Download Cell Membrane or Plasma Membrane

Chapter 2
Structure and function of cells
Plasma membrane
Movement (diffusion/Osmosis)
Surface area to volume ratio
Organelles
Tissues/Organs
Plasma membrane
Environments of cells
• All cells exist in a watery environment –
extracellular fluid
• Mullticellular organisms have an outer layer
that acts as a barrier and creates an internal
environment
Aspects of the internal environment
that need to be regulated:
•Salt concentrations
•Temperature
•Levels of nutrients
•pH
•Removal of wastes
•Ion concentrations
CELL MEMBRANE
The
role of the membrane is
very important in maintaining cell
stability and enabling the cell to
operate at optimum levels.
The
cell membrane (plasma
membrane),
- selectively controls the molecules
entering & leaving the cell.
- allows the cytoplasm to have a
different composition from the the
surrounding environment
Membrane Structure.
• The membrane is partially
permeable. Some substances pass
freely across the membrane while
others are excluded.
Phosopholipid bi-layer
• The cell membrane is formed from a double layer
of lipids with proteins embedded in it forming ion
channels.
• The lipid layer is capable of much movement, i.e.
it is fluid.
• Cholesterol molecules reduce the membrane
fluidity
• It is impermeable to water soluble substances.
• Lipid soluble substances e.g. alcohol pass through.
Hydrophobic,
‘water hating’ end
Hydrophillic,
When in contact with an aqueous
solution, the phospholipid
molecules line up with tails
pointing in (away from sol)
‘water loving’ end
EXAMPLE! Detergents
cause fats to form
micelles.
Protein Channels
• These are large proteins with
openings on both sides of the
membrane.
• Allow flow of
ions
•Carbohydrates
on the outer surface
are important in cell
adhesion and cell
recognition. These are attached to
recognition proteins.
(1) Fluid (2) Mosaic Model (Draw)
Carbohydrate
Embedded protein
Phospholipid
Bilayer
Embedded Cholesterol
Protein channel
Movement into and out of the
cell
Movement in and out of Cell
• Diffusion (simple)
• Osmosis
• Facilitated diffusion
• Active Transport
• Endocytosis and Exocytosis
Diffusion (simple)
Where?
What?
Through the small uncharged particles
phospholipid (water, urea, Oxygen, carbon
bilayer
dioxide) & lipid soluble
substances such as alcohol,
ether, chloroform.
Energy?
NO
Comments: Moves down Con~ gradient (high to low) The
diffusion rate increases with a high concentration gradient,
heat, small particles and with gaseous substances.
Movement is from a strong solution to a weak solution.
(think sugar cube /water) (lungs, CO2)
Osmosis
Where?
Through the
phospholipid
bilayer
What?
Water only
Energy?
NO
Comments: Osmosis is a special type of diffusion.
The process is the same but only water moves to
even up concentrations. Movement of water is
from a weak solution into a strong solution.
Example: water from the gut (diarrhoea)
Cell wall in plants
Diffusion across the (partially
permeable) membrane.
1
2
Active Transport.
Where?
Through the
protein
molecules
spanning the
membrane.
What?
Nutirent molecules, ions such
as chloride ions (Cl-), sodium
ions (Na+), potasssium ions
(K+) and water
Energy?
Yes
Comments: Active transport is movement against the
concentration gradient to ‘build up’ rather than
to‘even up’.
Bulk Transport (endocyctosis and
exocytosis).
Where?
Small
sections of
the plasma
membrane.
What?
Large molecules such as
enzymes, hormones and
antibodies and foreign
material.
Energy?
YES
Comments: Phagocytosis (solids - cell eating) and
pinocytosis (cell drinking – entry of liquid) are
forms of endocytosis.
Summary of common
substances and their passage
through the cell membrane
Surface area to volume ratio
Surface area to volume ratio
Organelles
CELL THEORY
 All living things are made up of one or more cells.
 All cells are formed from pre-existing cells and
these cells contain the hereditary information.
 The cell is the smallest organisational unit
Organisation
Atom /molecules
 cells 
tissues
 organs  organ systems 
individual  population and community
 ecosystem
Properties of cells
• Most cells have some common features:
Plasma membrane
Cytoplasm
Nucleus
Flagella or Cilia
Types of cells
• There are two types of cells
• Organisms are grouped according to what type of cell they have
• Prokaryotes – have cells that do not have a membrane surrounding
the nucleus and lack most organelles (unicellular or simple
multicellular organisms - Bacteria, cyanobacteria) (pic pg 23)
• Eukaryotes- have cells that are usually much larger and more complex
than prokaryote cells. The nucleus is surrounded by a membrane and
the cell contains organelles (protists, fungi, plants & animals)
Cell Organelles
Overview
Mitochondrion
• Cells require a continuous supply of
energy.
• Organelles where:
– food molecules are broken down.
– energy is released.
• The energy is then stored in other
molecules that can power cell reactions
easily.
• Mitochondria (plural) – use when you
refer to more than one mitochondrion.
Nucleus
• Usually the largest organelle in the
cytoplasm of a cell.
• Directs all the activities of the cell.
• Contains genetic blueprints for the
operations of the cell.
Centrioles
•
•
•
•
Self-replicating organelles
Made up of nine bundles of microtubules
Found only in animal cells.
Help in organizing cell division.
Cell membrane
• Forms the outer boundary of the cell.
• Allows only certain materials to move into and out of
the cell.
• Food, oxygen and water move into the cell through
the membrane.
• Waste products also leave through the membrane.
• Cells that perform photosynthesis (plants and some
protists) take in carbon dioxide through the cell
membrane instead of oxygen.
Cell wall
• The cell wall is a rigid structure outside
the cell membrane that supports and
protects the cell (for plants, fungi, and
some protists and bacteria but NOT
animals).
• Animal cells DO NOT have a cell wall.
• The cell wall is made of tough cellulose
fibres and other materials made by the
cell.
• Note: fungal cell walls contain chitin
instead of cellulose.
Cytoplasm
• Gel-like material inside the cell membrane
and outside the nucleus.
• Cytoplasm is the jelly-like material inside
the cell (but unlike gelatin it does flow;
cytoplasm constantly moves or streams.
• Contains a large amount of water (cytosol)
and many chemicals and structures that
carry out the life processes in the cell.
• The structures that the cytoplasm
contains are called organelles.
Endoplasmic reticulum
• A folded membrane that moves materials around
in the cell.
• Extends from the nucleus to the cell membrane
and takes up quite a bit of space in some cells.
• Two different types: Smooth ER and Rough ER.
Rough ER has ribosomes attached to its outer
membrane, while Smooth ER does not.
Golgi
bodies
Golgi bodies package and move proteins
•
• In a business, products are made, packaged, and moved
to loading docks to be carried away.
• In cells, structures called Golgi Bodies are stacks of
membrane-covered sacs that package and move proteins
to the outside of the cell.
• When something is secreted, it is given off by the cell.
• Note: Golgi Bodies are sometimes referred to as Golgi
Apparatus.
Vesicle
• Vesicles transport proteins.
Chloroplasts
• Chloroplasts take in sunlight,
water and carbon dioxide to
make oxygen and sugar.
• This process is called
photosynthesis.
• A plant's chloroplasts
convert light energy into
chemical energy.
• Contain a green pigment
called chlorophyll. This is
what makes plants green.
Vacuole
• Acts as a temporary storage space for the
cell.
• Vacuoles store water, food, pigments,
waste or other materials.
• Vacuoles are large in plant cells and small
in animal cells.
• Vacuoles can also be found in fungi and
protists.
Lysosomes
• An active cell constantly produces waste
products.
• Contain chemicals (enzymes) that:
– digest wastes and worn-out cell parts
– break down food.
Ribosome
• One chemical that takes
part in nearly every cell
activity is protein.
• Proteins are needed for
chemical reactions that
take place in the
cytoplasm.
• Cells make their own
proteins on small
structures in the
cytoplasm called
ribosomes.
Cilia and Flagella
• For single-celled eukaryotes, cilia and flagella
are essential for the locomotion of individual
organisms.
• In multicellular organisms, cilia function to move
fluid or materials past an immobile cell as well as
moving a cell or group of cells.
– Cilia lining nasal passage
– Sperm
Microfilaments
• Solid rods made of globular proteins called actin and are common to all
eukaryotic cells.
• Long chains of the molecules are intertwined in a helix to form individual
microfilaments.
• Filaments are primarily structural in function and are an important
component of the cytoskeleton, along with microtubules.
• In association with myosin, microfilaments help to generate the forces used
in cellular contraction and basic cell movements.
• They enable a dividing cell to pinch off into two cells and are involved in
amoeboid movements of certain types of cells.
• They also enable the contractions of muscle cells.
Microtubules• Straight, hollow cylinders are found throughout
the cytoplasm of all eukaryotic cells (prokaryotes
don't have them) and perform a number of
functions.
• Gives structure and shape to a cell,
• Serve as conveyor belts moving other
organelles through the cytoplasm
• Are the major components of cilia and
flagella, and participate in the formation of
spindle fibers during cell division (mitosis).
• These filaments are composed of linear
polymers of tubulin, which are globular
proteins, and can increase or decease in length
by adding or removing tubulin proteins.
Plant cell
Animal cell
Copy down the characteristics of cells in the 5
kingdoms
pg 26
HW - Q 1- 8