cell structure and transport
,B1 Cell Structure and Transport
1.1 The World of the Microscope — Study Notes
Why microscopes are important
● All living things are made of cells
● Most cells are too small to see with the naked eye
● Microscopes allow scientists to see cells and subcellular structures
Units used in microscopy
● 1 km = 1000 m
● 1 m = 100 cm
● 1 cm = 10 mm
● 1 mm = 1000 micrometres (µm)
● 1 µm = 1000 nanometres (nm)
● 1 nm = 1 × 10⁻⁹ m
Parts of a light microscope
● Eyepiece lens – where you look through
● Objective lens – magnifies the specimen
● Stage – holds the slide
● Slide – holds the specimen
● Light source – illuminates the specimen
● Coarse focus – large focus adjustments
● Fine focus – small, precise focus adjustments
Light microscopes
● Developed in the mid-17th century
● Use light to form an image
● Maximum magnification: ~×2000
● Resolving power: ~200 nm
● Advantages:
○ Cheap
○ Portable
○ Can view living specimens
● Disadvantages:
○ Lower resolution than electron microscopes
Electron microscopes
, ● Invented in the 1930s
● Use a beam of electrons
● Maximum magnification: ~×2,000,000
● Very high resolution
● Types:
○ Transmission electron microscope (TEM)
■ 2D images
■ Very high magnification and resolution
○ Scanning electron microscope (SEM)
■ 3D images
■ Lower magnification than TEM
● Disadvantages:
○ Very expensive
○ Large
○ Need special controlled conditions
○ Cannot view living specimens
Magnification
Formula:
Magnification=image sizereal size\textbf{Magnification} = \frac{\text{image size}}{\text{real
size}}
Magnification=real sizeimage size
Light microscope magnification:
● Eyepiece magnification × Objective magnification
● Example: ×4 eyepiece and ×10 objective
○ Total magnification = ×40
Calculating real size
Formula:
Real size=image sizemagnification\textbf{Real size} = \frac{\text{image size}}{\
text{magnification}}
Real size=magnificationimage size
Example:
● Image size = 1 mm
● Magnification = ×40
● Real size = 0.025 mm = 25 µm
Resolution (resolving power)
, ● Resolution = ability to distinguish two close points as separate
● Higher resolution = more detail visible
● Resolving power:
○ Light microscope: ~200 nm
○ SEM: ~10 nm
○ TEM: ~0.2–3 nm
Key exam facts ⭐
● Light microscopes:
○ Max magnification ≈ ×2000
○ Resolution ≈ 200 nm
● Electron microscopes:
○ Max magnification ≈ ×2,000,000
○ Resolution ≈ 0.2 nm
● Always label microscope drawings with the magnification used
Animal cells – structure and function
Animal cells are typical of the cells found in the human body. Most animal cells are 10–30
µm long.
Structures found in animal cells (and all cells)
Nucleus
● Controls the activities of the cell
● Contains genes on chromosomes
● Surrounded by a nuclear membrane
● About 10 µm in diameter
Cytoplasm
● Jelly-like liquid where chemical reactions take place
● Contains the cell organelles
Cell membrane
● Controls what enters and leaves the cell
● Allows substances like glucose and minerals in
● Allows waste products (e.g. urea, hormones) out
Mitochondria
● Site of aerobic respiration
● Release energy for the cell
● Very small: 1–2 µm long
Ribosomes
● Site of protein synthesis
● Make all the proteins needed by the cell
,B1 Cell Structure and Transport
1.1 The World of the Microscope — Study Notes
Why microscopes are important
● All living things are made of cells
● Most cells are too small to see with the naked eye
● Microscopes allow scientists to see cells and subcellular structures
Units used in microscopy
● 1 km = 1000 m
● 1 m = 100 cm
● 1 cm = 10 mm
● 1 mm = 1000 micrometres (µm)
● 1 µm = 1000 nanometres (nm)
● 1 nm = 1 × 10⁻⁹ m
Parts of a light microscope
● Eyepiece lens – where you look through
● Objective lens – magnifies the specimen
● Stage – holds the slide
● Slide – holds the specimen
● Light source – illuminates the specimen
● Coarse focus – large focus adjustments
● Fine focus – small, precise focus adjustments
Light microscopes
● Developed in the mid-17th century
● Use light to form an image
● Maximum magnification: ~×2000
● Resolving power: ~200 nm
● Advantages:
○ Cheap
○ Portable
○ Can view living specimens
● Disadvantages:
○ Lower resolution than electron microscopes
Electron microscopes
, ● Invented in the 1930s
● Use a beam of electrons
● Maximum magnification: ~×2,000,000
● Very high resolution
● Types:
○ Transmission electron microscope (TEM)
■ 2D images
■ Very high magnification and resolution
○ Scanning electron microscope (SEM)
■ 3D images
■ Lower magnification than TEM
● Disadvantages:
○ Very expensive
○ Large
○ Need special controlled conditions
○ Cannot view living specimens
Magnification
Formula:
Magnification=image sizereal size\textbf{Magnification} = \frac{\text{image size}}{\text{real
size}}
Magnification=real sizeimage size
Light microscope magnification:
● Eyepiece magnification × Objective magnification
● Example: ×4 eyepiece and ×10 objective
○ Total magnification = ×40
Calculating real size
Formula:
Real size=image sizemagnification\textbf{Real size} = \frac{\text{image size}}{\
text{magnification}}
Real size=magnificationimage size
Example:
● Image size = 1 mm
● Magnification = ×40
● Real size = 0.025 mm = 25 µm
Resolution (resolving power)
, ● Resolution = ability to distinguish two close points as separate
● Higher resolution = more detail visible
● Resolving power:
○ Light microscope: ~200 nm
○ SEM: ~10 nm
○ TEM: ~0.2–3 nm
Key exam facts ⭐
● Light microscopes:
○ Max magnification ≈ ×2000
○ Resolution ≈ 200 nm
● Electron microscopes:
○ Max magnification ≈ ×2,000,000
○ Resolution ≈ 0.2 nm
● Always label microscope drawings with the magnification used
Animal cells – structure and function
Animal cells are typical of the cells found in the human body. Most animal cells are 10–30
µm long.
Structures found in animal cells (and all cells)
Nucleus
● Controls the activities of the cell
● Contains genes on chromosomes
● Surrounded by a nuclear membrane
● About 10 µm in diameter
Cytoplasm
● Jelly-like liquid where chemical reactions take place
● Contains the cell organelles
Cell membrane
● Controls what enters and leaves the cell
● Allows substances like glucose and minerals in
● Allows waste products (e.g. urea, hormones) out
Mitochondria
● Site of aerobic respiration
● Release energy for the cell
● Very small: 1–2 µm long
Ribosomes
● Site of protein synthesis
● Make all the proteins needed by the cell
