Science Term 1
Mr. SB Maseko’s extensive
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Science Term 1
Content
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Photosynthesis
Carbon Cycle
Climate Change
Atomic Structure and Periodic Table
Trends in Groups within the Periodic Table
Chemical Bonding
Photosynthesis
Photosynthesis is the process by which plants, algae, and some bacteria covert light
energy into chemical energy, using sunlight, carbon, dioxide, and water. This process
occurs in chloroplasts, where chlorophyll absorbs light. The light energy splits water
molecules, releasing oxygen. The remaining energy is used to form glucose, which
provides energy for plant’s growth. Photosynthesis is critical for life on Earth, as it
produces oxygen and it is at the base of most food chains.
Plant Cell
Before we dive into plant cells it is important we understand what a cell is, what makes
up a typical cell, and what is the purpose of a cell:
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Firstly, a cell is the basic unit of life, making up all living organisms. Cells can
either be unicellular (Such as Yeast) or multicellular, (Like plants or Animals).
They are organized into structures called organelles that carry out the functions
of the cell. (e.g. The Nucleus). The main types of cells are prokaryotic (Without
nucleus) and eukaryotic (with nucleus).
Typically, a cell consists of a nucleus, cell membrane, cytoplasm and
mitochondria
So using this information we can conclude that a plant cell is a eukaryotic cell, with a
rigid cell wall, found in plants, that Is primarily made up of: 1. cytoplasm that houses
the cell’s organelles, including the chloroplasts which perform photosynthesis to
produce chemical energy ( Specifically in the form sugars ), 2. a large central vacuole
which maintains turgor and stores nutrients, 3. and the nucleus which houses the cell’s
genetic material. (DNA)
What is the job of the organelles in the plant cell
1. Large Vacuole: This large central sac that stores water, nutrients, and waste
products, and helps maintain cell turgor pressure, contributing to the cell’s
rigidity.
2. Cytoplasm: A jelly – like substance filling the cell, where various organelles
reside, and numerous metabolic reactions occur.
3. Nucleus: This the control center of the cell, it houses the cells genetic material
(DNA) and coordinates activities like growth, metabolism, and reproduction.
4. Chloroplast: These are organelles found within the cytoplasm that facilitate
photosynthesis, converting light energy into chemical energy stores in the form
of sugars.
5. Mitochondria: This is the powerhouse of the cell as the mitochondria generate
energy by converting nutrients into ATP through cellular respiration.
6. Cell Membrane: This is a very thin layer of fat and proteins and is partially
permeable, which means it lets some substances through but not others.
7. Cell wall: This a rigid layer composed of mostly cellulose that surrounds the cell
membrane, providing structural support and protection.
Inside The Leaf
Although a leaf is thin, it is made up of several layers of cell. You can see these all
these layers above. Each layer has its own a function. We will work it out from top
to bottom:
1. Upper Epidemies – The main function of this layer is to protect the cells
within the leaf, the cells in this layer are packed tightly together, to reduce
the quantity of water vapor from escaping the leaf. The upper epidermis
also secretes a waxy substance, which forms a thin, transparent,
waterproof covering called the waxy-cuticle. The cells In the upper
epidermis do not contain chloroplasts so this layer cannot
photosynthesis.
2. Palisade mesophyll – The palisade mesophyll contains cells that do most
of the photosynthesis, as it is close up to the top of the leaf where they
can receive more sunlight and are made up of very tall narrow cells that
contain a large number of chloroplasts.
3. Spongy Mesophyll- This layer has lots of air spaces to allow carbon
dioxide and oxygen to di^use into the cells, the cells in this layer also do
photosynthesis but not as much as much as the palisade layer, as they
have fewer chloroplasts.
4. Vascular Bundle – This layer consists of xylem tubes and phloem vessels
running side by side to form veins of the leaf.
a. Xylem – Used to transport water and dissolved minerals upwards
from the roots to the rest of the plant.
b. Phloem- Transports nutrients from the leaves to the rest of the
plant.
5. Lower epidermis- This layer also protects the cells inside the leaf, and on
some leaves the tissue secretes a waxy layer, but usually it does not, as
the underside of the leaf does not often have sunlight falling on it. Within
the lower epidermis, there is:
a. The stoma- An open pore-like structure that Regulates gas
exchange and is flanked by guard cells that control the opening
and closing.
b. Guard cells – Regulate the rate of transpiration of Carbon dioxide
and oxygen by changing the size of the stomata.
PLANT NUTRIENTS
MAGNESIUM
Magnesium is needed to produce the chlorophyll, chlorophyll is a key component in the
photosynthesis process, so without it or with little of it the plant will not grow well, and
chlorophyll is responsible for the green colour of leaves so without it the leaf is left
looking yellowish.
NITRATE
Nitrate contains nitrogen atoms which are needed to convert carbohydrates into
proteins. Proteins are essential in creating new cells, so without enough nitrate the
plants leaves die and the plant remains small.
CARBON CYCLE
The carbon cycle is a continuous loop in which carbon moves from the atmosphere to
living organisms and back to the atmosphere. This. Cycle is vital for maintain the earths
climate and sustaining life. Carbon is the back bone of various organic molecules, such
as proteins, carbohydrates and fats.
APAD F
1. Air, this represents the carbon dioxide in the air
2. Plants, which take in the carbon dioxide from the air during photosynthesis, and
release it back during respiration.
3. Animals, take in carbon from plants through consumption (Feeding) and also
respire to release carbon dioxide
4. Decomposers; when both plants and animals die their bodies get broken down
by decomposers which take in the carbon, decomposers also respire to release
Co2 back into the ai.
5. Fossil Fuels; if exposed to the correct conditions for millions of years dead plants
and animals can turn into fossil fuels, such as coal, oil, and natural gas. Fossil
fuels can be dug up and burnt down through human activities, releasing carbon
dioxide back into the air.
CLIMATE CHANGE
Climate refers to the long-term pattern of temperatures, wind and rainfall on earth.
Climate. So climate change refers to the change in the average temperatures and
weather cycles over a long period of time.
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Climate change is primarily driven by human activities such as burning fossil
fuels and deforestation, which release greenhouse gases such as carbon dioxide
and methane, these gases trap heat, this can lead to global warming and shifting
weather patterns. Climate change overall negative for our Earth. Here are some
impacts of climate change:
Environmental Impacts
1. Rising Temperatures – Global warming contributes to melting glaciers
and polar ice, which can in turn lead to rising sea levels and
unpredictable rainfall.
2. Extreme Weather – Climate change can cause an increased frequency
in storms, hurricanes, floods, and droughts which can in turn disrupt
ecosystems and destroy habitats.
3. Ecosystem Shifts – Changing climates can lead to species migration,
habitat loss, and even mass extinction.
Societal Impacts
1. Food Security – Altered weather patterns can lead to reduced yields
causing food shortages and increased food prices.
2. Public Health – Heatwaves and spread of diseases due to shifting
ecosystems can increase health risks.
3. Economic Burden – Damage from natural disasters can cause
economic strain, especially in vulnerable regions.
SPACE ROCKS
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An asteroid is a rocky or metallic mass that orbits the sun, they are usually
populated together in asteroid belts, and can vary in size from a few meters to
hundreds of kilometres.
Meteoroids are smaller fragments or particles that have been broken o^ from
asteroids or comets, they float near the earth.
Meteors are meteoroids that have entered that have entered the Earth’s
atmosphere, when they enter the earths atmosphere they start to heat up and
glow due to friction causing a trail of light. They are often referred to as “shooting
stars”
Meteorites are pieces of meteors that survive their fiery passage through the
Earth’s atmosphere and hit the Earth’s surface.
ATOMIC STRUCTURE AND PERIODIC
TABLE
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The periodic table Is structured in periods ( Horizontal) and groups (Vertical)
The mass of an atom increases as you move from right to left
The periodic table shows the mass number of an atom and the atomic number.
The mass number is a measure of how many protons plus neutrons.
The atomic number tells us how many protons the atom has.
Protons are positively charged, electrons are negatively charged, neutrons have
no charge, they are neutral.
Atoms have no overall charge as the number of protons is equal to the number
of electrons.
The atomic number tells us
how many protons/electrons
there are
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LI
Lithium
7
The mass number tells us how
many protons plus neutrons
there are in the atom
ATOMIC STRUCTURE
First Electron Shell
Second Electron Shell
Nucleus
Lithium
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Electrons move in electron shells.
Atoms can have one or even more electron shells.
The first electron shell can hold up to two electrons
The proceeding electron shells can hold up to 8 electrons.
Atoms are held together by electrostatic forces
o Electrostatic force in the atom is the attraction between the positively
charged protons in the neutron and the negatively charged electrons
on the outer shell.
TRENDS IN GROUPS WITHIN THE
PERIODIC TABLE
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The periodic table is columned into sections called groups.
These groups share common properties and trends within them
GROUP 1: THE ALKLAI METALS
The elements In group 1, also known as the Alkali Metals, includes the elements
Lithium, Sodium, and Potassium. (LSP)
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All the group 1 metals have one valence electron and give up this electron during
ionic bonding
As you move down the group the elements get progressively softer.
As you move down the elements in Group 1, the Atomic number and mass
number increase; this tells us the size of the atom is increasing.
The melting point and boiling point decreases as we move down the elements of
group 1.
o This is because as we move down group 1, the element’s atomic radius
increase. This increase in Atomic radius means the electrostatic
attraction between the nucleus and the outer valance electron is not as
strong. This weak attraction means the outer valance electron can easily
be shed and thus a weak metallic bond, weaker metallic bonds require
less energy to overcome, hence the low melting points.
§ This increase in atomic radius also increases the elements
reactivity. So as we go down the group 1 elements, the elements
get progressively more reactive, due to the weakening of the
electrostatic attraction between the outer valence electron and
the inner nucleus which causes easier electron shedding.
GROUP 7: THE HALOGENS
The elements in group 7,also known as the halogens, the group includes the elements
fluorine, chlorine, and bromine (FCB)
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The halogens are non-metals so they receive electrons during ionic bonding.
All of group 7 elements have 7 valence electrons on its valence shell.
As we move down the group 7 elements the atomic radii increases, thus meaning
its mass also increases.
As we move down group 7 the colour changes, becoming darker; fluorine has a
pale yellow colour, chlorine has a yellowish green colour, and bromine has a
brown colour.
The boiling point and melting point of the halogens increase as we go down the
group
o This is because as we move down the group, the atoms increase in size,
this increase in size means an increase in its weak intermolecular bond.
Called van der Waals force.
As we move down the group elements become less reactive.
o This is because as we move down the group atomic radii increases, this
increase in atomic radii means that the valence shell is further away from
the nucleus, so thus. The nucleus’ positive attraction as a weaker
attraction to incoming electrons.
GROUP 8: NOBLE GASES
The elements in group 8, also known as the noble gases, the group includes the
elements helium, neon, and argon. They are all gases and are inert, so they can’t form
compounds.
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As we descend down group 8 the elements increase in atomic radii, meaning
they become bigger. This increase in size leads to stronger London dispersion
forces, hence why the melting an boiling points increase.
They melting and boiling points also increase.
All group 8 elements have complete valence shells.
CHEMICAL BONDING
Atoms are more stable when their valence shell is completely full with electrons. There
is only one group of electrons that have a full valence shell, and that’s group 8, hence
why they don’t react with other elements.
All other elements do not have a full valence shell so they react to form compounds. In
doing so they fill up their valence shell with electrons. The elements in compounds are
held together by chemical bonds. These bonds can be formed in two ways:
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Atoms can gain or lose electrons – Ionic Bonding
Atoms can share electrons – Covalent Bonding
IONIC BONDING
Ionic bonding is a bond whereby one or more electrons are transferred from one atom to
another, resulting in the formation of oppositely charged ions. These ions are held
together by strong electrostatic attractions. Ionic bonding only occurs between nonmetals and metals.
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Metals give away electrons to form positively charged cations
Non-metals receive electrons to form negatively charged cations.
COVALENT BONDING
Covalent bonding is a chemical bond in which atoms share 2 or more pairs of electrons
to archive a stable electronic configuration. This happens between non-metals. They do
they do this to fill up their valence shell.