Bio Notes PDF

**Learning Intention**    - identify the components of mammalian blood  - describe the functions of different blood components  - draw and label red and white blood cells  - state the functions of plasma, red and white blood cells and platelets.  Blood has many different functions...

**Learning Intention**    - identify the components of mammalian blood  - describe the functions of different blood components  - draw and label red and white blood cells  - state the functions of plasma, red and white blood cells and platelets.  Blood has many different functions in mammals.  Blood helps the body to fight invasions by bacteria and viruses. Blood also helps to regulate body temperature and it clots if the skin is broken to prevent excessive blood loss.    If you take a sample of blood from a mammal and spin it in a special machine called a centrifuge, the blood separates out into two parts, as shown in the figure below. The blood separates into a clear liquid fraction called plasma and a dark reddish-brown solid fraction consisting of blood cells.  Sllao 90이8 2田S리d **Plasma**  Plasma is a sticky, yellowish liquid. It is 90% water and 10% substances carried in solution. These substances include digested food, such as sugars, amino acids, vitamins and minerals, excretory products, such as carbon dioxide and urea, hormones and large protein molecules, such as antibodies.  **Blood cells**  Blood cells are made in bone marrow. There are three main groups of blood cells:  Red blood cells -- these are cells that contain the red pigment haemoglobin that gives blood its colour.      Red blood cells do  not have nuclei.  White blood cells -- there are two types of white blood cell: lymphocytes and phagocytes.      The nucleus of each type has a characteristic shape.  Platelets -- these are fragments of cells made in the bone marrow.(thrombocytes)      They are very small (about 3 μm) but they are important for blood clotting.    The figure below shows the main groups of blood cells.     **Red blood cells**  Red blood cells do not have a nucleus so they cannot survive for more than three months. Old red blood cells are destroyed in the liver or the spleen.  Red blood cells contain the protein haemoglobin. Haemoglobin readily combines with oxygen in the tissues to form a bright red, unstable compound called oxyhaemoglobin. Where the oxygen concentration is low,  oxyhaemoglobin breaks down to release free oxygen.    This allows red blood cells to pick up oxygen molecules in the lungs and transport the oxygen to the cells and tissues of the body. Cellular respiration releases carbon dioxide which diffuses into the blood. Some of this forms hydrogencarbonate ions in the plasma. Haemoglobin carries the rest of the carbon dioxide in the red blood cells. When blood reaches the lungs, carbon dioxide diffuses from the plasma and the red blood cells into the alveoli where it is exhaled.    The figure below shows what happens to the red blood cells in the lungs and in other parts of the body.  Red blood cell (carries oxygen) The cell is tull of haemoglobin Capillary Haemoglobin blood To the lungs organs Haemoglobin OXYGEN goes into the blood OXYGEN goes into the cells Capillary moglobin From the To the organs Oxyhae- moglobin   **White blood cells**  White blood cells are larger than red blood cells. They do not contain haemoglobin so they appear translucent under a microscope unless they are stained. They have a nucleus.  Some microorganisms (bacteria and viruses) can get into the blood and tissues where they cause infection or disease. The two types of white blood cells, lymphocytes and phagocytes, protect the body by working quickly to  destroy harmful microorganisms and any other foreign substances that the body does not recognise in the blood. Foreign substances are called **antigens.**  When antigens come into contact with lymphocytes they stimulate the lymphocytes to produce antibodies which begin the process of destruction. The phagocytes complete the job by engulfing the foreign substances, such  as bacteria, digesting and killing them. The figure below shows how the immune response  process happens in our blood.    The table below summarises the components of blood and the main functions of each component.     - state how the body defends itself against pathogens  - describe the role of blood in defending the body and in developing natural immunity.    The human body has several defences against pathogens. External defences aim to prevent pathogens from entering the body. Internal defences operate inside the body to disable and kill pathogens which have managed to enter the body. The body's defences against disease are known collectively as the immune system. The immune system consists of the skin, parts of the respiratory system, parts of the digestive system and the blood.   The figure below shows the main components of the immune system and their role in defending the body against pathogens.  A diagram of a human body Description automatically generated **Internal defence systems**   The blood plays an important role in protecting the body and is responsible for immunity and the immune response.  **Immunity and the Immune Response**  Immunity is the body's resistance to a specific condition or disease. When a specific pathogen, such as measles, enters the body and is destroyed by the internal defences, we describe the person as being 'immune' to that disease.  The immunity may last for a short time or for life.  The body's immune response is its reaction to being invaded by specific foreign materials, such as viruses, bacteria, toxins or other unrecognised proteins. The body recognises that these substances are foreign and it responds by trying to destroy them. Substances which cause an immune response are called antigens. The immune response involves the lymphocytes and the production of antibodies. These are proteins which the body produces in response to specific antigens. The antibodies bind onto the targeted antigens and destroy them.     Antibodies produced against a particular antigen will attack only that antigen. The antibody is said to be  specific to that antigen. This means that the antibodies produced against the typhoid bacteria will not attack  the pneumonia bacteria. The body is able to produce tens of millions of specifi c antibodies in a lifetime.  **Natural immunity**  The antibodies that are produced against a microorganism may stay in the body for some time ready to  attack the same microorganisms when they attack the body again. Even if the antibodies do not remain in the  body, the antigens of the microorganism are recognised by the lymphocytes on further attacks. The lymphocytes  then rapidly produce large quantities of the antibody.  This means that the re-infection is dealt with by an immune reaction which is even more effective than the  first reaction. This means the body has become 'resistant' to the disease. This is why a second infections is unlikely with  chicken pox and measles.     **The action of lymphocytes and phagocytes**  You should remember that lymphocytes are a type of white blood cell produced in the bone marrow. Lymphocytes work together with phagocytes to keep the body healthy. They quickly destroy pathogens that infect  the blood or tissues and which the body does not recognise as its own.  Lymphocytes produce antibodies in response to antigens. Phagocytes engulf and destroy antigens.  **\ **     Immunisation is the process of protecting a person from a disease (or making them immune to a disease) by giving them a substance (by mouth or by injection) that provides artificial immunity. Immunisation can promote  active or passive immunity to disease-carrying microorganisms.  The substance that is injected or swallowed is called a vaccine and the process of being immunised is called immunisation or vaccination.    Vaccines are made from one of the following:  Dead microorganisms, for example, whooping-cough vaccine is made from dead bacteria.  A weakened form of the microorganism that is harmless. Vaccines made like this are called attenuated vaccines. The vaccine against tuberculosis is an attenuated vaccine.  A substance from the disease-causing microorganism, which does not itself cause the disease, for example, the diphtheria vaccine.  The processes of genetic engineering are also used to produce new vaccines.    **How do vaccines work?**  There are two types of vaccination. One provides active immunity, the other provides passive immunity.  **Active immunity** is acquired when the person is given a vaccine consisting of antigens. This stimulates the lymphocytes to produce antibodies specific to that antigen. These antibodies remain in the blood for a long time to provide a defence that can eliminate the microorganism should it infect the body in the future. Active immunity is acquired when you are vaccinated against diseases such as measles, tuberculosis, polio, diphtheria and whooping cough. In some cases, the levels of immunity may drop off  over time and booster injections may be needed to maintain the levels of immunity. For example, the polio vaccine is given to babies and then a booster injection is given at ages fi ve and 15.  Passive immunity is acquired when the person is given a vaccine consisting of antibodies produced by another organism in response to infection by a specific pathogen. This method is used when the person has been exposed to an antigen but has no immunity. For example, pregnant women who are exposed to German measles may be given a vaccine made from human serum or with antibodies from human serum. Similarly, if you cut yourself deeply on something dirty, you are given a tetanus injection made from antibodies. Passive immunity is important for babies. Babies are not able to  make their own antibodies until they are one to three months old, so they  are dependent on antibodies from their mothers. Some antibodies cross the placenta to provide immunity before the baby is born. However, most babies receive antibodies from their mother's milk when they are breastfed. The passive immunity they acquire is short-lived, but by the time it wears off, they are able to produce their own antibodies.  You have probably been immunised against some communicable diseases. Children are routinely vaccinated against six diseases that used to cause many deaths. These are:  diphtheria, which affects the throat and releases toxins that can damage the heart;  tetanus, which causes the muscles in the body to permanently contract and which can lock the jaw so that the person cannot swallow;  whooping cough, which is a serious cough that can lead to pneumonia and an increased risk of brain damage;  poliomyelitis, which damages the nervous system and can cause paralysis;  tuberculosis, which affects the lungs and is very infectious;  and German measles, which is not serious in children but can damage unborn babies if the mother is exposed to the virus.  The result of immunisation campaigns is that these diseases are now rare in most countries. However, if the number of people who are vaccinated were to drop, the number of cases would rise among unprotected people.    **Problems in the immune syste**m  The immune system does not always work properly.  In some cases, the immune system may over-function and lead to hypersensitivity reactions and auto-immune diseases. In a hypersensitivity reaction, the immune system attacks body tissues instead of the microorganism. An example of this is an allergic reaction that leads to asthma. In an auto-immune disease, the T-lymphocytes treat the body's own proteins as antigens. Rheumatoid arthritis is an auto-immune disease in which cells in the joints of the hands and feet are attacked and inflammation sets in.  The immune system may also under-function and lead to immune deficiency diseases. In an immune deficiency disease, the body's defences become suppressed and they are not able to defend against invading microorganisms. AIDS is probably the best-known immune deficiency disease. In AIDS, the HIV attacks the T-lymphocytes causing the body to be  vulnerable to opportunistic infections it would otherwise be able to fight off. The most common infections in AIDS patients are Kaposi's sarcoma (a type of skin cancer), a type of pneumonia and leucoplakia which causes thick white patches to develop on the tongue.  HIV spreads by invading T-lymphocytes. At first the virus does not multiply. When the T-lymphocyte is activated to fight another pathogen, the virus is activated and it spreads in the T-lymphocytes as they clone themselves and differentiate. By invading T-lymphocytes, the HIV effectively breaks down the body's own defences. The figure below shows you how  HIV infects cells.      Learning Intention      [What Is Soil Made of?](https://www.youtube.com/watch?v=eRGmoR1qlR8)    A screenshot of a computer Description automatically generated    ** **  **Components of soil**     There are many different soils, but all soils consist of the same basic components: **rock particles**, **organic matter**, **air**, **water** and **living organisms**. Soils are different because the amounts of these components vary from soil to soil. For example, **a rich fertile soil** **like loam** may have **more organic matter and water** than an infertile,** sandy soil. **     See the illustration below for examples of the different components of soil.      ** **  **Rock particles**  ** **  Rock particles are the** largest component** of soils, and they make up around 45% of the total volume of the soil. The rock particles come from rocks that have been eroded or weathered over thousands of years. Nutrients, in the form of minerals and salts, are slowly released from the rock particles into the soil.     **Organic matter**  Organic matter forms **only** about **5%** of the total volume of soil, but it is** extremely important**.  Organic matter originates mainly from** animal excretions** and the** remains of dead plants and animals**.   Small organisms called **decomposers** that live in the soil, such as** bacteria** and **fungi**, break down the** organic matter** to release **nutrients** that plants take up through their roots. This decomposed organic matter in the soil is called **humus**.     **Humus** is important in soil because it** provides the nutrients** that plants need as well as **food for small organisms**. It also helps to **improve the soil crumb structure**, so that it is not too compact or loose to hold plant roots.      Some of the ways in which humus is formed in the picture below.  **Air**  Air makes up about** 25%** of the volume of soil. Air is found in all the spaces between components  of the soil that are not filled with water.   Different soils have different amounts of space so they contain different amounts of air.   **Sandy soils** have the most open spaces, so they usually have more air than other soils. Air contains **oxygen**, **nitrogen**, and **carbon dioxide**.  Without the oxygen in air, organic matter cannot be broken down. So, if there is little air in soil, the nutrients from the organic matter are not released quickly and the soil is not very fertile.    **Water**  Water accounts for about** 25%** of the volume of soil. Water enters soil as rainfall or when people irrigate the soil. Water is found in the** open spaces in the soil** and in a **thin layer around the soil particles**. Different types of soil hold different amounts of water. **Clay soils** hold more water than **sandy soils because they have very small particles**.    **Living organisms**  Living organisms make up a very small proportion of the total volume of soil. In most soils they account for only about** 0.01%** of the volume. Even though they are such a small proportion of the soil, their role is very important for keeping the soil in good condition so that it can provide nutrients for plants and animals.    Macroorganisms are organisms that we can see with the naked eye. Some of the macroorganisms found in soil are earthworms, termites, ants, springtails, beetles, slugs, snails, spiders and woodlice. Macroorganisms keep the soil  loose by burrowing and turning the soil over. Their droppings also help to fertilise the soil.    Microorganisms are tiny organisms that we can see only through a microscope. These include bacteria and fungi that break down the organic material in the soil to release useful nutrients for plants. Without living organisms, the soil would become too compact for plant roots to grow through and nutrients would not be released from organic matter.    The components of soil are important to living organisms:    rock particles provide an anchor for plant roots and shelter for macroorganisms and microorganisms  organic matter makes the soil fertile and can prevent erosion  oxygen in soil is essential for respiration of plant roots and soil organisms  nitrogen (in air) is essential for the formation of nitrates  water is essential for plants and animals living in soil.    1. biotic factors   2. habitat   3. abiotic factors   4. microorganisms   5. macroorganisms   6. distribution   7. transect  8. quadrat abundance   9. density  10. ecology   11. ecosystem   12. autotrophs   13. producers   14. heterotrophs   15. consumers   16. herbivores   17. carnivores   18. omnivores   19. decomposers   20. trophic level   21. food chain   22. food web   23. symbiosis   24. commensalism   25. mutualism   26. parasitism   27. detritus   28. scavengers   29. detritivores   30. carbon cycle   31. nitrogen-fixing bacteria   32. denitrifying bacteria   33. nitrogen cycle   34. renewable   35. finite resources   36. population growth   37. ecological footprint   38. biodegradable   39. recycling   40. human activity   41. alien species   42. invasive species   43. pollution   44. acid rain   45. greenhouse effect   46. global warming   47. conservation   48. population   49. immigration   50. emigration   1. Draw and label diagrams of cells to show their structure  2. Name the structures found in cells  3. State the functions and importance of different cells' structures  4. Tabulate the differences between plant and animal cells  5. Examine plant and animal cells under a microscope    **The structure of cells**    The cell is the basic unit of life. Some organisms, such as **bacteria** and** protozoa**, consist of one cell. These are** uni-cellular** organisms.  Most plant and animal species are** multi-cellular**. This means consist of have many cells that work as a system to keep them alive.    **The illustration below shows the structure of an animal cell and the structure of a plant cell.  **    A diagram of a cell Description automatically generated   **Plant and animal cells are different, but all cells have the following properties:**    - The cell is covered by a cell membrane.  - The cytoplasm is the living part of the cell.  - The organelles are small structures found in the cytoplasm.   - They are mostly too small to be seen with the naked eye but they can be seen with an electron microscope.  - The nucleus controls the working and function of the cell, it also contains the chromosomes.  - The vacuole is an organelle with a membrane that holds liquid.  - The mitochondria are organelles which are responsible for cellular energy        **Animal cells**    - Animal cells do not have rigid cell walls so they may not have a fixed shape.  - If vacuoles are present in the cell they are normally small.   - Plant cells are normally larger than animal cells.   - They have a strong cell wall that encloses the cell and gives it a fixed shape.  -  Plant cells usually have a large vacuole which is filled with cell sap (a solution of water and sugars).  -  Plant cells that are involved in photosynthesis also have organelles called chloroplasts.   - Chloroplasts are organelles that contain the chemical chlorophyll.    The table below lists the differences between animal and plant cells.      **The different cell structures**    The structures found in cells all have specific functions that are important  for keeping each cell alive and helping it to function properly.     The table below summarises the function and importance of the different structures found in cells.      Revision Questions    - explain cell specialisation   - give some examples of cell specialisation in plants and animals  - define 'cells', 'tissues', 'organs' and 'organisms' and show how they are connected  - give examples of tissues from both plants and animals.      **Single cells can live as organisms**    Unicellular organisms consist of only one cell that carries out all the functions the organism needs to survive. Different types of unicellular organism look different to each other, but they all have the same basic structure:   a cell membrane, a nucleus and other organelles in their cytoplasm.  For example a generalised bacterium cell and an amoeba (a protozoan)       **Multicellular organisms**    Most cells cannot survive on their own, so they join together to function as multicellular organisms. Humans are multi-cellular organisms made up of** billions** of cells. In multicellular organisms, cells can become specialised to perform different functions in the body. These cells have different structures and functions, but they work together so that the organism can function as a whole.    A group of **similar cells** form a** tissue**. For example,** muscle cells** form the tissue of the stomach wall and the heart. Different tissues together form an organ. The stomach is an organ and the heart is an organ. The organs work together in an organised system. For example, the stomach, together with other organs, forms the digestive system.     **The illustration below shows the different levels of organisation in cells.**  In plants, the groups of cells form tissue, but we do not often talk about the organs of plants, we usually talk about the 'structures' or 'parts' of plants.    A diagram of a person\'s body Description automatically generated   A closer look at specialised cells  The human body has more than 200 different types of cell.             **Revision Questions**    1 Why are cells not all the same? Give examples to support your answer.    2 Which types of cell are needed to perform the following functions in a multi-cellular animal?     a Protective covering     b Carry messages between cells     c Move oxygen round the body     d Prevent dirt and bacteria from getting into the lungs    3 What is the function and importance of the following specialised plant cells?     a Root cells c Guard cells     b Chloroplasts d Phloem cells    4 What do you think happens to the fat cells in your body when you eat more food than you need for your body functions?    **Learning Intention**    - distinguish between breathing and respiration  - show that respiration takes place at a cellular level  - understand the function and role of ATP in transferring energy  - describe the process of aerobic respiration  - tabulate the differences between aerobic and anaerobic respiration  - carry out investigations to find out about the products of respiration.  [Anaerobic Respiration](https://www.youtube.com/watch?v=HZtXLhm7ISA)     **Releasing energy by respiration**  All living organisms need energy, in the form of chemical energy, in order to move, to send nerve messages, to build large molecules and to release heat. We get the chemical energy we need from the food we eat.   The food is converted into usable energy by a series of chemical reactions called **cellular respiration.**  It is important to understand that cellular respiration does not mean the same thing as breathing.   The inhaled air contains about 20% oxygen and around 0.04% carbon dioxide.   The exhaled air contains only about 16% oxygen but around 4% carbon dioxide.  The 'missing' oxygen is used up inside our cells to release energy and carbon dioxide in the process of respiration.  All living cells respire continuously in order to produce the energy they need to carry out metabolic processes. When they use oxygen in the process, it is called aerobic respiration.  **Aerobic respiration**  Aerobic respiration is the release of fairly large amounts of energy using oxygen to break down digested food. It involves many different chemical reactions which are all **catalysed** and controlled by **enzymes**.   Aerobic respiration can be summed up in words like this:  Glucose + Oxygen energy + Carbon Dioxide + Water   We can also represent this reaction as a balanced chemical equation:   C~6~H~12~O~6~ + 60~2~ energy + 6CO₂ + 6H₂O    Glucose and oxygen are the raw materials for aerobic respiration. Energy (approximately 16 kJ/g of glucose), carbon dioxide and water are the products of aerobic respiration. The energy released in the process is used by cells. The  carbon dioxide and water are expelled as wastes. Aerobic respiration releases the maximum amount of energy from the glucose because the molecule is completely broken down in the process.  The reactions that take place in aerobic respiration occur in the mitochondria of cells. Cells that need large amounts of energy, such as muscle cells and nerve cells, have many mitochondria. Cells that do not need a lot of energy,  such as fat cells, have few mitochondria.    **ATP and energy release**  During respiration, energy is released slowly in small amounts. If energy was released quickly in cells, the sharp rise in temperature would kill the cells. As glucose breaks down, the energy that is released is used to convert  a substance known as ADP (adenosine diphosphate) into energy-carrying molecules of ATP (adenosine triphosphate). Each molecule of glucose that is broken down produces about 38 molecules of ATP. ATP is the chemical that carries energy to the parts of the body that need it.  ATP is sometimes called the energy currency of cells. This makes sense if you think of your cells as a 'bank' that stores energy in the form of ATP (the currency). The cells 'earn' ATP by 'working' to convert glucose to energy.  They bank or store the products of these reactions, building up a positive balance of ATP. When you need a small amount of energy, you withdraw a small amount of ATP from the bank in the cells. When you need a larger  amount of energy, you withdraw more ATP from the bank in the cells. Using ATP as you need energy is more effi cient than producing large amounts of energy that gets wasted.    The energy that is released by ATP is used by your cells in different ways:  to synthesise (build) complex molecules, such as proteins, carbohydrates and lipids  for cell growth  to repair and maintain cells  in the process of active transport to move materials across cell membranes  to provide energy to specialised cells, such as nerve, muscle, sperm, liver and kidney cells.  Only about 40% of the energy stored in glucose is converted to ATP and stored. The rest is released as heat. The energy from respiration that is released in the form of heat is useful because it helps to keep our body temperature  constant at around 37 °C. This is the temperature at which our cells and enzymes function well.    **\ ** **Learning Intention**    - explain what is meant by 'gaseous exchange'  - understand the need for a continuous supply of oxygen and the removal of carbon dioxide and other waste products  **Gaseous exchange in humans**  The ability to exchange gases across a surface is a vital life process in both plants and animals.  Human cells need oxygen for cellular respiration. However, the cells cannot inhale oxygen directly from the air. They get the oxygen they need from the blood. This means that the oxygen has to be able to move across surfaces in our bodies to get from our lungs (where we inhale it), into our blood and into our cells. The carbon dioxide that is produced as a waste product in cellular respiration has to move across surfaces in the opposite direction: from the cells, into the blood and back into our lungs so we can exhale it.    **The importance of gaseous exchange**  The function of our respiratory system is to provide oxygen for cellular respiration and to remove the carbon dioxide that cells produce during the process. If cells do not get oxygen, they cannot respire and they will die fairly quickly. If the carbon dioxide is not removed, it combines with water in the blood to form carbonic acid. This acid lowers the pH of the blood and disturbs the delicate balance inside cells.    **Breathing and gaseous exchange**  Breathing is a mechanical process that involves inhaling air, which  contains oxygen, into the lungs and exhaling air that contains carbon  dioxide. Breathing allows gaseous exchange to take place across the  respiratory surfaces in the lungs.  Gaseous exchange is the exchange of gases across a respiratory surface. This takes place in the lungs where oxygen and carbon dioxide are exchanged between the alveoli of the lungs and the  blood. Gaseous exchange also takes place between the blood and the cells.      ***These processes are illustrated in the figure below***     **The Human Respiratory System**  The respiratory system in humans (and other mammals) consists of:  air passages, which allow air to move in to and out of the lungs  a pair of lungs, which provides a gaseous exchange surface  breathing muscles, which move the chest and allow air to enter and exit the lungs.    Breathing is involuntary and controlled by our brain. The brain controls the  rate at which we breathe and also the depth of breathing.   ***The figure below shows the Human Respiratory System.***  Nose Mouth Epiglo Trachea (windpipe) Bronchi Diaphragm Muscles between the ribs Ribs Lung Heart Thorax Air sacs (alveoli) Abdomen     ***The respiratory system at work***  Our upper respiratory tract, or air passage, consists of a tube from the nostrils and mouth to the lungs. The air passage is lined with a mucous membrane made up of ciliated columnar epithelial cells. The mucus that covers the membrane is produced by goblet cells in the membrane. Rows of fi ne hairlike structures called cilia, move backwards and forwards to sweep the mucus. The mucus is very important because it traps bacteria, viruses and dust and prevents them from getting into our lungs. The mucus membrane also helps to keep air moist and warm so that dry air does not enter and harm our lungs.  ***This figure is a representation of the mucus membrane showing the different types of cell found there.***     Air enters our respiratory tract through our nose and then passes through the throat and larynx (voice box) to our trachea (windpipe). The trachea divides into two branches called bronchi which lead into our lungs. The trachea and bronchi are kept open by C-shaped rings of cartilage.  In the lungs, each bronchus branches many times into small tubes called bronchioles. These form a network called the bronchial tree. The bronchioles divide and sub-divide into even smaller tubes which end in clusters of small sacs called alveoli.  The walls of the alveoli are very thin and they are surrounded by capillary blood vessels. The alveoli enlarge the surface area for gaseous exchange (in almost the same way as the villi enlarge the surface area of the small intestine). There are millions of alveoli in our lungs with a combined surface area of approximately 90 square metres -- almost the area of a tennis court!  Gases are exchanged between the air and the blood inside the alveoli. Oxygen passes through the walls of the alveoli into the blood in the capillaries. Some of the oxygen dissolves in the blood, but most of it combines with haemoglobin to be transported to the cells of the body. At the same time as  oxygen passes into the blood, carbon dioxide leaves the blood so that it can  be exhaled from the lungs.  ***The figure below shows you how gases are exchanged in the alveoli.***    ** **  **\ ** **Learning Intention**  - describe and explain the importance of breathing in humans  - draw and label simple diagrams of the human respiratory system      Breathing relies on movements in the chest cavity. The process of breathing has three phases:  - inhalation (breathing in or inspiration) where air flows into the lungs  - a short resting period  - exhalation (breathing out or expiration) where air is moved out of the lungs.  **Inhalation**  ***The figure below shows you what happens inside your chest when you inhale.***  Thoracic cavity: volume Increases; air pressure decreases Backbone Trachea (windpipe) The rib cage is raised The diaphragm flattens   The thorax or chest cavity is a cage formed by your ribs and your diaphragm.   It is elastic.   The diaphragm is a dome-shaped plate of muscle that stretches across the chest cavity.   When you inhale, the diaphragm contracts and flattens.   The intercostal muscles between the ribs also contract, lifting the ribs upwards and outwards.    These movements increase the volume of the thorax.   This causes the air pressure inside the lungs to decrease so that it is lower than the pressure of the air in the atmosphere.   Air therefore is drawn down the trachea into the lungs.   The lungs enlarge like balloons to contain the inhaled.      ***Exhalation***  The figure below shows what happens in your chest when you exhale.    When you exhale, the diaphragm relaxes and returns to its resting position.  The intercostal muscles also relax and the ribs return to their original positions.   The volume in the chest cavity is reduced.   As a result, the air pressure in the lungs increases and the air is forced out of the lungs through the trachea.      Plants and animals contain many different types of tissue.    **Key fact**  Fat cells can expand to 1000 times their normal size when they fill with fat.      **Plant tissue**  Plant tissue is made up of cells that have the same function and structure.    **The table below gives some examples of plant tissue, where each type is found and what it does. **     Epidermal tissue e.g. guard cells of stoma Packing tissue e.g. parenchyma cell of cortex Photosynthetic tissue e.g. palisade cell of leaf Phloem Xylem Transport tissue Figure 7.2.5 Different types of tissue are made up of groups of cells such as these   **Animal tissue**  Animal tissue can be grouped into epithelial tissue, muscle tissue, connective  tissue and nerve tissue. Each of these larger groups contains several subgroups  of tissue types.   **The table below shows the main groups of tissue and gives**  **examples of tissue found in each group**      **Revision Questions**    1. Copy and complete the following sentences:  a Bone is a type of\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_  b Tendons and ligaments are examples of\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_  c The heart is made of\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_  d \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_is the only tissue that is in a liquid form.  e \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_tissue forms a protective layer round your liver and other organs.    2. Name the main group to which each of these animal tissue types belongs:  **Learning Intention**    - explain the processes of diffusion and osmosis  - discuss the importance of diffusion, osmosis and active transport  in living systems.    Movement of substances through cells. Cells need a supply of water and other substances that dissolve in water so that they can stay alive. Cells also need to get rid of waste products. Dissolved substances move in to and out of cells across the cell membrane through the processes of diffusion and osmosis.  **Diffusion**  If you walk past the kitchen when someone is cooking you can usually smell the food from some distance away. This shows that smells spread through the air. Smells can also spread in water. Sharks, for example, can smell blood in the water from some distance away. We can smell food cooking and sharks can smell blood because of diffusion.  The molecules or particles of gas and liquid move around at random. The natural tendency of these particles is to move from where they are highly concentrated (close together) to where they are less concentrated (more spread out). The result is a movement of molecules of a substance along a concentration gradient from where the substance is highly concentrated to where it is in low concentration. This movement of particles through a gas (like air) or through a solution (when they are dissolved in liquid) is called diffusion.    The table below gives some examples of diffusion in living organisms    Diffusion takes place in the cells of all living organisms  The figure above is a simplified version of diffusion. It shows how diffusion allows substances like oxygen and food to get in to our cells and waste products like carbon dioxide and other chemicals to get out of our cells.  Diffusion is a passive process. It does not require added energy. Diffusion will continue until the molecules of the substance are evenly distributed through the gas or liquid.    **Osmosis**  The most important function of the cell membrane is that it allows water and nutrients to pass in and out of cells. The cell membrane is partially permeable. This means that some substances can pass through it, but others can't. The membrane has small pores (openings) in it that allow the movement of substances. In general, substances pass through a membrane if their particles are smaller than the pores in the membrane.     Water is one of the important substances that can move through cell membranes. When two solutions are separated by a partially permeable membrane, water passes through the membrane in both directions. The net fl ow of water is from the more diluted solution, which has a high concentration of water molecules, to the more concentrated solution, which has a lower concentration of water molecules. Water will continue to move through the membrane until the two concentrations are equal. The movement of water molecules from a more dilute solution to a more concentrated solution through a partially permeable membrane is called osmosis. You can think of osmosis as a special type of diffusion, in which only water molecules move from one area to another. You are now going to do some experiments on osmosis.    **Osmosis in plant cells**  Osmosis is the way that plants take up the water they need to stay alive. The cell membrane of the plant is a partially permeable membrane and allows the movement of water molecules into the cell.  **Turgidity**  Osmosis takes place across the cell membrane that separates solutions inside the cell from solutions outside the cell. The changes that happen inside plant cells as a result of osmosis cause visible changes in the plant.  When plant cells are placed in a solution that is less concentrated than the solution inside them, water passes through the cell wall and cell membrane, through the cytoplasm and into the vacuole. The cell fills with water and become turgid. See the figure below.     The diagram  above shows that water flows from the less concentrated solution outside the cell, through the cell wall and cell membrane into the cytoplasm and into the vacuole. The increased pressure in the vacuole is called turgor pressure and it causes the cytoplasm to press up against the cell wall. When the cell contains as much water as it can hold, it is said to be fully **turgid. **Turgid cells do not burst because the cell wall is strong enough to withstand the turgor pressure. Turgidity is important in plants because the turgid cells allow the plant to stay upright and gives it support. When cells lose water they become flaccid.       **Plasmolysis**  If plant cells are placed in a solution that is more concentrated than the solution inside them, then water passes out of the cells by osmosis. Water passes out of the vacuole, out of the cytoplasm, out through the cell membrane and cell wall and into the solution outside the cell. The pressure of the vacuole on the cytoplasm decreases until the cytoplasm pulls away from the cell wall, causing the cell to become flaccid. Cells in this condition are said to be plasmolysed.       **Osmosis in animal cells**    If animal cells are placed in a solution that is less concentrated than the solution inside them, water moves into the cells by osmosis and they swell up. If too much water flows into the cells they may burst because they have no cell walls.  When animal cells are placed in a solution that is more concentrated than the solution inside them, water fl ows out of the cells as a result of osmosis. This causes the cells to shrink.  For animals is it very important to maintain an osmotic balance between cells and body fluids. Maintaining this balance is called osmoregulation.    **Active transport**  Sometimes substances move across the cell membrane and other cell membranes from a region where they are present in low concentration to  a region where they are present in high concentration. That is, they move against a concentration gradient in the reverse direction to normal diffusion.  Such movement is called active transport. It allows cells to build up stores of substances which otherwise would be spread out by diffusion. Active transport is an active process, which means that it requires energy, unlike diffusion which is a passive process and does not require energy.    **Revision Questions**    1. Charles was walking through shallow water when he cut his foot on a shell.  A Explain, with reference to diffusion, why the cut looked much more serious in the water than it would       have looked if he had cut his foot on a shell while walking across the sand.  B Explain, with reference to diffusion, how sharks are able to smell blood in water.  2. Explain, giving an example, why diffusion is important in living cells.  3. Define 'osmosis'.  4. Explain, with reference to osmosis, why the following advice is sound:  a To make limp salad leaves crisp, you can soak them in cold water for an hour.  b To preserve fruit, you can cover it with a concentrated sugar solution.  c When you add fertilizer to pot plants, read the instructions carefully.      Too much fertilizer is as bad as too little fertilizer.  5. Explain why dehydration is dangerous and potentially fatal in humans.  6. Explain, with reference to their structure, why animal cells are more likely than plant cells to burst if too much water flows into them.  **Learning Intention**    - distinguish between autotrophic, heterotrophic and saprophytic nutrition  - compare the substances used by plants to make food with the substances used by animals to make food.    **Autotrophic and Heterotrophic nutrition**    Organisms can generally be placed into two main groups depending on how they obtain their nutrients:    **Autotrophs **are organisms that essentially make their own food. In autotrophic nutrition, organisms use **simple inorganic substances** from the **air and soil (such as carbon dioxide and water)** to build the **organic**  **molecules (such as glucose) **they need. **All green plants are autotrophs. **Plants use energy from sunlight for this process (photosynthesis). **Some bacteria are autotrophic. They use carbon dioxide and energy from the oxidation of substances such as iron, ammonia and nitrites to synthesize carbohydrates**. Autotrophic **bacteria are important in processes such as nitrogen fixation. Chemoautotrophs such as ***Desulfovibrio** **desulficans*** reduces sulphates in waterlogged soils and sewage to hydrogen sulphide, a gas with the rotten egg odour so common to such places.  Sulphur oxidising bacteria use various forms of available sulfur (S^−2^, S^0^, S~2~O~3~^−2^) in the presence of oxygen. They are the predominant population in the majority of hydrothermal vents because their source of energy is widely available, and chemosynthesis rates increase in aerobic conditions.(Producers in their food chain/ecosystem)**    **Heterotrophs **are organisms that cannot make their own food. In heterotrophic nutrition, the organism takes in complex organic substances which are generally made by plants (this is why plants are called the producers in any ecosystem). **Heterotrophs break down, or digest, the complex organic substances to produce the food substances they need.** Animals are heterotrophs which feed on plants and/or other animals. Fungi, some bacteria and some protoctists also rely on heterotrophic nutrition to meet their energy and nutrient needs.    **Saphrotrophs and Saphrophytic Nutrition**  Fungi and other **decomposers and detritivores **are heterotrophic but they do not obtain nutrients by eating other organisms. Instead, they obtain nutrients by **breaking down complex organic material from the dead and decaying remains of other organisms** in the process of **saprophytic nutrition**.  **As saprotrophs feed, they release vital chemical elements into the soil. These elements, in turn, are absorbed by autotrophs. **   **Bracket fungus shown in the picture below is an example of a fungus carrying out Saprophytic nutrition.**  It is growing on the bark of a dead decaying tree.    **The picture below shows an insectivorous plant. It grows in nitrogen deficient soils. It feeds by secreting an enzyme on the fly that it traps.**  The soluble nutrients especially proteins are absorb into the plant.    **Revision Questions**    1. For each of the following organisms, state the type of nutrition it relies on and identify **two** possible sources of its nutrients.  a A mushroom        e An aphid  b A palm tree        f A mosquito  c A horse               g Yeast (a single-celled fungus)  d A human being  2. In which ways are saprotrophs different from parasites?  3. How are predators different from parasites?        **Learning Intention**    - describe photosynthesis and give a generalized equation for the process  - outline the main stages in photosynthesis and where they occur  - state what happens to the products of photosynthesis    **Photosynthesis**  Feeding, or nutrition, in plants involves taking in the substances that the plants need to survive. Green plants can take in **simple inorganic substances** and use them to make **more complex carbohydrates(then used to make proteins, oils and other complex molecules)**. Animals get their **food and energy indirectly by eating plants **or by eating other animals that have eaten plants.    **The process of photosynthesis**  Photosynthesis is the process by which plants use energy from sunlight to change the simple inorganic substances of **water and carbon dioxide** into food. Plants take in **water** through their **roots. **The water is transported up the  plant to the leaves. Plants take in carbon dioxide gas (CO2) from the air. The carbon dioxide enters the leaves through microscopic pores called **stomata**. **Chlorophyll** (in the chloroplasts of cells) in the **leaves **absorbs radiant energy  from the Sun. The leaf cells use this energy to change carbon dioxide and water into glucose (a simple sugar). **Oxygen** is released by **diffusion **as a waste product during the process and returned to the air through the stomata in the leaves.  **The figure below is a simplified diagram that shows what happens during the process of photosynthesis.**  **Photosynthesis is a complicated process, but is can be summarised using the following equation:**                                             **  Sunlight**   Carbon dioxide + water \-\-\-\-\-\-\-\--\> glucose + oxygen                                       **Chlorophyll**  The arrow in the equation means 'changes to'. **Light energy** and **chlorophyll **are written above the arrow because they are necessary for the process to take place. The chemical equation for photosynthesis equation looks like this:  ** **  **The main stages in photosynthesis**  Photosynthesis takes place **continuously **in plants, but we can think of it as a process that happens in **two stages**. The products of the first stage become the raw materials for the second stage. Sunlight is necessary for the first stage, so  this is called the** light stage.** The second stage uses carbon dioxide and it can take place in the dark, so it is called the **dark stage.**    **The light stage**  In this stage, the chlorophyll in the leaves converts **sunlight **(light energy) into **chemical energy.** Some of the light energy is used to **split water molecules (H2O) into hydrogen (H) and oxygen (O2).** This process is called the evolution of **oxygen**. This process is called **photolysis.**    **The dark stage**  The** hydrogen **released (from water molecules) in the light stage **combines **with **carbon dioxide** to form **glucose** (a sugar). This process is called the **reduction of carbon dioxide**. The process requires some of the energy that was absorbed during the light stage but it does not require sunlight.    **What happens to the products of photosynthesis?**  Most photosynthesis takes place in the leaves of plants. However all parts of the plant need food, so the glucose needs to be transported to other parts. This is done through the phloem tubes.  Glucose can also be converted to starch and stored in different parts of the plant.  **The figure below shows how plants use the glucose made during photosynthesis.**  Oxygen is also produced during photosynthesis. This is released into the atmosphere through the stomata of the leaves.    **Revision Questions**    1. The figure below shows a leaf from a green plant where photosynthesis takes place.  ** (Introduction for Labs)**    a Identify the products of photosynthesis represented by C and D.  b Name the inorganic substances needed for photosynthesis.  c Where does the plant get substance B?  d What happens to substance A during photosynthesis? Show this using an equation.    2. State two ways in which plants use the glucose produced during photosynthesis.    3.  Explain why photosynthesis is important for animals as well as plants  - identify the environmental conditions that affect the rate of transpiration  - carry out an investigation to demonstrate how light, humidity and air movement affect transpiration rates.    **Factors affecting Transpiration**  Plants need to maintain their water balance. If the water that is lost through transpiration is not balanced by the uptake of water from the soil then the stomata on the leaves close to reduce the rate of transpiration. If the plant still does not get enough water from the soil, then the cells begin to lose turgor and the plant wilts.     Normally stomata are open during the day, so that gases can be exchanged during photosynthesis, and almost closed at night. So more transpiration takes place during the day. However, various environmental factors also  affect the rate of transpiration.    **External factors that affect transpiration**  Transpiration is a term which describes how water is returned to the atmosphere to form part of the water cycle, by evaporation from land and water surfaces and from plants by transpiration. The rate at which water evaporates from plants is affected by the conditions in the environment.     Transpiration is affected by:  temperature  humidity  wind velocity  light intensity  water content of the soil.    **Temperature**  When the temperature rises, the relative humidity of the air around the plant is lowered. Relative humidity is a measure of how much  water vapour the air contains expressed as a percentage of how much it could hold. So, for example if the relative humidity is 80%, then the air contains 80% of the total water vapour it could hold. Warm air is less dense that cold air, so it can hold more water vapour. This is what causes the drop in relative humidity when the temperature increases. At the same time, higher temperatures increase the rate of evaporation from the plant's leaves and water vapour diffuses more quickly from the leaves to the air.    **Humidity**  Diffusion takes places from areas of high concentration to a lower concentration. So, when the humidity in the air is low, water vapour from moist leaves diffuses more quickly into the air. Similarly, when the  humidity is high, less transpiration takes place because there is less of a diffusion gradient between the water content of the air and the water content  of the leaves.   **Wind speed**  When the air is still, the water vapour that diffuses out of a plant's leaves builds up around the leaves, creating a humid environment that does not favour transpiration. When the wind blows, the moist air is blown away  from the plant and the rate of transpiration increases. When it is very windy, plants may close their stomata to prevent too much transpiration taking place.     **Light intensity**  Light does not affect the rate of transpiration directly, but it does affect the opening and closing of the stomata, which in turn affect how much transpiration can take place. Transpiration is more rapid in bright sunlight because the stomata are fully open.    **Water content of the soil**  The amount of water in the soil affects the rate at which water can be taken up by the plant. If the soil dries out so that roots cannot take in water, the rate of transpiration in the plant slows down. The plant closes its stomata to stop transpiration. In conditions where the ground remains dry, the plant will eventually wilt and die.      - describe the processes involved in transpiration  -  explain what is meant by the 'transpiration stream'  - follow the transpiration stream from roots to leaves.    **Transpiration**  The movement of water through the xylem of plants depends on transpiration. Transpiration is the evaporation of water from the leaves of plants to the air. As water is lost from the leaves of the plant more water is pulled upwards through the xylem vessels. In this topic you are going to learn more about this process.  **Water movements in plants**  Water enters the plant through the root hairs by osmosis. The water moves  across the root cortex by osmosis and passes into the xylem vessels.     **Path taken by water from the soil through the roots to the xylem.**   Once in the xylem vessels, water forms unbroken columns from the roots, through the stem and into the leaves. Water evaporates from the leaves, mainly through the stomata (tiny pores) on the underside of the leaf by transpiration.  **The transpiration stream**  The water that is lost through transpiration from the plant has to be replaced by water taken in through the roots, otherwise the plant will wilt and die. The constant upward flow of water through a plant is known as the transpiration  stream.  The water that evaporates from the leaves during transpiration gets the transpiration stream going. This is called the **transpiration pull**. Water is drawn up the xylem vessels to replace the water that is lost. Xylem vessels are well suited to the process because they are very** narrow **and they act as** capillaries **for the water. The forces of attraction between water molecules** (cohesion)**  and the attraction between water molecules and the wall of the xylem vessels **(adhesion)** create enough to help to move water upwards.       **This action is known as capillarity.**  As water is sucked up through the xylem in the stem, more water is supplied to the bottom of the xylem vessels by the roots. This water increases the pressure in the root xylem. The **higher root pressure **pushes the water up the xylem to the areas of lower pressure created as water is lost. In this way, there is a continuous flow of water from the roots to the leaves.  The force that drives the transpiration stream is equivalent to as much as 30 atmospheres pressure -- strong enough to move water from the roots to the very top of the tallest tree.    **Revision Questions**  1. Define the terms:  a\. transpiration  b\. transpiration stream  c\. transpiration pull  d\. root pressure  e\. capillarity.  2.  Describe how water moves from the soil, through the roots and up to the leaves of plants. Use the correct biological vocabulary in your description.  3.  Explain why it is a bad idea to plant out young seedlings on a bright, windy day.  4.  How is it possible for water to reach the topmost branches of very tall trees?    - explain the importance of a transport system in plants  - identify the two main transport structures: xylem and phloem  - describe the structure of xylem vessels  - draw and label xylem vessels  - explain how the structure of xylem vessels suits their function  - observe water movement through the xylem.    **Transport structures**  Plant leaves are able to get the carbon dioxide they need for photosynthesis directly from the air by diffusion. They get the oxygen they need for respiration in the same way. However, for the plant to survive, cells in different parts of  the plant need to be supplied with the water and nutrients. Plants therefore have a transport system to allow for the movement of water from the roots to the leaves and other parts of the plant and for the movement of food made  in the leaves to other parts of the plant.  Uptake ot water in xylem Transport ot food in phloem dioxide Water and minerals from the soil Water and minerals taken by roots Sunlight Sugar made by photosynthesis Sugar moves down to growing root or up to growing bud   **The transport system of plants**  The transport system in plants consists of a network of very fi ne tubes made of specialised tissue known as xylem and phloem. Xylem vessels transport water and phloem tubes transport food. You can see a simplified version of  how this transport system works in the figure below  You will learn more about the structure and functions of phloem tubes in topic B14.4 which deals with the movement of food through plants. Now you will focus only on xylem vessels because they play an important role in water relations in plants.  **Xylem**  Xylem transports water and mineral ions upwards from the roots to the leaves of plants. Xylem tubes or vessels are made from dead cells thickened with woody material called lignin. Lignin strengthens the cells walls and  helps to make xylem vessels waterproof. The xylem cells join end to end and their cross walls break down to form long continuous hollow vessels through which water can pass freely. The strong walls of these non-living tubes also  help to give support, rigidity and strength to the stems of plants.   The diagrams that xylem vessels shows how they are well suited for transporting water. They are long, thin, hollow and waterproof so that water can move freely upwards through them. Them are like very thin drinking straws that the plant uses to suck water upwards from the roots to the leaves.    **Revision Questions**  1.  List two differences between the transport system in humans and the transport system in plants.  2.  Explain what is meant by the term 'vascular bundle'.  3.  Draw and label a section through a xylem vessel to show its structure.  **Learning Intentions**    - Explain what is meant by 'symbiosis'  - Define the terms 'commensalism', 'mutualism', 'predation' and 'parasitism'  - Identify symbiotic relationships between organisms  - Examine symbiotic relationships between organisms  - State the advantages and disadvantages of special feeding relationships for organisms involved    The relationship between different organisms that depend on each other in some way is called symbiosis. There are three types of symbiosis: commensalism, mutualism and parasitism.    **Beneficial relationships**  When organisms interact in ways that benefit and do not harm the organisms involved, the relationship is beneficial. Commensalism and mutualism are beneficial relationships.  **Commensalism**  When species interact in a way that benefits one species but is neutral or does not harm the other, it is called commensalism. In commensalism, the species are not dependent on each other for survival, that is they can survive without each other.  **Epiphytes **are orchids or ferns that grow on trees. The relationship between the epiphyte and the tree is an example of commensalism. You can see an epiphyte on a tree.  The epiphytes are supported by the tree but they do not obtain food from the tree. They also do not harm the tree in any way. Both the tree and the epiphyte can survive without the other.    **Adult barnacles are sea organisms **that cannot move by themselves to find food. They attach themselves to the skin of whales or the shells of large sea molluscs. As the larger animal moves, the barnacles are able to get food from rich sea-currents. The whales and molluscs do not benefit from the relationship but the barnacles do not seem to harm them either. Both species can survive without the other. This is another example of **commensalism.**  **The relationship between cattle egrets and grazing animals is commensal/mutualism.**  The birds sit on the backs of the cattle and feed on insects that are disturbed as the cattle move through the grass. The cattle do not benefit from this relationship but they are not harmed by the birds either. Both species can survive without the other.  **Mutualism**  If two species both benefit from a relationship it is called mutualism.  Mutualism is more common than commensalism.           Three examples of mutualism in an aquatic environment above.    **Further examples of mutualism are:**   **Lichen** is an association between an alga and a fungus. The cells of the algae are found among the strands that make up the fungus. In this relationship, the fungus benefits because the green cells in the  alga allow it to provide food by photosynthesis. The alga benefits  from the moist environment provided by the fungus.   **Nitrogen-fixing bacteri**a live in nodules (small lumps) on the roots of plants called legumes (beans and peas). The bacteria are able to absorb nitrogen from the air and convert it into a form that plants can use to make proteins. The bacteria benefit by getting sugars from the plant's roots.   **Ants and aphids **have a mutualistic relationship. The aphids live among ants. The ants feed on the sugary liquid produced by the aphids. The aphids are protected from other predators by the ants.   **Termites **eat wood and other cellulose material but they cannot digest it themselves. The termites have a mutualistic relationship with **protozoa **in their guts. The protozoa digest the cellulose and have a safe environment to live in whilst the termite gets food.    **Detrimental relationships**  In detrimental relationships, organisms interact in ways that benefit one species but harm the other. Parasitism is an example of a feeding relationship that is detrimental.  **Parasitism**  In parasitism one species (the parasite) gets its food from another species (the host). For example, lice are parasites that feed on human blood. **Ticks** (ectoparasite) are parasites that feed on the blood of animals (and sometimes people).  **Tapeworms(endoparasites)**, **bilharzia** and **malaria **parasites get into the bodies of animals or humans and feed off their nutrients.   Plants can also be parasitic. **Dodder** is a twisting plant that winds itself round other plants. It sends small suckers into the other plant to feed. **Dodder** often kills the host plant and spreads to another plant.      **Revision Questions **  1. What would you call the following symbiotic relationships?   Give a reason for each answer:  a An oxpecker bird feeds on ticks and other parasites on animals such as cows and buffaloes.  b Honeybees feed on nectar from flowers.   c An adult wasp lays its eggs inside the body of a caterpillar. When the larvae hatch, they eat the caterpillar from the inside.  d Sea anemones sometimes grow on the shells of hermit crabs    2. Find examples of relationships between bacteria and other organisms. Name the partners in the relationship, say what type of relationship each one is, and identify any advantages or disadvantages for the organisms in the relationship    **Learning Intentions**    - Explain how energy flows through producers in ecosystems  - Explain how energy flows through consumers at different feeding levels  - Show where energy is lost to the environment.      **Energy flow through producers**  The energy in ecosystems comes from sunlight. Green plants, algae and  some bacteria absorb sunlight and use its energy to convert carbon dioxide  and water into sugars in the process called photosynthesis. This is why food  chains and food webs all begin with producers (plants, algae or bacteria).  Plants do not absorb much of the sunlight that reaches them. The figure below  shows you why they absorb so little sunlight.        Plants need energy to stay alive. They get this energy from the sugars they  makes during photosynthesis. Some of the energy is used to keep the process  of photosynthesis going. However some of the energy is released in the  process of respiration. Plants use the rest of the energy to grow and live. This is the energy that is available to consumers as food. When a primary consumer eats a plant, energy is transferred to the primary consumer. This energy is transferred indirectly to consumers at higher trophic levels when they feed on the primary consumer.  Energy is also transferred from the plant when fruits and seeds are dispersed.  When the plant dies or loses its leaves, energy is transferred to decomposers in the ecosystem.    **Energy flow through consumers**  Only about 10% of available energy is transferred from one trophic level to the level above it. This means that 90% of the energy available at each level is lost to the environment. Why is the transfer of energy from level to level so wasteful? It is because:    Some plant material is not digested by primary consumers (herbivores).    This passes out of their bodies as faeces.  Some of the plant energy is used by the primary and secondary consumers to stay alive.   When the consumers die, their bodies contain stored energy and some of this is transferred to decomposers.  The figure below shows the energy flow through a primary consumer (a cow).  From the diagram more than half of the energy that the cow gets from the grass is transferred to the environment by its urine and faeces.  Energy is also transferred to the environment from the cow's body in the form of heat produced by respiration.      The figure below shows you the energy flow and energy loss for a whole ecosystem.      In a long food chain, energy is lost at each trophic level. This means that there is less and less energy available for higher level carnivores at the top of the food chain. A short food chain is far more energy efficient. For example, when humans eat plants directly, less energy is lost than when we feed plants to animals and then eat the animals. A short food chain can thus support more people than a long one with many feeding levels.      **Revision Questions**    1 Why do food chains begin with the Sun?  2 Why is the first organism in food chains a producer?  3 The graph in the figure below shows you how much energy (in kilojoules) is absorbed by different organisms in a food chain.    a What percentage of energy is passed on through each trophic level in this food chain?  b Give an example of a primary consumer in this system.  c What happens to the energy that is 'lost' at each level?  d If an eagle entered this food chain as a tertiary consumer, how much energy would it get from its food source?  **Characteristics of Living Organisms**    - **Movement**: an action by an organism or part of an organism causing a change of position or place  - **Respiration**: the chemical reactions that break down nutrient molecules in living cells to release energy for metabolism  - **Sensitivity:** the ability to detect or sense stimuli in the internal or external environment and to make appropriate responses  - **Growth**: a permanent increase in size and dry mass by an increase in cell number or cell size or both  - **Reproduction**: the processes that make more of the same kind of organism  - **Excretion**: the removal from organisms of toxic materials, the waste products of metabolism (chemical reactions in cells including respiration) and substances in excess of requirements  - **Nutrition**: the taking in of materials for energy, growth and development; plants require light, carbon dioxide, water and ions; animals need organic compounds, ions and usually need water    **MRS. GREN**  - Movement  - Respiration  - Sensitivity  - Growth and development  - Reproduction  - Excretion  - Nutrition  **How Organisms are Classified**    - There are millions of species of organisms on Earth  - A **species** is defined as a group of organisms that can reproduce to produce fertile offspring  - These species can be classified into groups by the features that they share e.g. all mammals have bodies covered in hair, feed young from mammary glands and have external ears (pinnas)    **The Binomial System**    - Organisms were first classified by a Swedish naturalist called **Linnaeus** in a way that allows the subdivision of living organisms into smaller and more specialised groups  - The species in these groups have more and more features in common the more subdivided they get  - He named organisms in Latin using the binomial system where the scientific name of an organism is made up of two parts starting with the genus (always given a capital letter) and followed by the species (starting with a lower case letter)  - When typed binomial names are always in italics (which indicates they are Latin) e.g. ***Homo sapiens***  - The sequence of classification is: **Kingdom, Phylum, Class, Order, Family, Genus, Species**        **Learning Intention: **    To classify organisms based their phylogenetic ancestry.  To examine organism and identify the groups they belong to base on characteristics        - The first division of living things in the classification system is to put them into one of five kingdoms. They are:  - Animals  - Plants  - Fungi  - Protoctists  - Prokaryotes      **A TYPICAL ANIMAL CELL**    - Main features of all animals:  - they are multicellular  - their cells contain a nucleus but no cell walls or chloroplasts  - they feed on organic substances made by other living things              ** A TYPICAL PLANT CELL**    - Main features of all plants:  - they are multicellular  - their cells contain a nucleus, chloroplasts and cellulose cell walls  - they all feed by photosynthesis            **The Animal Kingdom**      - Several main features are used to place organisms into groups within the animal kingdom  ***Vertebrates** * - All vertebrates have a backbone  - There are 5 classes of vertebrates    **Vertebrate Table**    \* * \* * \* * **Invertebrates*** *   - Invertebrates do not possess a backbone  - One of the morphological characteristics used to classify invertebrates is whether they have legs or not  - All invertebrates with jointed legs are part of the phylum Arthropods  - They are classified further into the following classes:    Invertebrate Table               **Learning Intention:**    **Success Criteria:**         [Features of Organisms 1  ](https://www.youtube.com/watch?v=GJJAktyCrbE)      - The first division of living things in the classification system puts them into one of five kingdoms    - They are:  - Animals  - Plants  - Fungi  - Protoctists  - Prokaryotes    - Main features of all fungi (e.g. moulds, mushrooms, yeast)  - usually multicellular  - cells have nuclei and cell walls not made from cellulose  - do not photosynthesize but feed by saprophytic (on dead or decaying material) or parasitic (on live material) nutrition    *A typical fungal cell*  **Main features of all Protoctists** (e.g. Amoeba, Paramecium, Plasmodium)  - most are **unicellular** but some are **multicellular**  - all have a **nucleus**, some may have **cell walls** and **chloroplasts**  - meaning some protoctists photosynthesise and some feed on organic substances made by other living things  **                 Two examples of Protoctist cells**  **Main features of all Prokaryotes (bacteria, blue-green algae)**  - often unicellular  - cells have cell walls (not made of cellulose) and cytoplasm but no nucleus or mitochondria      **The Plant Kingdom: Extended**    - At least some parts of any plant are green, caused by the presence of the pigment chlorophyll which absorbs energy from sunlight for the process of photosynthesis  - The plant kingdom includes organisms such as ferns and flowering plants  \* Ferns * - Have leaves called fronds  - Do not produce flowers but instead reproduce by spores produced on the underside of fronds  -   *erns reproduce by spores found in the underside of their fronds*  *Flowering plants * - Reproduce sexually by means of flowers and seeds  - Seeds are produced inside the ovary found at the base of the flower  - Can be divided into two groups -- monocotyledons and dicotyledons  *Sunflowers are dicotyledons*  *How do you distinguish between monocotyledons and dicotyledons? * 1\) Flowers  - Flowers from monocotyledons contain petals in multiples of 3  - Flowers from dicotyledons contain petals in multiples of 4 or 5  2\) Leaves  - Leaves from monocotyledons have parallel leaf veins  - Leaves from dicotyledons have reticulated leaf veins (meaning that they are all interconnected and form a web-like network throughout the leaf)  -     Viruses  - Viruses are not part of any classification system as they are not considered living things  - They do not carry out the seven life processes for themselves, instead they take over a host cell's metabolic pathways in order to make multiple copies of themselves  - Virus structure is simply genetic material (RNA or DNA) inside a protein coat       **Energy Transfer in a Human Food Chain**  - Humans are **omnivores**, obtaining energy from both plants and animals, and this gives us a **choice of what we eat**  - These choices, however, have an **impact on what we grow** and how we use ecosystems  -   A diagram of a diagram of a snail and a frog Description automatically generated   - Think of the following food chains both involving humans:         wheat  →  cow   →   human         wheat  →   human  - Given what we know about **energy transfer in food chains**, it is clear that if humans eat the wheat there is **much more energy available** to them than if they eat the cows that eat the wheat  - This is because **energy is lost from the cows**, so there is less available to pass on to humans  -   -   - Therefore, it is **more energy efficient within a crop food chain for humans to be the herbivores rather than the carnivores**  - In reality, we often feed animals on plants that we cannot eat (eg grass) or that are too widely distributed for us to collect (eg algae in the ocean which form the food of fish we eat)  \]      **Human Pressures on Other Species**      ***Biodiversity** *   - Is defined as the number of different species that live in a particular area  - Human activities have tended to force biodiversity downwards, whereas, high biodiversity is needed for stable ecosystems  - Habitat destruction by humans is a major downward pressure on biodiversity    ***Reasons for Habitat Destruction** *   - The increasing human population of the planet is causing destruction of many habitats from rainforest to woodland to marine  - Many habitats are destroyed by humans to make space for other economic activities, or by pollution from these activities, and this reduces the biodiversity of these areas  - This interrupts food chains and webs, meaning that more species may die because their prey is gone  - The main reasons for habitat destruction include:       *** Deforestation** * - Deforestation is the clearing of trees (usually on a large scale)  - If trees are replaced by replanting it can be a sustainable practise.    - Generally the trees are being cleared for the land to be used in a different way (for building, grazing for cattle, planting of monocultures such as palm oil plantations etc) and therefore it is not sustainable  - As the amount of the Earth's surface covered by trees decreases, it causes increasingly negative effects on the environment and is a particularly severe example of habitat destruction    - Undesirable effects of deforestation include:  - Extinction of species  - Loss of soil  - Flooding  - Increase of carbon dioxide in the atmosphere        Biodiversity  - Is defined as the number of different species that live in a particular area  - Human activities have tended to force biodiversity downwards, whereas, high biodiversity is needed for stable ecosystems  - Habitat destruction by humans is a major downward pressure on biodiversity  *Reasons for Habitat Destruction * - The increasing human population of the planet is causing destruction of many habitats from rainforest to woodland to marine  - Many habitats are destroyed by humans to make space for other economic activities, or by pollution from these activities, and this reduces the biodiversity of these areas  - This interrupts food chains and webs, meaning that more species may die because their prey is gone  - The main reasons for habitat destruction include:  REASON CLEARING LAND FOR FARMING AND HOUSING EXTRACTION OF NATURAL RESOURCES MARINE POLLUTION EXPLANATION - CROPS, LIVESTOCK AND HOMES ALL TAKE UP A LARGE AMOUNT OF SPACE - AS THERE IS AN INCREASING POPULATION AND DEMAND FOR FOOD, THE AMOUNT OF LAND AVAILABLE FOR THESE THINGS MUST BE INCREASED BY CLEARING HABITATS SUCH AS FORESTS (DEFORESTATION) - NATURAL RESOURCES SUCH AS WOOD, STONE AND METALS MUST BE GATHERED TO MAKE DIFFERENT PRODUCTS. - THEREFORE MANY TREES ARE CUT DOWN, DESTROYING FOREST HABITATS. IN ADDITION, SOME RESOURCE EXTRACTION TAKES UP A LARGE AMOUNT OF SPACE - FOR EXAMPLE: MINING, WHICH MEANS THAT THE LAND MUST BE CLEARED FIRST - HUMAN ACTIVITIES LEAD TO THE POLLUTION OF MARINE HABITATS - IN MANY PLACES, OIL SPILLS AND OTHER WASTE POLLUTES THE OCEANS, KILLING SEA LIFE - IN ADDITION, EUTROPHICATION CAN OCCUR WHEN FERTILISERS FROM INTENSIVELY FARMED FIELDS ENTERS WATERWAYS - THIS CAUSES A HUGE DECREASE IN BIODIVERSITY IN THESE AREAS AS MOST AQUATIC SPECIES LIVING IN THESE WATERWAYS DIE FROM LACK OF OXYGEN *Deforestation * - Deforestation is the clearing of trees (usually on a large scale)  - If trees are replaced by replanting it can be a sustainable practise  - Generally the trees are being cleared for the land to be used in a different way (for building, grazing for cattle, planting of monocultures such as palm oil plantations etc) and therefore it is not sustainable  - As the amount of the Earth's surface covered by trees decreases, it causes increasingly negative effects on the environment and is a particularly severe example of habitat destruction  - Undesirable effects of deforestation include:  - Extinction of species  - Loss of soil  - Flooding  - Increase of carbon dioxide in the atmosphere    **Untreated Sewage & Excess Fertiliser**    - Human activities have led to the pollution of land, water and air  - Pollution comes from a variety of sources, including industry and manufacturing processes, waste and discarded rubbish, chemicals from farming practices, nuclear fall-out, and untreated sewage           **Eutrophication**    - Runoff of fertiliser from farmland enters the water and causes increased growth of algae and water plants  - The resulting 'algal bloom' blocks sunlight so water plants on the bottom start to die, as does the algae when competition for nutrients becomes too intense  - As water plants and algae die in greater numbers, decomposing bacteria increase in number and use up the dissolved oxygen whilst respiring aerobically  - As a result there is less oxygen dissolved in water, so aquatic organisms such as fish and insects may be unable to breathe and would die        - Plastics have a large negative impact on both land and water habitats due to their non-biodegradability  - In marine habitats:  - Animals often try to eat plastic or become caught in it, leading to injuries and death  - As the plastic breaks down it can release toxins that affect marine organisms  - Once it has broken down into very small particles, it is commonly ingested by animals and enters the food chain  - On land:  - Plastic is generally disposed of by burying in landfills  - As it breaks down, it releases toxins into the surrounding soil and as such the land is no good for growing crops or grazing animals and can only be used for building on several decades after burial    Air Pollution  *Acid Rain * - Combustion of fossil fuels that contain sulfur impurities creates sulfur dioxide  - This is released into the atmosphere where it combines with oxygen to form sulfur trioxide  - Sulfur trioxide dissolves in water droplets in clouds and forms acid rain    **Sustainable Use of Resources**    - We use many resources from the Earth; some, such as food, water and wood, are sustainable resources  - A sustainable resource is one which is produced as rapidly as it is removed from the environment so that it does not run out  - Some resources, such as fossil fuels (coal, oil and natural gas), are non-renewable because what we use cannot be replaced  - These resources, once used, cannot be produced anymore and so they need to be conserved by reducing the amount we use and finding other, sustainable resources to replace them  - Fossil fuels are being used as an energy source in increasing amounts  - In addition, they are the raw materials for many other products we make - eg almost all plastics that are made start with oil as a raw material  - Some products, especially those made from paper, plastic, glass or metal, can be reused and recycled - this reduces waste in the environment and reduces the amounts of raw materials and energy needed to make new products  - Some resources, such as forests and fish stocks, can be maintained - enabling us to harvest them sustainably so that they will not run out in the future    **Sustainable Production**  ** **  - Sustainable development is defined as development providing for the needs of an increasing human population without harming the environment  - When developing the way in which we use resources to manage them sustainably, we have to balance conflicting demands - eg:  - the need for local people to be able to utilise the resources they have in their immediate environment with the needs of large companies to make money from resources such as forests and fish  - the need for balancing the needs of humans for resources with the needs of the animals and plants that live in the areas the resources are taken from (preventing loss of habitat and extinction)  - the need to balance what current populations need with what future populations might need - for example if we harvest all the fish we need to feed people now, this might lead to overfishing which would deplete stocks for future generations  - For development to occur sustainably, people need to cooperate at local, national and international levels in the planning and management of resources    **Sustaining Forests*** *   - Forests are needed to produce paper products and provide wood for timber  - Much of the world's paper is now produced from forests which replant similar trees when mature trees are cut, ensuring that there will be adequate supply in the future  - Tropical hardwoods such as teak and mahogany take many years to regrow but are highly desirable for furniture  - Using these types of wood has now been made more sustainable due to the introduction of several schemes designed to monitor logging companies and track the wood produced (eg the Forestry Stewardship Council)  - Education helps to ensure logging companies are aware of sustainable practices and consumers are aware of the importance of buying products made from sustainable sources       *More efforts are being made to manage forests sustainably so consumers know they are not causing damage to forests*  **Sustaining Fish Stocks*** *   - Managing fish stocks sustainably includes:  - Controlling the number of fish caught each year (quotas)  - Controlling the size of fish caught (to ensure there are enough fish of a suitable age for breeding remaining)  - Controlling the time of year that certain fish can be caught (to prevent large scale depletion of stocks when fish come together in large numbers in certain areas to breed)  - Restocking (breeding and keeping offspring until they are large enough to survive in their natural habitat then releasing)  - Educating fishermen as to local and international laws and consumers so they are aware of types of fish which are not produced sustainably and can avoid them when buying fish        **Conservation for Endangered Species**        **Endangered Species*** * - An endangered species is at risk of becoming extinct  - There are several reasons why a species can become endangered - the population of the species may fall below a critical level due to  - hunting  - climate change  - pollution  - loss of habitat  - introduction of non-native species that outcompete native species  - Endangered species can be helped by conservation measures such as:  - education programmes  - captive breeding programmes  - monitoring and legal protection of the species and of their habitats  - seed banks as a conservation measure for plants - seeds of endangered plant species are carefully stored so that new plants may be grown in the future  - A species may be at risk of becoming extinct if there is not enough genetic variation in the population as random changes in the environment may quickly cause extinction because the remaining organisms are all very similar and may not have the adaptations to survive such changes  - There are moral, cultural and scientific reasons for conservation programmes, including:  - reducing extinction rates of both plant and animal species  - keeping damage to food chains and food webs to a minimum and protecting vulnerable ecosystems (eg the rainforests)  - protecting our future food supply and maintaining nutrient cycles and possible sources of future medical drugs and fuels    **Reasons for Conservation**  - There are numerous reasons why conservation programmes are important  - Maintaining or increasing biodiversity  - Which allows ecosystems to remain stable  - Reducing extinction  - Helps to retain iconic species and maintain biodiversity  - Protecting vulnerable ecosystems which would have been quickly lost to human activity  - Maintaining ecosystem functions  - Nutrient cycling eg. carbon cycling to hold back climate change  - Resource provision, such as  - Food - making sure we have enough for the population  - Drugs - having access to plants for plant-based remedies  - Fuel - for improtant activities such as cooking  - Genes - so the gene pool remains wide and variety exists in all species    **Conservation Techniques**  - Certain conservation techniques can be used to maintain biodiversity  - Examples include  Artificial insemination (AI) in captive breeding programmes  This allows large numbers of offspring to be produced without the need for conventional sexual intercourse between males and females   In vitro fertilisation (IVF) in captive breeding programmes \   This allows gametes with known alleles to be used in ensuring the next generation remains biodiverse  **Risks to a species**  If its population size decreases, a species will experience reduced genetic variation  This renders the species more susceptible to environmental change  The species is less resilient and has a greater risk of extinction      - Explain the role of decomposers  - Explain how matter is recycled in nature  - Illustrate the carbon cycle and the nitrogen cycle.    **Decomposition**  In a forested area there is a mass of dead and decaying leaves, flowers and other matter on the ground.  The dead matter in an ecosystem is called **detritus.** In a **terrestrial** **ecosystem**, most detritus is made up of fallen leaves and flowers, broken twigs and dead plants and animals.   In an **aquatic ecosystem,** most detritus is made of dead algae and plants, pieces of plants that get broken off and the remains and waste products of animals.   In all ecosystems, dead matter contains nutrients, so detritus is a source of food.     **What eats detritus?**  **Scavengers** such as rats and crows are animals that feed on detritus. Small scavengers like **earthworms, maggots, snails** and **insect larvae** are know **detritivores**.    **Detritivores** feed on dead and decaying matter and break it down into small particles. The small particles are then broken down by decomposers, such as bacteria and fungi.  Detritivores get some energy from the detritus, but they get most of their energy from the decomposers that live on the detritus.  **Decomposers **feed by secreting enzymes over their food.   The enzymes break down complex substances into simple, soluble substances such as glucose, carbon dioxide, water (hydrogen and oxygen) and nutrients such as sulfates and nitrates.   The decomposers release these substances into the soil as they feed. All of these nutrients can be absorbed by plants.    The figures below shows how nutrients are decomposed and recycled in ecosystems.      **Cycling nutrients**  **The carbon cycle**  Carbon is found in all living organisms. Plants obtain carbon during  **photosynthesis** from the carbon dioxide in the air. Animals get carbon from the food they eat. So plants need carbon dioxide and all other animals, including humans, need plants. This makes carbon dioxide very important in ecosystems.  **Plants take in carbon dioxide through their leaves and they take in water through their roots.** They use the carbon dioxide and water to synthesize (build) sugars.   This reaction is called photosynthesis.  Photosynthesis takes place in green leaves in the presence of sunlight. Oxygen is formed during photosynthesis.  **Animals eat plants**, which contain starches and sugars, which contain carbon.  Animals also breathe in air, which contains oxygen. The oxygen that animals breathe in dissolves in the blood supply to the lungs. In the cells, some of the oxygen that is dissolved in the blood oxidises sugars  to carbon dioxide and water. This process is called **respiration. **Plants  and other organisms respire to obtain energy. Carbon is therefore an essential element in food chains. However the atmosphere does not have an infinite supply of carbon, so carbon needs to be recycled. During respiration, carbon is released and it returns to the atmosphere. Animals also recycle carbon by e