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SCIENCE 9
15
Why is the Nucleus so Important?
You won't find the nucleus in just any cell. For example, bacteria are
prokaryotic (this means “before the nucleus”). These cells do not
have a nucleus, although they do still have DNA. They also have no
membrane-bound organelles, such as chloroplasts or mitochondria.
On the other hand, eukaryotic organisms (animals, plants and fungi)
do have nuclei in their cells.
Structure
Notice in this diagram that a membrane surrounds the nucleus, and
that there are holes or pores, in this membrane. The membrane around
the nucleus is similar to the cell membrane because both allow only
certain substances to pass through.
Nuclear Membrane
Nuclear Pore
Nucleolus
Endoplasmic
Reticulum
Parts of the Nucleus
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SCIENCE 9
Function
The nucleus is often called the 'control center' for a cell, but what does
this really mean?
Please read BC Science 9, The Nucleus: Control Centre of the Cell, pages 125
to the end of Figure 4.7 on page 128 or BC Science Probe 9, From DNA to
Proteins, pages 42 to 44. Be sure to take time to understand the
illustrations in your textbook.
Note:
If you’re using the textbook BC Science 9, ignore the Creating DNA
Messages activity at the top of page 127.
As you read, make sure you understand the structure of the DNA
molecule, including the names of the four bases. Add any new
vocabulary to your vocabulary list, using the directions found in the
Science 9 SOS Package.
From your textbook reading, you will know that the nucleus is
responsible for several important things:
•
storage of DNA, which contains the “master set” of
instructions for all of the cell's activities
•
control of the cell's production of proteins by copying
information from DNA
•
containing the nucleolus, where ribosomes are made
Red blood cells are the only type of human cells that have
no nuclei.
MODULE 1
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SCIENCE 9
39
Cell Structure Crossword Puzzle
1
2
3
4
6
5
7
8
9
10
11
Across
2 . can be smooth rough; involved in lipid
and protein production
7 . site of protein production
8 . photosynthesis produces a plant's food
using this energy
11 . the watery fluid inside a cell
Down
1 . some animal cells have this to help them
move
3 . vacuoles are much larger in these cells
4 . site of cellular respiration
5 . packages and transports proteins
6 . photosynthesis occurs here
8 . vacuoles containing digestive enzymes;
they remove unwanted materials in a
cell
9 . provides support to plant cells
10 . contains genetic information; the 'control
centre' for a cell
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SCIENCE 9
The Story of Mitosis
We can tell the story of cell division by answering five simple
questions:
What? — Mitosis is division of a cell's nucleus into two equal
parts.
Where? — Mitosis involves only the nucleus.
Why? — A cell spends most of its time growing and carrying
out its normal functions. As the cell grows, the distance
between the centre and the cell membrane grows, so it's harder
for substances inside the cell to reach the cell membrane.
When a cell has grown large enough, it must either divide or
die.
When? — Before mitosis can occur, the number of
chromosomes in the nucleus must double.
How? — When a cell has reached the point where it must
divide, it undergoes mitosis and then cytokinesis to produce
two new cells from one original cell.
The Cell Cycle
All cells develop from other cells. The cell cycle describes the life of a
cell, including its growth and division.
mitosis
cytokinesis
cell growth;
chromosome
and centriole
duplication
The life cycle of a cell has two major phases—interphase and cell division.
Single-celled organisms reproduce by cell division. Multicellular organisms, like
plants and animals, repair damage and grow through cell division.
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Notice in the diagram that cell division takes a relatively short time in
a cell's life. After cytokinesis, cell division is complete. The two
'daughter cells' return to interphase and grow until they are large
enough to divide.
Once cytokinesis has occurred and the cycle is complete, the two new
cells are in interphase, and the cycle starts over again.
How Does Mitosis Work?
If you have access to a computer and the Science 9 Media CD,
learn more about mitosis and the phases by going to your:
Science 9 Media CD > Module 1 > Mitosis, Step by Step
Then skip forward to the Try this Memory Trick!
If you don’t have access to the Media CD, then continue reading.
To see exactly how cells divide, please read BC Science 9, The Cell Cycle
pages 153 to 155, Mitosis pages 156 to 157; and Cytokinesis page 158 . Read
in BC Science Probe 9, The Cell Cycle pages 49 to 51.
Be sure to take time to understand the illustrations in your textbook. In
your Science Notebook, list the main events that occur in each phase.
Pay particular attention to BC Science 9 (Figure 5.8 on page 156), or BC
Science Probe 9 (Figure 2 on page 50) and be sure you can identify each
diagram shown. Also, try to determine the main events that occur in
prophase, metaphase, anaphase, and telophase.
MODULE 2
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SCIENCE 9
9
Developing the Story of the Atom
Many scientists have contributed to the development of the modern
atomic theory. Read on to discover some of the more influential
contributions. There is still so much to learn and discover.
John Dalton’s Atomic Theory
In 1808, an English chemist named John Dalton published an
explanation of why elements and non-elements differ from each
other. He called his idea the atomic theory. For example, the atoms
that make up silver are different than the atoms that make up gold.
He defined the atom as the smallest particle of matter. Dalton's
atomic theory is summarized below.
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SCIENCE 9
J.J. Thomson Discovers Electrons
J.J. Thomson (1856–1940), a British physicist, discovered that atoms
contained smaller particles, which other scientists later called
electrons. He discovered these electrons while experimenting with a
gas discharge tube. These are tubes filled with gases similar to a
fluorescent light. He proposed that all atoms must contain electrons.
His model of the atom was called the “raisin bun” model. His model
was a round ball with negatively charged particles. The round ball was
like a bun and raisins were electrons.
Rutherford's Experiment
Ernest Rutherford (1871–1937), a scientist from New Zealand, was
working at a university in Montreal. He came up with an experiment
to look inside the atom. He aimed a beam of alpha particles at an
extremely thin sheet of gold foil. He found that most of the particles
went straight through the foil. From this he concluded that the atom
contained empty space, because the particles passed straight through.
A few particles, however, bounced back as if they had collided with
something heavy. Rutherford discovered that the atom has something
hard in the middle.
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Guided Practice 2.2D 1
Chemical Families
Fill in the blank with the answer for each statement
1. Alkali metals have a charge of _____________________.
2. Alkaline earth metals have a charge of _____________________.
3. Halogens have a charge of _____________________.
4. Noble gases have a charge of _____________________.
5. _____________________, a noble gas, is present in a sign that
glows with reddish light.
6. _____________________, a noble gas, is often found in regular
light bulbs.
7. _____________________, an alkali metal, is found in seawater.
8. _____________________ is the most common compound with
hydrogen.
9. The universe is _____________________ percent hydrogen.
Summary
You should now be a little more familiar with the periodic table, and
with some of the properties of the families. The properties of elements
are related to the number of electrons in the outer shells of their atoms.
You should be aware of the important properties of some of the
chemical families, including alkali metal, alkaline earth metals,
halogens, and noble gases.
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SCIENCE 9
Guided Practice 3.1C 1
Potential or Kinetic Energy?
Select either potential energy or kinetic energy for each of the
following statements.
If you have access to a computer, complete this activity using
your Media CD, go to:
Science 9 Media CD > Module 3 > Potential or Kinetic Energy?
If you don’t have access to a computer, complete the following activity
by circling the correct type of energy.
potential
energy
kinetic
energy
potential
energy
kinetic
energy
potential
energy
kinetic
energy
potential
energy
kinetic
energy
potential
energy
kinetic
energy
potential
energy
kinetic
energy
potential
energy
kinetic
energy
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SCIENCE 9
Parallel Circuits
Another kind of circuit to set up is one the current can travel through
different circuit paths. This type of circuit is called a parallel circuit. In
a parallel circuit, There is more than one way for electrons to travel
from the negative terminal to the positive terminal of a battery or cell.
You could think of several roads leading from your place to your
friend's place as parallel paths. Each path is a different route. But
ultimately, all the paths start in the same place and end up in the same
place.
Drawing a schematic diagram of a parallel circuit is a bit tricky. The
rules are the same as for series circuits. However, because there are more
loops, more rectangles have to be drawn for each loop.
In the next topic there are some parallel circuit schematic diagrams to
view. Once again, examine each diagram of a circuit then examine its
schematic diagram, drawn to represent the circuit.
Parallel Circuits: Schematic Diagrams
Diagram D:
A chemical cell is attached to a switch in series. It is also attached to two
light bulbs that are in parallel with each other.
light bulb
light bulb
switch
power source
circuit arrangement
schematic diagram
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In this first set-up, a second light bulb has been attached in parallel to
the first light bulb. When the switch is closed (that is, on), some of the
electric current from the chemical cell will flow through the first light
bulb. The rest of the current will flow through the second light bulb.
The branch in which the second bulb is placed acts as an alternate, or
parallel path, for electrons to flow.
Note also that the switch is attached in series with the chemical cell.
What will happen if the switch is turned off, or open? No current from
the cell will make it to either light bulb. The main circuit is broken, so
electric charges will not flow.
Before you move on to the diagram in the next topic, make sure you
understand how the schematic diagram matches the description from
Diagram D.
Diagram E:
A chemical cell is attached to three light bulbs that are in parallel with
each other. A switch is placed in series with the third light bulb, and
controls current through that bulb only.
light bulb
switch
light bulb
light bulb
power source
circuit arrangement
schematic diagram
MODULE 4
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SCIENCE 9
5
Section 4.1
The Universe and the Solar System
Section Overview
The universe is a pretty big place! It's made up of matter, energy, and a
whole lot of empty space. This section is an introduction to the
universe and everything in it. We will look at some scientific theories
about how the universe, and our solar system, came to be. We will
examine the parts of the universe that we know about: the galaxies,
stars, planets, moons, comets, and asteroids.
We know quite a bit about space, but there's even more we don't know.
It is important to think of our knowledge as a growing and changing
body of information. In order to do this, it is often helpful to look at
the history of our knowledge. Why did people want to investigate the
skies in the first place? What were some scientific theories about space
in the past? Through this investigation, we will see where our
knowledge has come from, and think about where it might lead us in
the future.
So buckle your seatbelt and get ready for a tour of the universe!
Note:
Remember to fill your Science Notebook (hard copy or electronic) with
vocabulary, diagrams, and other information you can refer to when
you do your section assignment. Your Notebook will be a handy study
tool to prepare for the module test. Or, if you're doing the module
project instead of the test, you can write down ideas for your project as
you work your way through the section.
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Glossary:
alkali earth metals
Any of the group 2 elements, such as, calcium,
beryllium, and magnesium—all are reactive, soft metals
alkali metals
Any of the group 1 metallic elements, such as, lithium
and sodium—strongly reactive, soft metals
amino acids
Building blocks of proteins; there are 20 different amino
acids
ammeter
A device used to measure electric current
ampere
Unit of electric current
anaphase
Phase of mitosis in which paired chromosomes pull
apart
artificial insemination
A reproductive technique widely used in agriculture, and
sometimes used with humans; involves collecting and
injecting sperm into a female
asexual reproduction
Type of reproduction that requires only one parent;
offspring are identical to the parent
asteroids
Small rocky bodies that revolve around the sun—
sometimes called minor planets or planetoids
atom
Smallest particle of an element
atomic mass
Mass of the atom under the symbol of the element on
the periodic table