OCR AS Biology F211

Notes on every section of F211.

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  • Created by: J.H
  • Created on: 04-05-13 18:16

Living Organisms consists of cells 1.1a

Magnification – the degree to which the size of an image is larger than the object itself.

Resolution - the degree to which it is possible to distinguish between two objects that are close together. The higher the resolution, the greater the detail that can be seen.

Light Microscope                             Scanning Electron                            Transmission Electron

·         x1500 magnification               x100 000 magnification                  x500 000 magnification

·         200nm resolution                    0.1nm resolution                             0.1nm resolution

Staining- stains bind to specific structures increasing contrast and making different structures more visible.

Magnification = Image Size / Actual Size

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Organelles- Structure and Function 1.1b

Nucleus - controls activity of the cell.

Nucleolus – RNA synthesis.

Nuclear Envelope – controls movement of mRNA out of the nucleus.

Rough ER – transports proteins.

Smooth ER – makes and transports lipids.

Golgi Apparatus – modifies and packages proteins.

Ribosomes – protein synthesis.

Mitochondria – aerobic respiration.

Lysosomes – contain powerful digestive enzymes.

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Organelles- Structure and Function 1.1b part 2

Chloroplasts – photosynthesis.

Plasma Membrane – controls entry and exit of molecules from the cell.

Centrioles – form the spindle (only in animal cells and some protoctists), which move chromosomes during nuclear division.

Flagella – Its microtubules contract to make the flagella move. Flagella propel cells forward e.g Sperm Cell

Cilia – Its microtubules all the cilia to move. This movement is used by the cell to move substances along the cell surface.

 

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Cells and living processes

Cytoskeleton

Cells contain a network of fibres made of protein. These fibres keep the cells shape stable by providing an internal framework called the cytoskeleton.

Actin filament fibres- These fibres cause the movement of some organelles around the inside of cells.

Microtubules – made from the protein tubulin.

·         Used to move a micro-organism through a liquid or to waft a liquid past a cell.

Microtubule Motors – move organelles and other cell content along the fibres. e.g. vesicles.

- use ATP to drive the movement.

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Organelles at work 1.1c

Eukaryotic Cells                                                 Prokaryotic Cells

·         Plasma membrane                                       ·         No plasma membrane

·         DNA wrapped around Histone Proteins           ·         N.ak.ed DNA

·         Larger Ribosomes                                        ·         Smaller Ribosomes

·         Mitochondria                                                ·         Mesosomes

Animal Cells                                             Plant Cells

·         Nucleus                                              ·         Nucleus

·         Centrioles                                           ·         Chloroplasts

·         Cell Membrane                                    ·         Cell membrane and  cell wall

·         Lysosomes

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Biological Membranes

Cell Membranes

Within Cells – control exchange of materials between organelles and cytoplasm.

·         provide separate areas for reactions (aerobic respiration in mitochondria).

·         isolate enzyme (lysosomes).

·         provide an internal transport system.

·         provide surfaces for reactions (chloroplasts & mitochondria).

Outside Cells – partially permeable barrier.

·         controls exchange of materials between the cell and its environment.

·         communicate by cell signalling.

·         receptor bind to specific hormones.

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The Fluid mosiac model part 1

Phospholipids – forms the basic structure, acting as a barrier to lipid and protein molecules.

Cholesterol – gives the membrane mechanical stability.

Glycolipids – cell recognition and cell adhesion.

Proteins – act as receptors for cell signalling; transport specific molecules.

Glycoproteins – receptors for cell signalling; cell adhesion; cell recognition.

Increasing Temperature – fatty acid tails of the phospholipid bilayer 'melt', increasing fluidity and allowing foreign molecules into the cell. Proteins denature at high temperatures. Reaction rate increase to the point until the proteins denature.

Decreasing Temperature – fatty acid tails of the phospholipids become more rigid. Reduced fluidity fluidity reduces growth and movement of the cell. Decrease in permeability means vital molecules cannot enter the cell. Cellular reactions slow down and stop.

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The fluid mosiac model part 2

Cell Signalling – cells communicate with one another by signals. Many molecules act as signals (hormones) - some signal during processes taking place inside the cells; others signal from one cell to others.

Diffusion – the movement of molecules from a region of high concentration to a region of lower concentration down a concentration gradient.

Faciliatated Diffusion – diffusion with the aid of carrier and transport proteins.

Active Transport – the movement of molecules or ions across membranes against the concentration gradient, which uses ATP to drive protein pumps within the membrane.

Endocytosis & Exocytosis – bulk transport of molecules via vesicles that can fuse with or break from the cell surface membrane.

Osmosis -the movement of water molecules from a region of higher water potential to a region of lower water potential across a partially permeable membrane.

 

 

 

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Crossing Membranes

Faciliatated Diffusion – diffusion with the aid of carrier and transport proteins.

Channel Proteins- these basically form pores in the memebrane, which are often shaped to allow only one type of ion through: many are also gatesd, meaning they can be opened or closed- gated soduim ion channel proteins are involved with the working of the nervous system.

Carrier proteins- these are shaped so that a specific molecule e.g. glucose can fit into them at the membrane surface- when the specific molecule fits, the protein changes shape to allow the molecule through to the other side of the membrane.

 

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New Cells

Cell Division, Cell Diversity & Cellular Organisation

Interphase (G1, S, G2) - DNA replicates at this time.

Mitosis- the nuclues divides and chromatids seperate. It consists of 4 stages:

Prophase – chromosomes coil and become visible.

Metaphase – chromosomes line up at the equator of the cell and attach to spindle.

Anaphase – chromosomes split at the centromere and move to opposite poles of the cell.

Telophase – nuclear envelope forms in each new cell, chromosomes uncoil.

Mitosis is used for growth, repair, asexual reproduction.

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Cell Cycles

Budding In Yeast - Interphase – bud appears as the cell swells on one side. DNA replicates.

Mitosisnuclear membrane remain intact

· Nucleus, cytoplasm and organelles move into the bud.  --> the nuclear membrane  divides to form two nuclei.

· Cell wall reforms, bud pinches off and leave a scar

Daughter cells are genetically identical to the parent cells in budding and mitosis.

Daughter cells are NOT genetically identical to the parent cells in MEIOSIS.

Homologous Pair Of Chromosomes – chromosomes that have the same genes at the same location.

Stem Cell – undifferentiated cells that are capable of becoming differentiated to a number of possible cell types.

Differentiation – the development and changes seen in cells as they mature to form specialised cells.

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Cell Adaptations part 1

Adaptations of Cells

Erythrocytes – Red blood Cells -carry oxygen and carbon dioxide.

·         biconcave shape to give a larger surface area for oxygen.

·         no nucleus so there is more room of haemoglobin, the protein which carries oxygen.

·         packed with haemoglobin molecules for transport of oxygen.

Neutrophils –White Blood Cells- remove pathogens

·         cytoplasm packed with lysosomes (digestive enzymes).

·         Digestive enzymes allow lysosomes to break down engulfed particles.

Sperm Cells

·         Flagella (undulipodium) for movement through the oviduct.

·         many mitochondria to provide energy for undulipodium.

·         acrosomes which contain digestive enzymes, to help penetrate the egg at fertilisation.

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Cell Adaptions part 2

Palisade Cells – traps light for photosynthesis

·         Thin cell walls, so carbon dioxide can easily diffuse into the cell.

·         many chloroplasts for photosynthesis.

Root Hair Cells – take up water and mineral ions form the soil.

- Elongated to give a large surface area for uptake.

-Thin, permeable cell wall, for entry of water ions.  

Guard Cells – control opening and closing of stomata

- In the light, guard cells take up water and become turgid.

- Thinner outer cell walls and thickened inner cell walls force them to bend outwards, opening stomata.This allows the leaf to exchange gases for photosynthesis.

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Tissues,Organs and Systems

Tissue – a group of similar cells that work together to perform a particular function

  

Organ – a collection of tissues that work together to perform a specific overall function or set of functions within a multicellular organism.

Organ System – a number of organs working together to perform a life function.

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Exchange Surfaces and Breathing

Multicellular organisms - have a lower surface area to volume ratio and may have high metabolic rate, this means diffusion is too slow and a specialised gas exchange surface is needed.

 

Single-celled organisms – have a high surface area to volume ratio and have low metabolic rates. This means the cells can obtain sufficient oxygen by diffusion across its surfaces.

 

Features of Effective Exchange Surface

·         larger Surface Area

·         thin (short distance)

·         diffusion Gradient

·         moist Surface

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Features of the Lungs

Features of the Lungs -

·         Many alveoli give a large surface area.

·         Many capillaries surround the alveoli, capillaries have one cell thick walls.

·         Walls of alveoli are one cell thick, this provides a short distance for diffusion.

·         Surface is well ventilated to maintain the diffusion gradient.

Cartilage – holds the airway open.

Cilia – waft mucus, containing trapped microorganisms and dust, upwards away from the alveoli towards the throat, where it’s swallowed.

Goblet Cells – Secrete mucus to trap microorganisms and dust. Reducing the chance of infection.  

Smooth Muscle – contracts to make the lumen of the airway narrower. Constricting the lumen can restrict airflow to and from the alveoli. Controlling the airflow to the alveoli may be important if there are harmful substances in the air.   

Elastic Fibres – On breathing in, the lungs inflate and the elastic fibres are stretched. Then, the fibres recoil to push the air out of the lungs more easily.  

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Breathing Movements in humans

Inspiration

·         Diaphragm contracts so becomes flattened

·         External intercostal muscles contract so ribs move up and out

·         Volume of chest cavity increases

·         Pressure in chest falls below atmospheric pressure

·         Air moves into the lungs

Expiration

·         Diaphragm relaxes and is pushed up

·         External intercostal muscles relax so the ribs move down

·         Volume of chest cavity decreases

·         Pressure in chest increases above atmospheric pressure

·         Air moves out of the lungs

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Different Elements of Lung Volume

Tidal Volume – the volume of air moved in and out of the lungs with each breath when you are at rest. Approx. 0.5dm3

Vital capacity – the largest volume of air that can be moved into and out of the lungs in any breath. Approx. 5dm3

Residual Volume – the volume of air that always remains in the lungs, even after the largest possible exhalation. Approx. 1.5dm3

Dead Space – the air in the trachea, bronchi and bronchioles. There is no gas exchange between this air and the body.

Inspiratory Reserve Volume- is how much more air can be breathed in (inspired) over and above the normal tidal volume when you take in a large breathe.

Epiratory Reserve Volume- is how much more air can be breathed out (expired) over and above the amount the that is breathed in a tidal volume breath.

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Transport In Animals

Single Circulatory System – blood passes through the heart once on each circuit of the body.

 

Double Circulatory System – blood passes through the heart twice on each circuit of the body.

 

Open Circulatory System – blood circulates around the body cavity without the use of vessels.

 

Closed Circulatory System – blood is always contained in vessels.

 

Cardiac Cycle – one complete sequence of contraction and relaxation (one heart beat).

 

Hydrostatic Pressure – pressure created by a fluid (blood) pushing against the sides of a container (capillary).Forces tissue flood out of the blood.

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How Heart Action Is Co-ordinated

1.     Myogenic cardiac muscle contracts and relaxes.

 

2.     Muscle contraction is generated by a wave of excitation that spreads across the heart.

 

3.     Excitation wave is generated by nervous impulses received by the Sino-atrial node (SAN).

 

4.     The wave is received by the atrio-ventricular node (AVN) and travels down the purkyne fibres to the apex of the heart.

 

5.     Contraction starts at the apex.

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Blood Vessels part 1

Arteries

·         Carry oxygenated blood away from the heart

·         Work under high pressure and accommodate for changes in pressure

·         The wall is relatively thick and contain Collagen, a fibrous protein, to give it strength to           withstand high pressure.

·         Thick Elastic Fibres (See elastic fibres) The recoil mantains the high pressure while the           heart relaxes.

·         Smooth Muscle- See smooth muscle

·         Narrow Lumen- to maintain high pressure.

-         The endothelium is folded and can unfold when the artery stretches.

 

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The Fluid Mosiac Model part 3

Channel Proteins- these basically form pores in the memebrane, which are often shaped to allow only one type of ion through: many are also gatesd, meaning they can be opened or closed- gated soduim ion channel proteins are involved with the working of the nervous system.

Carrier proteins- these are shaped so that a specific molecule e.g. glucose can fit into them at the membrane surface- when the specific molecule fits, the protein changes shape to allow the molecule through to the other side of the membrane.

 

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Blood Vessels part 2

Veins

·         Carry deoxygenated blood towards the heart

·         Allow large volumes of blood to move at low pressure

·         Collagen

·         Few Elastic Fibres

·         Thin Smooth Muscle

·         Wider Lumen- to ease the the flow of blood.

·         Valves- helps blood flow back to heart and prevent it flowing the opposite direction.  

Capillaries

·         Carries blood through tissues to allow exchange of gases and nutrients

·         Single layer of Squamous Epithelium- reduces the diffusion distance for the materials being exchanged.

·         Very Narrow Lumen- same diameter of red blood cell, this ensure they are squeezed as they pass along the the           capillaries. This helps them give up thier oxygen because it presses them close to the capillary wall.

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Blood

Blood

·         Red blood cells ,White blood cells and Platelets

·         Hormones and Plasma Proteins

·         Water

·         Dissolved Solutes

 

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Tissue fluid and lymph

Tissue Fluid

·         Some Phagocytic White Blood Cells, enter tissue when there’s an infection.  

·         Very few plasma proteins.

·         Water.

·         Dissolved solutes.

Lymph

·         Lymphocytes (White blood cells).  

·         Only antibody proteins.

·         Water.

·         Dissolve Solutes.

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Blood, tissue fluid and lymph

How Tissue Fluid Leaves the Blood

1.     At arteriole end, blood is under high hydrostatic pressure, due to the blood being under high pressure due to the contraction of the heart muscle.

2.     This pushes blood fluid out of the capillaries, leaving via the tiny gaps in the capillary wall.

3.     This is called tissue fluid (see tissue fluid).

 

How Tissue Fluid Enters the Blood

1.     Both blood and tissue fluid contain solutes giving them a negative water potential.

2.     The water potential of tissue fluid is less negative than the blood – setting up osmosis.

3.     At the venous end, the blood has lost hydrostatic pressure so hydrostatic pressure in the tissue fluid and osmosis sends the fluid back into the blood. Carrying carbon dioxide away.

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Carriage of Oxygen

Oxygen Dissociation Curve

·         Loading and unloading of oxygen from haemoglobin depends on the concentration of oxygen surrounding haemoglobin.

·         At high pO2 (in the lungs), haemoglobin has a high affinity for oxygen, so it has a high saturation of oxygen.

·         At low pO2 (in respiring tissues), haemoglobin has a low affinity for oxygen, which means it releases oxygen rather than combines with it.  

Bohr Effect

·         As carbon dioxide levels increase, more will diffuse into red blood cells and combine with water to form carbonic acid.

·         The levels of hydrogen ions increase, the hydrogen ions combine with haemoglobin causing dissociation of oxygen.

·         High partial pressure of carbon dioxide means that less oxygen is associated with haemoglobin. The curve shifts to the right. This is the Bohr Effect.

 

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Fetal Haemoglobin

Fetal Haemoglobin

·         Foetal haemoglobin has a much higher affinity for oxygen than adult haemoglobin.

·         In the placenta, the fetal haemoglobin must absorb oxygen from the fluid in the in the mothers blood.  

·         This reduces the oxygen tension within the blood fluid, which in turn makes the maternal haemoglobin release oxygen.

·         The oxygen dissociation curve for foetal haemoglobin shifts to the left of the adult curve.

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Transport In Plants

Xylem

·         Long cells with thick walls that have been impregnated with lignin.

·         Rings allow flexibility of the stem or branch.

·         Cells die and the end walls and contents decay. This leaves a long column of dead cells with no contents- a tube with no end walls – a xylem vessel.

·         Adaptations

·         Narrow tubes so water column does not break easily.

·         Pits in the lignified walls allow lateral movement of water.

·         Water flow is not blocked – no end walls or cell content.

·         Lignin thickening prevents the walls from collapsing.

·         Lignin deposited in the wall in spiral, annular or reticulate patterns allows xylem to stretch as the plant grows and enables the stem or branch to bend.

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Transport in plants part 2

Phloem

Sieve Tube Element

·         Contain little cytoplasm and no nucleus

·         Lined up end to end to transport sucrose.

·         Contain perforated cross walls at intervals called sieve plates.

Companion Cell

·         Has a large nucleus, dense cytoplasm, mitochondria for ATP.

·         Carries out the metabolic processes needed by sieve tube elements including loading of sucrose.

·         Cytoplasm of the companion cell is by plasmodesmata. These are the gaps in the cell walls allowing communication and flow of minerals between the cells.

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The movement of water

Apoplast Pathway – water moves through the gaps between the cellulose molecules and in the gaps between the cells themselves.

 

Symplast Pathway – enters through the plasma membranes then through the plasmodesmata from one cell to the next.

 

Vacuolar Pathway – similar to symplast but it also passes through the vacuoles as well.

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The movement of water

Apoplast Pathway – water moves through the gaps between the cellulose molecules and in the gaps between the cells themselves.

 

Symplast Pathway – enters through the plasma membranes then through the plasmodesmata from one cell to the next.

 

Vacuolar Pathway – similar to symplast but it also passes through the vacuoles as well.

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Transport in plants part 2

Phloem

Sieve Tube Element

·         Contain little cytoplasm and no nucleus

·         Lined up end to end to transport sucrose.

·         Contain perforated cross walls at intervals called sieve plates.

Companion Cell

·         Has a large nucleus, dense cytoplasm, mitochondria for ATP.

·         Carries out the metabolic processes needed by sieve tube elements including loading of sucrose.

·         Cytoplasm of the companion cell is by plasmodesmata. These are the gaps in the cell walls allowing communication and flow of minerals between the cells.

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Through The Root

1.     Root hair cells absorb minerals from soil by active transport using ATP.

 

2.     This lowers the water potential in the root hair cell so that water enters by osmosis down the water potential gradient.

 

3.     The Casparian ***** blocks the apoplast pathway and ensures water and dissolved nitrate ions pass into the cell cytoplasm.

 

4.     Endodermis cells move minerals by active transport from the cortex into the xylem decreasing the water potential in xylem, water enters the xylem by osmosis.

5.     Once water is in the xylem it cannot pass back into the cortex.

 

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Up The Stem

·    Root Pressure – loading minerals into the xylem by the endodermis forces       water into the bottom of the xylem and pushes water up.

 

·    Transpiration Pull – water lost from the leaves must be replaced – water molecules are attached to each other by cohesion – as molecules are lost at the top of the column the whole chain is pulled up as one. This creates tension in the column of water. This is why xylem is strengthened by lignin. (Cohesion Tension Theory).

 

·    Capillary Action – same cohesion forces attaching molecules to each other attract them to the sides of the xylem vessel (adhesion). Xylem is narrow so it is easier to pull water up the side of the vessel.

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Transpiration (see potometer)

Why?

  • A plant needs to open its stomata to let in carbon dioxide so that it can produce glucose by photosynthesis.
  • This lets out water- as there's a higher concentration of water inside the leaf than in the air outside, so water moves out of the leaf down the water potential gradient when the stomata open.

Factors affecting Transpiration rate:

  • Light - lighter it is the faster the transpiration rate. As stomata open when it gets light to allow for gaseous echange for photosynthesis, closed when dark.
  • Temperture - The higher temperature the faster the transpiration rate as the water molecules have more kinetic energy.  
  • Humidity - the lower the humidity, the faster the rate of transpiration.  This is because there is a greater water vapour potential gradient between the air spaces in the leaf and the air outside. Or opposite answer.  
  • Wind - Air moving outside the leaf will carry away water vapour that has just diffused out of the leaf. This will maintain a high water vapour potential gradient.  
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Translocation

1.     H+ ions are actively transported out of the companion cells in to the leaf cell (source).

2.     H+ ions and sucrose enter companion cells by facilitated diffusion through a co-transporter protein.

3.     Sucrose then diffuses from the companion cell into the sieve tubes.

4.     Water potential of sieve tubes decreases, so water enters the tubes by osmosis.

5.     Water enters from xylem and surrounding tissues.

6.     Hydrostatic pressure in sieve tubes increases.

7.     Contents are pushed along the phloem from a region of high hydrostatic pressure to a region of low hydrostatic pressure.

8.     At the root hair cell (sink), sucrose diffuses into the companion cells.

9.     From companion cells, sucrose enters surrounding cells by active transport and facilitated diffusion.

10.  Water potential of phloem increases so water leaves the phloem and hydrostatic pressure falls.

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Evidence For/ Against Mass Flow Hypothesis

For

· If you remove a ring of bark (which includes the phloem but not the xylem) from a woody stem a bulge forms above the ring. If you analyse the fluid from the bulge the, you’ll find it has a higher concentration of sugars than the fluid from below the ring – this is that there’s a downward flow of sugars.

· You can investigate pressure in the phloem using aphids. The sap flows out quicker nearer the leaves than further down the stem – this is evidence that there’s a pressure gradient.

· If you put a metabolic inhibitor (which stops ATP production) into the phloem then then translocation stops - this is evidence that active transport is involved.  

Against

· Sugar travels too many different sinks, not just to the one with the highest water potential, as the model would suggest.

· The sieve plates would create a barrier to mass flow. A lot of pressure would be needed for the solutes to get through at a reasonable rate.

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Comments

Leila Spicer

This is very helpful thank you!! :P

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