples of organs in the human body include the heart, stomach, brain,
uterus, and femur. Each of these is composed of various tissue types that
work together to help that organ carry out its job.
Organ System
,Organs are typically part of an organ system, a larger network of organs
that all work together to perform a specific function. The heart, for
example, is part of the circulatory system, which delivers nutrients and
removes waste products from all of the body’s tissues. The femur is part of
the skeletal system, which supports and protects the body and works with
the muscular system to produce movement.
Organism
All of the organ systems of the body combine to create the organism, an
individual living thing. Complex organisms, such as humans, are organized
into levels as described in this section. Other organisms, such as fungi,
algae, and sponges, may only have specialized cells or tissues that carry
out their life functions.
Cell Functions
One important function in cells is the passage of materials in and out of
the cell. This occurs through the cell membrane, the flexible barrier
surrounding the cell. It has special components that aid in this essential
function.
Methods of Transport
The transport of materials into and out of the cell can be differentiated
based on whether the cell uses energy to move materials. In passive
transport, materials cross the membrane without the use of energy.
Diffusion and osmosis are types of passive transport. In active transport,
the cells must use energy to move substances through the membrane.
Diffusion
Diffusion is the movement of substances from high concentration to low
concentration. They continue diffusing until the concentration on both
sides of the membrane is the same. Some substances can pass directly
through the membrane itself. Some substances, such as glucose, must use
special passageways in the membrane.
Osmosis
Osmosis is the diffusion of water. The movement of water through the
membrane depends on the concentration of solutes inside and outside of
the membrane. Terms related to differences in concentration include:
, isotonic—Concentration of solutes inside and outside the cell are equal. In
this case water will move into and out of the membrane equally, and there
is no net movement of water.
hypertonic—Concentration outside the cell is greater than inside the cell.
Water will move out of the cell until isotonic conditions are reached.
hypotonic—Concentration outside the cell is less than inside the cell. Water
will move into the cell until isotonic conditions are reached.
Filtration
In general terms, filtration is the passage of certain substances through a
barrier under pressure. In cells, filtration occurs when substances pass
through the cell membrane due to pressure from an outside source. This is
a type of passive transport. An example in humans would be kidney cells
filtering toxins from blood, aided by the pressure applied by the
cardiovascular system.
Cellular Respiration
Cellular respiration is the chemical reaction that breaks down glucose for
energy. Aerobic respiration occurs when oxygen is available. After oxygen
is delivered to individual cells, it is used to break down glucose (a food
molecule) for energy. The waste products of this reaction are water and
carbon dioxide. If needed, cells can break down glucose without oxygen in
a process called anaerobic respiration. It is not nearly as efficient as
aerobic respiration, and it produces lactic acid as a byproduct.
Genetics
Genetics is the study of how traits are inherited and expressed. In this
section, you will learn about some of the patterns and rules of inheritance,
as well as the cellular mechanism that turns a sequence of DNA into a
physical trait.
Basic Genetic Theory
A gene is a section of DNA that codes for a specific trait. One version of a
gene is known as an allele. Each organism has two copies of each gene,
one inherited from the mother and one from the father. If the two alleles
are identical, they are homozygous for that trait. If they are different, they
