Download Systems Ch 2 BI

i-Science – interact, inquire, investigate P5&6
Background information
Systems Ch 2 - Cells
Cells – The building blocks of life
Learning outcome:

Show an understanding that a cell is a basic unit of life
A cell is a basic unit of life. Every organism is made up of at least one cell. Organisms such
as bacteria, amoebae, yeast and paramecia are made up of only one cell. They are called
single-celled or unicellular organisms. Animals and plants are made up of many cells. They
are called multicellular organisms. A human being, for example, is made up of trillions of cells.
The study of cells began more than 300 years ago. In 1663, a scientist, named as Robert
Hooke, examined thin slices of cork using a self-made microscope. He observed a network of
tiny box-like compartments, which were similar to a honeycomb, and called these
compartments ‘cellulae’ (little rooms). This is how the term ‘cell’ was derived. What Robert
Hooke had observed were the cell walls of dead plant tissues.
The work of two scientists, Schleiden (a botanist) and Schwann (a zoologist), later led to the
cell theory, which proposed that the basic unit of structure and function in living organisms is
the cell.
The modern cell theory states the following:

All living things are made up of cells.

A cell is the structural and functional unit of all living things.

All new cells arise from other pre-existing cells.

All metabolic reactions of an organism take place in cells.

Cells contain the hereditary information of the organisms of which they are part of, and
this is passed on from the parent to the daughter cell.
Plant and animal cells
Learning outcomes:

Identify the different parts of a typical plant cell and animal cell and relate the parts to the
functions:
- Parts of plant cell: cell wall, cell membrane, cytoplasm, nucleus and chloroplasts
- Parts of animal cell: cell membrane, cytoplasm, nucleus

Compare a typical plant and animal cell
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Background information
Plants and animals are multicellular organisms made up of different types of cells. However,
the cells share many similarities.
A plant cell
Nucleus
Endoplasmic
reticulum
Golgi apparatus
Vacuole
Mitochondrion
Cytoplasm
Cell membrane
Chloroplast
Cell wall
An animal cell
Nucleus
Endoplasmic
reticulum
Golgi apparatus
Vacuole
Mitochondrion
Cell membrane
Cytoplasm
A cell is made up of many parts.
Cell membrane
It is a thin membrane separating a cell from its external environment. It allows only certain
substances to pass through, hence, it is called a partially-permeable membrane. Transport
across the cell membrane occurs to allow the cell to obtain nutrients, excrete waste materials
or secrete useful substances.
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Background information
Nucleus
It controls the activities of a cell. It contains chromatin, which is the loosely coiled form of
chromosomes. Chromosomes are made up of DNA (deoxyribonucleic acid) and proteins.
Segments of DNA which contain instructions to make proteins are called genes. Genes
control the activities of the cell and contain hereditary information which is passed on from
one generation to the next. (Note: Human red blood cells do not contain nuclei.)
Cytoplasm
It is a jelly-like material which fills the cell between the nucleus and cell membrane. It is
mostly made up of water with various chemicals, such as salt and proteins, dissolved or
suspended in it. Many chemical reactions which are involved in life processes take place
here. It contains organelles or cell parts such as mitochondria and Golgi apparatus. The
cytoplasm almost fills a typical animal cell but is reduced to a thin lining in a plant cell.
Chloroplasts
They are present in plant cells but not in animal cells. It contains the green pigment,
chlorophyll, and other pigments, such as carotenoids, which capture light energy for
photosynthesis. Photosynthesis takes place in the chloroplasts of plant cells.
Cell wall
It is present in plant cells but not in animal cells. The cell wall of a plant cell is made of
cellulose, a complex carbohydrate. The cell wall provides mechanical support and protection
to the plant cell and keeps it in shape. It prevents the cell from bursting and it is also a
pathway for the movement of water and mineral salts.
Endoplasmic reticulum (ER)
It is a continuation of the outer nuclear membrane. Some parts of the ER are smooth and are
called smooth ER. Smooth ER is important for the synthesis of lipids and membrane proteins.
Some parts of the ER are rough due to the presence of ribosomes on its surface. These parts
are called rough ER and are important for the synthesis of proteins.
Golgi apparatus
It is composed of flattened sacs piled up in stacks. It packages macromolecules for transport
to elsewhere in the cell, secretes carbohydrates involved in the production of new cell walls
for plant cells, transports and stores lipids and processes the proteins made in the ER.
Mitochondria
They are the organelles where cellular respiration takes place. They provide the energy
needs of the cell.
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Background information
Vacuole
It is a fluid-filled sac bound by a single membrane. It stores food and nutrients, such as
mineral salts, sugars and amino acids. It stores wastes too. Mature plant cells usually have
one large central vacuole. The vacuole of plant cells contains cell sap that keeps the cells
turgid. Animal cells usually have numerous and much smaller vacuoles.
A multicellular organism is made up of different types of cells. A human being, for example, is
made up of different cells, such as nerve cells, blood cells, muscle cells and skin cells. These
cells have different shapes and sizes to suit the functions they perform. A nerve cell, for
example, is long so that it can transmit signals quickly. A red blood cell has a large surface
area to volume ratio to absorb oxygen quickly.
Red blood cells
Nerve cells
Using a microscope
The following are some precautions to take when using a light microscope:

Do not place fingers on the cover-slips.

Hold the prepared slides at the ends or edges.

Do not touch the objective lenses with your fingers.

Place the specimen slide on the microscope stage such that the specimen is over the
middle of the hole on the stage and light can be seen passing through it.

Adjust the low power objective lens using the coarse focus knob until the low power
objective lens is about 5 mm from the slide.

Adjust the objective lens up (and not down) using the coarse adjustment until the
specimen is in focus by looking through the eyepiece. If the objective lens is adjusted
down, it may hit and damage the slide.

Keep both eyes open and use each eye in turn.
Internet links

Micrographs and microscopes
http://education.denniskunkel.com/index.php
http://school.discoveryeducation.com/lessonplans/activities/electronmicroscope/
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Background information
http://www.biology.ualberta.ca/facilities/multimedia/index.php?Page=284
http://micro.magnet.fsu.edu/primer/virtual/magnifying/index.html
http://www.bbc.co.uk/london/content/articles/2006/05/12/springwatch_microscope_featur
e.shtml

Cells
http://www.cellsalive.com/index.htm
http://www.sparknotes.com/testprep/books/sat2/biology/chapter4section1.rhtml
http://nature.ca/genome/03/c/03c_e.cfm
http://www.kathimitchell.com/cells.html
http://science.howstuffworks.com/cell.htm
Projects/Field trips

Make a 3D model of a plant cell or an animal cell. Pupils may use a computer software to
make a virtual 3D model of a cell. Label and describe the main parts of the cell.

Design a scarf using the shapes of different types of cells or unicellular organisms.
(Interdisciplinary project: art and science)

Write and illustrate a story about the discovery of cells by Antonie van Leeuwenhoek
(1632–1723) or Robert Hooke (1635–1703).
Recommended reading

The Usborne Internet-linked Complete Book of the Microscope (Publisher: Usborne)

The Usborne Internet-linked Introduction to Genes and DNA (Publisher: Usborne)

DK Megabites – Microlife (The Microscopic World of Tiny Creatures) (Publisher: DK)

DK Eyewitness Guides – Life (Publisher: DK)
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