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Grade 9 Science Unit 1: Reproduction Notes
Ch. 4 – Nucleus
Section 4.1 p. 112
The nucleus is an organelle that controls functions and heredity (passing of traits from parent
to offspring) within the cell. It determines what traits will be expressed by the organism. The
information is carried on long, two-stranded molecules called deoxyribonucleic acid (DNA). It
has a twisted ladder shape or helix. The rungs of the molecule are composed of 4 nitrogen
bases called cytosine, guanine, thymine and adenine, while the sides are composed of
phosphate and sugar. Adenine and thymine pair as do cytosine and guanine.
The DNA forms a loosely coiled mass (chromatin) but when the cell is ready to divide, it
becomes a tight, x-shaped structure called a chromosome. These are found in pairs and
species have different numbers of pairs. Humans have 23 pairs, one from each parent. Small
sections of DNA on the chromosomes, called genes, contain coded information to produce a
particular trait. Depending on the part of the gene a cell ‘reads’ it will become a particular kind
of cell such as muscle or bone.
Show Bill Nye: Genes
Section 4.2 p.122
Sometimes the order of the bases in a gene changes. This is a mutation and may change the
trait determined by the gene. The bases may be deleted, added or substituted for another. The
mutation can have positive, negative, or neutral effects on the organism’s ability to survive.
Mutagens are substances or factors in the environment that cause mutations in DNA.
Researchers are working to treat mutated genes with techniques called gene therapy. One
method is to inject a healthy gene into cells to replace the defective one.
Complete p.127 #s 2, 3; p. 131 #s 1, 3 – 7, 14; p. 132-33 #s 2-7, 9, 10, 12,13,16, &19.
Chapter 5: Mitosis
Section 5.1 p. 136
There are three stages in the life or cell cycle of cells: interphase, mitosis
(meiosis in sex cells) and cytokinesis.
Interphase
The longest stage in the cell cycle, interphase is a time when basic cell functions are carried
out and eventually, the cell doubles all material and organelles in the cytoplasm. DNA
replication occurs during this time when the DNA is a loosely coiled form.
Mitosis
This is the shortest stage in which the contents of the cell’s nucleus divide. It is divided into 3
steps (see diagrams p. 142-43): (pigs munch at two)
1. Prophase
a) Early prophase
 Replicated chromosomes pair up into x-shaped structures.
 Nuclear membrane begins to break down
 Spindle fibres begin to form from the centrioles
b) Late prophase
 Spindle is completed and attached to the centromeres
 Nuclear membrane completely disintegrated
2. Metaphase
 Spindle fibres pull chromosomes into a line across the equator of the cell
3. Anaphase
 Spindle fibres shorten, pulling the sister chromatids apart and to opposite
poles of the cell. When separate each is considered a single chromosome.
4. Telophase
 A complete set of chromosomes is at each pole.
 Spindle breaks down
 Nuclear membrane forms around each set of chromosomes
 Now the cell contains 2 nuclei and 2 sets of organelles etc.
Cytokinesis
The final stage, cytokinesis, separates the two nuclei into two daughter cells which are
identical to the parent cell. In animal cells the cell membrane pinches together to divide the
cytoplasm and organelles. In plant cells, a cell plate forms to divide the cell.
Check points are stages of the cell cycle when special proteins monitor cell activities to
determine whether the cell is fit to replicate and sends this information to the nucleus. It will
not replicate if the cell lacks sufficient nutrients for growth, the DNA has not replicated or the
DNA is damaged. If a mutation occurs in the gene producing the instructions for a checkpoint
protein, cell cycle control will be lost. Cancer results when cells divide uncontrolledly. Cancer
cells are not specialized so they do not function as a part of the body.
Complete p. 141 #s 2, 6; p. 146 #s 3, 4, 5; p. 151 #s 2, 3, 5, 6, 8, 10-12.
Section 5.2 p. 152
Through asexual reproduction, a single parent produces offspring that are genetically
identical to itself; clones. This type of reproduction occurs in many different ways by many
different kinds of species.
1. Binary fission is carried out by many unicellular organisms such as amoebas and
bacteria. In this form the parent replicates its DNA and other cellular materials and
divides into two parts (mitosis) which are the offspring. This type of reproduction can
result in extremely fast reproduction. Ex. bacterium
2. Budding occurs when a growth develops on an organism which grows into a complete
individual. The bud may or may not detach from the parent. Ex. Hydra, or yeast
3. Fragmentation is practiced by some animals and many plants such as starfish or
Japanese knotweed. The organism breaks apart due to injury and if the parts contain
enough genetic information both grow into a complete organism.
4. Vegetative Propagation/ Reproduction can be seen in many types of plants. It occurs
when special cells, usually in stems or roots divide repeatedly to form a new plant.
Tulips bulbs and strawberry runners are examples. Humans have devised methods of
carrying this out as well, such as cuttings and grafting.
5. Spore formation occurs in some bacteria, and fungi. Single-celled reproductive cells
called spores develop and when conditions are suitable, the spores grows into a new
organism. Ex. Rhizopus, mushrooms
Advantages and Disadvantages of Asexual Reproduction
Advantages
Large numbers of offspring formed quickly
Large colonies outcompete other species
for nutrients/water
Disadvantages
Large numbers produced in the same area
means that they must compete with one
another for resources
Offspring are genetic clones which means
that disease or environmental changes can
wipe out whole colonies if it cannot adapt to
these new conditions – no genetic diversity!
Large numbers mean that species may
survive environmental change such as
predator increases or temperature drops
Energy is not expended to find a mate
Complete p. 165 #s 1, 3-6, 11-14. Review p. 166-67 #s 1 – 11, 16, 18 – 20.
WHMIS (workplace hazardous materials information system) Symbols
Laboratory Write-up Format
 Title page containing course name/ grade, student name, teacher name, date due
and lab title and page.
 Purpose
 Observation table or results
 Questions for analysis
Ch. 6 Meiosis
Section 6.1p. 170
Meiosis is a type of cell division that results in daughter cells, called gametes. Since cell
division occurs twice (meiosis l & meiosis ll), the gametes contain half the total number
of chromosomes (haploid, n) as other body cells (diploid, 2n). After fertilization,
offspring get a randomly selected half of each parent’s DNA thus creating a genetically
unique organism (except identical twins).
Meiosis in males produces 4 haploid sperm, while in females one of the 4 haploid cells
contains most of the cytoplasm and is the only survivor.
Complete p. 175 #s 1 – 4; p. 179 #s 1, 3 – 7, 10, 12, & 16.
Section 6.2 p. 180
Sexual Reproduction
Sexual reproduction, composed of 3 stages, mating, fertilization and development,
results in an increase of variation in the species. The sperm and egg unite either
internally or externally.
External fertilization is the fusion of eggs and sperm outside the body.
Advantages:
 Little energy is used in finding a mate.
 Large numbers of offspring are produced meaning that in an environmental
change some individuals will survive.



Offspring are widely spread out, so do not compete with the parents or one
another for resources.
Little chance of offspring and parent reproducing, maintaining genetic variation.
Ex. fish such as salmon, mosses
Disadvantages:
 Many gametes do not survive outside the body
 Gametes may not meet.
 Zygotes are unprotected and often preyed upon.
 Usually no parental care so few offspring survive to adulthood.
Internal fertilization is the fusion of gametes inside the female(usually).
Advantages:
 Gametes usually meet
 Developing embryo protected increases survival rate
 Parental care after birth increases survival
Disadvantages:



A great deal of energy expended in finding a mate, mating
Energy expended caring for the young
Fewer zygotes produced
Complete p. 191 #s 1- 3.
Pollination in Flowering Plants p. 188
Through pollination, in flowering plants, male gametes, called pollen, is transferred
from the anthers to the eggs in the ovules. Pollen transport is often achieved through
insect activity, fruit development or winged structures(cone-bearing) which are carried
by wind.
Some plants do not produce flowers but cones which either produce pollen or eggs. Ex.
alder, black spruce (p. 190).
Insects often undergo a massive physical and functional change called metamorphosis
in their lifecycles. It may be complete with the egg, larva, pupa and adult stages or
incomplete consisting of egg, nymph and adult phases (see p. 192-3).
Advantages & Disadvantages Sexual Reproduction
Advantages
Little energy expenditure in
mating(external reproduction)
Great numbers of offspring (external)
Protection of embryo and parental care of
offspring(internal)
Offspring genetically unique, greater
variation
Table 6.1 P. 194
Disadvantages
Greater energy consumption (internal
reproduction)
Fewer offspring(internal)
Gametes, embryos and offspring are
unprotected and preyed upon(external)
Some beneficial traits may not be inherited
or maladaptive ones may be inherited
Sexual vs Asexual Reproduction
Asexual Reproduction
Number of parent cells
1
Gametes(eggs or sperm)
None – parent cell divides
Variation in offspring
Amount of energy required
Meiosis or mitosis
Very little (mutation), much
less than sexual
Very little – no mating, or
parental care of offspring
mitosis
Sexual Reproduction
2
2 - cells unite to form
zygote
Great genetic diversity
Energy required for mating
and parental care of
offspring
meiosis
Complete p. 191 #s 4, 5: p. 195 #s 1, 2, 4- 10, 12-17.
Section 6.3 Human Reproductive Systems p. 196
The male reproductive system functions to produce gametes – sperm and deliver them
to the egg’s environment for fertilization. See p. 196 table 6.2 for the structures and their
functions. The female reproductive system produces gametes, eggs and houses the
developing embryo. See table 6.3 for structures and functions.
Human development begins with a fertilized zygote which travels down the fallopian
tube to the uterus where it divides and undergoes differentiation for about 38 weeks,
becoming an embryo and then fetus. See table 6.4 p. 199 for details.
Complete p. 200 #s 1 – 4; read p. 201; complete p. 203 #s 1 – 12.
Section 6.4 Studying Genetic Changes p. 204
The understanding of genetics has evolved. Gregor Mendel’s experimentation with pea
plants in the 1800s provided scientific explanation for heredity through dominant and
recessive factors (genes). Watson and Crick’s model of DNA helped explain how and
why mutations occur. The Human Genome Project (HGP) has created greater insights
into how and why certain medical conditions occur and how to treat them. It has also
introduced the concept of genetically engineering people and related ethical issues.
Genetic engineering has applications in many areas such as food production and
health.
Complete p. 211 #s 1 – 3, 7, 9 – 11, 14 & 15.
Chapter Review:
Complete p. 212-213 #s 3, 5, 7, 9 & 15
Review STSE article ‘Heredity, Genetics and Genetic Engineering’
Other available practice questions: Chapter Review p. 212 -221 and Review handout