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Reproduction, Life Cycles, and Heredity
Chicks come from eggs. What other things come from eggs? Put an X next to each
thing you think comes from an egg.
_____ whale
_____ butterfly
_____ human
_____ worm
_____ soil
_____ bacteria
_____ rock
_____ mouse
_____ beetle
_____ alligator
_____ robin
_____ bean plant
_____ clam
_____ catfish
_____ single-celled organism
_____ frog
_____ spider
_____ cow
_____ cat
_____ oak tree
_____ turtle
Explain your thinking. What rule or reasoning did you use to decide if something
comes from an egg?
Uncovering Student Ideas in Life Science
Copyright © 2011 NSTA. All rights reserved. For more information, go to
Reproduction, Life Cycles, and Heredity
Teacher Notes
The purpose of this assessment probe is to elicit
students’ ideas about sexual reproduction. The
probe is designed to reveal whether students
recognize that multicellular organisms develop
from a fertilized egg.
Related Concepts
Egg, sexual reproduction, life cycle
The best answer is: Everything on the list comes
from an egg except for four things—soil, bacteria, rock, and single-celled organism. The rest
are multicellular plants and animals that reproduce sexually. During sexual reproduction, an
egg cell is fertilized by a sperm cell. This fertilized egg then divides and develops into an
organism. Soil and rock are not living things,
so they do not come from eggs (although soil
does contain living organisms). Although we
often refer to eggs as animal in origin, biologically plants also produce eggs. At the base of a
flower is the ovary. The ovary contains one or
more ovules. Each ovule contains an egg that
is fertilized by a sperm cell that develops in a
pollen grain. The fertilized egg within the ovule
develops into a seed, which may then germinate
and develop into the plant.
Although this is a simplified explanation
of a more complex process, the big idea is that
both plants and animals develop from fertilized eggs. Only multicellular organisms can
produce eggs. Bacteria do not produce eggs.
Bacteria and other single-celled organisms
generally reproduce asexually by binary fission or other means of cell division. Bacteria
are single-celled, as are egg cells; therefore, a
bacterium does not contain eggs within its
cell. Viruses are not considered cells and are
generally considered not to be living things.
They can only reproduce by replicating within
a living cell, using the cell’s DNA. Rocks and
soil are not living organisms and thus do not
produce eggs, although tiny eggs of worms and
insects can be found in soil.
N a t i o n a l S c i e n c e Te a c h e r s A s s o c i a t i o n
Copyright © 2011 NSTA. All rights reserved. For more information, go to
Reproduction, Life Cycles, and Heredity
Curricular and Instructional
Elementary Students
In the elementary grades, students learn about
the life cycles of plants and animals. They
observe the life cycles of various animals such
as butterflies, frogs, and chicks, and learn that
their life cycles begin with an egg. They learn
that some animals lay their eggs and that these
eggs develop outside the animal’s body. They
also learn that some animals develop inside the
mother’s body. They learn about the life cycles
of plants and recognize that the life cycle of a
plant begins with a seed. Elementary students
would not be expected to understand that a
seed developed from an egg within the ovule
of a flower. Later in middle school, students
learn about sexual reproduction in plants and
recognize that seeds develop from a fertilized
egg. See “Administering the Probe” for modifications appropriate for elementary students.
Middle School Students
At the middle school level, students learn
about the difference between sexual and asexual reproduction. They learn that multicellular
plants and animals develop from an egg fertilized by a sperm cell. They learn about the
structure and function of different parts of
a plant and animal, including the structures
where eggs are produced. As they learn about
the parts of a flower and the process of pollination, they recognize where the egg and sperm
come from and what happens when the egg is
High School Students
At the high school level, students build on
their basic understanding of sexual reproduction in plants and animals and examine life
cycles in more detail, including reproduction
in flowering and nonflowering plants. Students
use terms such as gametophytes to describe
specialized cells involved in reproduction. The
process of meiosis to produce eggs and sperm
is emphasized at this level. However, some
high school students will still revert to the
common misconception that eggs come only
from animals.
Administering the Probe
This probe is best used with students in grades
3–8. With younger children who are not yet
ready to learn about plant reproduction, consider modifying the probe to include only animals. Younger students may only choose animals that lay their eggs outside of their bodies
as egg producers, even though they learn that
life cycles of animals begin with a fertilized
egg. This probe can be administered as a card
sort (Keeley 2008). Instead of a paper-pencil
task, print each word from the list (p. 117 ) on
cards. Give each small group a set of cards and
have them sort them into two piles: things that
produce eggs and things that do not produce
eggs. Students discuss their justifications for
each choice while they are doing the card sort.
As you circulate among groups, listen carefully to students’ reasoning and probe further
if needed. For older elementary students, you
might replace bacteria with germ or leave it out
Related Ideas in National
Science Education Standards
(NRC 1996)
K–4 Life Cycles of Organisms
• Plants and animals have life cycles that
include being born, developing into adults,
reproducing, and eventually dying. The
details of this life cycle are different for different organisms.
5–8 Reproduction and Heredity
In many species, including humans,
females produce eggs and males produce
Indicates a strong match between the ideas elicited by the probe and a national standard’s learning goal.
Uncovering Student Ideas in Life Science
Copyright © 2011 NSTA. All rights reserved. For more information, go to
Reproduction, Life Cycles, and Heredity
sperm. Plants also reproduce sexually—
the egg and sperm are produced in the
flowers of flowering plants. An egg and
sperm unite to begin development of a new
individual. That new individual receives
genetic information from its mother (via
the egg) and its father (via the sperm). Sexually produced offspring never are identical to either of their parents.
9–12 Molecular Basis of Heredity
• Transmission of genetic information to
offspring occurs through egg and sperm
cells that contain only one representative
from each chromosome pair. An egg and a
sperm unite to form a new individual.
Related Ideas in Benchmarks
for Science Literacy
(AAAS 2009)
K–2 Human Development
• All kinds of animals have offspring, usually with two parents involved.
6–8 Heredity
In sexual reproduction, a single specialized
cell from a female merges with a specialized cell from a male.
The fertilized egg cell, carrying genetic
information from each parent, multiplies
to form the complete organism.
Suggestions for Instruction and
6–8 Human Development
• Human fertilization occurs when sperm
cells from a male’s testes are deposited near
an egg cell from the female ovary, and one
of the sperm cells enters the egg cell.
Related Research
Some children hold an “agricultural
model” of reproduction, believing that
eggs are “laid.” Some student use this
model to think of human eggs as similar
to hens’ eggs, incubated inside a mother’s
body (Driver et al. 1994).
A transition in understanding reproduction happens after a child tries to make
sense of the relationship between a mother
and father, acquiring information about
sexual intercourse and ideas about sperm
and eggs. By age 11, most children understand the role of the parents’ sperm and
egg (Driver et al. 1994).
In a study by Gott et al. (1985), 800
15-year-old students more often correctly
identified sexual reproduction in animals
than in plants. Many of the students did
not believe that plants can reproduce
sexually. Furthermore, studies confirmed
by teachers showed that this view is very
resistant to change, even after instruction.
Biology instruction appears to have little
effect in changing “folklore” concepts of
reproduction (Driver et al. 1994).
Combine this probe with “Does It Have a
Life Cycle?” in Uncovering Student Ideas in
Science, Vol. 3: Another 25 Formative Assessment Probes (Keeley, Eberle, and Dorsey
When younger students learn about life
cycles, starting with the egg, you should
explicitly develop the idea that this stage
in the life cycle is similar for all animals.
All animals start out as an egg, even those
that develop inside their mothers, such as
mammals. Later, when students are ready
to learn about the reproductive parts of
a flower, you can extend this generalization to plants. Once students have learned
about cells, they can understand that a life
cycle starts with a single-celled egg.
Probe deeper to find out what students’
conceptions of an egg is inside animals
that give live birth. Some students may
Indicates a strong match between the ideas elicited by the probe and a national standard’s learning goal.
N a t i o n a l S c i e n c e Te a c h e r s A s s o c i a t i o n
Copyright © 2011 NSTA. All rights reserved. For more information, go to
Reproduction, Life Cycles, and Heredity
still hold the “agricultural model” of an
egg with a developing fetus inside it, rather
than a model of cell division starting with
a fertilized egg.
Have students compare and contrast the
everyday common use of the word egg
with the scientific meaning of the word.
For example, in everyday usage, we think
of an egg as something that is laid or has a
shell. Add this to students’ growing list of
examples of the ways we use words in our
everyday language that are not always the
same in meaning when the word is used in
a scientific context.
Related NSTA Science Store
Publications, NSTA Journal
Articles, NSTA SciGuides,
NSTA SciPacks, and NSTA
Science Objects
Koba, S., with A. Tweed. 2009. Hard-to-teach biology concepts: A framework to deepen student
understanding. Arlington, VA: NSTA Press.
Konicek-Moran, R. 2009. Flowers are more than
just pretty. In More everyday science mysteries:
Stories for inquiry-based science teaching, 121–
134. Arlington, VA: NSTA Press.
Science Object: Cell Structure and Function: Cells—
The Basis of Life
American Association for the Advancement of Science (AAAS). 2009. Benchmarks for science literacy online.
Driver, R., A. Squires, P. Rushworth, and V. WoodRobinson. 1994. Making sense of secondary
science: Research into children’s ideas. London:
Gott, R., A. Davey, R. Gamble, J. Head, N. Khaligh,
P. Murphy, T. Orgee, B. Schofield, and G. Welford. 1985. Science in schools: Ages 13 and 15.
Report No. 3. London, UK: Department of
Education and Science, Assessment and Performance Unit.
Keeley, P. 2005. Science curriculum topic study:
Bridging the gap between standards and practice.
Thousand Oaks, CA: Corwin Press and Arlington, VA: NSTA Press.
Keeley, P. 2008. Science formative assessment: 75
practical strategies for linking assessment, instruction, and learning. Thousand Oaks, CA: Corwin Press and Arlington, VA: NSTA Press.
Keeley, P., F. Eberle, and C. Dorsey. 2008. Uncovering student ideas in science, vol. 3: Another
25 formative assessment probes. Arlington, VA:
NSTA Press.
National Research Council (NRC). 1996. National
science education standards. Washington, DC:
National Academies Press.
Related Curriculum Topic Study
Guide (in Keeley 2005)
“Reproduction, Growth, and Development
(Life Cycles)”
Uncovering Student Ideas in Life Science
Copyright © 2011 NSTA. All rights reserved. For more information, go to