Biology Revision B-test 4
Diffusion: The net movement of particles from an area of high concentration to an area of low
concentration e.g. the spreading out of particles of a gas, or any substance in solution.
What affects the rate of diffusion: Size of particles, temperature, concentration of particles
In general, the greater the difference in concentration, the faster
the rate of diffusion. The difference between the two areas is
called the concentration gradient.
The bigger the difference, the steeper the concentration gradient
and the faster the rate of diffusion.
This is due to the fact that an increase temperature means the
particles are supplied with more thermal energy. The more
energy the particles have, the more they move around and will
collide more often.
This means diffusion will happen much more rapidly.
Osmosis: the diffusion of water molecules from a region of high-water concentration (a dilute solution) to a region of
low water concentration (a concentrated solution) through a partially permeable membrane.
Partially permeable membrane: membranes that only let certain types of particles pass through.
Active transport: The movement of particles from an area of high concentration to an area of low concentration,
against a concentration gradient across a semi permeable membrane.
Dilute solutions have a high concentration of water molecules.
Concentrated solutions have a low concentration of water molecules.
Water is the solvent used in nature
How active transport differs from both osmosis and diffusion:
Active transport is not a passive process like diffusion and osmosis, active transport involves the transport of
substances against a concentration gradient, whereas diffusion and osmosis moves substances down a concentration
gradient. As this is an active process it requires energy, unlike the movement of substances by diffusion or osmosis.
Difference between diffusion and osmosis:
Diffusion refers to the movement of any gas particle or any particle in solution, whereas osmosis refers to the
movement of water particles only. Osmosis refers to the movement of particles across a semi-permeable
membrane, whereas this does not need to be the case for diffusion.
Why active transport is so important to plants:
Active transport is an important process to plants as this is how they are able to extract mineral ions from the soil.
Mineral ions, such as nitrates, are found in very dilute solutions in the soil. These solutions are more dilute than the
inside of the plant root hair cell. By using active transport the plant can absorb these minerals against their
concentration gradient. These minerals are important for plant growth and general health.
If the concentration of solutes in the solution outside the cell
is higher than the internal concentration, the solution is
hypertonic to the cell.
If the concentration of solutes in the solution outside the cell
is the same as the internal concentration, the solution is
isotonic to the cell.
If the concentration of solutes in the solution outside the cell
is lower than the internal concentration, the solution is
hypotonic to the cell.
Hypertonic: higher concentration than cell cytoplasm
Isotonic: same concentration as cell cytoplasm
Hypotonic: lower concentration than cell cytoplasm
Tissues and Organs in Plants:
Features than make this a plant cell
are a permanent vacuole,
Chloroplasts and cell wall made of
cellulose for strengthening the cell.
Xylem: carries water and minerals from the roots to the stem to the leaf. (Only one way) Made of elongated dead
cells.
Phloem: carries glucose and amino acids from the leaf to the rest of the plant for storage. This is called translocation.
Made from living cells.
Phloem and Xylem are found as vascular bundles in the plant.
Has less chloroplasts
because less sunlight
reaches them. Also, plants
save energy by reducing the
amount of chloroplasts
made in the spongy
mesophyll layer.
Guard cell
Plants that live in water don’t need a waxy cuticle as its
purpose is to reduce water loss from evaporation. Plants that
live in water already have an abundance of water available.
Carbon dioxide diffuses into the stoma of the leaf and oxygen
diffuses out.
Glucose is the food made by plants in photosynthesis.
There are no chloroplasts in the roots of a plant because
they are in the soil which gets no sunlight.
Carbon dioxide + Water -> Glucose + Oxygen
Liquid to gas: evaporation
For water to evaporate, particles need to be given enough energy to break the forces that hold the molecules
together.
If there is a substance dissolved in water and the water evaporates the substance will remain (solute remains).
Factors that affect evaporation: Wind, Heat, Humidity (the amount of water in the air), Surface area
Gas to liquid: condensation
Transpiration stream: The process of water going from the roots to the leaves and being evaporated into the
atmosphere.
Water from the soil is absorbed into the root hair cell by
osmosis. The water travels from the roots to the leaves
through xylem vessels in the stem. Once at the leaf,
water can be evaporated out into the atmosphere
through the stomata.
Factors that affect transpiration: temperature (more temp, more transpiration), air movement (more wind, more
transpiration), humidity (higher humidity, less transpiration), light intensity.
Gas exchange:
21% oxygen in the air
Gas exchange: when we breathe we take in oxygen and give out carbon dioxide. It happens at the end of lungs in air
sacs called alveoli which are elastic, like a rubber band on a sling shot.
Lungs are protected by the ribcage (they are delicate).
We breathe regularly to keep the concentration gradient high for the gas exchange gases. This makes it so that O2
and CO2 can continually diffuse in and out of the bloodstream (steeper the gradient, faster the diffusion).
Concentration gradient: the difference between the two areas.
Trachea: has rings of cartilage to stop the windpipe from
collapsing under the pressure of breathing.
Alveoli: large surface area (to increase the volume of gas
exchanged), very thin (one cell thick, for faster diffusion as it is
a shorter distance to travel), rich supply capillaries (maintains
the highest concentration gradient possible), moist lining
(faster diffusion).
Villi:
Thousands of tiny finger-like projections located inside your small intestine.
The villi is where all the nutrients from your digested food are absorbed into the blood.
The villi help this to happen quickly because they have a huge surface area.
If the intestine had a smooth lining, the fewer nutrients would be able to move across at the same time – absorption
would take much longer.
Each villus contains a network of tiny blood capillaries.
The blood is constantly moving, carrying away dissolved nutrients.
Some of the nutrients move into the villi by diffusion.
They can do this if their concentration in the digested food, inside the intestines, is higher than the concentration in
the blood.
The villi have very thin walls, this makes the diffusion pathway short.
Internal structure of a villus:
Inside an alveolus:
Each air sac is found to be a bundle
of air sacs. Together, they are
known as an alveolus. The outside
of the alveolus is covered with tiny
blood vessels. The total surface
area of the alveoli can range from
30-50 square metres. This
provides a huge surface area for
gas exchange to occur.
Videos:
Diffusion, osmosis and active transport :
https://www.youtube.com/watch?v=4Eq8rO3fABM
https://www.youtube.com/watch?v=LUPHohqlPTU
https://www.youtube.com/watch?v=tM0bGaaQ2jY
Transport in plants:
GCSE Biology - Structure of a Leaf and Stomata #50
https://www.youtube.com/watch?v=R0wjTdBK77o
https://www.youtube.com/watch?v=vgkaW9-vFaI
Plants, autrophs and heterotrophs:
Autotrophs and Heterotrophs (Not all)
Breathing and gas exchange/ exchanging materials:
AQA GCSE Science Revision Biology "Absorption in the Small Intestine"
https://www.youtube.com/watch?v=B44n2SMLv-s
https://www.youtube.com/watch?v=aPUPfzsqDgs
https://www.youtube.com/watch?v=mZvzl8KH6iI. Alveoli: Gas Exchange
