Science yearly exam- YR 8

Question 1

Define digestion

Answer 1

Digestion is the process of breaking down food into a usable form and making the nutrients available.

Question 2

Why do we need a digestive system?

Answer 2

The food you eat is not in a form that can be used by your cells. Bread, meat, fruit and vegetables are made of complex chemicals that have to be broken down, or digested, into simple, soluble chemicals that can be used by your own cells. Your body needs the chemicals in food for energy, growth and repair (they are known as nutrients).

Question 3

Identify the two main parts of the digestive system

Answer 3

Your digestive system consists of a digestive tract, the pathway that the food takes through a series of organs. Organs off to the side of the digestive tract that produce chemicals assist with digestion.

Question 4

What are the parts of the digestive system?

Answer 4

Mouth, Esophagus, Stomach, Pancreas, Liver, Gall bladder, Small intestine, Large intestine and (rectum, anus).

Question 5

What role does the mouth have in the digestive system?

Answer 5

The digestive process starts in your mouth when you chew. Your salivary glands make saliva, which moistens food so it moves more easily through your esophagus into your stomach, saliva also has an enzyme that begins to break down the starches in your food.

Question 6

What role does the Esophagus have in the digestive system?

Answer 6

After you swallow, peristalsis pushes the food down your esophagus into your stomach.

Question 7

What role does the Stomach have in the digestive system?

Answer 7

Glands in your stomach lining make stomach acid and enzymes that break down food. Muscles of your stomach mix the food with these digestive juices.

Question 8

What role does the Pancreas have in the digestive system?

Answer 8

Your pancreas makes a digestive juice that has enzymes that break down carbohydrates, fats and portions. The pancreas delivers the digestive juice to the small intestine through small tubes called ducts.

Question 9

What role does the Liver have in the digestive system?

Answer 9

Your liver makes a digestive juice called bile that helps digest fats and some vitamins. Bile ducts carry bile from your liver to your gallbladder for storage, or to the small intestine for use.

Question 10

What role does the gallbladder have in the digestive system?

Answer 10

Your gallbladder stores bile between meals. When you eat, your gallbladder squeezes bile through the bile ducts into your small intestine.

Question 11

What role does the Small intestine have in the digestive system?

Answer 11

Your small intestine makes digestive juice, which mixes with bile and pancreatic juice to complete the breakdown of proteins, carbohydrates and fats. Bacteria in your small intestine make some of the enzymes you need to digest carbohydrates. Your small intestine moves water from your bloodstream into your GI tract to help break down food. Your small intestine also absorbs water with other nutrients.

Question 12

What role does the Large intestine have in the digestive system?

Answer 12

More water moves from your GI tract into your bloodstream. Bacteria in your large intestine help break down remaining nutrients and make vitamin K. Waste products of digestion, including parts of food that are still too large become stool.

Question 13

What role does the Rectum and anus have in the digestive system?

Answer 13

The rectum is a temporary storage for stool and the Anus is the opening at the end of the digestive tract through which stool is extracted.

Question 14

What is mechanical digestion?

Answer 14

Mechanical digestion is when the food is broken down into smaller pieces. it is like cutting a slice of bread into smaller pieces. Mechanical digesting is a physical change because no new substances are made.

Question 15

What is chemical digestion?

Answer 15

In chemical digestion, the large, complex substances in the food are broken down into simpler chemicals. This produces new smaller chemicals at the body can also absorb, chemical digestion is a chemical change because new substances are produced.

Question 16

What’s an example of mechanical digestion?

Answer 16

when you tear and choose food with your teeth.

Question 17

What’s an example of chemical digestion?

Answer 17

this happens when sliding your mouth and gastric juice in your stomach break down your food EG breaks down carbohydrates protein and fats.

Question 18

Define respiration as a series of chemical reactions occurring inside the cells.

Answer 18

Respiration refers to the series of chemical changes that take place themselves to release energy. For humans and many other animals, breathing is a process by which the body takes in and lets out air. The system of organs and tissues that take the air into the body and ultimately makes the oxygen available to the cells is the respiratory system.

Question 19

What is breathing and how does your body do it?

Answer 19

as you breathe in the muscles between your ribs contract. this pulls the rib cage up and out. at the same time, the diaphragm- a sheet of muscle that separates the chest from the abdomen- contracts and flattens. As your lung expands the air pressure decreases and when the air is sucked in the air pressure inside your lungs is equal to the air pressure outside the body. When you exhale, all the muscles relax and your ribs move down and in. The volume inside the chest returns and the air pressure increases forcing the air out of the nose/mouth.

Question 20

What is respiration and how does your body do it?

Answer 20

begins once the oxygen and glucose are together in the cells, where the two chemicals React together. carbon dioxide and water are produced in the reaction and energy is released. The more energy your body requires the faster the reaction has to take place and the more oxygen and glucose are required.

Question 21

what are the 9 parts of the repository system?

Answer 21

Nose, Pharynx, Larynx, Trachea, Lungs, Bronchi, Bronchioles, Alveoli, Diaphragm

Question 22

What is the role of the nose

Answer 22

Air containing 20% oxygen enters the body through the nostrils. Air is cleared and warmed as it passes through the nasal cavity. Mucus and nose hairs serve to filter dust from the air. Mucus also moistens the inhaled air.

Question 23

What is the role of the Pharynx

Answer 23

A cavity at the back of the nose and mouth, both food and air pass through the pharynx.

Question 24

What is the role of the Larynx

Answer 24

The voice box. When we swallow food, a flap called the epiglottis closes over the top of the larynx, preventing food from entering the lungs. Below it, the trachea (windpipe) directs the airflow. As air passes through the vocal cords, different pitches of sound are produced.

Question 25

What is the role of the Trachea

Answer 25

– The windpipe lies in front of the oesophagus (food tube) and is protected at the front by C-shaped cartilage. Fine hair-like structures called cilia on the walls of the trachea “brush” dust upwards and out of the respiratory tract.

Question 26

What is the role of the Lungs

Answer 26

– Air enters the lungs, where oxygen moves into the blood and carbon dioxide moves from the blood to the lungs, where it is exhaled.

Question 27

What is the role of the Bronchi

Answer 27

– The trachea branches into two tubes called the bronchi, one going into each lung. Mucus and cilia cover the walls of the bronchi.

Question 28

What is the role of the Bronchioles

Answer 28

– The right and left bronchi branch into many smaller tubes called the bronchioles. The walls of the bronchioles are lined with mucus and cilia.

Question 29

What is the role of the Alveoli –

Answer 29

These are the balloon-like air sacs at the ends of the bronchioles. The walls of the alveoli are very thin and are surrounded by fine blood capillaries. The exchange or diffusion of oxygen into the blood from inhaled air, and of carbon dioxide out of the blood to the exhaled air, takes place here.

Question 30

What is the role of the Diaphragm –

Answer 30

A large, drum-shaped muscle that lies at the base of the chest cavity. The diaphragm contracts during inhalation and relaxes during exhalation.

Question 31

Describe the diffusion of oxygen and carbon dioxide into the alveoli and the exchange of these gases in the bloodstream

Answer 31

The walls of the alveoli are only one cell thick, surrounded by tiny blood vessels called capillaries. Oxygen dissolves in the alveoli’s moist surface and moves by diffusion across the short distance from the space inside the alveoli to the blood. Once in the blood, oxygen enters the red blood cells, and the flow of blood carries oxygen to the cells where it is needed. The blood flowing from the lungs is therefore rich in oxygen and appears bright red.
As the cells use oxygen to release energy from food, carbon dioxide is produced and moves from your cells into the blood and into the alveoli. The carbon dioxide mixes with the remaining air and then leaves your body with your next outward breath.

Question 32

What is the structure of the alveoli?

Answer 32

The walls of the alveoli are only one cell thick, and they are surrounded by tiny blood vessels called capillaries.

Question 33

Describe the diffusion of oxygen and carbon dioxide into the alveoli and the exchange of these gases in the bloodstream

Answer 33

Oxygen dissolves in the moist surface of the alveoli and moves by a process called diffusion across the short distance from the space inside the alveoli to the blood. Once in the blood, oxygen enters the red blood cells, and the flow of blood carries oxygen to the cells where it is needed.
As the cells use oxygen to release energy from food, carbon dioxide is produced and moves from your cells into the blood and into the alveoli. The carbon dioxide mixes with the remaining air and then leaves your body with your next outward breath.

Question 34

How does the blood change after oxygen enters it?

Answer 34

The blood flowing from the lungs is therefore rich in oxygen and appears bright red.

Question 35

what is breathing (in comparisin to respiration rate)?

Answer 35

Breathing rate is the number of breaths taken per minute and reflects how often we inhale and exhale. This rate can change based on physical activity, emotional state, or health conditions.

Question 36

what is Respiration rate (in comparison to breathing?)

Answer 36

Respiration rate is the rate at which gas exchange occurs in the lungs, specifically the exchange of oxygen and carbon dioxide. This can be influenced by the breathing rate, as a higher breathing rate usually means more oxygen is brought in and more carbon dioxide is expelled. When you exercise or your body needs more oxygen and needs to eliminate carbon dioxide quickly, both your breathing and respiration rate increase. During rest, your breathing rate slows, and the respiration rate also decreases.

Question 37

List the components of the circulatory system

Answer 37

Your circulatory system consists of your heart, blood vessels, arteries, veins, capillaries, and blood. The components of blood include red blood cells, white blood cells, platelets, and plasma. The heart pumps continuously to keep the blood moving. The blood carries all the materials needed by the body through the blood vessels. The blood vessels are the main pathways along which the blood flows.

Question 38

describe the heart

Answer 38

Your heart is about the size of your fist and is situated in the middle of your chest, behind the breastbone. It is made up of cardiac muscle, a type of muscle that does not get tired and works continuously in response to signals from an area of the heart called the pacemaker.

Question 39

the function of the heart in the circulatory system

Answer 39

The human circulatory system is referred to as a double system because there are two separate circuits through which blood flows, both starting at the heart. In one circuit, the blood flows from the heart to the body and back to the heart, carrying nutrients and oxygen to the cells. At the cells, it collects waste, including carbon dioxide. The other circuit goes from the heart to the lungs, where carbon dioxide passes out of the blood and oxygen passes into the blood. This oxygenated blood is then returned to the heart and pumped around the body.

Question 40

the functions of the veins in the circulatory system

Answer 40

Veins carry blood back to the heart. The pressure from the heartbeat is lost as the blood flows through very narrow capillaries, which do not need muscular walls. This happens due to the contraction of muscles pressing against your veins, ensuring that the blood flows in one direction only. There are valves along the length of the veins that open as blood flows toward the heart and close when it flows away from it. If you sit for long periods of time, blood flow slows, which can lead to clotting.

Question 41

the functions of the capillaries in the circulatory system

Answer 41

As arteries branch into smaller and smaller blood vessels, they eventually form the very finest blood vessels called capillaries, which reach nearly every cell in the body. Capillaries are only one cell thick, so materials can easily pass through them. Nutrients and oxygen needed by the cells pass out of the capillary and into the cells, while waste products from the cells, including carbon dioxide, pass into the capillary to be carried back to the heart. Capillaries join together to form veins.

Question 42

Define excretion as the way the body gets rid of waste it has produced

Answer 42

Expiration is the process of getting rid of wastes your body has produced. it is the function of the excretory system. The lungs, skin, liver and kidneys are involved in excretion.

Question 43

Describe the excretory role of the lungs

Answer 43

Respiration produces carbon dioxide and water as waste products. These are carried back to the lungs and breathed out. The lungs are part of the excretory system, as well as the respiratory system.

Question 44

Describe the excretory role of the Kidneys

Answer 44

The kidneys are two bean-shaped organs, about the size of a fist. They filter approximately 50 liters of blood every hour. The kidneys excrete urea, a protein waste product, and help control the level of water in the body. When the body has the correct amount of water, urine is clear or pale yellow. If the body is low on water, urine becomes more concentrated and darker in color. The kidneys also regulate salt levels in the blood. Too much or too little salt can prevent cells from working properly, so excess salt is removed in the urine. Together, the kidneys, bladder, ureters, and urethra form the urinary tract.

Question 45

how does your skeleton support your soft tissues?

Answer 45

Without a skeleton, your skin and internal organs would collapse. Unlike a jellyfish, which is supported by water and doesn’t need a skeleton, humans need a skeleton for support.

Question 46

how does your skeleton support your organs?

Answer 46

One of the main roles of the axial skeleton, which is made up of 80 bones, is to protect your vital organs. The skull protects the brain, the vertebrae protect the spinal cord, and the ribs and sternum (breastbone) protect the lungs and heart.

Question 47

how does your skeleton Allow Movement?

Answer 47

The main role of the appendicular skeleton, which consists of 126 bones, is to allow movement. This includes the bones in the pelvis, shoulder blades, collarbones, and the bones in your arms and legs.

Question 48

what are ligaments?

Answer 48

Ligaments are bands of tough, flexible tissue that hold the bones in a joint together. They prevent the bones of the joint from moving too far apart.

Question 49

what are tendons?

Answer 49

Tendons are tissues that attach muscles to bones and hold the muscles in position. When activated, muscles contract, becoming shorter and thicker. They pull on the bones they are attached to, causing them to move.

Question 50

what are muscles?

Answer 50

Muscles move your bones. They are tissues that are able to contract (shorten) and be stretched. You have about 640 muscles in your body. Muscles can only pull, not push. Therefore, another muscle is required to return the bone to its original position. This is why muscles are arranged in antagonistic pairs, meaning they work in opposition to each other. For example, the biceps and triceps are antagonistic muscles. The biceps contract when you pull something up and relax when you lower it, while the triceps contract to return the arm to its original position

Question 51

Define cell division in multicellular organisms.

Answer 51

When multicellular organisms grow, they do so by making new cells. Each cell can divide into two new cells in a process called cell division. By repeating this division, a few cells can produce the many cells that make up the tissues and organs that form the organism’s body

Question 52

How does cell division contribute to tissue repair?

Answer 52

Cell division allows multicellular organisms to repair themselves. Repair is the process of fixing damaged tissues, which is necessary for healing torn tissues like bones, muscles, tendons, and ligaments.

Question 53

What role does mitosis play in cell division?

Answer 53

Mitosis is the process in which a nucleus divides to form two cells with identical genetic information. Each new daughter cell is genetically identical to the parent cell.

Question 54

Q: Describe the stages of mitosis.

Answer 54

1. Interphase: Cell has fully grown, chromosomes not clearly visible.
2. Early Prophase: Chromosomes have replicated and are attached to the centromere.
3. Prophase: Nuclear membrane dissolves, chromosomes attach to spindle.
4. Metaphase: Chromosomes line up in the middle of the cell.
5. Anaphase: Chromosomes separate and move to poles of the cell.
6. Telophase: New cell membrane forms.
7. Interphase: New nuclear membrane forms, two new daughter cells are formed.

Question 55

Differentiate between asexual and sexual reproduction.

Answer 55

Sexual reproduction happens when a sperm from a male and an egg from a female join in fertilisation, requiring two parents. Asexual reproduction requires only one parent and occurs through cell division without sperm or eggs.

Question 56

What is a gamete?

Answer 56

Gametes are special reproductive cells—sperm in males and egg in females. Formed by meiosis, gametes contain half the genetic information of body cells.

Question 57

What is a zygote?

Answer 57

Fertilisation results in a zygote, a cell with all genetic information needed to grow into a new individual. The zygote divides to form many cells, eventually developing into a new organism.

Question 58

Explain internal and external fertilisation.

Answer 58

External fertilisation occurs outside the body (e.g., frogs), while internal fertilisation occurs within the body (e.g., land animals), which prevents sperm from drying out.

Question 59

Identify and describe the parts of a flower.

Answer 59

Petal: Attracts animals for pollination.
Anther: Produces pollen.
Filament: Holds anther.
Sepal: Protects bud.
Ovule: Contains egg.
Ovary: Encloses seeds post-fertilisation.
Style: Connects stigma and ovary.
Stigma: Site for pollen deposition.

Question 60

What are the functions of the root, stem, and leaf in flowering plants?

Answer 60

Root: Anchors plant and absorbs nutrients and water.
Stem: Supports plant and transports nutrients.
Leaf: Site of photosynthesis, producing food for the plant.

Question 61

Name the parts of the female reproductive system and their functions.

Answer 61

Fallopian tube: Guides egg to the uterus.
Ovary: Produces eggs.
Uterus: Where the baby grows.
Cervix: Holds uterus closed until birth.
Vagina: Site of penis insertion.

Question 62

Describe the process of fertilisation in the female reproductive system.

Answer 62

Eggs are produced in ovaries and released through fallopian tubes, where they may meet sperm for fertilisation. A fertilised egg then burrows into the uterine lining for development.

Question 63

Outline the steps from ovulation to implantation.

Answer 63

After ovulation, an egg is released, fertilised, and forms a zygote. The zygote divides, becoming a blastocyst, and implants in the uterine wall, marking the start of pregnancy.

Question 64

What is the role of the placenta?

Answer 64

The placenta supplies nutrients and oxygen from the mother to the embryo and removes waste via the umbilical cord. It acts as a barrier to prevent mixing of mother and embryo blood supplies.

Question 65

Definition of an element

Answer 65

Elements are substances made of only one type of atom.

Question 66

Examples of uses of common elements

Answer 66

Billions of invisible nitrogen and oxygen atoms surround you, and it is what is hitting our skin as the breeze blows. In addition to oxygen and nitrogen, there are many other elements that are useful in everyday life. For example, hydrogen and oxygen are essential for drinking water and cooking.

Question 67

what is an atom?

Answer 67

An atom is the smallest particle that can exist and is the building block of matter. Each element has a unique set of characteristics called properties, which can determine whether an element is classified as metallic or non-metallic.

Question 68

Describe some physical and chemical properties of metals

Answer 68

etals tend to be shiny or can be polished to make them shiny. This is referred to as being lustrous. Metals are solids at room temperature, except mercury, which is a liquid. Metals are good conductors of heat and electricity, allowing heat and electricity to flow easily through them. Metals can be stretched into wires. Metals are referred to as being ductile.

Question 69

Describe some physical and chemical properties of non- metals

Answer 69

Nonmetals tend to be dull, not shiny, and are solid or gases at room temperature, except bromine, which is a liquid. Nonmetals do not conduct heat or electricity and break or crumble when bent. Nonmetals are referred to as being brittle.

Question 70

How to correctly label chemical symbols?

Answer 70

Often, the chemical symbol of an element comes directly from its name. For example, calcium = Ca, carbon = C, and magnesium = Mg. However, sometimes the symbol of an element does not relate to the name at all. For example, potassium = K and sodium = Na. This is because their symbols come from the names in other languages.
Chemical symbols usually consist of two letters and the first letter is always capitalised.

Question 71

some examples of chemical symbols:

Answer 71

Hydrogen = H
Helium = He
Lithium = Li
Beryllium = Be
Nitrogen = N
Oxygen = O
Fluorine = F
Aluminium = Al
Sulphur = S
Chlorine = Cl

Question 72

State three ways that Atoms can be arranged as single-atom model molecules or lattices

Answer 72

Elements are made up of just one type of atom. However, the atoms in elements can be arranged in different ways. The atoms can exist:
As single atoms, this is referred to as being monatomic.
In classes of atoms called molecules.
In large grid-like structures called lattices.
The way the atoms are arranged in an element determines many of the physical properties of the element. Physical properties include whether the element is a solid, liquid, or gas, its melting and boiling points, how well it conducts heat or electricity, and if it bends or breaks when a force is applied.

Question 73

what is a molecule?

Answer 73

In molecular elements, molecules are composed of all the same types of atom. Most non-metallic elements are made up of molecules. Molecules are clusters of two or more atoms bonded or joined together. In a molecular element, all the molecules are identical, with the same size, shape, number, and type of atoms.

Question 74

what are molecule formulas?

Answer 74

molecule are formulas are the amount of each atom in a molecule. For example, oxygen contains 2 oxygen atoms, or O₂. Other non-metallic elements that are made up of molecules with just two atoms are nitrogen (N₂) and chlorine (Cl₂). Some non-metallic elements are made up of molecules with more than just two atoms. For example, sulfur (S₈) contains 8 sulfur atoms, while other rings contain S₆ and S₂₀.

Question 75

Describe the molecular structure of nitrogen, phosphorus, sulfur, and carbon:

Answer 75

Nitrogen molecules contain 2 nitrogen atoms.
Phosphorus molecules contain 4 phosphorus atoms.
Sulfur molecules contain 8 sulfur atoms.
A buckyball or carbon molecule contains 60 carbon atoms

Question 76

State all metals exist as crystal lattices

Answer 76

Crystal lattices are large, grid-like structures that repeat the same arrangement of atoms over and over. All metallic elements form crystal lattices. Only a few non-metallic elements form crystal lattices.
In metallic elements, the atoms in metals form lattices rather than molecules, which is a strong, dense structure. At room temperature, except mercury, they are solids. The atoms in metals are only weakly connected, so they can be bent, etc. Non-metallic elements: Only a few non-metallic elements form lattices. For example, silicon and carbon to make graphite and diamond.

Question 77

Define compound

Answer 77

Most substances you encounter every day are made up of more than one type of atom. These forms of matter are known as compounds. Like every element, every compound has a unique set of characteristic properties. Properties of compounds are usually very different from the properties of the elements that make them up.

Question 78

Define molecular compound

Answer 78

All molecules in a compound are identical in size, shape, and number of atoms. Example: One molecule of carbon monoxide (CO) is just one carbon atom and one oxygen atom. But molecules in other compounds contain thousands. Despite having very different properties, each molecule is made by containing different numbers of the same elements: oxygen, hydrogen, and carbon.

Question 79

Define Compound lattices

Answer 79

Compounds can also form crystal lattices, where the atoms are bonded strongly to each other. Example: Table salt or beach sand (sodium chloride, NaCl) in its chemical form. NaCl is not a molecular formula because NaCl does not contain molecules. Instead, the formula tells you that in the crystal lattice, there is one sodium atom for every chloride ion. Beach sand or silica has a chemical form of SiO₂, which indicates that in a grain of sand, there is one silicon atom for every two oxygen atoms.

Question 80

Distinguish between the type and arrangement of particles in elements

Answer 80

Only consist of one type of atom, meaning all particles are identical and arranged uniformly. This means they cannot be broken down into simpler substances by chemical means. For example, a gold element can only have gold atoms arranged.

Question 81

Distinguish between the type and arrangement of particles in compounds

Answer 81

Some compounds form molecules, such as water. In these compounds, each molecule contains two or more types of atoms. Other compounds form crystal lattices. For example, table salt is made up of a lattice consisting of sodium and chloride atoms, while beach sand is a lattice of silicon and oxygen.

Question 82

Distinguish between the type and arrangement of particles in mixtures

Answer 82

Many of the substances used every day are not simply elements or compounds but are mixtures of both elements and compounds. For example, air is a mixture of the elements oxygen (O₂) and nitrogen (N₂), with a compound such as water vapor (H₂O), carbon dioxide (CO₂), and carbon monoxide (CO). Anything that has a list of ingredients is a mixture. You cannot write chemical formulas for mixtures because they are made up of a variety of molecules and crystal lattices. All elements and compounds only contain one type of molecule or crystal lattice.

Question 83

Define the terms aqueous, mixture, solvent and solution

Answer 83

There are many different types of mixtures that you use every day. One common type of mixture is a solution. A solution is formed when a solid dissolves in a liquid. In a solution, the dissolving solid is known as the solute, and the liquid in which the solid dissolves is known as the solvent. Many common solutions have water as the solvent. These water-based mixtures are referred to as aqueous solutions. For example, sugar dissolves in water to form an aqueous sugar solution, where sugar is the solute and water is the solvent.

Question 84

Define physical changes

Answer 84

The key feature of a physical change is that no new substances are produced during the change. Physical changes include changing shape or form expansion and contraction, a change of state (solid, liquid, or gas), or mixing substances together. The physical properties of the substance may change, but the substance before and after the change is exactly the same. For this reason, physical changes can often be easily reversed.

Question 85

Describe examples of physical change: changes in shape

Answer 85

Changing shape or form is the simplest example of a physical change. In this case, forces are applied to break, bend, stretch, crush, twist, or compress an object. These changes do not produce new substances. For example, when you crush an aluminium can, it changes shape but is still made up of aluminium. Or crushing an aspirin tablet into powder — it is still aspirin but in a different form. These changes can be reversed relatively easily.

Question 86

Describe examples of physical change Expansion and contraction

Answer 86

Physical changes also occur when the temperature of a substance increases or decreases. When solids, liquids, and gases are heated, they expand and take up more space. When expansion occurs, the volume increases and its density decreases, but no new substances are formed. The reverse of expansion is contraction. When a solid, liquid, or gas is cooled, it contracts. The volume decreases as density increases. Thermometers use expansion and contraction of liquids to measure temperature. When the temperature increases, the liquid expands and moves up the thermometer. Hot air balloons use the expansion of heated air to lift off the ground. The air expands to fill the balloon and is much less dense than the cooler air outside, so it floats.

Question 87

Describe examples of physical change Changes of state

Answer 87

f enough heat is applied to a substance, it will not only expand but will also change state. From a solid to a liquid (melting), from a liquid to a gas (evaporation). When a substance is cool enough, it will not just contract but change state from a gas to a liquid (condensation). An example of condensation is when you breathe out fog on a cold day, which is just the water vapour condensing to form visible liquid water droplets. Or from a liquid to a solid (freezing or solidification). A few substances change directly from a solid to a gas (sublimation) or gas to solid (deposition). The physical properties may be different, but they’re both made up of the same substance.

Question 88

Describe examples of physical change Mixing

Answer 88

Mixing two substances is a type of physical change. For example, a bucket of different coloured balls is a mixture that can be seen by the eye. The different coloured balls mix, but no new balls are formed. When a substance is dissolved, it forms a solution. It is also a physical change. In a solution, the solute seems to disappear, but it’s actually broken down into invisible particles in the solvent. The solute can be removed by boiling or evaporation, and the particles form crystal lattices in a process called crystallisation. For example, sugar dissolving in water.

Question 89

Describe ways to detect the presence of a new substance

Answer 89

To distinguish between a chemical change and a physical change, you need to determine if a new substance has formed as a result. The new substances formed in a chemical change could be a solid, liquid, or gas. You could detect the presence of a new substance by a sudden change in colour, smelling gas, or seeing a new solid known as a precipitate forming in a clear solution. Other signs could include seeing light or feeling a change in temperature.

Question 90

Describe some examples of colour change that indicates chemical change

Answer 90

When something exchanges colour, it is very likely a chemical change because the new substance is produced and has a different colour from what you started with. For example, burning a match, paper, or wood produces black powder, which is carbon. When iron is left in the rain, it turns orange-brown because iron dioxide (rust) is produced. Other examples include changing the colour of leaves in autumn and bleaching or dyeing clothes or hair.

Question 91

Describe examples of gas formations that are chemical

Answer 91

The production of a gas usually indicates a chemical change. A gas produced during a chemical change may be observed as bubbles, a new smell, or smoke. For example, when vinegar is added to bicarbonate of soda, many bubbles of carbon dioxide (CO2) are formed. Carbon dioxide is also formed by chemical changes in soft drinks to create fizz, or when antacid tablets dissolve in water. Rotting is another example of chemical change, as a pungent smell of hydrogen sulfide (H2S) is produced. Similarly, burning is the first thing you notice, and this is because it causes a chemical change that produces smelly gases. An exception is boiling or sublimation.

Question 92

Describe the structure of solids

Answer 92

In solids, the attraction between particles bonds them tightly together. For this reason, solids are incompressible and hold their own shape. Although the particles in solids are fixed in position, they vibrate on the spot. These vibrations increase with temperature. In liquids, the particles are packed together, which means liquids are incompressible.

Question 93

Describe the structure of liquids

Answer 93

particles in a liquid are not stuck to each other as much as they are in solids. This gives liquids the ability to flow and take the shape of the bottom of the container. Particles in a liquid vibrate but can also move freely throughout the liquid.

Question 94

Describe the structure of gases

Answer 94

In gases, the particles are not stuck to each other at all, and there are large spaces between gas particles. For this reason, gases are highly compressible and able to be squashed. Particles are free to move anywhere within their container. The particles move in straight lines until they collide with other gas particles or the side of the container. This is why gases always fill their container.

Question 95

expansion and contraction in solids

Answer 95

In solids, the particles vibrate in fixed positions. As the temperature increases, so do the vibrations, pushing the particles further apart and causing the solid to expand. When a solid is cooled, the reverse happens: the particles vibrate less, allowing them to be packed more tightly, and the solid shrinks.

Question 96

expansion and contraction in liquids

Answer 96

The particles in liquids also vibrate more when they are heated, causing liquids to expand when heated and contract when cooled. However, in liquids, the particles are free to move, so liquids tend to expand and contract more than solids.

Question 97

expansion and contraction in gases

Answer 97

Gases will always expand and contract to fit their container. However, as the temperature of gases increases, the particles travel faster, which means they hit the sides of the container more frequently and with more force. If the container is flexible, such as a balloon, increasing the temperature of the gas will cause the balloon to expand. The reverse is also true: if the gas is cooled, the particles travel slower, hitting the sides less forcefully, and if they are contained in an inflexible container, the gas will contract.

Question 98

Describe how melting can be explained using a particle model

Answer 98

In a solid, particles vibrate but hold their position. As the temperature increases, the vibrations increase and expand until the solid melts. This is because the vibrations become so energetic that the attraction can no longer hold the particles in fixed positions. However, there is still a small amount of attraction that can hold the particles together as a liquid.

Question 99

Describe how freezing can be explained using a particle model

Answer 99

Freezing: The opposite of melting. In a liquid, free-moving particles slow down and become less energetic until the attraction between the particles is able to fix them in position, forming a solid.

Question 100

Describe how evaporation can be explained using a particle model

Answer 100

Evaporation: Evaporation occurs when particles in a liquid escape from the surface of the liquid to form a gas. The particles in a liquid are stuck together but only weakly, so as the liquid is heated, they vibrate faster until some are able to break through the surface and form a gas. At the boiling point, the particles are moving so fast they fly apart and form bubbles within the liquid.

Question 101

Describe how condensation can be explained using a particle model

Answer 101

The reverse of evaporation. As a gas cools, the particles slow down until the forces of attraction between them can hold and stick them together, forming liquid droplets.

Question 102

Describe the application of the particle theory of matter using everyday examples

Answer 102

All matter is made up of particles (atoms, molecules, ions) and has motion. All the particles in a singular substance are identical. Temperature is the main factor that affects the spread of the particles. Gases do not have bonds, unlike solids and liquids. One everyday example that expresses these rules is water (H₂O), as its state changes based on the temperature and the speed at which the particles move.