3.1
CHAPTER 3
Chapter 3 - Movement into and out of cells
3.1 - Diffusion
CONTENTS
1 Characteristics and classification of living organisms
1.1 Characteristics of living organisms
1.2 Concept and uses of classification systems
1.3 Features of organisms
2 Organisation of the organism
2.1 Cell structure
2.2 Size of specimens
3 Movement into and out of cells
3.1 Diffusion
3.2 Osmosis
3.3 Active transport
4 Biological molecules
4.1 Biological molecules
5 Enzymes
5.1 Enzyme action
6 Plant nutrition
6.1 Photosynthesis
6.2 Leaf structure
7 Human nutrition
7.1 Diet
Chapter 3 - Movement into and out of cells
3.1 - Diffusion
Diffusion
Diffusion is the net movement of particles from a region of their higher concentration
to a region of their lower concentration (i.e. down a concentration gradient), as a
result of their random movement
when the concentration of a substance is higher in one area than another, we refer
to there being a concentration gradient
Chapter 3 - Movement into and out of cells
3.1 - Diffusion
Diffusion
Diffusion is the net movement of particles from a region of their higher concentration
to a region of their lower concentration (i.e. down a concentration gradient), as a
result of their random movement
The energy for diffusion comes from the kinetic energy of random movement of
molecules and ions
Particles in a liquid or gas have kinetic energy
They move randomly, spreading out to fill the available space
Chapter 3 - Movement into and out of cells
3.1 - Diffusion
Diffusion
Diffusion is the net movement of particles from a region of their higher concentration
to a region of their lower concentration (i.e. down a concentration gradient), as a
result of their random movement
The energy for diffusion comes from the kinetic energy of random movement of
molecules and ions
Particles in a liquid or gas have kinetic energy
They move randomly, spreading out to fill the available space
Particles
constantly and
randomly move
until they are
evenly
distributed
Chapter 3 - Movement into and out of cells
3.1 - Diffusion
Diffusion
Some substances move into and out of cells by diffusion through the cell
membrane
Example
1. cell respires, using oxygen
2. concentration of oxygen molecules in the cell decreases
3. a concentration gradient is established
4. oxygen molecules diffuse across the cell membrane and into the cell
concentration gradient
OUTSIDE CELL
(high conc.)
INSIDE CELL
(low conc.)
cell membrane
Chapter 3 - Movement into and out of cells
3.1 - Diffusion
Diffusion
You need to describe the importance of diffusion of gases and solutes (dissolved
substances) in living organisms
Diffusion of gases
Oxygen diffuses from the lungs and into the bloodstream
Carbon dioxide diffuses from the bloodstream and into the lungs
alveolus (see ch 11)
CO2
O2
capillary
Chapter 3 - Movement into and out of cells
3.1 - Diffusion
Diffusion
You need to describe the importance of diffusion of gases and solutes (dissolved
substances) in living organisms
Diffusion of gases
Oxygen diffuses from the blood and into the respiring cells
Carbon dioxide diffuses from the respiring cells and into the blood
O2
capillary
muscle cells
CO2
Oxygen is needed for respiration in the cells. Carbon dioxide is released as a byproduct.
Chapter 3 - Movement into and out of cells
Diffusion
You need to describe the importance of diffusion of gases and solutes (dissolved
substances) in living organisms
Diffusion of gases
Carbon dioxide diffuses into the cells of plants through stomata (see ch 6)
Oxygen and water vapour from transpiration diffuse outwards (see ch 8)
Carbon dioxide is needed for photosynthesis. Oxygen is released as a byproduct.
3.1 - Diffusion
Chapter 3 - Movement into and out of cells
Diffusion
You need to describe the importance of diffusion of gases and solutes (dissolved
substances) in living organisms
Diffusion of gases
Carbon dioxide diffuses into the cells of plants through stomata (see ch 6)
Oxygen and water vapour from transpiration diffuse outwards (see ch 8)
Stomata are tiny openings that
allow gases and water vapour to
diffuse into and out of the leaf
Carbon dioxide is needed for photosynthesis. Oxygen is released as a byproduct.
3.1 - Diffusion
Chapter 3 - Movement into and out of cells
3.1 - Diffusion
Diffusion
You need to describe the importance of diffusion of gases and solutes (dissolved
substances) in living organisms
Diffusion of solutes
In the small intestine, water soluble vitamins diffuse into the bloodstream
In the kidneys, mineral ions and glucose are reabsorbed by diffusion
Water soluble vitamins diffuse through the
membrane of intestinal epithelial cells and into
the bloodstream (see ch 7)
Mineral ions are glucose are reabsorbed into
the blood by the kidneys (see ch 13)
Chapter 3 - Movement into and out of cells
3.1 - Diffusion
Factors that influence diffusion
Surface area
Larger surface area - faster rate of diffusion
CONC.
GRADIENT
CELL MEMBRANE
Larger surface area - more space for
molecules to diffuse across the membrane
Chapter 3 - Movement into and out of cells
3.1 - Diffusion
Factors that influence diffusion
Surface area
Larger surface area - faster rate of diffusion
Villi and microvilli increase the surface area of the small intestine, increasing rate of nutrient
absorption (see ch 7)
Chapter 3 - Movement into and out of cells
3.1 - Diffusion
Factors that influence diffusion
Surface area
Larger surface area - faster rate of diffusion
Temperature
Higher temperature - faster rate of diffusion
Molecules gain more
kinetic energy (spread
out more quickly)
Molecules lose kinetic
energy - slower rate of
diffusion
Chapter 3 - Movement into and out of cells
3.1 - Diffusion
Factors that influence diffusion
Surface area
Larger surface area - faster rate of diffusion
Temperature
Higher temperature - faster rate of diffusion
Concentration gradient
Steeper concentration gradient - faster rate of diffusion
slower diffusion
The greater the
difference in
concentration of a
substance on either
side of a membrane,
the faster it will
diffuse across it.
CONC.
GRADIENT
faster diffusion
Chapter 3 - Movement into and out of cells
Factors that influence diffusion
Surface area
Larger surface area - faster rate of diffusion
Temperature
Higher temperature - faster rate of diffusion
Concentration gradient
Steeper concentration gradient - faster rate of diffusion
Diffusion distance
Shorter diffusion distance - faster rate of diffusion
In the lungs, the walls of the alveoli and
capillaries are only one cell thick. This
reduces diffusion distance and speeds up
the rate of gaseous exchange (see ch 11)
3.1 - Diffusion
Chapter 3 - Movement into and out of cells
3.1 - Diffusion
Experiments on diffusion
Surface area
1. Cut four cubes from a block of gelatine with sides of 3cm, 2cm, 1cm and 0.5cm
2. Place into a beaker of methylene blue dye or potassium permanganate solution
3. Leave for 15 minutes, remove with forceps and place on a white tile
4. Cut each cube in half and measure the depth to which the dye has diffused
Precautions
Eye protection must be worn
Follow teacher instructions when using a knife
Dyes stain skin and clothing
Take care when handling hot water
Chapter 3 - Movement into and out of cells
Experiments on diffusion
Temperature
1. Prepare two beakers with equal volumes of hot water and iced water
2. Add a few grains of potassium permanganate to each beaker
3. Observe the rate at which the dissolved dye spreads through the water
3.1 - Diffusion
Chapter 3 - Movement into and out of cells
3.1 - Diffusion
Experiments on diffusion
Concentration gradient
1. Cut squares of litmus paper and dampen with water
2. Stick the squares to the inside of a wide, glass tube at regular intervals
3. Saturate a piece of cotton wool with a strong ammonia solution
4. Attach the cotton wool to a cork and close the glass tube
5. Record how long it takes for each of the squares to start turning blue
6. Repeat the experiment with a dilute solution of ammonia
Ammonia changes
the colour of litmus
from blue to red
For teacher demonstration purposes only (ammonia is corrosive and irritant)
3.2
CHAPTER 3
Chapter 3 - Movement into and out of cells
3.2 - Osmosis
CONTENTS
1 Characteristics and classification of living organisms
1.1 Characteristics of living organisms
1.2 Concept and uses of classification systems
1.3 Features of organisms
2 Organisation of the organism
2.1 Cell structure
2.2 Size of specimens
3 Movement into and out of cells
3.1 Diffusion
3.2 Osmosis
3.3 Active transport
4 Biological molecules
4.1 Biological molecules
5 Enzymes
5.1 Enzyme action
6 Plant nutrition
6.1 Photosynthesis
6.2 Leaf structure
7 Human nutrition
7.1 Diet
Chapter 3 - Movement into and out of cells
3.2 - Osmosis
Osmosis
Water is an excellent solvent (it dissolves substances to create a solution)
You need to describe the role of water as a solvent in organisms
A solution consists of a solvent (e.g. water) and a solute (e.g. mineral ions)
Chapter 3 - Movement into and out of cells
3.2 - Osmosis
Role of water as a solvent in organsisms
Digestion
water helps to break down food molecules by a chemical reaction called hydrolysis
it then dissolves the smaller molecules so that they can pass through the intestinal
wall and into the bloodstream (see ch 7)
Small, soluble molecules dissolve in
water and pass through the intestinal
wall (by diffusion or active transport)
Hydrolysis - the breakdown of a compound, when it reacts with water
Chapter 3 - Movement into and out of cells
3.2 - Osmosis
Role of water as a solvent in organsisms
Excretion
Water is a solvent for waste products (e.g. urea, used hormones, excess minerals)
Water dilutes waste products, reducing toxicity
Water transports waste products out of the body (in urine)
urine is formed in the kidneys (see ch 13)
urine is excreted via the bladder
Urine is a water based solution containing urea and excess minerals
Chapter 3 - Movement into and out of cells
Role of water as a solvent in organsisms
Transport
Blood plasma is a water based solution (see ch 9)
It transports gasses, nutrients, hormones, blood cells, and waste products
Water transports dissolved mineral ions and glucose in plants (see ch 8)
P L A S MA
Plasma is the liquid component of the blood. It comprises 55% of total blood volume.
3.2 - Osmosis
Chapter 3 - Movement into and out of cells
3.2 - Osmosis
Role of water as a solvent in organsisms
Transport
Blood plasma is a water based solution (see ch 9)
It transports gasses, nutrients, hormones, blood cells, and waste products
Water transports dissolved mineral ions and glucose in plants (see ch 8)
water transports
dissolved mineral
ions from the soil
to the leaves in
xylem vessels
water transports
dissolved sucrose
from the leaves to
the rest of the plant
in phloem vessels
Chapter 3 - Movement into and out of cells
3.2 - Osmosis
Osmosis
Osmosis is the movement of water through a partially permeable membrane
Molecules diffuse from areas of high concentration to areas of low concentration (i.e.
down a concentration gradient)
A dilute solution has a higher concentration of free water molecules than a
concentrated solution
If a dilute solution is separated from a concentrated solution by a partially permeable
membrane, water molecules will diffuse across the membrane from the dilute to the
concentrated solution
A partially permeable membrane allows some substances to pass through but not others
Chapter 3 - Movement into and out of cells
3.2 - Osmosis
Osmosis
Osmosis is the movement of water through a partially permeable membrane
OSMOSIS
partially permeable membrane
dilute solution
(higher concentration of
free water molecules)
concentrated solution
(lower concentration of
free water molecules)
A partially permeable membrane allows some substances to pass through but not others
Chapter 3 - Movement into and out of cells
3.2 - Osmosis
Osmosis
Osmosis is the movement of water through a partially permeable membrane
Water moves into and out of cells by osmosis through the cell membrane
If a cell is surrounded by a dilute solution
with lots of free water molecules, water
will diffuse into the cell by osmosis
If a cell is surrounded by a concentrated
solution like salt water, water will diffuse
out of the cell by osmosis
Animal and plant cell membranes are partially permeable
Chapter 3 - Movement into and out of cells
3.2 - Osmosis
Osmosis
Osmosis helps to maintain cell pressure in plants
Plants are supported by the pressure of water inside the cells pressing outwards on the
cell wall
Water moves into the vacuole by osmosis
Vacuole presses outwards against the cell wall
Cells become rigid (turgid)
Stems and leaves are supported
when water moves out, the plant becomes limp and wilts (see ch 8)
Chapter 3 - Movement into and out of cells
Experiments on osmosis
Investigate osmosis using materials
such as dialysis tubing
Method
Add dyed sugar solution to a length
of tubing
Secure to a capillary tube with an
elastic band
Cover the dialysis tubing with water
Observe for 10-15 minutes
Results
Level of liquid in the capillary tube
rises
Interpretation
Water molecules moved into the
concentrated solution in the dialysis
tubing by osmosis
3.2 - Osmosis
Chapter 3 - Movement into and out of cells
Experiments on osmosis
Investigate osmosis using materials
such as dialysis tubing
Method
Add dyed sugar solution to a length
of tubing
Secure to a capillary tube with an
elastic band
Cover the dialysis tubing with water
Observe for 10-15 minutes
Results
Level of liquid in the capillary tube
rises
Interpretation
Water molecules moved into the
concentrated solution in the dialysis
tubing by osmosis
3.2 - Osmosis
Chapter 3 - Movement into and out of cells
3.2 - Osmosis
Experiments on osmosis
Investigate and describe the effects on plant tissues of immersing them in solutions
of different concentrations
Method
Prepare 6 potato cylinders using a cork borer and cut to the same length (at least 50mm)
Add sucrose solutions of different concentrations to six labelled test tubes (0, 0.2, 0.4, 0.6, 0.8
and 1 mol dm-3)
Weigh the cylinders and place one in each test tube
Leave for 30 minutes
Surface dry and re-weigh the cylinders
Calculate the percentage change in mass of each cylinder and plot the results on a graph
0
0.2
0.4
0.6
0.8
1.0
Chapter 3 - Movement into and out of cells
3.2 - Osmosis
Experiments on osmosis
Investigate and describe the effects on plant tissues of immersing them in solutions
of different concentrations
Method
Prepare 6 potato cylinders using a cork borer and cut to the same length (at least 50mm)
Add sucrose solutions of different concentrations to six labelled test tubes (0, 0.2, 0.4, 0.6, 0.8
and 1 mol dm-3)
Weigh the cylinders and place one in each test tube
Leave for 30 minutes
Surface dry and re-weigh the cylinders
Calculate the percentage change in mass of each cylinder and plot the results on a graph
change in mass = mass at end - mass at start
percentage change in mass = ( change in mass / mass at start ) x 100
Chapter 3 - Movement into and out of cells
3.2 - Osmosis
Experiments on osmosis
Investigate and describe the effects on plant tissues of immersing them in solutions
of different concentrations
Method
Prepare 6 potato cylinders using a cork borer and cut to the same length (at least 50mm)
Add sucrose solutions of different concentrations to six labelled test tubes (0, 0.2, 0.4, 0.6, 0.8
and 1 mol dm-3)
Weigh the cylinders and place one in each test tube
Leave for 30 minutes
Surface dry and re-weigh the cylinders
Calculate the percentage change in mass of each cylinder and plot the results on a graph
Results | Interpretation
Cylinders in weaker solutions gain mass and feel firm (water moves from the solution and
into the cells down a concentration gradient)
Mass of one cylinder does not change (the concentration of one solution is similar to that of
the potato)
Cylinders in concentrated solutions lose mass and feel limp (water moves out of the cells and
into the solution by osmosis)
Chapter 3 - Movement into and out of cells
3.2 - Osmosis
Osmosis
Osmosis is the net movement of water molecules from a region of higher
water potential (dilute solution) to a region of lower water potential
(concentrated solution), through a partially permeable membrane
OSMOSIS
partially permeable membrane
Water molecules move in
both directions through
the membrane, but since
the dilute solution has a
higher water potential,
there is a net movement
from left to right
dilute solution
(high water potential)
concentrated solution
(low water potential)
Chapter 3 - Movement into and out of cells
3.2 - Osmosis
Osmosis
Water potential
A region of high water potential has a high proportion of free water molecules
A region of low water potential has a lower proportion of free water molecules
Dissolved substances attract water molecules and stop them moving freely
OSMOSIS
partially permeable membrane
Water molecules move in
both directions through
the membrane, but since
the dilute solution has a
higher water potential,
there is a net movement
from left to right
dilute solution
(high water potential)
concentrated solution
(low water potential)
Chapter 3 - Movement into and out of cells
3.2 - Osmosis
Osmosis
Turgor pressure
Pressure from the vacuole against the cell wall when a plant cell takes up water
Turgid cell
A fluid filled (pressurised) cell
CELL WAL
VACUOLE
L
Chapter 3 - Movement into and out of cells
3.2 - Osmosis
Osmosis
Turgor pressure
Pressure from the vacuole against the cell wall when a plant cell takes up water
Turgid cell
A fluid filled (pressurised) cell
Flaccid cell
Cells that undergo plasmolysis become flaccid (limp)
Plasmolysis
A loss of water from the cells
TURGID CELL
FLACCID CELL
PLASMOLYSIS
Chapter 3 - Movement into and out of cells
3.2 - Osmosis
Osmosis
In the potato experiment the concentrated solutions had a lower water
potential than the fluid in the potato cells. As a result plasmolysis occurred,
meaning water molecules were lost from the potato cells by osmosis. This
reduced the turgor pressure exerted by the vacuoles, causing the cells to
become flaccid and the potato to feel limp.
The dilute solutions had a higher water potential than the fluid in the potato
cells. As a result water molecules moved into the potato cells by osmosis.
The vacuoles expanded, exerting turgor pressure on the cell walls and
causing the cells to become turgid.
0 mol dm-3
1 mol dm-3
TURGID CELLS
FLACCID CELLS
Chapter 3 - Movement into and out of cells
3.2 - Osmosis
Osmosis
You need to explain the importance of water potential and osmosis in the
uptake and loss of water by organisms
Regulating water potential
As animal cells have no cell wall, it is important that the fluid in which they bathe
(blood plasma or tissue fluid) has a similar water potential to the cell contents
1. If the fluid has a higher water potential than the cells, water will enter by osmosis
causing them to expand and eventually burst
2. If the fluid has a lower water potential than the cells, the cells will become
plasmolysed and their function will be impaired
The brain monitors and the kidneys adjust the water potential of the blood (see ch 14 homeostasis)
Tissue fluid is extracellular fluid which bathes the cells of most tissues
An isotonic solution has the same water potential as the contents of the red blood cell
3.3
CHAPTER 3
Chapter 3 - Movement into and out of cells
3.3 - Active transport
CONTENTS
1 Characteristics and classification of living organisms
1.1 Characteristics of living organisms
1.2 Concept and uses of classification systems
1.3 Features of organisms
2 Organisation of the organism
2.1 Cell structure
2.2 Size of specimens
3 Movement into and out of cells
3.1 Diffusion
3.2 Osmosis
3.3 Active transport
4 Biological molecules
4.1 Biological molecules
5 Enzymes
5.1 Enzyme action
6 Plant nutrition
6.1 Photosynthesis
6.2 Leaf structure
7 Human nutrition
7.1 Diet
Chapter 3 - Movement into and out of cells
3.3 - Active transport
Active transport
Active transport is the movement of particles through a cell membrane from a region
of lower concentration to a region of higher concentration (i.e. against a
concentration gradient), using energy from respiration.
DIFFUSION
ACTIVE TRANSPORT
molecules move down the
concentration gradient
molecules move against the
concentration gradient using
energy from respiration
Chapter 3 - Movement into and out of cells
3.3 - Active transport
Active transport
The importance of active transport
Allows molecules to enter cells against a concentration gradient, so that they can
be absorbed from dilute solutions
Allows molecules to be removed from cells against a concentration gradient
This prevents the accumulation of substances (e.g. waste products) that would
otherwise impair cellular function
absorption of useful substances
removal of harmful substances
Chapter 3 - Movement into and out of cells
3.3 - Active transport
Active transport
The importance of active transport
Epithelial cells
Glucose moves into cells from small intestine, against a concentration gradient
Cells contain many mitochondria to provide energy for active transport
glucose
conc. gradient
epithelial cell
If not for active transport, significant quantities of usable
nutrients would pass through the gut without being absorbed
Chapter 3 - Movement into and out of cells
3.3 - Active transport
Active transport
The importance of active transport
Root hair cells
Mineral ions move into the cells from the soil, where their concentration is lower
Allows plants to absorb nutrients from dilute solutions
mineral ions enter the cells by active transport
low concentration of
mineral ions in soil
high concentration of
mineral ions in cells
root hair
Chapter 3 - Movement into and out of cells
3.3 - Active transport
Active transport
Carrier protein molecules
Embedded in cell membranes
Molecules bind to specific carrier proteins
Carriers change shape (using energy from respiration)
Molecules are released on the other side of the membrane
substance
binds
outside cell
inside cell
energy from
respiration
carrier
protein
molecule
CONC.
GRADIENT
substance
released