Download Primary 6 Science Term One The Cell

Primary 6
Science
Term One
The Cell
All living organisms are made of cells. They form the basic organizational
building block for living things. In general there are two kinds of cells: Animal
cells and Plant cells.
Animal cells and plant cells
Cells are very small and we need a microscope to see them. This is why they are
called microscopic units. The photographs show animal cells and plant cells, as
seen through a microscope.
These are cheek cells, seen through a microscope
These are onion cells, seen through a microscope
Animal cells come in all kinds of shapes and sizes but have the same basic
features.
Plant cells also come in a variety of forms but share similar features.
Example: Palisade cells in leaves have lots of chloroplasts.
Similarities and differences
As we have noticed plant and animal cells share the same basic structural
features, although plant cells have a few extra bits (organelles). It is easier to
explain what these bits (organelles) are by using diagrams like the ones below.
Animal cells usually have an irregular shape, and plant cells usually have a regular shape
Animal cells and plant cells both contain:
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cell membrane ( plasma membrane)
cytoplasm
nucleus
mitochondrion
centrosome
golgi body
Plant cells only also contain:
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chloroplasts (Plastids)
sap vacuole
cell wall ( the cellular wall )
The table summarizes the functions or jobs of these parts.
Part
Function
Cell (plasma)
membrane
Controls what substances can get into and out of the
cell.
Cytoplasm
Jelly-like substance, where chemical reactions happen.
In plant cells there's a thin lining, whereas in animal
cells most of the cell is cytoplasm.
Nucleus
Controls what happens inside the cell - it is not a
'brain'.
Chloroplast
Where photosynthesis happens – chloroplasts contain
a green substance called chlorophyll.
Vacuole*
It plays the role of intracellular digestion and the
release of cellular waste products. In animal cells,
vacuoles are generally small. In plant cells it is large
and contains a liquid called cell sap, which keeps the
cell firm.
Cell wall
Made of a tough substance called cellulose, which
supports the cell.
Mitochondrion
Tiny rod like or string like structures that process food
for energy. (Where the respiration takes place in the
cell).
Centrosome
It is a special organ of cell division.
Golgi body
To sort, package and ship proteins.
*Some animal cells do have a vacuole but not all of them do. In animal cells, it is
called vacuole, whereas, in plant cells it is called sap vacuole.
Cells and their functions
Humans are multi-cellular animals. We are made of lots of cells, not just one
cell. The cells in many multi-cellular animals and plants are specialized, so that
they can share out the seven processes of life that are common to living things.
These processes are respiration, nutrition, excretion, growth, sensitivity,
movement and reproduction. The cells work together like a team to support the
different processes in an organism.
You should be able to work out special features of a cell from a drawing, if you
are told what the cell can do. The tables below show examples of some
specialized animal and plant cells, with their functions and special features.
Type of
animal cell
Function
Special features
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Red blood cells
Nerve cell
Epithelial cell
Type of plant
cell
Root hair cell
To carry
oxygen and
carbon dioxide
during the
respiration
process
To carry nerve
impulses to
different parts
of the body
To make
mucus to trap
dust and
germs
Function
To absorb
water and
minerals
Palisade (Leaf)
cell
To absorb
sunlight for
photosynthesis
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Large surface area, for
oxygen to pass through
Contain hemoglobin,
which joins with oxygen
Have no nucleus and can
be squashed to be able to
pass easily through the
small blood vessels
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Long
Connections at each end
Can carry electrical
signals
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Found in the nose and
throat
Has tiny hairs called cilia
which move the mucus
out of your body
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Special features
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Has long finger-like root
hair which gives a large
surface area
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Found in plant leaves
Large surface area
Lots of chloroplasts near
the surface
Cells, tissues, organs, organ systems and organism
Some plants and animals are just a single cell (unicellular organisms) which
performs all life function. But most of us are multicellular organisms made up of
lots of cells all working together.
Some of these cells are all of the same type, collectively they are called a
tissue. They all do the same job, for example connective tissue, which is used in
animals to connect other tissues together - and stop us falling apart!
Next, some different tissues are grouped together to make up an organ such as
the stomach or a leaf.
Finally, some organs work together to form an organ system such as the
digestive system.
So we can say that Multicellular (many celled) organisms have the following 5
levels of organization ranging from simplest to most complex:
Cells: Are the basic unit of structure and function in living things. Examplesblood cells, nerve cells, bone cells, etc. The first scientist who discovered the cell
was the British scientist ' Robert Hooke". He called the cells ' rooms'. At birth,
the human body consists of three trillion cells and these cells are then divided to
become about 75 trillion cells.
Tissues: Animal cells and plant cells can form tissues. These are not paper
hankies! A living tissue is made from a group of cells with a similar structure
and function, which all work together to perform a specific job. Here are some
examples of tissues:
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Muscle
the lining of the intestine
the lining of the lungs
root hair tissue (for plants to take up water and minerals from the soil)
blood tissue
bone tissue
Organs: An organ is made from a group of different tissues, which all work
together to do a particular job. Here are some examples of organs:
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heart
lung
stomach
brain
leaf
root
Organ systems: An organ system is made from a group of different
organs, which all work together to perform a specific function for the organism.
Here are some examples of organ systems:
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circulatory system
respiratory system
digestive system
nervous system
reproductive system
leaf canopy
Organisms: They are entire living things that can carry out all basic life
processes. Meaning they can take in materials, release energy from food, release
wastes, grow, respond to the environment, and reproduce. Usually made up of
organ systems, but an organism may be made up of only one cell such as
bacteria.
The levels of organization in the correct order then are:
cells --> tissues --> organs --> organ systems --> organism
Two human examples are:
neurons (nerve cells) --> nervous tissue --> brain --> central nervous system -> human
bone cells
vertebrate
--> connective (bone) tissue --> bones --> skeletal system -->
The heart: An organ, such as the heart, is made up of groups of tissues that
work together to perform a specific function. The heart is a pump that keeps
blood flowing throughout the body. The heart is primarily made up of muscle
tissue, but also contains connective and nervous tissue. However, each of these
individual types of tissues has its own primary
function which differs from the basic function of
the heart.
Primary 6
Science
Term One
Unit One
The Cell
Exercises
A- Fill in the blanks:
1- A plant cell is protected by a stiff _________________, which an animal cell
lacks.
2- Plant cells contain _________________, which are the cell’s food factories.
3. The activities of a plant or an animal cell are controlled by the
___________________________.
4. A plant and an animal cell are alike in that they both have a thin outer
covering called the _______________________.
5. The jellylike substance that fills the cell is called ________________.
6. Most plant cells have a green coloring which most _______________ cells
lack.
7. Bacteria is different from plant and animal cells in that this one- celled
organisms lacks a _______________ or control center.
8. Bricks make up a wall just as _________________ make up an organism.
B) Put the level of organization in order from smallest to largest.
C) Choose the correct answer :
1- Which of these is similar in function to a vacuole?
A wall, an electric circuit, a bakery, a closet
2- Which of the following is not an organ?
A skin, the heart, bones, blood tissue
3- Where does cellular respiration occur?
In the lungs, in the vacuole, in the chloroplasts, in the mitochondrion
4- What part of the cell helps control what enters and leaves the cell?
Cytoplasm, mitochondrion, nucleus, cell membrane
5-Blood is considered a (n) ----------------Organ system, cell, organ, tissue
6-Which of the following is an organ?
Nerve tissue, blood tissue, muscle tissue, stomach
7-Chloroplasts capture energy from the-----------------to make food.
Moon, sun, soil, stored sugar
D - What is a cell?
E- What basic feature distinguishes plant and animal cells from bacteria?
F- What is a tissue?
G- What three structures does a plant cell have that an animal cell does not
have? Draw an animal cell and a plant cell.
H- Why do Plant cells have cell walls and Animal cells do not?
I- Why do think Plant cells have bigger vacuoles than Animal cells?
j- The diagram shows a generic animal and plant cell.
(1) What is the name given to the structure labeled A?
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(2) What is the function of the structure labeled A?
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(3) What is the name given to the structure labeled D?
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(4) What is the function of the structure labeled D?
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