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AS Biology
Unit 1- Cells, Exchangeand Transport (F211)
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Microscopes
Magnification- the number of times bigger an image is than the
object.
Resolution- the ability to distinguish to close together points asdistinct from each other
Sample staining- any process that helps to reveal or distinguish
different features. In light microscopy, stains may be colours of
fluorescent dyes. In electron microscopy, they are metal particles or
metal salts.
Sectioning- specimens are embedded in wax. Thin sections are then
cut without distorting the structure of the specimen. This is
particularly useful when making sections of soft tissue, such as brain.
Magnification=Image Size (m)
Actual Size (m)
To convert from mm to m times by 1000.
Light Microscope Transmission
Electron
Microscope
Scanning
Electron
Microscope
Magnification X1,500 X500,000 X100,000
Resolution 200nm 0.1nm 0.1nm
Advantages Inexpensive Goodmagnification
and resolution
Goodmagnification
and resolution,
3D images
produced
Disadvantages Low magnification
and resolution
Samples have to be dead, samples
have to be in a vacuum, extremely
expensive and require high degrees
of skill and training.
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Organelles
Nucleus- Contains the genetic information of the cell
Nucleolus- Makes RNA and ribosomesNuclear envelope- Contains holes called nuclear pores,
which allow relatively large molecules to pass through
Rough endoplasmic reticulum- Transport proteins that
were made on the attached ribosomes.
Smooth endoplasmic reticulum- Makes lipids and
steroids.
Golgi apparatus- Modifies proteins and packages them into
vesicles. They can then be transported to the surface forexocytosis.
Ribosomes- Site of protein synthesis
Mitochondria- Where ATP is made
Lysosomes- Contain digestive enzymes that break down
waste material in the cell
Chloroplasts- Site of photosynthesis in plant cells
Centrioles- Form spindle fibres during cell division
Flagella and cilia- Cellular extensions, which move in awave like manner. Flagella are long and few in number and
cilia are short and numerous.
Cell surface membrane- Controls the entry and exit of
substances into and out of the cell.
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Production and Secretion of Proteins
1. The instructions to make proteins are in the nucleus of the cell2. The gene containing the instructions for the production of the
hormones is copied onto a piece of mRNA3. The mRNA leaves the nucleus through the nuclear pores and
attaches to a ribosome.
4. The ribosome uses the codes to assembled the protein5. The assembled proteins inside the rough ER is pinched off in a
vesicle and transported to the Golgi apparatus.
6. Golgi apparatus processes and packages the molecules, readyfor release.
7. The molecules are pinched off in vesicles from the Golgiapparatus and moves towards the cell surface membrane.
8. Vesicles fuse with the cell surface membrane and themembrane opens to release the molecules outside- this is
exocytosis.
Cytoskeleton
The cytoskeleton is made up of
1. Microfilaments2. Microtubules3. Intermediate filaments
Its function is to
1. Keep the cells shape and strength and stability2. Whole cell movement3. Movement of organelles
Microtubules do not move, but they provide an anchor for protein to
move along e.g. kinesin attach one end to an organelle and the otherend to a microtubule. Using ATP it swivels, pushing the organelle
along. The head then reattaches itself to the microtubule and the
process is repeated.
Flagella and cilia are each made from one cylinder containing 9
microtubules. Flagella move with the aid of the protein, Dynein.
When a molecule of dynein swivels it pulls one microtubule past the
next, causing the cilium to bend.
Cilia move out of time with each other to create a wave.
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Prokaryotes and Eukaryotes
Prokaryotes EukaryotesNo nucleus (DNA
suspended freely)
Nucleus (contains DNA)
No membrane bound
organelles
Membrane bound
organelles (mitochondria,
chloroplast etc.)
Peptidoglycan cell wall Cellulose cell wall
Spiral flagella Waved flagellaSmaller ribosomes Larger ribosomes
Single-loop chromosomes Linear chromosomes
Single-celled One or more cell
Contains plasmids Do not contain plasmids
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Cell Membrane
Cholesterol- Gives the membrane stability by sitting between the
fatty acid tails and therefore making the barrier more complete,
preventing molecules like water and ions passing through the
membrane.
Glycolipids- Phospholipid molecules that have a carbohydrate partattached. They are used for cell signaling, cell surface antigens and
cell adhesion.
Glycoproteins- Protein molecules with a carbohydrate attached:
Act as antigens Enable the identification of cells as self or non-self Used in cell signaling Act as receptors or binding sites for hormones. They have a
specific shape that is complementary to the shape of the
communicating molecule which binds to the receptor Act as receptors on transport proteins to trigger movement Allow cell adhesion to hold cells together in a tissue Attach the water molecules to stabilize the membraneChannel proteins-Allow the movement of some substances, such as
the large molecule sugar, into and out of the cell as they cant travel
directly through the cell surface membrane.
Carrier proteins-Actively move substances across the cell surface
membrane.
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Function of membranes:
Separate cell contents from outside environment Cell recognition and signaling Holding the components of some metabolic pathways in place Regulating the transports of materials into or out of the cell Allow compartmentalisation Isolate harmful substances (e.g. lysosomes) Provide a surface (attachment of ribosomes)Temperature and permeability:
A high temperature boosts the kinetic energy of the componentmolecules of the membrane and the transported substance. Themembrane becomes more permeable.
Very high temperatures will denature the protein molecules,changing their shape and making the membrane permeable.
Eventually the membrane will be destroyed.
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Cell communication and signaling
Most messenger molecules are unable to directly crossthe membrane and must bind to the membrane boundreceptors in order to communicate with a cell.
Some integral proteins are receptors for hormones andneurotransmitters.
Different cells have specific receptors depending on therole in our body.
Via receptors and complementary shaped molecules onthe target cell.
Insulin
Pancreasliver and muscle cells
Purpose- regulate glucose
Transport- via the blood
Chemical message- insulin (protein)
Serotonin
NeuronsPurpose- nervous system
Transport- via the blood
Chemical messenger- serotonin
Drugs that bind to receptors and mimic the bodys normal
messengers are called agonists(e.g. HIV Virus)
Drugs that bind and block the bodys normal messengers arecalled antagonists(e.g. beta blockers)
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Diffusion
The movement of molecules from an area of high concentration of that
molecule, to an area of low concentration, down a concentration gradient.
Factors that affect diffusion
Temperature Concentration gradient Stirring/ mixing Surface area Distance/ thickness Size of moleculePassiveProcesses
DiffusionDown a concentration gradient. Smallmolecules/ lipid soluble.
Facilitated Diffusion Down a concentration gradient.
Charged/ hydrophilic molecules.
Through channel or carrier proteins.
Osmosis Down water potential gradient through
bilayer or protein pores.
Active
Processes
Active Transport Against concentration gradient via
carrier proteins that use ATP to change
shape.
Endo/exocytosis Bulk transport via vesicles that can fuse
or break from cell surface membrane.
Osmosis
Osmosis is the passage of water molecules through a partially permeable
membrane, from a region of high water potential, to a region of lower
water potential (down a water potential gradient.)
Water potential is denoted by the symbol and is measured in kilopascals
(kPa). Pure water has a value of 0, the more solutes that are dissolved the
more negative the water potential gets.
Animal cell
When water osmosis into an animal cell it can burst- this is called
haemolysis.
When water leaves the cell it shrinks- it becomes crenated.
Plant Cell
When water enters the cell, the cell wall prevents it from bursting- the cell
becomes turgid.
When water leaves the cell it pulls away from the cell wall- this is calledplasmolysis.
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Mitosis
Interphase
1. G1 Phase- Cells increase in size and ensure everything is ready forDNA synthesis.
2. S Phase- DNA in the cell is duplicated3. G2 Phase- Cell continues to grow and duplicated DNA is checked.
Mitosis
1. Prophase- DNA shortens and condenses by coiling to formchromosomes
2. Metaphase- the spindle fibres attach themselves to the centromeresof the chromosomes and align the chromosomes along the middle.
3. Anaphase- the spindle fibres shorten and the centromere splits.Sister chromatids are pulled apart.
4. Telophase- the nuclear envelope reforms before the chromosomesuncoil. The spindle fibres disintegrate.
Cytokinesis
Daughter cells split apart. A furrow forms and the cell is pinched in
two.
Homologous pair of chromosomes-The chromosomes that have the
same gene sequence pair up during the cell cycle. This pairing happens
between chromosomes that are homologous i.e. Chromosomes having the
same genes at the same loci but possibly different alleles.
Why mitosis is so important-
Asexual reproduction Growth- multicellular organisms grow by producing new extra cells. Repair- damaged cells need to be replaces by new ones. Replacement- red blood cells and skin cells are replaced by new
ones.
Budding in Yeast
The nucleus divides by mitosis. The cell swells on one side and bulges. Thenucleus, cytoplasm and organelles move into the bus and it pinches off as
the cell wall forms so the bud becomes a separate cell.
Meiosis
Meiosis produces 4 genetically un-identical cells. This is because the genes
from the father and mother wrap around each other and exchange
chromosomes.
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Stem Cells
A stem cellis an undifferentiated cell that is capable of becoming differentiated
to a number of possible cell types.
Cells becoming specialised to carry out a particular function is known as
differentiation.
Cells can differentiate with changes to:
The number of a particular organelle The shape of the cell Some of the contents of the cellErythrocytes and Neutrophils
Erythrocytes (red blood cells) and neutrophils (white blood cells) both begin
with the same set of chromosomes, produced from undifferentiated stem cells inbone marrow.
Erythrocytes loose their nucleus, golgi apparatus, rough endoplasmic
reticulum and mitochondria in order to make room for haemoglobin. Their
shape changes to become biconcave to increase the surface are for picking up
oxygen.
Neutrophils keep their nucleus. Their cytoplasm contains lots of lysosomes to
digest microorganisms. They are flexible for phagocytosis.
Xylem and Phloem
Both come from dividing meristem cells such as cambium meristem cells.
Undergo differentiation to form the different kinds of cells in the transporttissues,
Xylem walls become waterproofed and reinforced (lignin.) This kills the cells
contents. The xylem therefore becomes a long, dead, hollow tube.
Sieve plates are formed between cells, companion cells on the side of the
phloem with lots of mitochondria.
Sperm Cell
Mitochondria- Energy needed for the
movement of undulipodium
Acrosome- a lysosome that releases enzymesonto the outside of the egg so that the sperms
nucleus can penetrate the egg in order to fertilise it.
Undulipodium- helps to propel the cell towards the egg.
Shape- Long, thin to help ease movement.
Tissues- A collection of cell that are similar and preform a common
function. Examples- Xylem/ phloem.
Organs- A collection of tissues working together to preform a particular
function. Example- Plant leaves.
Organ System- Organs working together to preform an overall life
function. Example- Reproductive system.
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Squamous and Ciliated Epithelium Tissue
Squamous- made up of cells that are flattened, so they are very
thin. The cells together form thin, smooth, flat surfaces. This
makes them ideal for the lining inside of tubes such as bloodvessels/ walls of the alveoli. It provides a short diffuse ion
pathway for the exchange of oxygen and carbon dioxide.
Ciliated- made up of column-shaped cells. This type of tissue is
often found on the inner surface of tubes, for example, in the
trachea, bronchi and bronchioles.
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Special Surfaces for Exchange
Three factors affect the need for a transport system:
1. Size- as an animal has several layers of cells, any oxygen or nutrientsdiffusing from the outside are used by outer layers of cells.
2. Surface area to volume ratio- in larger animals the surface area tovolume ratio is not large enough to supply all the oxygen and nutrients
needed by the internal cells. (As the organism gets larger the SA: V ratio
gets smaller.)
3. Level of activity- an active animal needs a good supply of nutrients andoxygen to supply energy for movement.
Good exchange surfaces
Have a large surface area to provide more space for molecules to passthrough. (Alveoli increase surface area in the lungs.)
Short diffusion pathway to reduce the diffusion distance. (Squamousepithelium in the alveoli only one cell thick.)
Fresh supply of molecules to maintain concentration gradient.Tissues in the Lungs
Cartilage- Supports the trachea and bronchi, holding them open. This
prevents collapse when the air pressure inside is low during inhalation.
Ciliated Epithelium- These cells have cilia (tiny hairs) that waft mucus up
the airway to the back of the throat. The mucus is swallowed and the acidin the stomach kills any bacteria.
Goblet Cells- Secretes mucus to trap tiny particles from the air (including
pollen and bacteria) to reduce the risk of infection.
Smooth Muscle- When it contracts it constricts the airway. This makes the
lumen narrower and restricts the flow of air to and from the alveoli. This
may be important if there are harmful substances in the air.
Elastic Fibres- When the smooth muscle contracts it can not reverse the
effect of the narrowing the lumen. When it relaxes the elastic fibres recoil
to their original size and shape. This helps to dilate (widen) the airway.
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Inspiration
1.Diaphragm contracts and flattens2.
External intercostal muscles contract to raise the ribs3.Volume of the chest cavity increases
4.Pressure decreases5.Air moves down the pressure gradient into the lungs.
Spirometers
Tidal Volume- The volume of air moved in and out during
the breathing when you are at rest.
Vital capacity- The largest amount of air that can be moved
in and out of the lungs in one breath.
Soda lime is added to the spirometer to remove carbon
dioxide when it is breathed out.When air is breathed in the spirometer data logger moves
downwards.
Oxygen uptake can be calculated:
Change in volume
Change in time
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Circulatory Systems
Sing circulatory system- Blood flows through the heart
once during each circulation of the bodyDouble circulatory system-The blood flows through the
heart twice. Once to pick up oxygen (pulmonary circulation)
and then to carry oxygen to the body (systemic circulation.)
Open circulatory system- The blood is not always in
vessels (i.e. insects.)
Closed circulatory system- The blood is always contained
within vessels (i.e. fish)
Thickness of walls
The left ventricle has the thickest cardiac muscle as it has to
pump blood around the body. Next is the right ventricle
which has to pump the blood to the lungs. The atriums have
the least cardiac muscle as they only have to pump blood
into the ventricles.
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Cardiac cycle
When the atria are in diastole they fill with blood from the
vena cava/ pulmonary vein. They then contract (systole),
increasing the pressure. As the pressure is higher in the atria
then it is in the ventricle, the atroventricular valves
(bicuspid and tricuspid) open and blood flows into the
ventricles. The ventricle then contracts, increasing the
pressure and therefore causing the AV valve to close. This
also causes the semilunar valves to open and blood flows
into the pulmonary artery/ aorta.
Electrical Impulses
The sino-atrial node starts the excitation wave, which
spreads over the wall of the atria until it reaches the atrio-
ventricular node. The atria contract (atrial systole) and this
contraction is synchronised. There is a delay at the atrio-
ventricular node when the wave of excitation spreads down
septum and into the bundle of His and the Purkyne fibres.
This causes the ventricle to contract (ventricular systole)from the apex of the heart.
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Blood Vessels
Arteries
Carry blood at a high pressure, so in order towithstand the pressure the wall is thick, with
a thick layer of collagen to provide strength.
The endothelium is folded which prevents
damage as it can stretches under pressure
Must be able to maintain that high pressure.
There is a thick layer of elastic tissue to cause
recoil and a return to original size. There is a
thick layer of smooth muscle, which narrows
the lumen.
Veins
Carry blood at low pressure so do walls do
not need to be thick. Lumen is relatively
large to ease the flow of blood. The walls
have thinner layers of collagen, smooth
muscle and elastic tissue. They do no need to
stretch and recoil and are not activelyconstricted to reduce blood flow. Contain valves to prevent
blood flowing in the wrong direction. As the walls are thin, the
vein can be flattened by the action of the surrounding skeletal
muscles. Pressure is applied to the blood, forcing it to move
along in the direction dictated by the valves.
Capillaries
Walls consist of a single layer of flattened endothelial cells that
reduces the diffusion distance for the materials being exchanged.The lumen is the same diameter as the red blood cell (about
7m). This ensures that the red blood cells are squeezed as they
pass along the capillaries. The diffusion distance is shorter, so
they are more likely to give up their oxygen.
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Blood, Tissue Fluid and Lymph
Blood- The main transport fluid for substances to and from all regions of
the body.
Tissue Fluid- Leaks from the capillaries and passes around the cells.Oxygen and nutrients such as glucose can diffuse from the tissue fluid into
the cells and carbon dioxide and waste products such as urea diffuse out of
the cell.
Lymph- The fluid that drains from the tissues into lymph vessels and
eventually back into the blood.
Hydrostatic pressure is caused by the heart pumping blood. This
hydrostatic pressure pushes the blood fluid through the tiny gaps in the
capillaries walls. The fluid that leaves the blood consists of plasma with
dissolved nutrients and oxygen. All the red blood cells and platelets
remain in the blood. They are too large to fit through the gaps. The fluid
that leaves the capillaries is known as tissue fluid.
Feature Blood Tissue Fluid Lymph
Cells Erythrocytes,
leucocytes and
platelets
Some phagocytic
white blood cells
Lymphocytes
Proteins Hormones and
plasma proteins
Some hormones,
proteins secreted
by body cells
Some proteins
Fats Some transported
as lipoproteins
None More than in blood
Glucose 80-120mg per
100cm3
Less Less
Amino acids More Less Less
Oxygen More Less LessCarbon dioxide Little More More
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Haemoglobin
The ability of haemoglobin to take up and release oxygen depends on the
amount of oxygen in the surrounding tissue. The amount of oxygen is
measured by the relative pressure that it contributes to a mixture of gases.This is called partial pressure.
Fetal haemoglobin
Fetal haemoglobin has a higher affinity for oxygen then the adult
haemoglobin. This means fetal haemoglobin can bind to oxygen in the
placenta at relatively low partial pressure of oxygen, where the mothers
haemoglobin is dissociating (releasing oxygen.) (The curve shifts to the
left.)
Carbon Dioxide
Carbon dioxide is transported:
5% directly dissolved in the plasma10% combined with haemoglobin to form carbominohaemoglobin.85% transported in the form of hydrogencarbonate ions (HCO3-)
The Bohr effect- the change in the shape of the oxyhaemoglobin curve
when the carbon dioxide is present- this causes the oxyhaemoglobin to
release oxygen more readily. (The curve shifts to the right.)
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Transpiration
Xylem
Long, thick walls that have been impregnated by
lignin. As the xylem develops, the lignin
waterproofs the walls of the cell,
consequently, the cells die and their end walls
and contents break down. This leaves a long
column of hollow, dead cells. The lignin
strengthens the walls and prevents the
vessel from collapsing- the vessels stay open
even when water is in short supply.
The thickening of the lignin forms patterns on
the cell walls. This prevents the vessel from
becoming too rigid and allows the stem or
branch to be flexible.
In some places the lignification is not complete.
Pits and bordered pits, like pores in the walls, are left which
allow water to leave the vessel to either join another vessel
or pass into cells.
TranspirationThe loss of water by evaporation from the aerial parts of a plant
The stomata needs to be open in order for gaseous exchange to take
place. Therefore, water can be evaporated through the leaves.
Water uptake and movement up the stem
Minerals are actively transported into the root hair cell (using ATP.)
This reduces the water potential in the root hair cell- therefore water
moves down the water potential gradient into the roots (by osmosis.)
The water moves across cortex by osmosis. It can move through oneof three pathways:
1. Apoplast- through the cell wall, prevented by the casparian stripso it has to eventually join the symplast pathway.
2. Symplast- through the cytoplasm3. Vacuolar- through vacuolesWhen going up the xylem vessel the water molecules are attracted to
each other due to intermolecular hydrogen bonds. This is called
cohesion. Adhesion is the attraction of water molecules to the walls
of the xylem. This means that when one water molecule evaporates,the others follow up the xylem.
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Factors that affect transpiration
Number of leaves Number, size and position of stomata Presence of cuticle Light (the stomata open to photosynthesis) Temperature Relative humidity Air movement/ wind Water availabilityPotometer
1. Select plant to be used in experiment2. Underwater, cut the stem at an angle of about 33oc3. Keep the cutting beneath water level, thus ensuring the column of
water in the xylem is not broken.
4. Fill the photometer with water, being sure to introduce an airbubble.
5. Carefully insert the top of the cutting into the top of thephotometer (still under water) and ensure and air tight seal.
6. The plant can now be exposed to different environmentalconditions. Leave to acclimatize and then water uptake can be
measured.7. Results can be graphed as followed; rate of water transpired
against time.
Xerophytes
A plant that is adapted to reduce water loss so that it can survive in
very dry conditions is called a xerophyte.
Adaptations of xerophytes
A waxy cuticle to reduce water loss Smaller leaves Closing the stomata when possible Hairs to hold water and therefore reduce water vapour gradient. Pits to trap water (reducing the water potential gradient) Rolled leaves to trap water vapour
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Translocation
Translocation-The transport of assimilates throughout the plant in
the phloem tissue.
Source-Releases sugars into the phloem.
Sink-Removes sugars from the phloem.
At the source H+ ions are pumped out of the companion cells and
come back with sucrose (using co-transporter proteins.) They are
actively transported out and then diffuse back in.
At the sink sucrose molecules move by diffusion or active transport
from the sieve tube element into the surrounding cells. This increases
the water potential in the sieve tube element causing water to diffuse
out.
Evidence for and against translocation
For Against
Radioactive labeled carbon-16 issupplied to the plant and it shows up
in the phloem
Aphids feed on the sugars in thephloem
Ringing a tree to remove the phloemresults in a build up of sugars
The companion cells have manymitochondria
Translocation can be stopped byusing a metabolic process, the process
inhibits the production of ATP
The rate of flow is so high it cant justbe diffusion alone
The PH of the companion cells arehigher than that of surrounding cells
(due to H+ ions)
The concentration of sucrose it higherin the source than in the sink
Not all the solutes in the phloem sapmove at the same rate
Sucrose is moved to all parts at thesame rate, despite concentration
The role of sieve plates is unclear