Science 2024 Notes PDF

s c i e n c e \~2024 --------- \~ eric lu **Energy\~** - **Types of energy** Energy can either be - Kinetic energy- anything that moves has kinetic energy. The faster an object moves, the more kinetic energy it has. Heat/thermal energy- anything that gives off heat has heat energy. Any...

s c i e n c e \~2024 --------- \~ eric lu **Energy\~** - **Types of energy** Energy can either be - Kinetic energy- anything that moves has kinetic energy. The faster an object moves, the more kinetic energy it has. Heat/thermal energy- anything that gives off heat has heat energy. Anything that moves also has heat energy. Can come from the sun, stars, flames, chemical reactions, electrical devices or even a person or animal. Light energy- anything that gives off light has light energy. Natural sources of light include the Sun and stars etc. Artificial sources of light include light bulbs etc. Sound energy- any medium that vibrates gives off sound energy. Your eyes and ears interpret the vibrating of mediums as sound. Electrical energy- anything that has electricity has electrical energy. It's produced by power stations, solar cells and lightning. Electrical energy powers your TV, computer, microwave and toasters. Chemical energy- it is stored in a substance and can be converted to many forms of energy. Nuclear energy- it is the energy stored inside tiny atoms that make up all matter. Nuclear energy is released in a nuclear power plant, when a nuclear bomb explodes, inside the Sun etc. It produces heat and light. Electromagnetic energy- waves and spans a broad spectrum from very long radio waves to very short gamma rays. Energy transfer v.s. energy transformation: Energy transfer is where energy is moving from one place to another, while energy transformation is energy changing its form. Energy transfer examples - Energy transformation examples: - **Law of conservation of energy** - **Transfer of heat** Heat can be transferred in 3 ways, - - Examples of conduction include: - - Examples of convection include: - - Examples of radiation (heating) include: - **Useful and wasted energy** Useful and wasted energy is used to describe the effectiveness or utility of energy in a particular context. Examples of useful energy: - Examples of wasted energy: - **Energy Efficiency** Energy efficiency refers to the practice of using less energy to perform the same task or produce the same result. It involves reducing energy consumption while maintaining or improving the quality of services provided. The goal of energy efficiency is to minimise energy waste, lower costs, and reduce environmental impact. **Electricity\~** - **Atomic components and charges** - Electricity is powered through electrons. **Alike charges**: 2 things with the same charge repel each other. (similar to magnetism) **Different charges:** 2 things with different charges attract each other. (similar to magnetism) **Static electricity** Static electricity refers to the imbalance of electric charges on the surface of an object. It occurs when there is an excess or deficiency of electrons, leading to the build-up of an electric charge. However, there is no flow of electric current. E.g. if you rub against an object, the object that gains the electrons becomes negatively charged. The object that loses the electrons becomes positively charged. These two objects will be attracted to each other due to their different charges. - **Current electricity** Current electricity involves the flow of electric charge (usually electrons) through a conductor. It is a dynamic process where charges move from one point to another. It is also known as an electric current. **Electric currents** Our electrical devices are powered by the movement of charged particles, like electrons. Electrons move through thin strands of metal called wires. The movement of electrons through a wire is known as an electrical current. Without a current, our devices can\'t work at all. An electrical current must: - **Insulators**: a material that prevents or reduces the flow of electricity or heat (resistors) Generators: supply the energy (battery) **Conductors**: usually metal/copper wires allow electricity to flow through the circuit. **Circuit Diagram** Components of an circuit diagram: element description/diagram purpose ------------ ------------------------ --------------------------------------------- wire carries the current (good conductor) battery  supplies energy (generator) light bulb produces and transforms electric into light switch  starts and stops current fuse cuts off power when there's an overload resistor  slows the flow of electrons/current A circuit diagram is like a map that shows where the electricity travels. Each circuit component has its own symbol. Conventions of drawing circuit diagrams are: - Every component in a circuit has two metal contacts, called terminals, that allow electrons to flow into and out of them. The part that electrons flow out of is called the negative terminal (repels negative charge). The part that electrons flow into is called the positive terminal (attracted to positive charge). **Battery** Electrons need energy to move through a circuit and its components. That\'s why a circuit needs a power source like a battery. A battery is a type of power source that stores chemical energy. When a circuit connects the terminals of a battery, electrons are pushed away from its negative terminal and pulled toward its positive terminal. This gives electrons the energy to move around the circuit, creating a current. Along the way, electrons transfer this energy to components such as light globes, motors and heating elements. **Voltage** Voltage is a measure of how much electrical potential energy is available/given to the moving electrons in a circuit from the battery. It is measured in volts (V). Another way of thinking of voltage is by analogy with the pressure that pushes water through the pipes in a house, or how much you turn on the tap. The higher the pressure in the pipes, the more strongly the water is pushed through the pipes. Similarly, the higher the voltage supplied to a circuit, the bigger the \"push\" electrons receive, and the faster they move. **Current** The current is the rate of flow of electric charge or the speed of the electricity or the electrons. The greater the current, the more electric charge passes a given point in the circuit per second. Another way of thinking of it is the analogy of the speed of the water coming out of the hose. It is measured in amps (A/I). **Resistance** Resistance is measured in the special unit of ohms, symbolised by the Greek letter omega (Ω). The higher the resistance of a component, the harder it is for electrons to flow through it and the more energy they lose. The resistance of the connecting wires in typical electrical circuits is so low that we can assume it\'s zero. Resistors are special components with high resistance designed to lower the current passing through a circuit. One example of their use is to protect light-emitting diodes (LEDs). These light bulbs need low currents between 1 to 20 mA or they will burn out. Ohm's law: V = IR The higher the voltage, the faster the current (vice versa). The higher the resistance, the slower the current (vice versa). **Types of circuits** There are 2 types of circuits: - - **Chemistry\~** - The atom is made up of three subatomic particles: protons, neutrons and electrons. Charge Location Weight ----------- ---------- ---------------- -------- Protons Positive Nucleus Heavy Neutrons Neutral Nucleus Heavy Electrons Negative Around nucleus Light -  **Subatomic**: smaller than or occurring within an atom **Reaction**: a rearrangement of the atoms of more molecules of two or more substances that come into contact with each other, resulting in the formation of one or more new substances. Chemical reactions are caused by the electrons of one substance interacting with those of another. **Particles**: a relatively small part of something (matter). **Mixture**: When two or more pure substances mix with each other without participating in a chemical change (but are mixed physically), so that each substance retains its original properties and remains its own substance. Because of this, mixtures can be separated into their components, becoming individual substances once more without a chemical reaction. They can be represented through a particle model, where a mixture would have more than 1 type of particle. Mixtures can be made from any combination of solids, liquids and gases. The \"particles\" in a mixture might be solid fragments, liquid droplets or gas bubbles. Mixing these different components together can produce substances with new properties. For example, foams are formed by mixing gas bubbles into a liquid and some foams can hold their shapes in the way that solids do. **Compound**: two or more different elements chemically bonded in a fixed ratio. When the elements come together, they react with each other and form chemical bonds that are difficult to break. **Molecules**: two or more of the same elements chemically bonded while still retaining its composition and properties of that substance. Molecules are more common in gas or liquid form, as the atoms are more spread apart. **Matter**: something that occupies space and has rest matter. **Lattice**: a structure all bonded together. Lattices are more common in solid form as the atoms are more tightly packed together. **Polymer:** a wide range of compounds that make up important materials such as rubber and synthetic fibres. Polymers are made of very long chains of smaller molecules. **Purity levels** In chemistry, purity refers to the extent to which a substance is free from contaminants or impurities. A pure substance contains only one type of particle, whether it be an atom, molecule or compound. Understanding purity is essential in chemistry to ensure that substances used in chemical reactions are free from impurities that could affect the outcome of experiments, the quality of products and the safety of processes. It is also crucial in various industries such as pharmaceuticals, food production, and manufacturing to meet regulatory standards and ensure the effectiveness and safety of products. Least pure to most pure: - **Physical and chemical changes** Physical changes: - Chemical changes: - **Products and Reactants** Chemical change can be observed: - During a chemical change, atoms are never created or destroyed. A chemical reaction is when atoms rearrange to form new substances The starting substances of a chemical reaction are known as the reactants. The substances that are formed are known as the products. **Energy in chemical reactions** Energy plays an important part in chemical reactions. The atoms in molecules and lattices are held together by chemical bonds that store energy. It is the energy in these bonds that is released when you use a battery, burn fossil fuels like petrol or convert food into energy for your body. **Chemical equations** A chemical equation is one way of recording what happens when substances react together. On one side are the substances that react together. These are known as reactants. The other side are the substances that are produced. These are known as the products. Between the reactants and products is an arrow indicating the direction of the change. The substances to which the arrow is pointing are the products. **Spontaneous reactions** Some chemical reactions need a constant supply of energy while others will start and continue naturally. Reactions that proceed by themselves are known as spontaneous reactions. There are two types of spontaneous reactions. The first type can obtain enough energy from the surroundings to start and continue. Rusting is an example of this type of spontaneous reaction. Other spontaneous reactions need a kick- start from an external energy source but then produce enough energy to continue the reaction. Although you need an initial flame to start wood burning, the chemical reaction produces enough heat to continue the reaction spontaneously. **Non-spontaneous reactions** Other chemical reactions require energy to be added constantly---otherwise the reaction will stop. These reactions are known as non-spontaneous reactions. A hydrogen fuel cell converts water (H2O) into hydrogen (H2) and oxygen (O2). Although this is a clean source of energy, it requires an electrical current to be applied constantly for the reaction to proceed. **The Periodic Table\~** - **Metals and Non-metals** Scientists divide all elements into two types - metals and nonmetals. They do this because most metals or nonmetals have certain properties that are the same. **Metals** - **Non-metals** - **Chemical symbols** Each element has its own chemical symbol. This may be either: - **Chemical formula** The symbols for elements are used to show how atoms are arranged. For example, two oxygen atoms that are bonded together can be indicated by writing the symbol for oxygen followed by the subscript 2: O~2.~ A symbol that shows the chemical composition of a substance is called a chemical formula. **Atomic weight** Elements have different masses. Hydrogen is the lightest element. Carbon atoms are about 12 times heavier, and mercury atoms are about 200 times heavier. **Body Systems\~** - **The Digestive System** - - -  The digestive system is essentially a long, muscular tube with different sections in which various processes occur. All the processes act to break down the food from a complex form to a simple form. - The digestive systems of other animals are suited to their diets. **Monogastric animals**, such as humans, pigs and dogs, have a single-chambered stomach where food is digested. The digestive process is relatively straightforward involving mechanical digestion in the mouth and stomach and chemical digestion in the stomach and intestines. **Ruminant animals**, such as cows, sheep and goats, have multi chambered stomach (rumen, reticulum, omasum and abomasum) that allows them to digest tough plant materials like cellulose. The rumen contains bacteria that help ferment and break down food, which is then regurgitated as chud, chewed again, and swallowed for further digestion. **Carnivores** have a shorter digestive tract because meat is easier to digest. **Herbivores** have longer digestive systems to break down fibrous plant material. **Peristalsis** is a series of wave-like contractions that occur in the walls of the digestive tract. These contractions move food and waste through the digestive system. It begins in the oesophagus where a bolus of food is swallowed and continues through the stomach, small intestine and large intestine. This process ensures that food moves in one direction and allows for efficient digestion and absorption. **Mechanical and chemical digestion** Mechanical digestion - Chemical digestion - **The Circulatory System** - Arteries - Veins - Capillaries - Organs - Arteries Capillaries Veins ----------------------------- ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Function To carry oxygenated blood around the body Small blood vessels where the exchange of oxygen, carbon dioxide, waste, etc Carry deoxygenated blood back to the heart. Structure of wall Thick, flexible walls to withstand the high pressure of blood Very thin cell walls, only one cell thick, to allow for passing of oxygen better. Thinner walls because there is not as much blood pressure Lumen Small lumen to maintain blood pressure Very small lumen Large lumen because it does not require as much pressure. Valves Does not have any valves except for the aortic and pulmonary valve in the heart. Does not have any valves because it relies on diffusion to go slower. Has valves that prevent backflow of blood. How structure fits function Arteries do not have valves because it flows very quickly and will probably not backflow. It also has flexible walls so it can adapt to the blood pressure from the heart. It is very small so that it facilitates the exchange of oxygen and carbon dioxide better. It also has very small lumens so it increases surface area while volume is small, so it is more efficient in diffusion. Veins have valves so that the blood flows in the right direction. It has lower pressure because it loses a lot of pressure after the capillaries. It has thinner walls because it does not have as much pressure and can hold more blood. Flow of blood - **Respiratory system** - For humans and many other animals, breathing is the process by which the body takes in and lets out air. The system of organs and tissues that takes the air into the body and makes the oxygen available to the cells in the respiratory system. - When you breathe in, some air may come in through your mouth but most of it comes in through your nose. Within the **nasal cavity**, the air is warmed and moistened. Large dust particles are filtered out as the air passes through the hairs inside the nostrils. Glands in the skin lining the nose produce sticky mucus which helps tiny hairs called **cilia** to trap fine particles. The warm air then passes down the **trachea**. The thin walls of the trachea are reinforced with rings of **cartilage** that keep the trachea from collapsing. The trachea divides into two **bronchi** which divide into smaller tubes, which are called **bronchioles**, and eventually leads to alveoli. **Alveoli** are microscopic and there are about 500 million of them in your lungs. The alveoli have a very large surface area, allowing gas to be easily exchanged between the lungs and bloodstream. The walls of alveoli are only one cell thick and they are surrounded by capillaries. Oxygen dissolves in the moist surface of the alveoli and moves by a process of diffusion. The oxygen enters the red blood cells and joins the circulatory system. Red blood cells exchange carbon dioxide for oxygen, and the waste is breathed out. As you breathe in, the muscles between your ribs **contract**. This pulls the rib cage up and out. The diaphragm, a sheet of muscle that separates the chest from the abdomen, contracts and flattens. These changes increase the volume of space inside the chest. As your lungs expand, the air pressure in them decreases. Air is sucked in through the nose to fill up the space. This makes the air pressure inside the lungs equal to the air pressure outside the body. When you **exhale**, the muscles relax. The ribs move down and in, and the diaphragm arches upwards. The volume inside the chest returns to its normal size and the air pressure increases. Air is forced out of the lungs through the nose or mouth.  **Respiration** begins once the oxygen and glucose are together in the cells. The two chemicals react together and carbon dioxide and water are produced, as well as energy is released. The chemical reaction for respiration can be represented by a word equation Oxygen+glucose \-\--\> carbon dioxide+water+energy The more energy the body requires, the faster this reaction takes place and more oxygen and glucose is required. The amount of energy consumed in food needs to balance the amount of energy used. When you consume more energy than your body requires, the excess nutrients are converted to fat and stored in a layer under your skin surrounding your internal organs. Your mass increases. If you take in less energy in your food than your body requires, you use up fat stores and lose mass. However, if there are no fat stores, the body takes energy from muscles, including the heart. This can cause serious health issues. **Excretory system** - The **lungs** breathe out carbon dioxide produced during respiration. The lungs are therefore part of the excretory system as well as being part of the respiratory system. The **liver** carries out many processes. Some are involved in excretion. Amino acids are the end products of protein digestion. They are used by the body to make proteins and for growth and repair. Amino acids cannot be stored, so if there is more than needed, they are broken down and excreted. The liver breaks amino acids down into **urea**. Poisonous substances may enter the body from the digestive tract. These are carried to the liver, where they are broken down into harmless substances; the harmless substances are then returned to the blood and passed to the kidneys. The liver also breaks down old red blood cells. Any unwanted haemoglobin is added to bile and passes with the bile into the intestines. Chemical reactions taking place in the body produce heat as a by-product. Some of the heat is usd to maintain body temperature, but any excess heat is lost through sweating through the **skin**. Sweat contains a very small amount of urea. As the sweat evaporates, it cools the body down by removing the heat with the water. The **kidneys** are very important excretory organs. They are filters that process about 50 litres of blood every hour. The kidneys excrete urea, control the level of water in the body, and the salt levels in the blood. Urine is produced if there is water in the body. Urine is clear or pale yellow in colour. If the body has little water, the kidneys take out only a small amount of water, producing concentrated urine with a strong gold colour. Excess salt that passes through the kidneys are removed in the urine. **Urine** is a waste material that has filtered out of the blood by the kidneys. Urine is 95% water, 5% urea and small amounts of salts and pigment, which is from the breakdown of haemoglobin. Urine passes from the kidney down narrow tubes called **ureters** and into the **bladder**. It is stored in the bladder, which is a muscular bag. It can hold about 500 mL of urine. The **urethra** is the tube that carries the urine to the outside of the body. At the end of the urethra is a sphincter muscle that controls emptying the bladder. The kidneys, bladder, ureters and urethra make up the **urinary tract**. **Kidney stones** occur when chemicals combine to create hard crystals in the kidneys. Large kidney stones may have to be removed in an operation, or shattered into small pieces using ultrasound waves. They can then pass naturally from the body. The kidneys also use the **high blood pressure from the heart**. However, high blood pressure can damage the capillaries where blood is filtered. **Nephrons** are small sacs in the kidneys, similar to alveoli. They filter out the blood and extract excess salts, urea and water from the blood through diffusion within the **glomerulus**. A tube collecting urine wraps around the blood vessel carrying blood. The filtered liquid, called the filtrate, passes through a tube in the nephron that reabsorbs useful substances like water, glucose and salts back into the body. The cleaned blood leaves the nephron, and the urine continues down the ureter. **Skeletal/muscular system** The skeleton is the body's frame. It is made up of bones. The skeleton has three main functions: - **Bones** Bones need to be strong so they do not snap or crumble during normal activity. Compression forces squash bones and tension forces stretch them. The leg bones experience compression forces when you are standing. Your neck is usually under compression too. Your arms experience tension forces whenever you carry shopping bags or hang off a bar. Bones need to be slightly elastic as they must be able to flex and twist a little, and then return to their original shape and size. Bones also need to be light enough for the muscles to move. The strength and lightness of bones comes from their structure. Bone tissue has two different forms: - Bones are living tissues. They contain living cells that are surrounded by calcium phosphate, a substance that makes bones hard. They also contain collagen. Blood vessels supply bone with the nutrients it requires. Because they are living, bones are able to repair themselves and replace old cells. **Joints** A joint is a place in the body where two bones come together. Most joints allow movement and the type of joint determines the range of movement of the bones. Bone moving against bone would cause pain and the bone to wear down. To protect the bones from wear, joints have: - There are many types of joints. - - - - **Ligaments** are bands of tough, flexible tissue that hold the bones in a joint together. Ligaments prevent the bones of the joint from moving too far apart. Muscles move bones. Muscles are tissues that are able to contract and be stretched. You have 640 muscles. Tendons are tissues that attach muscles to bones and hold the muscles in position. When activated, muscles contract. They pull on the bones they are attached to, allowing them to move. Muscles can only pull. They cannot push. Therefore, another muscle is required to return the bone to its original position. The muscles are arranged in antagonistic pairs that work in opposition to each other. The biceps and triceps are antagonistic muscles in the upper arm. When activated, the biceps contract, pulling your forearm up. The biceps then relax. To lower the forearm, the tricep contracts. The relaxed biceps is stretched back to its original shape and the arm is straightened. Ligaments are strong but elastic. They hold the bones in place at the joint but allow some movement in different directions. If a ligament is stretched too far, it can tear and cause an injury called a sprain. A strain is an injury to a muscle or tendon. Muscles are made to stretch but if they are stretched too far, they can tear. **Reproductive system\~** There are two basic methods or reproduction: - **Sexual reproduction** Sexual production happens when a sperm from a male and an egg from a female join together in a process called fertilisation. Sperm and eggs are special reproductive cells, called gametes. The male sex cell is sperm and the female sex cell is the egg. Fertilisation results in a new cell, called a zygote, which then grows by dividing to form many copies of itself. The zygote eventually grows and develops into a new individual. A few species like tapeworms have individuals that have both male and female sex organs. They can therefore produce both sperm and eggs. Individuals with both sex organs are known as hermaphrodites. Advantages - - Disadvantages - **Sexual reproduction in plants** Flowers are reproductive structures in plants that produce the gametes and allow fertilisation to occur. This results in a seed. To form a seed, the pollen produced in the anther needs to be deposited on the stigma. The transfer of pollen to the stigma is known as pollination. The pollen grain develops into a long tube called the pollen tube that grows through the style. The pollen tube grows down to the ovary and into the egg. In flowering plants, the egg is inside a structure known as the ovule. During this process, the male gamete passes down the pollen tube to join the female gamete in the ovule. Seeds develop in a structure in plants called the fruit. A fruit is the remains of the ovary, plus all the seeds it contains. In some plants, fruit will appear as seed cases or pods. This means that fruit ranges from very juicy to hard and dry seed cases. A seed is a capsule containing a new plant, called an embryo. The embryo is at a very early stage of its development, supported by a food supply inside the seed. The embryo in a seed is dehydrated and requires water and warmth before it will grow. The seeds swell up by absorbing water. The embryo then sprouts out of the seed in a process called germination. The embryo uses the stored food in the seed and begins to grow. **Sexual reproduction in animals** Sexual reproduction can be very different in animals. There are differences such as how and where fertilisation occurs, where the young develop and the amount of parental care. Fertilisation can either be external or internal, depending on the animal. This means that it can either happen outside or inside of the body. Internal fertilisation is better for land environments because sperm shed into the air may dry out and die. The act of joining together to transfer sperm is called copulation. **Development** Development is the process in which the new individual changes to look like others of its type. The young can develop inside or outside the parent's body. Most mammals have internal development. Marsupials such as kangaroos have part internal and part external development. Most other animals have external development. They lay eggs and young develop inside the eggs until they hatch. **Parental care** Parental care is common in animals such as mammals and birds. These animals have relatively large brains that need time to develop. A human baby stays with its parents until it is mature enough to live independently. Birds also show a period of parental care. Most other animals show little or no parental care, especially once the eggs hatch. The general rule is that more complex animals need more parental care. **Asexual reproduction** Asexual reproduction requires only one parent. It occurs when a new individual grows from part of the parent's body. It does not involve sperm or eggs. In plants, asexual reproduction can occur by vegetative reproduction or by spores. - Fungi and plants such as ferns and mosses use spores to asexually reproduce. A spore is a microscopic single cell. Spores are used by plants and fungi to help them spread to many other places. This spread is called dispersal. Spores have a protective wall around them but are very light and easily carried by wind or water. Many simple organisms have bodies made of only one cell. Few animals reproduce asexually. Budding is the name for the process of asexual reproduction. Another type of asexual reproduction is called parthenogenesis, where offspring develop from eggs that have not been fertilised by a male gamete. Asexual reproduction is an effective method of reproduction for: - However, the major problem is if the environment changes in some way, all individuals in a species that uses asexual reproduction are identical. If a disease sweeps through a population, many individuals may die. Sexual reproduction produces offspring that are all different from each other. This helps a species survive in a changing environment. The survival of a species depends on some individuals being different to survive any changes in their environment. They can breed and continue the species. Cross-fertilisation occurs when hermaphrodites with both male and female sex organs do not fertilise themselves. They fertilise each other's eggs. Cross-fertilisation is common in flowering plants. Cross-fertilisation is important for the survival of a species that uses it. This is because it produces greater differences in the offspring than with self-fertilisation. Advantages - Disadvantages - **Cells\~** **Cell theory** is used to describe the properties and structure of cells. The three main components of cell theory are: - **Parts of a cell** Cell wall - Cell membrane - Nucleus - Cytoplasm - Vacuole - Mitochondria - Ribosome - Endoplasmic Reticulum - Lysosome - Chloroplast - **Plant cells**: have both chloroplasts and mitochondria. Chloroplasts convert light energy into chemical energy via photosynthesis, and mitochondria convert glucose into ATP via cellular respiration. **Animal cells**: only have mitochondria. They rely on consuming organic material for their glucose supply, and convert to ATP through cellular respiration.  **Diffusion and Respiration** - Small particles are able to pass through the cell membrane by diffusion. Substances that are required by the cell diffuse inside, and waste diffuses out of the cell. Substances move from high concentration to low concentration. High concentration inside the cell leads to movement outside. High concentration outside the cell leads to movement inside. The most important process in a cell is respiration. For respiration to occur, most cells need to obtain glucose and oxygen. In eukaryotic cells these are used by the mitochondria. Mitochondria release the energy trapped in glucose. This energy is then available for use by the cell to perform all its functions. Prokaryotic cells do not have mitochondria but respiration still occurs in their cytoplasm. Plants convert the sun's energy to glucose through photosynthesis. The main waste product cells need to remove is carbon dioxide. Small cells have a larger surface area compared to their volume, allowing for efficient transport of materials in and out of the cell. This helps them get nutrients and remove waste quickly. The surface area to volume ratio is important as higher ratios allow for more efficient transport of materials in and out of the cell. Cells with a larger surface area relative to their volume can exchange substances more rapidly. As cells grow larger, the ratio decreases and reduces efficiency and uses more nutrients. Cells like red blood cells are small and have a biconcave shape to maximise their surface area. **Cell Division\~** **Mitosis** To make new cells so you can grow, repair your body or replace lost cells, a cell makes another copy of its DNA. The cell and DNA divide by an orderly process called mitosis. During mitosis, the nucleus of one cell divides to form two nuclei. These then form two cells. Mitosis happens for a very short period of time. The parent cell's nucleus divides to form two nuclei. It copies and pastes the genetic information. Humans have 46 chromosomes and 23 pairs. Males have XX and females have XY. Chromosomes have DNA wrapped around protein. Nucleus - chromosomes - DNA - protein  Mitosis is a type of cell division done by most of your body cells. Meiosis is the reproduction of sex cells, sperm and eggs. Mitosis makes identical cells. Cancer is the overproduction of cells Interphase: the life story of the cell, occurs before mitosis - **The cell cycle** **Mitosis stages of division** - Cytokinesis is responsible for the final separation and by splitting the cytoplasm. **Stem cells** Most cells either live for a while then die, like red blood cells or skin cells, or stay in the body for the rest of your life, like nerve cells. Most cells do not reproduce and do not undergo mitosis. Stem cells are cells in your body that can divide by mitosis and make new cells, which can become a variety of different cells. Some stem cells are found in bone marrow. **Unicellular and multicellular** Unicellular organisms - Multicellular organisms -  **Muscle cells** The three types of muscles in your body are: - Surrounding the bones of your skeleton are muscles that you use to move around. You can choose to make these muscles move (or not) and so they are referred to as voluntary muscles. You have other muscles in your body that work without you having to think about it. They are the muscles involved in breathing and those that keep food moving though your gut. These muscles are known as involuntary muscles. All muscles (voluntary or involuntary) contain a large number of mitochondria. This is because muscles require a lot of energy to keep working and it is the mitochondria that provide the energy. Cardiac muscle is the type of muscle in the heart. Cardiac muscle is involuntary muscle but it has a striped appearance like voluntary muscles. Unlike other muscles that are striped, cardiac muscle does not get tired. It has very large numbers of mitochondria to provide a continuous supply of energy. These characteristics allow the heart to beat continuously. **Nerve cells** Nerve cells make up your brain. They also carry information from your brain to other parts of your body such as your muscles, and from your muscles back to your brain. Some nerve cells have very long fibres called axons extending from the cell. These allow the cell to carry messages over long distances. The longest axon of a human nerve cell reaches from the base of the spine to the toes, and can be over a metre long. **Blood cells** Red blood cells carry oxygen from your lungs around your body to the cells where it is used to release the energy you need. They also carry some of the waste carbon dioxide from the cells back to your lungs so that you can get rid of it from your body. The white blood cells have a different job. They are part of the immune system and help the body to fight infection. **Fat cells** There are two different types of fat cells in the body. Brown fat cells are used to produce heat for the body, especially when it gets cold and you are shivering. The white fat cells are used as a store of energy. They also form an insulating layer under the skin that helps to keep your body at a constant temperature. **Guard cells** Guard cells are found on the leaves and stems of plants. Guard cells work in pairs to open and close very tiny pores in the leaves called stomata. Gases needed by the plant enter through open stomata and unwanted gases leave the same way. Guard cells close the stomata when plants need to reduce water loss. **Photosynthetic cells** Cells near the surface of the green parts of stems and leaves have large numbers of chloroplasts. In the chloroplasts is a green chemical called chlorophyll. This chemical traps the Sun's energy, which the plant then uses in photosynthesis. Plant cells that are not exposed to sunlight, such as those in the roots, do not contain chloroplasts and are not green. Chlorophyll traps energy from sunlight so that photosynthesis can occur. Plants may use the glucose for energy, stored energy, cellulose walls, or combined with other nutrients for growth. **Root hairs** Plants cannot move around to get water from where it is available. This means they need an efficient way of taking in water where they are growing. Water comes into plants from the soil through the surface of their cells. The more surface they have in contact with the soil, the more water they will be able to take in. Some of the cells on the outer surface of roots have extensions called root hairs. These root hairs increase the surface area of the root by a large amount. **Conducting cells** Plants take in water from the soil through their roots. The water is needed in the leaves for photosynthesis. This means that water has to be transported from the roots to the leaves. Plants make their food in the leaves but the cells of the roots and stems need food if they are going to stay alive. This means the food has to be transported from the leaves to the roots and stems. Inside the plant there are cells that are specialised for transported water and food. These conducting cells are long thin tubes like drinking straws. **Structural cells** The cell walls act as the skeleton of plants. When plants grow they become bigger and heavier. Then their skeleton needs to get stronger. The cell walls of many cell types, especially the water-conducting cells in the plant stem, become thicker and stronger, providing more support. The wood of tree trunks is mostly cells with walls that are so thick that the cell has died. The living part of a tree trunk is just below the bark. **Microscopes\~** Parts of a microscope **Using a microscope** - Preparing a wet mount - **Drawing cells** - **Plants\~** **Vocabulary** - -  **Parts of a plant** Bud - develops into a flower, leaf or shoot Flower - reproductive organ which produces seeds for pollination Leaf - site of photosynthesis. Leaves rotate to allow maximum absorption of sun. can deposit waste materials on leaf (salt) Stem - transports water upwards. Also provides strong structure (rigidity) Roots - absorbs water via extensive root system (more surface are) and absorbs nutrients **Leaves** The role of the leaf is - Cuticle - thin waxy layer that covers the leaf surface. Protects the leaf from losing water. Some leaves only have it on one layer due to gravity and size. Upper epidermis - top layer of cells beneath cuticle. Allows light to pass through while protecting the leaf. Palisade layer - tightly packed cells beneath epidermis. Contains chloroplasts like tiny solar panels. Stomata - small holes found in lower epidermis. Lets gases in and out. CO2 in and O2 out. Guard cells - guards the stomata. Open and close the stomata. Xylem - carries water from root to leaf (up only) Phloem - carries sugars and nutrients up and down. **Flower** - Part of the Flower Definition Function ----------------------- -------------------------------------------------------------------------------- --------------------------------------------------------------------------- Stigma The top part of the pistil where pollen grains land Receives pollen during fertilisation Pistil The female reproductive part of the flower Consists of the stigma, style and ovary; responsible for producing seeds. Filament The stalk that holds the anther Supports the anther, positioning it to release pollen Ovule A small structure inside the ovary that contains the female reproductive cells Develop into a seed after fertilisation Sepal The outer parts of the flower, often green Protects the flower bud before it opens Stamen The male reproductive part of the flower Produces pollen consists of the anther and filament Petal The colourful parts of the flower Attracts pollinators, birds, insects. Style The tube like structure the connects the stigma and ovary Helps transport pollen from the stigma to the ovary Anther The part of the stamen that contains pollen Produces and releases pollen grains Ovary The enlarged base of the pistil, containing ovules. Develops into a fruit after fertilisation, protecting the seeds.  **Reproduction in Plants** Pollination - the process by which pollen is transferred from male to female parts of a flower. - Germination - seeds are dispersed and grow in favourable condition into new plants. Sexual reproduction - Asexual reproduction - **Transport Systems** Roots - Xylem - Phloem - Stem houses xylem and phloem Waste excreted out of the leaves Xylem and phloem tubes are grouped together in vascular bundles, separated by a layer of cambium cells.