Download 2.1.1 Microscopy - Ms Fennessy`s Biology Class

2.1 CELL STRUCTURE
2.1.1 Microscopy
The cell is the smallest unit of living organisms that shows the characteristics of life.
A general introduction to the microscope.
The light microscope
All cells are microscopic which means they can only be seen with the help of a microscope.
The light microscope is the most commonly used microscope in biology. It uses light to show
the image.
Light microscopes are also known as compound microscopes because they use two lenses –
an eyepiece lens and an objective lens.
The best light microscope will only magnify an image about 1000 times.
The total magnification of a microscope is calculated by multiplying the magnifying power of
the eyepiece lens by the magnifying power of the objective lens.
Functions of the parts of the light microscope
Part
Eyepiece
Nosepiece
Objective lens
Stage
Stage Clips
Diaphragm
Coarse focus wheel
Fine focus wheel
Light source (mirror)
Ms. B. Fennessy
Function
Magnifies the image
Rotates in order that an objective lens can be used
Magnifies the image
Holds the microscope slide
Holds the microscope slide in place
Controls the amount of light passing up through the slide
Used to make large adjustments in image clarity
Used for make smalls adjustments in image clarity
Shines light up through the slide
Loreto Secondary School
Fermoy
Co.Cork
2.1 CELL STRUCTURE
The Transmission Electron Microscope (TEM)
The transmission electron microscope (TEM) is a very powerful microscope. This microscope
sends a beam of electrons through the specimen. This shows the internal structure of the
specimen in great detail. The image is produced on a screen or photograph. So the
transmission electron microscope gives higher magnifications, greater resolution and greater
detail than the light microscope.
2.1.2 Cell Structure and Function
Components of the cell under the light microscope and their functions.
Animal cells: cytoplasm and nucleus.
Plant cells: cell wall, cytoplasm, nucleus, vacuole, and chloroplast.
Ms. B. Fennessy
Loreto Secondary School
Fermoy
Co.Cork
2.1 CELL STRUCTURE
Cell Component
Cytoplasm
Nucleus
Cell membrane
Cell wall
Vacuole
Chloroplast
Function
Site of chemical reactions
Controls the cell’s activities
Semi-permeable, controls what enters and leaves the cell
Gives the cell strength and support
Stores sugars & salts, gives the cell turgor (rigidity)
Carry out photosynthesis
Position and function of cell membrane
The cell membrane surrounds both plant and animal cells. Its function is to allow only
certain things in or out of the cell i.e. it is semi-permeable (selectively permeable).
2.1.3 Cell Ultrastructure
Ms. B. Fennessy
Loreto Secondary School
Fermoy
Co.Cork
2.1 CELL STRUCTURE
Identification and Function of the Cell Membrane
Identification
Cell membranes surround cells and all membranes have
the same structure.
They are made of a double layer of phospholipids. There
are proteins embedded in the phospholipid bilayer.
This concept of cell membrane structure is called the Fluid
Mosaic Model
Function



To control what enters and leaves the cell – semi-permeable.
To hold the cell contents
To recognise foreign particles and sense molecules that touch them
Identification and Function of the Mitochondrion
Identification
Mitochondria have a smooth outer membrane and a folded inner membrane with many
infoldings called cristae. They also have their own DNA.
Ms. B. Fennessy
Loreto Secondary School
Fermoy
Co.Cork
2.1 CELL STRUCTURE
Function
 To supply energy to the cell. They carry out respiration – powerhouse of the cell.
Active cells have a lot of mitochondria – muscle, brain and liver cells in humans,
meristematic cells (shoot and root tips) in plants.
Inactive cells have few mitochondria – fat in humans and ground tissue in plants
Identification and Function of the Chloroplast
Identification
Chloroplasts are only found in plant cells. They have a double membrane on the outside and
inside there are stacks of membranes called grana which are found in the liquid called stroma.
The green pigment (colour) chlorophyll is contained in the grana.
Function
 To carry out photosynthesis (Use light to make food for the plant).
Identification and Function of the Nucleus
Identification
The nucleus is surrounded by a double membrane which contains many nuclear pores. It
contains a nucleolus which makes ribosomes and heredity material called chromatin.
Ms. B. Fennessy
Loreto Secondary School
Fermoy
Co.Cork
2.1 CELL STRUCTURE
Function
 To control the cells activities. It is the control centre of the cell.
Identification and Function of Nuclear Pores
Identification
Nuclear pores are small holes found in the nuclear envelop or
double membrane.
Function
 To allow chemicals to pass in and out of the nucleus.
Identification and Function of DNA
Identification
DNA (Deoxyribonucleic acid) is found in the nucleus in structures
called chromosomes. Genes are found on the chromosomes and
are sections of DNA that contain the code for making proteins.
The chromosomes are usually in the form of fine threads called
chromatin.
Function
 To regulate the making of proteins in the cell
Identification and Function of Ribosomes
Identification
Ribosomes are tiny organelles found in the cytoplasm of the cell. They are made of RNA
and protein and consist of two pieces or subunits ( like a burger bun!)
Function
 To make proteins. They do this by joining amino acids.
Ms. B. Fennessy
Loreto Secondary School
Fermoy
Co.Cork
2.1 CELL STRUCTURE
H.2.1.4 Prokaryotic and Eukaryotic Cells
Cells are divided into two main types:
1. Prokaryotic cells
Prokaryotic cells have no true nucleus. They have a loop of DNA which is found in the
cytoplasm.
They have no mitochondria or chloroplasts. They are small primitive cells.
Bacteria cells are the only prokaryotic cells that exist.
Prokaryotic cells do not have a membrane- bound (true) nucleus or membrane-bound
organelles like mitochondria and chloroplasts.
2. Eukaryotic cells
Eukaryotic cells have a true nucleus. Their DNA is enclosed by a nuclear membrane.
They have mitochondria and chloroplasts. They are larger and more advanced cells and
evolved from prokaryotic cells.
Most organisms (plants, animals and fungi) are eukaryotes
Eukaryotic cells have a membrane-bound (true) nucleus and membrane-bound
organelles like mitochondria and chloroplasts.
Ms. B. Fennessy
Loreto Secondary School
Fermoy
Co.Cork