Transcript The Basic Structure of Cells

Chapter 4
The Basic Structure of Cells
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4.1
The Role of Cells in Organisms
4.2
4.3
The Microscope
The Basic Structure of a Cell
4.4
Levels of Organization in Organisms
4.5
Discovery of Cells
4.1 The Role of Cells in Organisms (p. 78)
Role of cells in organisms
Cell: the basic unit of life
They control the basic functions of life:
• Growth
• Reproduction
• Movement
• Detection of environmental changes
• Response
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4.2 The Microscope (p. 78)
How to magnify an object?
Hand lens / dissection microscope
• With magnification of 10 ~ 20 times
• For examining the external features of relatively large
specimens
Microscopes:
• Light microscope: with magnification up to
1,500 times
• Electron microscope: with magnification up
to
1,000,000 times
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4.2 The Microscope (p. 79)
What are the different parts of a light
microscope and their functions?
Coarse
adjustment knob
Fine adjustment
knob
Stage
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Eyepiece
Body tube
Nosepiece
Objective
Clip
Condenser
Diaphragm
Mirror
4.2 The Microscope (p. 82-83)
Practical 4.1
Using the light microscope for low-power magnification
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4.2 The Microscope (p. 82-83)
Analysis
1. How should the slide be placed and fixed in the correct position for
observation?
Ans: Place the slide on the stage so that the specimen is located
at the centre of the hole. Hold the slide in position with the clips
2. Which parts of the microscope is concerned with the direction,
brightness and uniformity of light respectively?
Ans: Mirror, diaphragm and condenser
3. How can the specimen be brought into focus?
Ans:
(a) Watch the objective from the side.
(b) Turn the coarse adjustment knob to lower the body tube
until the objective is close but not touching the slide.
(c) Look down through the eyepiece and turn the coarse
adjustment knob to raise the body tube slowly until the
specimen comes into focus.
(d) Turn the fine adjustment knob for fine adjustment of focus
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4.2 The Microscope (p. 81)
Table showing the comparison between low power
and high power magnification:
Magnification power
Details of the specimen
Low power
Smaller
Less
High power
Greater
More
Field of view
Image brightness
Large
Brighter
Smaller
Dimmer
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4.2 The Microscope (p. 81)
Critical Thinking 4.1
How can the magnification of an object be worked out?
The total magnification:
magnifying power of the eyepiece  magnifying power of the objective
Complete the table below:
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Eyepiece
Objective
Magnification of the object
5x
5x
25x
5x
10x
50x
10x
10x
100x
10x
40x
400x
15x
40x
600x
4.3 The Basic Structure of a Cell (p. 86)
What common features are found in animal cells?
Drawings of some human cells
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4.3 The Basic Structure of a Cell (p. 87)
Diagram
showing a typical animal cell (not drawn to scale)
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4.3 The Basic Structure of a Cell (p. 87)
Cell membrane
•
•
•
•
Located on the outer surface of the cell
A thin, elastic layer
Composed of fats and proteins
Function:
- control the movement of substances in
and
out of the cell (selectively permeable)
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4.3 The Basic Structure of a Cell (p. 87)
Cytoplasm
•
•
•
•
Bounded by the cell membrane
A flexible, jelly-like substance
The site for cellular activities
Water is the main constituent
• Contains: - chemical substances
- food granules (glycogen)
- vacuoles
- organelles (structures in a cell in
which
certain functions and processes are
carried
out)
Mitochondria
(singular: mitochondrion)
• Rod-like structure
• Function:
12 - release energy from the breakdown of food (respiration)
Mitochondria
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4.3 The Basic Structure of a Cell (p. 87)
Nucleus (pleural: nuclei)
• A dense and spherical structure in the cytoplasm
• Surrounded by a nuclear membrane
 controls the movement of substances in and
out of the nucleus
• Contains chromosomes
- composed of DNA and proteins
- carry genetic materials
• Functions:
- determine the organism’s characteristics
- control the normal activities of the cell
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chromosome
nucleus
cell
DeoxyriboNucleic Acid.
DNA
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4.3 The Basic Structure of a Cell (p. 88)
What common features are found in plant cells?
Drawings of some plant cells
Root hair cell
Guard cells
Palisade mesophyll cells
Epidermal cells
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4.3 The Basic Structure of a Cell (p. 89)
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Diagram showing a typical plant cell (not drawn to scale)
4.3 The Basic Structure of a Cell (p. 89)
Characteristics of plant cells:
• Comparatively more regular in shape
• Have all the structures found in an animal cell
(e.g. cell membrane, cytoplasm, nucleus and
mitochondria)
• Have a cell wall
• Possess a large central vacuole
• Have chloroplasts for photosynthesis
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4.3 The Basic Structure of a Cell (p. 89)
Cell wall
• A thick and rigid layer surrounding the cell
membrane
• Mainly composed of cellulose
• Freely permeable
• Functions:
- gives a definite cell shape
- protects the delicate internal structures
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4.3 The Basic Structure of a Cell (p. 89)
Chloroplasts
• A kind of organelle
• Contain chlorophyll and enzymes
• Function:
- carry out photosynthesis
Vacuole
• Surrounded by a membrane
• Filled with cell sap
- which contains a solution of sugars, proteins,
minerals and other substances
• Function:
- acts as a store of various substances
(e.g. water, food, pigments, enzymes, wastes, etc.)
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4.3 The Basic Structure of a Cell (p. 92)
What are the similarities and differences
between animal cells and plant cells?
Common structures:
• Both possess cytoplasm surrounded by a cell
membrane
• Both possess mitochondria
• Both possess a nucleus surrounded by a nuclear
membrane
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4.3 The Basic Structure of a Cell (p. 92)
Table showing the differences between animal cells
and plant cells:
Animal cells
1. Do not have a cell wall
Plant cells
Have a cellulose cell wall
2. Usually irregular in shape Usually regular in shape
3. Have small or no vacuoles Usually have a large central
vacuole
4. Do not have chloroplasts Some have chloroplasts
5. Usually have glycogen
granules
6. Nucleus usually at the
centre of the cell
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Usually have starch grains
Nucleus usually at the
edge of the cell
4.4 Levels of Organization in Organisms (p. 95)
How cells are organized to form organism?
Cellular level
Unicellular organism:
• Made up of a single cell
• Carries out all the life activities necessary for
survival on its own
• Examples: Amoeba, bacteria
Multicellular organism:
• Composed of a large number of cells
•23 Example: human
4.4 Levels of Organization in Organisms (p. 95)
Multicellular organism:
All the body cells carry out the basic life processes on their own
(e.g. respiration, process of getting rid of waste products)
Different types of cells work together to carry out
particular functions
In human body:
• Muscle cells  movement
• Nerve cells  transmitting signals
• Red blood cells  carrying oxygen
• White blood cells  killing germs
In plant body:
• Cells with chloroplasts  photosynthesis
•24 Strong and rigid cells  supporting the plant body
4.4 Levels of Organization in Organisms (p. 96)
How are cells organized into higher levels?
Tissue level
A tissue is formed when the same type of
cells are associated to carry out a particular
function
For examples:
In animals: bone, muscle, nerves etc.
In plants: vascular tissue
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bone
muscle
Vascular
tissue
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4.4 Levels of Organization in Organisms (p. 97)
Organ level
An organ is formed when different types of
tissues are grouped together to perform a more
complicated function
Example: The heart is an organ composed of
various tissues, including
- cardiac muscles
- blood vessels
- nervous tissues
- connective tissues
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4.4 Levels of Organization in Organisms (p. 97)
Other examples:
Some external organs of animals:
• Eyes
• Ears
• Nose
• Skin
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4.4 Levels of Organization in Organisms (p. 97)
Other examples:
Some
internal organsSmall
of animals: intestine
•
•
•
•
Lungs
Liver
Stomach
Kidneys
Liver
Stomach
Pancreas
Uterus
Caecum
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Heart
Lung
4.4 Levels of Organization in Organisms (p. 97)
Fruit
Other examples:
For plants:
• Roots
• Stems
• Leaves
• Flowers
• Fruits
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Flower
Leaf
4.4 Levels of Organization in Organisms (p. 98)
System level
A system is formed when different organs and tissues
work together to carry out a particular process
Examples:
In human body:
digestive system, breathing system, excretory
system, circulatory system, skeletal system,
muscular system, nervous system, endocrine system,
reproductive system
Examples:
In plants:
transporting system & supporting system
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4.4 Levels of Organization in Organisms (p. 98)
The different levels of organization in a
multicellular organism can be summarized as:
cells  tissues  organs  systems  organism
The digestive system, breathing system and excretory system
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4.5 Discovery of Cells (p. 99)
Discovery of cells
Robert Hooke:
• A British scientist in the
seventeenth century
• He observed a thin piece
of cork under the
microscope that he made
on his own
• He saw the structures
that look like “little rooms”
& gave the name “cells”
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4.5 Discovery of Cells (p. 99)
After further observation and studies by
scientists, the cell theory is formulated
Cell theory: The cell is the basic unit
of structure and function of living
things. There are many different types of
cells but they are similar in their basic
structure
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4.5 Discovery of Cells (p. 100)
Electron microscope:
• Allows scientists to observe even smaller
structures inside a cell
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4.5 Discovery of Cells (p. 100)
Scanning electron
microscope:
• Provides a threedimensional surface
view of structures
• With very high
magnification
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Chapter 4 (p. 100)
The following statements contain some wrong concepts commonly
held by students. Point them out and give correct statements.
1. The outermost layer of a cell is the cell membrane.
Ans: It is true only of animal cells since plant cell has a cell wall
outside the cell membrane
2. Vacuoles are found only in plant cells.
Ans: Sometimes, small vacuoles are also found in animal cells
3. A large number of cells form a tissue.
Ans: Only large number of similar cells form a tissue
4. All living animal and plant cells contain cytoplasm, cell
membrane and nucleus.
Ans: The statement is true in most ceases but mature red blood
cells have no nucleus
5. Chloroplasts are found in plant cells and mitochondria are
found in animal cells.
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Ans: Chloroplasts are found in plant cells, but mitochondria are
found in both plant and animal cells