exchange of materials. cells exchange matter and energy in: oxygen nutrients eg glucose (carbon...
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Exchange of materials
Cells exchange matter and energy
In:
Oxygen
Nutrients eg glucose
(carbon dioxide and light energy in plants)
Water
Ions
Out:
Carbon dioxide
Wastes eg urea
(oxygen in plants)
Water
Ions
Heat energy
Processes:
Respiration
Synthesis
Growth
Division
Photosynthesis (in plants)
Exchange of material
Occurs at the cell membrane
Involves the intake of essential materials eg nutrients and oxygen and the removal of unwanted materials eg wastes
The processes involved include diffusion, osmosis and active transport
Structure of the cell membrane
Fluid mosaic model
Describe the roles of:• PhospholipidsWaterproof barrier, acts as a bubble, main
constituent
• Proteins Act as carriers, receptor sites, antigens,
channels
• CarbohydratesAct as receptor sites, antigens
Cell membranes
Sketch a typical cell membrane according to the Fluid Mosaic model
Describe the roles of:• Phospholipids
• Proteins
• Carbohydrates
CellsSketch a typical cell membrane according to the Fluid Mosaic model .
Describe the roles of:Phospholipids = A – waterproof, flexible layer, that lets in small particles
Proteins = B – provides channels for larger particles (facilitated diffusions), acts as pumps (active transport), acts as receptor sites
Carbohydrates = C - acts as receptor sites
A
B
C
Exchange of material
Small particles eg water, ions can pass through the gaps between the phospholipids
Larger molecules pass through channels in the proteins or are carried by special proteins
TerminologySolution
Solute
Solvent
Permeable
Differentially permeable
Hypotonic
Hypertonic
Isotonic
Mixture of solvent and solute
Thing added to solvent
Liquid to which solute is added
Allows substances to move through
Allows some substances to move through, but not others
Less concentrated (dilute)
More concentrated
Concentrations are equal
Movement through membranes
Movement of particles - diffusion
Occurs without energy
Particles will move from higher concentrations to lower concentrations
Diffusion through membranesMembranes are differentially permeablePermeable substances (eg small particles) Impermeable substances (eg large particles)Movement is Energy
Move through
Can’t move throughFrom areas of high concentration to
areas of low concentration
Is not needed
Facilitated diffusion
Allows larger or less permeable substances to cross
Involves channel proteins
Energy is not needed
OsmosisMovement of waterThis occurs from areas of high water concentration (low
concentration of solute) to areas of low water concentration (high concentration of solute)
Concentration gradient
This refers to the difference in concentration across membranes
The steeper the gradient,
the greater the movement
Osmotic pressure refers to the pull of water due to concentration gradients
Active transport
Movement against a concentration gradient.Energy is needed
Ion pumps
Involves special proteins that act as pumps
Allows cells to maintain ion concentrations that are very different from the external environment
Energy is used
EndocytosisMovement due to folding of membrane and bringing in
the trapped substancesEnergy is needed Phagocytosis – solid substances trappedPinocytosis – liquids are trapped
Exocytosis
Movement due to vacuoles moving to membrane and attaching to release contents
Energy needed
Does size matter?
As size increases:What happens to volume?What happens to surface area?What happens to surface area to volume ratio?
decreases
increases
increases
Surface area and volume 2Size 1x1x1 2x2x2 3x3x3 4x4x4
Surface area
6 24 54 96
Volume 1 8 27 64
SA: Vol 6:1 3:1 2:1 1.5:1
Size of sides
10
2 3 4
Surface area
volume
SA:Vol
1
2
3
4
5
6
7
1
20
30
40
50
60
70
80
90
100
50
Affect of shape on surface area and volume
Calculate the volume and surface area for these:2x 2x2
1x1x8
4x2x1
8 cubic units
8 cubic units
8 cubic units
24 square units
28 square units
34 square units
How cells increase their surface area
• Size • Shape• Folding • Cell extensions
pseudopods
microvilli