Download CELLS: PLANT CELLS 20 FEBRUARY 2013 Key Concepts

CELLS: PLANT CELLS
20 FEBRUARY 2013
Lesson Description
In this lesson we will discuss the following:
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The Cell Theory
Terminology
Parts of Plant Cells: Organelles
Difference between plant and animal cells
Revision question
Key Concepts
The Cell Theory
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All living things are made up of cells and are either unicellular or multicellular.
Cells are the smallest working units of all living things that show the characteristics and
properties of life.
All cells come from preexisting cells through cell division.
Important Terms:
Cell wall
Cell membrane
Chromatin network
Cytoplasm
Endoplasmic reticulum
Golgi body
Mitochondrion
Nucleus
Nucleolus
Nuclear membrane
Organelle
Ribosomes
Vacuole
Chloroplast
Flaccid
Typical Plant Cells
Diagram showing the cross section of a plant cell
Turgid
Cell sap
Tonoplast
Vacuoles
Plasmodesmata
3D Diagram showing the cross section of a typical plant cell
Parts of Animal Cells
A typical plant cell consists of the following parts:
 A Cell Membrane
 Cell Wall
 Nucleus
 The Cytoplasm
 The Various Organelles
The Cell Membrane
Diagram showing the structure of a cell membrane
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The fluid mosaic model describes the structure of the plasma membrane.
Different kinds of cell membrane models have been proposed, and one of the most useful is
the Fluid-mosaic model. In this model the membrane is seen as a bilayer of phospholipids
in which protein molecules are embedded.
Cell Wall
Diagram showing the structure of a cell wall
One of the most important distinguishing features of plant cells is the presence of a cell wall.
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Structure: The cell wall is formed from fibrils of cellulose molecules, embedded in a watersaturated matrix of polysaccharides and structural glycoprotein.
Functions: The cell wall protects the cellular contents; gives rigidity to the plant structure;
provides a porous medium for the circulation and distribution of water, minerals, and other
small nutrient molecules; and contains specialised molecules that regulate growth and protect
the plant from disease. It provides the cell with great tensile strength.
Cell Wall & Plasmodesmata:
Diagram showing the structure of a cell wall and plasmodesmata
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Unlike cell membranes materials cannot get through cell walls. This would be a problem for
plant cells if not for special openings called plasmodesmata.
These openings are used to communicate and transport materials between plant cells
because the cell membranes are able touch and therefore exchange needed materials.
Nucleus
Diagram showing the structure on a nucleus
The nucleus is the control center of the cell. It is the largest organelle in the cell and it contains the
DNA of the cell. The DNA of all cells is made up of chromosomes.
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DNA (Deoxyribonucleic Acid) contains all the information for cells to live, perform their
functions and reproduce.
Inside the nucleus is another organelle called the nucleolus. The nucleolus is responsible for
making ribosomes.
The circles on the surface of the nucleus are the nuclear pores. These are where ribosomes,
and other materials move in and out of the cell.
The Cytoplasm
Diagram showing the internal contents of Cytoplasm
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Cytoplasm refers to the jelly-like material with organelles in it.
If the organelles were removed, the soluble part that would be left is called the cytosol.
It consists mainly of water with dissolved substances such as amino acids, vitamins and
nutrients in it.
Other Cellular Organelles
Chloroplast
Diagram showing the internal structure of a chloroplast
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It is an oval structure surrounded by a double unit membrane.
It has an internal medium called the stroma.
Stacks of thylakoids form granum which contain the pigment for photosynthesis.
These grana are connected to other grana by lamellae.
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The chloroplast is a cell organelle in which photosynthesis takes place. In this organelle the
light energy of the sun is converted into chemical energy.
Chloroplasts are found only in plant cells and not animal cells. The chemical energy that is
produced by chloroplasts is finally used to make carbohydrates like starch that get stored in
the plant.
Chloroplasts contain tiny pigments called chlorophylls. Chlorophylls are responsible for
trapping the light energy from the sun.
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Vacuoles
Diagram showing the structure of a plant vacuole
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Vacuoles and vesicles are storage organelles in cells. Vacuoles are larger than vesicles.
Functions: These structures may store water, waste products, food, and other cellular
materials.
In plant cells, the vacuole may take up most of the cell's volume.
The membrane surrounding the plant cell vacuole is called the tonoplast.
When a cell has its vacuole filled with cell sap it is referred to as a turgid cell. A cell in which
the vacuole has no or little water is referred to as a flaccid cell.
Mitochondrion
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Diagram showing the electron micrograph of a mitochondrion
Mitochondria are membrane-enclosed organelles distributed throughout the cytosol of most
eukaryotic cells.
Their main function is cellular respiration in which y convert the potential energy of food
molecules into ATP.
Every type of cell has a different amount of mitochondria. There are more mitochondria in
cells that have to perform lots of work, for example - your leg muscle cells, heart muscle cells
etc. Other cells need less energy to do their work and have less mitochondrion.
Diagram showing the internal structure on a mitochondrion
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Structure of Mitochondrion
Mitochondria have:
o an outer membrane that encloses the entire structure
o an inner membrane that encloses a fluid-filled matrix
o between the two is the intermembrane space the inner membrane is elaborately folded
with shelf like cristae projecting into the matrix.
Ribosome
Diagram showing the structure of a ribosome
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Ribososmes are organelles that help in the synthesis of proteins.
Ribosomes are made up of two parts, called subunits.
They get their names from their size. One unit is larger than the other so they are called large
and small subunits.
Both these subunits are necessary for protein synthesis in the cell. When the two units are
docked together with a special information unit called messenger RNA, they make proteins.
Some ribosomes are found in the cytoplasm, but most are attached to the endoplasmic
reticulum. While attached to the ER, ribosomes make proteins that the cell needs and also
ones to be exported from the cell for work elsewhere in the body.
Endoplasmic Reticulum
Diagram showing the structure of the endoplasmic reticulum
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It is a network of membranes throughout the cytoplasm of the cell.
There are two types of ER.
When ribosomes are attached it is called rough ER and smooth ER when there are no
ribosomes attached.
The rough endoplasmic reticulum is where most protein synthesis occurs in the cell.
The function of the smooth endoplasmic reticulum is to synthesize lipids in the cell.
The smooth ER is also helps in the detoxification of harmful substances in the cell.
Difference between Plant and Animals cells
Plants Cells
Most plant cells contain plastids
Surrounded by a cell wall and cell membrane
Usually one, large storage vacuole present
Generally have a regular shape
Animal cells
No plastids
Surrounded by a cell membrane only
No or few small specialised vacuoles present
Have more irregular and diverse shapes
Questions
Question 1
The following flow chart illustrates the relationship between two important processes found in the cells
of plants.
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Identify organelles X and Y
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Provide labels for parts A, B and C.
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Identify the metabolic processes that organelles X and Y control respectively.
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Organelle Y is called the “power house” of the cell. Suggest a reason for this.
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Name the carbohydrate that is formed by X and used by Y.
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In which cell would you expect to find more of organelle Y, in a skin cell or a liver cell?
Give a reason for your answer.
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g.) Described the interrelatedness between organelles X and Y based on the waste products
formed by these organelles during their respective metabolic processes.
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h.) Give ONE structural adaptation of each organelle and describe how this adaptation enables
the organelle to function efficiently.
(4)
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Links
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Magnification simulation http://www.cellsalive.com/howbig.htm
Animal / Plant Cell http://www.cellsalive.com/cells/cell_model.htm
3D animation of a cell: http://www.xvivo.net/the-inner-life-of-the-cell/