CGP KS3 Science Higher Level Revision & Practice PDF

CGP Key Stage Three Science Higher Level Complete Revision & Practice Everything you need for the whole course!  CGP The best that money can buy......from the country’s leading producer of revision material. e revision book...

CGP Key Stage Three Science Higher Level Complete Revision & Practice Everything you need for the whole course!  CGP The best that money can buy......from the country’s leading producer of revision material. e revision books “CGP sell morelse than anyone.” “Over 90% ofpro all schools use ts as an CGP revision theiducr cou integral part of rses.” “CGP books vanare by far the most concise, rele siont, clear and informative revi re.” books you “Science is my best subj ect because will nd anywhe of CGP's brilliant books. Oh, and I like this static electricity thing.” Edward Garlick Year 9 Crumplington High School Rutland  P CG Key Stage Three Science Higher Level There’s a lot to learn in KS3 Science... it’s enough to steam up anyone’s safety goggles. Not to worry — this brilliant all-in-one CGP book will help you see through the mist. It’s packed with clear notes and diagrams that explain every topic, plus plenty of practice questions and mixed-topic tests to make sure you’ve understood everything. And once you’ve worked through that lot, there’s a practice exam at the end of the book to really put your Science knowledge to the test! Complete Revision & Practice Everything you need for the whole course!  Contents Section One — Cells and Respiration Section Four — Inheritance, The Microscope.......................................... 1 Variation and Survival Cells........................................................... 2 DNA and Inheritance................................ 41 Cell Organisation........................................ 3 Variation................................................... 42 Respiration................................................. 4 Natural Selection and Survival.................. 43 Practice Questions.................................. 5 Extinction and Preserving Species............. 44 Revision Summary for Section One............. 7 Practice Questions................................ 45 Revision Summary for Section Four........... 47 Section Two — Humans as Organisms Nutrition..................................................... 8 Section Five — Classifying Materials Nutrition and Energy................................... 9 Solids, Liquids and Gases......................... 48 Digestion.................................................. 1 0 Particle Theory.......................................... 49 More on Digestion.................................... 1 1 More Particle Theory................................. 50 Practice Questions................................ 1 3 Physical Changes...................................... 51 The Skeleton............................................. 1 4 Heating and Cooling Curves..................... 52 The Muscular System................................ 1 5 Practice Questions................................ 53 The Force Applied by Muscles.................. 1 6 Atoms and Elements................................. 55 Practice Questions................................ 1 7 The Periodic Table..................................... 56 Gas Exchange........................................... 1 8 Compounds.............................................. 57 Breathing.................................................. 1 9 Naming Compounds................................. 58 Exercise, Asthma and Smoking.................. 20 Practice Questions................................ 59 Practice Questions................................ 21 Mixtures................................................... 60 Human Reproductive System.................... 22 Separating Mixtures.................................. 62 The Menstrual Cycle................................. 23 Practice Questions................................ 65 Having a Baby.......................................... 24 Properties of Metals.................................. 67 Health and Pregnancy.............................. 25 Properties of Non-metals.......................... 69 Drugs........................................................ 26 Properties of Other Materials.................... 71 Practice Questions................................ 27 Practice Questions................................ 72 Revision Summary for Section Two........... 29 Revision Summary for Section Five........... 74 Section Three — Plants and Ecosystems Section Six — Chemical Changes Plant Nutrition.......................................... 30 Chemical Reactions.................................. 75 Plant Reproduction................................... 31 Examples of Chemical Reactions.............. 76 Fertilisation, Seed Formation and Distribution Chemical Reactions and Catalysts............. 77................................................................. 32 Balancing Equations................................. 78 Investigating Seed Dispersal Mechanisms 33 Practice Questions................................ 79 Practice Questions................................ 34 Acids and Alkalis...................................... 80 Dependence on Other Organisms............ 36 Neutralisation Reactions........................... 81 Food Chains.............................................. 37 Practice Questions................................ 82 Food Webs................................................ 38 Reactivity Series and Metal Extraction....... 83 Practice Questions................................ 39 Reaction of Metals with Acids................... 84 Revision Summary for Section Three......... 40 Reactions of Oxides with Acids................. 85 Displacement Reactions........................... 86 Practice Questions................................ 88 Revision Summary for Section Six............. 90 Section Seven — The Earth Section Ten — Waves and The Atmosphere Water Waves..............................................1 36 The Earth’s Structure....................................91 Light Waves...............................................1 38 Rock Types...................................................92 Reflection..................................................1 39 The Rock Cycle............................................94 Refraction..................................................1 40 Practice Questions...................................95 How We See..............................................1 41 Recycling.....................................................97 Colour.......................................................1 42 The Carbon Cycle........................................98 Practice Questions.................................1 43 The Atmosphere and the Climate.................99 Sound........................................................1 45 Practice Questions.................................1 00 Hearing.....................................................1 47 Revision Summary for Section Seven.........1 01 Energy and Waves......................................1 48 Practice Questions.................................1 49 Revision Summary for Section Ten.............1 50 Section Eight — Energy and Matter Energy Transfer...........................................1 02 Section Eleven — More Energy Transfer.................................1 04 Electricity and Magnetism Energy Transfer by Heating.........................1 05 Conservation of Energy..............................1 06 Electrical Circuits.......................................1 51 Practice Questions.................................1 07 Measuring Current and Potential Difference Energy Resources.......................................1 09..................................................................1 53 Generating Electricity................................1 1 0 Series Circuits............................................1 54 The Cost of Electricity................................1 1 1 Parallel Circuits..........................................1 55 Comparing Power Ratings and Energy Values Practice Questions.................................1 56..................................................................1 1 3 Static Electricity.........................................1 57 Practice Questions.................................1 1 4 Magnets.....................................................1 58 Physical Changes.......................................1 1 5 Electromagnets..........................................1 59 Movement of Particles................................1 1 7 Practice Questions.................................1 60 Practice Questions.................................1 1 8 Revision Summary for Section Eleven........1 61 Revision Summary for Section Eight...........1 1 9 Section Twelve — The Earth and Beyond Section Nine — Forces and Motion Gravity.......................................................1 62 Speed........................................................1 20 The Sun and Stars......................................1 63 Distance-Time Graphs...............................1 21 Day and Night and the Four Seasons.........1 64 Relative Motion.........................................1 22 Practice Questions.................................1 65 Forces and Movement................................1 23 Revision Summary for Section Twelve........1 66 Friction......................................................1 24 Air and Water Resistance...........................1 25 Practice Questions.................................1 26 Section Thirteen — Exam Practice Force Diagrams..........................................1 28 Mixed Practice Tests...................................1 67 Moments...................................................1 29 Practice Exam............................................1 73 Forces and Elasticity...................................1 30 Pressure.....................................................1 31 Practice Questions.................................1 33 Revision Summary for Section Nine...........1 35 Answers.....................................................1 88 Index.........................................................202 Published by CGP From original material by Richard Parsons and Paddy Gannon. Editors: Mary Falkner, Christopher Lindle, Duncan Lindsay, Frances Rooney, Ethan Starmer-J ones and Charlotte Whiteley Contributors: J osephine Horlock and Lucy Muncaster SHS34 ~ 0322 - 241 51 Clipart from Corel® Illustrations by: Sandy Gardner Artist, email [email protected] Text, design, layout and original illustrations © Coordination Group Publications Ltd. (CGP) 201 7 All rights reserved. 0800 1 71 2 71 2 www.cgpbooks.co.uk  Section One — Cells and Respiration 1 The Microscope A microscope is used for looking at objects that are too small to see with the naked eye. The lenses in the microscope magnify objects (make them look bigger) so that you can see them. Learn the Different Parts of a Microscope Here are some of the main parts of a light microscope — make sure you can identify them. eyepiece lens body tube rough focusing knob fine focusing knob high and low power obj ective lenses handle stage mirror Follow These Easy Steps to Using a Light Microscope 1 ) Carry your microscope by the handle. 2) Place it near a lamp or a window, and angle the Don’t reflect direct sunlight mirror so light shines up through the hole in the stage. into the microscope — it 3) Clip a slide onto the stage. The slide should have the could damage your eyes. object(s) you want to look at stuck to it. 4) Select the lowest powered objective lens. 5) Turn the rough focusing knob to move the objective lens down to just above the slide. 6) Look down the eyepiece lens and adjust the focus using the fine focusing knob. 7) Keep adjusting until you get a clear image of whatever’s on the slide. DON’T BREAK THE SLIDE 8) If you need to see the slide with greater magnification, switch to a higher powered objective lens (a longer one). Always turn the rough focusing 9) Now refocus the microscope (repeat steps 5 to 7). knob so that the objective lens is moving away from the slide — so the lens and slide don’t crash together. Microscopes are great for looking at cells WORKINGALLY SCIENTIFIC A microscope lets you see all the tiny building blocks (called cells) that make up living things. Choosing the correct equipment and using it properly and safely is a key part of being a scientist. Section One — Cells and Respiration 2 Cells Living Things are Made of Cells 1 ) Another word for a living thing is an organism. All organisms are made up of tiny building blocks known as cells. 2) Cells can be seen through a microscope (see previous page) — but it helps if you stain them first (using a coloured dye). Animal and Plant Cells Have Similarities and Differences An Animal Cell A Plant Cell BOTH have: ONLY PLANTS have: 1 ) A Nucleus: 1 ) A Cell Wall: This controls what A rigid outer the cell does. coating made 2) Cytoplasm: of cellulose — it gives support This is a jelly-like stuff to the cell. where most chemical reactions happen. 2) A Vacuole: This is filled with 3) A Cell Membrane: cell sap — a This is a thin skin around weak solution of the cell — it holds the cell sugar and salts. together and also controls what goes in and out. 3) Chloroplasts: 4) Mitochondria: These contain chlorophyll These are tiny structures inside the cell where most of the used for photosynthesis reactions for aerobic respiration (see page 4) take place. (see p.30). Photosynthesis Respiration releases energy for the cell. makes food for the plant. Some Living Things are Unicellular 1 ) Animals and plants are made up of lots of cells. They’re multicellular organisms. 2) But many living things are made up of only one cell — these are called unicellular organisms. Unicellular organisms have adaptations to help them survive in the environment they live in, e.g. EUGLENA: AMOEBA: nucleus chloroplast flagellum water nucleus out contractile vacuole Some amoeba also live in water. They use a Euglena live in water. They have a tail-like contractile vacuole to collect any excess water inside structure called a flagellum to help them swim. them and squeeze it out at the cell membrane. Section One — Cells and Respiration  3 Cell Organisation Learn How Cells are Organised In organisms with lots of cells (like animals and plants), the cells are organised into groups. Here’s how: A group of similar cells come together to make a tissue. A group of different tissues work together to make an organ. A group of organs work together to make an organ system. A multicellular organism is usually made up of several organ systems. Here's a rather jolly example from a plant. Don't forget that the sequence applies just as well to animals. palisade CELLS......make up palisade TISSUE......which, with other...which, with more leaves tissues, makes up a and other organs, makes up A palisade cell is j ust the name leaf (an ORGAN)... the shoot system (an ORGAN for a particular type of plant cell. SYSTEM). Different organ systems make up a full plant (an ORGANISM). Stuff Moves Into and Out of Cells by Diffusion 1 ) Cells need things like glucose (a sugar) and oxygen to survive. They also need to get rid of waste products, like carbon dioxide. 2) These materials all move into or out of cells by a process called diffusion. 3) Diffusion is where a substance moves from an area of high concentration (where there’s lots of it) to an area of low concentration (where there’s less of it) — just like glucose in this diagram... glucose outside cell inside cell (lots of glucose) (not much glucose) There’s more on diffusion on p.50. cell membrane Cells are the building blocks of organisms ➙ ➙ ➙ ➙ Remember: cells tissues organs organ systems organisms. You need to get your head around diffusion too — it comes up all the time in KS3 science, so it’s worth getting to grips with now. Section One — Cells and Respiration 4 Respiration Respiration is one of the most important life processes there is. It’s worth learning really well. Respiration is a Chemical Reaction 1 ) Respiration happens in every cell of every living organism. 2) Respiration is the process of releasing energy from glucose (a sugar). 3) The energy released by respiration is used for all the other chemical reactions that keep you alive. For example, the reactions involved in building proteins, muscle contraction and keeping warm. Aerobic Respiration Needs Plenty of Oxygen 1 ) Aerobic respiration is respiration using oxygen. It takes place in the mitochondria (see page 2) of animal and plant cells. There’s more on chemical 2) In aerobic respiration, glucose and oxygen react to produce reactions and word carbon dioxide and water. This reaction releases lots of energy. equations on page 57. 3) Here’s a word equation to show what happens in the reaction — learn it: glucose + oxygen ➙ carbon dioxide + water + ENERGY These are the reactants. These are the products. Anaerobic Respiration Takes Place Without Oxygen 1 ) Anaerobic respiration is respiration without oxygen. 2) Anaerobic respiration is less efficient than aerobic respiration, so it releases less energy. 3) Because of this, anaerobic respiration usually only happens when cells can’t get enough oxygen, e.g. if your body can’t get enough oxygen to your muscle cells when you exercise, they start to respire anaerobically. Anaerobic Respiration is Different in Different Organisms 1 ) In humans, anaerobic respiration produces a substance called lactic acid: glucose ➙ lactic acid + ENERGY Lactic acid can build up in your muscles during exercise and can be painful. 2) In microorganisms like yeast, anaerobic respiration produces carbon dioxide and ethanol (alcohol): glucose ➙ carbon dioxide + ethanol + ENERGY When anaerobic respiration produces ethanol, it’s called fermentation. Fermentation is the process used to make beer. ION There are two types of respiration — learn the difference RE V IS TASK It can be tricky to get your head around respiration, but it just means turning glucose into energy. Make sure you’ve learnt those equations — cover the book and write them down. Section One — Cells and Respiration  5 Warm-Up and Practice Questions Take a deep breath then ease yourself in gently with these warm-up questions. Then attack the practice questions. All the answers are somewhere in this section, so there are no excuses. Warm-Up Questions 1) Why would you stain a cell before looking at it under a microscope? 2) Name three structures that are found in both plant and animal cells. Describe what they all do. 3) What is the difference between a tissue and an organ? 4) Which process is responsible for the movement of glucose from an area of high concentration to an area of low concentration? 5) Which sort of respiration involves oxygen? Write the relevant word equation. 6) Which sort of respiration is the most efficient? Practice Questions 1 The diagram below shows a plant cell. (i) (iii) (ii) (iv) (a) Name the cell parts labelled (i)-(iv) on the diagram. (4 marks) (b) Name two structures that are found in plant cells, but not in animal cells. (2 marks) (c) What is the function of the cell wall? (1 mark) (d) Some organisms are made up of only one cell. (i) What word describes organisms that have only one cell? (1 mark) (ii) Give an example of an organism made up of only one cell and explain how it is adapted to its environment. (3 marks) Section One — Cells and Respiration 6 Practice Questions 2 Respiration is a very important life process for all organisms. (a) In which part of animal and plant cells does aerobic respiration take place? (1 mark) (b) Sometimes respiration does not involve oxygen. (i) Which sort of respiration does not involve oxygen? (1 mark) (ii) Write the word equation for this process when it occurs in humans. (1 mark) (iii) In what situation might a human start respiring in this way? (1 mark) 3 (a) Use the following words to complete the gaps in the sentences below. a tissue cells an organ.......................... are the simplest building blocks of organisms. Several of these can come together to make up.......................... , and several of these can work together to make........................... (3 marks) (b) What is an organ system? (1 mark) 4 Alana’s class are investigating the cells in onion skin using light microscopes. Alana collects a microscope from the teacher and positions it near a window. (a) Light has to enter the microscope for it to work. (i) Which part of the microscope can be adjusted to allow light in? (1 mark) (ii) Which kind of light should not be allowed to enter the microscope? Explain your answer. (2 marks) (b) Alana clips a slide with a piece of onion skin stuck to it onto the stage. (i) Describe the steps she should take to get a clear image of the onion cells. (4 marks) (ii) Alana would like to make the image of the onion cells bigger. Describe how she can do this. (2 marks) Section One — Cells and Respiration  7 Revision Summary for Section One Welcome to your very first Section Summary. It’s full of questions written especially for finding out what you actually know — and, more importantly, what you don’t. Here’s what you have to do... Go through the whole lot of these Section Summary questions and try to answer them. Look up the answers to any you can’t do and try to really learn them (hint: the answers are all somewhere in Section One). Try all the questions again to see if you can answer more than you could before. Keep going till you get them all right. 1) What part of a microscope do you clip your slide onto?  2) What do the focusing knobs on a microscope do?  3) Why should you always move the objective lens away from the slide when you're focusing a microscope?  4) What is an organism?  5) What instrument would you use to look at a cell?  6) What do chloroplasts do? What sort of cell would you find them in?  7) Explain the meaning of: a) tissue b) organ. Give an example of each.  8) Give an example of an organ system.  9) What is diffusion?  1 0) Give two examples of substances that move into or out of cells by diffusion.  1 1 ) What’s the name of the process that goes on in every cell, releasing energy?  1 2) What is the energy released by this process used for? Give three examples.  1 3) What is aerobic respiration?  1 4) Write down all the reactants of aerobic respiration. Now write down the products.  1 5) Give two differences between aerobic respiration and anaerobic respiration in humans.  1 6) Write down the word equation for anaerobic respiration in yeast.  1 7) What is fermentation? What can fermentation be used to make?  Section One — Cells and Respiration 8 Section Two — Humans as Organisms Nutrition Nutrition is what you eat — and what you eat is really important for your health. A balanced diet will have the right amount of the five nutrients listed below, as well as fibre and water. 1 ) Carbohydrates These are like fuel for your body. Contained in Used for Active or growing folk need lots of carbohydrate. Bread / potatoes / cereals Energy Starch 2) Proteins Proteins are vital for Contained in Used for growth and to repair damaged areas. Proteins Meat / eggs / fish Building Cells 3) Lipids (Fats and Oils) Lipids act as a store of energy — which you Used for Contained in use if your body runs Fat Butter / cooking oil / cream Energy out of carbohydrates. 4) Vitamins Vitamins are only needed in E.g. A B1 B2 Contained in Used for very small amounts — they C D E keep many vital processes Vegetables / fruit / cereals happening. 5) Minerals E.g. — Iron Calcium Sodium Found in — Needed for — Blood Teeth/Bones Nerves Fibre Contained in Used for Fibre helps food move through your digestive system. Vegetables / fruit / cereals Water About 75% of your body is water and Contained in Used for all chemical reactions (e.g. digestion), take place in water – it's really important. Section Two — Humans as Organisms  9 Nutrition and Energy Your body needs energy all the time. Even when you’re asleep your body is using energy just to keep you alive. It’s important that you get this energy from a balanced diet, or a few nasty things can happen... An Unbalanced Diet Can Cause Health Problems Obesity 1 ) If you take in more energy from your diet than you use up, your body will store the extra energy as fat — so you will put on weight. 2) If you weigh over 20% more than the recommended weight for your height, then you are classed as obese. 3) Obesity can lead to health problems such as high blood pressure and heart disease. Starvation and Deficiency Diseases 1 ) Some people don’t get enough food to eat — this is starvation. 2) The effects of starvation include slow growth (in children), being more likely to get infections, and irregular periods in women. 3) Some people don’t get enough vitamins or minerals — this can cause deficiency diseases. For example, a lack of vitamin C can cause scurvy, a deficiency disease that causes problems with the skin, joints and gums. Different People Have Different Energy Requirements 1 ) The amount of energy you need each day depends on your body mass (“weight”) and level of activity. 2) Every cell (see page 2) in the body needs energy. So the bigger you are, the more cells you have, and the more energy you’ll need. A kJ is a unit 3) For every kg of body mass, you need 5.4 kJ of energy every hour. This is the of energy. basic energy requirement (BER) needed to maintain essential bodily functions. You calculate it like this: Daily BER (kJ/day) = 5.4 × 24 hours × body mass (kg) E.g. a 60 kg person requires 5.4 × 24 × 60 = 7776 kJ /day 4) You also need energy to move, and it takes more energy to move a bigger mass. 5) So, the heavier and the more active you are, the more energy you will need. 6) To find out how much energy you need in a day you have to add together your daily BER and the extra energy you use in your activities. For example, a 60 kg person will use about 400 kJ walking for half an hour, but 1 500 kJ running for half an hour. You need to eat a balanced diet to stay healthy Too much or too little food (or not eating the right foods) can lead to some serious health problems. Make sure you understand the health problems on this page. You also need to know how to work out someone’s daily energy requirement — it’s important for avoiding the health problems above. Section Two — Humans as Organisms 10 Digestion Digestion’s great. The body breaks down the food we eat, so we can use the nutrients it contains. But it’s not easy — lots of different organs have to work together to get the job done. Digestion is All About Breaking Down Food There are two steps to this. The first is quick, the second isn't: Canines 1 ) Breaking down the food MECHANICALLY, e.g. chewing with teeth: Molars 2) Breaking down the food CHEMICALLY — with the help of proteins Premolars called enzymes. Enzymes are biological catalysts — this means they Incisors speed up the rate of chemical reactions in the body. Eight Bits of The Alimentary Canal 1 ) Mouth 2) Oesophagus Digestion starts here Food pipe — links the mouth where the teeth have a to the stomach. good old chew and mix the food with saliva. Saliva contains an 3) Stomach enzyme (called amylase) 1 ) Here the food mixes with that breaks down protease enzymes which carbohydrates. digest proteins. The stomach contains muscular 4) Liver tissue to move the stomach wall and churn up food. The liver makes bile, which 2) Hydrochloric acid is breaks fats into tiny droplets present to kill harmful (emulsification). It's also bacteria and give a low pH alkaline to give the right pH for the enzymes to work. for the enzymes in the small intestine. 5) Pancreas 7) Large intestine The pancreas contains Here water is absorbed — glandular tissue, which makes so we don't all shrivel up. three enzymes: 1 ) PROTease digests PROTein. 8) Rectum 6) Small intestine 2) CARBOHYDRAse digests Food usually contains 1 ) This produces more enzymes CARBOHYDRAtes. some materials that we to further digest proteins, 3) LIPase digests LIPids can’t digest. carbohydrates and fats. — i.e. fats. This undigested food is 2) Food is also absorbed through stored as faeces. Here the gut wall into the blood, the digestion story ends which then takes it around the when it plops out of the body to wherever it's needed. anus — egestion. Section Two — Humans as Organisms  11 More on Digestion Well would you believe it? There’s more to learn about digestion. Absorption of Food Molecules 1 ) Big, insoluble food molecules can’t pass through the gut wall. ‘Insoluble’ 2) So enzymes are used to break up the big molecules ‘won’t disso means lve’. into smaller, soluble ones. means ‘will ‘Soluble’ dissolve’. See pag e 61 for mo re. 3) These small molecules can pass through the gut wall into the blood. 4) They are then carried round the body, before passing into cells where they are used. Blood flows from gut to body cells Larg e intestine Water absorbed The small molecules diffuse into the blood... Dig estion Absorption...and then out ag ain somewhere Small intestine else... Inside the g ut The blood Body cells You need to absorb all of these facts ION RE V IS TASK As well as looking pretty, the diagrams on digestion are really important for helping you understand how food is broken down and absorbed by the body — so look at them really thoroughly and absorb the information. Make sure you know the name and function of all eight bits of the alimentary canal. To test yourself, cover up these pages and draw the diagrams showing how food is digested. Include as much detail as you can remember. Section Two — Humans as Organisms 12 More on Digestion More on digestion — don’t worry, it’s the last page on it, I promise. (Apart from the questions anyway...) The Small Intestine is Covered with Millions of Villi 1 ) Food molecules are absorbed into the blood in the small intestine. 2) The small intestine is lined with tiny finger-like projections called VILLI. A villus Another villus Villi is the plural Good blood Absorption of villus — i.e. it’s supply one villus but two (or more) villi. 3) Villi are perfect for absorbing food because: They have a thin outer layer of cells. They have a good blood supply. They provide a large surface area for absorption. Bacteria are Really Important in the Gut 1) Bacteria are unicellular organisms (see page 2). 2) There are about 1 00 trillion bacterial cells in the alimentary canal. That’s loads. 3) Most of these are in the end part of the small intestine and in the large intestine. 4) Some types of bacteria can make you really ill if they get into your body, but the bacteria found naturally in your gut actually do a lot of good: They produce enzymes They produce useful hormones. that help to digest food. They make useful They reduce the possibility of harmful vitamins, e.g. vitamin K. bacteria growing in your intestines and making you ill. Who knew having bacteria inside you was such a good thing? Villi are brilliant absorbers of food. Make sure you know the three things that make villi so awesome at doing this — their large surface area, their blood supply and their thin outer layer of cells. Section Two — Humans as Organisms  13 Warm-Up and Practice Questions When you’ve digested all that information, have a crack at these questions to test what you know... Warm-Up Questions 1) Which two nutrients does the body get energy from? 2) Name one type of food that contains fibre. 3) What health risk is caused by taking in more energy than you use up? 4) What is meant by your daily basic energy requirement? 5) Name the two ways that food is broken down by the body. 6) Enzymes are biological catalysts. What does this mean? 7) Which part of the body does digestion start in? 8) Why do we need to digest our food? 9) What type of organisms are present in the gut and produce enzymes that help digest food? Practice Question 1 The diagram shows some of the organs of the human digestive system. mouth NOT TO SCALE F small intestine large intestine rectum (a) Draw a line pointing to the oesophagus and label it O. (1 mark) (b) Give two functions of organ F. (2 marks) (c) The small intestine is responsible for the absorption of digested food. It has millions of villi to help with this process. State three ways in which villi are adapted to help with the absorption of digested food. (3 marks) (d) What is the name of the organ that produces bile? (1 mark) Section Two — Humans as Organisms 14 The Skeleton The adult human skeleton is made up of 206 bones. Thankfully you don’t need to learn them all... The Skeletal System Bones are made from different types of tissue: The outer layer of bone is made from really strong and hard tissue — this makes bones rigid (they can’t bend). The inner layer is made from more spongy tissue, but it’s still strong. The skeletal system has four main functions: Mandible Cranium (J aw) (skull) 1 ) Protection Backbone Clavicle Bone is rigid and tough so it can protect (Collarbone) Sternum delicate organs — in particular the brain. (Breast bone) Rib Humerus Ulna 2) Support Carpals Radius Metacarpals Coccyx 1 ) The skeleton provides a rigid frame Phalanges for the rest of the body to kind of Femur hang off — kind of like a custom Patella made coat-hanger. (Kneecap) 2) All the soft tissues are supported by the skeleton — this allows us to Fibula stand up. Tarsals Tibia Metatarsals Phalanges 3) Production of Blood Cells 1 ) Many bones have a soft tissue called bone marrow in the middle of them. 2) Bone marrow produces red blood cells (which carry oxygen around the body) and white blood cells (which help to protect the body from infection). 4) Movement 1 ) Muscles are attached to bones (see next page). 2) The action of muscles allows the skeleton to move. 3) J oints (e.g. the knees and elbows) also allow the skeleton to move. A body without bones? Ever seen a tent without poles? ION RE V IS TASK Lots of bone-tinglingly exciting facts to learn here. You don’t need to learn the names of all those bones — the main thing here is to learn what it is that the skeleton actually does. The skeletal system has four main functions. Cover up the page and jot them all down. Section Two — Humans as Organisms  15 The Muscular System Another fun number for you — the muscular system is made up of around 640 muscles. The muscular and skeletal systems work together so you can move around. Tendons Attach Your Muscles to Your Bones 1 ) Muscles are attached to bones via tough bands called tendons. 2) When a muscle contracts it applies a force to the bone it’s attached to, which makes the bone move. 3) Muscles are found in pairs round a joint (see below). Muscles Tendons Antagonistic Muscles Work in Pairs 1 ) Antagonistic muscles are pairs of muscles that work against each other. 2) One muscle contracts (shortens) while the other one relaxes (lengthens) and vice versa. 3) They are attached to bones with tendons. This allows them to pull on the bone, which then acts like a lever (see next page). 4) One muscle pulls the bone in one direction and the other pulls it in the opposite direction — causing movement at the joint. 5) The biceps and triceps muscles in the arm are examples of antagonistic muscles: Arm bending Arm straightening Humerus Radius Triceps relaxes Ulna Triceps contracts Biceps contracts Biceps relaxes 6) The hamstrings and quadriceps in the legs are another example. ION When you show off your muscles, you can claim it’s revision RE V IS TIP Remember that antagonistic muscles just can’t get along — whatever one is doing, the other is doing the opposite. J ust like me and my sister... Section Two — Humans as Organisms 16 The Force Applied by Muscles A lot of your bones act like levers that get pulled by muscles. There’s a handy little formula you can use to work out how much force a muscle applies to a bone... enjoy. You Can Measure the Force Applied by a Muscle The study of forces acting on Let’s look at a muscle in the arm as an example: the body is called biomechanics. 1 ) Start by Calculating the Moment 1 ) A pivot is the point around which a rotation happens. A lever is a bar attached to a pivot. 2) When a force acts on something that has a pivot, it creates a “turning effect” known as a moment (see page 1 29). perpendicular distance force 3) The arm works as a lever with the elbow as a pivot. This means when a force acts on the arm there’s a moment. a right angle pivot 4) To calculate the size of a moment, you can use this equation: ‘Perpendicular distance’ is the Moment = force × perpendicular distance distance at a right angle from the pivot to the line of force. In newtons (N) In metres (m) In newton metres (Nm) 5) In the diagram here, the weight (a force) in the hand is creating a moment. 6) The weight has a force of 1 2 N. It is 0.3 m away from Muscle the pivot (the elbow). So using the equation above, the moment of the weight is 1 2 × 0.3 = 3.6 Nm. 7) But the weight is not the only thing applying a force to 12 N Tendon the arm — the muscle is applying a force to counteract the moment of the weight and keep the arm still. Elbow For the arm to stay still, the moment of the muscle has 0.05 m (pivot) to be the same as the moment of the weight (but acting Weight 0.3 m in the opposite direction). 2) Now Work Out the Force Applied by the Muscle You can rearrange the equation above to calculate the force applied by the muscle: In newtons (N) Force = moment ÷ perpendicular distance In newton metres (Nm) In metres (m) In the example above, the weight has a moment of 3.6 Nm, so the muscle must also have a moment of 3.6 Nm. The distance between the muscle and the pivot (elbow) is 0.05 m. So the force applied by the muscle is 3.6 ÷ 0.05 = 72 N. Hang on a moment... what? All this talk of forces and levers and moments can be tricky to get your head around. But stick with it — you’ll really impress if you can explain how muscles work and can use that formula to calculate a moment. Section Two — Humans as Organisms  17 Warm-Up and Practice Questions That’s it for bones and muscles. Make sure you know all the things your skeleton does and how your muscles put the whole thing in motion. Time to test how much of the last few pages has made it inside your skull by having a go at these questions... Warm-Up Questions 1) Name one property of bone that makes it suitable for protecting delicate organs. 2) Describe how the skeleton supports the body. 3) Which part of a bone makes blood cells? 4) What attaches muscles to bones? 5) Describe what antagonistic muscles are and how they work. 6) Give one example of a pair of antagonistic muscles. 7) Write down the equation you would use to calculate the moment caused by a force. Practice Question 1 The human skeleton has joints with muscles attached to the bones around them, which allow us to move. (a) Movement is one function of the skeleton. Write down the other three main functions of the human skeleton. (3 marks) (b) The diagram below shows someone holding a box. They hold their arm still. The weight of the box is 15 N. The distance between the person’s elbow joint and the box is 0.35 m. The elbow joint acts as a pivot. 0.35 m elbow j oint 15 N (i) Calculate the moment of the box about the elbow joint. (1 mark) (ii) What is the moment of the muscle that is keeping the arm and the box in the position shown? Explain your answer. (2 marks) (iii) The distance between the muscle and the elbow joint is 0.05 m. Calculate the force applied by the muscle to keep the arm still in this position. (1 mark) Section Two — Humans as Organisms 18 Gas Exchange You need to get oxygen from the air into your bloodstream and to get rid of the carbon dioxide that’s in your bloodstream. This all happens in your gas exchange system. Learn These Structures in the Gas Exchange System 1 ) The lungs are like big pink sponges. They’re protected by the ribcage. 2) The diaphragm is a muscle that sits underneath the ribcage. It moves up when Nasal Soft palate it relaxes and down when it contracts. This cavity movement helps to get air in and out of your lungs (see next page). Larynx 3) The air that you breathe in goes through the (voicebox) Trachea trachea. This splits into two tubes called (windpipe) ‘bronchi‘ (each one is ‘a bronchus’), Intercostal one going to each lung. Bronchus muscle 4) The bronchi split into smaller tubes called bronchioles. Bronchioles 5) The bronchioles end at small air sacs in the lungs called alveoli. These are where Rib Air sacs (alveoli) gas exchange takes place. Lung Diaphragm Gas Exchange Happens in the Lungs 1 ) Air is inhaled into the lungs. Body cells 2) Some of the oxygen in the inhaled LUNG air passes into the bloodstream to be Air sac Air in used in respiration (see page 4). O2 and out CO2 3) Carbon dioxide is a waste product of O2 respiration. In the lungs it passes out of the blood and is then breathed out. CO2 O2 4) The gases pass into or out of Blood capillary the bloodstream by diffusion — where a substance moves from (tiny blood BODY vessel) where there’s lots of it to where Capillary there’s less of it (see page 3). 5) The lungs are well adapted for gas exchange: 1 ) They're moist. 2) They have a good blood supply. 3) The alveoli (air sacs) give the lungs a big inside surface area. I love ribs — spare ones are my favourite though There are a couple of detailed diagrams here which need learning. Sooner or later you’re expected to learn all the structures in the gas exchange system and what they do, so you may as well start now. Section Two — Humans as Organisms  19 Breathing Breathing is how the air gets in and out of your lungs. It’s definitely a useful skill. The Mechanism of Breathing The bell jar demonstration shows us what’s going on when you breathe: Air rushes in 1 ) First you pull the rubber sheet down — like it's your diaphragm. Air Balloons fill up 2) This increases the volume inside the rushes out like lungs bell jar, which decreases the pressure. Balloons deflate 3) The drop in pressure causes air to rush into the balloons — this is like breathing in. 4) Let go of the rubber sheet — this is like relaxing your diaphragm. 5) The volume in the jar gets smaller. Pull This increases the pressure, so air rushes out. down Relax back up Inhaling and Exhaling is Breathing In and Out 1 ) The chest cavity is like a bell jar. Breathing in Breathing out (inhaling) (exhaling) 2) When you breathe in, the diaphragm moves down and the ribs move up. This increases Ribs pulled up Intercostal the volume of the chest cavity, and out by muscles intercostal muscles which decreases the pressure. relax So air rushes in to fill the lungs. Diaphragm moves down as it contracts Diaphragm relaxes — 3) When the diaphragm moves up and making the chest chest volume the ribs move down, air rushes out. volume bigger gets smaller Lung Volume Can Be Measured 1 ) Lung volume is the amount of air you can breathe into your lungs in a single breath. big breath 2) Lung volume is different for different people. in big breath out For example, taller people tend to have a bigger breathing lung volume than shorter people. And some in one breath emulov gnuL diseases may reduce a person’s lung volume. 3) Lung volume can be measured breathing using a machine called a spirometer. out 4) To use a spirometer, a person breathes into the machine (through a tube) for a few minutes. 5) The volume of air that is breathed in and out is measured and plotted on a graph (called a spirogram) like this one. Time Now take a deep breath and learn these facts Well, if ever you wanted to know how you breathe in and out, now you do. Learn how breathing works — use that bell jar demonstration to help you understand what goes on in your actual lungs. Make sure you know how lung volume can be measured too. You’ll be an expert in breathing soon. Section Two — Humans as Organisms 20 Exercise, Asthma and Smoking Exercise, asthma and smoking can all affect your gas exchange system and the way that you breathe. Exercise 1 ) When you exercise, your muscles need more oxygen and glucose so they can respire and release energy (see page 4) to keep you going. 2) During exercise, your breathing rate and depth of breathing increase so you can get more oxygen into your blood. 3) If you exercise regularly, the muscles that you use to breathe (the diaphragm and intercostal muscles) will get stronger. 4) This means that your chest cavity can open up more when you breathe in, so you can get more air into your lungs. 5) Over time, regular exercise can also cause an increase in the number and size of the small blood vessels in your lungs and in the number of alveoli. This makes gas exchange more efficient. Asthma 1 ) People with asthma (asthmatics) have lungs that are too sensitive to certain things (e.g. pet hair, pollen, dust, smoke...). 2) If an asthmatic breathes these things in, the muscles around their bronchioles contract. This narrows the airways. 3) The lining of the airways becomes inflamed and fluid builds up in the airways, making it hard to breathe. This is an asthma attack. 4) Symptoms of an attack are: difficulty breathing, wheezing, a tight chest. 5) When symptoms appear, sufferers can use an inhaler containing drugs that open up the airways. Smoking 1 ) Cigarette smoke contains four main things: carbon monoxide, nicotine, tar and particulates. 2) Tar in particular is really bad for you: Tar covers the cilia (little hairs) on the lining of the airways. The damaged cilia can’t get rid of mucus properly. The mucus sticks to the airways, making you cough more — this is known as smoker’s cough. The damage builds up and can eventually lead to bronchitis (a disease that inflames the lining of the bronchi) and emphysema (a disease that destroys the air sacs in the lungs). Both these diseases make it difficult to breathe. And there’s more... tar contains carcinogens (substances that can cause cancer). Smoking causes cancer of the lung, throat and mouth. ION This page is just breathtaking RE V IS TIP So there you have it, three different things that have an impact on the gas exchange system. Make sure you get to grips with all of them — cover up the page and see how much you can write about each one. Section Two — Humans as Organisms  21 Warm-Up and Practice Questions Take a deep breath, then have a bash at these questions... Warm-Up Questions 1) Why is it important to have a good blood supply going to the lungs? 2) What is meant by lung volume? 3) What does a spirometer measure? 4) Give two changes that can happen to your gas exchange system if you exercise regularly over a long period of time. 5) Explain why a person’s airways narrow during an asthma attack. Practice Questions 1 The diagram below shows the chest cavity of a healthy person. One of the lungs is drawn in cross-section to show the air sacs. trachea A heart rib diaphragm (a) Write down the name of the part of the chest cavity labelled A. (1 mark) (b) Which gas enters the blood from the alveoli (air sacs)? (1 mark) (c) Which gas leaves the blood to enter the lungs at the alveoli (air sacs)? (1 mark) (d) Describe what happens to the chest cavity as you breathe in. (4 marks) 2 Cigarette smoke contains tar which can damage your airways. (a) Name two other harmful substances present in cigarette smoke. (2 marks) (b) Explain why the tar in cigarette smoke causes smokers to cough more. (3 marks) (c) Name one disease that smoking can cause. (1 mark) Section Two — Humans as Organisms 22 Human Reproductive System Like all mammals, we have different male parts and female parts that allow us to reproduce. No giggling... The Male Reproductive System 1 ) Sperm are the male sex cells or ‘gametes’. 2) Sperm are made in the testes after puberty. 3) Sperm mix with a liquid to make semen, which is ejaculated from the penis during sexual intercourse. Tube from bladder Glands Sperm duct Urethra Erectile tissue Head of penis Foreskin (may be removed) Testis Scrotal sac (scrotum) The Female Reproductive System 1 ) An egg is a female sex cell or ‘gamete’. 2) One of the two ovaries releases an egg every 28 days. 3) It passes into the fallopian tube (or oviduct) where it may meet sperm, which has entered the vagina during sexual intercourse (sometimes known as copulation). 4) If it isn't fertilised by sperm (see next page), the egg will die after about a day and pass out of the vagina. Fallopian tube (or oviduct) Womb (uterus) Ovary Cervix Vagina Section Two — Humans as Organisms  23 The Menstrual Cycle The menstrual cycle — not the most exciting of things, but you wouldn’t be here without it. The Menstrual Cycle Takes 28 Days 1 ) From the age of puberty, females undergo a monthly sequence of events which are collectively known as the MENSTRUAL CYCLE. 2) This involves the body preparing the uterus (womb) in case it receives a fertilised egg. 3) If this doesn't happen, then the egg and uterus lining break down and are lost from the body through the vagina over a period of three to four days, usually. 4) The cycle has four main stages — they are summarised in the diagram and table below: STAGE ONE STAGE TWO STAGE THREE STAGE FOUR Lining of uterus Lining of the Egg released Lining of uterus Next breaks down uterus builds up maintained Cy cle Lining of the Uterus Day 1 Day 4 Day 1 4 Day 28 Day 4 Day What happens... 1 BLEEDING STARTS as the lining of the uterus (the womb) breaks down and passes out of the vagina — this is what’s known as “having a PERIOD”. 4 The lining of the uterus starts to build up again. It thickens into a spongy layer full of blood vessels ready for IMPLANTATION. (See next page.) 14 An egg is released from the ovaries of the female, so this is the MOST LIKELY time in which a female may become pregnant. (This day may vary from one woman to the next.) 28 The wall remains thick awaiting the arrival of a fertilised egg. If this doesn’t happen then this lining breaks down, passing out of the vagina. Then the whole cycle starts again. The end of the cycle depends on whether the egg’s fertilised… Phew, there are quite a few details to learn here. Make sure you know the names of all the bits and bobs in the male and female reproductive systems on page 22. You need to know exactly what happens at each of the four stages of the menstrual cycle and when they occur too. Section Two — Humans as Organisms 24 Having a Baby Once Dad’s sperm has fertilised Mum’s egg, an embryo forms, gestation happens, and a baby is born. Fertilisation and Development 1 ) Ovulation 2) Copulation 3) Fertilisation Fallopian tube Sperm The egg is Sperm duct Fallopian tube fertilised Fallopian tube when the Ovary Testis Egg nuclei of Egg Ovary Ovary the egg and Penis sperm join — An egg is released Ovum (egg) Vagina the fertilised from an ovary Millions of sperm egg is called (around day 1 4). are released from a ZYGOTE. the penis into the vagina during intercourse. 4) Cell Division 5) Implantation 24 HOURS after fertilisation the About one week after fertilised egg divides into two. After fertilisation, the embryo about 4 DAYS the egg has divided into starts to embed (implant) 32 cells. It's now called an EMBRYO. itself into the wall of the uterus and the placenta begins to develop. The Embryo Develops During Gestation Start here At 1 Month The body is about The embryo is 6 mm At 9 Weeks 25 mm long and long and has a brain, At 39 weeks heart, eyes, ears and legs. is completely formed — it's The baby is about 520 mm now called a long. It's fully developed FOETUS. and ready to be BORN. At 3 Months At 5 Months The foetus is At 7 Months 54 mm long and It's now about looks much more The foetus is 370 mm long and 1 60 mm long. like a baby. is 'VIABLE'. This means it would It kicks and its have a fair chance of surviving if fingernails can it were born at this stage. be felt. Section Two — Humans as Organisms  25 Health and Pregnancy Good health is a situation where you’re fine and dandy both physically and mentally. It’s important to make sure you look after your health if you’re pregnant, as your health affects the baby’s health. Health is More Than J ust the Absence of Disease Good health means having BOTH of these: 1 ) A healthy body that’s all working properly with no diseases. 2) A healthy mental state where you’re able to cope with the ups and downs of life. You should look after your body by eating a balanced diet, doing enough exercise and not abusing drugs. The Mother’s Lifestyle During Pregnancy is Important 1 ) The placenta lets the blood of the foetus and mother get very close to allow exchange of food, oxygen and wastes. Umbilical cord Mother’s blood Foetus Placenta Amniotic fluid (gives protection against knocks and bumps) 2) If the mother smokes, drinks alcohol or takes other drugs while she is pregnant, harmful chemicals in her blood can cross the placenta and affect the foetus. 3) For example, the foetus may not develop properly and could have health problems after it’s born. Well, that’s all a bit different to the stork story I got told There’s a lot to learn on these pages. Make sure you know all the different stages it takes to make an embryo and how an embryo develops into a baby ready to pop out into the world. Remember, having good health and a good lifestyle is important for everyone, but especially when you’re pregnant. Section Two — Humans as Organisms 26 Drugs Recreational drugs can have serious negative effects on your health. Drugs 1 ) A drug is any substance that affects the way the body works. The 7 Life Processes E.g. They may raise the heart rate or cause blurred vision. Movement — moving parts of the body. 2) There are LEGAL DRUGS and ILLEGAL DRUGS. Reproduction — producing offspring. Aspirin, caffeine and antibiotics are examples of Sensitivity — responding and reacting. legal drugs. Cannabis, speed and ecstasy are examples Nutrition — getting food to stay alive. of illegal drugs. Excretion — getting rid of waste. 3) RECREATIONAL DRUGS are drugs used Respiration — turning food into energy. for enjoyment, rather than as medicine. Growth — getting to adult size. They can be legal or illegal. 4) Drugs can affect life processes. For example, drugs that affect the brain are likely to affect movement and sensitivity. And drugs that affect the liver and kidneys will most likely affect excretion (as these are the organs that process waste). Solvents 1 ) Solvents are found in most homes — in things like paints, aerosols and glues. 2) They're drugs because they cause hallucinations, which are illusions of the mind. Solvents usually have a severe effect on behaviour and character. 3) They also cause serious damage to the lungs, the brain, liver and kidneys. Alcohol 1 ) Alcohol is found in beers, wines and spirits. It's illegal to buy it under the age of 1 8. 2) It's a depressant, which means it decreases the activity of the brain and slows down responses. 3) It's a poison which affects the brain and liver leading to various health problems, e.g. cirrhosis (liver disease). 4) It impairs judgement, which can lead to accidents. It's also very addictive. Illegal Drugs — Dangerous, Addictive and Life-Wrecking 1 ) Ecstasy and LSD are hallucinogens. Ecstasy can give the feeling of boundless energy which can lead to overheating, dehydration and sometimes DEATH. 2) Heroin and morphine were developed as painkillers. However they turned out to be highly addictive. They can both cause severe degeneration of a person's life. 3) Amphetamine (speed) and methedrine are stimulants. They give a feeling of boundless energy. However, users quickly become psychologically dependent on the drug (i.e. they think they need them), so behaviour and character deteriorate. 4) Barbiturates are depressants. They slow down the nervous system and therefore slow down reaction time. They can help you to sleep but they're seriously habit-forming. Drugs aren’t harmless fun — they’re a slippery slope ION RE V IS TIP It’s important that you know the different effects that drugs can have on your health. Make sure that you know how different types of recreational drugs can affect behaviour, health and life processes — use MRS NERG to remember the 7 life processes. Section Two — Humans as Organisms  27 Warm-Up and Practice Questions Well, that’s almost it for this section. J ust a few questions to go and you’re done. Warm-Up Questions 1) What are the male sex cells called? Where are they made? 2) On which day, approximately, will an egg be released from the ovary, during a ‘normal’ 28-day menstrual cycle? 3) State one function of the placenta, as the embryo develops inside the mother’s uterus. 4) You need a healthy body to have good health. What else do you need? 5) Explain why it’s not a good idea for a woman to smoke while she’s pregnant. 6) What is meant by a ‘recreational’ drug? 7) Name two things containing solvents that you can find in the home. 8) Name two organs that you can damage by using solvents. 9) Name two drugs that are hallucinogens. Practice Questions 1 The diagram below shows the human female reproductive system. Fallopian tube (oviduct) Womb Ovary (uterus) Cervix Vagina (a) A female will usually release an egg from an ovary roughly every 28 days. What is this process called? (1 mark) (b) (i) In what part of the female reproductive system does fertilisation usually take place? (1 mark) (ii) Underline the correct definition of fertilisation in the list below: When an egg cell is released from the ovary When the egg and sperm meet When the nuclei of the egg and sperm join When the egg and sperm attach to the uterus wall (1 mark) (c) After how many weeks of pregnancy is a human baby considered to be ‘fully developed’? (1 mark) Section Two — Humans as Organisms 28 Practice Questions 2 (a) Five parts of the human male reproductive system are named in the table below. Using the diagram, write the letter for each part next to its name. A B C D E name of organ letter sperm duct glands erectile tissue scrotum testis (5 marks) (b) What is the name of the substance ejaculated from the penis during sexual intercourse? (1 mark) 3 Alcohol is one type of legal drug. (a) Name one other type of legal drug. (1 mark) (b) Why does drinking alcohol slow down a person’s reactions? (1 mark) (c) Write down two organs in the body that can be damaged by drinking alcohol. (2 marks) (d) Alcohol is a depressant. Name one other type of drug that is a depressant. (1 mark) Section Two — Humans as Organisms  29 Revision Summary for Section Two Well, that’s the end of Section Two. Now what you've got to do is make sure you learn it all. And here again for your enjoyment are some more of those splendid questions. Remember, you have to keep coming back to these questions time and time again, to see how many of them you can do. All they do is test the basic simple facts. OK then — let's see how much you've learnt so far... 1) Name all five nutrients in a balanced diet. Say what each nutrient is important for in the body.  2) For each of the five nutrients, give three examples of foods that contain them.  3) Apart from the five nutrients, give two things that are needed in a balanced diet and explain why they’re needed.  4) What is obesity? How is it caused?  5) What health problems can be caused by getting too little food?  6) Give two things that affect how much energy a person needs each day.  7)* Sonia has a body mass of 54 kg. What is her daily basic energy requirement?  8) Name eight main bits of the alimentary canal. Say what goes on in each of the eight bits.  9) Why can't big molecules pass through gut walls? What has to happen to them first?  1 0) What are villi? What is their function (job) and how are they well-suited to do it?  1 1 ) Give four reasons why the bacteria found naturally in your digestive system are good news.  1 2) Explain how the skeleton protects part