Grade 7 Semester 2 Study Guide PDF

Homeostasis Stimulus & Response Stimuli ⚫Stimuli are changes that occur around us in the environment. ⚫Stimuli is known to us as touch, pain, heat, cold, sounds, food (chemicals) and light. ⚫For example: - You feel and touch objects - You look at things around you - You feel cold or hot - You fee...

Homeostasis Stimulus & Response Stimuli ⚫Stimuli are changes that occur around us in the environment. ⚫Stimuli is known to us as touch, pain, heat, cold, sounds, food (chemicals) and light. ⚫For example: - You feel and touch objects - You look at things around you - You feel cold or hot - You feel pain when you fall down - You hear sound - You taste a burger Stimulus & Response ⚫Stimulus means a lot of stimuli (or plural form of stimuli). ⚫When a stimuli or stimulus come to us, we respond to it or them. ⚫For every stimuli there is a response to it whether we aware or not. Eg; when we touch anything hot like an iron, we will feel pain and the response would be pulling back the hand to avoid pain. ⚫Human need to respond to stimuli in order to protect themselves from danger or for survival. So.... ⚫The change in the environment is the stimulus; the reaction of the organism to it is the response. Detecting Stimuli ⚫Living objects have sensors (or senses) that detect forms of energy from the world around them. They then convert the energy into a signal. ⚫Human senses include the sense of sight, hearing, smell, taste and touch. ⚫The signal from a sensor may be quite simple or very complex, as in the case of information on images detected by the eye. Signal Interpretation ⚫An organism will process or interpret the signal from the sensor, resulting in a response or being ignored. ⚫The signal may be processed near the sensor, in the brain, or in an area in between. ⚫Plants and lower level animals don't have brains – so deal with this differently. Signal Interpretation Processed before the brain: ⚫Eg; the skin can detect heat. If the heat is interpreted as dangerously high, the person will jerk away from the source of heat. ⚫The signal does not have to reach the brain for the interpretation to cause the response in this situation. Processed in brain: ⚫Eg; the nose of a dog senses the odour from food being offered. The signal reaches the brain which interprets the smell as something good to eat. The dog then responds by salivating. ⚫This response is its behaviour to the stimulus. Signal Interpretation ⚫On a more complex level, a person may hear a song on the radio. The song is sensed and processed, and its words are interpreted for their meaning. ⚫This goes well beyond responding to a loud noise. The words and melody are presented as complex information, and their interpretation can result in an emotional response or behaviour. Types of Responses ⚫The response to a stimulus can be positive, negative, or ignored as not important. ⚫A positive reaction means that the being wants more or is attracted to the stimulus. ⚫A negative reaction means that the being wants to avoid the stimulus. Examples of Types of Responses Positive ⚫A plant grows toward sunlight. ⚫A person laughs after hearing a funny joke. Negative ⚫The roots of a plant avoid a piece of copper in the ground. ⚫You make a face or cover your nose after smelling a pungent unpleasant odour. Ignored ⚫A dog pays no attention to sounds from the television. ⚫You pay no attention to slight changes in the room's temperature. Homeostasis ⚫Homeostasis is the term we use to describe the constant state of the internal environment. ⚫The cells in your body work best when their surroundings are kept constant. ⚫Your body has many mechanisms that keep the cells surroundings constant even though your external environment is changing. This is homeostasis. ⚫Homeostasis is very important because when it fails you could become ill or may even result in death. THE ENDOCRINE SYSTEM WHAT IS THE ENDOCRINE SYSTEM? The function of the endocrine system is the production and regulation of chemical substances called hormones. The endocrine system regulates all biological processes in the body from conception through adulthood and into old age WHAT MAKES UP THE ENDOCRINE SYSTEM? GLANDS AND HORMONES ENDOCRINE GLANDS The primary endocrine glands are the pituitary (the master gland), pineal, thyroid, parathyroid, adrenals, ovaries in the female and testes in the male. HORMONES….. A hormone is a chemical transmitter. It is released in small amounts from glands, and is transported in the bloodstream to target organs or other cells. Hormones are chemical messengers, transferring information and instructions from one set of cells to another. HORMONES…. regulate growth and development, mood, tissue function, metabolism, and sexual function. HORMONES…. Hormones act slower than nervous impulses but cause longer-lasting effects Hormones are used to stabilize the body’s internal environment (homeostasis) HORMONES…. The endocrine system and nervous system work together to help maintain homeostasis…Balance The hypothalamus in the brain is the primary link between the two systems. It produces chemicals that either stimulate or suppress hormone secretions of the pituitary gland. HOW COMMUNICATION HAPPENS? Hormones follow a complex path to reach their target. Generally a releasing hormone is released from the hypothalamus. This releasing hormone acts on cells in the pituitary gland to release a stimulating hormone which then acts on the endocrine gland or organ. If there is a break anywhere in the path it can cause disorder or disease. PITUITARY GLAND THYROID Produces the hormone thyroxine: Regulates rate of metabolism. Excess causes hyperactivity. Deficiency causes weight gain and sluggishness. ADRENAL GLAND ‘FIGHT’ OR ‘FLIGHT’ The "fight or flight response" is our body's primitive, automatic, inborn response that prepares the body to "fight" or "flee" from perceived attack, harm or threat to our survival. ‘FIGHT’ OR ‘FLIGHT’ The release of adrenaline and norepinephrine from the adrenal glands to the respiratory centres, heart, and blood vessels is triggered by the production and release of the hormone acetylcholine from the nerves. These hormones are responsible for the constriction of blood vessels, the increase in breathing and the heart rate, the tightening of muscles. They work during times of real or perceived danger. PANCREAS Produces the hormone glucagon: Converts of glycogen back to glucose in the liver. Produces the hormone insulin: Controls the conversion of blood glucose to glycogen, which is stored in the liver. REPRODUCTIVE ORGANS REPRODUCTIVE ORGANS Cells Cells Cells are the basis of life Living organisms range from single celled organism (unicellular) to complex organisms (multicellular) Cell theory 1. All living things are composed of one or more cells 2. The cell is the smallest entity that retains the properties of life 3. All cells come from pre-existing cells. Structure of cells Living things are classified into different kingdoms based on the characteristics of their cells. Plants and animals have specific types of cells with similarities and differences. Plant and animal cells contain membrane bound organelles, these are tiny structures that carry out specific functions within the cell. Plant cell structure Animal Cell Structure Plant V Animal Cell Matter What is Matter? Everything around us that takes up space and has mass is known as matter. Matter has both mass and volume Matter includes solids, liquids and gases. These different forms of a substance are called states of matter. Chemistry is the study of matter. It is the study of what matter is made of, how matter changes, and what the properties of matter are. What is Matter? Mass can be define as a measure of the amount matter / colour / texture in an object. The greater an object’s mass, the more / less matter it will contain and the heaver / lighter it will be. The amount of space an object takes up is known as its mass / volume. The more matter / volume an object has, the more space it will take. There are two / three / four main states of matter on Earth. These are s________, l________ & g________ Solids, Liquids & Gases Solids o Hold their own shape, are hard to compress and can be smooth or rough Liquids o Do not have shape, they take on the shape of the container they are in o Flow – slowly (like honey) or quickly (like water) Gases o Do not have shape and spread to fill the space they are in Water and Matter Particle Theory of matter The Particle Model - Features o All matter is made up of tiny particles o There are spaces between these particles, some big, some small. o The particles that make up matter are always moving o Forces of attraction hold the particles together o Energy makes particles move o Adding heat (energy) makes particles move faster and break free of the forces holding them together The Particle Model - Solids o Particles are tightly packed together o Particles do not move around freely, however, they constantly vibrate o This is why solids have a fixed mass, volume and shape o Cannot be poured (except in granulated form e.g. salt) o They are not able to be compressed The Particle Model - Liquids o Particles in a liquid can slip by one another, able to flow o This means liquids do not have a fixed shape o Liquids have a fixed mass and volume, take the shape of the bottom of the container they are in. o They are not able to be compressed o Can expand with heat and contract when cooled The Particle Model - Gases o Very large spaces between particles, they will spread out to take the shape of the container o Particles move freely o Gases do not have a fixed volume or shape o Can be compressed (pushed in to make them take up a smaller amount of space) Changes of State When Substances Change The world around you is constantly changing. Whether it be the passing of the seasons, a cool breeze or ice-blocks melting in a drink, changes are occurring. Most of these changes can be classified as physical or chemical changes depending on whether any new substances are produced. Changes of State and the Particle Model The particle model explains changes of state It looks at the relationship between how the particles move and the attraction between them. Changes of State o Substances can change from one physical state to another o Particles need to gain or lose heat energy for this to happen so it is measured as a change in temperature o Solids have the lowest energy and gases have the highest Demonstration Why do substances change state? Energy out Energy in Changes of State and the Particle Model Melting In a solid, the particles vibrate but are held in position by the forces of attraction between them. As the temperature increases, the vibrations increase and the solid expands. As the temperature is increased further, the solid melts. The vibrations become so energetic that the attraction between the particles can no longer hold them in a fixed position. At this point, the particles become unstuck and start moving freely. However, there is still a small amount of attraction between the particles that holds them together as a liquid. Changes of State and the Particle Model Freezing/Solidification As the free moving particles in the liquid are cooled The particles become slow and less energetic until the attraction between the particles is able to fix them in position Forms a solid. Changes of State and the Particle Model Evaporation Occurs when the particles in a liquid escape to form a gas. The particles in a liquid are stuck together by only weak forces of attraction. As the liquid particles are heated, they move faster until they are able to escape from the surface of the liquid to form a gas. Changes of State and Particle Theory Condensation As a gas is cooled the particles move slower They reach a point where the forces of attraction between the particles can hold and stick them together to form liquid droplets. Pure substance and mixtures Elements    Elements are the simplest pure substances. The smallest particle of an element that has the properties of that element is an atom. Examples:  O-Oxygen  H- Hydrogen  Na- Sodium  C- Carbon  Fe- Iron  Pb- Lead Compounds    Compounds are pure substances that are made of more than one element bound together. A molecule is formed when two or more atoms chemically combine. Examples:  H2O and CO2 Chemistry - Definitions - Structure and Scale of the atom Definitions: 1. 2. 3. 4. 5. 6. 7. 8. 9. Define each: Matter Atom Element Compound Molecule Proton Neutron Electron. Write the following definitions. Matter Any substance that has mass and volume. Atom The fundamental building block of all materials; it consists of a cluster of protons and neutrons surrounded by a cloud of electrons. Compound A pure substance that is made up of two or more different types of atoms chemically combined. Element A substance made up of only one type of element. Molecule Two or more atoms joined chemically. Proton A positively charged sub-atomic particle in the nucleolus of an atom. Neutron A sub-atomic particle with no electrical charge, located in the nucleus of an atom. Electron A small negatively charged sub-atomic particle; clouds of electrons surround the nucleus of an atom. Electron Configuration The number of electrons surrounding the nucleus of an atom is exactly equal to the number of protons in the nucleus. As a result, atoms have an overall neutral charge. The first shell can only hold 2 electrons. The second shell can hold 8 electrons. The third shell can hold 18 electrons. The fourth shell can hold 32 electrons. The number of electrons in each shell of an atom is known as electron configuration. For example, the electron configuration for Lithium is 2, 1. What you need to know 1. The Atomic Number of an atom = number of protons in the nucleus. 2. The Atomic Mass of an atom = number of Protons + Neutrons in the nucleus. 3. The number of Protons = Number of Electrons. 4. Electrons orbit the nucleus in shells. 5. Each shell can only carry a set number of electrons. ATOMIC STRUCTURE He 2 4 Atomic number the number of protons in an atom Atomic mass the number of protons and neutrons in an atom number of electrons = number of protons ATOMIC STRUCTURE Particle Charge Mass proton + ve charge 1 neutron No charge 1 electron -ve charge nil ATOMIC STRUCTURE Electrons are arranged in Energy Levels or Shells around the nucleus of an atom. first shell a maximum of 2 electrons second shell a maximum of 8 electrons third shell a maximum of 8 electrons ATOMIC STRUCTURE There are two ways to represent the atomic structure of an element or compound; 1. 2. Electronic Configuration Dot & Cross Diagrams ELECTRONIC CONFIGURATION Write the electronic configuration for the following elements; a) Ca 20 b) Na 40 2,8,8,2 d) Cl 17 35 2,8,7 11 23 c) 2,8,1 e) Si 14 28 2,8,4 O 8 16 2,6 f) B 5 11 2,3 DOT & CROSS DIAGRAMS With Dot & Cross diagrams elements and compounds are represented by Dots or Crosses to show electrons, and circles to show the shells. For example; X Nitrogen X X N XX X X N 7 14 DOT & CROSS DIAGRAMS Draw the Dot & Cross diagrams for the following elements; X 8 17 X a) O b) Cl 35 X 16 X X X X X X X X X Cl X X X X X O X X X X X X X X X