The Cell Membrane (Plasma Membrane) The fluid mosaic model

Phospholipid bilayer

Functions of the phospholipids Lipid soluble substances can easily enter and leave Lipid soluble substances can easily enter and leave Water soluble substances cannot enter – the cell can differentiate Water soluble substances cannot enter – the cell can differentiate The membrane is flexible (fluid mosaic model) The membrane is flexible (fluid mosaic model)

Proteins in the membrane Proteins arranged in the membrane (mosaic) Proteins arranged in the membrane (mosaic) Can be Extrinsic – on either surface Can be Extrinsic – on either surface Or Intrinsic – Completely span membrane Or Intrinsic – Completely span membrane

Support Carrier Proteins for water soluble products Ion channels – active transport Recognition Adhesion Receptors

How do we investigate Cell Organelles? First we have to remove the Cell Organelles… We call this CELL FRACTIONATION and it takes place in two stages 1.Homogenation 2.Ultracentrifugation

Cell Fractionation Cells are broken apart and the organelles are isolated Cells are broken apart and the organelles are isolated The cells must be placed in COLD, ISOTONIC, BUFFERED SOLUTION…why? The cells must be placed in COLD, ISOTONIC, BUFFERED SOLUTION…why?

Homogenation This is where the cells are broken apart This is where the cells are broken apart A blender or high frequency sound waves can be used A blender or high frequency sound waves can be used This produces a fluid known as HOMOGENATE. This produces a fluid known as HOMOGENATE. This is filtered to remove unbroken cells are large pieces of cell debris This is filtered to remove unbroken cells are large pieces of cell debris

The Homogenate is then centrifuged The Cell Online: Chapter 1 – Animations The Cell Online: Chapter 1 – Animations The Cell Online: Chapter 1 – Animations The Cell Online: Chapter 1 – Animations Watch this link to see what happens. Watch this link to see what happens. Then read pages 41 and 42 of your text book and answer questions Then read pages 41 and 42 of your text book and answer questions

Viewing Organelles We can use 1 of 3 types of microscope We can use 1 of 3 types of microscope 1 – Light Microscope 2 – Scanning Electron Microscope 3 – Transmission Electron Microscope

Units used in microscopy 1 metre = 1,000 mm 1 metre = 1,000 mm Millimetre 1mm = m =.001m Millimetre 1mm = m =.001m Micrometre 1  m = m = m Micrometre 1  m = m = m Nanometre 1nm = m = m Nanometre 1nm = m = m next

Light Microscope We will make Temporary Mounts and use Light Microscopes to view our slides

Disadvantages of the Light Microscope Poor Resolution- Due to the long wavelength of light. Relatively low Magnification

POWER of MICROSCOPES MAGNIFICATION: how many times an image is enlarged. RESOLUTION (resolving power): the ability to distinguish two points as being separate. (resolving power of the naked eye is about 0.2mm).

Electron Microscope Advantages – Higher Resolution as short wavelength electrons are used instead of long wavelength light. Higher Magnification.

Transmission E.M. The specimen is very thin The specimen is very thin May contain ‘artefacts’ May contain ‘artefacts’ Must be viewed in a vacuum Must be viewed in a vacuum So samples must be dead So samples must be dead A slow process to build an A slow process to build an overall 3D view overall 3D view Complex staining method Complex staining method A beam of electrons is focused onto the specimen Parts of the specimen absorb electrons They appear dark Other parts allow electrons to pass So appear light

Scanning E.M. Samples do not need to be as thin as TEM Beam of electrons does not penetrate Same negative points as TEM - Vacuum - Dead Samples - Complex staining used Lower resolution than TEM

An Electron Micrograph of an animal cell.

A TEM image of a plant cell

A TEM image of a Chloroplast

A Plant Cell – which type of microscope?

A White Blood Cell – which Microscope?

Which Organelle? Which Microscope?

Magnification How many times bigger the object is made. How many times bigger the object is made. The magnification can be worked out by… The magnification can be worked out by… Size of image Size of object

This equation can be rearranged Size of Object = Size of Image Magnification Magnification REMEMBER – ALL UNITS MUST BE THE SAME!!

Units 1 millimetre = mm 1 millimetre = mm 1 micrometer = µm = 1000 times smaller 1 micrometer = µm = 1000 times smaller 1 nanometer = nm = times smaller 1 nanometer = nm = times smaller

Resolution How clear an image is How clear an image is Resolution depends on whether the light or electrons can pass between two objects. Resolution depends on whether the light or electrons can pass between two objects.

Difference between light and electron microscopes Light microscopes have a low resolution as light has a long wavelength Light microscopes have a low resolution as light has a long wavelength Electron microscopes have a high resolution as the beam of electrons have a short wavelength. Electron microscopes have a high resolution as the beam of electrons have a short wavelength.

The Plasma Membrane The fluid mosaic model

Transport Across Membranes Diffusion Diffusion Osmosis Osmosis Active Transport Active Transport

Diffusion Animation: How Diffusion Works Animation: How Diffusion Works Animation: How Diffusion Works Animation: How Diffusion Works Particles in constant motion – kinetic energy Particles in constant motion – kinetic energy Random motion Random motion Particles bounce off one another and other particles Particles bounce off one another and other particles Passive – the energy is just kinetic Passive – the energy is just kinetic

NET movement of particles down a concentration gradient until DYNAMIC EQULIBRIUM is reached

Rate of Diffusion Fick’s Law. Fick’s Law. Rate = surface area x difference in conc. thickness of diffusion pathway thickness of diffusion pathway

Question Use Fick’s Law to explain why the lungs are an efficient gas exchange surface. Use Fick’s Law to explain why the lungs are an efficient gas exchange surface.

Facilitated Diffusion Facilitated Diffusion Diffusion which happens through specific protein channels. Diffusion which happens through specific protein channels. Water soluble substances can diffuse in this way Water soluble substances can diffuse in this way Read page 55 and 56 of your textbook, then answer the questions in the green box. Read page 55 and 56 of your textbook, then answer the questions in the green box. Click

Osmosis The passage of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane. The passage of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane. A more specialised form of diffusion. A more specialised form of diffusion. Click

Water Potential Ψ Pure water = water potential of 0 (Ψ = 0) Pure water = water potential of 0 (Ψ = 0) Less water = more concentrated Less water = more concentrated Ψ Ψ 0 is the MOST WATER Ψ More concentrated = more negative Ψ

Which way will water move? Cell A Ψ = -167 Cell B Ψ = -98

Which way will water move? Cell A Ψ = 0 Cell B Ψ = -26

Isotonic = a solution that is the same concentration as the cytoplasm Now explain these diagrams in terms of water potential.

Plasmolysis photosynthesis elodea animation - Google Videos photosynthesis elodea animation - Google Videos photosynthesis elodea animation - Google Videos photosynthesis elodea animation - Google Videos

Look at the tables on page 59 and 60 of your textbook. Look at the tables on page 59 and 60 of your textbook. Complete the practical on osmosis. Complete the practical on osmosis.