Revision notes- CellsCells- 1660s, Hooke looked at slices of cork from tree bark and under a light microscope he made, saw that the slices were made up of chambers that looked like monk cells, and so he called them cellsMagnification- the number of times greater an image is than the objectResolution- the ability to see two see two distinct points separately Light microscope

The eyepiece magnifies the specimen x10. There are usually four objective lenses x4, x10, x40, x100 (oil immersion- oil placed over specimen).Eyepiece MagnificationObjective MagnificationOverall Magnification

X10X4X40

X10X10X100

X10X40X400

X10X100X1000

Preparing specimens for the light microscopeStaining- coloured stains contain chemicals which bind to chemicals in/on the specimen which allow it to be seen clearly (acetic orcein bins to DNA, Gentian violet bind to bacterial cell walls)Sectioning- thin sections can be made by embedding the specimen in wax and cutting thin slices. These thin slices let more light through and so they are easier to seeRelationships between units of measurements

Relationship between actual size, magnification and image size

Using an eye piece graticle and a stage micrometer to determine cells sizeAn eye piece graticle is like a small ruler and is placed into the microscope eye piece. When you look through this ruler is superimposed over the specimen

The eye piece graticle need to be calibrated using a slide micrometer which is placed on the microscope stage. The stage micrometer is 1mm long and divided into 100 divisions so each division is 10 micrometres.

In example (a) above, the magnification was x40, so 40 eye piece units equals the 1mm (or 1000 micrometre) slide micrometer (in pink).So each eye piece unit (EPU) is 1000/40 which is 25 micrometersIn example (b), the magnification is times 100. So 1 EPU equal 1000/100= 10 micrometresHow to use the graticule to work out the size of specimen/feature of interest example- if a nucleus is 3.2 epu long and you have worked out your epu is worth 10mm then 3.2 multiplied by 10 gives you the length of 32mmElectron microscopesLight microscopes have low resolution so when you increase the magnification above x1500, the image is not clear (resolution 200nm)Electron microscope resolution is 0.2nm so you can magnify a specimen more and still see it clearly. 2 types of electron microscope Transmission electron microscope (TEM) Scanning electron microscope (SEM)TEM- electron beam is passed through a very thin section of a specimen. The electrons do not pass through denser parts of the specimen so easily, giving a two-dimensional image SEM- the electrons do not pass through but bounce off the sample giving a 3D image Caparison of light and electron microscopes

False-colour- images from electron microscopes are always black and white and so false-colour is added afterwards using computer software

Electron microscopes need to operate in a vacuum i.e. no air particles present so that electrons are not scattered by the air particles making the image clearer. Cells and living processesSeven characteristics of living things (MRS GREN)- movement, reproduction, sensitivity, growth, respiration, excretion, nutrition Different structures in the cell are used in carrying out these different characteristic functions.Ultrastructure- detail of the inside of the cell seen with an electron microscopeDivision of labour- each organelle in the cell has a particular role within the cell. Movement and stability of cellCytoskeleton- is a network of protein fibres which keeps the cells shape stable. Some of these fibres are made of actin which can contract and bring about movement in white blood cells, and can move organelles within the cell. Some fibres are known as microtubules and are made of the protein tubulin. These can move microbes through liquid. Proteins (microtubule motors using ATP) present on microtubules can move organelles in the cell e.g. chromosomes in cell divisionFlagella (unipodia) and cilia- are hair-like extensions from the cells and contain 11 microtubules in a 9+2 arrangement (9 in a circle and 2 in the middle)

Ciliated epithelial cells have many cilia to sweep substances e.g. in the lungs. Unipodia are like cilia but are longer and cause movement e.g. as the tail of a sperm and occur in ones or twos.Organelles in the cell

Nucleus- contains the genetic material. The chromatin is surrounded by the nuclear envelope which contains nuclear pores. Inside the nucleus is a spherical structure called the nucleolus (where ribosome synthesis occurs)Endoplasmic reticulum- smooth endoplasmic reticulum is involved in making lipids and rough endoplasmic reticulum is studded with ribosomes and is where proteins are madeGolgi apparatus- is where proteins made in the ribosomes are carried in vesicles to be modified Mitochondria- are spherical or sausage-shaped (depending on which plane they are cut in). They have an outer and inner membrane and the inner membrane is folded into cristae. The central part is called the matrix. ATP is made in the mitochondria Chloroplasts- found in plants and has two membranes with the inner one folded into flattened sacs called thylakoids. Many thylakoids are stacked in granum. In chloroplasts, light energy is used to synthesise carbohydrate form carbon dioxide and water

Lysosomes- are spherical sacs which contain digestive enzymes to breakdown materials. Organelles without membranes surrounding them-Ribosomes- are bound to endoplasmic reticulum and are the site of protein synthesisCentrioles- are small tubes of protein fibres (microtubules) and take part in cell division as they form fibres making up the spindleOrganelles and their involvement in making protein

Prokaryotes and eukaryotesEukaryotes- have a true nucleusProkaryotes- do not have a true nucleus e.g. bacteriaProkaryotes- have only one membrane (no nuclear membrane). Do not have a membrane around organelles. They have cell walls (made of murein NOT cellulose) DNA is in a circular loop and lies in an area called the nucleoid. ATP production in infolds of the surface region called mesosomes. Some prokaryotes have flagella (unipodia) for movement. Some prokaryotes have resistance coded into the plasmid DNA for antibiotics (e.g. MRSA methicillin-resistant staphylococcus aureus). They can pass this resistance on to their daughter cells. Prokaroytes can be useful e.g. in cheese and yoghurt making. In mammalian gut they make vitamin K and help digest some food.

Plasma membranesRoles- separate cells contents from outside, cell components from the cytoplasm, used for cell recognition and signalling, regulate movement of materials in and out of cellsPlasma membrane and phospholipids-Phospholipids have a phosphate group head (hydrophilic) and two fatty acid tails (hydrophobic) If phospholipids are surrounded by water, they form a bilayer Specialised plasma membranes- plasma membranes of growing shoots contain receptors to detect growth regulating substances. Muscle cell membranes have a large number of channels to take up glucose to provide energy for contraction. White blood cell plasma membranes contain special proteins to recognise antigens.Permeability- permeable to water and some solutes and so is called partially permeable.

Fluid mosaic model

Model proposed by Singer and Nicholson in 1972Model consists of :- Phospholipid bilayer Protein molecules floating in the bilayer Extrinsic proteins (partially embedded in the bilayer) and intrinsic proteins (span the bilayer)Glycolipid and glycoproteins- have carbohydrate attached to them are attached to the bilayer (involved in cell signalling and some are hormone receptors)Cholesterol- gives stability to the bilayerChannel proteins- molecules that are too large (e.g. sugar) or too hydrophilic can pass through these channels to get across the bilayerCarrier proteins- actively move substances across the membrane using ATPReceptor sites- are on the membrane for substances such as hormones or drugs to bind and affect cell metabolism e.g. glycoproteins and glycolipidsMetabolic processes- In the membrane in chloroplasts photosynthesis occurs, and in the membrane of mitochondria, respiration takes place

Effect of temperature on membranes- when temperature increases, molecules gain kinetic energy and the plasma membrane becomes more leaky. Organisms that live in extremes temperatures have different cholesterol content to stabilise the membrane.Communication and cell signallingSingle-celled organisms need to respond to signals around them e.g. presence of nutrients and the cells of multicellular organisms need to respond to internal and external signals. Cells need receptors (often made of protein or modified protein) to detect these signals and bring about a response.Hormone receptors- any cell with a receptor for a hormone molecule is called target cell. The receptor is a complementary shape to the hormone molecule. When the hormone binds to the receptor in the target cell responds in a particular way.Example insulin hormone- insulin is released by beta-cells of the Islet of Langerhans in the pancreas. It attaches to protein receptors on cells such as muscle and live cells. When the hormone attaches to the receptor, more glucose channels open allowing more glucose to enter cells.Drugs interfering with receptors- Beta-blocking drugs block receptors on heart muscle cell plasma membranes preventing increase in heart rate. Movement of substances across the plasma membrane Passive movement simple diffusion and facilitated diffusion Active processes- active transport, endocytosis and exocytosisPassive movementSubstances need to get into cells for metabolic reactions and waste needs to be removedSimple diffusion- there is a net random movement of molecules across the plasma membrane as the molecules have kinetic energy and they move down a concentration gradient. No energy is required- passive. In living organisms there are features that ensure that equilibrium is never reached e.g. in plants cells use carbon dioxide for photosynthesis and so carbon dioxide levels are lower in the cell than outside. Factors affecting the rate of diffusion:- Temperature, concentration gradient, stirring/movement, surface area, distance/thickness, size of moleculeLipid-based molecules (including hormones) can easily diffuse across the phospholipid bilayer along their concentration gradient.Very small molecules and ions are small enough to pass through the bilayer even if they are polar e.g. waterFacilitated diffusion- molecules which are small and charged or large molecules cannot diffuse through the bilayer. These can travel through proteins which span in bilayer and do move by facilitated diffusion.2 protein types Channel proteins- form pores through the membrane and only allow one type of ion through e.g. sodium and calcium. Many are gated so can be opened and closed Carrier proteins- shaped to the specific molecule which travels through them. When the molecules fits into the carrier protein, the protein carrier changes shape which allows the molecule to be released on the other side of the membrane e.g. glucose and amino acids Active transportSometimes substances need to be transported across the plasma membrane against their concentration gradient and this requires energy.Carrier proteins and active transport- some carrier proteins act as pumps and take molecules (large or charged ions) across the membrane against their concentration gradient. Like the ones used in facilitated transport, the carrier proteins are a complementary shape to the molecule but the molecule is moved in only one direction across the membrane, it is faster and ATP is required. ATP changes the shape of the carrier protein and so now the molecule no longer fits and leaves the carrier on the other side of the membrane e.g. calcium involved in muscle fibre contraction.Bulk transport (moving large amounts)- this require ATP and large quantities of material are moved into a cell (endocytosis) or out of a cell (exocytosis).

Naming bulk transport- Endo- inwards exo= outwardsPhago= solid material pino= liquid materialSo exopinocytosis= movement of liquid material out of a cellOsmosisIs a special type of diffusionIt is the movement of free water through a partially permeable plasma membrane, along its concentration gradient

If a solute dissolves in water (solvent) to form a solution, there is less free water available.Water potential is the tendency of free water to move from one place to another. When water is pure it has a water potential of zero. When solutes are dissolved in it, the water potential is lowered (goes below zero) as there is less free water to move. This means that strong solution that have a lot of solute dissolved in it have a very negative water potential.

Osmosis in plant and animal cells MitosisMitosis is cell division that results in two daughter cells that are genetically identical to the parent cell, but is only a small part of the overall cell cycle for the cell

(above are the stages of the cell cycle)

Copying of DNA for cell division to produced identical cells- In eukaryotes, the DNA in the chromosomes is wrapped in proteins called histones (DNA + histone proteins= Chromatin). When new cells are going to be produced, chromosomes are copied, and the two copies of each chromosome are held together at the centre by a centromere. Copies of chromosomes are proof-read by enzymes to ensure that the genes are copied precisely otherwise mutations can occur.Why are new cells needed- Growth- multicellular organism need to produce genetically identical new cells to grow Repair- damaged cells need to be replaced with new ones Replacement- RBCs and skin cells need to be replaced with new ones when they die Asexual reproduction- single-celled organisms divide and produce two separate organisms (Paramecium). Some multicellular ones (Hydra) produce offspring from parts of the parents. The offspring are called clonesStages of mitosis- Are 4 stages to mitosis1. Prophase2. Metaphase 3. Anaphase4. TelophaseProphase- chromosomes supercoil and become visible, the nuclear envelope breaks down, centrioles divide and move to opposite poles of the cell.Metaphase- chromosomes move to the middle of the cell and protein threads attach from the centrioles to the centromeres of the chromosomesAnaphase- spindle fibres shorten and pull the sister chromatids apart (now called chromosomes again) towards the poles of cells.Telophase- spindle breaks down and nuclear envelope forms around each set of chromosomesCytokinesis- this is where the cell splits into two identical daughter cells. In animal cells, cytokinesis starts with the cell pinching in from the outside but in plant cell a cells plate forms along the middle of the cell. Bacteria do not divide by mitosis by rather by binary fission, as mitosis is cell division involving chromosomes and bacteria do not have these, but have naked DNA not associated with histone proteins, and they are free in the cytoplasm as there are no nuclear envelopesPlant clones- Produced when a plant is grown from a cutting, and plants such as strawberry plants that grow clone plants at the end of runnersAnimal clones- Dolly the sheep was a clone. A nucleus from a sheeps udder cell (full set of chromosomes) was placed in the egg cell of another sheep where the nucleus had been removed. The egg cell containing a full set of chromosomes was placed in the uterus of another sheep. When the lamb is born it is a clone of the sheep from which the full set of chromosomes was originally obtained.Stem cell- called omnipotent or totipotent as can differentiate to become any sort of specialised cell. Stem cells can be obtained in small numbers from bone marrow. More can be obtained from left-over embryos from IVFGrowth in animals and plants- most animal cells can undergo mitosis and cytokinesis but in plants only cells in the meristem (shoot tips and roots) can.

Producing genetically different cellsHappens during sexual reproduction Gametes (egg and sperm) are produced by meiosis cell division and result in half the number of chromosomes. Homologous chromosomes have the same genes e.g. eye colour but the alleles (versions of the same gene) may be different e.g. blue colour allele, brown colour allele. When meiosis cell division occurs some eggs/sperm will have the gene for blue eyes and other for brown eyes.Meiosis is different from mitosis as cells produced have half the number of chromosomes and are genetically different from each other Cell specialisationDifferentiation- this is where cells become different from others to carry out a particular role. They become specialised for that role.Cells can become differentiated in a number of ways such as changes to the number of a particular organelle, shape of the cell, or some of the contents of the cell.Examples of differentiated cells- Blood cells produced in the bone marrow are undifferentiated (stem). If they lose their nucleus, mitochondria, Golgi, and RER, they become red blood cells (packed with haemoglobin to carry oxygen from the lungs to the tissues). If the cells remain the same but have loads of lysosomes they become white blood cells which ingest and kill microbes. Tissues- made up of similar cells that carry out a common functionOrgans- made up of different tissues working together to perform a particular functionOrgan systems- made up of different organs which work together to perform an overall life function.Plant tissues Xylem tissue- made up of xylem vessels with parenchyma cells and fibres. Meristems produce small cells that elongate. They then reinforce their walls with lignin and this also makes the cells waterproof (because Xylem transports water). The waterproofing kills the cell. The ends of the cells disintegrate to form tubes running the whole length of the plant. They transport water up the plant and help support the plant. Phloem tissue- Meristem makes small cells that elongate and line up end to end. The ends do not completely break down this time but have many holes so they are called sieve plates. They are alive this time and they each have a companion cell that does a lot of the metabolic work for the phloem (bit like a life support system for the phloem cell as it has been changed so much)Animal tissues4 main groups of animal tissues1. Epithelial cells layers and linings i.e. lining of the intestines2. Connective Tissues Holds structures together and provides support e.g. cartilage and bone3. Muscle tissues- specialised to contract to cause movement4. Nervous tissues- Cells that can convert stimulus into electrical signals and conduct those impulsesSquamous epithelial cells- These are flattened thin cells that form thin, smooth flat surfaces. This makes them perfect for lining tubes like blood vessels. Smooth to allow quick flow and thin to allow diffusion through them. They secrete basement membrane (bit like glue) made from collagen and glycoproteins to attach themselves to connective tissuesCiliated epithelial cells- These are column shaped cells with cilia on the top. Found on the inner surface of tubes: e.g. lungs, uterus and oviducts. Some produce mucus. So for example in the lungs they secrete mucus to trap particles that are inhaled, the cilia then beat in rhythmic waves to move the mucus and trapped dirt back up the throat to where they are swallowed Plants tissues working together for photosynthesis

Upper epidermis- transparent top layer to let light through Palisade layer- long thin neatly packed cells full of Chloroplasts (containing Chlorophyll) Spongy Mesophyll Layer- loosely packed to allow the movement of gases Lower epidermis layer- containing pores called stomata (they can open and close) these let gases into and out of the leaf Xylem and Phloem tubes - bring in water and take away the glucose made by photosynthesis

Opening and closing of stomata Gas exchange occurs through the stomata Guard cells contain chloroplasts unlike the rest of the lower epidermis

When glucose is made by photosynthesis in the guard cells, water potential decrease and so water moved in. This causes the guard cells to bulge and open the stomata to allow more gases in and out of the leaf.