\input{../include.tex} \input{../units.tex} \begin{document} \title{IGCSE Biology Notes} \date{2006---2009} \author{} \maketitle \tableofcontents %\listoftables \listoffigures \clearpage \section{The Variety of Life} \subsection{Taxonomy} This is the scientific name for putting things into groups -- classification and naming. This largest group is called a `kingdom'. The system was devised in the 18\thth\ Century by Carl Linnaeus. \\ \bigskip --- Kingdom\\ \phantom{a}\hskip 2cm --- Phylum \hskip 6cm \begin{tikzpicture} \path[use as bounding box] (0,0) rectangle (2,0) ; \draw[->,rotate=-15] (0,0) -- (1,0) node[above,rotate=-15] {increasing\ similarity} -- (2,0); \end{tikzpicture} \\ \phantom{a}\hskip 4cm --- Class\\ \phantom{a}\hskip 6cm --- Order\\ \phantom{a}\hskip 8cm --- Family\\ \phantom{a}\hskip 10cm --- Genus\\ \phantom{a}\hskip 12cm --- Species\\ \subsection{The Binomial Naming System} All organisms have two Latin (a universal language) names -- Genus and Species. The Genus is written with a capital letter. When handwriting, both words are underlined. When typing, they are put in italics. For example: {\fontspec{Zapfino Extra LT Pro}\underline{Homo Sapiens}} (Handwritten)\\ \textit{Felix cattus} (Typed) \subsection{Kingdoms} \begin{itemize} \item Animalia \item Plantae \item Bacteria (monera, prokaryote) \item Fungi \item Protoctista \end{itemize} \subsubsection{Animal Kingdom} There are 34 Phyla. Among them are: \begin{itemize} \item Chordates (vertebrates) {\small(in order of evolution:)} \begin{itemize} \item Fish \item Amphibians \item Reptiles \item Birds \item Mammals \end{itemize} \item Arthropods \begin{itemize} \item Insects \begin{itemize} \item Grasshoppers, butterflies, beetles, ants etc. \item 1000,000 described world species \item Three body regions: head, thorax, abdomen \item Six legs attached to the thorax (which has 3 segments) \item Adults with one or two pairs of wings attached to the thorax (some have none) \item Tow antennae \item Lateral compound eyes \end{itemize} \item Arachnids \begin{itemize} \item Spiders, scorpions, ticks, moites, etc. \item 65,000 described world species \item Two body regions: cephalothorax, abdomen \item Eight legs \item No antennae \item Mouth parts are chelicerae (modified appendages) which in spiders are fangs \end{itemize} \item Crustaceans \begin{itemize} \item Technically a subphylum \item Classes include crabs, shrimps, lobsters, barnacles, isopods etc. \item 44,000 described world speies \item Two body regions \item Two pairs of antennae \item 5 or more pairs of legs \item Primarily aquatic, few terrestrial \end{itemize} \item Myriapods \begin{itemize} \item Chilopods \begin{itemize} \item Centipedes \item 2,800 described world species \item well-defined head \item first pair of legs modified for envenomation \item flattened top to bottom \item one pair of legs persegment \item one pair of antennae \end{itemize} \item Diplopods \begin{itemize} \item Millipedes \item 10,000 described world species \item Two pairs of legs per segments, first four segments have 1 pair of legs \item one pair of antennae \item well-defined head \item usually cylindrical \end{itemize} \end{itemize} \end{itemize} \item Nematodes \begin{itemize} \item Roundworms \item Can be microscopic, or up to 10m in length \item Can be free living or parasitic \item No circulatory or respiratory system \item Structure is a ``tube within a tube'' \item No chaetae \item Use sexual reporoduction \end{itemize} \item Molluscs \begin{itemize} \item Soft bodied \item No segmentation \item Single muscular foot \item Hard external shell (calcium carbonate) or internal shell \item Most have rasping tongue (radula) \item Filter feeders -- mussels \item Carnivorous -- octopi \item Marine organisms with shells (except barnacles and crustaceans) \item Terrestrial -- snails \& slugs \end{itemize} \item Annelids \begin{itemize} \item Segmented worms (e.g. earthworm) \item Leeches \item Sexual and asexual reporoduction (depending on species) \item Vascular and nervous system \item No legs but may have chaetae (stiff hairs) to aid movement \item may have obvious head \end{itemize} \end{itemize} \subsubsection{Protoctista} \begin{itemize} \item Single-celled -- Eukaryotes -- Protista\footnote{They have a proper nucleus as opposed to Bacteria. Eukaryots are aquatic/plant-like organisms that don't fit in the Animal/Plant/Bacteria kingdoms.} \begin{itemize} \item Protozoa \& Protophyta \end{itemize} \item Multicelled \begin{itemize} \item Seaweed \begin{itemize} \item Kelp \item Algae \end{itemize} \item Slime molds \item Amoeba \item Ciliates \item Diatoms \item Paramecia \item Forams \item etc. \end{itemize} \end{itemize} \subsection{Characteristics of Living Things} \begin{description} \item[M]ovement \item[R]espiration \item[S]ensitivity \item[G]rowth \item[R]eproduction \item[E]xcretion \item[N]utrition \end{description} \subsection{Branching Keys} A key is a means of identifying an unfamiliar organism from a selection. Individual organisms are found by following a series of paired, numbered options, or a chart which offers no more than two choices at each stage. A key either written in couplets, or as a chart: \subsubsection{Couplets} \begin{enumerate} \item Hairy skin --- \textsc{gooseberry}.\\ Non-hairy skin --- go to 2. \item External pips --- \textsc{strawberry}.\\ No external pips --- go to 3. \item Near spherical shape --- go to 4.\\ Other shape --- \textsc{banana}. \item Smooth surface --- \textsc{apple}.\\ Indented surface --- go to 5. \item Structure made up of sub-units --- \textsc{blackberry}.\\ Structure made up of single unit --- \textsc{orange}. \end{enumerate} \subsubsection{Key} \begin{centering} \hfill \begin{minipage}{0.3\textwidth} Foop: \raisebox{-2ex}{\includegraphics{foop}} \end{minipage} \hfill \begin{minipage}{0.3\textwidth} Woop: \raisebox{-2ex}{\includegraphics{woop}} \end{minipage} \hfill \begin{minipage}{0.3\textwidth} Moop: \raisebox{-2ex}{\includegraphics{moop}} \end{minipage} \hfill \begin{tikzpicture}[level distance=2cm,style={sibling distance=4cm}] \node {Does it have three antennae?} child {node {Does it have three eyes?} child {node {Is it round?} child {node {It's a Moop.} edge from parent node [left] {\textsc{yes}}} child {node {It's a Foop.} edge from parent node [right] {\textsc{no}}} edge from parent node [left] {\textsc{yes}}} child {node {It's a Woop.} edge from parent node [right] {\textsc{no}}} edge from parent node [left] {\textsc{yes}}} child {node {It does not exist.} edge from parent node [right] {\textsc{no}}} ; \end{tikzpicture} \end{centering} \section{Cells, Diffusion \& Osmosis} \begin{figure}[htbp!] \begin{centering} \includegraphics[width=\textwidth]{bacterium} \smallskip {\tiny Source: \texttt{http://en.wikipedia.org/wiki/File:Average\_prokaryote\_cell-\_en.svg}} \end{centering} \caption{A bacterium.} \end{figure} \begin{figure}[htbp!] \begin{centering} \includegraphics[width=\textwidth]{plant_cell_structure} \smallskip {\tiny Source: \texttt{http://en.wikipedia.org/wiki/File:Plant\_cell\_structure\_svg.svg} (Public Domain)} \bigskip \begin{tabular}{cc} \hline \textbf{Organelle} & \textbf{Function} \\ \hline Nucleus & Controls the cell's activities, contains DNA \\ Cytoplasm & Where metabolic reactions take place \\ Cell membrane & Partially permeable, controls the entry/exit of substances \\ Mitochondria & Where aerobic respiration takes place \\ Cell wall (plants only) & Fully permeable, prevents cell from bursting \\ Permanent vacuole & Storage area, contains cell sap \\ Chloroplast (plants only) & Where photosynthesis takes place \\ \hline \end{tabular} \end{centering} \caption{A typical plant cell.} \end{figure} \begin{figure}[htbp!] \begin{centering} \includegraphics[width=\textwidth]{animal_cell_structure} \smallskip {\tiny Source: \texttt{http://en.wikipedia.org/wiki/File:Animal\_cell\_structure\_en.svg} (Public Domain)} \bigskip \begin{tabular}{cc} \hline \textbf{Organelle} & \textbf{Function} \\ \hline Nucleus & Controls cell activities, contains DNA \\ Cytoplasm & Where metabolic reactions take place \\ Cell membrane & Partially permeable, controls entry/exit of substances \\ Mitochondia & Site of aerobic respiration \\ \hline \end{tabular} \end{centering} \caption{A typical animal cell.} \end{figure} \begin{table} \scalebox{0.8}{ \begin{tabular}{cc} \hline \textbf{Plant cells} & \textbf{Animal Cells} \\ \hline Always have cell wall made of cellulose and hence a definite shape & No cell wall, hence no difinite shape \\ Usually have large, permanent vacuole & Any vacuoles are small and temporary \\ Some have chloroplasts & Never have chloroplasts \\ Up to 1mm long & Usually less than 0.05mm long. \\ \textbf{Examples:} & \\ \hline palisade cells & cheek lining cells \\ phloem sieve tube elements & muscle fibres \\ root hair cell & red blood cells \\ \hline \end{tabular}} \caption{Differences between plant and animal cells.} \end{table} \subsection{Specialised Cells} All cells are designed to do a particular job in an organism. This is called \textsc{cell specialisation}. Examples of specialised cells are shown below. \begin{description} \item [Sperm cell] designed to fertilise eggs \\ A sperm cell is very small and has a little tail which provides movement so it can swim and find an egg to fertilise.\\ Its head contains enzymes (in the vacuole) which allow it do digest its way through an egg membrane so the two nuclei can join.\\ It contain half the number of chromosomes in the nucleus -- these caryy genetic information from the father, which will be passed on to the offspring. \item [Ovum (egg) cell] designed to be fertilised \\ An ovum is large and bulky because no active ovement is needed -- it just sits and waits for the sperm to find it.\\ It contains yolk (in the cytoplasm) which provides a large food store needed for the developing young organism once it's fertilised. \\ It contains half the number of chromosomes, which carry genetic information from the mother -- this will be passed on to the offspring. \item [Palisade cell] for photosynthesis \\ A palisade cell is tall with a large surface area. It's found on the top side of a leaf -- ideal for good absorpion of carbon dioxide and light -- both are needed for photosyntheses.\\ They're packed with chloroplasts, which contain the green pigment chlorophyll, which is needed for photosynthesis. \item [Ciliated cell] to stop lung damage \\ Ciliated cells line all the air passages in the lungs. Mucus is sticky and so traps dust and bacteria. The cilia waft and sweep up the mucus to the back of the throat where it is swallowed. The bacteria are then killed by the acid in the stomach. \item [Root hair cell] for absorbtion \\ The long hair cell increases the surface area of the root, which helps absorption of water and minerals. \\ It has a very thin cell wall, which makes it easier for minerals to pass across into the root itself. \item [Red blood cells (erythrocytes)] for transport \\ They do not contain a nucleus, so there is more room for the protein molecule to carry oxygen. Their biconcave shape gives them a large surface area for gas exchange. \item [Muscle cells] for movement\\ Muscle cells have protein strands that can slide across each other for contraction. Each cell has several nuclei. There are 3 types -- smooth, skeletal and cardiac. \end{description} \begin{description} \item [Tissues] A tissue is a group of similar cells, working to perform the same function, e.g.\ muscle tissue is made from muscle cells. \item [Organs] Different tissues are arranged to form an organ. They work together to perform a particular function, e.g.\ the heart. \item [Organ Systems] A group of organs working together form an organ system, e.g.\ the circulatory system. \end{description} \subsection{Cell Activities} All cells exchange gases, nutrients and other materials between themselves and their surroundings. \begin{description} \item [Diffusion] is the free movement of particles of a substance (atoms, ions or molecules) from regions of high concentration to regions of lower concentraion. The process continues until the particles are evenly distributed. This is movement down a concentration gradient. Diffusion is the usual way in which molecules move into or out of cells. \item [Concentration gradient] refers to the difference in concentration between one region and another. The greater the difference in concentraion, the steeper the concentration gradient, and the faster the rate of diffusion. Surfaces qhere gas exchange occurs often maintain a steep diffusion gradient so that idffusion occuras rapidly. For example: \begin{itemize} \item across the linging of the air sacs (alveoli) in the lungs of humans \item across the surface of cells bordering air spaces in the leaves of plants \end{itemize} \item [Osmosis] is a specific type of diffusion. It is the diffusion of water from a dilute solution to a more concentrated soution throuh a partially permeable membrane. Cell membranes are partially permeable membranes, and it is by osmosis that water moves into and out of cells. In osmosis, water diffuses from a high water concentration to a low water concentration (see Figure \ref{fig:osmosis}). \begin{itemize} \item Cells placed in distilled water will gain water by osmosis. This is because there is a lower concentration of water inside than outside. The cells are said to be turgid. \item Cells placed in a concentrated solution will lose water by osmosis. This is because there is a greater concentration of water inside the cell. The cells are said to be flaccid. In severe cases the cell membrane is pulled away from the cell wall. The cells are then said to be plasmolysed. Eventually the process may stop because the concentrations on both sides of the cell membrane have equalised (see Figure \ref{fig:turgor}). \end{itemize} \item [Active transport] is a chemical process that results in a movement of particles in an opposite direction to that expected by diffusion. Substances are taken scross a membrane from a region of low concentration to a region of higher concentration, i.e.\ against a concentration gradient. As its name implies, it is an active process and requires energy supplied by respiration. \end{description} \begin{figure}[htbp!] \hfill\includegraphics[width=0.65\textwidth]{osmosis}\hfill\hfill \caption{The process of osmosis.}\label{fig:osmosis} \end{figure} \begin{figure}[htbp!] \begin{centering} \includegraphics[width=0.75\textwidth]{turgor} \smallskip {\tiny Source: \texttt{http://commons.wikimedia.org/wiki/File:Turgor\_pressure\_on\_plant\_cells\_diagram.svg} (Public Domain)} \end{centering} \caption{A plant cell reacting to different types of turgor pressure.}\label{fig:turgor} \end{figure} \section{Enzymes} Enzymes are \textbf{biological catalysts}. They speed up the chemical reactions which go on inside living things, and are extremely efficient. Enzymes are made inside cells. Once formed, the enzymes may leave the cell and do its job outside. Such enzymes are called \textbf{extracellular enzymes}. They include the digestive enzymes which break down food substances in the gut. Other enzymes work inside the cell. They are called \textbf{intracellular enzymes}. Their job is to speed up he chemical reactions occurring in cells, and also control them. An example of a reaction controlled by an enzyme: \[\mathrm{maltose (substrate)} \xlongrightarrow{\mathrm{maltase (enzyme)}}{} \mathrm{glucose (product)}\] The substance which the enzyme acts on it called the \textbf{substrate} -- in this case maltose. The new substance or substances formed as a result of the reaction are the \textbf{products}. In this case there is just one product, glucose. The enzyme catalysing this particular reaction is maltase. This reaction can go in either direction -- it is \textbf{reversible}. If there is a lot of maltose present compared with glucose, the reaction will go from left to right. If there is a lot of glucose compared to maltose, it will go from right to left. Most metabolic reactions are reversible. \subsection{Properties of Enzymes} \begin{enumerate} \item \textbf{They are always proteins} \\ We need to take proteins in, via our food to produce enzymes. \item \textbf{They are specific in their action} \\ Each enzyme controls one particular reaction, or type of reaction -- maltase will only act on maltose, and sucrase on sucrose. \item \textbf{They can be used multiple times} \\ They are not altered by the reaction that they catalyse. However, they ``run down'' eventually and have to be replaced. \item \textbf{They are destroyed by heating} \\ In common with all proteins, they are \textbf{denatured} by proteins. Normally this happens at 45\degc. \item \textbf{They are sensitive to pH} \\ Their effectiveness depends on the degree of acidity or alkalinity of the solution which they are in. Most intracellular enzymes work best in neutral conditions. \end{enumerate} \subsection{How Enzymes Work} \begin{figure}[htbp!] \begin{centering} \includegraphics[width=0.75\textwidth]{enzyme} \smallskip {\tiny Source: \texttt{http://en.wikipedia.org/wiki/File:Induced\_fit\_diagram.svg} (Public Domain)} \end{centering} \caption{The action of an enzyme.}\label{fig:enzyme} \end{figure} Figure \ref{fig:enzyme} shows in a simplified way how enzymes are believed to work. When a substrate molecule happenes to impact on the active site of an enzyme, the reaction takes place and the products leave, freeing up the enzyme for another reaction. Each enzyme's active site has a specific shape, into which only one type of substrate will fit. This is why the enzyme is specific in its action. When an enzyme is denatured by heat, the shape of its active site changes, so substrates no longer fit in it, and it is not effective. Anything which helps substrates to come into contact with the enzyme at a faster rate will increase the rate at which the enzyme can catalyse reactions. Higher temperatures mean that molecules move around mroe quickly -- a rise in temperature of 10\degc can double the rate of reaction. Some minerals and vitamins also increase the rate of reaction. Some poisons, such as cyanide and arsenic, inhibit enzymes by blocking the active site. Some poisons block active sites permanently, others temporarily. This is also how some pesticides work. \subsection{Uses for Enzymes} Enzymes can be extracted from organisms in a purified form, and then used in many scientific, domestic and industrial processes. A common useage is in \textbf{biological washign powders}. Various protein-digesting (proteases) are added to the washing powder, and they dissolve protein stains. Biological washing powders are advantageous because they work at relatively low temperatures. This means they are usefulfor washing delicate fabrics, and can save electricity. However, some people are allergic to them. Enzymes are normally extracted from microbes, which are grown on a large scale in fermenters. Some examples of enzyme use: \begin{description} \item [Proteases] are used for tenderising meat, skinning fish, removing hair from hides, and breaking down proteins in baby foods. \item [Amylases] convert starch to sugar in making syrups, fruit juices, chocolates and other food products. \item [Cellulase] breaks down cellulose and is used for softening vegetables, removing the seed coat from cereal grain, and extracting agar jelly from seaweed. \item [Isomerase] converts glucose into fructose. Fructose is muchsweeter than glucose; this makes it useful in sweets, syrups and slimming foods, as only small amounts are needed to sweeten the product. \item [Catalase] releases oxygen from hydrogen peroxide, and is used in making foam rubber from latex. \end{description} \subsection{Immobilisng Enzymes} Biotechnologists have developed a better method of using enzymes than simply mixing the enzyme with the substrate. The enzymes are attachedf to an inert surface, usually glass or plastic beads. The beads are then brought into contact with the substrate so that the reactions can take place. One way of bringing the beads into contact with the substrate is to immerse them in a solution of the substrate, and then wait for the reaction to be completed before collecting the product and starting again. This is called \textbf{batch processing}. The other way is to slowly pour a solution of the subtrate through a column of the beads, and the collect the product from the bottom. The substrate is acted upon progressively as the solution trickles down the column. This is called \textbf{continous flow processing}, because the product is collected all the time. it is more efficient than batch processing. \section{Nutrition \& Balanced Diets} Nutrition is the study of food and feeding processes. Food is the material from which organisms obtain the energy and the raw materials to construct, maintain and repair the body. Plants are \textbf{autotrophic} -- they produce their own food, and come at the bottom of the food chain. Humans and other animals are \textbf{heterotrophic} (also known as \textbf{holozoic}) -- they eat other plants and animals, and cannot produce their own food. Humans require a \textbf{balanced diet}. This is one which supplies the different types of food in adequate amounts and the correct proportions, and provides the body with sufficient energy for its needs. A balanced diet maintains a healthy and active life and, where necessary, growth. Humans use food for: \begin{itemize} \item Energy for body processes (usually obtained from carbohydrates and fats -- sometimes from protein when in a state of starvation). \item Building materials, to build the cells of the body (proteins, fats, vitamins, minerals). \item Chemical reactions in the body (proteins, vitamins, minerals, water). \end{itemize} There are seven chemical components of a balanced diet: \begin{description} \item [Carbohydrates] To provide energy. \begin{description} \item [Sugar] Different kinds of food contain different types of sugar: glucose or fructose in fruit, lactose in milk, or sucrose in ordinary table sugar. The formula for glucose, the simplest possible sugar, is \ce{C6H12O6}. It is a monosaccharide -- it is made into chains of polysaccharides. Two glucose molecules bonded together form one maltose molecule. \item [Starch] is found in bread, potatoes and cereals. Starch is a polysaccharide made of a spiral chain of glucose molecules, and is used as the food reserves of plants. \item [Cellulose] is a polysaccharide made of a straight chain of glucose molecules, and is used to build plant cell walls. \item [Glycogen] is a polysaccharide, and is used as the food reserves of animals, stored in the liver and muscles. \end{description} \item [Fats] To provide energy, insulation, and to construct parts of cells. \begin{description} \item [Animal] fats are obtained from livestock, such as cattle or pigs. They are eaten in the form of butter, dripping or lard. They contain saturated fatty acids, which are unhealthy in large amounts. Fat contains twice as much energy per gram as carbohydrates and proteins do, and they are solid at room temperature. \item [Plant] fats, or oils, for example olive oil or corn oil, are liquid at room temperature. They contain polyunsaturated fatty acids, which are more healthy than satureated fatty acids. \end{description} \item [Proteins] To build muscle, make enzymes and hormones, and construct parts of cells. It is normally obtained from the muscles of animals. The disease caused by protein deficiency is called \textbf{kwashiorkor}. Some plants, such as soya beans and maize, contain relatively large amounts of protein compared to other plants, so it is possible to obtain most of the necessary amino acids from plant-based foods. Proteins are made from amino acids. of which there are 20 different types. An organism's DNA provides the template for linking amino acids in different orders to produce proteins (there are a large number of possible combinations). Protein contains Nitrogen and Sulphur. \item [Minerals] are ions of certain elements (i.e.\ inorganic), which are needed for particular purposes within the body. For example: \begin{description} \item [Calcium] is needed for bone formation. Without calcium, bones are soft. Calcium deficiency is called \textbf{rickets}. \item [Iron] is required for haemoglobin, in blood. Oxygen is transported around the body by binding to haemoglobin. Iron is plentiful in liver and kidneys. Iron deficiency results in \textbf{anaemia}. \end{description} \item [Vitamins] Various biological compounds required by the body. Some examples: \begin{description} \item [Vitamin A] is neede by the eyes. Vitamin A deficiency is called \textbf{xerophthalmia} and leads to blindness. \item [Vitamin C] keeps the lining of the mouth and gums healthy. It is found in green vegetables, but is destroyed by heating. Lack of it causes \textbf{scurvy}. \item [Vitamin D] is needed to enable calcium to harden bones. Lack of it causes rickets. \end{description} \item [Water] Makes of 60-80\% of the body. The body's chemical reactions take place in it. Humans need about 1 litre of water every day. \item [Fibre] Stimulates the smooth passage of food through the gut. Mainly made of cellulose, it aids faeces formation. \end{description} Too much energy-rich food will cause the individual to become overweight, while too little will cause them to become underweight. Malnutrition is the result of not having a properly balanced diet. If the body does not receive the correct chemical components in the right proportions, it cannot function efficiently. In humans, as in other animals, complex organic food can enter body cells \textbf{only} if it is first broken down into smalll soluble molecules. In humans, the stages int his process are: \begin{description} \item [Ingestion] Food is taken into the mouth. \item [Digestion] The breakdown of complex organic foods into small, soluble molecules. \item [Absorption] The uptake of soluble food substances into the body across cell membranes. \item [Assimilation] The use of soluble food substances by cells in the body. \item [Egestion] The removal of undigested food from the body (not to be confused with excretion or secretion). \end{description} In humans, the alimentary canal (gut) is responsible for the ingestion, digestion, absorption and egestion of food. \subsection{Food Tests} \subsubsection{Sugar} \begin{enumerate} \item Mash the food and add water. \item Add 2cm$^3$ of the food to a test tube. \item Add 2cm$^3$ of Benedict's solution to the test tube. \item Shake the test tube. \item Place the test tube in a waterbath for approximately 2 minutes. If a precipitate develops, sugar is present. The colour of the mixture gives a rough indication of how much sugar is present: green is the lowest concentration, yellow higher, brown still higher, and red the highest concentration. \end{enumerate} \subsubsection{Starch} \begin{enumerate} \item Add 3 drops of dilute iodine solution to the food sample. \item If the colout changes to blue-black, starch is present. \end{enumerate} \subsubsection{Fat} \begin{enumerate} \item Pour approximately 1cm$^3$ of absolute ethanol into a test tube. \item Add a small amount of the food sample to the ethanol. \item Shake the test tube. \item Add approximately 2cm$^3$ of water to the test tube. \item If the mixture turns cloudy white, fat is present. \end{enumerate} \subsubsection{Protein (Biuret test)} \begin{enumerate} \item Mash the food and add water. \item Add 2cm$^3$ of the food to a test tube. \item Add a small amount of dilute sodium hydroxide solution until the mixure clears. \item Add a few drops of dilute copper sulphate solution. \item Shake the test tube. \item If the solution turns purple, protein is present. \end{enumerate} \subsection{Drugs} A drug is something which changes the way the body works. Useful drugs include painkillers and antibiotics. Harmful drugs can be addictive, and harm the body in some way. Addiction can be chemical -- when the body becomes adjusted in such a way that it needs the drug, or psychological -- when the addicted person feels a constant need for the drug. Withdrawal symptoms from a drug include fever, and nausea. \subsubsection{Alcohol} \begin{itemize} \item Reduces activity of nervous system. \item Removes inhibitions, causes relaxation. \item Impairs judgement \item Is poisonous to the liver. Alcohol poisoning causes a coma and death. \end{itemize} \section{Digestion \& Absorption} \begin{figure}[htbp!] \begin{centering} \includegraphics[width=0.75\textwidth]{digestive_system} \smallskip {\tiny Source: \texttt{http://commons.wikimedia.org/wiki/File:Digestive\_system\_diagram\_en.svg} (Public Domain)} \end{centering} \caption{The alimentary canal (digestive system).}\label{fig:digestion} \end{figure} Food must get into the blood in order to be carried to the bodiy's cells. Only soluble food can do this. Most food is insoluble, and is broken down into soluble particles through the process of digestion, which occurs in the digestive system (see Figure \ref{fig:digestion}). Digestive juices break down the food, starting in the mouth with saliva (from the salivary glands). The food is then swallowed, and other juices from the liver and pancreas are added. Bile is producewd in the liver, and then stored in the gall bladder, before being added to food in the stomach. Muscles keep the walls of the stomach and small intestine moving, mixing up the food and digestive juices, and keeping blood mving through the digestive system. When the food has been completely broken down, it is absorbed into the blood in the small intestine, which has a good blood supply and thin walls, which allows food to pass easily into the blood through the process of diffusion. Some food cannot be digested, and is egested through the anus. \begin{enumerate} \item Food in chewed and mixed with saliva in the \textsc{mouth}. (1 minute) \[\mathrm{Starch} \xlongrightarrow[\mathrm{amylase}]{\mathrm{salivary}} \mathrm{Sugars}\] \item The \textsc{\oe sophagus} carries the chewed-up food to the stomach, using muscular walls which push food with a wave of contraction (\textbf{peristalsis}). (10--15 seconds) \item Acid digestive juices, ideal for pepsin (an enzyme that breaks down proteins), are added in the \textsc{stomach}. The food and the digestive juices are mixed. (1--6 hours) \[\mathrm{Proteins} \xlongrightarrow{\mathrm{pepsin}} \mathrm{Amino \:\: acids}\] \item More alkaline juices from the pancreas (to neutralise the stomach acid) are added in the \textsc{small intestine}. There is more mixing, then the fully digested food is absorbed into the blood. (5--6 hours) \[\mathrm{Starch} \xlongrightarrow[\mathrm{amylase}]{\mathrm{pancreatic}} \mathrm{Sugars}\] \[\mathrm{Fats} \xlongrightarrow{\mathrm{bile}} \mathrm{Fat \:\: droplets}\] \[\mathrm{Fat \:\: droplets} \xlongrightarrow{\mathrm{lipase}} \mathrm{Fatty \:\: acids \:\: and \:\: Glycerol}\] \item Only undigested waste material reaches the \textsc{large intestine}. The water is taken back into the body, leaving solid waste. (12--24 hours) \item Undigested food is stored in the rectum, and then the solid waste is egested through the anus as faeces. \end{enumerate} \subsection{Teeth} \begin{figure}[htbp!] \begin{centering} \includegraphics[width=0.5\textwidth]{tooth} \smallskip {\tiny Source: \texttt{http://commons.wikimedia.org/wiki/File:Tooth\_Section.svg} (Public Domain)} \end{centering} \caption{A cross-section of a human tooth.}\label{fig:tooth} \end{figure} An adult teeth has, at most, 32 teeth. Thre are four main types: \textsc{incisors}, \textsc{canines}, \textsc{pre-molars} and \textsc{molar}. Incisors are for cutting pieces off food, while canines are for griping it. Pre-molars and molars are for grinding the food down until it can be swallowed easily. The outside of a tooth is formed by hard enamel. Beneath this is a layer of hard dentine. In the centre is a soft area called the pulp cavity, which contains small blood vessels and a nerve (see Figure \ref{fig:tooth}). Tiny channels containing extensions of living cells tun outfrom the pulp cavity into the dentine. These make the dentine sensitive. The enamel and dentine are made hard by the presence of calcium phosphate, the same substance that makes bones hard. The outside of the root is covered by a material called cement. Attached to the cement are tough fibres which run into the jaw bone. These fibres hold the tooth in its socket; they allow the tooth to move slightly, and cushion it from being jarred when it hits something hard. \subsubsection{Tooth Decay} Tooth decay is caused by bacteria in the mouth. These bacteria form an invisible layer called plaque on the surface of the teeth. After a meal, the bacteria feed on any sugar present and turn it into acid. The acid eats into the teeth. Within approximately one hour the acid is neutralised by the saliva. However, the decay has often already started by this time. Decay usually starts between the teeth and in the crevices on the crowns. The acid eats through the enamel into the dentine, allowing bacteria to get into the pulp cavity. In severe cases the bacteria may spread to the base of the tooth, causing an abscess. Bacteria may also get between the tooth and the gum, causing the gum to bleed. Sometimes the fibres attaching the tooth to the jaw are attacked, in which case the tooth gets loose and eventually falls out. There is strong evidence that fluoride helps to prevent tooth decay. It strengthens teeth when they are forming, and makes the enamel more resistant to acid. Where there is not enough fluoride naturally occuring in public drinking water supplies, it is added artificially. This has led to a large improvement in the general dental health of the population. \subsection{Duodenum} Food leaving the stomach enters the \textsc{duodenum}. Secretions from the liver and pancreas are added (pancreatic juice contains all three types of digestive enzymes). Bile is stored in the gall bladder, and emulsifies fats. Sodium hydrogen carbonate neutralises the stomach acid. \subsection{Small Intestine (Ileum)} Digestion is completed in the \textsc{small intestine} (or \textsc{ileum}), which secretes digestove enzymes, and absorbs food. \begin{figure}[htbp!] \begin{centering} \includegraphics[width=0.5\textwidth]{villus} \smallskip \end{centering} \caption{A single human villus from the small intestine.}\label{fig:villus} \end{figure} The small intestine is covered in millions of tiny protusions called \textsc{villi} (see Figure \ref{fig:villus}). They increase the surface area, and so increasing the rate at which the small intestine can absorb food. Each villus has a thin surface layer, so there is only a short distance for absorption. Inside is a network of capillaries to caryy away the absorbed sugars and amino acids. There is also a lacteal, to carry away the absorbed fatty acids to the lymhpatic system. Connected to the capillaries is a blood vessel, which carries the absorbed foods to the hepatic portal vein, and then on to the liver. \subsection{Liver} Many cells perform a wide range of functions in the liver, in processing the absorbed foods. \bigskip \begin{centering} \begin{tabular}{rl} \raisebox{-0.55cm}{\scalebox{0.75}{\tikz \node[rotate=15] {$\xLongleftrightarrow[\mathrm{insulin}]{\mathrm{glucagon}}$};}} & Glycogen stores \\ Glucose $\longrightarrow$ & Energy via Respiration \\ \tikz \node[rotate=-20] {$\longrightarrow$}; & to other tissue via the circulation \\ \end{tabular} \end{centering} \bigskip \begin{centering} \begin{tabular}{rl} \raisebox{-0.55cm}{\tikz \node[rotate=20] {$\longrightarrow$};} & Synthesis of plasma proteins e.g.\ fibrinogen \\ Amino acids $\longrightarrow$ & Excess are deaminated $\longrightarrow$ Urea for excretion \\ \tikz \node[rotate=-20] {$\longrightarrow$}; & to other tissue via the circulation \\ \end{tabular} \end{centering} \bigskip \begin{centering} \begin{tabular}{rl} \raisebox{-0.55cm}{\tikz \node[rotate=20] {$\longrightarrow$};} & Fat stores \\ Fatty acids $\longrightarrow$ & Fats for cell membranes \\ \tikz \node[rotate=-20] {$\longrightarrow$}; & Energy via respiration \\ \end{tabular} \end{centering} \subsection{Large Intestine} Water and salt are absorbed in the \textsc{Colon}. Undigested food is stored in the \textsc{rectum}, along with bacteria and some dead cells. This forms faeces and is passed through sphincters out of the anus. \section{Nutrition in Plants} \subsection{Photosynthesis} \textsc{Photosynthesis} is the process by which green plants make glucose and other organic molecles from inorganice molecules, using light energy. The light energy is trapped by chlorophyll. The overall process for photosynthesis can be summarised as: \[ \mathrm{Carbon \: \: Dioxode} + \mathrm{Water} \xlongrightarrow[\mathrm{light \:\: energy}]{\mathrm{chlorophyll}} \mathrm{Glucose} + \mathrm{Oxygen} \] Glucose is not the only organic substance made by photosynthesis. Other carbohydrates are also formed, which can then be converted to fats, or, by combining with minerals, form amino acids and vitamins. Photosynthesis is the source of all organic substances in the plant. \begin{tikzpicture} \node (equation) {$\mathrm{Carbon \:\: dioxide} + \mathrm{Water} \xlongrightarrow[\mathrm{light \:\: energy}]{\mathrm{chlorophyll}} \mathrm{Glucose \: and \: other \: sugars} + \mathrm{Oxygen}$}; \node (uses) [below=of equation,xshift=2cm] {% \parbox{3cm}{ respired or used to make: \begin{itemize} \item starch \item sucrose \item cellulose \item proteins \item fats \item vitamins \item chlorophyll \end{itemize} } }; \node (oxygenuses) [below right=of equation,yshift=-2cm,xshift=-1.5cm] {\parbox{1cm}{excreted or respired}}; \draw [->,dotted,thick] ($(equation.south east) - (0.6cm,-0.25cm)$) -- (oxygenuses.north); \draw [->,dotted,thick] ($(equation.south) + (2cm,0.25cm)$) -- (uses.north); \end{tikzpicture} \paragraph{Products of Photosynthesis} Glucose and other sugars: \begin{itemize} \item Much of the glucose is converted to \textsc{starch} for temporary storage in the leaf. At night, the starch may be broken down to the sugar \textsc{sucrose} and transported through th phloem to other parts of the plant. \item In the leaf, and throughout the plant, glucose is broken down in \textsc{respiration} to release energy. \item In growing regions, glucose is converted to \textsc{cellulose} to make cell walls. \item In the leaf, some glucose is combined with nitrate to form \textsc{amino acids}. These are later incorporated in to \textsc{proteins} to make enzymes and to make structural parts of cells, such as membranes. If there is a shortage of nitrate, the plant is unable to grown properly, and is weak and unhealthy. \item In the leaf and elsewhere, glucose and other sugars are used to make \textsc{fats} for structures such as cell membranes and to make \textsc{vitamins} which have essential uses for the plant. \item Some glucose is combined with minerals, especially magnesium, to form \textsc{chlorophyll}, the green pigment used to trap light in photosynthesis. \end{itemize} Oxygen: \begin{itemize} \item Used in \textsc{aerobic respiration} throughout the plant. \item Excreted through stomata as a \textsc{waste gas}. \end{itemize} \subsection{The Leaf} \begin{figure}[htbp!] \begin{centering} \includegraphics[width=\textwidth]{leaf} \smallskip {\tiny Source: \texttt{http://en.wikipedia.org/wiki/File:Leaf\_anatomy.svg (CC-BY-SA-2.5)}} \end{centering} \caption{A typical leaf.}\label{fig:leaf} \end{figure} Each leaf is attached to the stem or branch by a \textsc{leaf stalk}, This leads to the \textsc{veins} in the leaf. Leaves are covered by a layer of waxy metrial called the \textsc{cuticle}, which is normally thick and waterproof. It prevents the leaf from losing too much water in hot weather. Immediately under the cuticle is a layer of cells called the \textsc{epidermis}. which forms the `skin' of the leaf. The epidermis may be pierced by lots of tiny holes called \textsc{stomata} (singular \textsc{stoma}). The stomata are mainly on the lower side of the leaf. They allow gases to diffuse in and out of the leaf, and water vapour to escape. Each stoma is flanekd bvy a pair of \textsc{guard cells} which can open and close. They close in hot, dry weather to prevent too much water evaporating from the leaves. Leaves are generally flat, sometimes large, and often numerous. The result is that they have a large surface area for aborbing Carbon dioxide and ligt. The veins help to support the leaf, and hold it out flat, so that it can catch the maximum amount of light. In many plants the leaves are positioned in such a way that they don't shade each other. Between the upper and lower epidermis are ltos of cells which together makes up the \textsc{mesophyll}. These cells contain \textsc{chloroplasts}, and this is where photosynthesis takes place. The mesophyll towads the upper side of the leaf consists of cells shaped like bricks, and arranged neatly side by side. They are called \textsc{palisade cells}. The other mesophyll cells are rounded and more irregular in their arrangement. They are called \textsc{spongy cells}. Between the mesophyll cells are \textsc{air spaces} into which he stomata open. When photosynthesis is taking place, carbon dioxide diffuses through the open stomata into the air spaces. It then diffuses into the cells. Phototsynthessis takes place mainly in the palisade cells. They contain most of the chloroplasts, and they are near the surface of tyhe leaf that gets most light. the chloroplasts are often clustered towards the tops of the cells, in the best position for catching light. The vein is made up of two parts: the \textsc{xylem} towards the top, and the \textsc{phloem} below. The xylem brings water and mineral salts to the elaf. The phloem takes soluble sugar and other products of photosynthesis away from the leaf. Together thexylem and phloem are calld \textsc{vascular tissues}. \subsubsection{Chloroplasts} Chloroplasts are filled with rows of thin interconnected \textsc{membranes}. Millions of \textsc{chlorophyll} molecules are laid out on these membranes. Chlorophyll is a complex organic green \textsc{pigment} which contains \textsc{magnesium}, and it plays a vital role in photosynthesis, by absorbing blue and red light, but reflecting green light. \begin{figure}[htbp!] \begin{centering} \includegraphics[width=\textwidth]{chloroplast} \smallskip {\tiny Source: \texttt{http://commons.wikimedia.org/wiki/File:Chloroplast.svg (CC-BY-SA-(any version) or GNU FDL)}} \end{centering} \caption{A chloroplast. On each membrane are many molecules of chlorophyll.}\label{fig:chloroplast} \end{figure} \subsubsection{Stomata} \begin{figure}[htbp!] \begin{centering} \includegraphics[width=0.8\textwidth]{stoma} \smallskip \end{centering} \caption{A single stoma.}\label{fig:stoma} \end{figure} Stomata allow carbon dioxide and oxygen to diffuse in and out of leaves. They are also the main route by which water vapour excapes from the plant. In hot, dry weather there is a risk that the plant may run short of water. For this reason it is important that the stomata should be able to open or close according to the weather conditions. When th estoma opens, the guard cells take up water from the neighbouring epidermal cells; as a result the guard cells swell up and become more turgid. As they swell up they bend, so the gap between them widens (see Figure \ref{fig:stoma}). They swell up because the inner wall of the guard cells is thicker, and less elastic, than the outer wall. The stoma closes by the reverse rocess. Water passes out of the guard cells, so they become less turgid. As a result the guard cells straighten, and the gap between them narrows. Around the stoma are sausage-shaped \textsc{guard cells}. \section{Transport in Animals} All organisms which are large require a transport system, to move substances around the body. Single-celled organisms with low levels of activity do not require transport systems. Humans have two main transport systems: \begin{itemize} \item Circulatory system \item Lymphatic system \end{itemize} \subsection{The Circulatory System} \paragraph{Single Circulatory Systems} e.g. fish: \hfill \begin{tikzpicture} \node (heart) {Heart}; \node (gills) [below right=of heart] {Gills}; \node (tissues) [below left=of heart] {Tissues}; \draw[->] (heart) -- (gills); \draw[->] (gills) -- (tissues); \draw[->] (tissues) -- (heart); \end{tikzpicture} \hfill \hfill Blood passes once through the heart on its way around the body. \paragraph{Double Circulatory Systems} e.g. humans: \hfill \begin{tikzpicture} \node (0,0) (heart) {Heart}; \node (tissues) [left=of heart] {Tissues}; \node (lungs) [right=of heart] {Lungs}; \draw [->,blue] (heart.north east) .. controls ($(heart.north east) + (0,0.5)$) and ($(lungs.north west) + (0,0.5)$) .. node [label=above right:deoxygenated blood] {1} (lungs.north west); \draw [->,red] (lungs.south west) .. controls ($(lungs.south west) + (0,-0.5)$) and ($(heart.south east) + (0,-0.5)$) .. node [label=below right:oxygenated blood] {2} (heart.south east); \draw [->,red] (heart.north west) .. controls ($(heart.north west) + (0,0.5)$) and ($(tissues.north east) + (0,0.5)$) .. node [label=above left:oxygenated blood] {3} (tissues.north east); \draw [->,blue] (tissues.south east) .. controls ($(tissues.south east) + (0,-0.5)$) and ($(heart.south west) + (0,-0.5)$) .. node [label=below left:deoxygenated blood] {4} (heart.south west); \end{tikzpicture} \hfill \hfill \subsubsection{Arteries} \begin{description} \item[Aorta] takes oxygenated blood from the heart to the body \item[Pulmonary artery] takes deoxygenated blood from the heart to the lungs. The only artery which carries deoxygenated blood. \end{description} \subsubsection{Veins} \begin{description} \item[Superior Vena Cava] brings deoxygenated blood from the head and arms back to the heart \item[Inferior Vena Cava] brings deoxygenated blood from the body back to the heart \item[Pulmonary Vein] brings oxygenated blood from the lungs back to the heart. The only vein which carries oxygenated blood. \end{description} \begin{figure}[htbp!] \begin{centering} \includegraphics[width=\textwidth]{heart} \smallskip {\tiny Source: \texttt{http://commons.wikimedia.org/wiki/File:Human\_healthy\_pumping\_heart\_en.svg (Public Domain)}} \end{centering} \caption{Diagram of a human heart.}\label{fig:heart} \end{figure} \begin{itemize} \item When the heart is relaxed (\textsc{diastole}), both sides fill up with blood from the veins. \item The atria then contract (\textsc{atrial systole}). So blood is forced into the ventricles through the valves. \item A fraction of a second later, the ventricles contract (\textsc{ventricular systole}). The valves between the atria and ventricles close, so blood is squeezed in to the arteries. \item The heart relaxes again and fills up with blood. \end{itemize} \begin{description} \item[Cardiac arrest/Myocardial infarction] Heart attack \item[Atheroschlerosis/atheroma/angina] Lack of oxygen to ehart due to fat build-up in coronary arteries, leading to chest pain. \item[Sinoatrial node] Group of cells taht regulate heart beat (pacemaker). \item[Hypertensive] High blood pressure \item[Stroke] Atheroschlerosis deprives an arteryin the brain of oxygen. \end{description} \begin{figure}[htbp!] \begin{centering} \includegraphics[width=\textwidth]{blood} \smallskip \end{centering} \caption{Human blood vessels. The lumen in the artery is much smaller than the lumen in the vein, as the blood is at a much higher pressure.}\label{fig:blood} \end{figure} \subsubsection{Composition of the Blood} Plasma is 90\% water. Plasma transports carbon dioxide from the organs to the lungs, soluble products from the small intestine to the organs, and urea from the liver to the kidneys. The following cells are suspended in it: \paragraph{Red Blood Cells -- Erythrocytes} Red blood celsl are disc-shaped and biconcave. These cells have no nucleus, so they can carry more oxygen. Red blood cells contain a chemical called \textsc{haemoglobin}. This combines with oxygen to form oxyhaemoglobin. A red blood cell's lifespan is about four months. After this time it goes to the spleen, which removes worn out red blood cells from circulation. \begin{figure}[htbp!] \begin{centering} \includegraphics[width=0.4\textwidth]{rbc} \smallskip {\tiny Source: \texttt{http://commons.wikimedia.org/wiki/File:Erythrozyten\_und\_Osmotischer\_Druck.svg (Public Domain)}} \end{centering} \caption{Red blood cells.}\label{fig:rbc} \end{figure} \paragraph{White Blood Cells -- Phagocytes \& Lymphocytes} There are several different types of white blood cells. They are all larger than red blood cells, and have a nucleus. Lymphocytes have a nucleus which occupies most of the cell. White blood cells protect the body from bacteria. Phagocytes can squeeze through capillary walls, move towards bacteria, and ingest them. Lymphocytes produce chemicals which destroy bacteria, by makign them stick together. \paragraph{Platelets} These are fragments of blood cells budded off in the red blood marrow. These cells have a sticky surface, and help to clot the blood at wounds, to stop bleeding. \subsubsection{Blood Clotting} \begin{enumerate} \item Blood vessel wall is damaged or broken. \item The protein within the blood vessel wall is exposed. This causes platelets to release an enzyme (thrombin). \item Blood plasma carries a soluble protein called \textsc{fibrinogen}.\item Enzymes secreted by platelets cause soluble fibrinogen to turn into insoluble \textsc{fibrin}. \item Fibrin forms long threads which precipitate out of the blood. \item The fibrin threads tangle together and trap red and white blood vessels in the clot. \item The clot dries and hardens, forming a scab. \end{enumerate} \subsubsection{Tissue Fluid Formation} \begin{enumerate} \item Arteriole brings blood into the capillary bed \item The arteriole divides into a network of small capillaries \item Fluid leaks out of the capillaries, especially at the beginning of the capillary bed, and bathes the body cells. \item The fluid is called \textsc{tissue fluid}. It carries glucose and oxygen from the blood to the cells. \item Tissue fluid containing \ce{CO2} and urea leaks back into the cappillaries at the venous end of the capillary bed. \item Venule carries blood back to a vein. \end{enumerate} \subsection{The Lymphatic System} Lymph nodes contain white blood cells, and act as traps for bacteria and foreign particles. Tissue fluid containing foreign and waste materials drain into the lymphatic system, pass through a lymph node, and re-enter the blood circulation. \subsubsection{The Immune System} All cells have protein molecules on their surface membranes called \textsc{antigens} (See Figure \ref{fig:antigens}). \begin{wrapfigure}{r}{0.35\textwidth} \vspace{-1cm} \begin{center} \includegraphics[width=0.09\textwidth]{antigens} \end{center} \caption{Antigens on a cell.\label{fig:antigens}} \vspace{-1cm} \end{wrapfigure} Lymphocytes (see Figure \ref{fig:lymphocyte}) produce \textsc{antibodies}. These are chemicals which react to foreign antigens and destroy the foreign cells. Lymphocytes `recognise' antigens on the surface of body cells and do not produce antibodies against them. \begin{wrapfigure}{r}{0.3\textwidth} \vspace{-1cm} \begin{center} \includegraphics[width=0.09\textwidth]{lymphocyte} \end{center} \caption{A lymphocyte.\label{fig:lymphocyte}} \vspace{-0.8cm} \end{wrapfigure} If foreign cells, e.g.\ bacteria, enter the body, lymphocytes recognise these as foreign due to their different antigens. The lymphocytes will then release antibodies to destroy the bacteria. \begin{figure}[p] \begin{centering} \includegraphics[width=\textwidth]{immune_system} \end{centering} \caption{A lymphocyte indentifying a bacterium.} \end{figure} There are thousands of lymphocytes which each produce a different antibody. Thus, thousands of different pathogens can be destroyed. Lymphocytes also produce `memory cells', which remain in the lymph nodes. These memory cells can produce antobodie very quickly if the same foreign antigen enters the body again. These antibodies destroy the bacteria before they cause a large infection -- the body is immune to that species of bacterium. \subsubsection{Transplants} If a patient needs to have an organ transplanted into their body, dctors must ensure that the antigens on the donor organ are very similar to the patient's antigens. Otherwise, there is a chance that the patients lymph nodes will produce antibodies against the organ, rejecting it. Brothers and sisters have similar DNA and are often used as donors. Patients are kept in sterile conditions after the operation, and are on drugs to suppress their immune system for the rest of their life {immunosuppressive drugs). \section{Transport in Plants} Plants need transport systems to: \begin{itemize} \item Move water from the soil to the leaves for use in photosynthesis. \item Move photosynthetic products from the leaves to other parts of the plant e.g.\ fruit amd growing parts of the plant. \end{itemize} \begin{description} \item[Xylem vessels] transport water from the roots to the leaves. Xylem vessels are long, continuous tubes -- it is dead tissue containing \textsc{lignin}. Lignin makes the xylem vessels strong, and is deposited unevenly, which leads to pits in the walls through which water can enter and leave the tubes. \item[Phloem tubes] (sieve tubes) are living tissue. At the end of each cell making up the tube, the cell wall is perforated to allow easy movement of sucrose. The movement of sucrose from the leaves to where it is needed is called translocation. Phloem cells contain few organelles. The majority of activities are performed by a companion cell which provides energy to the phloem cell. \item[Root hair cells] are found on young roots. They increase the surface area of the root for absorption of water an mineral ions. They last for approximately one day. \\[8pt] \end{description} \begin{figure}[pbth!] \begin{centering} \begin{tikzpicture} \filldraw[fill=brown!80!white,double,double distance=0.25cm,rounded corners=8pt] (0,0) -- (2,0) -- (2,2) -- (7,2) -- (7,3) -- (2,3) -- (2,3.5) -- (0,3.5) -- cycle; \node at (0.75,2.75) (nucleus) [circle=10pt,fill=black] {}; \node at (-1.5,2) (nuclabel) {nucleus}; \node at (-1.5,-0.5) (memlabel) {cell membrane}; \node at (3.5,1.5) (cytlabel) {cytoplasm}; \node at (2.5,-0.5) (cwlabel) {cell wall}; \draw[->] (nuclabel.north east) -- (nucleus.south west); \draw[->] (memlabel.north) -- (0.125,0.25); \draw[->] (cwlabel.north) -- (2,0); \draw[->] (cytlabel.west) -- (1,2); \end{tikzpicture} \end{centering} \caption{A root hair cell\label{fig:root}} \end{figure} \subsection{Osmosis} Water moves by osmosis across the root. Osmosis is the net diffusion of water molecules from a region of high water potential to a region of low water potential through a partially permeable membrane (down a water potential gradient). Water potential of a substance is a measure of how much water there is int it, and how easily the water molecules can move around. Substances with a lot of water have a high water potential. Substances with a little water have a low water potential. Water moves from areas of high water potential to areas of low water potential. \subsection{Transpiration} Water does not move by osmosis in the xylem. The xylem is dead tissue, and there are no cell membranes. Water moves up the xylem because of transpiration. Transpiration is the loss of water vapour from a leaf through the stomata. \begin{itemize} \item 98\% of water that is absorbed is lost in transpiration. \item The remaining 2\% is used in photosynthesis. \end{itemize} As water leaves the xylem vessels it reduces the water pressure at the top of the xylemm, so water moves upwards towards a lower pressure. Transpiration produces a tension (pull). Water molecules are sticky; they stick to each other (\textsc{cohesion}), and this helps water to be pulled up the xylem. Transpiration is aided by this cohesion. \subsubsection{Factors Affecting Transpiration} \begin{description} \item[Wind speed] Wind removes water vapour from around the stoma, so it increases the water potential gradient (the water potential of the atmosphere around the toma becomes more negative) (see Figure \ref{fig:trans}). \\ \textbf{\small higher wind speed, higher transpiration} \item[Humidity] The higher the humidity, the lower the water potential gradient, so less water evaporates from the leaves. \\ \textbf{\small higher humidity, lower transpiration} \item[Light intensity] During sunlight, stomata open to allow \ce{CO2} in for use in photosynthesis. \\ \textbf{\small higher light intensity, higher transpiration} \item[Temperature] One a hot day, water evaporates more quickly from the leaf \\ \textbf{\small higher temperature, higher transpiration} \\ If the plant loses too much water, it loses turgor pressure in the cells and may wilt -- the stomata will close at this point. \item[Water supply] If there is not enough water, the plant will clsoe its stomata to conserve water. \\ \textbf{\small lower water supply, lower transiration} \item[Leaf surface area] A greater leaf surface area means more stomata for water to siffuse out of. \\ \textbf{\small higher surface area, higher transpiration} \item[Stomata] Water is mainly lost through stomata -- the more stomata there are, the more transpiration there is. Most stomata are located on the underside of the leaf. \\ \textbf{\small more stomata, higher transpiration} \item[Air spaces] More air spaces in the spongy mesophyll of a leaf mean there is mroe space for water to collect. \\ \textbf{\small mroe air spaces, higher transpiration} \end{description} \begin{figure} \begin{centering} \begin{tikzpicture} \draw[very thick,green!50!black] (-3,0) -- (-0.5,0); \draw[very thick,green!50!black] (0.5,0) -- (3,0); \foreach \x in {0.25,0.5,0.75,1} \draw[dashed] (\x,0) arc (0:-180:\x); \node at (1,1) (stomalabel) {stoma}; \draw[->] (stomalabel) -- (0,0); \node at (-2.5,-2) (leaflabel) {leaf underside}; \draw[->] (leaflabel.north) -- (-2,-0.1); \node at (2,-2) (vapourlabel) {\parbox{2.5cm}{boundary layer (water vapour)}}; \draw[->] (vapourlabel.north) -- (0.8,-0.8); \end{tikzpicture} \end{centering} \caption{Water vapour build-up around a stoma.}\label{fig:trans} \end{figure} \subsection{Xerophytes} Xerophytes are plants taht are specially adapted to live in extreme conditions. Some examples of adaptations: \begin{description} \item[Thick cuticle] stops uncontrolled evaporation through leaf cells. \item[Small leaf surface area] less surface area for evaporation, e.g.\ conifer needles, cactus spines \item[Low stomata density] smaller surface area for diffusion \item[Sunken stomata] maintains humid air around stomata, e.g.\ marram grass, cacti \item[Stomatal hairs (trichores)] maintains humid air around stomata, e.g.\ marram grass, couch grass \item[Rolled leaves] maintains humid air around stomata, e.g.\ marram grass \item[Extensive roots] maximise water uptake, e.g. cacti \end{description} \subsection{Movement of Photosynthetic Products} Photosynthesis occurs in the leaves. It produces glucose -- leaves are a \textsc{source}. Glucose is converted into sucrose for transport around the plant. Sucrose is a disaccharide. it is less reactive than glucose, and does not get used up as easily as glucose. Sucrose enters the phloem tubes, and is taken to wherever it is needed, e.g.\ growign shoots, developing fruits, roots (anywhere where respiration is happening). The places where sucrose is taken to are called \textsc{sinks}. movement of organic substances is called \textsc{translocation} (also applies to amino acids, lipids etc.). Once at the sink sucrose may be converted to starch for storage (e.g.\ potatoes), or it may be converted to other sugars (e.g.\ fructose in fruits). In this way very high concenterations of sugars can be built up without affecting the water potential of cells. Sucrose can also be converted back to glucose for respiration. \subsection{Systemic Pesticides} Systemic pesticides are absorbed into the plant and transported throughout the plant in the phloem. The targeted organism (e.g.\ an insect) feeds on the plant and eats the pesticide and dies. Systemic pesticides are much more effective than contact pesticides, but long term effects on humans are unknown, and consumers may not want to eat products treated with them. \section{Respiration \& Gaseous Exchange} Every cell in every living organism needs energy. Energy is obtained from food by the process of respiration. There are two types of respiration: \subsection{Aerobic Respiration} The break-down of glucose using oxygen to release energy used by cells (38 mol Adenosine Tri-phosphate (ATP)). Energy (in the form of ATP) is used in muscle contraction, active transport, \textsc{anabolic} reactions (building up substances), \textsc{catabolic} reactions (destroying substances). Anabolic and catabolic reactions are together known as \textsc{metabolic} reactions. Some energy is released as heat. \[ \mathrm{Glucose} + \mathrm{Oxygen} \longrightarrow \mathrm{Carbon \:\: dioxide} + \mathrm{Water} + \mathrm{energy} \] \[ \ce{C6H12O6} + \ce{6O2} \longrightarrow \ce{6CO2} + \ce{6H2O} + \ce{38 \mathrm{mol} \: ATP} \] \ce{CO2} and \ce{H2O} are byproducts of respiration. \subsection{Anaerobic Respiration} The break-down of glucose without oxygen to release energy used by cells. Less energy is produced (2 mol ATP). \subsubsection{Yeast} Yeast is a single-celled fungus which can respire anaerobically. \[ \mathrm{Glucose} \longrightarrow \mathrm{Ethanol} + \mathrm{Carbon \:\: dioxode} + \mathrm{energy} \] \[ \ce{C6H12O6} \longrightarrow \ce{2C2H5OH} + \ce{2CO2} + \ce{2 \mathrm{mol} \: ATP} \] \subsection{Calorimeters} Different foods contain different amoutns of energy. Fats contain about twice as much energy as carbohydrates and proteins. The amount of energy in food can be measured using a calorimeter. \begin{figure}[htbp!] \begin{centering} \includegraphics[width=0.5\textwidth]{calorimeter} \smallskip \end{centering} \caption{A simple calorimeter -- used to measure the energy value of a respiratory substrate.}\label{fig:calor} \end{figure} \subsection{The Lungs} \begin{figure}[htbp!] \begin{centering} \includegraphics[width=\textwidth]{lungs} \smallskip {\tiny Source: \texttt{http://en.wikipedia.org/wiki/File:Diagrama\_de\_los\_pulmones.svg (GNU FDL)}} \end{centering} \caption{The lungs.}\label{fig:lungs} \end{figure} \begin{figure}[htbp!] \begin{centering} \includegraphics[width=\textwidth]{alveolus} \smallskip {\tiny Source: \texttt{http://commons.wikimedia.org/wiki/File:Alveolus\_diagram.svg (Public Domain)}} \end{centering} \caption{Some alveoli.}\label{fig:alveoli} \end{figure} \begin{figure}[htbp!] \begin{centering} \includegraphics[width=0.5\textwidth]{inhalation}\includegraphics[width=0.5\textwidth]{exhalation} \smallskip {\tiny Source: \texttt{http://commons.wikimedia.org/wiki/File:Expiration\_diagram.svg (Public Domain)}} \end{centering} \caption{The action of breathing.}\label{fig:breathing} \end{figure} The alveoli are adapted for efficient gas exchange: \begin{description} \item[Large surface area]Increased by the alveoli. 350,000,000 alveoli $\approx$ 70m$^2$. \item[Thin epithelium] A Two cell layer separates the air in the alveoli from the blood in the capillaries -- only a short distance forgases to diffuse. \item[Moist] Gases dissolve in solution before diffusion -- more efficent effusion. Prevents dehydration of cells. \item[Blood supply] A good blood supply to and from the lungs by a capillary network keeps concentration gradients different by removing oxygenated blood from the lungs and bringing deoxygenated blood to the lungs. \end{description} \subsubsection{Increase in Breathing Rate} ncreased respiration causes an increase in the production of \ce{CO2}. \ce{CO2} dissolves in water to form carbonic acid. \[ \ce{CO2} + \ce{H2O} \rightleftharpoons \ce{H2CO3} \rightleftharpoons \ce{H+} + \ce{HCO3-} \] \ce{H+} ions lower the pH of the blood, and are taken up by oxyhaemoglobin, which then releases oxygen. Increased \ce{CO2} is detected by chemoreceptors located in the carotid arteries, aorta, and medulla in the brain. Chemoreceptors send impulses to the medulla. The medulla then sends impulses to the intercostal muscles and the diaphragm, causing them to contract more frequently (increased ventilation). \begin{figure}[htbp!] \begin{centering} \includegraphics[width=\textwidth]{cilia} \smallskip \end{centering} \caption{Part of the lining of the respiratory passages.}\label{fig:cilia} \end{figure} \subsubsection{Cigarette Smoke} There are three major chemicals in cigarette smoke: \begin{description} \item[Nicotine] \begin{itemize} \item An addictive drug \item Higher heart rate \item Higher blood rate \end{itemize} \item[Tar] \begin{itemize} \item Paralyses the cilia on ciliated cells \item Makes goblet cells over-produce mucus \item Too much mucus \begin{itemize} \item Smoker's cough to remove the mucus \item This can damage the alveoli walls, which can lead to emphysema (surface area of alveoli reduced, so less oxygen can be absorbed) \end{itemize} \item Is a carcinogen (benzene) \end{itemize} \item[Carbon monoxide] binds irreversably with haemoglobin, therefore the oxygen carrying capacity of the blood is greatly reduced. Smokers have $\approx10\%$ of their haemoglobin bound to \ce{CO} -- this forms Carbaminohaemoglobin. \end{description} Other smoking-related diseases: \begin{description} \item[Chronic bronchitis] Smoke irritates the bronchi and bronchioles, damages the mucus membranes, and narrows the tubes. It reduces the cilia action, so mucus cannot be removed, which leads to bacterial infections. It is more difficult for \ce{O2} to diffuse into the blood. \end{description} \section{Excretion \& Homeostasis} \subsection{Excretion} Excretion is the removal from the body of waste products of metabolism (which may be toxic) and substances which are in excess of requirements, e.g.\ \ce{CO2} and urea. \ce{CO2} is removed via the lungs. Urea is removed via the kidneys. \begin{figure}[htbp!] \begin{centering} \includegraphics[width=0.8\textwidth]{excretory_system} \smallskip \end{centering} \caption{The excretory system.}\label{fig:excretory} \end{figure} \begin{description} \item[Rhenal artery] Brings oxygenated blood full of urea to the kidneys. \item[Rhenal vein] Takes deoxygenated blood which is free from urea back towards the heart via the Vena Cava. \item[Kidney] Removes unwanted (and excess) substances from the blood, turns them into urine, and passes the urine on to the bladder. It does this by filtering the blood. 1000cm$^3$ of blood is filtered by the kidneys every minute. \item[Ureter] Tubes which connect the kidneys to the bladder. \item[Bladder] A muscular bag which can store urine. Can store up to about 400cm$^3$ before the need to urinate (micturation) becomes compelling. \item[Sphincter] Muscle which, when it contracts, urine is prevented from leaving the body, and when it relaxes, urine can leave the body. \item[Urethra] Tube which carries urien from body. \end{description} \begin{figure}[htbp!] \begin{centering} \includegraphics[width=\textwidth]{urea} \smallskip \end{centering} \caption{Urea production.}\label{fig:urea} \end{figure} \begin{figure}[htbp!] \begin{centering} \includegraphics[width=0.6\textwidth]{aminoacid} \smallskip \end{centering} \caption{The Structure of an amino acid. \textbf{R} can stand for anything. The \ce{NH3} part of the molecule (ammonia) is toxic, and is converted into urea. Deamination is the removal of the nitrogen-containing part of the amino acid.}\label{fig:amino} \end{figure} \begin{sidewaysfigure}[htbp!] \begin{centering} \begin{tikzpicture}[x=1pt,y=1pt,scale=1.2] \draw[white,use as bounding box] (0,0) rectangle (501,389); \node at (250.5,194.5) {\includegraphics[scale=1.2]{urine_nolabels}}; \node at (435,360) (a) {\parbox{100pt}{\center \tiny 1. Blood vessel bringing blood to the glomerulus is wider than the one taking it away. This causes a pressure to build up in the glomerulus. More water can be absorbed under the influence of ADH\footnote{ADH is a hormone.}. }}; \node at (428,280) (b) {\parbox{100pt}{\center \tiny 2. Fluid containing small molecules -- e.g.\ urea, salts, glucose -- is filtered out of the blood into Bowman's capsule (ultra-filtration). }}; \node at (400,215) (c) {\parbox{100pt}{\center \tiny 3. Filtrate moves along the Rhenal Tubule. Useful substances are reabsorbed back into the blood, e.g.\ glucose, some salts, and some water (selective reabsorption) for this purpose. This requires active transport, which in turn requires ATP. The cells lining the Rhenal tube contain many mitochondria for this purpose. }}; \node at (230,33) (d) {\parbox{100pt}{\center \tiny 4. Salty tissues surrounding the Loop of Henle means that water diffuses out of the Loop of Henle into the tissue. }}; \node at (130,178) (e) {\parbox{90pt}{\center \tiny 5. Fluid containing water, salts and urea continues along the Rhenal tube. }}; \node at (177,267)(f) {\parbox{120pt}{\center \tiny 6. Clean blood passes out of the kidney via the Rhenal vein. }}; \node at (40,158) (g) {\parbox{100pt}{\center \tiny 7. Urine exits the kidney via the ureter. }}; \node at (221,125) (h) {\parbox{50pt}{\center Loop of Henle }}; \node at (305,168) (j) {\parbox{50pt}{\center Rhenal tubule }}; \draw (j.west) -- (267,177); \end{tikzpicture} \smallskip \end{centering} \caption{How urine is produced -- there are two processes: ultra-filtration, and selective reabsorption.}\label{fig:urine} \end{sidewaysfigure} \begin{figure}[htbp!] \begin{centering} \includegraphics[width=0.5\textwidth]{glomerulus} \smallskip {\tiny Source: Gray's Anatomy 1918 (Public Domain)} \end{centering} \caption{An individual glomerulus.}\label{fig:glom} \end{figure} \begin{figure}[htbp!] \begin{centering} \begin{tikzpicture}[x=1pt,y=1pt] \draw[white,use as bounding box] (0,0) rectangle (476,470); \node at (238,235) {\includegraphics{dialysis_nolabels}}; \node at (386,417) (a) {\parbox{90pt}{\center Air trap and air detector}}; \draw (a.west) -- (260,380); \node at (406,387) (b) {Clean blood}; \draw (b.west) -- (315,365); \node at (236,450) (c) {Venous pressure monitor}; \draw (c.south) -- (235,420); \node at (333,46) (d) {\parbox{80pt}{\center Removed blood for cleaning}}; \draw (d.north) -- (300,207); \node at (227,46) (e) {\parbox{80pt}{\center Arterial pressure monitor}}; \draw (e.north) -- (268,208); \node at (83,103) (f) {Blood pump}; \draw (f.east) -- (178,104); \node at (77,167) (g) {\parbox{90pt}{\center Heparin pump (to prevent clotting)}}; \draw (g.east) -- (180,170); \node at (74,204) (h) {\parbox{90pt}{\center Dialyser inflow pressure monitor}}; \draw (h.east) -- (154,207); \node at (59,247) (i) {Used dialysate}; \node at (59,316) (j) {Fresh dialysate}; \node at (96,280) (k) {Dialyser}; \draw (k.east) -- (170,280); \node at (407,275) (l) {Patient}; \end{tikzpicture} \smallskip {\tiny Source: \texttt{http://commons.wikimedia.org/wiki/File:Hemodialysis-en.svg} (GNU FDL and CC-BY-SA-ALL)} \caption{Kidney failure -- if one or both kidneys fail then dialysis is used or a transplant performed to keep urea and solute concentration in the blood constant.}\label{fig:dialysis} \end{centering} \end{figure} \begin{figure}[htbp!] \begin{centering} \includegraphics[width=0.6\textwidth]{kidney_transplant} \smallskip \end{centering} \caption{Kidney transplant may be necessary as Rhenal dialysis is inconvenient for the patient and costly.}\label{fig:transplant} \end{figure} \subsection{Homeostasis} Homeostasis is the maintenance of a constant internal environment. Examples: \begin{itemize} \item Body temperature \item Blood pH \item Blood pressure \item Blood glucose concentration \item Blood water concentration \end{itemize} The mechanism by which homeostasis is maintained is by using negative feedback systems, which maintain stability in the body. \bigskip \begin{centering} \begin{tikzpicture} \node at (0,0) (normleft) {\Huge NORM}; \node [above right=of normleft] (bodyup) {\parbox{5.5cm}{Body detects change and a corrective mechanism is put in place.}}; \node [below right=of bodyup] (normright) {\Huge NORM}; \node [below right=of normleft] (bodydown) {\parbox{5.5cm}{Body detects change and a corrective mechanism is put in place.}}; \draw[->] (normleft.north) to [out=90,in=180] node [above left] {\parbox{1.5cm}{\center\small Rise above Norm}} (bodyup.west); \draw[->] (normleft.south) to [out=270,in=180] node [below left] {\parbox{1.5cm}{\center\small Decrease below Norm}} (bodydown.west); \draw[->] (bodyup.east) to [out=0,in=90] node [above right] {\parbox{1.5cm}{\center\small Return to Norm}} (normright.north); \draw[->] (bodydown.east) to [out=0,in=270] node [below right] {\parbox{1.5cm}{\center\small Return to Norm}} (normright.south); \end{tikzpicture} \bigskip \begin{tikzpicture} \node (stimulus) {\textsc{stimulus} (i.e.\ a change)}; \node [below=of stimulus] (receptor) {detected by a \textsc{receptor}}; \node [below=of receptor] (co-ordinator) {co-ordinated by a \textsc{co-ordinator}}; \node [below=of co-ordinator] (effector) {a change occurs in an \textsc{effector}}; \node [below=of effector] (response) {which causes a \textsc{response}}; \draw[->] (stimulus) to (receptor); \draw[->] (receptor) to (co-ordinator); \draw[->] (co-ordinator.south) to (effector); \draw[->] (effector) to (response); \draw[->] (response) to [out=180,in=180] (stimulus); \end{tikzpicture} \end{centering} \bigskip \begin{description} \item[Sweating] \begin{itemize} \item water evaporates, takes heat from the surface of the skin \end{itemize} \item[Vasodilation] \begin{itemize} \item causes more blood to travel to capillaries near skin surface \item heat is radiated away from the body \item skin appears flushed, because there is more blood flowing through the surface capillaries \end{itemize} \item[Raised hairs] \begin{itemize} \item traps air (which insulates) next to skin surface \end{itemize} \item[Vasoconstriction] \begin{itemize} \item reduces blood flow to surface capillaries \item skin is pale, because there is hardly any blood flowing through surface capillaries \end{itemize} \end{description} \newcommand{\mpc}[2]{% \begin{minipage}{#1}% \center #2% \end{minipage}% }% \begin{sidewaysfigure}[htbp!] \begin{centering} \scalebox{0.75}{ \begin{tikzpicture}[box/.style={rectangle,draw=black,thin,inner sep=4pt,minimum size=1cm}] \node [box] (top) {% \begin{minipage}[c]{0.25cm} \rotatebox{90}{\textsc{high}} \end{minipage} \hfill % \begin{minipage}[c]{3cm} \center environmental temperature \end{minipage} \hfill % \begin{minipage}[c]{0.25cm} \rotatebox{270}{\textsc{low}} \end{minipage} }; \node [box,below=of top] (skin) {% \begin{minipage}[c]{0.25cm} \rotatebox{90}{\textsc{increase}} \end{minipage} \hfill % \begin{minipage}{3cm} \center skin temperature \end{minipage} \hfill % \begin{minipage}[c]{0.25cm} \rotatebox{270}{\textsc{decrease}} \end{minipage} }; \node [box,left=of skin,xshift=-2cm] (warm) {\begin{minipage}{4cm}\center skin warm receptors\end{minipage}}; \node [box,right=of skin,xshift=2cm] (cold) {\begin{minipage}{4cm}\center skin cold receptors\end{minipage}}; \node [box,below=of skin] (cortex) {\begin{minipage}{4cm}\center cerebal cortex\end{minipage}}; \node [box,below left=of cortex,xshift=-1cm] (loss) {\begin{minipage}{6cm}\center anterior hypothalamus \\ \textsc{heat loss centre}\end{minipage}} child[sibling distance=3cm,->] {node {\mpc{3cm}{sweating}}} child[sibling distance=3cm,->] {node {\mpc{3cm}{skin arterioles dilate}}} child[sibling distance=3cm,->] {node {\mpc{3cm}{metabolic rate decreases}}} child[sibling distance=3cm,->] {node {\mpc{3cm}{hairs on body lie flat}}}; \node [box,below right=of cortex,xshift=1cm] (gain) {\begin{minipage}{6cm}\center posterior hypothalamus \\ \textsc{heat gain centre}\end{minipage}} child[sibling distance=3cm,->,yshift=-0.5cm] {node {\mpc{3cm}{shivering}}} child[sibling distance=3cm,->,yshift=-0.5cm] {node {\mpc{3cm}{skin arterioles constrict}}} child[sibling distance=3cm,->,yshift=-0.5cm] {node {\mpc{3cm}{hair raised}}} child[sibling distance=3cm,level distance=1cm,->] {node {\mpc{3cm}{adrenaline}} child[sibling distance=3cm,level distance=1.5cm,grow=south east,->] {node {\mpc{3cm}{metabolic rate increases}}}} child[sibling distance=3cm,level distance=1cm,->] {node {\mpc{3cm}{thyroxine}}}; \draw[->] (gain-5) -- (gain-4-1); \node [box,below=of cortex,yshift=-5cm] (blood) { \begin{minipage}[c]{0.25cm} \rotatebox{90}{\textsc{decrease}} \end{minipage} \hfill \begin{minipage}{3cm} \center blood temperature \end{minipage} \hfill \begin{minipage}[c]{0.25cm} \rotatebox{270}{\textsc{increase}} \end{minipage} }; \node [below=of loss,yshift=-0.5cm] (lbrace) {$\underbrace{\hskip 12cm}$}; \node [below=of gain,yshift=-1cm] (rbrace) {$\underbrace{\hskip 12cm}$}; \draw [double,->,thick] (lbrace.south) -- (blood.north west); \draw [double,->,thick] (rbrace.south) -- (blood.north east); \draw [dashed,<-] (loss.west) -- ($(loss.west) - (4,0)$) |- node [near end,above] {\it negative feedback} (blood.west); \draw [dashed,<-] (gain.east) -- ($(gain.east) + (4,0)$) |- node [near end,above] {\it negative feedback} (blood.east); \draw [->] ($(top.south west) + (0.25cm,0)$) -- ($(skin.north west) + (0.25cm,0)$); \draw [->] ($(top.south east) - (0.25cm,0)$) -- ($(skin.north east) - (0.25cm,0)$); \draw [->] (skin) -- (warm); \draw [->] (skin) -- (cold); \draw [->] (warm) -- (loss); \draw [->] (cold) -- (gain); \draw [->] (warm.south) -- (cortex.west); \draw [->] (cold.south) -- (cortex.east); \draw [->] (cortex.south west) -- (loss.north east); \draw [->] (cortex.south east) -- (gain.north west); \draw [->] ($(loss.east) + (0,0.25cm)$) -- node [above] {\it inhibition} ($(gain.west) + (0,0.25cm)$); \draw [->] ($(loss.east) - (0,0.25cm)$) -- node [below] {\it inhibition} ($(gain.west) - (0,0.25cm)$); \end{tikzpicture} } \caption{A summary of how body and blood temperature are maintained.} \end{centering} \end{sidewaysfigure} \subsection{The Pancreas} The pancreas is both an \textsc{exocrine} gland and an \textsc{endocrine} gland. \begin{description} \item[Exocrine gland] a gland that secretes externally through a duct --- the pancreas secretes pancreatic juice, produced in Acinar cells, into the pancreatic duct. \item[Endocrine gland] a gland that secretes hormones directly into the bloodstream --- the pancreas secretes the hormones insulin and glucagon, from the Islets of Langerhans, into the bloodstream. \end{description} %\section{Coordination \& Response to Stimuli} % \section{Reproduction} \subsection{Asexual Reproduction} \begin{itemize} \item One parent \item Offspring is genetically indentical \item Does not involve gametes \item New diploid cells are produced directly by mitosis (by other diploid cells) \end{itemize} \subsubsection{Bacteria} Bacteria reproduce by binary fission. \begin{tikzpicture} \end{tikzpicture} \subsubsection{Funghi} %\section{Genetics \& Evolution} % %\section{Organisms in their Environment} % %\section{Human Influences on Ecosystems} \end{document}