Section 2: structures and functions in living organismsa) Levels of organisation2.1 describe levels of organisation within organisms: organelles, cells, tissues, organs and systems

Organelles are tiny structures within cells. You can only see them using a powerful microscope Some typical organelles found in an animal cell: nucleus, cell membrane, cytoplasm Some typical organelles found in a plant cell: nucleus, cell membrane, cytoplasm, cell wall, vacuole, chloroplasts Cells are specialised: to carry out a specific function therefore structures can vary: For example in humans, red blood cells are specialised for carrying oxygen, and white blood cells are specialised for defending the body against disease.

Similar cells are organised into tissues: a tissue is a group of similar cells that work together to carry out a particular function. For example the xylem tissue (for transporting water and mineral salts) and phloem tissue (for transporting sucrose and amino acids) A tissue can contain more than one cell type Tissues can be organised into organs An organ is a group of different tissues that work together to perform a function Lungs in mammals and leaves on plants are two examples of organs, they are both made up of several tissue types Organs make up organ systems Each organ system does a different job, for example in mammals the digestive system is made up of different organs including the stomach, the intestines, the pancreas and the liver.

b) Cell structure2.3 describe cell structures

Nucleus: the organelle that contains the genetic material that controls the cells activities. It is surrounded by its own membrane Cell membrane: thos membrane forms the outer surface of the cell, and controls the substances that go in and out Cytoplasm: a gel like substance where most of the cells chemical reactions take place. It contains enzymes which control these chemical reactions Mitochondria: these generate energy, which aids respiration Chloroplasts: photosynthesis, making food for the plant. These contain a green substance called chlorophyll which is used in photosynthesis Cell wall: a rigid structure made of cellulose, which surrounds the cell membrane. It strengthens and supports the cell Vacuole: a large organelle that contains cell sap (a weak solution of sugars and salts) it helps to support the cell.

2.4 compare:BothPlantAnimal

NucleusChloroplasts

Cell MembraneCell Wall

CytoplasmVacuole

Mitochondria

Practical: Look at onion cells under a microscope using iodineTissue from an onion is a good first exercise in using the microscope and viewing plant cells. The cells are easily visible under a microscope and the preparation of a thin section is straightforward. An onion is made of layers, each separated by a thin skin or membrane. In this exercise you will make awet mounton a microscope slide and look at the cells of the onion membrane magnified by thehigh power, compound microscope.Method: 1. First add a few drops of water or solution on the microscope slide to avoid dryness and wilting2. Take a small piece of onion and using forceps (tweezers), peel off the membrane from the underside (the rough side).3. Lay the membrane flat on the surface of the slide4. Using a pin, lower a thin glasscover slipor cover glass onto the slide. Make sure there are no air bubbles 5. Make sure the lowest power objective lens (the shortest lens if there are several present) is in line with the optical tube, and the microscope light is turned on. Then place the prepared slide onto the stage of the microscope.6. Looking from the side (NOT through the eyepiece), lower the tube using the coarse focus knob until the end of the objective lens is just above the cover glass. Do this carefully so as not to crack the cover glass (and possibly damage the objective lens).7. Now look through the eyepiece and turn ONLY the smaller, fine focusing knob to move the optical tube upwards until an image comes into focus. The cells should look something like lizard skin.8. Swap the objective lens for a higher powered one so that you can see the cells at greater magnification. You should be able to make out a nucleus in each cell.9. Repeat the process after adding a dye solution (iodine). Be very careful; this dye can stain your skin and clothes.

Section 1: the nature and variety of living organismsa) 1.1 Characteristics of living organisms: All living organisms are composed of units called cells Simple things are made from single cells, but more complex plants and animals are composed of millions of cells multicellular There are 8 life processes which are common to most living things: Movement by the action of muscles in animals, and slow growth in plants. Move towards things like food and water. Move away from things like predators and poisons. Respiration - releases and gains energy from food (aerobic and anaerobic) Stimulus (response to) are sensitive to changes in surroundings Growth - increase in size and mass using materials from their food Reproduce produce offspring in order for their species to survive Excrete toxic waste products are removed (i.e. urea and carbon dioxide) Nutrition either to make their own food (plants) or eat other organisms (animals), which provides energy for things such as growth and repair. Nutrients can include proteins, fats, carbohydrates, vitamins, and minerals.

b) Variety of living organisms

Plants Plants are multicellular They have chloroplasts which means they can photosynthesize Their cells have walls which are made of cellulose Plants store carbohydrates such as sucrose or starch Examples include flowering plants like cereals (e.g. maize) or herbaceous legumes (e.g. peas and beans)

Mitochondria

Animals Animals are multicellular They dont have chloroplasts therefore cant photosynthesize Their cells dont have cell walls Most have a nervous coordination meaning they can rapidly respond to changes in their environment They can usually move around from one place to another They often store carbohydrates in the form of GLUCOGEN Examples include mammals (e.g. humans) and insects (e.g. houseflies and mosquitoes) Mitochondria

Fungi

Some are single celled Others have a body called a mycelium which is made up of hyphae (thread like structures) these contain a lot of nuclei They cant photosynthesise Their cells have cell walls made of chitin Most feed by saprotrophic nutrition they secrete extracellular enzymes into the area outside their body to dissolve their food so they can absorb the nutrients They can store carbohydrate as glycogen Most common examples are yeast (single celled fungus) and mucor (multicellular has a mycelium and hyphae)

Bacteria These are single celled and microscopic They dont have a nucleus They have a circular chromosome of DNA Some can photosynthesise Most bacteria feed off other organisms living or dead Examples include lactobacillus bulgaricus (used to make milk go sour and turn into yoghurt rod shaped) and pneumococcus (spherical)

Protoctists These are single celled and microscopic Some have chloroplasts and are similar to plant cells (e.g. chlorella) Others are more like animal cells (e.g. amoeba) A pathogenic example is plasmodium causes malaria

Viruses These are small particles, much smaller than bacteria They can only reproduce inside living cells. These are known as pathogens they depend on other organisms to live They infect all types of living organisms They come in lots of different shapes and sizes They dont have a cellular structure they have a protein coat (capsid) around some genetic material (either DNA or RNA) Examples include influenza virus, HIV, tobacco mosaic virus (makes the leaves of tobacco plants discoloured by stopping them from producing chloroplasts)

Pathogens Pathogens are organisms that cause disease. They include some fungi, protoctists, bacteria and viruses: Protoctist: plasmodium, which causes malaria Bacterium: pneumococcus, which causes pneumonia Viruses: influenza virus, which causes flu and HIV which causes AIDS

Section 2: structures and functions in living organismsc) Biological molecules 2.5 ID the chemical elements present in carbs, proteins and lipids (fats and oils)

Carbohydrates Carbohydrates are made up of simple sugars Carb molecules contain the elements carbon, hydrogen and oxygen Starch and glycogen are large, complex crbohydrates, which are made up of many smaller units (e.g. glucose or maltose molecules) joined together in a long chainStarch

Maltose (and other simple sugars e.g. glucose)

Proteins Proteins are made up of long chains of amino acids They all contain carbon, nitrogen, hydrogen and oxygen atoms

Amino AcidsProteins

Lipids Lipids (fatty oils) are built up of fatty acids and glycerol Lipids contain carbon, hydrogen and oxygen atomsLipid Glycerol and fatty acids

Testing for: Testing for glucose: if glucose is present, Benedicts Solution will spot it. Add Benedicts solution to a sample and heat it. (Use an excess of Benedicts to make sure all the glucose reacts). Make sure it doesnt boil. If glucose is present (a positive test) it will form a coloured precipitate (solid particles suspended in the solution). The colour of the precipitate changes from blue green yellow orange brick red. The higher the concentration of glucose, the further the colour change goes. You can use this to compare the amount of glucose in solutions. Testing for starch: if starch is present, dilute iodine will spot it. If starch is present, the sample changes from browny-orange, to a dark, blue-black colour. If no starch is present, it stays browny-orange. Testing for fat: simple* rub the food onto a piece of thin paper. If the paper goes translucent when held up to light, fat is present. Testing for fat: complicated* pour about 1 of absolute ethanol into a test tube. Add a small amount of the food, and then shake the test tube. Add about 1 of water to the tube. If a cloudy white precipitate develops, fat is present. Testing for protein: if food isnt in liquid form, mash up with mortar and pestle. Add a little water. Pour around 2 of the food into the tube. Add a little sodium or potassium hydroxide until the solution clears. Add a few drops of dilute copper sulphate and shake. If the solution goes purple, protein is present.

Enzymes Enzymes are biological catalysts: made by all living things to speed up the rate of chemical reactions (without being used up themselves) All chemical reactions in the body are called metabolism These reactions need to be carefully controlled to get the right amount of substances in the cells Enzymes are all proteins, and all proteins are made up of chains of amino acids. These are folded up into very unique shapes which enzymes need to do their jobs Enzymes are very specific Chemical reactions usually involve things being split apart or joined together A substrate is a molecule that is changed in a reaction Every enzyme has an active site the part where the substrate joins on to the enzyme. Enzymes are very picky, they usually only speed up one reaction. This is because for an enzyme to work, a substrate has to be the correct shape to fit into the active site complimentary This is called the lock and key model.

Changing the temperature changes the rate of an enzyme-catalysed reaction The higher temperature increases the rate of reaction. This is because more heat = enzymes and substrate particles have more energy = enzymes and substrate move about more quickly = more likely to meet and react = higher collision rate Low temperature decreases rate of reaction = lower collision rate If the temperature is too hot, some of the bonds holding the enzyme will lose its shape = its active site will not fit the substrate anymore = cant catalyse = rxn stops. This is when it becomes denatured. This change is irreversible Each enzyme has its own optimum temperature when it goes the fastest. This is the temp just before it gets too hot and the enzyme denatures. The optimum temp for most of the human enzymes is 37 - our body temp

Optimum temp/ph

Changing the PH also affects enzymes. If the PH is too high or to low, the PH interferes with the bonds holding the enzymes together. This changes the shape of the active site and denatures it All enzymes have an optimum PH they work best at. Its often neutral, PH7, but not always. E.g. pepsin is an enzyme that is used to break down proteins in the stomach. It works best at PH2, as it is well suited to the acidic conditions of the stomach.

Practicals 1. You need to be able to recall an experiment you have done that explores the effect of temperature on enzymes. An example is the enzyme Catalase, which breaks Hydrogen peroxide into Water and Oxygen;

Catalase is found in potatoes. Therefore, putting potato chips into peroxide will produce O2. The rate of reaction is, therefore, proportional to the volume of O2 given off. Changing the temperature will alter the volume (i.e. initially increase it, reach an optimum, then decrease quickly as the Catalase becomes denatured)

d) Movement of substances into and out of cells

Diffusion Diffusion is net movement of particles from an area of high concentration to an area of lower concentration. Diffusion happens in both liquids and gases (because particles are free to move in both) Cell membranes are clever because they hold the cell together but they let stuff in and out as well. Only very small molecules can diffuse through cell membranes, things like glucose, amino acids, water and oxygen. Big molecules such as starch and proteins cant fit through the membrane. Partially permeable membrane

Glucose Amino acidStarchProteinNet movement

Just like with diffusion in air, particles flow through the cell membrane from where theres a higher concentration to a lower concentration Theyre only moving about randomly, so they go both ways. But if there are a lot more particles on one side of the membrane, there will be a new (overall) movement from one side to the other.

Diffusion Experiment (non-living system) Phenolphthalein is a PH indicator pink in alkaline solutions and colourless in acidic solutions.1. Make up some agar jelly with phenolphthalein and dilute sodium hydroxide. The jelly will be pink.2. Fill a beaker with some dilute hydrochloric acid. Using a scalpel cute a few cubes from the jelly and put them into the acid3. Observe after a while the cubes will turn colourless the acid will diffuse into the agar jelly and neutralise the sodium hydroxide solution. You can investigate the rate of diffusion by using different sized cubes of agar jelly and time how long it takes for each cube to go colourless. The cube with the largest surface area to volume ratio will lose its colour the quickest.Dilute HCLDilute NaCl

Osmosis Osmosis is the net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower concentration. A partially permeable membrane is just one with very small holes in it, so that only tiny molecules can fit through (like water) and big ones cant (e.g. sucrose) The water molecules can pass both ways through the membrane during osmosis; this is because water molecules move about randomly. But because there are more molecules on one side than the other, there is a steady net flow of water into the region with fewer molecules (e.g. the sucrose solution) This means the sucrose solution becomes more dilute, because the water acts like it is trying to even up the concentration either side of the membrane.watersucrose solutionNet movement of water molecules partially permeable membrane

Water moves into and out of cells by osmosis Tissue fluid surrounds the cells in the body basically water + oxygen + things dissolved in it. This is squeezed out of the blood capillaries to supply the cells with everything they need. The tissue fluid will usually have a different concentration to the fluid inside the cell. This means that fluid will either move into the cell from the tissue fluid, or out of the cell by osmosis If a cell is short of water, the solution inside will be concentrated. Thus, the solution outside will be more dilute and so water will move into the cell by osmosis If a cell has lots of water, the solution inside the will be more dilute. Thus, the solution outside will be more concentrated and so water will be drawn out of the cell and into the fluid outside, by osmosis. PLANTS ARE SUPPORTED BY TURGID CELLS. When a plant is well watered, all its cells will draw water in by osmosis and become plump and swollen. When the cells are like this, they are said to be turgid. The contents of the cell push against the cell wall. This is called turgor pressure. Turgor pressure helps to support plant tissues.

When there is no water in the soil, the plant starts to droop (wilt). This is because the plants lose their water and so lose their turgor pressure. The cells are said to be flaccid. The plant doesnt totally lose its shape though, as the cell walls are inelastic, which keeps it in position.

Osmosis Experiment (Living System)Potato cylinders.1. Cut up potato into identical cylinders (bore a wedge)2. Obtain beakers with different sugar solutions (one should be water, another should be very concentrated sugar solution, then have some with in-between concentrations)3. Measure the length of the potato cylinders, and leave a few in each of the different concentration solutions for around an hour. 4. Then take them out, and measure the length again. 5. If the cylinders have drawn in water via osmosis, theyll be slightly longer. If they have had water drawn out, theyll have shrunk.6. The only thing you should change here is the concentration of the sugar solution. Everything else (i.e. volume of solution, and amount of time the experiment lasts for) must be kept the same for the experiment to be a fair test. Pure WaterConcentrated Sugar Solution

Osmosis Experiment (Non-Living System)Visking Tubing1. tie a piece of wire around one end of visking tubing, and put a glass tube in the other end, fixing the tubing around it with wire.2. Pour some sugar solution down the glass tube, into the visking tubing3. Put the visking tubing in a beaker of pure water measure where the sugar solution comes up to on the glass tube4. Leave the tubing overnight, and measure where the liquid is in the glass tube. Water should be drawn into the visking tubing by osmosis, and the will force the liquid up the glass tube5. NB: visking tubing is a partially permeable membrane.

Visking tubing containing sugar solution Pure waterGlass tube

Active Transport The movement of particles against a concentration gradient. (i.e. from an area of lower concentration to an area of higher concentration) Using energy released from respiration Used to move substances in and out of cells E.g. used in digestive system: low conc. of nutrients in the gut but a high conc. of nutrients in the blood allows nutrients to be taken into the blood, despite the fat that the concentration gradient is the wrong way. This is essential to stop us from starving Plants also use active transport its how they get minerals from the soil (lower conc.) into their root hair cells (higher mineral conc.)

Three main factors affecting the movement of substances:

1. Surface area to volume ratio The rate of diffusion/osmosis/active transport is higher in cells with a larger surface area to volume ratio. Think of cells as cubes here:3x3x3

Here, the smaller cube has the largest surface area to volume ratio. Therefore substances would move in and out of this cube faster than the larger one. 2x2x2

Surface area2x2x6 = 243x3x6 =54

Volume2x2x2 = 83x3x3 = 27

Ratio24:8 = 3:154:27 = 2:1

2. Temperature As the particles in a substance get warmer, they have more energy so they move faster. This means as temperature increases, substances move in and out of cells faster.3. Concentration gradient Substances move in and out of a cell faster if theres a bigger difference in concentration between the inside of the cell and the outside. If there are lots more particles on one side, there are more to move across. This only increases the rate of diffusion and osmosis though; concentration gradients do not affect the rate of active transport.

e) Nutrition

Flowering Plants Photosynthesis: the process that produces food in plants. This food is glucose, Photosynthesis happens in the leaves of all green plants this is largely what the leaves are for. Photosynthesis happens inside the chloroplasts, which are found in leaf cells and in other green parts of a plant. Chloroplasts contain a pigment called chlorophyll which absorbs sunlight and uses its energy to convert carbon dioxide and water into glucose and oxygen Photosynthesis is important because it converts light energy into chemical energy, which is stored in the glucose. The chemical energy is released when glucose is broken down during respiration. Photosynthesis is affected by the amount of light, the amount of , and the temperature of its surroundings. Photosynthesis slows down or stops if these conditions arent right. The limiting factor: something that stops photosynthesis from happening any faster. Light intensity, , concentration and temperature can all the limiting factor The limiting factor depends on the environmental conditions e.g. in winter low temperaures might be the limiting factor. At night, the light is likely to be the limiting factor. There are 3 important graphs for rate of photosynthesis:

1. Not enough light slows down the rate of photosynthesisLight intensity Rate of photosynthesisPlenty of and warmth or temp needs to be increased

Chlorophyll uses light energy to perform photosynthesis. It can only do so as quickly as the light energy is arriving. If the light intensity is increased, the rate of photosynthesis will increase steadily, but only up to a point. Beyond that, it wont make a difference because it will either be the temperature or the level that will be the limiting factor.2. Not enough CO