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Grade 9 Science –summary notes for unit test
2012
Unit 1 – Reproduction
Key Concepts
 How the cell theory was developed
 The important role that mitosis and cell division play in the cell cycle
 The various types of asexual reproduction in living organisms
 Some advantages and disadvantages to asexual reproduction
 How knowledge of asexual reproduction is used in plant production
Key Skills
 Update your skills in using a microscope to observe the process of cell division
 Predict the number of cell divisions required to produce a certain number of organisms
 Investigate the phases of mitosis and cell division
Key Terms
 Cell Theory
 Organelles
 Nucleus
 DNA
 Chromatin
 Nucleolus
 Ribosomes
 Cell Membrane
 Cytoplasm
 Golgi Bodies
 Pistil
 stigma
 ovum
 prophase
 anaphase
 helix
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clone
Cell Wall
Chloroplasts
Mitosis
Replication
Chromosomes
Centromere
Prophase
Metaphase
Vacuoles
Ovary
stamen
filament
metaphase
cytokinesis
variation
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Mitochondria
Interphase
Cell Cycle
Centrioles
Asexual Reproduction
Binary Fission
Fragmentation
Pollination
Genes or traits
Meiosis
style
ovary
anther
telophase
base pairs
somatic cells
The Cell Theory
The cell theory states:
 All living organisms are composed of one or more cells.
 Cells are the basic units of structure and function in all organisms.
 All cells come from previously existing cells.
 The activity of an entire organism depends on the total activity of its independent cells.
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Grade 9 Science –summary notes for unit test
2012
The Cell: The Basic Unit of Life
Cells have numerous membrane-bound organelles. Organelles are structures that perform
specific functions (or have certain jobs) in the cell.
The nucleus is an organelle bounded by a double-layered porous membrane and it acts as the
control center. It coordinates, controls and manages cell functions and it is the storage center
for all information and instructions for the organelles.
Chromosomes are thread-like structures found within the nucleus that carry genetic
information. Each chromosome contains many different genes. Genes are units of genetic
information that determine the specific characteristics of an individual.
The nucleolus is a darker area within the nucleus. It is believed that the nucleolus is involved in
the making of proteins.
Ribosomes are organelles that build proteins essential for cell growth and reproduction.
The cell membrane encloses or covers the cell contents. This membrane acts like a gatekeeper;
it controls the movement of materials in and out of the cell.
The cytoplasm is a jelly-like material enclosed by the cell membrane. The cytoplasm supports
the nucleus and the other organelles. This is the area where work is done within the cell;
nutrients are absorbed, transported and processed here.
The endoplasmic reticulum is a folded membrane that forms a series of canals that transports
materials to different parts of the cell.
Mitochondria are tiny, oval-shaped organelles that provides cells with energy.
Golgi bodies store proteins until they are needed either inside or outside of the cell.
Centriole is a small protein structure critical to cell division (found only in animal cells).
Vacuoles are fluid-filled storehouses that contain water, food, wastes and other materials.
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Grade 9 Science –summary notes for unit test
2012
Differences Between Animal and Plant Cells
Plant cells have a structure called a cell wall. It lies outside the cell membrane. This fibrous
wall provides structure and support for the cell. Multicellular plants rely on the strength of
their cell walls to provide support for the entire organism. The cell wall is composed of a
material called cellulose.
Plant cells also contain chloroplasts. This organelle allows plant cells to make their own food
through the process of photosynthesis.
Animal Cells
Cell Membrane
Centrioles
Vacuoles are very small
Plant Cells
Rigid Cell Wall
Chloroplasts
Vacuoles are very large
The Importance of Cell Division
Cell division is when one cell divides into two identical cells. Cell division occurs for three main
reasons:
 Healing and Tissue Repair
 Growth
 Reproduction
The Cell Cycle
The cell cycle is the sequence of events that occurs from one cell division to the next cell
division. Cell division is only a small phase in the entire process of the cell cycle.
Getting Ready for Mitosis
Before mitosis can begin, replication must occur. Replication occurs when the nucleus makes an
identical copy of the chromatin. Now there are two complete sets of DNA. The replicated
chromatin coils up to form double-stranded chromosomes, which are joined in the middle by a
centromere. Now the nucleus is ready for mitosis to begin.
The Phases of Mitosis
Mitosis involves four major phases that always take place in the same order: prophase,
metaphase, anaphase and telophase.
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Grade 9 Science –summary notes for unit test
2012
Phase 1: Prophase
During this phase, the nucleolus and the nuclear membrane disappear. In animal cells, spindle
fibres begin to form and stretch across the cell from the centrioles that have moved to
opposite ends of the cell. The spindle fibres attach to one side of each centromere.
A similar process in the cells of plants, fungi and some protests occurs. They also form
spindle fibres, but not centrioles.
Phase 2: Metaphase
In metaphase, the spindle fibres pull the double-stranded chromosomes into a line across the
middle of the cell.
Phase 3: Anaphase
In anaphase, the spindle fibres begin to contract and shorten. This action pulls the centromere
apart, allowing one of each of the replicated strands to move to opposite ends (poles) of the
cell.
Phase 4: Telophase
One complete set of chromosomes is now at each pole of the cell. The spindle fibres begin to
disappear and a nuclear membrane forms around each set of chromosomes. A nucleolus appears
within each new nucleus. Single-stranded chromosomes start to uncoil into thin strands of
chromatin. Now there are two nuclei in one cell, and the cell itself is ready to divide.
Cell Division
At the end of mitosis, there is still only one cell, but it now has two identical nuclei. The next
event in a cell’s life is cell division.
In animal cells, the cell membrane pinches in near the middle of the cell, dividing the cytoplasm
into two cells.
In plant cells, a cell plate develops across the center of the cell, forming a new cell wall between
the two new cells.
In both plant and animal cells, each new cell after division is an exact copy of the original.
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Grade 9 Science –summary notes for unit test
2012
Interphase
Mitosis and cell division take up only a small fraction of the cell’s life. Interphase is the stage
at which the cell spends most of its time. During interphase, the cells grow, replicate their
DNA, and prepare for the first phase of mitosis.
The cell cycle is the continuous process of mitosis, cell division and interphase.
Asexual Reproduction
Mitosis and cell division are the basis for asexual reproduction in many organisms. Asexual
reproduction is the formation of a new individual that has identical genetic information to its
parent.
Asexual Reproduction in Bacteria
Bacteria are unicellular organisms that do not contain a true nucleus. Instead, bacteria contain a
single chromosome that is not surrounded by a nuclear membrane. Bacteria reproduce asexually
through a process called binary fission.
In binary fission, a parent cell divides so that each new cell contains a single chromosome
carrying a complete set of DNA that is identical to its parent cell.
Asexual Reproduction in Protists
Unicelluar organisms in the kingdom Protista, such as the amoeba, also rely on asexual
reproduction to increase their population. The DNA of protist is contained within a true nucleus.
Mitotic cell division in these unicellular organisms results in the formation of two identical
offspring.
Asexual Reproduction in Fungi
Moulds, yeast and mushrooms are members of the kingdom Fungi. The bodies of these
organisms are composed of many thin filaments called hyphae. The hyphae grow over the
surface of and into the bodies of other organisms to obtain food. Members from this kingdom
can use one of three methods of reproducing asexually: fragmentation, budding and spores.
Fragmentation occurs when a small piece breaks away from the main mass of hyphae and grows
into a new individual.
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Grade 9 Science –summary notes for unit test
2012
Budding is the way yeast reproduces asexually. First, a copy of the nucleus is made and then a
tiny bud begins to form on the cell wall. The new nucleus continues to grow larger and eventually
it breaks away to become a single, independent cell.
Asexual Reproduction in Plants
The ability of plants to reproduce asexually and repair themselves is, as in all other kingdoms,
the result of mitotic cell division. Asexual reproduction in plants ensures that each new plant
will have the same DNA as its parent.
Some plants have the ability to reproduce asexually from their roots (asparagus) tubers.
In other plants, the stem divides to produce cells that will become a new plant (strawberries).
These plants have special stems called runners. Pieces may be broken off in a process called
fragmentation.
7.2 Meiosis
Meiosis is the process that ensures that each gamete contains only one-half set of
chromosomes. This process also ensures that each gamete has a different combination of the
chromosomes. Once the chromosome number has been halved a sperm cell and a egg cell
combine during fertilization to form a diploid zygote. Only a zygote can function as the
offspring’s first body cell.
Organisms that reproduce sexually show greater variance, meaning differences in
characteristics, than those that reproduce asexually. An offspring receives a set to 23
chromosomes from each parent. The chromosomes that are similar in shape, size and gene
arrangement are combined together to form a pair of chromosomes. The appearance of the
organism is determined by the way the genes from this pair interact. (colour of hair, eyes,
etc…)
Phases of Meiosis
Organisms that reproduce sexually contain two types of cells. Cells that reproduce by normal
cell division and mitosis are called somatic cells (skin cells and muscle cells). Reproductive
cells are the second type of cell. These cells produce sex cells that contain only half the
number of chromosomes through the process of meiosis.
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Grade 9 Science –summary notes for unit test
2012
Meiosis involves two cell divisions that produce four cells with single sets of chromosomes.
Meiosis I
Meiosis I is that phase where the first cell division occurs. In this phase, homologous
chromosomes move to opposite poles of the cell. During this division, a pair(2n) becomes two
single cells (n).
Meiosis II –Final stages where four daughter cells are produced. All daughter cells are
single sets of chromosomes.
Mitosis
Asexual- one cell produces two daughter cells
that are identical to the parent
Meiosis
Sexual-one cell produces 4 daughter cells that
have half the chromosomes of the original cell
7.3 Reproduction in Flowering Plants
The reproductive cells of plants are found within their flowers. The male sex cells of the
flower, the pollen, are produced in the anthers, which are at the tips of the stamens. Female
sex cells, called eggs, are located in a structure call the ovary, which is at the base of the pistil.
Pollination is the process of fertilization in plants. This occurs when the pollen moves from the
anther and reaches the egg cells of the female.
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Grade 9 Science –summary notes for unit test
2012
Pollen from one plant can sometime fertilize the same plant. However, more commonly, the
pollen of one plant must reach the egg of a different plant. The pollen can be transported by
wind, insects and animals, and humans (artificially).
The fertilized eggs of the flower become the seeds. As the seeds are developing, the petals
slowly shrivel up and fall off the plant. In some plants, the ovary surrounding the seeds
develops into a fruit (to help protect and disperse the seeds).
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Sepal - green, leaf-like structure that protects the budding flower.
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Petal - colorful and often scented part of the flower that attracts insects.
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Stamen - the part of the flower that produces pollen. Consists of a filament and an anther.
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Anther - sac located at the tip of the filament that contains pollen.
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Filament - stalk that connects to and holds up the anther.
Pistal - consists of the stigma, style, and ovary.
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Stigma - the tip of the carpel that is sticky in order to collect pollen.
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Style - the slender, neck-like portion of the carpel that leads to the ovary.
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Ovary - structure at the base of the carpel that houses the ovule or egg.
DNA: The Genetic Material
The chromosomes in all living beings are made up of a chemical known as deoxyribonucleic
acid (DNA). This chemical gives directions to your cells to repair damaged cell parts or to
make new cells. DNA also tells cells how to respond to changes in their environment and how
to respond to messages sent by other cells.
The Structure of DNA
DNA molecules are shaped like a twisted ladder. Sugars and phosphate molecules make up
the sides of the ladder to give DNA its shape. The rungs (or middle) of the ladder are made
up of nitrogen bases. The order (or sequence) that the nitrogen bases are placed in the
strands of DNA is known as the genetic code. The genetic code is arranged in three
character sequences (of nitrogen bases) or “words,” and all these words combined tell
“stories” or information about an individual’s genes (eye colour, hair colour, artistic ability,
etc.).
The nitrogen bases are combined in pairs. Adenine always pairs with thymine and cytosine
always pairs with guanine.
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