OCR Biology Unit 1 Revision Cards-Cells, Exchange & Transport

Key notes on the concepts of Biology Unit 1 (Cells and Exchange & Transport)



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 very close together.

                         Light Microscope                  SEM                      TEM    

Manification      x1500                                   x100,000               x500,000

Resolution        200nm                                  0.1-0.2nm              0.1-0.2nm     

Staining-chemicals bind to chemicals on or in the specimen. This allows different areas to be seen and helps to distinguish features.

Sectioning-specimens are embedded in wax, and thin sections are then cut by distorting the specimen.                                               I       e.g. image size/ actual size

mm-->nm = x1000         The IAM triangle-   A     M         = magnification

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CYTOSKELETON-network of protein fibres found within cells that give structure and shape to the cell, and also helps move organelles around inside cells. Actin filaments move white blood cells, microtubules move microorganisms through a liquid or they can waft a liquid past a cell (e.g. move chromosomes and vesicles.)

Flagella and cilia-hair-like structures-movement for different reasons.


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RER-studded with ribosomes, transports proteins that were made on the attached ribosomes.

SER-flattened membrane bound sacs, no ribosomes, makes lipids.

Golgi apparatus-membrane bound flattened sacs, receives proteins from the ER and modifies them before packaging them into vesicles and they are transported.

Mitochondria-two membranes-cristae (folded), matrix, ATP production.

Chloroplasts-flattened sacs called thylakoids, stack is called a granum, site of photosynthesis.

Lysosomes-spherical sacs surrounded by a single membrane, contain digestive enzymes to break down materials.

Ribosomes-tiny organelles, some in cytoplasm and some bound to the RER. Two subunits, site of protein synthesis, mRNA is used to assemble proteins from amino acids.

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Centrioles-small tubes of protein fibres (microtubules), come in pairs, take part in cell division-form spindles and move the chromosomes during nuclear division.

Nucleus-largest organelle-surrounded by a nuclear envelope. Nuclear pores go right through the envelope-large molecules can pass through. There is a dense spherical structure called a nucleolus inside the nucleus. This houses all of the genetic material. Chromatin inside (contains DNA and proteins)-has instructions for making proteins. Nucleolus makes RNA and ribosomes.

Roles of different organelles in the production and secretion of proteins:

RER-transports proteins made on the attached ribosomes.

Ribosomes-site of protein synthesis.

Golgi apparatus-modifies and packages proteins into vesicles.

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Eukaryotic cells-have a nucleus, can contain two membranes, have membrane bound organelles, large ribosomes, linear chromosomes (separate strands) of DNA, DNA surrounded by a membrane, ATP production takes place in the mitochondria, larger, cell wall made of cellulose.

Prokaryotic cells-no nucleus, one membrane, no membrane bound organelles, small ribosomes, DNA in single loop free in liquid, ATP in infolded regions, smaller, murein cell wall.

PHOSPHOLIPID BILAYER-basic structural component of plasma membranes. Two layers of phospholipid molecules-creates a barrier to many molecules.

5 roles of membranes: separate cell contents from cytoplasm, separate cell contents from outside environment, cell recognition and signalling, holding the components of somes metabolic pathways in place, regulating the transport of materials into and out of cells.

All membranes are permeable to water molecules because water molecules can diffuse through the phospholipid bilayer.

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FLUID MOSAIC-a bilayer of phospholipid molecules, protein molecules and proteins which are embedded in the bilayer.

Glycoproteins and glycolipids-carbohydrates attached to the proteins or phospholipids. They are involved in cell signalling and bind cells together in tissues. They have a specific shape complementary to a trigger molecule, binds to the receptor in the glycoprotein/lipid.

Cholesterol-gives mechanical stability-fits between fatty acid tails. Makes the barrier more complete.

Channel proteins-allows the movement of some substances across the membrane e.g. glucose.

Carrier proteins-actively move substances across the membrane using ATP.

Increasing temperature=more kinetic energy, so molecules move faster, leaky membranes. Allows substances that would not normally do so to enter or leave the cell.

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CELL SIGNALLING-communication between cells where receptors recognise a signal and initiate a response.

Hormones-chemical messengers, bonds to a receptor on a target cell surface membrane as the two have complementary shapes.

Insulin-triggers internal responses when it attaches, so cells have more glucose channels present, enabling the cell to take up more glucose from blood, reducing blood glucose levels.

Medicinal drugs-complementary to the shape, intended to block receptors.

DIFFUSION-the movement of molecules from a region of high concentration to a region of low concentration down a concentration gradient, through a partially permeable membrane.

PASSIVE TRANSPORT-molecules continue to diffuse down their concentration gradient without using energy from the cell.

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FACILITATED DIFFUSION-proteins allow large substances to pass through the membrane-uses channel pores/proteins or carrier proteins (specifically sheped e.g. glucose).

MEMBRANE PROTEINS-enable large insoluble molecules or ions to pass through the membrane.

Simple diffusion--> oxygen, carbon dioxide, hormones.

Facilitated diffusion (channel proteins)--> ions-Fe and Ca.

Facilitated diffusion (carrier proteins)--> larger molecules (glucose, amino acids.)

ACTIVE TRANSPORT-the movement of molecules or ions across membranes, which uses ATP to drive protein 'pumps' within the membrane. Each protein pump carries a specific molecule. Go in opposite direction to the concentration gradient, and the rate is faster.

ENDOCYTOSIS-bringing materials into the cell.

EXOCYTOSIS-moving material out of the cell.

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PHAGO-solid material         PINO-liquid material

BULK TRANSPORT-moving large quantities of material into or out of a cell. Requires ATP to move membranes to form vesicles and move them e.g. hormones such as insulin and white blood cells.

OSMOSIS-the movement of water molecules from a region of high concentration to a region of low concentration down a concentration gradient across a partially permeable membrane.

0kPa=highest water potential           -500kPa=lower water potential

Animal cell in concentrated salt solution=crenated.

Animal cell in pure water=lysis.

Plant cell in concentrated salt solution=plasmolysed.

Plant cell in pure water=turgid.

WATER POTENTIAL-a measure of the tendency of water molecules to diffuse from one place to another.

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CELL CYCLE-the events that take place as one parent cell divides to produce two new daughter cells which then each grow to full size.

4 stages: interphase-DNA replicates in this stage.

               mitosis-nucleus divides and chromatids separate.

               cytokinesis-cytoplasm divides forming two complete new cells.

               growth phase-each new cell grows to full size.

Mitosis occupies only a small percentage of the cell cycle and the remaining larger proportion includes copying and checking genetic information on the DNA and processess associated with growth.

MITOSIS-refers to the process of nuclear division where two genetically identical nuclei are formed from one parent cell nucleus.

Why do new cells need to be made? Asexual reproduction, growth, repair, replacement.

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Prophase-chromosomes shorten and thicken. Nuclear envelope disappears. The centriole divides and the two centrioles move to the poles of the cell to form the spindles.

Metaphase-chromosomes move to the equator of the spindle. Each is attached by its centromere.

Anaphase-chromatids are separated when the centromere splits, and each chromatid becomes an individual chromosome. Spindle fibres shorten, pulling sister chromatids towards the poles, V-shaped as the centromere leads.

Telophase-as chromosomes reach the poles of the cell, a new nuclear envelope forms around each set. The spindle disappears and the chromosomes uncoil.

STEM CELLS-undifferentiated cells that are capable of being able to differentiate into a number of different cell types.

CLONES-genetically identical cells or organisms derived from one parent.

HOMOLOGOUS PAIR OF CHROMOSOMES-pair of chromosomes that are genetically identical.

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Cells of yeast undergo cytokinesis by producing a small 'bud' that rips off the cell in a process called budding.

MEIOSIS-produces cells containing half the number of chromosomes, and produces cells that are genetically different from each other, and from the parent cell.

DIFFERENTIATION-changes occurring in cells of a multicellular organism so that each different type of cell becomes specialised to perform a specific function.

Erythrocytes-lose their nucleus, mitochondria, golgi and the RER. Packed full of haemoglobin, become biconcave discs.

Neutrophils-keep nucleus, lost of lysosomes.

Sperm cells-many mitochondria for movement, acrosome to penetrate the egg, long and thin, undulipodium, half number of chromosomes.

Root hair cells-hair like projection into the soil to increase the surface area for absorption.

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TISSUE-a group of cells that are similar to each other and perform a common function e.g. xylem, phloem, epithelial and nervous tissue.

ORGAN-a collection of tissues working together to perform a particular function e.g. leaves, liver.

ORGAN SYSTEM-a number of organs working together to perform an overall life function e.g. reproductive and excretory system.

Xylem and phloem come from dividing meristem cells (cambium).

Xylem-meristem cells produce small cells that elongate, walls reinforced by deposits of lignin, ends break down so they become continuous long tubes with a wide lumen. Well suited for the transport of water and minerals up the plant. Supports.

Phloem-sieve tubes and companion cells. Meristem tissue produces cells that elongate and line up to form a long tube. Ends don't break down completely, but form sieve plates, which allow movement up or down. Companion cells are next to the sieve tubes. They are metabolically active and their activities help with movement up or down.

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Squamous epithelial tissue-flattened cells, very thin, flat surface, ideal for lining blood vessels, containing collagen and glycoproteins-attaches epithelial cells to the connective tissue.

Ciliated epithelium-column shaped cells-inner surface of tubes e.g. trachea are covered in cilia, some produce mucus. Wave in a synchronised rhythm, moving the mucus.

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All organisms need specific substances to keep them alive-oxygen, glucose, proteins, fats, water, minerals.

Removing waste products-carbon dioxide, oxygen, urea, ammonia.

Single celled/small organisms have a large surface area:volume ratio-gas exchange can take place across their body surface.

Larger organisms-small surface area:volume ratio-no gas exchange across their body surface as they need a transport system with certain features (large surface area, thin barrier, fresh supply of molecules on one side, removal of molecules on the other side.)

EXCHANGE SURFACE-a specialised area that is adapted to make it easier for molecules to cross from one side of the surface to the other.

GAS EXCHANGE-the movement of gases by diffusion between an organism and its environment across a barrier.

The lungs-large surface area, small alveoli in large numbers, a permeable barrier to oxygen and carbon dioxide, thin barrier to reduce diffusion distance.

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Alveolus wall is one cell thick, capillary wall is one cell thick, flat cells, narrow capillaries, moisture lines alveolus (surfactant).

Inhaling/inspiration-diaphragm contracts to become flatter, pushes digestive organs down, external intercostal muscles contract to raise ribs, volume of chest cavity increases, pressure in chest cavity drops below atmospheric pressure, air moves into lungs.

Exhaling/expiration-diaphragm relaxes and is pushed up by displaced organs underneath, external intercostal muscles relax and ribs fall, volume of chest cavity decreases, pressure in lungs increases and rises above atmospheric pressure, air moves out of lungs.

Cartilage-C shaped rings-supports trachea and bronchi, holds them open and prevents collapse.

Smooth muscle-contracts to restrict the airway in response to an allergen.. Restricts the flow of air.

Elastic fibres-when the smooth muscle contracts, the elastic fibres deform and stretch. As the smooth muscle relaxes, the elastic fibres recoil. Widens airways.

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Goblet cells-secrete mucus, trap tiny particles so that they can be removed.

Ciliated epithelium-tiny hair like structures called cilia move in synchronised pattern to waft mucus up the airway. It is swallowed at the top and stomach kills bacteria.

TIDAL VOLUME-volume of air moved in and out of the lungs in each breath while you are at rest.

VITAL CAPACITY-the maximum volume of air that can be moved in and out of the lungs in any one breath.

RESIDUAL VOLUME-the volume of air moved that always remains in the lungs.

DEAD SPACE-air within bronchioles, bronchi and trachea.

INSPIRATORY AND EXPIRATORY RESERVE VOLUME-how much more air can be moved in/out over the tidal volume.

SPIROMETER-chamber filled with oxygen that floats on a tank of water. Person breathes through a mouthpiece, breathing in causes the chamber to sink down and breathing out causes the chamber to rise up, producing a spirometer trace. Soda lime is used to absorb the carbon dioxide exhaled.

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Main factors that affect the need for a transport system: size-multiple layers of cells, surface area:volume ratio-large animals have a small surface area:volume ratio, level of activity-animals need energy from food which they release by respiration.

Features of a good transport system: a fluid to carry nutrients and oxygen (blood), a pump (heart), exchange surfaces, tubes or vessels, two circuits.

SINGLE CIRCULATORY SYSTEM-single circuit from heart-->gills-->body-->heart (fish).

DOUBLE CIRCULATORY SYSTEM-two separate circuits, one is pulmonary, one is systemic, two pumps, heart-->body-->heart-->lungs-->heart (mammals).

Advantages of double circulation-the blood is at higher pressure than in single circulation.

HEART-muscular double pump, two sides, right pumps deoxygenated blood to be oxygenated, left pumps blood to the rest of the body.

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ATRIA-very thin walls because their job is to push blood into the ventricles.

RIGHT VENTRICLE-thicker than the atria walls, pumps blood out of the heart and to the lungs.

LEFT VENTRICLE-thicker than the right ventricle, pumps blood to the rest of the body.

CARDIAC CYCLE-sequence of events involved in one heartbeat.

1. Diastole-both atria and ventricles are relaxing, blood flows into ventricles.

2. Atrial contraction-atria contract together, pushing blood into the ventricles, ensures ventricles are full of blood. This is called atrial systole. Then the ventricles begin to contract, filling the atrioventricular valve flaps with blood, shutting them.

3. Ventricular contraction-short period where all 4 valve flaps are shut. Walls of ventricles contract. This is called ventricular systole. Contraction starts at the bottom, pushing blood up towards the arteries. Semilunar valves open and blood is pushed out.

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Semilunar valves-open when ventricles contract, close when pressure is low in ventricles.

Atrioventricular valves-open when pressure is low in ventricles, close when ventricles contract.

SAN-the hearts pacemaker, it is a small patch of tissue that sends out waves of electrical excitation at regular intervals to initiate contraction.

AVN-where the wave of excitation is delayed.

PURKYNE TISSUE-specially adapted muscle fibres that conduct the wave of excitation from the AVN down the septum to the ventricles.

Heart muscle is myogenic-it can initiate its own contraction without nervous impulse.

The path of the wave of excitation: SAN generates wave of excitation which spreads across the atria from top to bottom, causing the cardiac muscle to contract. The wave passes over the AVN which delays the wave to allow time for the atria to finish contracting. Wave is then carried down the Purkyne tissue in the septum. At the base it spreads upwards, so the ventricles contract from bottom to top.

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OPEN CIRCULATORY SYSTEM-blood is not always in vessels. Blood fluid circulates through the body cavity. Tissues and cells are bathed directly in blood e.g. ant.

CLOSED CIRCULATORY SYSTEM-blood always remains within vessels. Tissue fluid bathes the tissues and cells. Blood is pumped at a higher pressure e.g. fish (heart-->arteries-->gills-->veins-->body tissues-->veins-->heart.

Arteries-carry blood away from the heart. Small lumen, thick collagen wall, elastic tissue, smooth muscle.

Veins-carry blood back to the heart, large lumen, thin layers of collagen, smooth muscle and elastic tissue, contain valves.

Capillaries-very thin walls, single layer of flattened endothelial cells, narrow lumen, presses blood cells close to the capillary wall.

BLOOD-held in the heart and blood vessels. Blood cells in plasma.

TISSUE FLUID-bathes the cells of individual tissues. Does not contain most of the cells found in blood.

LYMPH-held within lymphatic system, contains lymphocytes-drained tissue fluid.

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How tissue fluid is formed: blood at high pressure at the arterial end of the capillary. This pushes blood fluid out of the capillaries through tiny gaps in the capillary wall (red blood cells, platelets and most white blood cells don't fit through the gap.) At the venous end, the fluid is pushed back as it is under pressure and it has a negative water potential which is higher than in the blood, so it moves back in.

Formation of lymph: tissue fluid that is drained away into the lymphatic system.

Blood: white and red blood cells, platelets, hormones, plasma proteins, quite a lot of glucose, amino acids and oxygen, less carbon dioxide.

Tissue fluid-white blood cells, some hormones, no fat, less glucose, amino acids and oxygen.

Lymph-lymphocytes, some proteins, lots of fats and carbon dioxide, less glucose, amino acids and oxygen.

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Oxygen is transported in red blood cells which contain haemoglobin. When it takes up oxygen it becomes oxyhaemoglobin. Haemoglobin has 4 subunits, each with a protein chain and a haem group, which contains an Fe(2+) ion which attracts and holds an oxygen. It has an affinity for oxygen. Each haemoglobin molecule can carry 4 oxygen molecules. At low oxygen tension, haemoglobin has a low affinity for oxygen, because the haem groups are in the centre of the molecule. As the oxygen tension increases the diffusion gradient increases, so 1 molecule diffuses and associates, causing a conformational (shape) change in the molecule, allowing more oxygen molecules to diffuse into the haemoglobin more easily. It is more difficult for the 4th oxygen molecule, and difficult to achieve 100% saturation.

Fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin. In the protein the fetal haemoglobin absorbs oxygen in the mother's blood fluid, reducing oxygen tension so the maternal haemoglobin releases oxygen. On an oxygen dissociation curve, fetal haemoglobin is to the left of adult haemoglobin.

How is carbon dioxide transported? Combines with haemoglobin to form carbaminohaemoglobin, transported in the form of HCO3- ions.

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As carbon dioxide diffuses into the blood, some enters the red blood cells. It combines with water to form carbonic acid. This is then catalysed by the enzyme carbonic anyhydrase:

CO2 + H20 --> H2CO3-this dissociates to release H+ and CO3- ions. These then diffuse into the plasma. The charge inside the red blood cells is maintained by the movement of chloride ions (Cl-) from the plasma into the red blood cells. This is the chloride shift. The H+ ions could cause the contents of the red blood cell to become very acidic, so they are taken up by haemoglobin to produce haemoglobinic acid.

Releasing oxygen-as the blood enters the respiring tissues, the haemoglobin is carrying oxygen in the form of oxyhaemoglobin. The oxygen tension is lower in respiring tissues because oxygen is being used up, so the oxyhaemoglobin dissociates to release oxygen to the tissues. The H+ ions compete for space on the haemoglobin molecule, so when carbon dioxide is present, the H+ ions displace the oxygen on the haemoglobin, so more oxygen is released. This is the Bohr effect. The oxygen dissociation curve shifts to the right and downwards. Advantages for respiring tissues.

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XYLEM-transports water up the plant. Found in vascular bundles.

PHLOEM-transports sugars and assimilates up and down the plant.

ROOT-xylem in the middle, usually an X shape, phloem found between the lines of the X, meristem cells and endodermis on the edge.

STEM-vascular bundles all around the edge of the stem. Xylem closest to the middle of the stem and phloem closest to the edge of the stem. Cambium in the middle.

LEAF-xylem in the centre midrib and phloem surrounds the xylem.

Xylem-xylem vessels are long cells with thick walls impregnated with lignin. Lignin waterproofs the xylem. Cells die, and the end walls decay, leaving a long column of dead cells. Lignin strengthens the vessel and prevents collapse. Forms a pattern-spiral, annular (rings), broken rings Provides flexibility. in some places lignification is not complete, creating pits or bordered pits, which allow water to move between vessels. Adaptations: narrow tubes, allowing capillary action, lignin allows xylem to stretch as the plant grows.

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Phloem-sieve tubes (sieve tube elements)-no nucleus, little cytoplasm-lined end to end to form a tube. Contains cross walls at intervals, perforated by pores (sieve plates.) Companion cells-mitochondria, carry out metabolic processes needed by the sieve tube elements. ATP is used to load sucrose into the sieve tubes. Linked by plasmodesmata (gaps in the cell wall allowing communication and flow of minerals between the cell.) Cytoplasm of the companion cells and the sieve tube elements are linked through these plasmodesmata.

WATER POTENTIAL-measure of the tendency of water molecules to diffuse from one place to another. Water always moves from a region of high water potential to a region of low water potential. The highest water potential is 0.

APOPLAST PATHWAY-water passes through the cell wall.

SYMPLAST PATHWAY-water passes through the plasmodesmata between cytoplasms.

VACUOLAR PATHWAY-water passes through the plasmodesmata between vacuoles and cytoplasm.

PLASMODESMATA-a fine strand of cytoplasm that links the contents of adjacent cells.

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COHESION-attraction of water molecules for one another.

ADHESION-attraction of water molecules to the walls of the xylem.

Movement across the root: driven by a process in the endodermis, containing a waterproof ***** called the Casparian *****, which blocks the apoplast pathway, forcing water into the symplast pathway. The endodermis cells move minerals by active transport from the cortex into the xylem. This decreases the water potential, so water moves from the cortex through the endodermal cells to the xylem by osmosis. This reduces the water potential in the cells outside the endodermis, creating a water potential gradient.

What is the role of the Casparian *****? Blocks the apoplast pathway between the cortex and the xylem, ensuring that water and dissolved nitrate ions pass through the cell cytoplasm. There are transporter proteins in the cell membrane which can actively transport the nitrate ions into the xylem, which lowers the water potential.

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Three ways water moves up the stem:

ROOT PRESSURE-action of the endodermis moving minerals by active transport drives water into the xylem by osmosis. This forces water into the xylem and drives the water up the stem.

TRANSPIRATION PULL-cohesion forces hold water molecules in a column. As molecules are lost at the top of the column, the whole column is pulled up. This is the transpiration stream. It is the cohesion-tension theory.

CAPILLARY ACTION-adhesion forces pulling the water up the sides of the stem as they are so narrow.

TRANSPIRATION-the loss of water by evaporation from the aerial parts of a plant. Three processes-osmosis from the xylem to mesophyll cells, evaporation from the surface of mesophyll cells into the intercellular spaces, diffusion of water vapour from the intercellular spaces out through the stomata.

A potometer can be used to estimate the rate of transpiration. Make sure that there are no air bubble. Water lost by the leaf is replaced from the water in the capillary tube. The movement of the meniscus can be measured. 

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Factors affecting the rate of transpiration: number of leaves, number  of stomata, size of stomata, position of stomata, presence of cuticle, light, temperature, humidity, air movement, water availability.

XEROPHYTE-a plant that is adapted to reduce water loss so that it can survive in very dry conditions. Adaptations: smaller leaves, dense spongy mesophyll,  thick waxy cuticle, closing stomata when water availability is low, hairs, pits, rolled leaves, low water potential inside leaf cells.

TRANSLOCATION-the transport of assimilates throughout the plant in the phloem tissues.

SOURCE-releases sucrose into the phloem e.g. leaf.

SINK-removes sucrose from the phloem e.g. root.

Sucrose is loaded into the phloem by an active process. ATP used by the companion cells to set up a diffusion gradient by actively transporting H+ ions out of their cytoplasm and into the surrounding tissue. The H+ ions then diffuse back into the companion cells, through special cotransporter proteins which enable the sucrose molecules to be brought into the companion cells. As the concentration of sucrose increases in the companion cells, they diffuse into the sieve tube elements through the plasmodesmata.

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At the source-sucrose enters the sieve tube element-reduces the water potential, so water moves into the sieve tube element by osmosis, increasing hydrostatic pressure.

At the sink-sucrose used in cells surrounding the phloem. May be converted into starch or used in respiration. 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, so water molecules move into the surrounding cells by osmosis, reducing hydrostatic pressure.

MASS FLOW-water entering the phloem at the source, moving down the hydrostatic pressure gradient and leaving the phloem at the sink-produces a flow of water along the phloem.

Evidence for translocation: ringing in trees causes sugars to collect above the ring, labelled carbon dioxide appears in the phloem, aphids feeding from the phloem, companion cells have many mitochondria, translocation can be stopped by using a metabolic poison that inhibits the formation of ATP, pH of companion cells is higher than surrounding cells, concentration of sucrose is higher at the source.

Evidence against translocation: not all solutes move at the same rate, role of sieve plates is unclear, sucrose is moved to all parts of the plant at the same rate.

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Quite good. Would have been nice to have the object (i.e. mitochondrion / nucleus / etc) on a seperate page to the function (i.e. ATP synthesis / chromosome container / etc).



Ive just discovered this website and it has really made an impact on my revision techniques! thankyou  :)

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