N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
6th Grade Science
Unit 8
Cells & Heredity
Spring 2006
CELLS AND HEREDITY
In this 6th grade unit, students will be exposed to a study of cells for the first
time. Students need to build a strong knowledge base on cells in the 6th grade
since this information will not be revisited in 7th or 8th grade and may appear on the
TAKS test. Students are not required to learn all of the organelles of a cell as
this will be covered in high school biology. They do learn some basic organelles and
should be able to differentiate between animal and plant cells. All 6th grade
students should be exposed to examination of cells through use of a microscope.
The relationship between structure and function is a unifying concept in science.
Throughout this unit, there should be an emphasis on this relationship. Structure
is the shape or material something is made of, and the function is the job that it
does. Students may need to be exposed to concrete examples when first learning
this concept. For example, the shape of the ear is shaped to collect and funnel
sound and a hummingbird’s beak is shaped to reach nectar within a flower. The
emphasis on the relationship between structure and function should continue as
students examine the different levels of organization of living things.
The 6th grade student will also study heredity as a part of this unit. They are to
identify some changes in traits that can occur over several generations through
natural occurrence and selective breeding. They should also be able to identify
cells as structures containing genetic material and interpret the role of genes in
inheritance. In previous grades, students learned that heredity is the study of
how parents pass their traits to offspring. The elementary student also
differentiated between inherited traits and learned characteristics.
Life Processes
The cell is the basic unit of living things that carries on functions to sustain life.
These functions are referred to as the basic life processes, and all living things
carry them out. These life processes allow us to distinguish between a living and
nonliving object. If any one of these processes is not present, then an object is
not classified as an organism. Students should examine these processes as they
lay the foundation for all of their studies in middle school life science studies,
including their unit on cells. The life processes are as follows:
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
6th Grade Science
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Unit 8
Cells & Heredity
Spring 2006
All living things are made of one or more cells.
All living things obtain and use energy.
All living things grow and develop.
All living things reproduce.
All living things respond to their environment.
Cells
Cells were not discovered until the 1600’s because they were too small to be seen,
and the microscope had not yet been invented. Robert Hooke was the first person
to observe cells, examining cork from a tree. The cork looked like it was made up
of tiny rooms, or cells. In Latin, cell means “tiny room.” Students will be exposed
to many different representations, pictures, or diagrams of cells throughout life
science studies. This provides the teacher with an excellent opportunity to discuss
the different models and identify their limitations. Many teachers also utilize the
“cell as a factory” conceptual model to assist their students in understanding the
functions of the various organelles.
All living things are composed of at least one cell. Organisms made up of only one
cell are referred to as unicellular. Organisms made up of many cells are called
multicellular. Large organisms, such as humans, have billions of cells. Students
might think that most organisms on Earth are multicellular. In fact, the majority
of organisms are microscopic, single-celled organisms such as bacteria, algae,
certain fungi, and protozoa.
Students should understand that even unicellular organisms carry out all of the life
processes. They have structures for obtaining food, movement to respond to their
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
2
N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
6th Grade Science
Unit 8
Cells & Heredity
Spring 2006
environment, etc. The following illustrates the cillia and flagella for mobility that
assist many unicellular organisms in their daily functions, such as obtaining food:
Cells grow and divide, producing more cells. Organisms grow by increasing the
number of cells, not by one cell getting larger. Cells take in nutrients that are used
to provide the energy required for cells to accomplish their various functions.
Cells are made of parts, collectively referred to as organelles, each of which
provides an important function within the cell. The 6th grade student should be
familiar with the cell theory which summarizes these concepts. The Cell Theory
has 3 components as follows:
1. All organisms are made of cells
2. The cell is the basic unit of life.
3. All cells come from other cells.
The three main parts of any cell are the nucleus, cytoplasm, and cell membrane.
These organelles are listed, along with some others, in the chart that follows. The
chart provides the basic information 6th grade students should master when
learning about the structure and function of cells. The chart also provides the
necessary information to differentiate between animal and plant cells.
Structure
Animal
vs. Plant
nucleus
usually found near cell
center
both
cell membrane
thin; surrounds cell
both
cytoplasm
watery gel throughout
cell
both
Function
command center
holds chromosomes
controls what enters
and leaves the cell
holds all of the other
parts of the cell
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Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
3
N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
6th Grade Science
Unit 8
Structure
mitochondrion
vacuole
chloroplast
cell wall
membrane-bound
organelle found in the
cytoplasm
 1, large in plant
cell
 several, small in
animal cell
green, contains
chlorophyll
thick, tough layer;
surrounds cell
Cells & Heredity
Animal
vs. Plant
Spring 2006
Function
both
provides the energy
needed for cell activities
both
for storage of food or
water
plant
plant
chlorophyll traps sunlight
for photosynthesis
provides support and
protection
Students should have the opportunity to examine a variety of different animal and
plant cell models. The illustrations that follow are very basic and this often
creates the misconception among students that all plant or animal cells look alike.
Students should understand cells come in many different shapes and sizes. For
example, nerve cells do not look like muscle cells. Muscle cells that move your arm
do not look like those that pump your heart. Cells located in different parts of an
organism are structured to function as a part of the tissues and organs they
support.
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
4
N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
6th Grade Science
Unit 8
Cells & Heredity
Spring 2006
Examples of cell variety:
Levels of Organization
Groups of cells work together to perform a particular job, forming tissue. There
are many types of tissues with which students will already be familiar. Examples
include blood and muscle tissue in animals and bark in woody plants. Students may
readily identify muscle tissue, but may not realize that blood is tissue as well.
Two or more tissues working together, to perform a particular function, form an
organ. Some organs with which students are already familiar include the heart,
lungs, stomach, and eyes in animals. Students will probably not think of their own
skin as an organ and may be surprised to learn that the skin is the larges human
organ. Roots, stems, and leaves are organs found in many plants.
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
5
N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
6th Grade Science
Unit 8
Cells & Heredity
Spring 2006
Organs generally do not work alone, joining with tissues and other organs to form
organ systems. An organ system is comprised of all of the organs that work
together to perform a particular function. At this level, students should not be
expected to identify the various organs that make up a particular organ system.
Humans have organ systems for digestion of foods, respiration, circulation, etc. In
plants, the roots, stem, and leaves work together as an organ system, providing
support and nutrients to the plant.
The following diagram of the respiratory system provides an an example of how the
different levels of organization function within an organism. Cells in the lungs help
move oxygen into the bloodstream. These cells form a type of lung tissue, called an
air sac (alveoli). These and other tissues together form a lung, which is an organ.
The nose, mouth, and trachea are other organs that work with the lungs in the
process of breathing, forming the respiratory system. This system is responsible
for the oxygen and carbon dioxide exchange for the cells of all the other organ
systems in the human body, a complete organism.
Organisms of the same kind that live in the same area are called populations. Two
or more populations that coexist in an area or region are called a community. Living
populations that make up a community, along with the nonliving parts of that
environment, make up an ecosystem.
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
6
N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
6th Grade Science
Unit 8
Cells & Heredity
Spring 2006
LEVELS OF ORGANIZATION IN LIVING SYSTEMS
STRUCTURE
Cells
Examples of FUNCTIONS
 Obtaining nutrients needed to
survive
 Producing new generations of cells
Protection
Absorption
Support
Conduction
Transportation
EXAMPLES
 Some animal cells include blood cells, muscle cells,
nerve cells, brain cells and skin cells.
 Some plant cells include root cells and leaf cells.
 Blood is a tissue that transports nutrients throughout
the organism.
 Connective tissue holds other tissues together
 Nerve tissue conducts impulses
 Bone tissue provides internal support
Tissues
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Organs
 Producing chemicals
 Pumping fluids
 Absorption
 The stomach is made of tissues that work together to
digest food.
 The heart is made of tissues that work together to
pump blood.
 Plants roots are organs made of tissues that absorb
water and minerals, and anchor the plant.
Examples in animals:
 Digestion
 Reproduction
 Respiration
 The central nervous systems includes the brain and
the spinal cord
 The digestive system includes the stomach, liver, large
and small intestines, and other organs
Organisms
 Form mutually beneficial
relationships
 Transmit traits through genetic
material
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Populations
Survival of the species
 All Redwood trees in Redwood National Forest
 All striped bass in Braunig Lake
• Symbiosis
• Diversity
• Balance of nature
• Protection
• Survival
 All inhabitants of a tide pool
 All inhabitants of a lake
 All inhabitants of a forest
Organ Systems
Communities
people
plants
bacteria
insects
mushrooms
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
7
N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
6th Grade Science
Unit 8
Cells & Heredity
Spring 2006
Cells and Heredity
Students have studied cells and how cells are part of a bigger system that involves
many levels of organization. One of the most vital processes occurring within
these systems involves the passing of traits and instructions for functions at each
level. The passing of traits from parent to offspring is called heredity. The study
of heredity is called genetics. The 6th grade student is introduced to the fact that
the cell contains genetic material, or chromosomes, which are composed of the
chemical DNA. Humans have 23 pairs of chromosomes, located in the nucleus of
cells. The DNA that makes up these chromosomes contains the blueprint for an
individual. It controls everything from what an individual will look like to how it will
function. Different types, or species, of organisms will have different segments of
DNA. Each individual within a species will also have different DNA. Segments of
DNA are called genes. Humans have thousands of different genes. Different
genes will control different traits. The following diagram illustrates the
relationship between cells, chromosomes, DNA, and genes:
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
8
N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
6th Grade Science
Unit 8
Cells & Heredity
Spring 2006
When organisms reproduce, traits are passed from parents to offspring in the sex
cells. In sexual reproduction, the male sex cell is called the sperm and the female
sex cell is called an egg. While human body cells contain a total of 46
chromosomes, sex cells contain 23 chromosomes. Through the process of
fertilization, the sperm and egg combine to provide the resulting offspring with all
the needed genetic material. The reason people do not look exactly like their
parents is because one half of the genetic material comes from the mother and one
half comes from the father.
Although students need to understand this process, depicted below, it is not the
role of the classroom teacher to further expand on this information or explain the
specific processes of reproduction, especially when it comes to human organisms.
This is the role of the school nurse and should only be covered during maturation
classes.
Sixth grade students should be able to identify the role of genes in inheritance,
but they should not be expected to understand the significance of dominant and
recessive alleles, differentiate between genotype and phenotype, or develop and
interpret Punnett squares. These topics will be introduced in 7th and 8th grade
science. In addition, the 7th grade student will be introduced to the concept of
sexual vs. asexual reproduction. The 6th grade student should know what DNA is,
and it would be appropriate for them to recognize a model of the double helix.
Middle school students do not need to be able to recognize the detailed structure
regarding nitrogen base pairs, as this is covered in high school biology.
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
9
N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
6th Grade Science
Unit 8
Cells & Heredity
Spring 2006
Traits over Generations
Over generations some traits can change naturally through a process called natural
selection. As students identify and explore some of the diverse traits of various
organisms, they should have the opportunity to compare how various species have
changed over time. Organisms have characteristics and behaviors that improve
their chances for survival These are called adaptations. Offspring inherit
adaptations and pass them on to their own offspring. It is important that students
realize organisms are not able to affect an immediate change in their body
structure. This is a common misconception among students. Students should be
guided to understand most organisms cannot make immediate changes in their
normal behavior in response to a change in the environment. A trait that ends up
being a successful adaptation originally appeared by chance alone in individuals of a
species. This trait may have been a mutation. These traits only become a part of
the entire gene pool of a species as they are passed on by successful offspring
over many generations and over long periods of time.
Selective breeding can also be used to increase the frequency of certain traits
appearing in a species. Over time, this may result in a change within the species as
less desirable traits disappear from the gene pool. Farmers, ranchers and
breeders of certain animals use selective breeding. An example would be the
production of corn that is resistant to drought. Another example would be the
creation of watermelon or other vegetable that does not have any seeds. An
important point in this process is that selective breeding is done intentionally using
techniques created by scientists.
A look at domestic dogs and cats can provide a glimpse into some positive and
negative aspects of selective breeding. For example, some of the larger dog
breeds are much larger today than the original standard. Large dogs were bred to
other large dogs in an attempt to increase the size of the offspring. This
eventually resulted in a higher incidence of unique health problems, such as hip
dysplasia.
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
10
N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t
6th Grade Science
Unit 8
Cells & Heredity
Spring 2006
The following illustration shows how selective breeding is responsible for the many
different varieties of domestic dogs we have today:
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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